chapter impacts of waste pollutants on human health

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WARNING ATTENTION

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-0 Cfdt: J. JOOOY, L.A. b#W?k/y

Chapter 6

Impacts of Waste Pollutantson Human Health

CONTENTS

Page

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...................123Limitations of Human Health Effects Data. . . . . . . . . . . . . . . . . . . . . . ............124Toxic Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...........124

General Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......124Pathways to Humans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............125Potential and Actual Human Health Impacts . . . . . . . . . . . . . . . . . . . . . .........125

Toxic Organic Chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............127General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127Pathways to Humans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . ........129Potential and Actual Human Health Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . ...129Classes of Organic Chemicals . . . . . . . . . . . . . . . . . . . . . . . ....................131

Human Pathogens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..................133General Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...133Pathways to Humans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..........135Potential and Actual Human Health Impacts . . . . . . . . ......................135Shortcomings of Current Microbiological Standards . .......................138The Effect of Treatment on Pathogenic Microorganisms . ...................139Land Application of Sewage Sludge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......139Deputation of Shellfish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..................139

TablesTable No. Page

8.

9.

10,

Properties and Effects of Metals of Primary Concernin the Marine Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .126Properties and Effects of Major Classes of Organic Chemicals in WastesDisposed of in Marine Environments . . . . . . . . . . . . . . . . . . . . . .............,130FDA’s Criteria for Initiating Enforcement Actions Against Seafood . . . . . . . . ..136

Figure No.

24.

25.

Box

L.M.N.

Ability ToCategoriesNew York

FiguresPage

Conduct Health-Hazard Assessment of Substances in Sevenof Chemicals in Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .128Bay-Newark Bay Fishing Sites and Advisory Areas . .............132

BoxesPage

Public Health Advisories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ....131Classes of Human Pathogens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..134Exposure to Toxic Chemicals and Pathogens Through Seafood . ............136

Chapter 6

Impacts of Waste Pollutants on Human Health

I N T R O D U C T I O N

Many substances found in wastes disposed of inmarine environments have the potential to producea variety of acute and chronic human health effects.The likelihood of human exposure to these pollut-ants depends on their physical, chemical, and bio-logical form; concentration; and persistence or sur-vival. The character of the disposal environment,method of disposal, and nature of environmentalpathways leading to human exposure are also im-portant variables.

There are two major contaminant pathways to

humans. Contaminants can pass direcdy from con-taminated media (water or air) to humans, typi-cally by uptake through the skin or lungs, orthrough ingestion (e. g., swallowing water). Alter-nately, they can reach humans indirectly by inges-tion of plants or animals that have taken up thesesubstances directly or indirectly from contaminatedenvironments. The relative significance of these twokinds of pathways varies for different pollutants.

Indirect exposure from water can be a signifi-

cant route of exposure to toxic organic chemicalsand metals because many of these substances havea capacity to persist in the environment, to con-centrate in particular parts of the environment, andto bioaccumulate in certain plants and animals. Di-rect human exposure to toxic organic chemicals andmetals from water is generally less significant be-cause these substances are typically present in waterat relatively low concentrations. 2 For pathogens,

1.il U( h of the information prcst>n[cd in this chapter is dcrl~”cd f’rorncx(cnsi~c anal}sc”s ( onta]nc(] In tm (1 ( c)ntrac t reports prc’pared for 0’I’A( 205, 409).

~W’hcrr hlqh c-on( ent rations are present, d It-e{ t exposure of humansto SU( h suhstan( c’s In water ( .tn rausc si~nili( ant impact~. Su( h c’x -posurcs might be cxpcrlcn( cd, for example. b}. bathers swimming ata bca( h in the immcdia[c \i( init~ of an inrfust rial d]schargc or b} dilrrsworking In h i,qhl} polluted maters.

both direct and indirect exposure can be significantbecause only small numbers of microorganisms arerequired to induce disease, and because micro-organisms can reproduce in the environment or ininfected animals.

Another general distinction can be made betweendifferent types of pollutants based on the extent to

which they persist or are degraded in the environ-ment. “Conservative” and ‘‘persistent’ pollutants(e.g., toxic metals, PCBs) are broken down slowlyor not at all, while ‘‘nonconservative’ and ‘‘labile’pollutants (e. g., biodegradable or volatile organicchemicals) are rapidly rendered harmless or are re-moved from the system by environmental proc-esses. Most of the problem substances in marineenvironments are in the former categories: theirenvironmental persistence enhances their potentialto reach and affect humans. Microbial contami-nants of both types exist as well; some microbesare killed or inactivated by environmental proc-esses, while others can actually proliferate.

Human health impacts can be associated withthree major categories of pollutants that are presentin wastes disposed of in marine environments, andthat have the potential to reach and cause adverseimpacts in humans. These categories are:

1.

2.

3.

toxic metals: arsenic, cadmium, lead, andmercury;synthetic organic chemicals: polycyclic aro-matic hydrocarbons (PAHs), chlorinatedhydrocarbons, and “specialized” chemicals(polychlorinated biphynyls (PCBS), pesticides,dioxins); andhuman pathogens: viruses, bacteria, fungi,and parasites.

123

63-983 - 87 - 5 : (QL 3

124 • Wastes in Marine Environments

LIMITATIONS OF HUMAN

Major impediments exist that limit a thoroughevaluation of the human health impacts caused bywaste-borne pollutants. Information is lacking onmost of the individual substances detected in wastesand there is often uncertainty or controversy sur-rounding those for which there are data. In addi-tion, it is difficult to accurately predict the behaviorof a substance based only on data for chemicallysimilar substances. An accurate assessment is alsohindered by the complexity of most wastes, whichare typically contaminated by a mixture of poten-tially harmful substances. Existing data typicallyallow at most an assessment of acute, short-termimpacts associated with a particular waste; it israrely possible to adequately assess chronic, long-term effects.

Moreover, studies of the environmental or eco-logical impacts of individual chemicals introducedinto the environment through waste disposal rarelymeasure or sufficiently consider the potential hu-man health effects. In fact, the human health risksassociated with exposures to the vast majority—90 percent or more —of all chemicals found in dif-ferent wastes are unknown (386). Knowledge about

TOXIC

General Characteristics

Metals are chemical elements and as such can-not be destroyed or broken down through treatmentor environmental degradation. However, a num-ber of environmental processes—both chemical andbiological-can alter the mobility and bioavailabil-ity of metals,

In general, toxic metals (including arsenic, beryl-lium, cadmium, chromium, cobalt, copper, lead,mercury, molybdenum, nickel, selenium, and zinc)are of potential concern whether they are found inwastes that will be disposed of on land or in theocean. With respect to human health impacts aris-ing from disposal of wastes in the marine environ-ment, four metals are of primary concern: arsenic,cadmium, lead, and mercury. These are particu-larly important because of their known toxicity tohumans and their presence in relatively high con-

HEALTH EFFECTS DATA

the human health effects of environmental pollut-ants generally comes from studies of only a few toxiccompounds, such as mercury, cadmium, and PCBs(409); and these effects are often recognized onlyafter large-scale occupational exposure, industrialaccidents, or massive discharges of waste into theenvironment.

The accumulated knowledge in the field of toxi-cology is based primarily on experimental workwith laboratory mammals. Thus, estimating hu-man health risks from the disposal of chemical com-pounds in marine environments is generally basedon extrapolating information on the toxicity of spe-cific chemicals to laboratory mammals to the con-centrations observed in marine organisms or hu-mans. The estimates must also attempt to accountfor the persistence of such substances in the envi-ronment and their tendency to bioaccumulate orto biomagnify in marine organisms that might beconsumed by humans. Public health informationon human pathogens is largely derived from inves-tigations of past incidents and, more rarely, on pro-spective epidemiological or clinical efforts.

METALScentrations in wastes disposed of in estuaries andcoastal waters. Metals of secondary concern includechromium, copper, and selenium. Other toxic me-tals are present in much lower concentrations bothin wastes and in regions of the marine environmentthat are likely to lead to human exposure (409).

In marine environments, most dissolved metalsare rapidly adsorbed and remain bound to partic-ulate material that eventually settles out of the watercolumn and is incorporated into sediments. How-ever, some metals (e. g., cadmium, copper, nickel,and zinc) can be slowly —over a period of monthsor years—released from the sediment’s oxidizedsurface layer and sublayers (124). In addition, me-tals can be released through other chemical and bio-logical changes or processes, for example, bychanges in salinity that commonly occur in estua-rine waters. The action of microorganisms can alsomobilize metals: for example, bacteria in sediments

Ch. 6–Impacts of Waste Pollutants on Human Health • 125

can convert slightly toxic inorganic mercury to thehighly toxic and volatile methyl mercury (26). Fi-nally, the burrowing of animals into sediments (bi-oturbation) and physical processes such as stormscan release metals from sediments through oxida-tion and direct physical resuspension (709).

Pathways to Humans

Indirect pathways to humans vary with the par-ticular environment and method used for disposal.In marine environments, consumption of con-taminated seafood is generally the major routeof human exposure to metals. Direct human ex-posure to metals is usually less important becausethey generally attain very low concentrations in thewater column (409). However direct exposure re-sulting from volatization of certain metals (e. g.,mercury, arsenic, and lead) due to their methyla-tion by microorganisms, or direct exposure to ma-rine waters with high concentrations of metals,would be a concern.

Bioaccumulation and biomagnification3 areimportant processes that largely determine the po-tential for indirect human exposure to toxic me-tals and organic chemicals that result from marinewaste disposal. Marine organisms, especially ben-thic organisms, can bioaccumulate metals by filter-ing water during feeding or swimming, ingestingparticulate matter onto which such substances areadsorbed, or ingesting other contaminated organ-isms (46,232 ,260). Bioaccumulation generally in-creases as the degree of water or sediment contami-nation increases, but it varies considerably amongmetals, species of marine organisms, and types ofsediment.

Biomagnification of a metal can result in the step-wise increase in an organism tissue concentrationof several orders of magnitude or more, and hencerepresents a major potential pathway for humanexposure. According to available evidence, mosttoxic metals do not biomagnify into higher trophiclevels of the marine food chain (33,260). However,

‘ 1 n (h IS t CJrrtcxt, [hc tt’rrrl I)I(JJ{ { u m u]at ion rcf’ers to the processwhrrt,)>} d ~u b>tanc c rn tcr~ an aquiit i{ f}r~an i jrn, ci rhcr d i rrrtll’ fmmthe w atrr- thmuqh qIlls {Jr cp]thc] Id t]jsuc, or- lndirrc[ly through t (Jrl-surn pt ion of other ory,in]>rns Bl[)rrl,irqrifi( ation rt’fkrs to the resulr.intpr(x c’~f M }It.r[t)y I IS>U{ ( 1):1( (,rrl r<i[ il)rls of ljI(ki( ( umulatml Sut)st<ln( ~,~I rr( rt.,iw, as r h( rrl.ttcrr,t] I \ paiwy] u p t hrou qh m (Irx. than (Int ( r[)ph i(l(i (1 ]n I}](> t(xxl ( h.i]n (260)

methyl mercury, and perhaps selenium4 and zinc,are important exceptions to this rule.

Of the metals of primary concern, cadmium andmercury have significant potential for transport tohumans through consumption of contaminated sea-food (table 8). Arsenic is largely converted to non-toxic forms by marine organisms (129), and nei-ther arsenic nor lead have been shown to accumu-late significantly in seafood (409).

Even when bioaccumulation is not a factor, sig-nificant quantities of metals can concentrate in thegut or gills of marine organisms without actual ab-sorption into the tissues. This is especially true forshellfish that filter large quantities of seawater andingest solid matter during feeding (e. g., oysters,clams, mussels). Because people generally eat theseorganisms in their entirety, toxic substances canbe passed to humans even in the absence of anyactual bioaccumulation. This mechanism probablyaccounts for most instances of shellfish contamina-tion involving metals that do not bioaccumulate. s

Potential and Actual HumanHealth Impacts

Toxic metals are capable of inducing a varietyof human health effects—lethal and sublethal, acuteand chronic. Some of the known properties and ef-fects of exposure to the metals of primary concernin marine environments are summarized in table 8.

Acute environmental effects attributable to toxicmetals may occur if concentrations are sufficientlyhigh. Although documentation of human poison-ing from consuming seafood contaminated withtoxic metals is uncommon, there have been sev-eral well-known, catastrophic events. In Minamata,Japan, for example, over 100 people died and 700others suffered severe, permanent neurologicaldamage after consuming shellfish contaminated byindustrial discharges of methyl mercury into Mina-mata Bay (128). A similar, though less severe, eventoccurred in Niigata, Japan in 1965 (550).

126 ● Wastes in Marine Environments

Table 8.—Properties and Effects of Metals of Primary Concern in Marine Environments

Arsenic Cadmium Lead Mercury

Bioaccumutation

Biomagnification

Low except in some fishspecies

Moderate Low or none Significant (methylatedform)

Significant (methylatedform)

Metallic form: relativelyinsoluble

Readily methylated bysediment bacteria tobecome more soluble,bioavailable,persistent, and highlytoxic

Low or none Low or none Low or none

Metallic form: relativelysoluble

Not subject tobiomethylation

Less bioavailable in marinethan in fresh water

Long biological residencetime

Synergistic effects withlead

Sediments

Generally insolubleAdsorption rate age-

dependent, 4 to 5 timeshigher in children thanadults

Synergistic effects withcadmium

Properties Metallic form: insolubleReadily methylated by

sediment bacteria tobecome highly soluble,but low in toxicity

Major environmentalsink

Major routes of humanexposure:Marine environments

Sediments Sediments Sediments

Seafood: very minor route,except for some fishspecies

Inhalation: the major route

Seafood contributes == 1OO/.

of totai for generalpopulation

Food, primarily grains

Seafood comparable toother food sources

Seafood is primarysource of humanexposure

Terrestrial pathways areminor sources incomparison

Kidney dysfunction;neurological disease;skin lesions;respiratoryimpairment; eyedamage; animalteratogen andcarcinogen

Other environments Diet and drinking water

Health effects Acute: gastrointestinalhemorrhage; loss ofblood pressure; comaand death in extremecases

Chronic: liver andperipheral nerve damage;possibly skin and lungcancer

Emphysema and other lungdamage; anemia; kidney,pancreatic, and liverimpairment; bonedamage; animal (andsuspected human)carcinogen and mutagen

Acute: gastrointestinaldisorders

Chronic: anemia;neurological and blooddisorders; kidneydysfunction; jointimpairments; male/femalereproductive effects;teratogenic

References a Doull, et al., 1980Barrington, et al., 1978O’Connor and Kneip, 1986Woolson, 1983

Chapman, et al., 1968Nriagu, 1981O’Connor and Kneip, 1986Wiedow, et al., 1982

Callahan, et al., 1979Heltz, et al., 1975Kneip, 1983NAS, 1980O’Connor and Kneip, 1986O’Connor and Rachlin, 1982

Grieg, et al., 1979Kay, 1984Nriagu, 1979Windom and Kendall,

1979

asee list of references at end of repot

SOURCE: Office of Technology Assessment, 1987

Other events involving metal contamination offood sources (though not seafood) have occurred.These include dietary transport of lead and cad-mium from the application of sewage sludge to agri-cultural lands (470,47 1); and the pollution of Jap-anese rice paddies by industrial cadmium dis-charges, which resulted in 60 deaths (404).

in part responsible for the paucity of data docu-menting such human health effects.

Mercury is of special concern because it is eas-ily taken up by humans through a diversity of ex-posure routes, including inhalation, ingestion, andthrough the skin. The source of mercury responsi-ble for contamination of marine organisms differsamong the various marine waters. In the openocean, natural sources of mercury predominate,whereas in some estuaries and coastal waters, in-puts from land-based sources are commonly themajor source of contamination. In fact, marine

Substantial laboratory evidence documents thepotential for lethal and sublethal chronic effects toresult from exposure to metals contributed by wastedisposal activities. However, our capacity to detectchronic impacts in the field is limited, and this is

Ch. 6—Impacts of Waste Pollutants on Human Health • 127

organisms from polluted estuaries typically containfive or more times as much mercury as marineorganisms from relatively clean estuaries (702).

Ingestion of contaminated shellfish and finfish,especially long-lived predatory fish such as tuna,is the primary route of human exposure to mer-cury (202,702). Again, however, in open-ocean fishmercury is generally attributable to natural sources,while shellfish contamination is typically moreclosely correlated with waste disposal.

Cadmium is used extensively in metal elec-troplating and found in a wide variety of wastes.It is more mobile than most other toxic metals.Large-scale cadmium contamination of estuarinewaters by industrial and municipal wastewater dis-charges has occurred in some urban areas, for in-stance in the Hudson River estuary, and this hascaused significant contamination of marine foodchains (272,409). For example, studies show that

shellfish harvested near an industrial outfall for-merly used to discharge cadmium wastes containedlevels high enough to induce acute cadmium poison-ing in an unwary consumer or urban fisherman (refs.229,696; also see box N later in this chapter). Otherstudies of the entire Hudson estuary found thatmoderate consumption of shellfish could lead to ex-posure exceeding recommended safe levels (41 1).

The actual mechanism by which cadmium istransported through the marine food chain is con-troversial. Some investigators have found that cad-mium present in sediments of some urban embay -ments is readily taken up by organisms, and thatcontaminated sediments represent the most likelysource of human exposure (229). However, otherssuggest that sediments are not a significant contrib-utor of cadmium even to contaminated organismsharvested from marine waters near urban-industrialareas (491).

T O X I C O R G A N I C C H E M I C A L S

General Considerations

Some 65,000 chemical compounds are used inindustry worldwide (386). Of these, approximately10,000 are used regularly in one or more indus-trial processes; about 1,000 new chemicals are in-troduced into commerce each year (23 1). Clearly,individual evaluation of the health effects of eachof these compounds is a hopeless enterprise. Forseveral broad categories of industrial chemicals, fig-ure 24 shows the paucity of data available on whichto base health hazard evaluations.

Organic chemicals vary considerably with respectto their behavior in natural environments. Somechemicals accumulate in organisms; others do not.Some decompose rapidly if exposed to light, heat,or water; others are highly persistent. Some com-pounds may be metabolized by organisms intoother compounds that may be more or less toxic

‘Organ ic chemicals possess a molecular skeleton made of carbonand hydrogen and generally contain relatively few other elements, suchas oxygen, nitrogen, or chlorine. Chlorine-containing organic com-pounds are referred to as ‘ ‘chlorinated. ‘‘ Metals or metal-containingsubstances are usually termed ‘‘ inorganic, although in some casesmetals can be chemically bound to organic compounds (e. g,, meth>lmercury).

than the original compound; others resist biodegra-dation. Toxicities may vary from one organism toanother, and toxic levels may also be affected bythe presence of other compounds, producing syner-gistic or antagonistic effects.

Given this complexity, it is essential to invokesome system to simplify classification if a health haz-ard evaluation is to become manageable. One ap-proach is to classify compounds according to howthey behave in the environment, that is, on the basisof environmental fate. This approach can be usedto reduce the size of the chemical universe downto those substances that have a potential to reachhumans; information on human health effectswould then only need to be developed for thissubset.

Several relatively well-understood relationshipsexist between chemical properties of organic com-pounds and their fate in natural environments:

Chemical Property: Related to:Solubility in water Adsorption, route of absorption,

mobilityVapor pressure Atmospheric mobility’, environmcntal

volatility) persistenceSolubility in animal Bioaccumulation potential, adsorption

tissue by organic matter or sediments. per-sistence in organisms


Figure 24.—Ability To Conduct Health-Hazard Assessment of Substances in Seven Categories ofChemicals in Use

CategoryNumber ofchemicalsin category

Estimated mean percent of each category

Pesticides and inertingredients of pesticideformulations

Cosmetic ingredients

Drugs and excipientsused in drug formulations

Food additives

Chemicals in commerce:at least 1 millionpounds/year

Chemicals in commerce:less than 1 millionpounds/year

Chemicals in commerce:production level unknownor inaccessible

3,350

3,410

1,815

8,627

12,860

13,911

21,752

. . . . . . . . . , . , .,.,.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 24 2 26 38

2 14 10 18 56

18 18 3 36 25

5 14 1 34 46

. . . . . . .. . . . . .. . . . . . .. . . . . .. . . . . . .. . . . . .. . . . . . .

11 11 78

12 12 76

,. ...,. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .,., . . .. . . . . .. . . . . .10 8 82

. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .Complete Partial Minimal Some No toxicity

health health toxicity toxicity informationhazard hazard information information available

assessment assessment available availablepossible possible (but below minimal)

SOURCE: National Academy of Sciences, ToxicIty Testing: Strategies To Determine Needs and Priorities (Washington, DC: National Academy Press, 1984).

Ch. 6–impacts of Waste Pollutants on Human Health • 129

Using a scheme based on determinants of envi-ronmental fate such as these, it is possible to iden-tify, for example, a class of compounds with lowwater volubility and high tissue volubility (e. g.,PCBs, dioxins) that is likely to persist for longperiods in the environment and bioaccumulate inorganisms. Another class with the characteristicsof high volubility and high volatility (e. g., chloro-form, toluene) is likely to have low potential for ac-cumulation in the food chain, but may pose a haz-ard to humans from inhalation or ingestion indrinking water. These considerations form the basisof the classification of organic chemicals used in thissection (table 9).

Pathways to Humans

The most serious risks to human health are gen-erally posed by those organic chemicals that aretoxic, persistent, and have some means of reach-ing humans (i. e., present in significant concentra-tions in what has been termed the human exposurezone). As was the case for metals, humans can beexposed to organic chemicals either directly fromthe water (by absorption through the skin, by drink-ing contaminated water, or by inhaling contami-nated air), or indirectly through ingestion of con-taminated plants or animals.

In marine environments, many organic chemi-cals partition into sediments or onto the water’s up-per surface (the surface microlayer), where they arepotentially available to marine plants and animals;this can provide an indirect pathway to humansthrough ingestion of contaminated seafood. Directhuman exposure to organic chemicals is less com-mon because these substances generally can bepresent in the water at only very low concentra-tions, although in some cases they may be of sub-stantial concern.

As was the case for metals, the consumption ofcontaminated seafood is the primary pathway forhuman exposure to most organic chemicals inwastes disposed of in marine environments. Indeed,compounds such as PCBs and DDT have beenshown to accumulate in humans through consump-tion of contaminated seafood (249,409),

Not surprisingly, the importance of bioaccumu-lation and biomagnification varies greatly fordifferent organic chemicals and for different organ-

isms. Several classes of organic chemicals, particu -larly those that are relatively insoluble in water,have a high bioaccumulation potential because oftheir volubility in animal tissue. Some of these or-ganic compounds, including PCBs, benzo[a]py -rene, naphthalenes, and chlorinated pesticides (e. g.,kepone, mirex, and possibly DDT), also appear tohave a potential for biomagnification by marineorganisms.

Other compounds that bioaccumulate but prob-ably do not biomagnify include chlorinated phenolsand benzenes, and most PAHs. However, there isrelatively little information on the long-term fateand behavior of most organic compounds in aquaticenvironments (260).

Potential and Actual HumanHealth Impacts

Few documented cases of human health impactsfrom waste-derived organic chemicals in marineenvironments exist. 7 However, the potential forsuch exposure and effects clearly exists in the UnitedStates. Numerous estuarine and coastal areas—e.g., New Bedford Harbor, New York Harbor, andportions of Puget Sound—are sufficiently contami-nated with toxic chemicals to preclude the harvestof fish and/or shellfish (box L; refs. 211 ,507). Com-mercial and recreational fishing for striped bass,bluefish, tautog, and eels has been curtailed in largeportions of the New York Bight’s apex due to highconcentrations of PCBs and other organic com-pounds (28,30,237).

PCBs and PAHs are widely distributed in inlandand coastal sediments and have been found in deepocean sediments as well (62,325,484). PCBs andseveral other highly persistent and toxic chemicals(e. g., DDT) have been banned from further pro-duction or use in commerce in the United States.It can be expected, therefore, that the sediment con-centrations and body burdens of these toxic com-pounds will probably decrease gradually over time

~Sc\eral cases intol,ing land-based food sources ha~e been reported,The most infamous is a disease outbreak in Japan, known as the }’ushoincident, that was caused by the leakage of PCBS (in combination withd ibcnzofu rans) from an industrial heat exchanger into a rice oil m~n -ufacturing process, }rusho symptoms included reduced birthweightsand skin disorders such as chloracnc and hyperpigmentation ( 287).

Table 9.—Properties and Effects of Major Classes of Organic Chemicals in Wastes Disposed of in Marine Environments

Primary routesChemical class Major examples Properties to humans Health effects References a

Benzene: central nervous system(CNS) effects, blood disease,leukemia

Toluene: possible CNS effects,low toxicity

Xylene: irritant; teratogen

CTET and chloroform: liver,kidney, blood, andgastrointestinal disorders; liverand kidney cancer

Methylene chloride: possible CNSeffects

Callahan, et al., 1979Doull, et al., 1980NAS, 1977O’Connor and Kneip,Snyder, et al., 1984

Low molecular weighthydrocarbons

BenzeneTolueneXylene

Volatile InhalationBiodegradable Drinking waterLow bioaccumulation potential

1988

1988

1988

Volatile InhalationLipid-insoluble Drinking waterLow bioaccumulation potentialSome (e.g., CTET and

chloroform) are persistent;others (e.g., methylene

Callahan, et al., 1979Doull, et al., 1980O’Connor and Kneip,Thorn and Agg, 1975

Chloromethanes:carbon tetrachloride (CTET)

Low molecular weightchlorirlatedhydrocarbons chloroform

methylene chloride

chloride) are readily

Inhalation

biodegraded

VolatileLipid-insolubleLow bioaccumulation

VolatileLow bioaccumulation

Range of volatilitiesLipid-soluble

All: CNS effects, liver toxicityTri- and tetrachloroethy lene: liver

cancer

Animal and human carcinogen;liver toxicity

Hexachlorobenzene: carcinogen

Callahan, et al., 1979Doull, et al., 1980Sittig, 1985

Doull, et al., 1980

Trichloroethylene,tetrachloroethylene,tetrachloroethane

Vinyl chloride

Chlorobenzenes

Drinking waterpotential

Inhalationpotential

Food (includingseafood)

Doull, et al., 1980O’Connor and Kneip,

Significant bioaccumulationpotential

Nonvolatile Food (includingHigh bioaccumulation potential seafood)Moderate to high toxicityMost are highly persistent

Known or suspected humancarcinogens; neurotoxic effects;chloracne and other skindiseases

Doull, et al., 1980Mrak, 1989NAS, 1977Sittig, 1985Walker, et al., 1989

Chlorinated pesticides Cyclodiene pesticides:dieldrin, heptachlor,chlordane

DDT and metabolizes

aldrin,

Chlorinated phenoxyaceticcompounds (2,4,5-T; 2,4-D)

Hexachlorocyclohexanes:Iindane, BHC

Polychlorinated biphenyls(PCBs)

Chlorinated dioxins TCDD)Chlorinated dibenzofurans

Phthalate esters (e.g., DEHP)Polycyclic aromatic

hydrocarbons (PAHs)

Kimbrough, et al., 1975Koibye and Carr, 1984Murai and Juroiwa, 1971Poiger and Schlatter,1983

FDA, 1974Giam, et al., 1978MacLeod, et al., 1981NAS, 1977

Nonvolatile Food (includingHigh bioaccumulation potential seafood)Moderate to high toxicityHighly persistent

All: neurological, liver, and skindisorders

PCBs: tumor promoters orcarcinogens

TCDD: highly carcinogenic

High molecular weightchlorinatedhydrocarbons

Aromatic hydrocarbons Low to moderate volatility Food (includingHighly insoluble seafood)Range of bioaccumulation

potentialLow to moderate toxicity

Phthalates: many are teratogensDEHP: possible carcinogenPAHs: many (e.g., benzo(a)pyrene)

are carcinogens; some areteratoaens

asee list of references at end of report.

SOURCE: Office of Technology Assessment, 1987.

Ch. 6—Impacfs of Waste Pollutants on Human Health ● 131

(57,519).’ Indeed, recent evidence shows such a de-cline along the west coast of the United States (340).

Direct exposure of humans to organic chemicalspresent in marine waters is possible in places whereindustrial discharges are 1ocated near bathing

beaches. For example, a wastewater discharge froma New Jersey pharmaceutical firm, which entersmarine waters about 2,500 feet from shore, hasbeen identified in bioassays as the most mutagenic

industrial discharge in the State (T, Burke, NewJerse y Department of Health, pers. comm., 1986)The wastewater from a Florida paper mill dis-charged into the Amelia River estuary has beenfound to be the most toxic among the State’s ninemills (8). In neither case, however, has an actualeffect on the health of bathers been demonstrated.

Classes of Organic Chemicals—.. . .— -

To simplify the evaluatio n of organic com-8However, the manufacture and use of many of these chemic~s havenot been curtailed in other countries; in addition, existing stocks of pounds, they can be classified on the basis of simi-some of these chemic~$ continue to pose major dispos~ problems, larities in their chemic~ structure, physicochemi-


Figure 25.—New York Bay-Newark Bay FishingSites and Advisory Areas

Newark Bay

Railway Bridge

3

(/J .- fHudson Co. Park

Port Newark North ‘:

NEW JERSEY

kii:m

New York Bayrty State Parken Point Pier

Miles

Bulkhead

NEW YORK

Raritan -River “ !a>eti~%,g

r -.

The PCB advisory for limited consumption of striped bass andbluefish applies to the coast and all the rivers and tributaries shown.Sale for human consumption of striped bass and American eel frommost of these rivers is also prohibited.

SOURCE: T, Belton, et al,, “Urban Fishermen: Managing the Risks of Toxic Ex-posure, ” Errvirorrrnent 28:19-20,30-36, November 1966.

cal properties (e. g., volatility, tissue volubility), andmolecular weight. Chemicals having similar char-acteristics often tend to exhibit similar environ-mental fates or behavior, and therefore may fol-low similar pathways to reach humans. In somecases (though less predictably), compounds in thesame group may also have similar toxicity charac-teristics. It should again be emphasized, however,that although such grouping of organic compoundshelps determine their potential for significant hu-man exposure, each compound must still be exam-ined individually for specific environmental andhealth effects.

Table 9 lists the primary classes of organic chem-icals that have some potential for reaching humansand inducing adverse health effects. Chloro-benzenes, chlorinated pesticides, high molecularweight chlorinated organic compounds, and aro-matic hydrocarbons are of major concern in marineenvironments due to their ability to bioaccumulatein organisms. While wastestreams containing manyof these compounds are specifically prohibited fromocean dumping, the major pathway by which theyenter marine environments is as trace contaminants

in industrial wastewater effluents, sewage sludgeand effluent, and dredging spoils.

Clorobenzenes exhibit a range of volatilities andtissue solubilities (and therefore bioaccumulationpotential), dependent primarily on the degree ofchlorination. Of all the low molecular weight chlo-rinated hydrocarbons, chlorobenzenes pose thegreatest risk of transport to humans through ma-rine or terrestrial food chains.

Cldorinatedpesticides are significant because ofthe high risk of human exposure through consump-tion of contaminated seafood. They strongly asso-ciate with organic matter and sediments, where theyare readily available to marine organisms. Theirhigh molecular weight and complex, chlorine-con-taining structures make these compounds very resis-tant to degradation by bacteria or the metabolic sys-tems of higher organisms. This class of substancesexhibits a range of toxicities, from several cyclo-diene pesticides that show adverse effects at thelowest doses tested (682) to DDT and related com-pounds that have moderate toxicity to humans andlaboratory animals. Most of these compounds areknown or suspected carcinogens.

Chlorinated organic compounds include PCBsdioxins, and dibenzofurans. These compounds gen-erally share the same properties described for thechlorinated pesticides: low volatility, generally highbioaccumulation potential, strong ability to bindto organic matter and sediments, and high resis-tance to degradation by bacteria or the metabolicsystems of higher organisms.

PCBs are actually a group of over 200 individualcompounds possessing unique chemical and toxico-logical properties (494). PCBs are accumulated bymarine organisms with very high efficiency. Forexample, one study found 85 to 95 percent assimi-lation of PCBs across the gut of striped bass (447).The ubiquity of PCBs in the environment and theirextreme persistence and toxicity to marine and ter-restrial organisms, led to a ban on their produc-tion in the United States in 1979.

Dioxins and dibenzofurans (the most well-studiedof which are 2,3,7,8-tetrachlorodioxin (TCDD) and2,3,7,8-tetrachlorodibenzofuran (TCDF)) arefound as contaminants of numerous chemical prep-arations (467). Both sets of compounds are quitetissue-soluble, and are therefore easily bioaccumu-


lated to high levels. TCDD and TCDF are amongthe most toxic compounds known and can producelethal effects at low doses in aquatic organisms andbirds (191 ,365).

Aromatic hydrocarbons include phthalate esters,which are common contaminants in water, sedi-ment, and marine organisms (72) as well as in vari-ous types of wastes, especially sewage (73). Themost common are diethylhexyl phthalate (DEHP)and dibutyl phthalate (DBP). Phthalate esters havelow water solubilities, tightly adsorb to sedimentparticles, and are not readily degraded through bio-logical activity (72 ,541 ). Chronic effects from ex-posure to phthalate esters include reduced weightgain, enlarged livers and kidneys (381 ), and an in-creased incidence of liver cell cancers (274).

Polycyclic aromatic hydrocarbons (PAHs) are de-rived from petroleum and other chemical processesand constitute most of the ‘ ‘oil and grease regu-lated as a conventional pollutant under the CleanWater Act. Major sources to marine environmentsinclude spills and routine releases from ships, nat-ural seepage, and municipal wastewater, sewage

sludge, dredged material, and runoff from urbanareas (409). PAHs are readily adsorbed by sus-pended particulate and bottom sediments, wherethey persist and can accumulate to levels as highas 1 percent (10,000 parts per million) in highlyindustrialized areas such as New York Harbor(325).

Marine organisms, particularly mollusks, havea high potential for bioaccumulating PAHs, andthey can achieve tissue levels far in excess of waterconcentrations and roughly comparable to sedimentconcentrations (409). Certain PAHs (e. g., benzo-[a]pyrene and naphthalenes) can also biomagnifyin higher level predators of the marine food chain(260). Disposal of wastes at sea is considered themost likely source of PAHs to marine waters; sub-sequent transport of PAHs to humans can then oc-cur through the food chain (409). How seafood con-sumption compares to other sources of PAHexposure is not well-understood, however, so thesignificance of PAH contamination of seafood asa source of exposure to humans is uncertain.

HUMAN PATHOGENS

General Considerations

Essentially all wastes that are disposed of in themarine environment either contain microorganismsor have the potential to modify the microbial com-munity at the disposal site. Among the micro-organisms entering the marine environment throughwaste disposal, or induced to proliferate as a re-sult of such activity, are a variety of human path-ogens, microorganisms that are capable of induc-ing human disease (box M).

Human pathogens in the marine environmentcome primarily from discharges of raw sewage andfrom sewage sludge and wastewater effluent fromsewage treatment plants. For example, it is esti-mated that about 40 million gallons of raw sewageare discharged daily into the Hudson and EastRivers of New York City. 9 Pathogens are also found

“’1’h is disc hargc IS w hcduled to hc halted in 1987 when a nc\\ w.(-ondary t reatmen ( plant is c omp]cted ( (;. I.u IZI( , N’c.w, }’{)rk (: I t \ I)(. -par(ment of’ En\’ironmental Pr[)tc( tlon. pt>r~, comrn, , 1 986)

in domestic and commercial food wastes, animalwastes, and biological wastes from hospitals andlaboratories, many of which are discharged to sur-

face waters or sewage treatment plants. Where com-bined sewer systems are employed, overflows dur-ing times of heavy precipitation can also be asignificant source of pathogens. In rural areas, mostbacterial contamination comes from non-urbanrunoff, animal wastes, poor septic systems, andpoorly treated sewage discharges. Finally, the ma-rine environment itself is a source of pathogens,because some pathogens naturally occur and prop-agate in marine waters.

In the United States, the most importantwaste-borne agents of human disease are virusesand bacteria, with respect to both their concen-trations in wastes and the environment, and the in-cidence of disease attributable to them. 10 Enteric

] (IH<)W ~.l. (.r, irl S{)nl(. ,Jarts of” [ h e > w o r l d patho%cn> [rmn o t h e r ~ l~~~w’~

can be ~ery ]mpurtdnt “I”hc W’ur]d Hcal[h organlzatlon” h,is indl( at[dthat tht’ par-as] t I( helm i nt h .$chr srosoma is w’cond onl\ [o nl.dar],t i n( auslng diw.asc and cic,~th ]n the tr-op][ \ ( 2.32)

[Page Omitted]

This page was originally printed on a gray background.The scanned version of the page is almost entirely black and is unusable.

It has been intentionally omitted.If a replacement page image of higher quality

becomes available, it will be posted within the copy of this report

found on one of the OTA websites.

Ch. 6—Impacts of Waste Pollutants on Human Health ● 135

viruses are especially significant with respect to dis-posal of wastes in water, since they are ideally suitedto be spread by contact with contaminated water(205).

Pathways to Humans

Both direct and indirect exposure pathways canbe significant for pathogens because only a smallnumber of organisms are required to induce dis-ease, and because they can reproduce in wastes,contaminated media, or infected organisms. Sev-eral properties of pathogens are important in de-termining their potential to pose risks to humanhealth.

Survival

A growing body of evidence indicates that somebacteria, including a number of known humanpathogens, may persist in the marine environmentfor periods of many months or longer in a noncul-turable, but virulent form (205,366). For example,the agent responsible for an outbreak of choleraalong the Gulf coast of Texas appears to have per-sisted for at least 5 years in coastal waters (35). Inaddition, many viruses and parasites are extremelyresistant to environmental inactivation or de-struct ion.

Viruses and bacteria strongly adhere to partic-ulate matter, which provides a degree of protec-tion and increases their survival in sediments (183).Concentrations of enteroviruses may be 10 to10,000 times greater in coastal sediments than inthe overlying water; most pathogens are concen-trated in the surface layers of bottom sediments(197). Subsequent dredging of these sediments mayincrease the concentrations and availability of hu-man pathogens in the areas where dredging or dis-posal of dredged materials takes place (203,204). ”

A number of human pathogens appear to sur-vive better in estuarine and other coastal environ-ments than in the open ocean (253). However, insome cases, the colder temperature of the openocean, especially bottom waters beyond the con-

] 1 For examp]e, a tota] restriction on shell fishing has been imposedin estuarine waters around a dredging project near Cape May, NJ,because disturbance of the sediments was shown to cause ele~’ated den-sities of coliform bacteria in the water (J. Staples, New Jersey De-partment of Environmental Protection, cited in ref. 10),

tinental shelf, can actually enhance the survival ofsome pathogens, although it also retards growth (16),

Propagation

Different classes of pathogens have different re-quirements for propagation. In the absence of anappropriate host, viral or parasitic propagation gen-erally cannot occur, so there are no mechanismsavailable for increasing the number of viruses insewage material or the marine environment; theycan, however, become concentrated in sludge orsediment. Bacteria introduced through wastes havethe potential to replicate and increase their num-bers, but this potential has not been well-studiedfor most organisms. Some pathogenic bacteria thatnaturally occur in the marine environment are fullycapable of propagation (e. g., certain species ofVibrio).

Exposure and Infection

For viruses and microorganisms present in themarine environment to exert an impact on humanhealth, they must both reach and infect humans.The ability of microorganisms to infect humans de-pends on numerous factors, including the minimuminfective dose. As few as 10 to 100 bacteria, or asingle virus, are capable of inducing infection anddisease under the appropriate conditions (205).Moreover, the tendency for viruses and bacteriato adhere to particulate matter increases the riskof exposure and infection in two ways: 1 ) survivalis enhanced through the protection the particles pro-vide; and 2) because particles literally serve to ‘ ‘col-lect’ viruses and bacteria on their surfaces, a sin-gle ingested particle can contain a large dose ofmicroorganisms. The concentration of viruses andbacteria in sediments also increases the potentialfor their uptake by shellfish.

Potential and ActualHuman Health Impacts

Shellfish-Borne Disease

Large areas of estuarine and coastal waters havebeen closed to shellfishing and/or finishing becausethey are contaminated with sewage-derived micro-organisms in excess of Federal standards (see boxN). While such closures have largely eliminated


outbreaks of serious shellfish-borne, bacterial dis-ease, including epidemics of typhoid and para-typhoid fever, they cause major economic impacts.In Washington, 21 percent of the shellfish-growingareas are closed and another 11 percent are onlyprovisionally open because of bacterial contamina-tion. Moreover, contamination appears to be in-creasing: six previously pristine areas in PugetSound have been closed in the last 3 years (463).Fishing in many other areas has been restricted

periodically due to sewage contamination (e. g.,Boston Harbor, New York Harbor, and portionsof Narragansett Bay, the Delaware River estuary,Chesapeake Bay, Mobile Bay, and San FranciscoBay).

Overall, the incidence of shellfish-borne diseaseis not decreasing in the United States and may beincreasing (197). This trend largely involves in-creases in the number of outbreaks of viral disease

Ch. 6—Impacts of Waste Pollutants on Human Health . 137

Photo credit. Northeast Technical Services Adrn/nistrat/err, U S Food and Drug Administration

Contamination of shellfish is a significant problem nationwide. The problem is growing, particularly in rapidlydeveloping areas such as coastal portions of the Gulf of Mexico and southern Atlantic States.

(e. g., 80,367). For example, in the State of NewYork in 1982 alone, consumption of contaminatedshellfish was identified as the cause of 103 differ-ent reported outbreaks of viral gastroenteritis in-volving over 1,000 people (367). Smaller outbreaksof more serious bacterial diseases also have beenreported. In a series of apparently related casesstretching back over the last 14 years, several dozenpeople contracted cholera after consuming shellfishharvested from coastal marshlands in southwest-ern Louisiana (81,82). These represent the first in-digenous outbreaks of cholera in the United Statessince 1911 (78).*2

[(. choler-a natural - at I r in IS thought to -

of, 1 ) marsh water. , from

(In i ) human - ( 3 5). The n marsh

fish, f rorn the> u (

Water-Borne Disease

While the implementation of water quality guide-lines and sewage treatment requirements has sub-stantially reduced the outbreaks of serious humandiseases attributable to direct contact with pollutedwaters, bathing in sewage-impacted waters is re-sponsible for relatively high rates of gastrointesti-nal illness in the United States. In fact, the num-ber of outbreaks of water-borne disease, particularlynonbacterial diseases such as viral gastroenteritisand hepatitis,has been steadily increasing in re-cent decades (79, 197). 13 Recent epidemiologic evi-dence has shown that the incidence of gastrointes-tinal illness is significantly elevated in people

.—— - —— t hls unreported

I\ natu the u I h I - u of Data on t -borne d ist Ix. fresh


swimming at several heavily used New York Citybeaches (63,641) and in Lake Pontchartrain in NewOrleans, Louisiana (285).14

Epidemics of serious bacterial disease, while rare,have been caused by swimming in sewage-contaminated water. For example, in 1974 an out-break of shigellosis was traced to swimming in astretch of the Mississippi River downstream of asecondary treatment plant. Fecal coliform countsin the river were almost 90 times higher than theFederal standard (489). Similarly, outbreaks of ty-phoid fever in Australia and Egypt have beencaused by swimming in sewage-contaminated ma-rine waters (205).

Scuba diving in contaminated marine waters canalso lead to increased incidence of waterborne dis-ease (1 13,192,205,435). These diseases include der-matitis, wound infections, and other skin-relatedailments, as well as enteric illness. Under-reportingof such diseases is judged to be considerable (205).

Shortcomings of CurrentMicrobiological Standards

Many observers have raised concerns about theadequacy of current efforts to control and monitormicrobiological contamination of marine watersand resources. Three major shortcomings need tobe addressed:

1.

2.

3.

current standards designed to protect humansagainst microbiological agents in marinewaters or seafood may be too lenient,monitoring protocols are inadequate to detectperiodic violation of the standards, andstandards based on use of fecal coliform indi-cators do not adequately measure pathogensurvival.

Current techniques used to measure marinewater quality are probably significantly underesti-mating the true number of viable pathogens thatare entering the marine environment, for at leastfour reasons (205). First, coliform bacteria, which

14These studies are significant because they demonstrate that notonly can the presence of sewage-derived material in the marine envi-ronment result in human disease, but also that disease rates that aresignificant from a public health perspective can be difficult or impos-sible to discern in the absence of carefully performed, thorough (andexpensive), epidemiologic studies.

have been used to indicate sewage contaminationof water for 75 years, generally are not pathogenic,and do not survive as well as other pathogenic bac-teria or viruses (481). In fact, studies show that gas-troenteritis associated with swimming (at least inmarine waters) is better correlated with enterococcalbacteria than with coliforms (63,285,641). In addi-tion, outbreaks of gastroenteritis have been asso-ciated with shellfish harvested from waters that weredeemed acceptable using traditional indicators(451 ,700).15

Second, existing standards use bacteria as indi-cators of contamination, while viruses appear to bethe major cause of diseases resulting from exposurethrough both direct (swimming, diving) and in-direct (seafood consumption) pathways (197).Third, current standards are based solely on waterquality, while levels in sediments and shellfish areneither regulated nor routinely monitored. Yet sedi-ments are probably an equal or more likely sourceof pathogens in shellfish (197).

Finally, increasing evidence suggests that bac-teria (including certain human pathogens) intro-duced into the marine environment do not die offas rapidly as once believed, but remain viable forextended periods of time (e. g., months to years).These pathogens cannot be cultured in the labora-tory and their presence cannot be detected usingtraditional tests, but they can be reactivated withina host organism (106,206). Thus, the apparent lackof human pathogens in the open ocean, especiallyat or near past sewage sludge disposal sites, maysimply reflect our inability to detect these appar-ently viable, non-culturable pathogens (205).

The public health significance of the viable-but-not-culturable phenomenon is far from clear, how-ever, and remains controversial. No definitive linkhas been established between the survival of bac-terial pathogens through this mechanism and theoccurrence of human disease. Moreover, becausemost disease related to exposure to marine watersor fish is caused by viruses rather than bacteria,the role that pathogenic bacteria in marine envi-

15EPA has recently adopted enterococci as an indicator of micro-biological water quality for marine recreational waters (664). It is notyet clear what influence adoption of the new standard and indicatorwill have on consideration of alternative indicators and standards formonitoring of the quality of shellfish and shellfish-harvesting waters(205).


ronments play in human disease is probably of sec-ondary importance.

The Effect of Treatment onPathogenic Microorganisms

Sewage Treatment

Wastewater treatment results in the partitioningof waste constituents into sewage effluent andsludge. Wastewater treatment and subsequentsludge treatment processes can in many cases sig-nificantly reduce the numbers of some types of sew-age microorganisms. However, the actual extentof reduction varies considerably from operation tooperation, and among classes of microorganisms.A full discussion of this topic is included in chap-ter 9.

Chemical Disinfection ofWastewater Effluents

In most instances, bacteriological water qualitystandards for recreational and shellfish-growingwaters are met by chemically disinfecting sewageeffluent prior to discharge. Chlorination tradition-ally has been viewed as an effective and economi-cal means to reduce levels of microorganisms in ef-fluent. However, concerns have been raised thatchlorinated hydrocarbons (e. g., chloroform) formedas byproducts of chlorination pose significant risksto organisms in the immediate vicinity of treatmentplant discharges. One alternative to chlorinationis the use of long deep-ocean outfalls such as thoseemployed in southern California. These achievewater quality standards through dilution.

The effectiveness of either approach in reducingpathogen exposure risks is questionable, however,given the traditional use of coliforms as the stand-ard indicator species and the growing evidence thatbacteria discharged in sewage effluent may persistin marine waters in a viable but nonculturableform. Substantial data indicate that:

1. chlorination is more effective against coliformsthan against pathogenic viruses or even nu-merous pathogenic bacteria;

2.

3.

pathogenic viruses and bacteria can survivesignificantly longer in the marine environmentthan can coliforms; andchlorination may only temporarily inactivate,rather than destroy, microorganisms presentin effluent (205,297).

These findings suggest that the routine dis-charge of sewage effluent and the dumping ofsewage sludge into estuaries, coastal waters, andthe open ocean may be introducing large num-bers of viable microorganisms, including path-ogens, and that their densities in both the waterand sediments may be increasing. Further studyof the public health consequences of these prac-tices is needed, particularly in light of the in-creasing incidence of shellfish- and water-bornedisease.

Land Application of Sewage Sludge

Because sewage sludge is applied to land as fer-tilizer and for reclamation purposes, the survivaland availability of pathogens in the sludge is of con-siderable public health significance. Viruses, bac-teria, and parasites can survive in soil for many daysor months depending on soil temperature, pH, claycontent, cation exchange capacity, surface area,moisture content, and organic content. Viable path-ogens have been found, for example, in surface run-off from sludge-amended fields. However, there areno documented cases of human disease resultingfrom land application of treated sewage sludge, al-though untreated sewage-derived wastes have oftenbeen implicated in disease outbreaks (60,205,379).Land application and landfilling of treated sewagesludge appear to pose less potential health risks tohumans than disposal in freshwater or estuarineenvironments.

Deputation of Shellfish

Some countries (e. g., Japan) allow or even en-courage the culturing and harvesting of shellfish insewage-contaminated water to take advantage ofthe nutritive content of such wastes. Prior to mar-keting, these shellfish are depurated (i. e., placed


in clean water for several days) to allow the shell- These and other studies suggest that further sys-fish to purge themselves of pathogens. This prac- tematic study of the health risks associated withtice is controversial, however, because evidence in- various forms of deputation should be conducteddicates that deputation does not eliminate all prior to its use as an accepted means of decon-pathogens, especially small bacteria or viruses such taminating shellfish (205),as the- Hepatitis A ‘virus (186,209,298,368,523).

chapter impacts of waste pollutants on human health

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