art. contaminacion mundial del agua y salud humana

EG35CH05-Schwarzenbach ARI 18 September 2010 7:4

Global Water Pollutionand Human HealthRene P. Schwarzenbach,1 Thomas Egli,1,2

Thomas B. Hofstetter,1,2 Urs von Gunten,1,2

and Bernhard Wehrli1,21Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zurich, 8092 Zurich,Switzerland; email: [email protected], Swiss Federal Institute of Aquatic Science and Technology, 8600 Dubendorf,Switzerland

Annu. Rev. Environ. Resour. 2010. 35:10936

First published online as a Review in Advance onAugust 16, 2010

The Annual Review of Environment and Resourcesis online at environ.annualreviews.org

This articles doi:10.1146/annurev-environ-100809-125342

Copyright c 2010 by Annual Reviews.All rights reserved

1543-5938/10/1121-0109$20.00

Key Words

agriculture, geogenic, micropollutants, mining, pathogens, wastes

Abstract

Water quality issues are a major challenge that humanity is facing in thetwenty-rst century. Here, we review the main groups of aquatic con-taminants, their effects on human health, and approaches to mitigatepollution of freshwater resources. Emphasis is placed on chemical pol-lution, particularly on inorganic and organic micropollutants includingtoxic metals and metalloids as well as a large variety of synthetic or-ganic chemicals. Some aspects of waterborne diseases and the urgentneed for improved sanitation in developing countries are also discussed.The review addresses current scientic advances to cope with the greatdiversity of pollutants. It is organized along the different temporal andspatial scales of global water pollution. Persistent organic pollutants(POPs) have affected water systems on a global scale for more than vedecades; during that time geogenic pollutants, mining operations, andhazardous waste sites have been the most relevant sources of long-termregional and local water pollution. Agricultural chemicals and waste-water sources exert shorter-term effects on regional to local scales.

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Improved sanitation:a safe way to handleexcreta, including itscollection, treatment,and disposal or reuseto avoid spreadingdiseases and pollution

Contents

INTRODUCTION . . . . . . . . . . . . . . . . . . 110AQUATIC MICROPOLLUTANTS:

THE CHALLENGE OFDEALING WITH CHEMICALCOMPLEXITY . . . . . . . . . . . . . . . . . . . 111

SELECTED TOPICS OFCHEMICAL WATERPOLLUTION . . . . . . . . . . . . . . . . . . . . 113Persistent Organic Pollutants:

A Long-Term Global Problem . . 115Agriculture and Water Quality . . . . . 116Geogenic Contamination Sources:

The Problem with Arsenic inGroundwater . . . . . . . . . . . . . . . . . . . 117

Surface Water Contaminationfrom Mining Operations . . . . . . . . 118

Groundwater Contamination bySpills and Hazardous WasteSites . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

Pharmaceuticals in Wastewaterand Drinking Water . . . . . . . . . . . . 121

VIRUSES AND MICROBIALPATHOGENS: THECHALLENGES CONCERNINGWATERBORNE DISEASES . . . . . . 122Global Health Problems Related to

Sanitation and Drinking Water . . 122Wastewater Treatment

and Water Reuse . . . . . . . . . . . . . . . 124Detecting Pathogens

and Waterborne Diseases . . . . . . . 125The Multibarrier Concept for

Improved Sanitation and SafeDrinking Water Supply . . . . . . . . . 125

CONCLUSION . . . . . . . . . . . . . . . . . . . . . 126

INTRODUCTION

Many of the major problems that humanity isfacing in the twenty-rst century are related towater quantity and/or water quality issues (1).These problems are going to be more aggra-vated in the future by climate change, result-ing in higher water temperatures, melting of

glaciers, and an intensicationof thewater cycle(2), with potentially more oods and droughts(3). With respect to human health, the mostdirect and most severe impact is the lack ofimproved sanitation, and related to it is the lackof safe drinking water, which currently affectsmore than a third of the people in theworld.Ad-ditional threats include, for example, exposureto pathogens or to chemical toxicants via thefood chain (e.g., the result of irrigating plantswith contaminated water and of bioaccumula-tion of toxic chemicals by aquatic organisms,including seafood and sh) or during recreation(e.g., swimming in polluted surface water).

This reviewdealswith the pollutionof fresh-water resources, including lakes, rivers, andgroundwater. Because numerous reviews haveappeared recently that cover the various aspectsof waterborne diseases in a comprehensive way(4), more emphasis is placed on chemical pollu-tion. More than one-third of Earths accessiblerenewable freshwater is consumptively used foragricultural, industrial, and domestic purposes(5). Asmost of these activities lead towater con-tamination with diverse synthetic and geogenicnatural chemicals, it comes as no surprise thatchemical pollution of natural water has becomea major public concern in almost all parts ofthe world. In fact, a recent Gallup poll taken in2009 revealed that pollution of drinking wateris the primary U.S. environmental concern (6).

Chemical water pollutants can be dividedinto two categories, the relatively small numberof macropollutants,which typically occur at themilligram per liter level and include nutrientssuch as nitrogen (7) andphosphorous species (8)as well as natural organic constituents (9). Thesources and impacts of these common classi-cal pollutants are reasonably well understood,but designing sustainable treatment technolo-gies for them remains a scientic challenge (10).For example, high nutrient loads can lead toincreased primary production of biomass, oxy-gen depletion, and toxic algal blooms (11, 12).Increasing salt loads entering surface water viaroad salt and excessive irrigation pose anotherlong-term problem (13). High salt concentra-tions prevent the direct use as drinking water

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and inhibit crop growth in agriculture. Theproblem is accentuated in many coastal areas,such as India and China, by marine salt intru-sion into groundwater owing to overexploita-tion of aquifers and sea level rise (14). Technicaland political strategies to cope with these clas-sical problems have been discussed extensivelyin the literature (15, 16) and are therefore notaddressed here.

In this review, we focus on the thousands ofsynthetic and natural trace contaminants thatare present in natural water at the nanogramto microgram per liter level. Many of thesemicropollutants may exert toxic effects evenat such low concentrations, particularly whenpresent as mixtures. The large number andgreat structural variety ofmicropollutantsmakeit, however, usually very difcult to assess suchadverse effects, which often are not acute but aresubtle, chronic effects (5). This contrasts withthe common, acute health effects of the rathersmall number of well-known pathogens thatmay be present in polluted water. Therefore,considering the difculty of assessing the effectsof micropollutants on aquatic life and humanhealth and that appropriate, affordable watertreatment methods for their effective removalare not available inmany parts of theworld,ma-jor efforts (such as restricted use, substitutionor oxidative treatment) have to be undertakento prevent these chemicals from reaching natu-ral water. However, as should become evidentfrom the examples discussed in this review, thistask often represents a formidable challenge notonly from a technical but also from economic,societal, and political standpoints.

The sources of micropollutants in naturalwater are diverse. About 30%of the globally ac-cessible renewable freshwater is used by indus-try andmunicipalities (17), generating togetheran enormous amount of wastewaters containingnumerous chemicals in varying concentrations.In many parts of the world, including emerg-ing economies such asChina, these wastewatersare still untreated or undergo only treatmentthat does not effectively remove the majorityof the micropollutants present (18). The latteralso holds for municipal wastewater in indus-

Macropollutants: therelatively smallnumber of mostlyinorganic pollutantsoccurring at themilligram per literlevel

Micropollutants: thethousands of inorganicand organic tracepollutants occurring atthe nanogram tomicrogram per literlevel

trialized countries (see below). Other impor-tant sources of micropollutants include inputsfromagriculture (19), which applies severalmil-lion tons of pesticides each year; from oil andgasoline spills (20); and from the human-drivenmobilization of naturally occurring geogenictoxic chemicals, such as heavymetals andmetal-loids. Additional naturalmicropollutants are bi-ologically produced taste and odor compounds(21), which are not primarily a toxicologicalproblem but are of great aesthetic concern.There are also the millions of municipal and,particularly, hazardous waste sites, includingabandoned industrial and former military sites,from which toxic chemicals may nd their wayinto natural water, especially into groundwater.Finally, when considering that more than100,000 chemicals are registered and most arein daily use (22), one can easily imagine numer-ous additional routes by which such chemicalsmay enter the aquatic environment.

By addressing a series of very different typesof micropollutants from different sources, weattempt to give a representative picture of thescales and extent of this global water pollutionproblem, without a claim of completeness. Asan introduction to these selected topics, we startwith some general remarks on the problemsand challenges in assessing micropollutants innatural water.

AQUATIC MICROPOLLUTANTS:THE CHALLENGE OF DEALINGWITH CHEMICAL COMPLEXITY

A proper assessment of any chemical pollu-tion of natural water relies on ve elements:(a) knowledge of the type and origin of the pol-lutants, (b) the availability of analytical methodsfor quantication of the temporal and spatialvariability in concentrations of the chemical(s)present, (c) a profound understanding of theprocesses determining the transport and fateof the chemical(s) in the system considered,(d ) mathematical transport and fate modelsof appropriate complexity to design optimalsampling strategies and to predict futuredevelopments of a given pollution case, and

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Complexation: theinteraction between apositively chargedmetal ion in solutionand a negativelycharged ion or amolecule with anunshared electron pair

(e) methods for quantication of the adverseeffects of the chemicals on aquatic life andhuman health. Notably, the same analyticaltools and process knowledge are also pivotalfor the design and operation of treatment tech-nologies and in situ remediation procedures.In the following, we address some fundamentalaspects related to these ve elements of anexposure assessment of micropollutants.

Considering the large number of struc-turally diverse micropollutants that may un-dergo numerous interactions with other natu-ral or anthropogenic, dissolved or particulatechemical species and materials (e.g., naturalorganic matter, mineral surfaces, redox activespecies), with light, and even with living or-ganisms, exposure assessment of aquatic micro-pollutants is commonly quite a challenging taskand requires a broad interdisciplinary approach(5, 23).

For inorganic pollutants, including heavymetals (e.g., Cr,Ni, Cu, Zn, Cd, Pb,Hg,U, Pu)andmetalloids (e.g., Se, As), themain challengein assessing environmental risks is related totheir contrasting behavior under different redoxconditions. These elements are not subject todegradation like many of the organic pollutants(see below); the major processes that determinetheir transport and their bioavailability includeoxidation/reduction, complexation, adsorp-tion, and precipitation/dissolution reactions.Most metallic elements exhibit widely differentsolubility in the presence of oxygen and underreducing conditions. Under oxic conditions,the most abundant redox sensitive metalsiron and manganeseform nely dispersedoxide particles, which strongly adsorb heavymetals and metalloids (24). When oxygen isdepleted, these oxide particles undergo reduc-tive dissolution and release their adsorbed toxicload (25). The precipitation and dissolution ofsuch reactive particles in the environment areoften governed by microorganisms. Analyzingpathways and rates of iron and manganesedispersal under environmental conditions re-mains a challenging task, but recently, progressin mass spectrometry opened new analyticalwindows to trace microbial processes via the

stable isotope signatures of metallic elements,such as iron (26).

The large variety of different mineral phasesand possible interactions between solutes,which are relevant for adsorption processes,complicate the environmental assessment ofmetal pollution and its health effects (27). Rapidprogress in X-ray spectroscopy was instrumen-tal in elucidating the structure of metal ions ad-sorbed on mineral surfaces because the methodallows identication of the specic molecu-lar neighbors of metal ions in complex min-eral environments (28). Such molecular-levelinformation helps develop an understandingof the factors affecting the mobility of toxicmetal ions. A precondition for biological ac-tion is the potential ability of metal ions tocross cell membranes. Strong bonds to mineralparticles and stable macromolecular complexestypically prevent uptake. As a consequence, di-rect methods have been developed to assess themobility and bioavailability of metal contam-inants in complex media, e.g., soils or sedi-ments (29). To determine the fate and distri-bution of metals in the environment, insightfrom molecular-level studies and in situ eldobservations can then be scaled up using simpleor more sophisticated reaction/transport mod-els (30), which combine physical, chemical, and(micro)biological processes (26). The last stepof an assessment procedure addresses the ef-fects of biological uptake. The analysis of po-tential effects of nanoparticles provides an il-lustrative example. In recent years, the rapidlygrowing use of engineered nanoparticles forindustrial and commercial applications causedconcern about the biological effects of this typeof new anthropogenic pollutant for the aquaticenvironment and human health. There is nowpreliminary evidence that such particles do notonly release toxic metals at constant rates butcould also exert direct specic harmful effects,which require further research (31). So far,much progress has been made in elucidatingmolecular mechanisms, relevant geochemicaland microbial reactions, and integrating reac-tion and transport pathways in biogeochemi-cal models. The most critical knowledge gap


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relates to our limited ability to predict andquantify adverse effects of inorganic pollutantson aquatic life and human health.

When dealing with organic pollutants, themajor challenge is to cope with the large num-ber and the great variety of chemicals cover-ing a wide range in physical-chemical prop-erties and reactivities (23). As an illustration,Figure 1 (see color insert) shows the large dif-ferences in partitioning behavior betweenwaterand air or water and an organic phase, respec-tively, that may exist between different typesof chemical micropollutants. For example, theapolar, hydrophobic polychlorinated biphenyls(PCBs) partition reasonably well from waterinto air and extremely well from water into anorganic phase, such as octanol, and are thushighly bioaccumulative. In contrast, more po-lar, hydrophilic compounds, such as the sul-fonamide antibiotics, partition very poorly intoboth air and an organic phase. This differentpartitioning behavior means that these com-pounds exhibit a very different transport andphase transfer behavior in the environment.Also, their analysis in environmental samples(e.g., air, water, sediment, soil) requires a differ-ent methodological approach because usuallyseveral enrichment and separation steps are in-volved, which rely on the partitioning behaviorof the compound. Themajor analytical difcul-ties are encountered withmore complex, multi-functional polar chemicals, which includemanyof the biologically active compoundssuch asmodern pesticides, biocides, and pharmaceuti-cals (32, 33). The same holds for the quanti-cation of the environmental partitioning of or-ganic pollutants (e.g., sorption from water toparticles, soils, or sediments), which is most dif-cult for polar, complex organic chemicalsincluding those exhibiting ionizable functionalgroups (34, 35).

The major challenges in assessing orpredicting transformation reactions of or-ganic micropollutants in the environmentare presented by the biologically (micro-bially) mediated processes. This is partlydue to the intrinsic difculty of classify-ing or even quantifying biological activity

Persistent organicpollutants (POPs):the globallydistributed pollutantsthat exhibit a highbioaccumulationpotential

in complex natural systems. Moreover, incontrast to models describing homogeneouschemical or photochemical reactions (23),the treatment of enzymatic and surface-mediated reactions, which are often linkedto biological processes, is still in its infancy.Depending on the environmental conditions(e.g., pH, redox potential, type of surfacespresent), a given compound may react byvarious pathways and/or at very different rates.Furthermore, even compounds exhibiting onlyminor differences in their structures may reactvery differently (23). Therefore, future researchshould be directed more intensively toward de-veloping tools for assessing (bio)transformationprocesses in environmental settings becausethese processes represent the most powerfulremoval mechanisms for organic pollutantsin natural water. In addition, predictivemodels for biodegradability using structuralinformation need to be developed (36).

Finally, there are a signicant number ofcases in which chemical water pollution issuspected, but the types and sources of the pol-lutants are not known and/or cannot be ex-haustively analyzed. In such cases, a batteryof effect-oriented routine methods that wouldallow one to assess whether or not action isneeded would be useful to investigators. Al-though promising examples of effect-orientedmethods have been reported (37, 38), there isstill ample room for future developments.

SELECTED TOPICS OFCHEMICAL WATER POLLUTION

Table 1 gives an overview of the topics thatare discussed in the following sections. Thesetopics address and illustrate various aspectsof global water pollution, including importanttypes of pollutant sources and pollutants as wellas different temporal and spatial scales of waterpollution, ranging from long-term global per-sistent organic pollutants (POPs) to long-termregional (e.g., geogenic pollutants, mining) tolong-term local (e.g., hazardous waste sites) toshort-term regional (e.g., agriculture) to short-term regional or even local (e.g., wastewater)


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Table

1The

discussion

ofwater

pollu

tion

issues

inthisreview

follo

wsthesequ

ence

ofpo

llutant

sourcesas

show

nin

thisoverview

oftopics

Pollutant

sources

Source

type

Pollutant

type

saddressed

Illustrative

exam

ples

aMainwater

quality

prob

lems

Major

challeng

esM

ultip

le(w

aste

sites,

spills,

agricu

lture,

combu

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and

othe

rs)

Globa

llydistribu

tedpo

int

anddiffu

se

Persisten

torg

anic

pollu

tant

s(P

OPs)

PCBs,

PBDEs,

DDT,

PAH

s,PCDDs,

PCDFs

Biomag

nic

ationin

food

chain,

dive

rsehe

alth

effects

Pha

seou

texistingPOPs,

con

neex

istin

gso

urce

s,pr

even

tuse

ofne

wPOPs

Agr

icultu

reDiffus

ePestic

ides

Triaz

ines,

chlorace

anilide

s,DDT,

linda

ne

Con

taminationof

grou

ndan

dsu

rfac

ewater

with

biolog

ically

activ

ech

emicals;

accide

ntal

poison

ing(partic

ularly

inde

veloping

coun

tries)

Con

trol

ofpe

sticideru

noff

from

agricu

lturallan

d,pe

sticidemisus

e

Natur

alco

ntam

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tsGeo

genic

cont

aminan

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nicco

ntam

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ts

Diffus

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nicco

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ts,

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tastean

dod

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mpo

unds

As,

F,Se

,U,m

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cystins,

geos

min

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health

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ents,

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acut

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hron

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ation,

metal

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ents

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uswaste

Point

Diverse

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ts,n

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explos

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g-term

cont

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ofdr

inking

water

reso

urce

s

Con

tainmen

tofp

ollutant

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ofmiti

gatio

npr

ocessesinclud

ingna

tural

attenu

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Urb

anwastewater

inindu

strialized

coun

tries

Point

Pha

rmac

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als,

horm

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logica

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ctsin

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rs,fem

inizationof

sh

Red

uctio

nof

micro

pollu

tant

load

sfrom

wastewater

bypo

lishing

trea

tmen

tUrb

anwastewater

inde

veloping

and

emerging

coun

tries

Point

Micro

orga

nism

san

dviru

ses

Cho

lera,typ

hoid

feve

r,diarrh

ea,h

epatiti

sA

and

B,s

chisto

somiasis,

deng

ue

Hum

anhe

alth

,child

mor

talit

y,malnu

triti

onIm

prov

ingsanitatio

nan

dhy

gien

e,safe

drinking

water,c

heap

adeq

uate

drinking

water

disinf

ectio

ntech

niqu

es

a Abb

reviations

:As,

arsenic;

F,u

orine;

PCBs,

polych

lorina

tedbiph

enyls;

PBDEs,

polybr

ominated

diph

enyl

ethe

rs;D

DT,d

ichlor

odiphe

nyltr

ichlor

oeth

ane;

PAH

s,po

lycy

clic

arom

atic

hydr

ocarbo

ns;P

CDDs,

polych

lorina

teddibe

nzo-

p-diox

ines;P

CDFs

,polyc

hlor

inated

dibe

nzofur

ans;

Se,s

elen

ium;U

,uranium

.


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pollutants. The examples should also illustratethat any mitigation and adaptation strategies tosolve a givenwater pollution problemhave theirown technical, economical, political, and soci-etal boundary conditions.

Persistent Organic Pollutants:A Long-Term Global Problem

A group of chemicals that have been and con-tinue to be of greatest environmental concernare denoted as POPs. They include a diverse setof high-volume production compounds that areintentionally produced as well as compoundsthat form as accidental by-products of a vari-ety of combustion processes. A compound iscommonly classied as a POP if it exhibits thefollowing four characteristics:

1. Persistent in the environment, whichmeans that chemical, photochemical, andbiological transformation processes donot lead to a signicant removal of thecompound in any environmental com-partment;

2. Prone to long-range transport, thus toglobal distribution, even in remote re-gions where the compound has not beenused or disposed, owing to the com-pounds physical-chemical properties;

3. Bioaccumulative through the food web;and

4. Toxic to living organisms, including hu-mans and wildlife.

Some prominent classical POPs (also calledlegacy POPs or the dirty dozen) have beenlisted and dealt with in two international con-ventions (the Aarhus Protocol and the Stock-holm Convention) with the goal to assess thePOPs global presence and to reduce their emis-sions to the environment (39). They primar-ily encompass highly chlorinated compounds[e.g., dichlorodiphenyltrichloroethane (DDT),PCBs, polychlorinated dioxins and dibenzofu-ranes] and polycyclic aromatic hydrocarbons(PAHs). However, recognizing that there aremany other high-volume production chemicalspotentially falling into the POP category (40),

Diffuse sources:widespread activities,with no discretesource, that causepollution

these conventions allow addition of new com-pounds to the list. Recent examples of suchemerging POPs that are under considerationto be added are the polybrominated diphenylethers (PBDEs) widely used as ame retardants(41, 42), and a variety of peruoroalkyl chem-icals (PFCs) that, because of their very spe-cial properties (43), are used in numerous in-dustrial applications (44). It should be pointedout that many emerging pollutants, includ-ing some POPs, may have already been presentin the environment for decades but werenot detected because of analytical limitations(32, 33). From a toxicological point of view,POPs may threaten the health of both humansand wildlife because of their various adverse ef-fects, including disruption of the endocrine, thereproductive, and the immune systems, as wellas their ability to cause behavioral problems,cancer, diabetes, and thyroid problems.

In the context of global water pollution,POPs pose a severe problem primarily becauseof their particularly large bioaccumulation andbiomagnication potential in aquatic foodwebs(45, 46). A series of monitoring studies have re-vealed critical concentrations of POPs in fresh-water and marine sh and in marine mammalsand, as a consequence, in human milk and hu-man tissues of peoplewho depend on these foodsources (47, 48). Owing to various long-rangetransport mechanisms, accumulation of POPsis particularly pronounced in the worlds coldregions (e.g., in the Arctic) (46, 49). Even legacyPOPs, such as DDT or PCBs that have beenbanned or are restricted in their use, remainof great concern because they continue to bereleased from various old deposits, includingwaste sites and contaminated sediments.

For emerging POPs, such as, for example,the PBDEs in the past 30 years, there hasbeen an exponential increase by a factor ofabout 100 in concentration in human tissueswith a doubling time of about 5 years, whichcan be observed in various parts of the world(Europe, Japan, North America). This is, ofcourse, the result of several different exposureroutes, including primarily terrestrial ones(47). However, very similar trends can also be


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Point source: a singleidentiable localizedsource of pollution

seen in marine mammals in North Americaand northern Europe (47).

As is evident from the still ubiquitous globalpresence of many legacy POPs in the environ-ment, global control strategies aimed only atreducing production and use of POPs do notnecessarily lead to an immediate reduction ofemissions because of the presence of various oldsources. To identify and design optimal mitiga-tion strategies, further development of emissioninventories, as attempted for PCBs (50), and ofmore renedmodels for assessment and predic-tionof (a) the (global) transport anddistributionbehavior (51) and (b) the effects on humans andwildlife (52) of legacy and emerging POPs isstill important on the research agenda. There-fore, the inuence of climate change on thedistribution and the effects of POPs in theenvironment needs to be addressed (53). Froman environmental policy point of view, themost urgent actions to be taken by the inter-national community are to phase out POPsthat are still in use, to improve source controlswherever possible, and to make sure that nonew chemicals with POP characteristics appearon the market (22).

Agriculture and Water Quality

Several million tons of chemicals are consumedannually for agricultural production to main-tain and increase crop yields by controlling

GLOBAL PESTICIDE CONSUMPTION

Three to seven million tons of pesticides are produced annually(60). Estimates of pesticide use vary between approximately 0.2and 2 kg of active substance per hectare (ha) of arable land indeveloping versus developed countries, respectively (54). Suchestimates are imprecise by nature. The amount of active chem-icals required to control pests depends on the crop treated, thetype of pesticide used, the application technique, as well as geo-graphic and climatic boundary conditions. More recently devel-oped agrochemicals generally operate at lower doses compared toestablished products, but toxic loads per dose of active ingredientvary widely among different agrochemicals.

fungi, weeds, insects, and other pests (seethe sidebar Global Pesticide Consumption;54). Pesticides and related agrochemicals areavailable on the market as tens of thousandsof different commercial products that containapproximately hundreds of different activechemical ingredients (55, 56). Owing to thetoxicity of these chemicals for biota andhumans and their intentional release into theenvironment, the use of new and establishedagrochemical products is regulated in detail:Country-specic registration and risk assess-ment procedures aim at protecting not onlysoil and water resources/ecosystems but alsofarmers and consumers (5659).

Contamination of water resources in catch-ment areas of agricultural land and continuousexposure of humans and biota to biologicallyactive chemicals are of great concern. Peak con-centrations of pesticides and their transforma-tion products, such as the frequently detectedtriazines or chloroacetanilides in U.S. rivers(61), can exceed ecotoxic levels for nontargetorganisms in soils and aquatic systems and com-promise the use of surface and groundwater fordrinking water supplies (61). Quantifying theshare of used pesticides that reach surface andgroundwater (62) and designing effective miti-gation measures (63, 64) beyond a case-by-casebasis are challenging because of the substantialspatial and temporal variability of pesticidelosses (65). Typical agricultural point sourcesinclude pesticide runoff from hard surfaces,mostly from farmyards or storage facilitiesduring the handling of agrochemical productsor accidental spills. Depending on connectionsto sewer systems, pesticides can either inltrateinto the nearby soil or enter aquatic systemsvia sewage treatment plants. Point sources cancause high-concentration peaks in the outlet ofa catchment area, but they do not necessarilyconstitute a major share of the mass input (66).Instead, diffuse losses, including eld runoff,drainage/leaching into the subsurface, or spraydrift, are of much greater concern, and abroad variety of mitigation measures have beenevaluated to minimize their impact on waterresources (67). The occurrence of pesticide


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losses from runoff is determined largely by thesoil hydraulic properties (permeability, waterow patterns), topography, and meteorolog-ical conditions, whereas compound-specicproperties (e.g., sorption behavior to the solidmatrix) are less relevant (68). Restricted ap-plication of pesticides to such hot spots proneto increased runoff would be a more effectivemitigation measure than replacing pesticideproducts and/or alternative application timing(6668).

Water contamination also arises in drainageand sewer systems from pesticide applica-tions in nonagricultural/urban areas throughincreased runoff of pesticide-containing rain-water over sealed surfaces, such as roofs androads (69). From the perspective of the overallenvironmental impacts of extensive agriculture,a reduction of soil and water pollution by pes-ticide emissions is considered a key element inagricultural management practices to minimizeecological changes and to maintain biodiversity(60, 70). Finally, acute poisoning from directpesticide exposure is a considerable risk for agri-cultural workers. Although the impact of thisexposure pathway is debated in North Americaand Europe (71, 72), accidental exposure anddeliberate misuse of agrochemicals seem morefrequent in developing countries (7375), re-sulting in an estimated poisoning of 3 millionpeople with as many as 20,000 unintentionaldeaths per year (76).

Apart from distinct climatic/ecological con-ditions and grown crops, agricultural practice inmost developing countries is driven by the needto achieve or maintain food security for grow-ing populations and the economic/politicalimplications of this overarching goal (60).Together with trends toward urbanizationand industrialization, these agricultural de-velopments are causing water quality issues(77). Pesticide use per hectare of cropland (seethe sidebar Global Pesticide Consumption)increased over the recent years, even if, asdocumented for China, contributions to cropyield were marginal (78). In developing coun-tries, resources and capabilities for monitoringpesticide concentration in aquatic systems

and assessing the risk for humans and theenvironment are often limited (79), and atti-tudes toward enforcement of regulations arescant (80). Monitoring programs of pesticideoccurrence and distribution illustrates that thespectrum of active ingredients can still differfrom those used in the developed countries.Especially, the persistent organochlorinepesticides [DDT, hexachlorocyclohexanes(HCHs)] are applied extensively for agricultureand sanitation purposes because they are stillcomparatively cheap and effective (74, 81)

Geogenic Contamination Sources:The Problem with Arsenic inGroundwater

The geological composition of aquifers in someareas of the world is the main cause of leachingof toxic elements into drinking water supplies.The main elements of concern are arsenic,uoride, selenium, and a few others, such aschromium and uranium. Among all these ge-ogenic contaminants, arsenic has so far causedthe greatest negative health effects as well asglobal concern. For this reason, arsenic is dis-cussed as an illustrative example. In Bangladeshalone, arsenic-contaminated groundwateraffects between 35 and 75 million people (82).About 6 million people are at risk inWest Ben-gal in India (83), and other regions of concerninclude the highly populated river deltas inCambodia and Vietnam (84). In these regions,arsenic poisoning developed over the pastdecade as a result of efforts to provide safedrinking water. Until the 1970s, most peoplein these rural areas depended on untreateddrinking water from rivers and ponds, whichare often a source of infectious diseases. Thehigh mortality of up to 250,000 children peryear in Bangladesh alone triggered large-scaleprograms to install groundwater wells to pro-vide safe drinking water. More than 95% of thepopulation now uses groundwater from about10 million tube wells. About 60% of these wellsalong the Ganges-Brahmaputra River systemin Bangladesh are affected by arsenic levelsexceeding the World Health Organization


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WHO: World HealthOrganization

(WHO) limit (85). Arsenic pollution is also ofconcern in other parts of the world, such as theUnited States (86, 87) and Eastern Europe (H.Rowland, E. Omoregie, R. Millot, C. Jiminez,J. Mertens & M. Berg, submitted).

Factors responsible for the arsenic con-tamination are the high weathering rates ofarsenic-rich source rocks in mountain ranges,deposition of organic-rich deposits in riveroodplains, and a at and humid terrain withlong residence times of water in the aquifer,leading to anoxic conditions whereby adsorbedarsenic is released into the water (88). A secondpathway of arsenic mobilization is occurring inarid areas, such as in the U.S. Midwest, easternAustralia, and central Asiawhere high-pHconditions mobilize arsenic in oxygen-richgroundwater. Because the chemical factorsgoverning arsenic mobilization are well un-derstood, the risk of arsenic contaminationin groundwater has been modeled at a globalscale (Figure 2; see color insert) (89).

Chronic arsenic poisoning leads to an ac-cumulation of the element in the skin, hair,and nails; this accumulation results in symp-toms such as strong pigmentation of hands andfeet (keratosis), high blood pressure, and neuro-logical dysfunctions (82). Another health prob-lem is the carcinogenic effect of arsenic [i.e,an increased risk of cancers of the skin, lung,and other internal organs (90)], which has beenknown for a long time. The estimated risk ofarsenic-induced cancer could be as high as 1 in100 individuals, who consume drinking waterat the former maximum contaminant level of50 g As/L (91). In 1993, WHO reduced thestandard for safe drinking water to 10 g As/L,which still results in a smaller margin of safetycompared to typical organic pollutantswith car-cinogenic properties. Thus, arsenic illustratesthe dilemma between public health concernsand economic feasibility. High safety marginswould result in widespread requirements forvery costly drinking water treatment.

For industrialized countries, a broad rangeof technologies is available for the adsorptionof arsenic to achieve or improve on the WHOlimit (92). In critical areas, switching to bottled

water may be more economical than large-scale treatment of the whole water supply. Forrural areas in developing countries, however,simple but effective household-level treatmenttechnologies need to be implemented (93, 94).Alternative drinking water sources, such asdeep aquifers or rainwater harvesting, provideanother potential solution (95). Although ar-senic in drinking water remains a technologicalchallenge for water supplies, there is recentevidence that enrichment of arsenic along thefood chain is not of primary concern (96).Furthermore, themechanisms that produce thearsenic problems in groundwater work as a self-purication system at the soil surface: Seasonalooding during the monsoon season leads toreducing conditions in the soil matrix, whichfavors arsenic mobilization and ushing of thistoxic element into river systems and the sea (25).

Surface Water Contaminationfrom Mining Operations

Mining activities worldwide mobilize morethan 50 109 metric tons of geological mate-rial per year, which is similar to the ux of par-ticles transported by rivers from the continentsto the sea (97). Most mining operations trig-ger signicant environmental and social prob-lems as they result in largewaste deposits, whichare exposed to oxidation by air and weather-ing by precipitation, and subsequent pollutionof water resources (98). Mining for coal, lig-nite, building materials, and iron involves thelargest mass movements with a signicant yieldof end products (Table 2). The extraction ofraremetals, such as copper, nickel or gold, how-ever, produces up to 1,000 tons of waste mate-rials per kilogram of pure metal. These massivewaste streams are accompanied by problematicgeochemical weathering reactions and specicpollutant loads, which are introduced as miningchemicals. Ores, such as coal, iron, and copper,typically contain large fractions of suldemate-rial; this material is oxidized in contact with airand water and releases sulfuric acid in the formof acid mine drainage (99). Because the sul-fur concentrations can reach high proportions


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(120 wt% pyrite in the case of coal), a conser-vative worldwide estimate assumes that about20,000 river kilometers and 70,000 ha of lakeand reservoir area are seriously damaged byacidic mine efuent (100).

In addition, mining and extraction of pre-cious metals are associated with intense useof chemicals, energy, and water that posesgreater pollution hazards and environmentalrisks. Gold production serves as an illustrativeexample. As the average ore grade decreasedover the past two centuries, chemical extrac-tion either by mercury amalgamation in arti-sanal gold mining or via the industrial cyanideextraction process became increasingly impor-tant. Both reagents are extremely toxic to hu-mans and the environment. Artisanal gold min-ing with mercury is increasingly practiced byabout 13 million miners in 55 countries, suchas Brazil, Tanzania, Indonesia, and Vietnam(101). Traces of gold are dissolved in liquidmercury, which is then removed by heating andevaporation to the atmosphere. Mine workersare thereby directly exposed to hazardous lev-els of the neurotoxic metal, and the local en-vironmental contamination of water resourcescan be severe. A review based on detailed casestudies in Brazil (102) estimates that more than100 tons of mercury are discharged into the en-vironment every year, and about 50% of thisis mobilized into surface water, where mercurybiomagnies up to 106-fold in predatory shand then represents a health risk to indigenouspopulations.

At lower gold concentrations and largervolumes, the cyanide extraction facilitates ox-idative leaching of gold as a complex intoaqueous solution. Dissolved gold is then ad-sorbed, and the cyanide solution is recycled.Typically, 700 tons of water and 140 kg ofcyanide are required to extract 1 kg of gold(103). Cyanide blocks the function of iron- andcopper-containing enzymes in the respiratorychain of higher organisms (104). It is acutelytoxic to humans at a level of a few 100 mg foran adult person. Fish react at about 1,000 timeslower levels and are killed in water containingas little as 50 g/L of cyanide. Gold mining

Table 2 Estimated global mass movements by mining activities inmillion metric tons per yeara

Mining activity Total Refined product WasteCoal 18,444 3,787 14,657Building stone 14,186 10,430 3,756Lignite 9,024 930 8,094Copper 4,190 9.3 4,181Petroleum 3,489 3,065 424Iron 3,138 604 2,534Gold 2,138 0.002 2,138Phosphate 477 119 358Nickel 403 0.72 402Aluminum 302 101 201

aSources (97, 106).

operations are therefore often associated withspectacular sh kills. Most aquatic organismswere killed along the main stem of the TiszaRiver inHungary, andmostwater supplies wereclosed when a dam failure at a tailing pond inRomania triggered the release of about100,000 m3 of cyanide-containing waste inJanuary 2000 (105).

More sustainable mining practices requiremitigation measures for existing tailings andimproved processes and safety procedures forongoing activities (106). Highly toxic chemi-cals, such as cyanide or mercury, should be re-placed by less harmful extraction agents, suchas halogens or thiourea, or a zero-emission pol-icy should be enforced (107). Such technicalmeasures should be supplemented by clear in-ternational regulations (108) and corporate so-cial responsibility in themining industry, whichis based on open information policies (109).Although international agreements and prac-tice codes cannot substitute for stronger en-forcement of environmental regulations bydeveloping countries, they represent helpfulbenchmarks for protecting water quality.

Groundwater Contamination by Spillsand Hazardous Waste Sites

Contamination of groundwater from munici-pal solid waste landlls, hazardous waste sites,accidental spills, and abandoned production


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facilities is a prominent cause of water pollu-tion. Several hundred thousands of sites can befound throughout the world, where 100milliontons of wastes have been and still are discarded.Many of them contain large amounts of haz-ardous or radioactivematerial (110112).How-ever, estimates point to an even higher numberof unknown, groundwater-contaminating land-lls (111). Even thoughmanyof the ofcial con-taminated sites are under control, the large ma-jority of them are expected to release chemicalsinto the environment. In addition, thousandsof oil, gasoline, and other chemical spills occureach year on land and in water from a variety

REDOX PROCESSES CHANGECONTAMINANT BEHAVIOR

Many physical and chemical properties of organic and inorganiccontaminants are determined by their redox state. Therefore, re-dox conditions in subsurface environments directly impact con-taminant fate, and the control of redox conditions is essential forthe design of successful mitigation processes.

Metal contaminants from radioactive waste repositories or re-processing sites, such as uranium (U)or assionproduct like tech-netium (Tc), are generally present in their oxidized state [U(VI),Tc(VII)] in contaminated soils and groundwater. The same istrue for chromium [Cr(VI)] waste from tannery operations. Al-though these metal anions are very mobile and thus a threat tohumans and the environment, they are sparingly soluble in theirreduced forms [U(IV), Tc(IV), Cr(III)]. Consequently, creatingor maintaining reducing conditions in the subsurface, for exam-ple, through in situ stimulation of microbial activity with organicsubstrates (134), is seen as a key process for the metal immobi-lization and containment of hazardous materials.

Different approaches apply to organic contaminants becausethey can, in principle, be mineralized to carbon dioxide and othernonproblematic compounds. However, organic water contami-nants, such as the explosives di- and trinitrotoluene or the sol-vents tetra- and trichloroethene, are persistent because they arehighly oxidized. Complete transformation is possible only aftertransient reduction by metal catalysts or microbes. These pro-cesses partially lead to reduced products, like aromatic amines orvinyl chloride (23, 121), which are of even greater toxicity thanthe parent contaminant. These electron-rich products, however,are much more susceptible to complete oxidation by microbes.

of types of incidents, including transportationand facility releases.

Estimating the number and uxes of toxicchemicals from such contaminated sites to thegroundwater is difcult (113, 114). In manycases of spills, waste disposal sites, and aban-doned facilities, their primary contaminantsare known: fuel hydrocarbons (115), chlori-nated ethenes (116), PCBs and polychlorinateddibenzo-p-dioxines (PCDDs) from wastes ofpesticide manufacturing (117), methylmercuryfrom contaminated soils and wastewater (118),radionuclides from former nuclearweapons testsites (119) and radioactive waste repositories(120), and nitroaromatic explosives from am-munition plants (121), to name just a few. Dis-carded materials are, however, often not wellcharacterized and heterogeneous (114). Apartfrom some predominant contaminant species,the leachate composition from the landll ma-terials cannot be predicted in detail (122).Because the hydrogeology of such sites is in-herently complex, the dynamics of pollutantrelease can only be quantied reliably on acase-by-case basis through combined continu-ous on-site monitoring and adequate ground-water models (see the sidebar Redox ProcessesChange Contaminant Behavior; 123).

Owing to the widespread use of ground-water as a drinking water resource and thepersistence of contaminations for decades ifnot centuries, assessment of human healthrisks of exposure to mixtures of chemicals andimplementation of appropriate, cost-effectiveremediation strategies are essential (112, 124).Typical approaches for the active mitigationof groundwater contaminants from spills andwaste sites are site excavation, pump-and-treatprocedures, permeable reactive barriers, andphytoremediation (125, 126). The mitigationconcepts either aim at removing the contam-ination source or intend to catalyze reactionsthat lead to an immobilization (metals) ortransformation to benign and biodegradableproducts (organic contaminants). However,many remediation approaches are often eithertoo expensive or inefcient in that they requiretreatment for years to decades (125). To this


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end, strategies focusing on microbial or abioticdegradation in situ (natural attenuation) areincreasingly being considered as viable long-term treatment options (116, 127). Bioavailablecarbon loads and microbial activity at contam-inated sites and in leachate plumes can oftenlead to anoxic conditions. Such reducing envi-ronments not only alter some properties of thesolid matrix for contaminant retention but alsogenerate conditions that promote the growth ofalternative microbial communities, for examplefor dehalorespiring bacteria that are capableof initiating the reductive dehalogenation ofpolychlorinated organic compounds (116, 128).Anoxic environments, especially iron-reducingconditions, can also lead to the formationof abiotic reactants through the activity ofmetal-reducing microorganisms (129). Suchiron-bearingminerals are capable of transform-ing organic and inorganic pollutants (130132).Thus, a comprehensive assessment of con-taminant exposure, and thus water pollution,requires a sound understanding of the dynamicsof biogeochemical processes in the subsurfaceand their interplay with contaminant mobilityand reactivity. One of the major scienticchallenges and prerequisites for a thoroughassessment of groundwater pollution by spillsand hazardous waste sites is thus to quantify thesite-specic, relevant processes that determinethe transport and transformation behaviorof a given pollutant and its transformationproducts. One promising analytical tool toobtain such information is compound-specicstable-isotope analysis (133).

Pharmaceuticals in Wastewaterand Drinking Water

Municipal wastewater contributes signicantlyto the micropollutant load into the aquatic en-vironment (135). The main concerns are phar-maceutical compounds and personal care prod-ucts. Approximately 3,000 pharmaceuticals areused in Europe and the United States today,including painkillers, antibiotics, beta block-ers, contraceptives, lipid regulators, antidepres-sants, and others (136). In Germany, 30 new

pharmaceuticals are launched on themarket ev-ery year with 8% of the worldwide researchand development (R&D) expenditure (137).Onthe basis of the worldwide R&D expenditure ofabout US$83 billion in 2007 (137), it can be ex-trapolated that on average more than 300 newpharmaceutical compounds are launched everyyear.Theworldwidemarket of pharmaceuticals[100,000 tons per year (138)] was US$773 bil-lion, with the highest per capita sales ofUS$676in the United States (137). In most Europeancountries, per capita sales vary between aboutUS$200 (in the United Kingdom) and US$400(in France) (137).

Pharmaceutical compounds are highlybioactive, and therefore, undesired effectsin organisms cannot be excluded after theirdischarge into the aquatic environment, where,owing to their polarity, they tend to be quitemobile (Figure 1) (139). Even though thepresence of pharmaceuticals in wastewaterand natural water could be expected fromtheir large production and widespread use,only developments in analytical chemistry(LC-MS/MS) allowed the analysis of thesecompounds in the nanogram to microgramper liter range, which is typical for wastewaterand aquatic systems (135, 140). The observedconcentrations of human pharmaceuticals inraw sewage of up to several micrograms perliter conrm that municipal wastewater isthe main pathway for their discharge to thereceiving water bodies (141).

Currently, in wastewater systems, pharma-ceuticals are removed unintentionally by sorp-tion to sludge and by biodegradation (142).Biodegradation of pharmaceuticals in wastewa-ter often does not lead to their full mineraliza-tion but to the formation of metabolites. In thecase of iopromide, an iodinated X-ray contrastmedium, 12 metabolites were identied (143).Therefore, in terms of the (eco)toxicological ef-fects of the discharged wastewater, not only theparent compounds but also their wastewater-borne metabolites have to be considered. For-tunately, the more hydrophilic metabolites areexpected to have a smaller (eco)toxicologicalpotential than their more hydrophobic parent


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compounds, unless another specicmode of ac-tion becomes important (38). It was shown re-cently by a mode-of-action test battery withve in vitro bioassays that nonspecic effects,such as bioluminescence and growth rate inhi-bition, and specic effects, such as acetylcholineesterase activity, estrogenicity, and genotoxic-ity, decreased dramatically from primary waste-water to the efuent despite the fact that manydifferent pharmaceuticals and their metabo-lites were detected in the wastewater efu-ent (144). However, an assessment of the dis-charge of 742 wastewater treatment plants inSwitzerland showed that for diclofenac, an anti-inammatory agent and its metabolites, thewater quality criterion of 0.1 g/L (a sum ofthe parent compound and metabolites) was ex-pected to be exceeded in 224 river sections(145).

Although the main issues related to phar-maceutical in wastewater efuents are con-nected to their ecotoxicological effects, thereis a growing concern about human health be-cause of the presence of some of these com-pounds in drinking water derived from indirector direct potable reuse. In indirect reuse sys-tems, wastewater-derived pharmaceuticals andtheir metabolites can inltrate into the aquifersthrough the riverbank. Luckily, the riverbankappears to be a good barrier for many of thesecompounds. In a study where 19 antibioticswere found in a surface water in concentrationsbetween 5 and 151 ng/L, only sulfamethox-azole could be detected in the bank ltrate(146). However, even in the worst case of sul-famethoxazole, a removal of 98% from 151ng/L to 2 ng/L was observed. Nevertheless, arecent reviewon residues of humanpharmaceu-ticals in aqueous environments presented evi-dence that a complete removal of all potentialpharmaceutical residues by riverbank ltrationcannot be guaranteed (147). A comparison ofdrinking water concentrations of pharmaceu-ticals, such as the antibiotic sulfamethoxazole,shows a difference of >6 orders of magnitudecompared to the therapeutic dose of this com-pound. For other compounds, the safety mar-gin might be in the range of 4 to 6 orders of

magnitude. These factors are still signicantlyhigher than the safety factor of 1,000, which isapplied to potentially carcinogenic compoundssuch as the herbicide atrazine (148). Further-more, from a human toxicological point ofview, pharmaceuticals are probably the mostrigorously tested synthetic organic chemicals.Authorization of a new pharmaceutical com-pound requires detailed information on phar-macology, pharmacokinetics, toxicology (e.g.,carcinogenicity, genotoxicity, reproductive anddevelopment toxicity), and clinical tests (149).On the basis of this assessment, the risk for con-sumers fromexposure to individual pharmaceu-ticals in drinking water seems rather low. How-ever, more information is needed for long-termexposure to small concentrations and mixturesof pharmaceuticals.

Because wastewater is a major point sourcefor pharmaceuticals, several options for pol-ishing treatment, such as activated carbon andozonation, are discussed as mitigation strate-gies (150). Recently, full-scale studies haveshown the feasibility of ozonation with accept-able operation costs (141). Polishing treatmentof wastewater efuent has the advantage thatthe aquatic environment, including the waterresources, is protected from human pharma-ceuticals and endocrine-disrupting compounds(see the sidebar Endocrine Disruption in theAquatic Environment and Its Inuence onEnvironmental Sciences). Alternatively, if thepresence of these compounds in drinking wa-ter is the major concern, various drinking watertreatment processes, such as granular or pow-dered activated carbon, oxidation, and nanol-tration/reverse osmosis, can be used for the re-moval of these compounds (151).

VIRUSES AND MICROBIALPATHOGENS: THE CHALLENGESCONCERNING WATERBORNEDISEASES

Global Health Problems Related toSanitation and Drinking Water

The problems related to sanitation, hy-giene, and drinking water differ fundamentally


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between industrialized and developing coun-tries. In high-income countries, maintenanceand replacement of the installed sanitation andwater supply infrastructure are the predomi-nant tasks during the next 2030 years. In de-veloping countries, where most of the sewageis discharged without treatment, the improve-ment of sanitation and access to safe drinkingwater are of primary importance (1). However,becausemost of the population increase will oc-cur in urban areas of developing countries, cur-rent estimates predict that 67% of the worldspopulation will still not be connected to publicsewerage systems in 2030 (1).

Currently, 1.1 billion people lack accessto safe water, and 2.6 billion people do nothave proper sanitation, primarily in developingcountries, and an imbalance exists between ru-ral and urban areas in access to both improvedsanitation and safe drinking water supply. Fourout of ve of the worlds inhabitants with noaccess to safe sources of drinking water live ina rural environment (155). On a global scale,the restricted access to safe water and to im-proved sanitation causes 1.6 million deaths peryear (156); more than 99% thereof occur in thedeveloping world. Nine out of ten incidentsaffect children, and 50% of childhood deathshappen in sub-Saharan Africa (157). The easilypreventable diarrheal diseases caused by unsafewater and lack of sanitation and hygiene con-tribute to 6.1% of all health-related deaths; onereport estimates that unsafe water is responsi-ble for 15% to 30% of gastrointestinal diseases(158).

The main acute disease risk associatedwith drinking water in developing and transi-tion countries is due towell-knownviruses, bac-teria, and protozoa, which spread via the fecal-oral route (158). According to WHO recordsof infectious disease outbreaks in 132 coun-tries (from 1998 to 2001), outbreaks of water-borne diseases are at the top of the list, withcholera as the next most frequent disease, fol-lowed by acute diarrhea, legionellosis, and ty-phoid fever (159). It is alarming that, after anabsence of almost 100 years, cholera reappearedin Africa and accounted for 94%of the reported

ENDOCRINE DISRUPTION IN THE AQUATICENVIRONMENT AND ITS INFLUENCE ONENVIRONMENTAL SCIENCES

One of the main triggers in the eld of pharmaceuticals and en-docrine disruptors was the discovery of intersex sh in Englishrivers downstream of municipal wastewater discharge in 1978(152). Later, this observation was attributed to the presence ofestrogenic compounds in wastewater efuents (153). The activeingredient of the contraceptive pill [17-ethinylestradiol (EE2)]and to a lesser extent industrial chemicals, such as alkylphenolsor bisphenol A, were recognized to be able to cause feminiza-tion of shes in exposed populations. In a more recent study,it was shown that the sh population (fathead minnow) in anexperimental lake in northwestern Ontario, Canada, was nearlyextinct after a seven-year exposure to 56 ng/L EE2 (154). Theearly observations of intersex sh and 30 years of research ledto (a) development of analytical methods to determine polarcompounds in municipal wastewater efuent in the ng/L range;(b) novel highly sensitive biological in vitro test systems, whichcan detect various toxicological end points; (c) recognition of mu-nicipal wastewater as a source for micropollutants; and (d ) devel-opment of mitigation strategies to reduce their discharge into thereceiving water bodies.

global cholera cases in this period. In additionto cholera, the most proliferate waterborne dis-ease outbreaks were due to (para)typhoid fever(caused by Salmonella typhi and S. paratyphi,respectively). Also hepatitis A and E viruses,rotaviruses, and the parasitic protozoa Giar-dia lamblia are often found associated with in-adequate water supply and hygiene (158). Astudy in Bangladesh reported that 75% of di-arrheal and 44% of the control children wereinfected with either Cryptosporidium parvum,Campylobacter jejuni, enterotoxigenic and en-teropathogenic Escherichia coli, Shigella spp.,or Vibrio cholerae (160). In high-income coun-tries, outbreaks caused by pathogenic E. coliand cryptosporidiosis are often reported, andLegionella pneumophila is increasingly dis-tributed in warm water supplies and air-conditioning systems of large buildings, such ashospitals.Outbreaks of typhoid fever occur onlysporadically.


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MDG: millenniumdevelopment goal

Even though health problems associatedwith wastewater and drinking water supply areintimately linked, issues related to sanitationare treated politically with lower prioritythan water supply problems, and more fundsare allocated to the latter. Throughout theOrganization for Economic Co-operationand Development (OECD) projects relatedto drinking water and sanitation, 82% ofthe funding was directed toward drinkingwater projects (161). This preference contrastswith strong epidemiological evidence, whichsuggests that improved sanitation would dras-tically reduce the burden of infectious diseasesand, linked to this, also malnutrition. In Africaalone, owing to the lack of access by a part ofthe population to sanitation and safe drinkingwater, the overall economic loss is estimatedto be 5% of the gross domestic product (1).

To reduce the human health burden due topoorwater quality and the lack of improved san-itation and hygiene,WHO and the UnitedNa-tions Childrens Fund have launched as a mil-lennium development goal (MDG) to halve thepopulation without access to safe drinking wa-ter and basic sanitation by 2015 (157). In 2006,87% of the worlds population used safe drink-ing water sources compared to 77% in 1990(155). With respect to sanitation, however, thenumbers are less encouraging; the total popula-tion without access to improved sanitation hasdecreased only slightly since 1990 from approx-imately 2.5 to 2.4 billion (1).

Wastewater Treatmentand Water Reuse

Mitigation of wastewater streams from house-holds and industry is one of the key compo-nents for improving sanitation and maintain-ing public and ecosystem health. Treatmentof municipal wastewater aims at eliminatingnutrients (carbon, nitrogen, phosphorous) andpathogenic microbes. Nutrient removal leadsto a reduction of the biological oxygen de-mand (BOD) of efuent water and thus a de-crease in eutrophication of inland water bodiesand coastal areas. In industrialized countries,

connectivity tomunicipal wastewater treatmentplants is in the range of 50% to 95%, whereasmore than 80% of the municipal wastewater inlow-income countries is dischargedwithout anytreatment, polluting rivers, lakes, and coastalareas of the seas (1). Industrial wastewater is,however, not only a source of BOD but alsoa point source of chemical pollution of heavymetals and synthetic organic compounds. Inindustrialized countries, these pollutants havebeen reduced signicantly through implemen-tation of internal water recycling and recoverysystems and end-of-pipe treatment using ad-vanced technologies, such as activated carbon,advanced oxidation, or membrane processes.The water efciency of industrial wastewatertreatment (i.e., the product revenues per treatedvolume of process water) is highly variable,ranging from approximately US$140 per m3 inDenmark to only US$10 per m3 in the UnitedStates (1) and even less in low-incomecountries.These numbers depend on the type of industrialactivity. To date, a substantial potential existsfor water reuse, which would strongly reducethe discharge of potentially polluted water.

Water recycling and reuse for agricultureand for drinking water through surface andgroundwater bodies are common and long-established practices (162, 163). Today, aframework of integrating aspects of risk assess-ment and risk management is recommendedby WHO to ensure water safety for agricul-tural reuse. This includes water safety plansthat rely on hazard analysis of critical con-trol points (HACCP) and the multibarrierprinciple (163). Furthermore, with increasingwater scarcity, wastewater reuse for drinkingand industrial water becomesmore widespread.For example, in Windhoek, Namibia, wastew-ater has been recycled since 1973, using a se-ries of advanced processes to obtain drinkingwater (164). In many other urban areas thatare under water stress (California, Australia,Singapore), direct or indirect potable or indus-trial reuse is practiced on large scales. Thesesystems mostly rely on membrane technolo-gies (microltration followed by reverse osmo-sis) to treat secondary wastewater efuent and


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remove micropollutants and pathogens ef-ciently (164).

Detecting Pathogensand Waterborne Diseases

Enteric diseases spread mostly via water con-taminated with feces from ill persons and ani-mals. Hence, assessing treatment schemes, in-cluding the potential for water recycling, withregard to the transfer of waterborne pathogens,requires reliable hygienic drinking water qual-ity parameters. Despite the urgent need forso-called pathogen indicators, fast, cheap, andeasy-to-use methods for a worldwide applica-tion are still lacking. Todays hygiene conceptrelies on the detection of such indicators as ahygienic drinking water quality parameter, andthe enteric bacterium E. coli is used worldwideas an indicator of possible fecal contamination(163). In addition, the general microbiologicalstate of water is assessed by counting the totalnumber of colony-forming microbes growingon a nutrient agar plate (the heterotrophic platecount, HPC). As the HPC method largely un-derestimates the number of heterotrophic mi-crobial cells present in a water sample (165),the HPC was omitted from the recent lists ofhygiene parameters of WHO, the EuropeanUnion, and the United States (163, 166). Asa consequence, it is becoming current practiceto rely exclusively on the presence/absence ofE. coli to judge the hygienic quality of drinkingwater. However, this approach is not suited formonitoring the hygienic quality of water treat-ment and distribution (discussed in depth inReference 167). The vulnerability of this con-cept was demonstrated painfully in Milwaukeein 1993 when chlorine-resistant Cryptosporid-ium oocysts from an upstream cattle farm con-taminated the drinking water. Despite chlori-nation and absence of E. coli, more than 50people died after consumption of contaminatedwater and 400,000 persons suffered from cryp-tosporidial diarrhea (168).

Although the detection of E. coli willremain the hygiene parameter for the nextdecades, a wealth of cultivation-dependent

HPC: heterotrophicplate count

and -independent microbiological methodsis currently being proposed for the detectionand quantication of pathogens and indicators(169). For practical testing of treated watersamples, ow cytometry (FCM) is one of themost promising approaches. FCM enableson-site and online enumeration of microbialcells independent of their cultivability, allowsfast screening for specic pathogens (170, 171),and permits detection ofmicrobial activity afterdisinfection (172). A total microbial cell countcan be obtained within 15 min (173). However,FCM-based methods require a paradigmchange regarding the number of microbes thatare expected in raw and disinfected water: in-stead of a tolerableHPC count of less than 300500 bacterial cells per milliliter, FCM countsamount to 100,000200,000 cells per milliliterin high-quality (nondisinfected) drinking water(174).

Complementary approaches are currentlybeing tested to address the spreading ofinfectious diseases on an epidemiological scale.Increasing water temperatures as well as severerainfall and ooding events as a consequenceof climate change are likely to impact thespreading patterns and frequency of infectiousdisease outbreaks (175). To this end, satellitesurveillance data for weather and climate fore-casting may become an essential early warningsystem for water-related diseases because theirspread can be correlated with heavy rainfallsand/or increased water temperatures (176).The potential of this approach is illustratedby the successful prediction of outbreaks ofinfectious diseases, such as dengue, West Nilefever, yellow fever, and malaria (177, 178).

The Multibarrier Concept forImproved Sanitation and SafeDrinking Water Supply

Because many waterborne pathogens spreadprimarily via feces-contaminated water, a clearseparation between wastewater and drinkingwater systems is key to successful water man-agement. To reduce the load of pathogenicmicrobes and viruses into surface water from


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wastewater, amultiplicity of conventional treat-ment methods are available, and feasible op-tions for low-income countries have recentlybeen comprehensively summarized (162).Mostof thesemethods rely on physical elimination ofthe pathogens by coagulation, sedimentation,and ltration, typically eliminating pathogensby 13 log units (162). Today, disinfectionof treated wastewater by UVC irradiation orchemicals (UVC, chlorination, ozone) is per-formed in some countries. Even disinfection ofthe raw wastewater is practiced occasionally.

One of the main ways of producing safedrinking water is by the removal and/or inac-tivation of pathogenic microbes through mul-tiple barriers. These barriers include ltrationby soil aquifer treatment, riverbank ltration,sand ltration, or membrane systems and alsodisinfection steps, such as boiling, chemicaldisinfection, or UV light. Chlorination is stillthe most widely used technique for disinfectingdrinking water because it is effective and eco-nomical, and it maintains a disinfectant residualconcentration during distribution as additionalsecuritymeasure. The formation of chlorinateddisinfection by-products is today consideredinsignicant when compared to the healthbenets from the inactivation of pathogens(162). During the past decade, membrane-based processes became cost-effective for theirapplication in municipal water treatment andare increasingly used as polishing steps toremove microbes and viruses from pretreatedwater (179). Recent work suggests that gravity-driven low-ow ultraltration may becomea valid option for producing drinking waterdirectly from low-quality source water evenfor low-income countries (180).

The efcacy of the above disinfectionprocesses strongly depends on their imple-mentation as centralized versus decentralizedsolutions. In densely populated urban areas,centralized drinking water production anddistribution systems are economically favorableand, therefore, the usual case in industrializedcountries. However, experiences from largecities in low-income countries also show thatcentralized systems often fail to supply safe

drinking water to their customers (179). Thereasons are manifold and include insufcientmaintenance owing to lack of nances orexpertise, as well as to pressure failure, illegaltapping, etc. Hence, in low-income countries,treatment at the household level is requirednot only in rural areas (for example, by solardisinfection) but also in cities with existingcentralized systems. The impact of household-based methods in low-income countries fordrinking water treatment on human health iscurrently debated (181). The reliability of suchmethods, however, is of primary importancebecause even occasional consumption of unsafewater results in an increased health risks,particularly for children (182).

CONCLUSION

Tackling global water pollution requires an ef-fective set of policies, technologies, and sci-entic advances on very different scales. Thelegacy of persistent priority pollutants, such asPCBs, calls for a general phase-out and a regu-latory effort on the global scale. Volatile chem-icals, such as halogenated compounds or mer-cury, which are not subject to biodegradationbut accumulate in the food chain, should be re-stricted in their use to applications in strictlyclosed systems. Human food production sys-tems require rigorous protection against com-pounds with a potential for bioaccumulation;thus water as the key commodity for agricul-ture needs the same attention. In addition, theprecautionary principle has to be applied in de-signing potential substitutes for such prioritypollutants to make sure that todays solutionwill not become tomorrows problem.

Global agriculture faces the challenge to in-crease production yields and at the same timesafeguard the environment and protect the foodchain against contamination. Improving waterquality in agricultural areas requires more inte-grated approaches to farming. Precision agri-culture is based on local characteristics such assoil type, topography, irrigation and drainagesystems, and makes sure that the optimal cropmanagement practices are implemented in the


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right place at the right time, thereby reducingthe risk of emitting nutrients and pesticides intosurface water (183).

Geogenic contaminants act as diffusesources of toxic elements at regional scales, in-icting chronic diseases on large populationson all continents. As the main geochemicaldrivers are known, geochemicalmodelingbasedon hydrogeochemical data and spatial analysishelps identify the populations at risk and imple-ment advanced treatment technologies for cen-tral water distribution systems. In many partsof the developing world, however, rural pop-ulations depend on contaminated groundwaterwells. For these settings, identifying alternativewater resources or implementing simple, reli-able household-centered water treatment tech-nologies requires special effort.

Cleaning up large-scale water pollutionfrom mining activities and groundwater con-tamination from waste sites requires science-based decisions that take into account the spe-cic hydrological conditions, the microbial and

geochemical transformationpathways, andpos-sible remediation technologies to choose themost effective strategies. Such waste manage-ment strategies need to be superseded in thelong run by proactive strategies based on life-cycle assessments and cradle-to-grave steward-ship for toxic compounds. Global water cyclesshould no longer be used as transport pathwaysfor pollutants; it is the responsibility of eco-nomic actors to keep toxic compounds withincontrolled, closed loops.

Finally, the many point sources of waterpollution from urban water systems need in-creased attention and investments over the nextdecades. To reach the MDGs to provide im-proved sanitation and safe drinking water forabout 2 billion people, concerted efforts to de-velop and implement cost-effective sanitationsystems in the growing megacities in areas withwater stress are of highest priority. Developingthe techniques and social networks to improvehousehold-centered sanitation in rural areas re-quires an effort of similar magnitude.

SUMMARY POINTS

1. The increasing global chemical pollution of natural water with largely unknown short-and long-term effects on aquatic life and on human health is one of the key problemsfacing humanity.

2. The point and diffuse sources of chemical pollution are manifold, and their temporaland spatial impacts on water quality range from short-term local to long-term global.Agriculture, mining activities, landlls, industrial and urbanwastewater, as well as naturalgeogenic releases are the most relevant pollutant sources.

3. Owing to the enormous variability of micropollutants, mitigating a given chemical wa-ter pollution problem is commonly a quite challenging task. Each case requires its owninterdisciplinary scientic knowledge and methods, and each has its own technical, eco-nomical, and societal dimensions.

4. Reliable wastewater collection and treatment systems are critical for sanitation and forhuman and ecosystem health. Centralized municipal wastewater systems provide reliablesolutions to many of these problems but lead to estimated global annual infrastructurecosts of US$100 billion over the next 20 years. Such a nancial outlay may be prohibitivefor low-income countries.

5. Access to improved sanitation for one-third of the worlds population is an urgent issue,and lack of proper sanitation systems is responsible for the spreading of waterborneinfections and for unsafe drinking water. Despite this fact, 80% of the nancial aid forwater-related projects is spent on drinking water instead of sanitation issues.


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6. At present, cheap production in emerging economies is too often accompanied withunacceptable pollution of natural water. International chemical regulation, consumerinformation, and good practice codes should therefore work synergistically to preventlarge-scale emission of chemicals into the hydrosphere in all parts of the world.

FUTURE ISSUES

1. Despite the anticipated advances in water treatment technologies, efforts to reduce intro-duction of problematic chemicals into the (aquatic) environment should be given highestpriority. This requires the improvement of the scientic tools to identify those existingchemicals that need to be substituted and phased out and the political will to enforcesuch action.

2. In the chemical industry, the green chemistry approach should be more strongly im-plemented, including efciency engineering of chemical processes to minimize materialows into the environment and emphasizing the design of new chemicals that are com-pletely biodegradable and therefore of less environmental concern. In addition, improvedtreatment and removal technologies will allow coping with the legacy of existing waterpollutants.

3. Surface- and groundwater pollution from mining activities, known and unknown land-lls, and spill sites will continue to threaten our water supplies. Mitigation of thesecontaminant sources will require enormous nancial resources over the next decades andresearch on effective removal technologies.

4. The high costs of centralized wastewater systems and their low water efciency requirethe development of alternative solutions, possibly decentralized systems. They will allowreusing the water and nutrients locally and lead to low discharge systems.

5. The goal of cheap, fast, and reliable detection of a broad variety of micropollutants andpathogens in natural water calls for innovative developments in analytical technologiesand internationally compatible protocols for water quality assessment.

6. T

art. contaminacion mundial del agua y salud humana

Documents

water systems

wastewater sources

local water pollution

wastewaterand drinking

safedrinking water supply

geogenic contamination

global problem115agriculture

global scale