PURDUE UNIVERSITY COOPERATIVE EXTENSION SERVICE • WEST LAFAYETTE, IN 47907

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PURDUE PESTICIDE PROGRAMSPURDUE PESTICIDE PROGRAMS

Purdue University Cooperative Extension Service

PESTICIDES AND WATER QUALITYPRINCIPLES, POLICIES, AND PROGRAMS

Fred Whitford, Coordinator, Purdue Pesticide ProgramsJeffrey Wolt, Technical Leader, Environmental Chemistry Laboratory, DowElanco

Henry Nelson, Surface Water Branch, U.S. Environmental Protection AgencyMichael Barrett, Ground Water Section, U.S. Environmental Protection Agency

Sarah Brichford, Extension Water Quality Specialist, Purdue UniversityRonald Turco, Associate Director, Indiana Water Resources Research Center, Purdue University

Edited by

Arlene Blessing, Purdue Pesticide Programs

TABLE OF CONTENTS PAGE

Introduction .................................................................................................................................... 3

The Earth’s Water Cycle: Nature’s Oldest Recycling Program ...................................................... 5

The Fate of Pesticides in the Environment .................................................................................... 10

The Pesticide Testing Process ...................................................................................................... 18

Regulatory Evaluation of Environmental Fate Data for Water Quality Concerns .......................... 28

Risk Assessment of Pesticides for Water Quality Concerns ......................................................... 40

The Pesticide Label ....................................................................................................................... 44

Public Policy, Pesticides, and Water Quality ................................................................................. 49

Special Initiatives ........................................................................................................................... 51

Conclusions ................................................................................................................................... 55

Acknowledgments .......................................................................................................................... 57

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INTRODUCTION

Today we face challenges concerning water re-sources, both in our own communities and nationwide.Proponents of economic development and supportersof environmental conservation debate the use of water.As the turn of the century approached, there was nodebate over water as a renewable and limited re-source; rather, its availability was generally assumed tobe unlimited. Rivers and streams were viewed ascheap, dependable sources of water in support of thenational surge in manufacturing, construction, andemployment; and they often served as prime avenuesfor the disposal of waste materials.

By the turn of the century, the oppression of surfacewater was evident; and the dumping of sewage effluentand by-products of manufacturing and agriculture hadbecome associated with the terms contamination andpollution. Rivers and streams once considered pristinewere tainted from the repeated introduction of waste.Several contamination incidents received significantmedia attention, sparking public concern for waterquality. Some evoked such emotional outrage thatpublic coalitions demanded legislative attention. Theresulting multitude of new laws—both state andfederal— specified policies and goals for establishingwater quality, placing the responsibility for compliancesquarely on the cities and industries (including agricul-ture) releasing pollutants into water.

Protecting water quality is a top environmentalpriority as we approach the twenty-first century. How-ever, the pendulum of public debate has shifted fromgovernment regulation to one of cooperation amonggroups with divergent viewpoints. This shift evolved asfactions began to view a community’s prosperity as afunction of its development of water policies that blendboth economic goals and environmental incentives.While cooperation is now common, major differencesstill exist among public, industrial, regulatory, andenvironmental groups. Ideas presented and solutionsoffered may differ, but there is universal agreement thatwater resources must be pollution-free and abundant ifthe nation is to prosper economically.

Pesticides and Water QualityUsing pesticides effectively while maintaining water

quality presents an important challenge. As citizens, wemust recognize the significant role of pesticides inmaintaining a high quality of life. We must acknowledgethat the effective production of food and fiber relies onpesticides to control weeds, insects, and plant diseases

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that interfere with the growth, harvest, and marketabilityof crops. As pest control operators and homeowners—rural as well as urban—we must acknowledge theimportance of pesticides in controlling pests in ourhomes, restaurants, hospitals, parks, ornamentalplantings, golf courses, etc. But at the same time wemust be aware that pesticide applications can affectwater quality. Human and environmental health may bethreatened when excessive concentrations of pesti-cides enter surface or ground water.

‘Pesticides and water quality’ is a complex subject,both technically and politically; but if current and futureexpectations for community life, agriculture, industry,wildlife, and natural habitats are to be met, input froman educated public is essential. A basic knowledge ofthe subject is important to allow informed participationin the ongoing debate. This publication presentsinformation on water science, environmental fate, andpublic policy to assist the reader in developing anunderstanding of the issues surrounding pesticide useand water quality.

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THE EARTH’S WATER CYCLE:NATURE’S OLDEST RECYCLINGPROGRAM

Oceans contain 97 percent of the world’s watersupply. The remaining three percent is fresh water, ofwhich approximately 70 percent is stored as ice inglaciers. Nearly all of the unfrozen fresh water on theplanet occurs in aquifers below ground; only onepercent is stored in lakes, streams, and rivers.

Water drawn from rivers and tapped from deepwithin the earth’s aquifers is not ‘new’. It has beencontinuously recycled between land and atmospherefor thousands of years through intricate processes ofevaporation, transpiration, precipitation, overlandrunoff, and infiltration. Together these processes arelinked as the hydrologic (water) cycle.

The sun energizes the hydrologic cycle. Solarenergy converts surface water to atmospheric watervapor through the process we know as evaporation.Plants absorb water from the soil and can release it

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into the atmosphere by transpiring (giving off) watervapor from leaves. Water vapor rises, then condensesin the cooler atmosphere to form clouds; water storedin clouds is eventually returned as precipitation in theform or rain, hail, sleet, and snow which can fall directlyinto rivers, streams, lakes, ponds, and wetlands. Wateralso can move into these bodies by overland runoff orpercolation below ground. Water entering the soil caninfiltrate deeper to reach ground water which, in turn,can discharge to surface water or arrive back at thesurface through wells, marshes, and springs. Once onthe surface, water is again energized by the sun torepeat the evaporation and transpiration processes thatprovide water vapor for cloud formation and continua-tion of the hydrologic cycle.

Ground Water: The Hidden Resource

Ground water is a widely distributed natural re-source found beneath the earth’s surface. Many peoplehave the mistaken impression that ground water occursas underground rivers and reservoirs. However, mostground water occurs in tiny voids (spaces) betweengrains of sand and gravel, between silt and clay, or incracks and fractures in bedrock.

Geology of Ground Water

The geology of a particular location dictates thedepth and volume of ground water. Usable groundwater available to supply wells and springs comes fromgeologic formations called aquifers, which may beshallow (near the earth’s surface) or very deep (hun-dreds of feet below the surface). As a general rule,fresh water aquifers tend to lie 60–300 feet belowground.

Aquifers are composed of various materials such asrock, sand, and gravel that reflect local geology. Someconsist of unconsolidated (loose) deposits of sand,clay, silt, or gravel containing water in the voids be-tween particles and rock fragments. Other aquifersoccur as cracks in bedrock or consolidated (solid)materials such as igneous rock (granite, basalt),sedimentary rock (limestone, siltstone, sandstone), ormetamorphic rock (slate).

Aquifers are characterized as either confined orunconfined. Confined aquifers lie below a layer of lesspermeable clay or rock—a confining layer—whichgreatly slows the vertical movement of water. Thewater in confined aquifers can be recharged from waterthat moves into the water-bearing zone from distantareas where there are no confining layers.

Unconfined aquifers do not have a confining layerand are ‘open’ to water moving down from surfaces

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directly above. The water surface of unconfinedaquifers—the water table—fluctuates with changes inatmospheric pressure, rainfall, and other factors.Unconfined, unconsolidated aquifers are particularlyvulnerable to contamination because, typically, they arequite shallow and surface water can infiltrate quicklydown to the water table (ground water) in certain soils.

Downward Movement of Water

Between top soil and water-saturated soils, voids ofunconsolidated materials fill with water and air, formingthe vadose (unsaturated) zone. The portion of thevadose zone near the soil surface is where plants root,vegetation decays, and animals burrow; it is in this areathat most terrestrial plants and soil organisms reside.The lower portion of the vadose zone hosts lessbiological activity.

Precipitation either runs off sloping land or infiltratesonly the upper few inches of soil, then percolatesdownward and permeates the upper vadose zone. Aswater enters soil voids, a variety of physical processespull it into the vadose zone, replacing air. The watertable is defined as the area that separates the vadoseand saturated zones. Water below the water table isground water.

All soils can store water in voids. A soil’s ability tostore and transfer water downward in saturated orunsaturated conditions is a function of numerousinterrelated processes and features. For example, thenature of soil particulates and the way they aggregateinfluence features such as porosity and how water isattracted to soils. Soils with small voids can store morewater than those with larger voids. Under saturatedflow, porosity and the pull of gravity greatly influencewater movement. Under unsaturated conditions,attraction of water to soil surfaces (matrix potential),movement along a maze-like flow path, and very smallpores (capillaries) influence water movement.

Natural ground water movement is often (but notalways) in the direction defined by local topography.Horizontal flow of ground water generally is slow and ismeasured in inches per day or feet per year, dependingon the porosity and the permeability of the materialsmaking up the aquifer.

Surface Water: The Visible WaterResource

Surface water is water stored or flowing at theearth’s surface: natural bodies of water such as rivers,lakes, and wetlands, as well as constructed (artificial)water reservoirs such as canals, man-made lakes, anddrainage ditches. The quantity and quality of surfacewater is important for many activities: consumption,

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recreation, transportation, waste assimilation, agricul-tural production, and industrial use.

Movement of Surface Water

Surface water is linked to both ground water andatmospheric water through the hydrologic cycle.Surface water moves into ground water by infiltratingthe soil and percolating downward; it also enters theatmosphere through evaporation and transpiration.Likewise, water from the atmosphere and ground watercan recharge surface waters. Atmospheric water fallsas precipitation: rain, sleet, hail, and snow. Groundwater that moves to the earth’s surface contributes tothe base flow of streams, lakes, wetlands, and otherwaterways.

Rainfall and melting snow initially infiltrate the toplayers of the soil at a rate commensurate with the soil’sporosity and initial water content, as well as the inten-sity and duration of precipitation. Continuing precipita-tion may saturate the upper few inches of the soil,temporarily exceeding its capacity to hold water; waterbegins to accumulate on the land surface and perhapsflow overland to lower elevations. This movement,termed overland flow or surface runoff, may occuracross a small or large area, depending on the amountand intensity of precipitation and on the local terrain.Soil type, land slope, and vegetative cover are contrib-uting factors. A gentle rain lasting all day may result inonly moderate runoff; but an intense summer thunder-storm producing a large amount of rainfall in a shorttime may yield significant runoff. The amount of runoffproduced by a storm also is influenced by the moisturelevel of the soil prior to the storm, and by local topogra-phy. Runoff also can result from miscalculated timing,intensity, and duration of irrigation.

Runoff flows down slope until it reaches a storagearea (e.g., a stream, pond, or low spot); and when thestorage/infiltration capacities of that area are exceeded,runoff will flow even farther down slope. Floodingoccurs when precipitation exceeds the storage capacityof surface depressions and bodies of water for a givenarea. Large amounts of runoff for an extended timeraise stream levels, spilling water onto adjacent land—the flood plain.

Erosion and Sedimentation

Surface water flows in defined channels such asstreams and rivers. The amount and rate of flow varyprimarily with precipitation, channel substrate andgeometry, and gradient.

Flowing water can carry dissolved pollutants andothers adsorbed to suspended sediment. Suspended

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sediment comes from eroded soil, which is carried inrunoff, and from the channel’s sides and bottom. Thedistance it travels varies, depending on the size andsurface characteristics of the materials and the waterflow rate. When flowing water meets stored water, suchas when a stream enters a pond, the flow rate is greatlydecreased and much of the coarser, larger, heaviersediment settles to the bottom; finer, smaller, light-weight materials such as clays may stay in suspensionfor longer periods of time. Generally, sediment isdeposited, resuspended, and redeposited by flowingwater. Conversely, storage waters tend to host pollut-ants for longer periods of time although, because ofdilution, concentrations may be lower than in a stream.

The Surface Water System

A surface water system is characterized by itswatershed or drainage basin. A watershed is the areaof land draining to a specific river; the watershedboundary is defined by a region’s topography. Water-sheds vary in size and can be nested within otherwatersheds of increasing size, similar to a familygenealogy or the branching of a tree. For example, theentire Mississippi River watershed draining into theGulf of Mexico is a large area encompassing most ofthe central United States; it consists of thousands of

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smaller subwatersheds, each contributing to the totalwater volume flowing into the Gulf.

The watershed concept is important because it linksland area to bodies of surface water along a sequenceof increasing scale. Land use within a watershedlargely determines the quality of the local surfacewater. The quality of water leaving a watershed can, inturn, affect the cumulative quality of water far down-stream. For example, pesticides detected in a city’sdrinking water supply could come from lawn and otherurban uses or from an upstream watershed whereagriculture is predominant. The potential exists forcompounds to move off site and travel downstreamthrough the surface water system; however, manybiological, physical, and chemical processes affect thefate of pesticides in the environment.

Within a watershed, surface water occurs in anetwork of storage and flow areas; e.g., soil constitutesa large internal catchment (storage body) for waterwithin a watershed. Catchments can cycle their water;in other words, a ‘new’ volume of water can replace the‘old’ volume. The storage time of water—also known ashydrological residence time— depends on the hydro-logic characteristics of the catchment. The meanhydrological residence time, stated as a ratio of theaverage volume to the average flow, represents howlong it takes to replace an ‘old’ volume of water with a‘new’ volume.

The interaction of pesticides with soils, surfacewater, and ground water is complex. Pesticide fate iscontrolled by numerous simultaneous biological,physical, and chemical reactions. Comprehending thefate of pesticides requires an understanding of certainprocesses: transformation; transfer; and transport.Transformation refers to biological and chemicalprocesses that change the structure of a pesticide orcompletely degrade it. Transfer refers to the way inwhich a pesticide is distributed between solids andliquids (e.g., between soil and soil water), or betweensolids and gases (as between soil and the air it con-tains). Transport is the movement from one environ-mental compartment to another, such as the leachingof pesticides through soil to ground water; volatilizationinto the air; or runoff to surface water.

THE FATE OF PESTICIDES IN THEENVIRONMENT

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When a pesticide is applied to a field, certainreactions follow. Foliar-applied pesticides stick toleaves, where they are absorbed. But rainfall inevitablywashes some of the chemical off the leaf surface ontothe soil below; and some may be transformed bysunlight. Soil-applied pesticides generally interact firstwith moisture around and between soil particles,influencing how the chemical ultimately will react in theenvironment. Thus, a ‘soil solution’ can be viewed as achemical staging area for most reactions controllingenvironmental fate. For instance, sorption processes(transfer), degradation by microbial and chemicalreactions (transformation), volatilization to the atmo-sphere, leaching into deeper soil profiles, and overlandflow (transport) all occur predominantly from soilsolution.

SorptionSorption is a transfer process by which pesticides

are dispersed between solid matter and water, in soil; itis important in regulating the concentration of pesti-cides in soil water. One important environmental sink(retention or storage site) for many pesticides isorganic matter. The transfer—called ‘partitioning’—of apesticide into organic matter in soil is a somewhatnonspecific mechanism.

Much organic matter (humus) is made up of a seriesof organic polymers (long chains or mats of molecules)

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and generally consists of two systems: a hydrophilic(water-loving) surface; and a hydrophobic (water-hating) interior. The convention of ‘like dissolves like’holds for pesticide interactions with organic matter insoil. Nonionic (noncharged or neutral) pesticidesescape from soil solution into the hydrophobic interiorand, as a result, a pesticide equilibrium is set upbetween organic matter and soil solution. Pesticidesmove between organic matter and water in soil. Also,pesticides may undergo an aging process, over time,whereby the chemical moves deeper into organicmatter and becomes unavailable to move back into soilsolution. Pesticides that are water soluble tend toremain at the surface of soil organic matter, while thosethat are insoluble will penetrate to the hydrophobicinterior.

The amount of pesticide sorbed is largely a functionof the total amount of organic matter (sorption regions)in the soil. Sorption to clay mineral particles also occursbut usually is less significant than sorption to organicmatter in determining environmental fate, unless thesoil has very low organic matter content.

Many pesticides develop a charge as the result ofsoil solution pH (a measure of acidity); i.e., neutralpesticide molecules can become ionic (charged) andmore reactive. If the pH-induced charge is positive, thepesticide can bind to negatively charged soil. If theinduced charge is negative, the pesticide may actuallybe repelled from the negatively charged surfaces of soilsolids.

Sorption to soil particles is also dependent on soilwater content because water is necessary for chemicalmovement; and water molecules will compete withpesticide molecules for attachment sites on clay andorganic matter. Therefore, pesticide sorption tends tobe greater in dry soils than in wet soils. Decreased soilwater content forces the pesticide to interact with soilsurfaces; however, the amount of sorption also de-pends on the type of clay and organic matter content.

The bond between a pesticide molecule and a soilparticle determines, to a large degree, the environmen-tal fate of the pesticide. For instance, pesticides thatare tightly sorbed to soil particles have decreasedmobility and are less likely to contaminate groundwater. The bond may decrease the rate at which thepesticide is degraded by soil microbes, leading tolonger environmental persistence. Pesticides stronglysorbed to soil particles may travel primarily with erodedsoil and enter surface water, while weakly sorbedpesticides that are more water soluble may be releasedinto soil water solution and enter surface water asrunoff.

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Microbial DegradationCommunities of soil microorganisms are very

diverse. For example, researchers have estimated thatbetween 5,000 and 7,000 different bacterial speciesmay exist in a single gram of fertile soil. Populations ofbacteria can often exceed one hundred million individu-als in one gram of soil, and populations of fungalcolonies can exceed ten thousand.

Microbial degradation is a transformation processthat results when soil microorganisms (bacteria andfungi) either partially or completely metabolize (breakdown) a pesticide. Microorganisms can cause changesin a pesticide when this activity occurs; in the presenceof oxygen it is termed aerobic metabolism, and in theabsence of oxygen, anaerobic metabolism. Mostmicroorganisms inhabiting the soil profile where oxygenis plentiful degrade pesticides via aerobic metabolism.As a pesticide undergoes aerobic metabolism, it isnormally transformed into carbon dioxide and water.Under anaerobic metabolic conditions, microorganismdegradation may produce additional end products suchas methane. Those microorganisms using anaerobicmetabolism for breaking down pesticides are typical ofthe microbes inhabiting waterlogged soils in terrestrialsystems or living in the bottom sediments of ponds,lakes, and rivers. These organisms are also present inground water and, to some extent, in the soil profile.

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Pesticides, along with many other naturally occur-ring organic molecules, may serve as a source of foodor energy for soil microbes. Because they occur at verylow environmental concentrations, however, it isunlikely that their capacity to serve as a food source isadequate to sustain high numbers of microbes. Pesti-cides are more apt to serve as incidental food sourcesfor microbes also drawing from other food sources.

Most soil microbes are associated in colonies on thesoil surface, not free in soil solution. A pesticide in soilsolution has to move to these microbial colonies andcross the microbial cell membrane into the cell tometabolize. Some microbes produce enzymes whichare exported from the cell to predigest pesticides thatare poorly transported. Once inside an organism, apesticide can metabolize via internal enzyme systems.Any energy derived from the breakdown of the chemi-cal can be used for growth and reproduction; anyportion not fully degraded to carbon dioxide or incorpo-rated into cells is released back into soil solution asintermediate chemical metabolites.

Recent studies have revealed that multiple organ-isms often are involved in the degradation phenom-enon. Previous notions that single species are solelyresponsible for microbial degradation of a pesticideprobably are not correct. Different species havedifferent capabilities, and together they can form a ‘poolof talent’ resulting in degradation of the pesticide. Thelikelihood that the chemical will be completely de-graded is decreased if any of the microbes are missingfrom the pool. The ability of microbes to degrade apesticide is related to their metabolic capacity and thecomplexity of the molecule, and to environmentalfactors that regulate microbial activity (water content,temperature, aeration, nutrients).

Abiotic DegradationAbiotic (chemical) degradation is the breakdown of

pesticides by nonbiological reactions (i.e., without theinvolvement of living organisms) occurring in soilsolution and on the soil surface. Factors which affectabiotic degradation include the chemical nature of thepesticide as well as its temperature, water content, andpH. Hydrolysis (reaction with water) is important for thedegradation of many pesticides, as is photodegradation(reaction with sunlight); these two processes generallyare the most important abiotic mechanisms involved.Abiotic degradation results in less transformation of amolecule than does biological degradation.

Hydrolysis is a common chemical reaction—aprocess by which a pesticide reacts with a watermolecule. Hydrolysis reactions generally substitute anhydroxyl (OH) group from water (HOH or H

20 is the

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chemical structure of water) into the structure of thepesticide, displacing another group. Reaction withwater breaks apart the molecule, and the extent ofbreakdown is pH dependent.

Photodegradation (photolysis) involves the break-down of organic pesticides by direct or indirect energyfrom sunlight. Light energy can be absorbed by thepesticide or by secondary materials (e.g., organicmatter) which become ‘activated’ and, in turn, transferenergy to the pesticide. In either case, pesticidesabsorb energy from sunlight, become unstable orreactive, and degrade. Photolysis can occur in water, inair, or on surfaces such as soil or a plant leaf. Pho-tolytic reactions occur near the surface of the ground(in the top few hundredths of an inch) or near watersurfaces, where light can penetrate.

Volatilization

Volatilization is the process whereby a solid or liquidevaporates into the atmosphere as a gas. The processprovides a significant pathway of transfer for somepesticides. In principle, volatilization is an escapemechanism. Compounds with high vapor pressure andlow water solubility have a tendency to volatilize. Thetendency of a pesticide to volatilize from water isapproximated by the ratio of its vapor pressure to itsaqueous solubility. The same is partially true for soils,but the tendency for a pesticide to volatilize from soilalso can be inversely proportional to its potential tobind to soil.

Specific environmental factors that tend to increasevolatilization include high temperature, low relativehumidity, and air movement. A pesticide that is tightlysorbed to soil will have a lower solution concentrationand be less likely to volatilize. That is, less volatilizationoccurs from drier soils because the lack of water allowsthe pesticide to sorb onto soil particles. Volatile pesti-cides usually are incorporated (plowed into the soil)after application to reduce loss into the atmosphere.However, it has also been shown that pesticide volatil-ization from soil is complex and highly dependent onthe movement of water to and from the soil surface.

Once a pesticide enters the atmosphere as a gas, itcan become ‘diluted’ in water droplets and, as a result,highly susceptible to long-range transport from theapplication site. Within the atmosphere, the pesticidemay undergo reactions with light (photolysis) and water(hydrolysis) and sorb to suspended materials such asdust particles. Pesticides in a gaseous state maydissolve in atmospheric water and be transferred backto the soil surface during rainfall.

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Leaching

Leaching is the term for the transport process ofdownward movement (infiltration) of pesticides inwater. Two kinds of phenomena are associated withleaching: preferential flow, and matrix flow.

Preferential flow allows pesticide molecules to moverapidly through a section of the soil profile, with re-duced likelihood that the molecules will be retained bysoil particles or degraded by microbes. Preferential flowis characterized by water that flows rapidly throughworm holes, root channels, cracks, and large structuralvoids in soil.

Matrix flow results in a slower migration of waterand chemical through the soil structure; the pesticidemoves slowly with water into small pores in soil andhas more time to contact soil particles.

The potential for volatilization and photolysisdiminishes considerably as the pesticide infiltrates thefirst few hundredths of an inch of soil. As the pesticidemoves lower into the root zone, there is generally lessorganic matter, more compaction, and lower bioticactivity. Once the pesticide leaches past the root zone,abiotic degradation reactions frequently become moreimportant than biotic reactions because microbial

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populations generally are smaller below the root zone.In fact, microbes in deeper soils operate under ‘starva-tion’ and are less energetic due to a lack of carbon andnitrogen. In addition, pesticides rarely reach deep intothe soil profile; so microbes, therefore, are not adaptedto degrade them quickly.

The most important factors in determining whether apesticide will leach are its degradation (persistence)capabilities, its sorption characteristics, and its inclina-tion to release rapidly into soil solution once it issorbed. Pesticides that are weakly sorbed by soil andresist degradation are more likely to leach to groundwater than are those that remain bound to soil. Factorssuch as soil type, topography, and rainfall also mayimpact the leaching potential of a pesticide; and factorssuch as application rate, frequency, and type (foliar,pre- and post-emergence) need to be considered.

The fate of pesticides in aquifers is unclear. Studieshave shown that degradation will occur in the capillaryfringe (the region above the aquifer) and in groundwater. Subsurface rates of degradation tend to belower than those in surface soils, perhaps reflectingsmaller microbial populations, limitations in essentialsecondary nutrients, or lack of adaption (of microbialpopulations) to use the compound.

Runoff and Erosion

Runoff—movement of water across the soil sur-face—occurs when water collects (due to rainfall,irrigation, or melting snow) at a rate faster than it caninfiltrate the soil. As rain falls, small soil particlesbecome dislodged and are carried laterally by water ina process known as erosion. Because pesticides areapplied directly to the soil, large amounts eventuallyend up there; and as water runs off and soils erode,dissolved and sorbed pesticides go along. Runoff anderosion have the potential to move more pesticide offsite than leaching, due to the fact that runoff is asurface phenomenon. Surface runoff and erosion movepesticides and other pollutants laterally from points ofhigher elevations to collection points (streams, rivers,ponds, lakes) at lower elevations. Climatic factors suchas rainfall timing, duration, and intensity, and surfacefeatures such as slope length and grade, soil perme-ability, and surface cover greatly influence the degreeto which pesticides are mobilized by runoff and erosion.Similarly, pesticide management factors may signifi-cantly affect runoff; for example, a soil-incorporatedpesticide is less likely to run off site than the samecompound applied to the soil surface.

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The goal of modern pesticide chemistry is toproduce pesticides that are effective in smaller quanti-ties, more target-specific, and less persistent in theenvironment. Pesticide structures are developed tomimic—and therefore substitute for—specific mol-ecules in targeted biological reactions; i.e., the pesti-cide mode of action is unique to the targeted pest.Such specificity is achievable with complex chemicalstructures which disrupt target-specific biologicalprocesses to effect the desired control and yield lesspersistence in the environment.

Pesticide products new to the marketplace beganthe registration journey seven to nine years earlier in aresearch laboratory. After development, two years ofexploratory research are needed by the manufacturerto define the chemical’s biological and environmentalcharacteristics and to make comparisons with existingproducts. Pesticides identified as commercially viableare studied for an additional three to five years to

THE PESTICIDE TESTING PROCESS

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ensure that they meet the health and environmentalcriteria established by company philosophy and policy,and government regulations. During this additionaltesting period, an average of 120 studies are com-pleted to satisfy testing mandates as specified by theFederal Insecticide, Fungicide, and Rodenticide Act(FIFRA) administered by the U.S. EnvironmentalProtection Agency (EPA). Typically, the developmentand registration of a new pesticide costs between $40million and $50 million; and upon completion, the entireresearch package is submitted to EPA for review.

The EPA review process takes two or more years,followed by assignment of an EPA registration number(a legal requirement that must be met before the newproduct can be sold to the public). Under FIFRA, aproduct may be granted a registration number only ifsupporting data indicate that its potential benefits tosociety outweigh the probability of risk to people,wildlife, and the environment when used as directed inits labeling. Recouping development costs from yearsof research and subsequently generating profits for thecompany to reinvest in new pesticide research hingeon the ability of the product to compete successfullywith others in the marketplace.

Because of the time lag between discovery andproduct registration, manufacturers must foresee anyeffects which imminent environmental regulations mighthave on current research data. Failure to anticipatechanges in environmental regulations could lead toadditional years of research prior to registration.

Development of Environmental FateData

Discovery of ‘environmentally acceptable’ pesti-cides requires researchers to unravel the complexitiesof chemical behavior in the environment. Experimentsdesigned to do so are time-consuming and costly andrequire expertise from numerous scientific disciplines.

Discovery PhaseMost manufacturers employ a screening process to

identify promising compounds for further study andunfavorable ones to be discarded. Primary screens areused to pinpoint chemicals with pesticidal properties.Their impact on growth, development, behavior, andmortality of pest insects, weeds, and diseases iscarefully observed and recorded. It is important that theprocess uncover novel modes of action rather thangenerating copycats of those already in the market-place. From a marketing standpoint, chemicals lackingdistinct advantages in terms of efficacy and selectivityare unlikely to generate revenues sufficient to support

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the significant costs associated with development,registration, and field support.

Pesticides entering the screening trials may besynthesized with specific targets in mind or producedby microorganisms inhabiting the soil. Others may bediscovered by examining structural activity relation-ships coupled with molecular modeling. New pesticidesoriginate from industrial manufacturing waste streamsand from by-products of other industries; these sourcesprovide about 30,000 chemicals annually for inclusionin pesticide screening programs.

Fewer than 200 of the 30,000 chemicals per yeardisplay the kind of activity on pests that warrantsfurther evaluation. Most compounds are excluded fromadditional testing because they are not sufficientlyselective, the cost to the manufacturer is unacceptable,the potential market is too small, or they demonstrateunacceptable hazards. In order to be economicallyviable, the pesticide must be used commercially for oneor more major crops (corn, soybeans, wheat, orcotton).

Secondary screening (on compounds which havesurvived primary screening) involves the use of proven,reliable predictors of biological and environmentalproperties to identify negative chemical attributes.Biological, environmental, and economic questionspertinent to the commercial potential of these chemi-cals are listed below.

• What is the water solubility of the material?• How mobile is the compound in soil?• How persistent is the compound in the environ-

ment?• What are the short-term effects on laboratory test

animals such as rats?• How toxic is the compound to man, birds, aquatic

organisms, insects, and nontarget plants?• Will the chemical be toxic to desirable nontarget

plants?• Does the material bioaccumulate (that is, does it

build up in the environment)?• What prototype formulation will be tested?• Can the material be produced in sufficient quantity

to continue testing?• What kinds of manufacturing processes may be

needed?• Is there a market, and does it meet other commer-

cial objectives?• Can it be produced at a cost that will provide a

product at a price that the users will pay?• What are the strengths and weaknesses of current

and expected competing products?

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Research and economic development teamsevaluate the relative strengths and weaknesses ofeach chemical and, in turn, their analyses are consoli-dated into product profiles. Many products are shelvedbecause their profiles indicate undesirable health orenvironmental attributes, manufacturing problems, orsales potential insufficient to capture an adequateshare of the market. Decisions to eliminate certainproducts carry an expensive price tag: two years ofresearch costing a million dollars for each chemical inthe secondary screen.

Predevelopment PhaseChemicals which survive the secondary screening

process are tested extensively to produce a databasethat supports EPA registration of the product. Manufac-turers must conduct and analyze research and presenttheir findings according to protocol outlined by EPA. Alldata submitted in support of pesticide registration mustresult from research conducted under Good LaboratoryPractices (GLPs). GLPs are regulations issued by EPAthat prescribe the procedures for extensive documenta-tion and verification of every step of the testing pro-cess. This assures that the data were developed byappropriately trained scientists and verifies the authen-ticity of the data used to achieve the results. Theauditing of data and reports to assure GLP complianceis a very expensive component of the product develop-ment process.

Summary of Environmental Fate StudiesRequired by EPA

Three basic questions on environmental fate mustbe answered in the data supporting EPA registration:(1) How fast and via what pathways does the pesticidedegrade? (2) What are the breakdown products? (3)How much of the pesticide or its metabolites willmigrate, and where will they accumulate in the environ-ment? Environmental fate data generated from labora-tory and field experiments are then used to assess thepotential for negative impact on the environment. Riskassessment involves comparing effects data fromvarious toxicological studies with fate and exposuredata to predict potential health and environmentalimpacts—and to protect natural resources in general.

A tiered approach to testing is used to simplify theprocess of investigating environmental fate data forpesticide registration. The first tier of environmentalfate studies addresses hydrolysis; photodegradation inwater and soil; aerobic soil and anaerobic aquaticmetabolism; mobility; and terrestrial field dissipation.The second tier consists of field soil studies andadditional laboratory research triggered by results offirst tier work.

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Finally, a third tier addresses key transport mecha-nisms indicated (by preliminary studies) as significantin assessing the ultimate environmental impact of theproduct—for example, small scale ground watermonitoring studies or surface water runoff evaluations.If a product’s margin of safety is low in any environ-mental compartment, large scale surface and groundwater monitoring programs and ecosystem investiga-tions may be conducted under ‘conditional’ registrationfor the purpose of demonstrating in-use safety.

Abiotic Degradation Studies

The reactions of a pesticide with water (hydrolysis)and light (photolysis) are important in predicting achemical’s ultimate environmental fate. When a pesti-cide reacts with water or absorbs solar energy, eitherdirectly or indirectly, the chemical bonds holding theparent molecule together are broken. Degradationstudies are conducted to document the formation anddecline of the parent compound, as well as transforma-tion products.

Controlled hydrolysis studies are conducted accord-ing to federal regulations to identify how a pesticidereacts with water. The chemical is added to watersterilized to kill pesticide-degrading microorganismsand buffered to test hydrolysis under acidic, alkaline,and neutral conditions. Pesticides containing taggedradioactive carbon-14 can be used to help scientists

track the environmentalfate of the chemicalthrough its degradedproducts. Placement indark incubatorsprevents the pesticidefrom reacting with light.Test samples arecollected periodicallyfor 30 days andanalyzed to determinethe amount of parentmolecule remainingand the productsgenerated, and toaccount for all of theradioactive carbon-14.

Pesticide transformation also can occur via photoly-sis. Studies of photodegradation in water are con-ducted in a manner similar to hydrolysis experiments,except that they are conducted in the presence ofsimulated or actual sunlight. Photodegradation on soilis studied by applying a radiolabeled pesticide to a thinlayer of sterile soil. The treated water or soil is irradi-ated with simulated or actual sunlight and degradation

1

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is charted. Samplesare collected over a30-day period andanalyzed as in hy-drolysis studies.Aqueousphotodegradationstudies, compared tohydrolysis studies,show how sunlightaffects chemicalbreakdown in water.Soil photodegradationstudies show how soilcomponents (e.g., clayand organic matter)affect pesticidebreakdown. These data can be compared and path-ways for the two systems established.

Metabolism Studies

In addition to plant metabolism and uptake studies,the biological degradation of pesticides by microorgan-isms in soil is examined. The term metabolism is usedsince most pesticides are degraded primarily bymicroorganisms in soil that metabolize all or part of thepesticide molecule.

Three kinds of environmental metabolism studiesare required under FIFRA: a one year aerobic soilmetabolism study using selected field soils; a 30-dayaerobic aquatic metabolism study using sediment and

2

3

4

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natural water; and a one-year (maximum) anaerobicaquatic metabolism study using sediment and naturalwater. These studies seek to determine how fast parentmolecules are degraded by biological processes(mainly microorganisms) in different soils, aerobicsediment and water, or anaerobic sediment and water,and to determine what metabolites are formed. To bevalid, these studies also must account for the radioac-tive carbon-14 used as a tracer.

Field soils known to be previously unexposed topesticides are used in the various metabolism studies.Oxygen is maintained for aerobic metabolism studies,while anaerobic studies require that the soils or sedi-ments be purged of oxygen. A radiolabeled pesticide isapplied to the soil or sediment and, at specified inter-vals, researchers remove and analyze samples for theparent pesticide and any metabolites. If volatile materi-als and CO

2 are released, they are trapped and ana-

lyzed.

Mobility StudiesScientists estimate potential mobility of a pesticide

by first determining its sorption in soil. Soil and waterare made into a slurry which is then treated with arange of pesticide concentrations. After a period oftime, the slurry is centrifuged to separate the soil andwater, after which the chemical concentration in each isdetermined.

Pesticide retention is a sorption coefficient (Kd)

expressed as a ratio of the concentration of chemicalsorbed to soil to the concentration of chemical remain-

ing in water: Kd = sorption:solution.

The Kd is relevant to understanding

pesticide transport since chemicalsremaining in soil solution can leach orbecome available in the water of apond or stream. Because pesticides insoil solution are subject to leaching,the extent of sorption as measured bythe K

d serves as a predictor of mobility:

the higher the Kd, the lower the

tendency to move in soil. For example,if a K

d is lower than 2, the molecule is

termed highly mobile; if it’s between 2and 5, the molecule is consideredmobile; and if the K

d is greater than 5,

it’s deemed immobile with respect toleaching.

Frequently, the Kd is expressed as

a Koc

by dividing the Kd by the fraction

of organic carbon present in the soil:Koc = Kd ÷÷÷÷÷ fraction organic carbon.This mathematical transformation

5

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allows the potential mobility of a chemical to be com-pared with that of other chemicals, regardless of soiltype. A K

oc value greater than 500 is usually associated

with immobile pesticides.

Field Dissipation Studies

Terrestrial field studies are conducted to verify theintegrated routes and rates of pesticide degradationand mobility demonstrated in the laboratory; the lengthof time required to complete the terrestrial studies isestimated from data generated in the lab. Pesticideswhich are persistent—those that have a soil metabo-lism half-life greater than 6 to 12 weeks under optimalconditions for degradation—generally require at leasteighteen months per study. Field studies with lesspersistent pesticides often can be completed within ayear.

When a pesticide is proposed for use over largeareas and/or multiple crops, several field test locationsand cropping scenarios are required for field dissipationstudies. The test sites must be established and main-tained according to best management practices for theintended crop or noncrop use. Preapplication samplingand analysis of the soil to a depth of three feet areperformed to confirm that no pesticide is present. Anend-use product is applied with typical applicationequipment at the highest rate stated on the proposedlabel. At timed intervals, representative samples areremoved at prescribed depths and analyzed for thepresence of the parent product and environmentallysignificant metabolites. Since terrestrial dissipationstudies are most frequently conducted with unlabeledchemicals, precise method development to assuresensitive analysis of soil residues is necessary. Pesti-cides that are active at low rates require sophisticatedand highly sensitive analytical methods for extractionand analysis of the parent molecule and significantmetabolites; measurements in parts per billion arenecessary.

Dissipation studies also must be conducted todetermine the environmental fate of pesticides desig-nated for aquatic crop and noncrop uses. Protocols forconducting aquatic studies and the timetables involvedare similar to those of terrestrial field studies. Waterand sediment (and sometimes animal and plant)samples are collected for analysis to detect the parentmolecule and significant metabolites.

Decisions to Move Toward Commercialization

Successful development of a product requiresteams of scientists working on various test componentsand discussing their results at every level of the testing

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process. Discussion on the chemical’s fate and behav-ior, short- and long-term health effects, ecotoxicity,environmental toxicity, and production and economicinformation is ongoing. The benefits of the productversus its risk potential are under constant scrutiny.The project may terminate at any time during thepredevelopment process if evidence suggests potentialbiological, environmental, or marketing problems. Onlyone or two chemicals out of 30,000 survive the rigors ofthe seven- to nine-year research and evaluationprocess, and those must assume the burden of recoup-ing production costs for all.

Development/Registration Phase

Final internal review and discussion are conductedby the developer to ensure the validity, accuracy, andinterpretative summaries of all data. Each experimentmust be accompanied by complete descriptions of theprocedures used, by experimental designs, and bydetails that allow EPA data evaluators to reconstructthe experiment. Environmental tests include qualitativeand quantitative descriptions of the active ingredientand metabolites; and besides the data, per se, asummary of data, data analysis, and sufficient descrip-tion to verify statistical procedures are required. Oncethe internal company review is satisfactorily completed,the scientific data can be forwarded to EPA as part ofthe registration package.

The registration package and the application forregistration are processed at EPA and assigned to aProduct Manager (PM) in the Registration Divisionwithin the Office of Pesticide Programs (OPP). It is theresponsibility of the Registration Division to concludewhether a new pesticide product satisfies the require-ments of FIFRA and should be registered. The Regis-tration Division is supported by others within OPP inthe review and evaluation of the supporting datapackage. The PM tracks the current status of theregistration request and serves as liaison between EPAand the registrant (i.e., pesticide manufacturer). EPAhas been mandated by the United States Congress toensure that the conduct of the investigations meetsscientific protocols.

Prior to the time a registration application is submit-ted to EPA, a company developing the product usuallyrequests permission (in the form of an experimentaluse permit) to use the new pesticide under field condi-tions in numerous marketing areas. Prior to issuing anexperimental use permit, EPA must make the decisionthat use will not present unreasonable adverse effectsto man or the environment.

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An experimental use permit is issued for finiteperiods of time and allows the company to developdata in support of registration that can be obtained onlyunder normal use conditions (as prescribed by theproposed labeling). This work often is conducted byuniversities and consultants using farms or researchfield stations. Experimental use permits are requiredwhen field research is conducted on ten acres or more.Once all of the required supporting data are developed,the application for registration is submitted to EPA forreview and evaluation.

EPA may meet with company representatives todiscuss research methodologies or conclusions, or torequest the original data. The registrant may be askedto repeat experiments, redesign research methods, orconduct additional testing. Registration ultimately willbe granted only when EPA concludes that the benefitsof the product (increased production, lower food costs,etc.) outweigh any potential for harm to people, wildlife,or the environment. Since pesticide registration deci-sions, by law, are based on benefits as well as riskassessment, all registrations are conditional; EPA mayrequire the registrant to conduct further studies,suggest and implement strategies to minimize risks tothe environment, or monitor for the presence of thepesticide and its metabolites in ground and surfacewater. Product registration covers only the uses andcrops addressed in the studies submitted; additionalstudies may be required to qualify the product forexpanded registration.

Product Stewardship Phase

The average cost of developing a single marketableproduct from among 30,000 chemicals screened isestimated at $35 million to $50 million; total expendi-tures might reach $150 million if the cost of manufac-turing plants, etc., were factored into the equation.Moreover, nearly half of the original 17-year patent lifeis spent on research, development, and registrationprocesses; and the pesticide that survives to earn anEPA registration number is not guaranteed success inthe marketplace. Manufacturers must exercise goodstewardship in maintaining and supporting their pesti-cide product and ensuring that its use is consistent withthe label. They are required under FIFRA to report anyevidence of problems relative to the use of the productwhich are identified after registration; as a result,additional label restrictions, suspension, or cancellationof the product might be imposed—and themanufacturer’s investment in the pesticide productmight be lost in the process!

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The environmental fate studies discussed previ-ously provide the basis for screening pesticide registra-tion candidates for effects on water quality. Evaluationsalso may take place for previously registered pesticideswhen their use has generated water quality concerns orwhen their data packages need to be upgraded tocurrent regulatory standards. The scope of the regula-tory screening process focuses on two aspects ofpesticide behavior which affect leaching and runoff: 1)persistence, or how long it takes for the pesticide to betransformed into an essentially harmless substance;and 2) mobility, or how easily the pesticide can betransported to ground or surface water.

As described previously, information on the persis-tence of the pesticide is obtained primarily from soilmetabolism, hydrolysis, photolysis, and field dissipationstudies. Information on the mobility of the pesticide isobtained primarily from sorption experiments, leaching,and field dissipation studies. A complete set of environ-mental fate studies generally is sufficient for identifyingpesticides that have the potential to leach into groundwater or to enter surface water as runoff.

The results of environmental fate studies are notalways sufficient to estimate concentrations of apesticide in aquifers or surface waters when thechemical is used in different geographical areas, or todefine specific areas where water contamination mightoccur. Therefore, presumptive decisions on userestrictions or limitations must be made for pesticideswith the potential to affect water quality. These deci-

sions might be madelong after registration,as cumulative infor-mation warrants;labels may be modi-fied to be more or lessrestrictive, dependingon the results ofsurface and/or groundwater monitoringstudies.

Although there issome interactionbetween surface andground water, theprimary mechanisms

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REGULATORY EVALUATION OFENVIRONMENTAL FATE DATA FORWATER QUALITY CONCERNS

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of pesticide entry into the two usually are quite differ-ent. Therefore, EPA addresses concerns regardingpesticide contamination of surface and ground waterindependently.

Screening Pesticides for Potential toLeach into Ground Water

In most cases, a period of a few months to severalyears is required for a pesticide to leach considerabledistances through soil to reach ground water. There-fore, a pesticide generally needs to be both persistentand mobile to reach most aquifers.

The extent of pesticide movement through soildepends on the degree of interaction between thepesticide and soil particles, soil microorganisms, andweather. The amount of pesticide that will reach lowsoil depths varies dramatically with slight environmentalfluctuations, making estimation difficult. A judgment canbe made on the overall likelihood of ground watercontamination by comparing the mobility and persis-tence of a chemical to those of similar pesticidespreviously detected in ground water at multiple usesites. Many factors affecting the environmental fate of apesticide are not well understood. Site-specific behav-ior of pesticides in soils cannot be predicted unlessactual field data are available for comparison.

Assessment of Comparative LeachingPotential

Several methods are used by federal and stateregulators to assess a pesticide’s leaching potential.Most estimates rely heavily on soil half-life and K

d as

the most consequential parameters.Modeling results should never be considered

equivalent to real data. All pesticide leaching modelsare mathematical tools (with varying degrees of com-plexity and sophistication) that attempt to reduce whathappens in the ‘real world’ to formulas. However, noformula can cover every possible contingency in thenatural environment; there is still a great need tovalidate models by collecting pesticide residue andenvironmental condition data from the field. As morevalidation work is done, models will come closer tosimulating the real world; but they probably never willbe sufficiently sophisticated to completely eliminate theneed for collection of field data.

Trigger Values

In this simplest of assessment methods, pesticidesare presumed to have ground water contaminationpotential if environmental fate studies trigger multiplecriteria for both mobility and persistence. Trigger values

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are based strictly on laboratory data. Further refine-ments of ground water assessment of the pesticideshould consider additional field parameters such asapplication rate, soil, and target crops. Trigger valuesare determined from a group of reference pesticideswhich have a history of use and extensive groundwater monitoring. The following values may be used byregulators as an initial step to identify pesticides mostlikely to leach to ground water:

Trigger Values Related to Persistence1. Aerobic soil metabolism half-life of greater than

two to three weeks;2. Field dissipation half-life of greater than two to

three weeks;3. Photolysis half-life greater than one week; or4. Hydrolysis half-life greater than 60 days in sterile

water.

Trigger Values Related to Mobility1. K

oc usually less than 300;

2. The pesticide is a weak to moderate acid whichwould not be attracted to most soil particles; or

3. Water solubility greater than 30 parts per million(ppm).

The Groundwater [sic] Ubiquity Score

The Groundwater [sic] Ubiquity Source (GUS) isanother estimator model which, like trigger values, isuseful for comparing the intrinsic leaching potential ofpesticides. The GUS model is more sophisticated thantrigger values because it uses a formula that combinespesticide mobility and persistence parameters. Tocalculate the GUS, average values for only two pesti-cide parameters are needed: the soil degradation half-life, and the soil K

oc. Pesticides with a GUS greater than

2.8 are more likely to leach to ground water, whilethose with GUS values between 1.8 and 2.8 aresomewhat less likely to leach. Pesticides with GUSvalues less than 1.8 are unlikely to leach to groundwater.

The Pesticide Root Zone Model

The Pesticide Root Zone Model (PRZM) has beendeveloped by EPA and provides site-specific leachingestimates. PRZM, like other pesticide soil fate andtransport models, incorporates soil characteristics andhydrology, weather, irrigation, and crop managementpractices into complex mathematical formulas thatestimate leaching potential. EPA uses PRZM (andsimilar models) to make multiple site comparisons ofthe leachability of a pesticide to older, referencepesticides with histories of use and extensive groundwater monitoring. Models like PRZM also provide

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estimates of the concentration of a pesticide that willleach, but these estimates should be confirmed withactual field data.

The Pesticide Assessment Tool for RatingInvestigations of Transport

The Pesticide Assessment Tool for Rating Investi-gations of Transport (PATRIOT) is a site-specificscreening model. That is, PATRIOT provides a quickestimation of the relative leaching potential of a pesti-cide at representative sites. The PATRIOT user firstmust select crops, geographical areas, and soil typesof interest. PATRIOT automatically simulates weather,using historical records from stations with soils thatclosely resemble those selected for modeling; and itautomatically incorporates appropriate irrigationschemes. Pesticide characteristics needed for model-ing are also provided by PATRIOT; however, for newerpesticides the user must input personal estimates ofthe required values. Finally, PATRIOT performssimulations of pesticide leaching and provides esti-mates of pesticide leaching under varying conditions.Therefore, the leaching potential of a pesticide indifferent cropping systems or in different soil types canbe evaluated with PATRIOT.

Special Studies to Evaluate LeachingPotential

When analysis of environmental fate data indicatesa potential for ground water contamination, EPA mayrequire ground water monitoring studies (called secondtier studies) to determine if pesticide use limitations arenecessary. Ground water monitoring studies may berequired for a registered pesticide when new data(such as ground water detections at multiple sites)indicate contamination not initially anticipated. Groundwater monitoring studies also may be required as acondition of registration when properties of a newpesticide fall within an area where actual field data areneeded to better ascertain risks.

Before requiring a ground water study for pesticideswith established uses, EPA must determine that thereis a likelihood that ground water contamination atmultiple sites has occurred or may result from currentlyregistered uses. EPA also considers various environ-mental and toxicological effects that may be present.

Typically, field-scale studies are conducted in areasthat are relatively vulnerable to ground water contami-nation. These studies track the movement of an appliedpesticide and a tracer—a substance such as bromideused to follow the subsurface movement of waterthrough the soil profile—into ground water. Tracer data

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help analyze how readily a pesticide moves with waterthrough the soil profile.

Soil cores (soil-water sampling devices throughoutthe subsoil) and the monitoring of wells which drawground water from the upper portion of the aquifer areused to track the movement of the pesticide and tracer.Irrigation must be used as supplemental precipitation toensure that the site receives moisture equal to thatwhich would occur naturally in a wetter than averageyear.

Sampling in ground water monitoring studies iscontinued until the degree of ground water contamina-tion by the pesticide, if any, is well characterized.Results from completed studies are used to evaluatethe magnitude of ground water contamination that mayoccur over the proposed use area.

Pesticide leaching models such as PRZM may becompared to actual field study results at a given site todetermine their reliability in predicting leaching poten-tial. If found sufficiently reliable, these models then canbe used to estimate the impact of a pesticide over anentire use area. The quality of data from ground watermonitoring studies influences estimates of predictedbehavior in the use area. Modeling based on real-worlddata from ground water monitoring studies is useful inevaluating the potential for pesticide exposure. Addi-tionally, modeling may be used to develop use restric-tions to mitigate the potential for pesticides to reachground water.

Ground water monitoring data also are used by EPAto evaluate the impact of pesticide use on ground waterquality in the public domain. One major effort in thisarea is the collection of data in the Pesticides inGround Water Database which is maintained by EPA'sOffice of Pesticide Programs. The Pesticides in GroundWater Database summarizes (by state and county)monitoring data from various state entities, federalagencies, and other sources. Validated data collectedfrom these sources according to rigorous, prescribedprocesses may be used by EPA to support regulatorydecisions. In recent years, the U.S. Geological Survey(USGS) has greatly increased the number of pesticideanalyses included in their ground water monitoringprograms. USGS data often are of particular value toregulators because, traditionally, they have beencentral to the USGS mission to collect a full comple-ment of hydrogeologic data to facilitate interpretation ofwater resources monitoring data that they collect.USDA’s Agriculture Research Service also is increas-ingly involved in collecting monitoring data.

Even under optimum conditions, not all questionson the potential of a pesticide to impact ground watercan be answered from field scale monitoring studies

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conducted in support of registration—or from outsidemonitoring studies.

Often there are some use situations where thelikelihood of a pesticide leaching to ground waterremains uncertain. Pesticide producers (registrants)cooperate more and more with state regulatory,agricultural, and environmental agencies to designmonitoring programs to ensure that unexpected andundesirable environmental effects do not surface aftera pesticide is registered. Should uncertainties remainwhen a product is registered, pesticide registrants mayagree to conduct ongoing monitoring programs de-signed to provide information that can be used to headoff potential ground water contamination problems.

Screening Pesticides for Runoff Potential

The runoff potential of a pesticide is influenced bythree factors: type of soil; slope of terrain; and theintensity and timing (with respect to pesticide applica-tion) of rainfall. All three factors should be consideredwhen estimating runoff potential. A nonpersistentpesticide (i.e., one which does not sorb to soil particlesor organic matter) can be transported from its applica-tion site to major bodies of surface water in as little as afew minutes or hours when heavy rains occur shortlyafter application. A pesticide exhibiting strong sorptionto soil usually will have a lower runoff potential than apesticide exhibiting weak sorption, but it can still reachsurface water if sorbed to soil particulates eroding withthe flow.

Data describing persistence and sorption are usedto categorize pesticides and their major degradationproducts into one of nine categories. These ninecategories qualitatively separate pesticides accordingto their relative potential to contaminate surfacewater—in terms of both magnitude and duration ofoccurrence expected. Pesticides also are distinguishedaccording to their relative propensity to occur in thedissolving or sorption phase.

In evaluating surface runoff potential, pesticides areassigned to the nine categories based on their half-lives and sorptive K

oc. The following criteria apply:

• Sorptive K oc

1. Low sorption: Koc

less than or equal to 1000

2. Intermediate sorption: Koc

greater than 1000and equal to or less than 10,000

3. High sorption: Koc

greater than 10,000

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• Persistence (Half-Life) in Soil

1. Short: half-life equal to or less than 2 weeks

2. Intermediate: half-life greater than 2 weeksbut less than or equal to 2 months

3. Long: half-life greater than 2 months

Thus, using the prescribed criteria, pesticides canbe grouped into nine categories representing eachpossible combination of low, intermediate, and highsorption relative to short-term, intermediate, and long-term persistence (e.g., low sorption/short persistence;or high sorption/intermediate persistence).

Persistence grouping helps predict how long apesticide will remain in the soil and, therefore, suscep-tible to runoff. Such considerations are important sincesome mitigation procedures effective in reducing soilerosion are not necessarily effective in reducing runoffvolume, and vice versa. Sorption characteristicsinfluence how much of a pesticide dissolves in waterduring runoff as opposed to how much is carried intorivers, streams, ponds, lakes, etc., where it remainssorbed to sediment.

Assessment of Runoff Potential andSurface Water Contamination

The following methods may be used to assess thepotential of a pesticide to enter surface water as runoff.

Surface Water Monitoring Studies and Database

EPA uses data on surface water concentrations ofthe widely used herbicides atrazine, cyanazine, si-mazine, alachlor, and metolochlor for risk assess-ments. For other pesticides, EPA must rely on partiallyvalidated computer modeling because data frommonitoring studies are limited. In cases where risk tonontarget organisms is known or predicted to be high,EPA’s Office of Pesticide Programs requires runoff andsurface water studies to verify the effectiveness ofmitigation in reducing amounts of pesticides reachingsurface water through runoff.

EPA is developing a database for monitoringpesticide residues in surface water. It will consist ofdocumented data which can be used in place of, or inconjunction with, modeling predictions to performaquatic risk assessments. Data from the ongoingUSGS National Water Quality Assessment Program,the multi-agency Environmental Monitoring and Analy-sis Program, state agencies, water supply systems,and pesticide registrants are used.

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Computer Modeling

Environmental fate data can be used in computermodels to predict pesticide contamination of surfacewater in more locations, over longer periods of time,and under more diverse conditions than are feasiblefrom field use or monitoring studies. Runoff and surfacewater monitoring studies are subject to unpredictableweather factors, but computer modeling uses historicalweather data gathered over long time spans and widegeographical areas.

Models currently used for predicting the potential forpesticide runoff into surface water include PRZM andGround Water Loading Effects of Agricultural Manage-ment Systems (GLEAMS). The input to both modelsincludes pesticide fate properties, soil characteristics,management practices, and daily weather. Output fromboth models includes estimated runoff volumes,sediment yields, and associated pesticide concentra-tions at the edge of the field. Estimated pesticide runoffconcentrations from PRZM or GLEAMS and estimatedpesticide concentrations from spray drift are input to

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receiving surface watermodels such as theExposure AnalysisModeling System(EXAMS) or the WaterQuality AnalysisSimulation Program(WASP). In addition topesticide concentra-tions from runoff andspray drift, input toboth EXAMS andWASP includespesticide fate proper-ties and receivingwater characteristics.Output—described asa function of time and location—from both EXAMS andWASP includes estimated peak and varied durationaverage pesticide concentrations (1) present in water,(2) sorbed to suspended sediments, and (3) sorbed tobottom sediments.

Temporal and geographical distributions of pesticideconcentrations based on computer estimates (or onadequate monitoring data) are used to predict whereand how frequently maximum, short-term average, orlong-term average concentrations will exceed acute orchronic toxicity thresholds for humans and othernontarget organisms. The temporal and/or geographi-cal distributions of computer-estimated or measuredconcentrations generally are plotted as cumulativefrequency curves. Such curves are created by plottingmaximum, short-term average, or long-term averagepesticide concentrations against the percentage ofyears or sites where equal or higher concentrationswould be expected. Such approaches are usefulbecause they allow scientists and regulators to betterassess the likelihood of runoff and to predict when apesticide might exceed a level of health or environmen-tal concern.

The primary disadvantage of computer modeling isa general lack of controlled field monitoring data tovalidate the results. Validation with the appropriate datais needed to ensure accurate model estimates. Due tothe conservative assumptions used and a knowledge ofexisting field and monitoring data, scientists at theEnvironmental Fate and Ground Water Branch of EPAare reasonably confident their modeling estimates ofpesticide runoff and concentrations in surface water(using PRZM) are conservative—that is, higher thanactual and therefore protective. Although some valida-tion has been performed, additional work is needed,particularly with respect to pesticide fate modeling.

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Studies to Evaluate Runoff to SurfaceWater

Runoff studies are not routinely required underFIFRA. When available, the results of field and smallscale runoff studies are used to assess the effective-ness of mitigation methods. Such results also are usedto verify and to better quantify preliminary and model-ing estimates of the runoff potential of pesticides andtheir major products of degradation.

Both field and small scale studies provide data onthe amounts of water, soil, and pesticide transported inrunoff from agricultural fields during and followingrainfall. Small scale runoff studies are gradually gainingfavor over large scale field studies because they arelarge enough to consider the effects of formulation,tillage, crop cover, soil type, and slope on the transportof water, soil, and pesticides from the field, yet smallenough to allow the use of weather-independent rainfallsimulators. Consequently, the problem of unpredictableweather patterns in field studies is eliminated. Small

39

scale studies also are much cheaper to conduct thanare field studies, so for the same cost more combina-tions of factors affecting runoff can be studied.

The major disadvantage of small scale studies isthat the amount of water, soil, and pesticide trans-ported by runoff from each unit area often is substan-tially higher than from agricultural fields. Some of thisdifference apparently is due to site-specific hydrologicalfactors such as sediment deposition, ponding, andinfiltration. Experimental conditions such as the use ofhigh intensity artificial rainfall in small scale studies alsomay account for much of the effect in variable output.

Surface Water Monitoring StudiesSurface water monitoring studies provide data on

the concentration of pesticides in streams, rivers, lakes,and reservoirs. Pesticide concentrations in streams andrivers are highly seasonal, with peak concentrationsoccurring during the first few runoff-producing stormsafter application, followed by rapid decline. However,pesticide concentrations remain longer in lakes andreservoirs than in rivers and streams due to longerhydrological residence times.

Pesticide concentrations in samples collectedinfrequently, or in samples collected at set samplingtimes not coincident with significant runoff, often do notaccurately reflect peak concentrations. Pesticideconcentrations in samples collected from a singlelocation can vary as much as tenfold from year to year.Consequently, surface water samples taken on only afew occasions, or over a short span of time, often donot adequately represent the source. The multitude ofpesticide detection possibilities, the methods of differ-entiating between zero concentrations and parts perbillion, and the necessity of precise, timely, repetitivesampling make surface water monitoring studies quitecostly.

Spray Drift StudiesSpray drift studies and modeling also are used to

estimate drift and the correlated deposition of pesti-cides into adjacent bodies of surface water and ontonontarget plants. The Spray Drift Task Force (SDTF), acoalition of 32 pesticide registrants formed to develop acomprehensive database of off-target drift informationin support of pesticide registration requirements, hasconducted spray drift studies and evaluated spray driftmodels. The results should afford EPA the ability topredict pesticide spray drift deposition into surfacewater based on distance from sites of application, andto predict the effectiveness of land buffers and applica-tion techniques in reducing pesticide spray drift tosurface waters.

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Human Risk AssessmentThe Safe Drinking Water Act was implemented in

1974 to protect public water supplies from all types ofcontaminants. EPA’s Office of Drinking Water evalu-ates, describes, and communicates health risks fromcontaminants in drinking water through Health AdvisoryLevels and Maximum Contaminant Levels.

Health Advisory Levels

A Health Advisory Level (HAL) is considered themaximum level of a drinking water contaminant, inmilligrams per liter (parts per million, or ppm) or micro-grams per liter (parts per billion, or ppb), that would notbe expected to cause noncarcinogenic health risksover a given duration of exposure. This does not mean

RISK ASSESSMENT OF PESTICIDESFOR WATER QUALITY CONCERNS

41

that levels above the HAL will necessarily pose healthrisks but, rather, that uncertainty warrants prevention ofexposure above the HAL. However, HALs are nonen-forceable standards.

Understanding the toxicological properties of adrinking water contaminant is necessary when calculat-ing a health advisory. Toxicological profiles for pesti-cides generally are derived from animal tests becausehuman testing is not possible. Data from humanepidemiological studies can be used, but such datagenerally are unavailable. The Lowest ObservedAdverse Effect Level (LOAEL) or No Observed Ad-verse Effect Level (NOAEL) are two important toxico-logical endpoints determined from animal tests.

The NOAEL is the maximum daily dose (of thechemical tested) per unit of body weight shown toproduce no adverse health symptoms in test animals.The LOAEL is the lowest daily dose per unit of bodyweight confirmed to affect test animals adversely. Instudies conducted for EPA, the NOAEL and LOAEL areobtained from experiments where test animals con-sume the pesticide through drinking water or as part oftheir dietary intake. The NOAEL and LOAEL representdaily doses expressed as milligrams (or micrograms) ofa contaminant per kilogram of body weight: mg/kg (orµg/kg).

EPA standards for exposure differentiate betweenadults and children on the basis of body weight: 10kilograms (22 pounds) for children; 75 kilograms (155pounds) for adults. It is speculated that children mightconsume one liter (about a quart) of water daily,whereas an adult might drink two liters. Multiplication ofthe representative body weights by the NOAEL andLOAEL yields total daily doses on which to base thepotential for acute and chronic adverse effects.

Since the NOAEL and LOAEL values are derivedfrom animal testing, there is uncertainty as to whetherhumans might be more sensitive than test animals tothe contaminant. To allow for that contingency, EPAapplies ‘uncertainty factors’ which further reduce theacceptable dose for drinking water. Typically, NOAELvalues for children and adults are divided by an uncer-tainty factor of 100 or more. If the Health Advisory iscalculated from the LOAEL, an uncertainty factor of1000 or more is used.

Thus, a HAL is based on toxicological evidence andconservative assumptions about the data. A HAL iscalculated as follows:

HAL (mg/L or µg/L) =(NOAEL or LOAEL) x body weight

uncertainty factors x water consumption

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Note that the HAL represents a concentration inwater, which is very different from the actual doseconsumed (i.e., the total mass of contaminant taken inby a person).

Duration of Exposure

HALs are derived for the following exposure peri-ods: one day; ten days; longer-term; and lifetime. Theone-day HAL is calculated for a child exposed to thedrinking water contaminant for one day. The ten-dayHAL provides information relative to a child drinking thecontaminant for one to two weeks. The longer-termHAL is derived for both a child and an adult andassumes an exposure duration of seven years or tenpercent of an individual’s lifetime. A lifetime HealthAdvisory is derived for an adult and assumes that theindividual will be exposed for a lifetime of 70 years.

Examples of Health Advisory Levels for a specificpesticide in drinking water are presented in the follow-ing table. The NOAEL and the LOAEL for this specificpesticide are 15 ppm and 150 ppm, respectively.

Exposure Population HAL UncertaintyDuration Segment (ppb) Factor

1 day child 100 10010 days child 100 1007 years child 50 1007 years adult 200 10070 years adult 3 1000

Maximum Contaminant Levels

The Safe Drinking Water Act (SDWA) directs EPAto protect human health by establishing MaximumContaminant Levels (MCLs) for pesticides and otherpotential contaminants of drinking water. MCLs arelegally enforceable standards which may not beexceeded. An MCL is the highest annual averageconcentration of a contaminant allowed in public watersupplies. Like the lifetime HAL, the MCL is a calculatedvalue based on the assumption that the averageperson weighs 70 kilograms, lives for 70 years, anddrinks two quarts of contaminated water daily. Calcula-tion of the MCL trigger value, however, also includesconsideration of the costs, feasibility, and practicality ofcurrent technology to further reduce contaminantconcentrations. MCLs may change as new technolo-

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gies evolve, making the reduction of contaminantconcentrations feasible.

MCLs for noncarcinogenic contaminants arecalculated much like health advisories. The MCL isestablished at a level 100–1000 times lower than thelowest dose known to affect the most sensitive testanimals; this ensures against the possibility thathumans might prove more sensitive to the contaminantthan are the animals tested.

For pesticides and other potential contaminants ofdrinking water that are carcinogenic, risk estimates arerated on the basis that exposure, at some level, willcause one additional cancer per 100,000 or 1,000,000people over a lifetime of 70 years (by extrapolation ofthe results in animals studies where carcinogenicitywas observed). For pesticides or other chemicals whichare determined to be carcinogenic, MCLs must be setat the lowest level feasible.

Currently, public water utilities are required bySDWA to collect at least four samples per year fromthe finished water supply (tap water) for contaminationanalysis. If the annual average residue of a pesticide(as determined from the samples) exceeds the maxi-mum contaminant level, consumer notification isrequired. Water utilities may have to use an alternativewater supply, remove the contamination by filtration, orblend the supply with water from an uncontaminatedsource.

Ecological Risk AssessmentMCLs are designed to ensure that adverse human

health effects do not accrue from pesticide use, butthey do not address potential adverse effects onnontarget plants and animals; however, pesticideregulators are bound by legislative mandate to ensurethat pesticide use does not cause adverse environmen-tal effects. Various (plant and animal)organisms undergo a series of toxicity teststo determine what pesticide concentrationlevels might cause adverse effects. Someinvolve aquatic organisms such as fish oralgae which might be exposed to pesticideresidues entering streams and lakes asrunoff from urban and/or rural sources.

Examples of Risk Assessments

Prevention of ground and surface water contamina-tion is of primary concern where there is shown to be apotential for toxic effects on people, animals, andplants at concentrations which might realistically beexpected to occur. See examples (page 45) of expo-sure and toxicity profiles for two herbicides with verydifferent toxicological properties.

Contact the Purdue UniversityCooperative Extension Servicefor a copy of the publicationPesticides and Wildlife (PPP-30)for additional information onecological considerations.

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Both herbicide A and herbicide B (in the examples)tend to be more toxic to plants than to other organisms.Herbicide A is the more potent herbicide, affectingterrestrial plants at concentrations of only a few hun-dredths of a part per billion in irrigation water. HerbicideA residues might produce unforeseen ecosystemeffects in some surface waters; thus, its use nearendangered plants might be restricted.

Herbicide B is not as toxic as herbicide A but mayaffect certain sensitive plants exposed (through irriga-tion) to concentrations in surface or ground water.Herbicide B is somewhat more toxic than herbicide A tosome animal species, including mammals; based onlaboratory animal studies resulting in low MCLs, it ismore likely (than herbicide A) to receive a restricted-use classification. Unless new data are generated anda substantial increase in the MCL is realized, herbicideB likely will receive a restricted-use classification— orcancellation—to prevent unacceptable levels in drink-ing water.

Contact the Purdue UniversityCooperative Extension Service fora copy of the publication Pesticidesand the Label (PPP-24) whichoffers additional information onpesticide labels.

THE PESTICIDE LABEL

Each pesticide product is accompanied by a labelbearing directions for appropriate use. The label alsoprovides strict precautionary statements relative to theprotection of human health, wildlife and its habitat, andwater resources.

The intent of precautionary statements (normallyfound in the Environmental Hazards section of thepesticide label) is to protect ground and surface water

quality for aquatic organisms and wildlifethat use aquatic systems, and to preventcontamination of ground water.

EPA-mandated instructions and precau-tionary statements are supported by thebattery of toxicological and environmentaltests required for pesticide registration.Pesticides intended for outdoor uses (otherthan aquatic uses) will always contain

general precautionary statements. Labels on pesticidesused to control weeds in aquatic environments—ponds,reservoirs, and other impoundments—contain precau-tionary statements relative to the use of the treatedbody of water.

Protection of Surface Water The Environmental Hazards section of the pesticide

label may contain information concerning the impact ofsurface water contamination on wildlife. Example: ‘Thispesticide is toxic to aquatic organisms.’ Such state-ments are based on the cumulative evaluation of

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Examples of General Statements

'Do not apply directly to water or to areas where surface water is present, or tointertidal areas below the mean high water mark.'

'Do not contaminate water when disposing of equipment wash water or rinsate.'

Examples of Specific Statements

‘Do not use fish from treated area for food or feed within 3 days of treatment.’

‘Do not use water from treated area for watering livestock, for preparing agriculturalsprays for food crops, for irrigation, or for domestic purposes for (a length of time is givenbased upon the rates applied).’

‘Areas can be used for swimming twenty-four hours after treatment.’

laboratory toxicity studies and are required when‘trigger levels’ have been exceeded. If the concentra-tion in the environment is less than the level of con-cern, the statement is a reminder that use directionsare to be followed to avoid serious consequences. Ifthe environmental concentration exceeds the level ofconcern, specific label language may be mandated toprevent an even greater environmental risk.

Examples of Warning Statements Related toToxicity

‘Runoff and drift from treatment areas may behazardous to aquatic organisms.’

‘The pesticide is toxic to fish, aquatic invertebrates,and wildlife.’

‘Drift and runoff may be hazardous to aquaticorganisms in neighboring areas.’

‘This pesticide is extremely toxic to fish and wildlife.’

Examples of Actions to Mitigate Entry intoSurface Water

‘Avoid over-watering since excessive watering mayreduce performance and increase runoff.’

‘Do not apply to turf sites that border lakes, ponds,or streams.’

‘Do not apply to fairways.’‘Do not apply when weather conditions are likely to

cause drift from treated area.’‘This product may not be applied aerially or by

ground within 66 feet of the points where field surfacewater runoff enters perennial or intermittent streamsand rivers.’

‘If the product is applied to highly erodible land, the66-foot buffer or set-back from runoff points must beplanted to a crop or seeded with grass or other suitablecrop.’

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‘Remove frompremises or tightlycover fish tanks anddisconnect aeratorwhen applying indoorswhere such containersare present.’

‘Keep out of lakes,streams, ponds, tidalmarshes, and estuar-ies for waterfowlprotection; do notapply immediatelybefore or duringirrigation or on fields inproximity to waterfowlnesting areas.’

‘Do not apply where fish, shrimp, crabs, and otheraquatic life are important resources.’

Protection of Ground WaterThe Environmental Hazards section of the label

may contain specific directions to prevent the occur-rence of the pesticide in ground water. A productalready on the market becomes subject to restrictionsand advisories when it is detected in ground water. Therestrictions are based on the chemical and physicalproperties of the compound (mobility, persistence,environmental fate) and levels of concern for humanhealth, as well as plant and aquatic life. For instance, anew registration for a pesticide must include specificprecautionary statements if the pesticide has beenidentified as a potential leacher.

Examples of Warning Statements Related toEnvironmental Fate

If it has been found in ground water: ‘This chemicalis known to leach through soil into ground water undercertain conditions as a result of agricultural use. Use ofthis chemical in areas where soils are permeable,particularly where the water table is shallow, may resultin ground water contamination.’

If it has not been found in ground water but hasleaching characteristics: ‘This chemical demonstratesthe properties and characteristics associated withchemicals detected in ground water. Use of thischemical in areas where soils are permeable, particu-larly where the water table is shallow, may result inground water contamination.’

Examples of Actions to Mitigate Entry intoGround Water

‘Care must be taken when using this product toprevent back-siphoning into wells, to prevent spills, and

8

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to dispose of excess pesticides, spray mixture, orrinsates appropriately.’

‘Check valves or antisiphoning devices must beused on all mixing and or irrigation equipment.’

‘Users are advised not to apply this product to sandand loamy soils where the water table (ground water) isnear the surface and soils are permeable.’

‘This product may not be mixed, loaded, or usedwithin 50 feet of all wells, including abandoned wells,drainage wells, and sink holes.’

Restricted-Use PesticidesPesticides are classified for restricted use if they

carry significant potential to harm people, wildlife, orthe environment. Classification is based on how closeestimated environmental concentrations are to levels ofconcern. When very near levels of concern, predictedenvironmental concentrations must be mitigated (as inthe previous examples). Pesticides may be assigned a

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10

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restricted-use classification limiting their purchase anduse to certified and licensed pesticide applicators (orpersons working under the direct supervision of acertified and licensed applicator).

Nearly two decades have elapsed since commercialpesticide applicators and farmers (private applicators)were first required to meet proficiency standards. EPAand state pesticide certification programs educatecommercial and private applicators in the judicial use ofpesticides, and applicators are continually updated onsafe handling procedures. More than a million commer-cial and private pesticide applicators are certified andlicensed, currently.

The pesticide certification process is enhanced bylegal requirements for retail dealers who sell restricted-use pesticides. Dealers must meet recordkeepingrequirements which include documentation of thepurchaser's name, address, and current pesticideapplicator license number; they also must record thename and amount of product sold. This recordkeepingsystem allows regulatory agencies to monitor the saleand use of restricted-use pesticides.

PUBLIC POLICY, PESTICIDES, ANDWATER QUALITY

Changes in public expectations and new scientificknowledge mandate continual evaluation of pesticideuse by local, state, and federal agencies. As a result,public debate surrounding the use of pesticides hasdriven frequent reassessment of their benefits tosociety versus risks attributable to their use. This shiftin public policy decision relies on a framework ofproposing, discussing, and drafting legislative man-dates to ensure that pesticides' benefits to societyoutweigh their potential risks to human and environ-mental health.

During the 1950s, pesticide production escalated ascompanies began to commercialize their discoveries.The pesticide technology of the ’50s spurred federaland state governments to pass amendments to existingregulations to ensure adequate control of pesticidesused in the United States. Early policies requiredUSDA to register all pesticides and to establish stan-dards for label content.

In the 1960s a number of issues developed, raisingalarming and bothersome questions relative to environ-mental risks associated with pesticides. The viewsexpressed in Rachel Carson’s Silent Spring in 1962

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outraged, coalesced, and engaged the public. Govern-ment leaders subsequently made environmental issuesa priority when assessing a pesticide for registration.

The creation of the United States EnvironmentalProtection Agency in 1970 represented a dramaticchange in the federal regulation of pesticides. Empha-sis during the registration process shifted from aproposed product's benefits to the potential risks itsuse might pose to human and environmental health.Pesticide registration hinged on manufacturers' abilityto meet stringent guidelines via increasingly compre-hensive testing procedures; i.e., research data insupport of specific health and environmental publicpolicy objectives became crucial to the registrationprocess. Pesticide labels became the conduit linkingresearch data to user instructions designed to reducethe potential for adverse health and environmentaleffects.

As Americans have increasingly distanced them-selves from their agricultural roots, they have becomeless tolerant of traditional arguments favoring thebenefits of pesticides. Public concern has triggeredstringent testing requirements in pursuit of productregistration, and society's perception of the benefit-to-risk scenario plays a major role in determining the fateof pesticides—that is, whether or not they'll remain onthe market. Legislators draft laws and regulations toreflect the desires of their constituents, and effectivecommunication will be the key in educating the public insupport of pesticide use.

Public Policy Establishes Water QualityLegislation

Public policy strategies for dealing with pesticidesare decided by government. The process involves theprioritization of issues to be addressed, development ofa plan, and implementation; as a unit, these stepscomprise reaction. The speed with which governmentreacts to a pesticide issue may be influenced by localsituations or by large-scale strategies orchestratedwithin the executive or legislative branch of the federalgovernment. Changes may be instituted via legaldecisions and interpretations rendered by courts of law.In essence, Congress passes laws (governing pesti-cides), and EPA establishes regulations and policies bywhich to enforce them. In turn, courts determinewhether or not EPA enforces the intent of Congress—and the public drives the speed and direction of theoverall reaction.

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Federal and State RegulatoryResponsibility

State and federal agencies are responsible forimplementing and managing

• legislative statutes,

• executive branch policy decisions, and

• judicial interpretations

that deal with pesticides and their potential to impactwater resources. Legislation sets goals and providesthe framework which guides federal agencies inexecuting prescribed programs.

State and federal regulations require pesticidemanufacturers, government agencies, and the generalpublic to take certain actions relative to the manufac-ture, transportation, storage, application, and disposalof pesticides in order to meet statutory goals. Regula-tions may

• require that specific pesticides meet new registra-tion standards,

• stipulate mandatory pesticide use education, and

• mandate environmental monitoring to determineany adverse effects on water resources.

Ground Water Protection Strategy. EPA continu-ally seeks national cancellation of pesticides that posea threat to water quality. Currently, EPA's efforts toprevent pesticides from reaching ground water include

• Predicting (on the basis of research data submit-ted by the manufacturer) a pesticide's potential to leachinto ground water

• Establishing national label restrictions addressingconcerns on leaching

• Requiring a restricted-use classification, triggeringadditional training requirements for users

• Providing each state the opportunity to developand implement a State Management Plan for eachpesticide identified as a potential leacher

• Cancelling pesticides known to contaminateground water despite aversion efforts

SPECIAL INITIATIVES

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The cornerstone to EPA's ground water protectionpolicy is the State Management Plan (SMP), by whichstates can tailor their own strategies to prevent groundwater contamination. The basic components of theSMP include philosophy and goals toward protectingground water:

• Roles and responsibilities of state agencies

• Legal authority

• Resources

• Basis for assessment and planning

• Monitoring

• Prevention actions

• Response to detections of pesticides

• Enforcement mechanisms

• Public awareness and participation

• Information dissemination

• Records and reporting

Use of pesticides identified as risks to ground waterare tightly controlled by EPA-approved SMPs:

• EPA determines the need for an SMP.

• EPA stipulates a time period for SMP developmentand approval, during which use of the pesticide maycontinue.

• Use of the pesticide is allowed only in accordancewith the approved SMP.

Pesticide Reregistration

More than 50,000 pesticide products have beenregistered in the United States since FIFRA wasenacted in 1947. Congress amended FIFRA in 1988and mandated through legislative language that allpesticides registered before November 1984 would besubject to reregistration by EPA. The goal of the nine-year reregistration program was to ensure that allchemicals on the market have been fully evaluated.The amendment prescribed that each pesticide’schemistry, toxicology, and environmental effects bereexamined using current scientific, medical, andregulatory guidelines.

FIFRA amended 1988 made necessary the reevalu-ation of 1150 active ingredients in 45,000 formulatedproducts. The active ingredients were assigned to 612chemical cases (groups) of related pesticide activeingredients. The 612 chemical cases were subdividedinto lists A, B, C, and D based on the ranking of variousreference criteria such as the potential for adverseeffects to food; drinking water; human health; plants

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• 1150 active ingredients (45,000 formulations)

• 612 chemical cases (groups) subdivided into four lists(A,B,C,D) based on ranking of reference criteria:

• potential for residues in/on food• potential for drinking water contamination• potential for adverse effects on human health• potential for adverse effects on animals and plants

and animals. EPAproducesReregistration EligibilityDocuments (REDs)once a substantiallycomplete set of data ona chemical case hasbeen reviewed and nosignificant issuesremain concerning useof the pesticide.

EPA's Review After PesticideRegistration

The responsibilities of EPA and pesticide manufac-turers do not end at the point of registration. Productinformation is continually collected, assembled, re-viewed, and analyzed in cases where scientific studiesand field use indicate a potential for adverse impactson human health (such as long-term health effects andworker poisoning), environmental pollution (such asground water contamination), and toxic effects onnontarget organisms (such as fish poisonings resultingfrom pesticide runoff).

Reporting Adverse Information AfterRegistration

EPA can obtain information on the adverse impactsof pesticides via two reporting mechanisms:

• FIFRA section 6(a)(2) reporting

• Incident reporting

FIFRA states in Section 6(a)(2) that "if at any timeafter the registration of a pesticide the registrant hasadditional factual information regarding unreasonableadverse effects on the environment of the pesticide, heshall submit such information to the Administrator." The6(a)(2) reporting requirement is a legal obligation andapplies solely to the registrant. Reports to EPA canoriginate from scientific research conducted by themanufacturer with the intention of supporting continuedregistration; but more often they result from data (onadverse effects) collected in field use situations. Thepesticide manufacturer provides EPA informationclearly identified as a 6(a)(2) report; in addition, themanufacturer must identify the newly observed adverseeffect. Examples of incidents requiring 6(a)(2) reports:

• When pesticides impact aquatic organisms at alower dose than previously shown

• When evidence from additional toxicologicalstudies shows new types of potentially adverse effects

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Incident reporting is used to measure the impact ofa pesticide in the marketplace. Incident data canoriginate from many sources: universities, poisoncontrol centers, state and federal fish and gameagencies, state departments of agriculture, EPAregional offices, or the news. Essentially, any adverseimpact is subject to incident reporting.

All section 6(a)(2) and incident reports submitted toEPA are categorized and indexed on the Incident DataSystem—part of the Pesticide Information Networkoperated by EPA that is publicly available in the UnitedStates. Information concerning new, potentially adverseeffects is submitted to the proper division for reviewand analysis to determine if an immediate EPA reviewis warranted. For instance, the Environmental Fate andEffects Division would examine potential impacts onwildlife, while human health concerns would be re-viewed by the Health Effects Divisions within the Officeof Pesticide Programs.

An EPA work group meets weekly to discuss FIFRA6(a)(2) and incident reports. Priority is given to thosepesticides with the most serious problem potential inorder to expedite review, response, and remedialaction. Those responsible for minimizing recurrent riskfrom the use of the product in question are monitoredto ensure that appropriate measures are taken.

Special ReviewThe special review process allows EPA the regula-

tory flexibility to reevaluate the registration of a pesti-cide. A special review may be initiated when newevidence suggests that the legal use of a specificactive ingredient may pose unreasonable risk to humanhealth or the environment.

The process officially begins with an EPA letter ofnotification (called the Grasley-Allen letter) to theregistrant, stating that the active ingredient is formallybeing placed under special review. The letter providesa brief summary of the reasons why.

Information pertinent to the suspected risk associ-ated with the active ingredient is scrutinized by EPAreviewers who, in turn, prepare a 'risk review' forcomparison with its projected benefits. The availabilityand efficacy of the pesticide, as well as the cost ofalternative controls, are appraised in a benefit-to-riskanalysis. Conclusions drawn from analysis are for-warded to the FIFRA Scientific Advisory Panel, toUSDA, and to the general public (through the FederalRegister) for comments on the scientific accuracy, datainterpretation, and rationale behind proposed riskreduction measures. If after taking all comments underadvisement EPA concludes that risk reduction mea-sures are needed, there are four avenues of pursuit:

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alteration of label language; classification of productscontaining the active ingredient for restricted use;elimination of specific uses; suspension or cancellationof the registration.

EPA’s Lower Risk Pesticide PolicyEPA has identified four areas for implementation of

a voluntary reduced-risk pesticide initiative for pesticidemanufacturers: developing criteria to identify lower-riskpesticides; streamlining the overall registration process;improving pesticide labels to effect well-informedchoices in the marketplace; and encouraging (viastatutory changes which would extend the period ofexclusive use of data, or patent protection) the devel-opment of reduced-risk pesticides.

Under this voluntary approach, manufacturers ofproducts containing a new active ingredient thought tobe worthy of reduced-risk classification must submitsubstantiative data. Claims of reduced risk must besupported by evidence of reduced toxicity to humansand other nontarget organisms, and evidence of theenvironmental fate of the active ingredient must besubstantiated. Incorporation of the pesticide into anintegrated pest management program must be consid-ered in comparison to alternative products. EPA willdetermine the sequence of application review accord-ing to these elements, as described.

EPA's intent is to promote pesticides that poselower or reduced risks in comparison to alternativepesticides. Applications documenting lower-risk charac-teristics will be granted priority consideration, therebygaining a distinct marketing advantage. In 1996, EPAwill strengthen the reduced-risk initiative further bydenying review of registration data for pesticides thatfail the agency’s reduced-risk screen.

Protection of ground and surface water quality iscritical to economic viability, as well as human healthand environmental quality. Although pesticides areessential in the production of an adequate, economicalfood supply, rural (agricultural) as well as urban usesloom as possible sources of water contamination.Detection of pesticides in water aroused public interestin the environmental impact of agricultural chemicals;and the resulting heightened concern is reflected instrict legislation which impacts the pesticide industrysignificantly.

CONCLUSIONS

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In the interest of minimizing risks associated withpesticides, significant public resources have beenallocated for the development and implementation ofrational, pesticide use policies based on solid scientificevidence. Compliance involves extensive, detailed,expensive laboratory research and field studies todetermine the behavior and environmental fate ofpesticides—that is, in deriving the solid scientificevidence—and it follows that manufacturers mustcommit significant financial resources to productdevelopment en route to the marketplace.

A pesticide's route and rate of entry into the environ-ment, as well as its degradation characteristics, are keyto understanding and predicting its potential impact onsurface and ground water. Preregistration researchdata also play a significant role in determining usepattern and hazard statement language for the pesti-cide label. Research findings also influence the strin-gency of post-registration monitoring programs.

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Technological breakthroughs that allow for pesti-cide detections at very low concentrations, combinedwith increased scrutiny of water resources by research-ers and regulators, have increased scientific under-standing of the potential for pesticides to contaminatewater resources. The pesticide industry seeks todevelop pesticides and pesticide management prac-tices with the lowest possible potential for adverseenvironmental impact. The public interest is well servedby a cooperative effort among regulators, universityresearchers, and industry to establish reasonable userestrictions. These efforts should ensure that, whenused appropriately, pest control products will not posea threat to water quality.

ACKNOWLEDGMENTS

Special thanks to Marty Risch, U.S. GeologicalSurvey, for his constructive comments and ideas thataided the development of this publication.

Thanks also to R. David Jones, U.S. EPA, for thefigure which appears on page 36; and to Ron Parker,R. David Jones, and Siros Mostaghimi, U.S. EPA, forthe figure on page 38. Partial funding was provided byU.S. EPA, Region 5.

All complementary illustrations are the work of artistStephen Adduci; his work is sincerely appreciated. Thefollowing individuals are acknowledged for their invalu-able, thorough reviews of this document.

K. Balu, Ciba Crop ProtectionAldos Barefoot, DuPont Agricultural ProductsElizabeth Behl, U.S. EPADon de Blasio, U.S. EPA, Region 5Kevin Costello, U.S. EPAHarry Craven, U.S. EPAAllan Felsot, Washington State UniversityDick Green, University of Hawaii at ManoaSidney Harper, Tennessee Valley AuthorityPaul Hendley, ZenecaScott Jackson, BASFHenry Jacoby, U.S. EPAWilliam Koskinen, USDA, ARSDennis Laskowski, DowElancoTerry Lavy, University of ArkansasMark Lenz, Bayer, Inc.Jim Lin, Bayer, Inc.George Oliver, DowElancoP.S.C. Rao, University of Florida

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REVIEWED: 5/01

The information given herein is supplied with the understanding that no discrimination is intended and no endorsement by the Purdue University Cooperative Extension Service is implied.

It is the policy of the Purdue University Cooperative Extension Service, David C. Petritz, Director, that all persons shall have equal opportunity and access to the programs and facilities withoutregard to race, color, sex, religion, national origin, age, marital status, parental status, sexual orientation, or disability. Purdue University is an Affirmative Action employer.