89 Rpt Mercury Aquatic Habitats

8/10/2019 89 Rpt Mercury Aquatic Habitats

http://slidepdf.com/reader/full/89-rpt-mercury-aquatic-habitats 1/80

NOAA Technical Memorandum NOS ORCA 100

Cont am inant s in Aquat ic Habi t a t s a t Hazard ous Wast e Si t es: Mercury

December 1996Seattle, Washington

noaa NATIONAL OCEANICANDATMOSPHERICADMINISTRATION

National Ocean Service



Office of Ocean Resources Conservation and AssessmentNat ional Ocean Service

Nat ional Oceanic and Atmospher ic Adminis t ra t ionU.S. Depar t m ent of Comm erce

The Office of Ocean Resources Conservation and Assessment (ORCA) providesdecisionmakers comprehensive, scientific information on characteristics of theoceans, coastal areas, and estuaries of the United States of America. Theinformation ranges from strategic, national assessments of coastal and estuarineenvironmental quality to real-time information for navigation or hazardous materialsspill response. Through its National Status and Trends (NS&T) Program, ORCAuses uniform techniques to monitor toxic chemical contamination of bottom-feedingfish, mussels and oysters, and sediments at about 300 locations throughout theUnited States. A related NS&T Program of directed research examines therelationships between contaminant exposure and indicators of biological responsesin fish and shellfish.

Through the Hazardous Materials Response and Assessment Division (HAZMAT)

Scientific Support Coordination program, ORCA provides critical scientific supportto the U.S. Coast Guard for planning and responding to spills of oil or hazardousmaterials into marine or estuarine environments. Technical guidance includes spilltrajectory predictions, chemical hazard analyses, and assessments of the sensitivityof marine and estuarine environments to spills. To fulfill the responsibilities of theSecretary of Commerce as a trustee for living marine resources, HAZMAT’sCoastal Resource Coordination program provides technical support to the U.S.Environmental Protection Agency during all phases of the remedial process toprotect the environment and restore natural resources at hundreds of waste siteseach year. As another part of its marine trusteeship responsibilities, ORCAconducts comprehensive assessments of damages to coastal and marine resourcesfrom discharges of oil and hazardous materials.

ORCA collects, synthesizes, and distributes information on the use of the coastaland oceanic resources of the United States to identify compatibilities and conflictsand to determine research needs and priorities. It conducts comprehensive,strategic assessments of multiple resource uses in coastal, estuarine, and oceanicareas for decisionmaking by NOAA, other Federal agencies, state agencies,Congress, industry, and public interest groups. It publishes a series of thematic dataatlases on major regions of the U.S. Exclusive Economic Zone and on selectedcharacteristics of major U.S. estuaries.

ORCA implements NOAA responsibilities under Title II of the Marine Protection,Research, and Sanctuaries Act of 1972; Section 6 of the National Ocean PollutionPlanning Act of 1978; the Oil Pollution Act of 1990; the National Coastal MonitoringAct of 1992; and other Federal laws. It has four major line organizations: CoastalMonitoring and Bioeffects Assessment Division, Hazardous Materials Response andAssessment Division, Strategic Environmental Assessment Division, and the DamageAssessment Center.



NOAA Techn ical Mem or and um NOS ORCA 10 0

Contaminants in Aquatic Habitats at Hazardous Waste Sites: Mercury

Nancy Beckvar 1

Jay Field 1

Sandra Salazar 2

Rebecca Hoff 1

1NOAA/HAZMAT2EVS Consultants Seattle, Washington

Seattle, Washington

United States National Oceanic and National Ocean ServiceDepartment of Commerce Atmospheric Administration W. Stanley Wilson

Mickey Kantor D. James Baker Assistant AdministratorSecretary Under Secretary for Oceans for Ocean Services andand Atmosphere Coastal ZoneManagement



Hazardous Materials Response and Assessment DivisionOffice of Ocean Resou r ces Con serv at ion and Assessm entNational Ocean ServiceNational Oceanic and Atmospheric Adminis t ra t ionU.S. Department of CommerceSilver Spr ing, Mar yland

CITATION

Please cite this report as “Beckvar, Nancy, Jay Field, Sandra Salazar, and Rebecca Hoff. 1996.Contaminants in Aquatic Habitats at Hazardous Waste Sites: Mercury . NOAA TechnicalMemorandum NOS ORCA 100. Seattle: Hazardous Materials Response and Assessment Division,National Oceanic and Atmospheric Administration. 74 pp.

NOTICE

This report has been reviewed by the National Ocean Service of the National Oceanic andAtmospheric Administration (NOAA) and approved for publication. Such approval does not signifythat the contents of this report necessarily represent the official position of NOAA or of theGovernment of the United States, nor does mention of trade names or commercial products constitute

endorsement or recommendation for their use.



Contents

Executive Summary ....... ............................................................................................................................................ i

Environmental Chemistry................................................................................................................iBioaccumulation.............................................................................................................................ii

Toxicity..........................................................................................................................................iiiApplications...................................................................................................................................ivSummary........................................................................................................................................vi

Acronyms ................................................................................................................................................viiGlossary ..................................................................................................................................................viii

Introduction................................................................................................................................................................

1

Environmental Chemistry ..... ................................................................................................................................ 1Chemical Speciation.......................................................................................................................2Distribution in theEnvironment...................................................................................................9

Bioaccumulation of Mercury .......................................................................................................................... 12 TheEffect of theFormof Mercury on Bioaccumulation..........................................................13ExposurePathways......................................................................................................................17Biological Factors AffectingAccumulation of Mercury...............................................................21Other Factors AffectingAccumulation........................................................................................23

Toxicity of Mercury ............................................................................................................................................... 25 Toxicity of Mercury in Water.....................................................................................................27 Toxicity of Mercury in Sediment.................................................................................................32 Toxicity Associated with Mercury in Tissues..............................................................................33Interactions with Other Metals...................................................................................................36

Criteria and Guidelines ...................................................................................................................................... 36Ambient Water Quality Criteria..................................................................................................36Sediment Guidelines.....................................................................................................................38

Tissue............................................................................................................................................38



Contents, cont.

Applications ............................................................................................................................................................... 38

Samplingand MonitoringConsiderations...................................................................................39Approaches to Remediation........................................................................................................41Analytical Considerations.............................................................................................................43

Summary ..............................................................................................................................................44

References ...................................................................................................................................................................... 45

Figure1 Mercury speciation.........................................................................................................................3

Tables1 Toxicity of Mercury in Water.....................................................................................................282 Toxicity Associated with Mercury in Tissues..............................................................................35



EXECUTIVE SUMMARY

This document r eviews publ ished li teratu re on mercury chemistry ,bioaccumulation and toxicity, and is intended to serve as guidance for NOAACoastal Resource Coordinators in t heir work with EPA on hazardous waste sites.The purpose of thi s document is to highlight factors to consider in designin g andevalu ating ecological r isk assessments; and, in th e sampling, monitoring andanalyses of environmental media in aquatic habitats affected by mercury. Thoughmany qu estions about mercury remain, th e science is evolving rapidly. This papershou ld be reviewed with th e knowledge that inform ation can change as newstu dies are publi shed.

Environmental Chemis t ryThe fate of mercury in the envi ronment depends on the chemical form of m ercuryreleased and the environmental condit ions. Elemental mercury, inorganic mercury,and methylmercury are the th ree most im portant form s of mercury in natu ralaquatic environm ents. Most mercury is released in to the environment as inorganicmercury, which is primarily bound to particul ates and organic substances and maynot be available for di rect uptake by aquatic organi sms. The process of meth ylationof inorganic mercury t o methyl mercury, which is highly bioavailable, is thus animportant key to the fate of mercury in the environment.

Elemental mercury has a high vapor pressure, a low solubility, does not combinewit h inorganic or organic ligands, and is not available for methylation. Themercurous ion (Hg[I]) combines wit h i norganic compounds only and cannot bemethy lated. The mercur ic ion (Hg[II]) combines wit h both in organic and organicligands, and can be methy lated. Methylation in aquatic habitats is prim arily abiological process. Mono- and dimethylm ercury are formed by microorganisms inboth sediment and water through the methylation of inorganic mercuric ions

(Hg[II]). Dimethylm ercury, which is highly volatile, is generally not persistent inaquatic envi ronm ents.

Methylation i s inf luenced by environmental variables that affect both theavailability of mercuric ions for m ethyl ation and the growth of th e methy latingmicrobial populations. Methylation rates are higher under anoxic condi tions, in

i



freshwater compared to saltwater, and in low pH environments. The presence of organic matter can stim ulate growth of microbial populations (and reduce oxygenlevels), thereby enhancing the formation of methy lmercury . Sul fide can bindmercury and lim it methy lation. Methylm ercury production can vary due to

seasonal changes in nu tr ients, oxygen, temperature, and hydrodynamics. In m oststudies, methylation increased dur ing t he summer month s when biologicalproductivi ty w as high, and decreased during th e winter month s.

Measurements of total mercury concentrations in the sediment do not provideinformation on the form of mercury present, methylation potenti al, or availability toorganisms locally and downstream. If environm ental condit ions are conducive formethylation, methyl mercury concentrations may be high in proportion to thesupply and distribution of total mercury.

Bioaccumulat ionMercury is accumu lated by fish, invertebrates, mamm als, and aquatic plants andthe concentration t ends to increase with increasing troph ic level (mercurybiomagnifies). Althou gh inorganic mercury is the dominant form of mercury in theenvironment and is easily t aken u p, it i s also depurated relatively quickly .Methylmercury accum ulates quickly, depurates very slowly, and thereforebiomagnifies in h igher trophic species. The percentage of methylmercury, ascompared to total mercury, also increases wi th age in both f ish and in vertebrates.Uptake and depuration rates vary between ti ssues wi th in an organism. Parti tioningof mercury between tissues within aquatic organisms is influenced by the chemicalform of mercury and rou te of exposure (ingestion or via the gill s). Due to it spreferential uptake, abili ty to be transferred among t issues, and slow depuration,most of the mercury in fish mu scle tissue ( ≈99%) is methylmercury.

Marine mammal tissues have some of the highest concentrations of mercury foundin all marine organisms, wit h t he liver generally h aving the highest total mercury

concentration. Alth ough many juvenile and adul t marine mammals primaril y feedon fi sh, whi ch contain h igh percentages of methylmercury, high concentrations of inorganic mercury are found in adult specimens. Apparently , adult m arin emammals can mi neralize methylm ercury int o inorganic mercury . Juvenil e marinemammals have lower concentr ations of total mercury than adul ts; but u nli ke fishand invertebrates, the percentage of methyl mercury is higher in juvenil e mammals.

ii



Invertebrates generally have a lower percentage of methylmercury, as compared tototal mercury , in t heir t issues th an do fish and marine mammals. The percentage of methylmercury in invertebrates varies greatly and can range from one percent indeposit -feeding pol ychaetes, to close to 100% in crab.

Bioconcentration factors (BCFs) reflect u ptake from water in laboratory experiments.BCFs for m ercury are variable, with th e highest factors determined formethy lmercury. BCFs for methy lmercury in brook tr out range from 69,000 to630,000, depending on th e ti ssue analyzed. BCFs for inorganic mercury (mercuricchloride) in saltwater species range from 129 for adult lobster ( Homarus

americanus ) to 10,000 for oysters ( Cr assostr ea vi rgi ni ca ).

While sediment is usually the primary source of mercury in most aquatic systems,the food web is the main pathway for accumu lation. High trophic level speciestend to accumulate the highest concentrations of mercury, with concentrationshighest in fi sh-eating predators. Mercury concentrations in h igher trophic speciesoften do not correlate with concentrations in environmental media. Correlationshave been made between sediment and lower troph ic species th at typi cally have ahigh percentage of inorganic m ercury , and between mercury concentrations inhigher troph ic species and their prey items. The best measure of bioavailabili ty of mercury in any system can be obtained by analyzing mercury concentrations in th e

biota at th e specific site.

Toxic i tyToxicity is inf lu enced by the form of mercury, the envi ronmental media,environmental condit ions, the sensiti vity or tolerance of the organism, and the lifehistory stage. Inorganic mercury is less acut ely toxic to aquatic organisms th anmethy lmercury, but the range in sensiti vity among indivi dual species for eith ercompound is large. Toxicity was found to be greater at elevated temperatures,

lower oxygen content , reduced salin iti es in marine environments, and in thepresence of metals such as zinc and l ead.

In general, toxic effects occur because mercury bin ds to proteins and alters proteinproduction or synthesis. Toxicological effects inclu de reproductive impairment ,growth inhibition, developmental abnormalities, and altered behavioral responses.

iii



Reproductive endpoints are generally more sensitive than growth or survival, withembryos and th e early developmental stages th e most sensitive. Mercury can betransferred from ti ssues of th e adult female to developing eggs. Exposure to lowconcentrations of mercury may not resul t in mortali ty di rectly, but may retard

growth thereby increasing the risk of predation.

Data available on the effects of mercury-contaminated sediment on aquaticorganisms reviewed by Long and MacDonald (1992) resulted in effects range-low(ERL) and effects range-median (ERM) concentrations of 0.15 mg/kg and0.71 mg/kg, respectively. However, these numbers were less accurate than ot hermetals in predicting adverse effects, highlight ing the need for site-specific effectsdata to determine concentrations of mercury in sediment that pose a threat toaquatic biota.

Few stu dies report both ti ssue residues and effects in l ong-term exposure to lowconcentrations of mercury. However, results from studies on dif ferent freshwaterspecies indicate that reprodu ctive effects could be expected to occur in sensit ivefish species at ti ssue concentrations close to the FDA action level of 1 mg/kg (ppm).The interaction of mercury and oth er trace elements (e.g., cadmiu m, copper,selenium, and zinc) can be both antagonistic and synergistic, primarily dependingon exposure concent rations and form of mercury. Effects were generally less th an

addit ive (antagonistic) at lower exposure levels and greater th an addi tive(synergisti c) at high er levels. Zinc and cadmiu m were reported to reduce th eteratogenic effects of methylm ercury to k il lif ish whi le selenium reduced mercury’stoxic effects on development in medaka embryos.

Appl ica t ionsEcological assessments of waste sites with elevated concentrations of mercury inthe aquatic envi ronm ent are particularly challenging due to the complexity of th efactors th at affect the availabili ty of mercury to aquatic organisms. Dependi ng on

th e magni tu de of the problem (local versus system-wi de), th e level of effortnecessary to evaluate mercury contamination may range from simple moni toring of chemical concentrations to more complex programs inclu ding moni toring of nu merou s physical, chemical and biological parameters. The distr ibut ion of totalmercury in sediment , which in most cases is predominantly inorganic m ercury, maynot by itself provide useful information about the bioavailability of mercury to

iv



aquatic species. Concentrations of total mercury in sedim ent that decrease withincreasing distance from th e source may sti ll pose a th reat to organisms if t hebioavailability of the mercury increases (i.e., environmental conditions are moreconducive for methylation). Mercury concentrations in aquatic organisms,

parti cularly higher trophic-level organisms, may provi de the best measure of th eavailabil ity of m ercury in a parti cular area.

In sit es where a whole system has been affected, evalu ation of remedial alternativesmay need to be based on an understanding of the system-specific processes thatlead to increased methylation and the pathways to resources of concern. Anassessment of environmental parameters that affect the activity of methylatingmicrobes (e.g., nut rients, temperature, pH, and dissolved oxygen) and th e factorsaffecting the availabil ity of inorganic mercury for methylation (e.g., theresuspension of sediment , total organic carbon , and sul fides) may be warrantedwhen designing sampling plans for a remedial investigation.

To establi sh protective sediment target cleanup concentrations and remedialoptions for mercury-contaminated sites, we must understand the extent of contamination, the major pathways of transport, and bioavailability. Therefore,data on the accum ulation of mercury in tissues of aquatic organisms shou ld beincluded in assessment stu dies because it addresses potent ial hu man health

concerns and availabili ty to aquatic receptors. In addi tion, stu dies shoul d assesstoxicity to aquatic organisms, focusing on early l ife stages and reprodu ctive effects.

Detection l imit s shoul d reflect th e program objectives. Contract Lab Program (CLP)meth odology m ay be appropriate for screening level assessments; however,biologically relevant detection limi ts are often required and not available at CLPlaboratories. Thus, analytical laboratories that can achieve lower detection limitsmay need to be used. Quali ty control is an im portant aspect of any testing programbut is parti cularly im portant wh en analyzing mercury in environmental matrices.In water, very low concentrations need to be measured; the separation of thedifferent forms of mercury requires special analyt ical techniques. Matrix effects inthe extraction of mercury from tissue may interfere with accurate analyses formethy l and total mercury . When analyzing mercury in water, sediment , and t issue,analysis of cert if ied standards for the appropriate matrix mu st be included as part of the quality control plan.

v



Summary

NOAA recomm ends a sit e-specific approach t hat focuses on determining theavailabil ity of mercury and th e potential for toxic effects. The accum ulation of mercury in aquatic biota is often the prim ary concern at mercury sites and isuseful for assessing availabili ty . Bioaccum ul ation studies shou ld measur e ti ssueconcentrations in m ore than one resident and/or transplanted caged species,preferably with species representing different trophic levels or different food webpathways. It may not be possible to correlate sediment m ercury concentrationswit h concentrations in biota. However, correlations between mercuryconcentrations in predator and prey species may be useful in determiningpathways of mercury transfer.

Toxicity tests such as th e standard amphipod t ests shoul d also be conducted toassess mercury toxicity t o benth ic organisms. At major mercury sites, chronictoxicicty endpoint s shoul d be included in th e assessment—in particular, fish earlyli fe stage or r eproductive endpoin t t ests. Because of the persistence of mercury inaquatic systems, sour ce control alone may not be sufficient to permit recovery.Addit ional remedial actions may be required to reduce th e total mercury burden inthe system. Long-term monitoring of tissue concentrations of mercury in aquaticbiota is needed to assess remedial effecti veness.

vi



ACRONYMS AND ABBREVIATIONS

AVS aci d-volat ile su lfidesAWQC Ambient Water Quality CriteriaBAFs Bioaccumulat ion factorsBCFs Bioconcentrat ion factorsCd cadmiumCLP Contract Lab ProgramCu copperDOC dissolved organic carbonEh oxidation-redu ction potentialERL effects range-lowERM effects range-median

FDA U.S. Food and Drug Administrat ionFe ironHg mercuryMn manganeseMT metallothioneinsµeq/ l micro equivalent per l iterµ g/l micrograms per literµm micrometermg/kg mill igrams per kilogramm g/l m illigram s per literppm parts per millionSe seleniumSRB sulfate-reducing bacter iaTOC total organic carbonZn zinc

vii



GLOSSARYacid labi le mercur y

Determined by SnCl 2 reduction on acidified samples, includes inorganic

complexes, labile organic associations, elemental mercury, and labil e

particulate mercury. Doesn't measure organic forms (C-Hg bound) of mercury such as meth ylmercury. Same as reactive mercury.

acid solu ble mercur y

Mercury that passes through a 0.45 µm membrane filter after the sample isacidif ied to pH1-2.0 with nit ric acid (EPA 1984). Strongly sorbed Hg is notmeasured, but all toxic form s as well as some non-tox ic forms are measured.

alkylmercury

Includes phenyl-, monom ethyl-, and dimethylmercurybioaccumulation

Net uptake of a contaminant in to t issue from all pathwaysbioaccum ula ti on factors (BAF)

Ratio of ti ssue concentration t o concentration in m ediu m, with exposurefrom the food web and th e medium

bi oconcentr ati on f actors (BCF)

Ratio of ti ssue concentration t o concentration in m ediu m, with exposureonly through the medium

biomagnification

Tissue concentration increases as trophic level increasesD OC (dissolved organi c car bon)

Includes all sources of carbon, including hum ic and fu lvic matter as well ascarbohydrates, proteins, etc.

demethylation

Conversion of m ethylmercury back to an inorganic form.depuration

Elim ination of a contaminant from the body of an organismdimethylmercury

Organic form of mercury consisting of a single mercury atom and twomethyl grou ps [(CH 3)2Hg], highly volatile and not persistent in the

environment.Effects ran ge-l ow

Concentration equivalent to that reported at the lower 10 percent ile of th e

viii



available screened sediment toxicity data for predominantly marine andestu arine toxicity stu dies. This nu mber represents th e low end of th e rangeof concentrations at which effects were observed in t he stu dies compiled(Long and M acDonald 1992).

Effects r an ge-m edi an Concentration equivalent to that reported at the 50th percent ile of th eavailable screened sediment toxicity data for predominantly marine andestuarine toxicity studies (Long and MacDonald 1992).

elementa l m ercur y

Not in ion ic form, cannot be methylatedha l ide

Binary compound of a halogen (flu orine, chlori ne, bromi de, iodine andastatine)

in organic mercury

Includes elemental mercury and mercury bound to other inorganicmolecules and compounds, including inorganic ligands and sulfides.

labi le mercur y

Includes Hg(OH)2, HOHgCl, HgCl2, and weakly bound organo-complex

formsl igand

Any group, ion, or molecule that binds to another, called a receptor

methylmercury Includes both mono- and dimethylm ercury

mercuric-Hg[II]

Forms both inorganic and organic complexes, this is the only ionic form thatcan be methylated

mercurous-Hg[I]

Forms inorganic compl exes, cannot be methylatedmethylation

Addit ion of a methyl (CH3) group

monomethylmercury

Organic form of mercury with one methyl group attached to a mercury atom(CH3Hg) - highly toxic and readily accumu lated by l iving organisms

organi c mercur y

Includes mercury complexes with organic ligands (e.g. humic/fulvic acids,

ix



amino acids, but wit hou t a Hg-carbon bond) and organic mercury boun d viaa carbon atom (CH 3-HgOH, CH3HgCl, CH3HgCH3)

organo-mercury

Mercury compounds with a Hg-carbon bond

pinniped Mammals of the fami ly Pinnipedia, includes all seals and walruses

piscivorous

Feeds on fishesr eactive mer cur y

“Easily reducible,” determined by SnCl 2 reduction on acidified samples,

includes inorganic complexes, labile organic associations, elementalmercury, and labile parti culate mercury, doesn't i nclude C-Hg bou ndmercury such as meth ylmercury and dimethylmercury. Same as acid labil emercury.

total mercur y

Includes all forms of mercury

x



INTRODUCTIONAs a trustee for m arine, estu arin e, and anadrom ous resources, NOAA is responsiblefor ensuri ng th e well -being of those trust resources potent ially affected by releasesfrom hazardous waste sit es. Metals, in parti cul ar, pose a th reat because of th eir

persistence and toxicity in aquatic environments. The importance of mercury inmany aquatic environments is underscored by the fact that 35 states have fish andwildlife consumption advisories in place for mercury (EPA 1996).

Althou gh th e hazards of mercury to hum ans are well -known, less information isavail able on the ri sks to aquati c organisms. In order to define and address th epotent ial effects and extent of mercury contami nation at h azardous waste sit es, anu mber of questions are often asked: Is th e mercury present in a bioavailableform? Wh at concentrations in water, sediment, and tissues are potent ially harmfu lto aquatic resources? Wh at types of sampl ing and analysis are necessary to definepotent ial r isks to aquatic organi sms? Is th ere a relation ship between sedimentconcentrations and tissue concentrations in aquatic organisms? Wh at level shou ldbe used for cleanu p? Wh at are important factors to consider when selecting aremedy and designing monitoring plans at a site?

ENVIRONMENTAL CHEMISTRY

Mercury is among t he most toxic of th e heavy metals, has complex behavior in theenvironment, and may persist for decades following abatement of the source.Mercury’s envi ronmental persistence is due in part to it s high affini ty forparticulates and organic matter. Even if mercury concent rations in sediment andwater decrease over time, concentrations in organisms may not decrease due to th eslow rate of elim ination of the highly bioavailable methylmercury form . Thephysical properti es, bioavailability, and toxicity of mercury are governed byspeciation int o both organic and inorganic forms.

Elemental mercury, bivalent inorganic mercury, and monomethylm ercury are theth ree most important forms of mercury occurring in natu ral aquatic envi ronm ents(Battelle 1987). Elemental mercury in aquatic environments has a high vaporpressure, a low solubility in water, and an octanol-water partition coefficient(Kow)=4.15 (Shoichi and Sokichi 1985 as cited in M ajor et al. 1991). Elemental and

1



dimeth ylmercur y can occur as dissolved gaseous mercury. Mercury can also occuras particulate and dissolved ion ic and monomethylmercury species. In natu ralwater, ionic mercury is consum ed by methylation, reduction, and parti culatescavenging (Mason et al. 1995a). Bivalent inorganic mercury binds to inorganic and

organic ligands, especially sulfur-containing ligands, and forms both inorganic andorganic complexes. Figure 1 shows a schematic of some comm on pathways of mercury speciation in the envi ronment .

Althou gh most mercury occurs in the inorganic form, methylmercury , an organicform, is the most toxic and readily bioaccumulated form of mercury.Methylmercury normally occurs in the environment at extremely lowconcentrations; how ever, it i s taken up easily by aquatic organisms andbioaccumu lated. Consequently, methylm ercury may comprise more than 95% of the mercury in fish tissue whi le only 5-15% of the total mercury bu rden insediments and water of contaminated lakes is methy lmercury (Saroff 1990).

Chemical SpeciationInorganic and total mercury versus methylmercury

Chemical speciation terms commonly used include total, inorganic, organic, andmeth ylmercury and are based on th e oxidation state and associated compoun ds.Mercury h as th ree stable oxidation states: th e native element (Hg[0]), mercurou s(Hg[I]), and mercuric (Hg[II]). Inorganic mercury includes elemental Hg and somecomplexes of the mercurous and mercuric oxidation states. Hg [I] forms inorganiccompounds only and, like Hg[0], cannot be methylated. Hg [I] compounds inclu demercurou s salts (halides) and m ercurou s chlorides such as calomel. Both Hg[0] andHg[I] can be oxidized to form Hg[II]. Hg[II] (bivalent mercury), the form that can bemethy lated, forms both organic and inorganic compounds. Mercury [II] cancombine with inorganic li gands includi ng chlor ide, hydroxide, nit rate, and sulfateanions (Benes and Havlik 1979) to form inorganic mercury compounds that

include mercuric halides, mercuric chloride (cinnabar), and mercuric sulfides.Chlor ide concentration and pH affect the proportions of th e uncharged inorganicspecies in solu tion. For example, at low chloride concent rations most of theinorganic mercury occurs in the form of mercuric hydroxide (Hg(OH) 2), withmercuric chl oride (HgCl2 ) and mercury hydroxide chloride (HgOHCl) also

important (Mason et al. 1996). As chloride concentration increases

2



S E D I M E N T S E A W A T E R A I R

( C H

3 ) 2 H g

( C H

3 ) 2 H g

X =

C l n

, ( O H ) n

, ( S H – ) , h u m

i c / f u l v i c a c i d s , a m

i n o a c i d s

C H

3 H g

( C H

3 ) 2 H g

d i m e t h y l m e r c u r y

H g 0

e l e m e n

t a l

m e r c u r y

H g 0

H g 0

H

g 2 +

H g 1 +

H g X

a q u a t

i c b i o t a

C H

3 H g X

H g X

H g S

H g X

i n o r g a n

i c m e r c u r y

b a c t e r i a

p H

b a c t e r i a

b a c t

e r i a

l o w E h

p H

b a c t e r i a

C H

3 H g X

m e t h y l m e r c u r y

F i g u r e

1 .

I m p o r t a n

t p a

t h w a y s o

f m e r c u r y s p e c

i a t i o n

i n t h e a q u a

t i c e n v i r o n m e n

t .

3



(e.g., hi gh-chloride lake water), th e propor tion of HgCl 2 increases and th e other two

species consti tu te only a few percent of the total inorganic mercury. As pHincreases, more Cl is needed than at lower pHs to increase the percent of H gCl 2. Ateven higher chloride concentrations, HgCl 42- becomes th e dominant species. This

speciation chemistry affects the accumulation and toxicity as described later in thisreport.

The term organi c mercur y can include different types of organically bou nd m ercury .Hg [II ] combines with organic compounds (hu mic/fulvic acids, amino acids) via anorganic ligand bond to form organomercury salts. The Hg [II]-organic li gand bondis relatively weak compared to a C-Hg bond. The organomercury salt s resembleth eir corresponding inorganic mercuri c salts in their properties and reactions. Theorganomercury compounds methylmercury, dimethylmercury, and phenylmercuryhave a C-Hg bond; methyl (CH 3) and phenyl groups (C 6H5) link to a mercury

atom via a carbon atom . Some aut hor s group the organically bound Hg [II]complexes (without a C-Hg bond) with i norganic mercury compoun ds, while othersgroup all organically bound mercury together as organic mercury .

Mercury compounds may be grouped accordin g to their form based on chemicalspeciation discussed above, or based on th e analyt ical technique used t o measurethe mercury. The analyti cal techniqu e determi nes which forms of mercury are

detected. Mercury terms based on analyti cal procedures include names such asacid-solu ble, reactive or acid labile, and calciu m chlor ide-extractable.

Measurements of reactive mercury include Hg [II] bound to inorganic substancesand weakly bound to organic matter (however, methy lmercury is not included dueto th e strong C-Hg bond). To estimate meth ylmercury concentrations, someauthors measure total mercury and reactive mercury, then subtract the reactivefrom the total measurement. Total mercury measurements include all th e variousinorganic and organic forms of m ercury , including dissolved, colloidal, and/orparticulate states. Analytical groupings are defined in the glossary. Unless th especific type of mercury is mentioned, the reader should assume that the term“mercury” refers to total mercury.

Speciation of mercury is affected by environmental conditions such as pH,oxidation-reduction potential (Eh), oxygen content, sul fide content, chloride

4



concentration, organic matter content , and microbial activi ty . Similarly, biologicaland chemical processes control the conversion of inorganic mercury tomethy lmercury. The factors that enhance and in hibit m ethylation, and affect thedistribu tion of inorganic and m ethylm ercury are discussed in th is section of t he

paper.

M ethylation of M ercury

In both freshwater and saltwater envi ronments, mercury is converted frominorganic bivalent mercury (Hg[II]) to methylmercury primarily by microorganisms(Berman and Bartha 1986), although chemical methylation also occurs (Craig andMoreton 1985; Weber 1993). Two forms of monomethylmercury, methy lmercuri chydroxide (CH3HgOH) and methylm ercuri c chloride (CH 3HgCl) occur in both

fresh and saltwater, with the former dominant at low chlori de concentrations (lowchlori de freshwater) and t he latter dominant at h igh chloride concentrations (highchloride lakes, seawater). As wi th inorganic mercury, th e organic chloride species(Kow = 1.7) is more hydrophobic than the hydroxide species (K ow = 0.07; Major etal. 1991; Faust 1992; Mason et al. 1996). Dim ethylmercury (K ow = 182) readily

volatil izes from surface water and is generally not persistent in aquaticenvironments at concent rations of concern; therefore, discussions of methy lmercury in th is review refer to th e monomethylmercury species, un lessoth erwise stated.

Methylmercury production depends on both the availability of Hg[II] formethy lation and microbial activi ty. Methylation i s usually greatest at the sediment-water in terface, but also occurs in the water column. Net methylmercuryproduction i s a fun ction of both the rate of methylation and the rate of demethylation (Korth als and Winfrey 1987). Methylmercury is not readilydecomposed so the methy lation rate is usually higher th an t he demethylation rate.Degradation of methylmercury is also primarily a microbial process.

Methylation is influ enced by the availability of Hg[II], oxygen concentration, pH,redox potential (Eh), presence of sulfate and sulfi de, type and concentrations of complexing inorganic and organic agents (Parks et al. 1989), salin ity (Blu m andBarth a 1980), and organic carbon (Jackson 1989; Wi nfrey and Rudd 1990). Strongl yboun d Hg[II] is not available for methylation. For example, insoluble mercur ic

5



sul fide (HgS) wil l be methylated in aerobi c sediments at rates 100 to 1,000 ti messlower than for the less strongly bound HgCl 2 (Olson and Cooper 1976).

Anaerobic, sul fate-reducing bacteria (SRB) are th e primary methylators of mercury

in both lacustrine and estuarine sediments (Compeau and Bartha 1985; Gilmourand Henry 1991). The primary methyl ators of mercury in th e water column havenot been identi fied. SRB are common in sulfate-rich estu arine sediments (Hin es etal. 1989) but are more limi ted in freshwater sediment wit h lower sul fateconcentrations. A sul fate concentration of 200-500 µM in t he water colum n isoptim al for mercury methylation by SRB in sediment (Gilm our and Henry 1991).The activi ty of the methylating microbes is affected by environmental condit ions(Jackson 1986) wi th nu tri ent availabil ity and seasonality parti cularly important.The concentration of i norganic mercury in envi ronmental media may not be a goodindication of th e concentration of methylm ercury present due to the inf luence of environmental variables and biological activi ties. The importance of environmentalfactors in th e production of methy lmercury is as follows:

pH : Neutr al or low pH conditi ons favor the production of monomethylmercuryover dimethylmercury (Beijer and Jernelov 1979). An alkaline (high) pH favors th eformation of d imethylm ercury , which t ends to escape into the atmosphere.Elevated ti ssue concentrations of methy lmercury have been noted in numerous

pristine lakes of the nor th ern United States and Canada that receive acid rain andno point sources of mercury (Xun et al . 1987; Bloom et al. 1991). The mechanism(s)causing increased bioaccumu lation in low pH lakes are not un derstood (Ramlal etal. 1985; Winfrey and Rudd 1990; Richardson and Currie 1996). The factorsprim arily responsible for net m ethylm ercury production in lakes are, in decreasingorder of im portance, pH, dissolved organic carbon (DOC) concentration, andmicrobial respiration (Miskimmin et al. 1992). The importance of pH and sedimentproperties (Fe and Mn content) on methylation rates in saltwater environments hasnot been well studied.

Sulfi de, Sulfate, and O ther Ions: In t he presence of sulfides, th e mercuric ion(Hg[II]) becomes tightly bou nd to sulfide as insoluble mercuric sul fide and is notavailable for methylation. Sul fide activi ty may be the main factor influencing theavailabil ity of Hg[II] (Bjornberg et al. 1988) and the concentration of methylmercuryin sediment (Craig and M oreton 1983). If pH is high or Eh i s low, sul fide activi ty

6



wil l be high and mercury wi ll be precipitated as insoluble mercuric sul fide. If th esul fide is oxidized to sulfate, the mercuric ion wil l become available formeth ylation. Both free sulfi des and acid-volatile sulfi des (AVS) appear to inh ibitmeth ylation (Gilmour and Capone 1987). The presence of other minerals may

affect th is relationshi p. Excess ferrou s iron has been fou nd to bind the sul fide andlimi t i ts Hg-bindin g effectiveness such that n o di fference in m ethylation rates arenoted between sulfide-rich and sulfide-poor sediments (Rudd et al. 1983). Seleniumsimilarly bi nds the Hg [II] ions and reduces their availabil ity for methylation. Theredox cycling of manganese in lakes may be more important than iron-scavengingof mercury (Bonzongo et al. 1996).

Addit ion of sul fate to anoxic lake sediment slu rri es or the overlying water columncan increase methylmercury production by stim ulatin g th e SRB population(Gilmou r et al. 1992). SRB can both methylate mercury and produce sulfi de, wh ichinhibits methylation: the kinetics of thi s are not understood. Mercury methylationwas once viewed as a detoxification process in SRB, but it may u lt imately servesome other function (Gilmour and Henry 1991).

Oxygen Condi t ions/Eh : Although methylation occurs under both aerobic(oxidizing) and anaerobic (reducing) conditions, methylation is greater underanaerobi c conditions (Callister and Winfrey 1986; Weis et al. 1986; Regnell 1994).

In addition, demethylation rates are lower under anaerobic conditions, so the netmethy lmercury production is higher in oxygen-depleted environments (Jackson1987). Over 90 percent of methylmercury is formed biochemically in anaerobicsediment (Berman and Bartha 1986).

In anoxic lake bottoms containing hydrogen sul fide, mercury is bound t o sedimentas insolu ble mercur ic sulfi de. If condi tions become aerobi c due to a decrease in t heorganic load or seasonal turnover, sulfi de can be oxidized to sulfate, releasing themercury in t he ionic form Hg[II], which i s available for methylation (Jernelov 1968).

N utr i ents /O rgani c content : / D O C : Nu tr ients can enhance th e rate of methy lmercury production by stimulating the methy lating bacteria. Decayingorganic m atter can enhance microbial activi ty and create low oxygen conditions,both of wh ich cause higher methy lation rates (Olson and Cooper 1974; Gilmourand Henry 1991). In f reshwater areas with a high organic inpu t, methylation rates

7



can become locally elevated if other environmental condit ions do not in hibitmeth ylation (i.e., hi gh sulf ide levels; Jackson 1986). Wh en sul fide and sul fateconcentrations are not li mi tin g, organic matter may be the major factor controll ingmercury methylation rates in estuarine sediments (Choi and Bartha 1994).

Increased DOC levels may inhibit methylation due to th e binding of free mercuryions (Jackson 1989; Winfrey and Rudd 1990) even though supplemental DOCincreases microbial respiration (Miskimm in et al. 1992). In clear freshwater lakes,DOC and pH may in teract such that l ess of th e Hg [II] is bound by DOC at low pH,resul ting in hi gher methylation rates. Acid rain may also limi t the amount of DOCtransported in to a system because at l ower pH, DOC solubil ity and mobi li ty isreduced (De Haan 1992; Schindler et al. 1992).

H umi c/Fulvic materi al: The geochemistry of Hg in lake and stream water may bedominated by h umic material interactions (Mierle and In gram 1991). Hg complexeswit h hu mic and ful vic substances and H g retent ion and export from watersheds inCanada have been correlated wit h th e export of hum ic substances. Hi ntelmann etal. (1995) assum ed that the methylmercur ic ion is bound to sulfidic binding sites of hu mic acid. At lower pHs, the amount of free unbound methylmercury ion washigher in their laboratory study of hum ic and ful vic acids. Acidifi cation couldpotentially release bound m ethylm ercury from hu mic acids int o th e aqueous phasewhere it wou ld be readily bioavailable.

Salinity : There appears to be a negative correlation between the rate of methy lmercury formation and salinit y in estu arine sediments (Blum and Barth a1980). The rate is lower in more saline envir onments because th e bicarbonatecomponent of seawater slows methylation of Hg [II] u nder both aerobic andanaerobi c condit ions (Compeau and Bartha 1983). The release of reactive Hg [II]and Hg [0] is slowed when chloride ions bind to mercury , thereby inh ibi tin gmeth ylmercury form ation (Craig and Moreton 1985). Salinity also affectsmethy lation due to th e high pore-water sulfide concentr ations as a resul t of rapidsulfate reduction in saline water compared to sulfate-limited freshwaterenvironments (Gilmour et al. 1992). Along a salinit y gradient in the lower HudsonRiver, methylation rates decreased downriver with increasing salinity and sedimentsulfide concentrations (Gilmour and Capone 1987).

8



The percentage of total m ercury that i s methylmercury is higher in freshwatersediments (up to 37%) and water (up to 25% in aerobic water and 58% in anoxicbottom water) than in estu arine and m arine water (<5%) and associated sediments(<5%) (Gilmour and H enry 1991). Dissolved reactive mercury (inorganic species)

forms the majority of th e total mercury in open oceans (Bloom and Creciliu s 1983;Gill and Fit zgerald 1987).

Season : Biological productiv ity of methylating microbes is affected by seasonalchanges in t emperatu re, nu tri ent supply, oxygen supply, and hydrodyn amics(changes in suspended sediment concentrations and flow rates). Methylmercuryconcentrations varied seasonally by an order of magnitu de at m ost sites stu died(Parks et al. 1989). Methylation may tend to increase during the sum mer month swhen biological productivity and temperatu re are high and decrease during wintermonths when biological productivity and temperatu re are low (Calli ster andWinfrey 1986; Jackson 1986; Weis et al. 1986; Korth als and Winfrey 1987; Parks etal. 1989; Kelly et al. 1995; Leermakers et al. 1995). Although th e potent ialmethy lmercury production i s greatest du ring the summer, actual produ ction maynot peak du ring th is time (Kelly et al. 1995). In Onondaga Lake, New York, themercury species in the water column varied temporally (Battelle 1987; Bloom andEffler 1990). Total mercury concentrations may also vary seasonally du e tophysical factors such as winter storms resuspendin g mercury-contaminated

sediments (Gil l and Bru land 1990).

Dist r ibu t ion in t he Env i ronm entThe distribution and abundance of inorganic mercury and methylmercury in theenvironment may vary i ndependently as they are controlled by differentphysicochemi cal processes. The concentration of total mercury (which is mainlyinorganic) in th e envi ronment is generally not a good predictor of m ethylmercuryconcentration (Gilmour and Henry 1991; Kelly et al. 1995). Inorganic mercury h asa high affin ity for sediments; a signif icant portion of the total mercury in freshwater is in parti culate form (Gil l and Bru land 1990). Most of the mercury inestuaries was associated with particulate matter (Cossa and Noel 1987). Theenvironmental distribu tion of inorganic mercury appears to be controlled byprocesses such as transport , sort ing, and sedimentation as related to th e hydrol ogicregim e. Resuspension and resettling of sediments caused persistently h ighconcentrations of mercury in th e sur face sediments of Lavaca Bay (Reigel 1990).

9



Total mercury concent rations in surface water may decrease as mercury boun d toparticulate matter settles or is transported downstream (Bonzongo et al. 1996). Thedistribu tion of biotically produced methyl mercury init ially depends on t hemicrobial populations that methylate the mercury. Alth ough more abundant in the

sediment where it is formed, methylmercury forms a greater percentage of the totalmercury in the overlying water column (Gilmour et al. 1992).

The distri but ion of both inorganic and m ethylmercury is also affected by th e larger-scale physical characteristics of the environment such as type of system (river, lake,estu ary, ocean) and it s physical conf iguration, water circulation patterns, catchmenttype, sediment characteristics, rainfall, and the introduction of terrestrial sediments.The physical characteristics of th e system influ ence th e mechanisms of mercurydistribu tion, availability, and cyclin g in varying degrees. Water flow regimes inparticular subenvironments (mainstream versus backwater), characteristics such asthe stratifi cation cycle and amount of nu tri ents in lakes, or th e configuration of th eestu ary (open circulation versus restr icted), may have very di fferent, distinctfeatu res that control both t he persistence of mercury in the envi ronment and howth e different species of mercury behave and are distr ibu ted among sediment, water,and organisms.

In freshwater systems, Kelly et al. (1995) found a predictive, linear relationship

between t otal and methylmercury concentrations in u nfi ltered water samples fromsome specifi c lake systems, but not f rom stream systems. Run off f rom wetlandcatchments contribut ed more methyl mercury to lake systems than did ru noff fromupland catchm ents (St. Louis et al. 1994). In estu arin e systems, total di ssolvedmercury concentrations were found to be enhanced where salinity was less than 10ppt, coinciding with the maximum turbidity zone (Cossa and Noel 1987; Cossa etal. 1988).

Terrestr ial sediment inf lu xes can also affect mercury availabili ty. In th e estu arineAla Wai Canal in Hawaii, total mercury increased over t wo orders of magnitude inpolychaetes and shr imp during th e rainy season (Luoma 1977). Mercury bou nd tofreshwater sediments and int roduced in to th e estuary from u rban runoff du ringrainfall was desorbed upon contact wi th saline water. The increased concentrationof dissolved mercury temporarily increased total m ercury in fil ter-feeding wormsand shr imp. Total mercury concentrations in the water column and biota

10



decreased after the runoff stopped. In cont rast, lower mercury concent rations werefoun d in plankton in a freshwater lake after input of hi gh concentrations of clean,fine-grained sediment. Sediments washed in to th e lake duri ng rainfall bou nd themercury, inhibit ing uptake by plankton (Jackson 1988).

Sediment composit ion can also affect th e way that mercury i s distribu ted in theenvironment. Mercury concentrations in freshw ater benthi c organisms appeared tobe determined by the sediment composition, such as the concentration of hydratedFe and M n oxides and carbon-ri ch hu mic matter in bottom sediment . The mercuryappeared to be less available when i t was bound by i ron hydrox ide (FeOOH),manganese hydroxide (MnOOH), and possibly by higher-molecular-weight hu micsubstances (Jackson 1988).

In a freshwater river-lake system in Canada (Parks et al . 1989) methylmercuryconcentrations in surface water were hi ghest 80 ki lometers downstream from themost contaminated sediments (contaminated wi th inorganic mercury). Fish werecontaminated as far as 270 km downstream from the inorganic mercury source,wit h the most contaminated fish fou nd more than 100 km downstream of th issour ce. Methylmercury concentrations in the water increased as inorganic mercuryconcentrations in the sediment decreased. The most high ly contaminatedsediments were located near a sewage outfall. The researchers surmised th at the

mercury in these sediments was bound to sul fide and th us not available formethy lation. Fur ther downstream the mercury became available for methylationprobably due to a decrease in sediment sulfide levels. Even though concentrationsof inorganic mercury in the sediment here were much lower th an u pstreamconcentrations, methylmercury produ ction was mu ch higher and biota were morecontaminated.

There may be a similar situation in low-salinity water of Berrys Creek, New Jersey,where high inorganic sediment mercury concentrations were also foun d next t o asewage outfall (Weis et al. 1986). However, concentrations of mercury in fishinhabiting th e area were not as hi gh as expected. This was attr ibut ed to thepresence of sul fide, which bi nds mercury and limits methylation. No downstreamstudies have been conducted to determin e whether the mercury is morebioavailable fur ther from the source of high sulfide concentrations.

11



An eight-ton cargo of elemental mercury located within th e hold of th e sunkenEmpi re Kni ght in offshore marin e waters did not contaminate invertebrates liv ingout side the hold of the ship (Hoff et al . 1994). Only a small percentage of invertebrates sampled from within t he hold h ad elevated concentrations of total

mercury. However, it i s not know wh ether the mercury was incorporated in to theti ssue of the organisms. The large source of elemental mercury in th is envir onmentwas not bioavailable to organisms located away from th e source.

BIOACCUMULATION OF MERCURY

Mercury bioaccumul ates in aquatic plants, invertebrates, fish, and mamm als.Concentrations increase (biomagni fy) in higher-trophic-level organisms. Eventhough the different types of mercury h ave relatively low K ow values (compared to

organic compoun ds such as PCBs), th ey are readily accumulated. Inorganicmercury (excluding elemental) and m ethylmercury’s strong reactivi ty withintracellu lar ligands is thought to be responsible for their high degree of accumu lation. Uptake and accumu lation of mercury are affected by the type of mercury present, with neut ral m ercury species (e.g., HgCl 20 and CH 3HgCl0)absorbed more effi ciently th an charged mercury species (e.g., HgCl - 3 CH3Hg+;

Mason et al. 1996 ).

Despite th e fact that t he neutral in organic and organic complexes have similar lipidsolubilities, methylmercury is selectively accumulated (due to a higher transferefficiency and lower rate of elimination), resul tin g in bi omagnif ication in highertrophic levels (Mason et al. 1995b). Inorganic mercury species are not biomagnified(Surma-Aho and Paasivir ta 1986; Riisgård and Hansen 1990; Hil l et al. 1996).

Envi ronmental factors that enhance mercury methylation resul t i n greaterbioavailabil ity and accumu lation of methylm ercury . Envi ronmental variables alsoinflu ence the bioavailabil ity and accum ulation of inorganic mercury. Althou gh

concentrations of mercury in the environment may correlate with concentrations inresident plants and biota, correlation i s often diffi cult . Correlatin g total mercury insediment wit h total mercury in u pper-troph ic-level organisms is complicated byhigh methylmercury concentrations in h igh-trophic-level organisms relative to lowmethylmercury concentrations in the environment.

12



Tissue concentrations of mercury are often positively correlated with organismlength , weight, and/or age. Diet has a significant role in the overall body bu rden of mercury, both between and wi th in species. Dif ferences in total mercuryconcentrations between species reflect diet differences due to trophic posit ion;

wi th in -species differences are related to dietary requirements of variousdevelopmental stages.

The Effect of t he Form of Mercury on Bioaccum ulat ionBoth inorganic and methylmercury are taken up directly from water and food (oringested sediment). However, methylmercury is more efficiently accumulated thaninorganic mercury for most aquatic organisms (Fowler et al. 1978; Jul shamn et al.1982; Rii sgård and Hansen 1990; Mason et al. 1995b). The uptake and depurationof mercury depends on th e form of mercury , source of mercury (water or food), andthe type of receptor tissue, resul tin g in different patterns of accumu lation.Methylmercury is readily tr ansferred across biological membranes. With in theorganism, methylmercury is strongly bound to sul fhydryl groups in proteins of ti ssues such as mu scle, and is much slower to depurate than inorganic mercury.Thu s, methylmercury has a much greater potential for bioaccumu lation and alonger half-life in organisms than inorganic mercury.

Fish

The accum ulation of mercury from water occurs via the gill membranes. Gills takeup aqueous methylm ercury more readily than in organic mercury (Huckabee et al.1979; Boudou et al. 1991 ). Methylmercury is eventually t ransferred from the gills tomu scle and oth er ti ssues wh ere it is retained for long periods of tim e (Julshamn etal. 1982; Riisgård and Hansen 1990).

Inorganic mercury taken up wi th food in iti ally accum ulates in t he tissues of theposterior in testine of fish (Boudou et al. 1991). Inorganic mercury is not easily

transferred throu gh th is organ to other parts of the body. After 15 days, 80% haddepurated from t he fish intestine. Liver and kidney in fish tend to have higherpercentages of inorganic mercury than m uscle tissue, although percentages vary byorgan and species (Windom and Kendall 1979; Riisgård and Hansen 1990).

13



Methylmercury ingested in food is efficiently tr ansferred from the intestin e to otherorgans (Boudou et al. 1991). Methylmercury h as been reported to constitut e from70 to 95% of th e total mercury in skeletal mu scle in fi sh (Huckabee et al. 1979; EPA1985; Riisgård and Famme 1988; Greib et al. 1990; Spry and Wiener 1991).

Methylmercury accounted for almost all ( ≈99%) of the mercury in mu scle tissue ina wide variety of both freshwater and saltw ater fish found in waters not h ighlycontaminated by oth er organomercur ial species (Bloom 1992).

The ratio of liver to mu scle total mercury concentration usually flu ctuates aroundone and can reflect the exposure hi story of th e organisms. For example, th eliver:muscle ratio may be less th an one in chronically exposed fish, wh ile a recentexposure to mercury m ay resul t in a ratio greater than one (Riisgård and H ansen1990).

McKim et al. (1976) reported th at m ercury could be transferred from adul t tooffspring in brook t rout. Exposure of the parent population t o aqueousmethy lmercury concentrations of 0.03 to 2.93 µg/l in the laboratory resul ted inmercury concentrations as high as 2 mg/kg in their embryos. Total mercuryconcentrations in eggs of several species of adult fish from Swedish lakes weremu ch lower th an concentrations in other t issues; therefore, spawni ng did not lowertheir total mercury body bu rden (Lindqvist 1991).

The main depuration pathway is th rough the kidney and liver in fish. Half-lives formethy lmercury in fish range from one to th ree or more years (McKim et al . 1976;Pentreath 1976a, b; Riisgård and Famme 1986; Riisgård and Hansen 1990), whileestim ates of h alf-lives for inorganic m ercury are much lower, ranging fromapproximately f ive days to five month s (Pentreath 1976a, b; Hu ckabee et al. 1979).

Invertebrates

Invertebrates accumulate and parti tion inorganic and methylmercury in tissuessimilar to the trends exhibited by f ish ( Fowler 1978; Riisgård and Famm e 1986;Saouter et al. 1991; Saouter et al. 1993). However, invertebrates generally contain alower percentage of methylmercury than fish or mammals (Lasorsa and Allen-Gil1995), wit h h ighly variable concentr ations. Thi s wide variation of mercury contentin invertebrates is most l ikely a function of different feeding strategies (and troph ic

14



levels) and dif ferent environmental exposures. Reported percentages of methy lmercury compared to total m ercury concentrations are less th an 1% for thepolychaete N er ei s succi nea (Luoma 1977); 10% in copepods, mussels and shrimp(Horvat 1991); 10-100% in th e cockle (Møhlenberg and Riisgård 1988); 16% in

urchin gonads (Eganh ouse and You ng 1978); 30-90% in lake zooplankton(Lindqvi st 1991); 87% in crab muscle (Eganh ouse and Young 1978); and 100% inred rock crab, Dungeness crab, and spot shr im p (Bloom 1992). Becker and Bigham(1995) found an increasing percentage of methylmercury compared to totalmercury i n h igher trophic levels in the Onondaga lake food web. Lake watercontained 5% of total mercury as methylmercury ; phytoplankton 24%; benthi cmacroinvertebrates 26%; zooplankton 40%; and fish fillets 96%.

Viscera in mussels contained the highest tissue concentration of total mercury(Fowler et al. 1978). The total mercury concentration was hi ghest in the midgutand muscle tissue in crab (Bjerregaard and Christensen 1993) and in th e viscera inshr imp (Fowler et al . 1978). The shr imp molts had the lowest mercury content;therefore, molt ing i s not considered an important depuration pathway incrustaceans (Fowl er et al. 1978).

Half-lives for t otal mercury in salt -water mu ssels ranged from t wo month s to oneyear (Riisgård et al. 1985). Inorganic mercury was eliminated more rapidly th an

methylmercury in mussels and shrimp (Fowler et al. 1978).

Marine mammals

Marine mammals have some of the highest tissue mercury concentrations of allmarine organisms investigated (Andre et al. 1991a); however, concentrations arehighly variable both withi n and amon g species. These variations have beenattr ibut ed to collection locations (Wren 1986), concentrations in prey items (Szeferet al. 1993), and organism age (Julshamn et al. 1987; Thompson 1990). For

exampl e, species th at feed pr imarily on benth ic invertebrates, such as walruses andbaleen whales, tend to have relatively low mercury concentrations. In contrast, fish-eating species, such as porpoises and seals, exhibit relatively h igh mercu ryconcentrations (Born et al. 1981).

15



In contrast to fish, adult marine mammals have a much higher percentage of totalmercury as inorganic mercury, althou gh th e concentration of methylmercury mayalso be elevated. Less th an 10% of th e total mercury content i s meth ylmercury(Eisler 1987). Juveniles tend to have high er percentages of meth ylmercury.

The liver generally exhibit s the highest total and m ethylm ercury concentration(Holden 1978; Wagemann et al. 1983; Jul shamn et al. 1987; Thom pson 1990; Andreet al. 1991a), fol lowed by ki dney and mu scle tissues (Szefer et al. 1993). Julshamnet al. (1987) measured the highest concentrations of methyl- and total mercury (13and 150 mg/kg) in pi lot whale livers ( Gl obicephal us melean us ) compared to total andmethy lmercury concentrations in muscle (2.8 mg/k g total mercury; 1.7 mg/k gmethy lmercury) and kidney (15.3 mg/kg total mercury ; 5.1 mg/kg methylmercury).Andersen et al. (1987) also measured th e highest methylmercury concentrations inpilot whale liver (20 mg/kg; 14% of total mercury). The fraction th at is methylated,however, is usually lower in th e liver compared to muscle and k idney. Themethy lated fraction of total mercury ranged from 1% to 36% in seal l iver (Holden1978); 30% in older specimens to 100% in young specimens in th e muscle of harbor porpoise (Joiris et al. 1991); and 24% to 86% in the muscle of pilot whales(Gl obicephal us melean us ; Jul shamn et al. 1987). The liver:mu scle ratio formethy lmercury concentration i n h arbor porpoises was approxim ately one, while th eratio for l iver:muscle for total mercury concentration was two. In some of theharbor porpoises and some oth er species (sperm whale, common dolph in , and adul t

bott le-nose dolphin) th e liver:muscle ratio for total m ercury ranged u p to 20 (Joiriset al. 1991) while th e liver:muscle ratio for methylmercury was stil l one.Schintu et al. (1992) observed an age-related change in the percentage of methy lmercury compared to total mercury in pilot whale livers. The liver of th ree-to seven-year old pilot whales (with a relatively low total mercury body bu rden)contained 30% to 60% organic mercury, compared to 3% t o 17% organic mercuryin livers of 30- to 40-year old pilot whales (with a relatively h igh t otal mercuryload). Porpoises exhibit ed a sim il ar trend. Juveni les had a high er percentage of methy lmercury in l iver (100%), while the percentage of methylmercury in adultspecimens decreased to 2 to 3% of the total mercury (Joiris et al. 1991).

Althou gh mercury in the diet of m any m arine mammal species is predominantl ymethylmercury, it has been proposed that the mammals are able to mineralizemethy lmercury in to th e more harmless inorganic form, which then accumu lates inth e liver of adu lt specimens (Holden 1978; Joir is et al. 1991). The estimated half-life

16



of total mercury i n pin nipeds and dolph ins is about 1.4 and 2.7 years, respectively(Eisler 1987; Andre et al. 1991b).

Plants

Vascular plants accum ulate both inorganic and methylmercury from sediment andwater in root , stem, and leaf section s (Alberts et al. 1990; Boudou et al. 1991). Therooted macrophyte Elod ea d ensa accumu lated different concentrations of methy lmercury versus inorganic mercury from sediment (uptake was 40 timeshigher for methy lmercury). Tissue concentrations were similar th roughout th eplant when th e mercury source was water (ratio of 1.5 methylm ercury to inorganic;Boudou et al. 1991).

Chlor ide concentration and pH in flu enced uptake of inorganic mercury by a marin ediatom. Rates were low in seawater and low-chloride freshwater with neutral pH(Mason et al. 1996). Methylm ercury uptake rates were high in high-chloride watersand were not infl uenced by pH. The uptake rate of methyl mercury only becamelimi ted when very low chlori de concentr ations decreased the concentration of CH3HgCl. Elemental and dimethylm ercury were not significantly accumu lated.

Exposure PathwaysAquatic organisms can accum ulate mercury from water (includi ng pore water) andfood sources (including sediment). Quantity accumu lated is a fun ction of theexposure path way and th e physical and environm ental factors such as temperature,pH, salinity, total organic carbon, and sulfides. If condi tions are favorable formethy lation, organisms can accumulate high concentrations of mercury even wi thlow concentrations in the water and sediment.

Water

Phytoplankton , invertebrates, fish (inclu din g eggs and larvae), and mammals take

up inorganic and organic mercury from the water column (McKim et al. 1976;Pentreath 1976a; 1976b). In phytoplankton , algae, and microorganisms, mercuryuptake is primarily a passive process th at occurs by adsorpt ion to t he cell surfaceeither th rough interaction with functional groups in the cell wall or throughsorpt ive properties associated wit h th e ext racellul ar matri ces (Darnell et al. 1986;Gadd 1988). Passive dif fusion of lipid-solu ble species (uncharged chloride

17



complexes) is responsible for mercury uptake in a marine diatom (Mason et al .

1996). Uptake in ph ytoplankt on and aquatic plants has been correlated with theconcentration of m ercury in the water (Windom and Kendall 1979; Lenka et al.1990). Water is an important exposure pathway for mercury uptake by lower

organisms and th us in to the food web (Francesconi and Lenanton 1992). Dissolvedmercury concentrations in water are typically very low; the major i ncrease inmercury concentrations occurs between water and phyt oplankton of about a factorof 105 to 106 (Mason et al. 1995b). In cont rast to microorganisms, upt ake isprimari ly an active process for fish and i nvertebrates, and is related to respirationrate and metabolic rate (Rodgers and Beamish 1981). Uptake of methylmercur icchlori de in water by different ti ssues of brook trou t was found to be directly relatedto the water concentration of the mercury (McKim et al. 1976).

BCFs are the concentration of mercury in ti ssue divided by the concentration in theexposure water. They have been calculated from laboratory experiments for m anyspecies of aquatic organi sms to estimate uptake from water. However, BCFs havelimi ted use for several reasons. First, BCFs reported in the li terature most lik elyunderestimate actu al values because laboratory stu dies were done before the use of trace-metal f ree protocols and used h igher water concentrations than found in thefield (Zil lioux et al. 1993). More recent BCF calculations for mercury h ave yieldedvalues one to two orders of magnitude higher t han previous estim ates . Second,

BCFs only reflect uptake of a contaminant from th e water. Hi gher trophi c speciesaccumu late mercury pr imarily th rough the food web. Reported BCFs for mercuryvary considerably due to differences between species, exposure concentration, andduration. Further, BCFs for th e same species may be several orders of m agni tu dehigher for m ethy lmercury than for inorganic mercury.

Brook t rout exposed to varying concentrations of methylmercury for 28 to 38weeks had bioconcentration factors ranging from 69,000 to 630,000 (McKim et al.1976). The wide range of BCFs reported for brook trout are related to th e ti ssueanalyzed. Bioconcentration factors for mu scle ti ssue in brook t rou t were hi gher atlower water concentrations of mercury. BCFs for ot her t issues remained the samewhen water m ethylm ercury concentrations were varied.

18



Bioconcentration factors for inorganic m ercury (mercuric chlori de) in saltwaterspecies were 129 for adult l obster ( H omarus ameri canus ), 1,000 for mussels, and10,000 for oysters ( Cr assostr ea vi r gin i ca ; Kopfler 1974; Roesijadi et al. 1981).Bioaccumu lation factors (BAFs) were calculated from f ield studies for yearl ing

yellow perch from five freshw ater lakes. These factors ranged from 106

-107

formethylmercury and more than 10 4 for oth er mercury species (Bloom 1992).

Sediment

Sediment is an important exposure pathway for all forms of mercury to aquaticorganisms. High concentrations of organic substances and reduced sul fur th atcomplex free Hg[II] ions in sediment can reduce the availabil ity of mercury to biota(Luom a 1977; Rubinstein et al. 1983). Correlating mercury concentrations in

sediment with concentr ations in bi ota may be diff icul t, parti cularly for h igher-trophic-level species.

The bioavailabil ity of total m ercury to benth ic invertebrates was reported to beinversely correlated to the organic content of the sediment (Langston 1982, 1986).Normalizing sediment mercury concentrations to percent organic matter improvedthe correlation between t otal mercury concentrations in sediment and invertebratespecies (including gastropods, polychaetes, and deposit- and suspension-feedingbivalves) in a marine environment (Bryan and Langston 1992). Good sediment -tissue correlations for mercury have been found in amphipods from a freshwaterlake (Becker et al. 1993). Breteler et al. (1981) stu died mercury uptake by pl antsand invertebrates from several types of sediments in salt marsh environments.Concentrations of total mercury in mu ssels, fiddler crabs, and Sparti na altern ifl ora

increased as organic matter in sediments decreased.

Many investigators report no correlation between sediment and tissueconcentrations of mercury for higher-trophic-level species (Nishimura and Kumagai

1983; Jackson 1988; Rada et al. 1989b; Lindqvist 1991; Duckerschein et al. 1992).Organic carbon n ormalization of sediment concentrations did not improve thecorrelations for pik e, a hi gh trophic level species (Lindqvi st 1991). The difficul ty incorrelatin g mercury in sediment wit h m ercury in organisms reflects the complexityof variables that affect both the methylation of mercury in surface sediments andthe transfer of mercury between t rophi c levels. Since methylation occurs primaril y

19



in sur face sediments, th e physical factors that affect th e rate of meth ylation (anddemethylation) also affect th e availability of mercury for u ptake by organisms.Sediment total-mercury concentr ations alone may not provide information on th eexposure potenti al of resident organi sms.

Food web

Thou gh sediment m ay be the ul tim ate source of mercury for many h igher troph icspecies, th e food web is th e primary pathway to most organisms (Lindqvist 1991;Bryan and Langston 1992). Most of the dif ferentiation between inorganic andmethy lmercury accum ulation occurs durin g troph ic transfer (Mason et al. 1995b)because of the differences in assimilation of the different mercury forms and howefficiently the different forms are transferred to predators.

Mason et al. (1995b) detected an assimilation efficiency four t imes greater formethylmercury compared to inorganic mercury from phytoplankton tozooplankton, and ten ti mes greater between ph ytoplankt on and planktivorous fish.The transfer efficiency of methy lmercury over inorganic mercury in zooplanktonwas att ribu ted to mercury parti tion ing in th e algal cell . Methylmercuryaccumu lated in the algal cytoplasm, which zooplankton digest, with 62% of th emethylmercury transferred, while inorganic mercury was primarily bound to thiolsin the algal cell m embrane. Therefore, a smaller percentage (15%) of inorganicmercury was transferred t o zooplankton.

As methylmercury increases in prey i tems, th e transfer efficiency also increases(Windom and Kendall 1979). Since methylmercury concentrations are hi ghest infish, piscivorous fish wi ll be exposed to h igher concentrations of methylmercuryth an fish that feed on invertebrates. For example, walleye accumulated mercury ata faster rate and at h igher concentrations than pike from th e same freshwater lake(Mathers and Johansen 1985). A high propor tion of the diet of walleye was smelt ,

the most contaminated prey i tem, whereas pike ate only a small proportion of th isprey item. Dietary changes during life hi story developm ent, or due to season orhabitat di fferences can change exposure. Dietary shif ts in prey it ems of similartroph ic levels but f rom different h abit ats, or d ietary shi fts due to a dif ferent sizestructure of prey, can also affect the mercury concentrations in top-level predators(Lindqvist 1991).

20



The relative importance of dietary versus aqueous mercury uptake pathways isunclear. Probably less th an 10% of the mercury in fi sh t issue residues is obtainedby direct (gil l) uptake from water (Francesconi and Lenanton 1992; Spry and Wiener

1991). Methylm ercury concentrations used in l aboratory studies of aqueous uptakeare 1,000 to 10,000 tim es the ambient concentration of m ethylm ercury in naturalwater (Spry and Wi ener 1991), thereby overestimating the signifi cance of dir ectaqueous uptake. The proportion of mercury taken u p from dietary sources versuswater in invertebrates has not been estimated. Suspension-feeding bivalves mayprincipally accumulate mercury by consuming algal cells (Riisgård and Hansen1990).

Althou gh mercury correlations are complicated by th e importance of th e food-chain exposure path way, mercury concentrations in predators and prey have beencorrelated (e.g., Allard and Stokes 1989; Lindqvist 1991; Spry and Wiener 1991). Forexample, mercury concentrations in smallmouth bass from Ontario lakes weredirectly correlated wit h mercury in crayfish, which comprised 60% of their diet.

Detritu s can be a very important source of mercury, parti cularly in estuarinehabitats. Organic detri tus from Sparti na altern ifl ora may contain 30 times moremercury t han plankton. Organisms in detr itus-based food webs are th us exposed to

higher mercury concentrations than are anim als feeding on plankton (Lindberg andHarr iss 1974). Mercury associated wi th hu mic matter in lakes is fed upon bybacteria and zooplankton, which incorporate mercury into the detri tal food web(Lindqvist 1991).

Mercury i n th e fecal matter of marine mammals can also be a signifi cant source tooth er aquatic organisms near breeding colon ies or h aul-ou t areas (Eisler 1987).

Biological Factors Affecting Accumulation of Mercury

The primary biological factors governing th e accum ulation of m ercury include age,weight, and diet. Differences in accumul ation between the sexes have beenattributed to di fferences in diet.

21



Fish

Numerous field studies have shown that the concentration of t otal mercury in fi shposit ively correlates wi th length , age, and weight (Hall et al. 1976a, b; Hu ckabee etal. 1979; Rada et al. 1986; Møhlenberg and Riisgård 1988; Greib et al. 1990; Leah etal. 1992). However, total mercury concentrations may not always correlate wi thsize due to di fferences associated with diet, residence time in a contaminatedhabitat, and t ype of mercury (Francesconi and Lenanton 1992). The percentage of methy lmercury increases with age in both fish and invertebrates (Møhlenberg andRiisgård 1988; Riisgård and Hansen 1990).

In some species of f ish and invertebrates, sex differences in m ercury ti ssueconcentrations have been reported. For exampl e, total mercury concent rations in

th e muscle tissue of freshwater sun fish were greater i n females th an males at ages 2to 3 (Nicoletto and H endricks 1987). This may be due to increased food demandsfor females related to reprodu ction . In contrast, th ere was li tt le relationshipbetween sex and bioaccumul ation of mercury in th ree species of fi sh (roach, perch,and pike) collected from Swedish lakes (Lindqvi st 1991).

Bloom (1992) did not fin d a relationship between li pid content and methylmercuryconcentrations in a variety of fresh- and saltwater fish.

Invertebrates

Cockles ( Cardiu m edule ) from a pollu ted estu ary were found to have a positi velinear correlation between their age and the percentage of organic mercury in th eirti ssues (Møhlenberg and Riisgård 1988). Organic mercury comprised 30% of th etotal mercury in two-year old cockles; 60% in th ree-year olds; and 90% in four-yearolds. This relationship was attr ibu ted to th e rapid loss of inorganic mercury andcontinued uptake of organic mercury over time. However, the correlation was notas strong when weight was used instead of age due to variations in growt h rate atdifferent locations. Total mercury concentrations in mussels were found to behigher in 27 m m than 31-mm sized indivi duals (Riisgård and H ansen 1990). Thisdifference was perhaps due to a decrease in both weight-specific fi lt ration rate andsurface area-to-volume ratio in larger mussels (Fowler et al. 1978; Riisgård et al.1985).

22



Total m ercury concent rations may (Allard and Stok es 1989) or may not (Rada et al.1986) correlate with weight or age in cru staceans.

Concentrations of mercury in male and female emergent mayflies ( Hexagenia

bilineata ) in the upper Mississippi River differed. The authors recommend samplingmale and female mayflies separately (Dukerschein et al. 1992).

Marine Mammals

Mercury concentrations (both organic and inorganic) are posit ively correlated withbody length in marine mammals (Arima and Nagakura 1979; Wagemann et al.1983; Joir is et al. 1991). Hansen et al. (1990) found a hi ghly significant correlationbetween age and tissue content of mercury in wh ales from West Greenland. Thi s

correlation has been u sed to separate immatu re specimens from adults. Joir is et al.(1991) found that th e concentration of methylmercury in mu scle and l iver ti ssue inharbor porpoises did not increase with increasing length as strongly as did tot almercury.

Leonzio et al. (1992) suggest that the elevated concentrations of inorganic mercurymeasured in mammals, as compared to fi sh, may be related to differences inrespiratory systems. In cont rast to fi sh, where the gil ls allow cont aminants to belost to th e envi ronment because blood f low has contact with the water, themamm alian respiratory system does not have a similar exchange. Mammals havedeveloped dif ferent defense mechanisms. For example, selenium combines wi thmercury to form th e non-toxi c compoun d tiemannite that is stored within cells.The processes of int racellul ar storage tend to increase concentrations of the metalin certain organs while reducing the toxicity. In marin e mammals, in tracellularstorage of mercury occurs as complexes of both selenium and metallothioneins(MTs).

Other Factors Affecting AccumulationTemperatu re and season influence the availability and accumulation of mercury inaddit ion to the factors already discussed. Changes in temperature can affectmercury concentrations in organisms either di rectly by affecting metabolic rate andthereby exposure, or indirectly by in flu encing th e methylation of mercury andtherefore enhancing availabili ty. Rates of methy l- or in organic mercury uptake

23



increase with increasing aqueous concent rations and/ or increasing temperature inth e water for some species (e.g., phytoplankton, gastropods, fish; Windom andKendall 1979; Rodgers and Beami sh 1981; Tessier et al. 1994). A rise intemperature (and a corresponding rise in respiratory volu me) can increase the rate

of u ptake via the gill s (EPA 1985).

Total concentrations of mercury in ki ll ifi sh f rom an estuarin e wetland were fivetimes higher in spring and summer than in oth er seasons (Weis et al. 1986),presum ably du e to higher methylation rates in summer. Zooplankt on mercuryconcentrations peaked in Jun e in Swedish l akes and fish ti ssue levels varied by afactor of two, reaching a maximu m in spring (Lindqvist 1991). Mercury content of mu ssels from th e Gul f of St. Lawrence estu ary varied seasonally by a factor of t wo(Cossa and Rondeau 1985).

The relationship of pH, conductivi ty, and salin ity to mercury accum ulation is notwell u nderstood. Elevated mercury concentrations have frequently been found inpiscivorous fish in poorly buffered (alkalin ity < 55 µeq/l and calcium < 2 m g/l), low-pH lakes (pH 6.0-6.5) in areas removed from industrial inpu ts of mercury (Rada etal. 1989a; Winfrey and Rudd 1990; Spry and Wiener 1991). Total mercuryconcentrations in yellow perch were inversely correlated wi th pH i n t en Wisconsinlakes (Cope et al. 1990). Mercury concentrations in zooplankton in Swedish lakes

were correlated wi th pH but the relative importance of th is correlation changedover time (Lindqvist 1991).

In freshwater lakes removed from direct sources of mercury, conductivity explained54% of th e variabili ty in mercury concentrations in crayfish (Allard and Stokes1989). Conductivity was also highly correlated wi th calcium, magnesium,alkalinity, pH, and sodium. This correlation suggests that the buffering capacity of the lake was an im portant in flu ence on crayfish accum ulation of mercury. Lowcalcium ion concentrations enhanced th e efficiency of methylmercury uptakeacross th e gill s of rainbow trout (Rogers and Beamish 1983).

24



TOXICITY OF MERCURYThe toxicity of mercury to aquatic organisms is affected by both abiot ic and biot icfactors including the form of mercury (inorganic versus organic), envi ronmentalcondi tions (e.g., temperature, salinity, and pH), th e sensit ivity of individual species

and life history stages, and the tolerance of indiv idual organisms. Toxicologicaleffects include neurological damage, reproductive impairment, growth inhibit ion,developmental abnormalit ies, and altered behavioral responses. Wiener and Spry(1996) concluded that n eurotoxicity seems to be the most probable chronicresponse of wild adul t f ishes to m ethylmercury exposure, based on observed effectssuch as un coordination, inabili ty to feed, diminished responsiveness, abnormalmovements, lethargy, and brain lesions. In laboratory studies, reprodu ctiveendpoints are generally m ore sensiti ve than growth or survival, with embryos andth e early developmental stages being the most sensitive (Hansen 1989). Impairedreproduction in sensitive aquatic organisms has been shown to occur at aqueousconcentrations of mercury between 0.03 and 1.6 µg/l (Eisler 1987). Long-termmercury exposure to adult fish also has been shown to resul t in retarded growth of offspring (Snarski and Olson 1982) and teratogenic effects (Weis et al. 1981).Chronic exposure to low concentrations of mercury m ay resul t in populations thatbecome tolerant to th e toxic effects of mercury contamination (Weis and Weis1989).

The toxic concentration of mercury compounds can vary by an order of magni tudeor more dependin g on the exposure condit ion . For example, toxicit y is greater atelevated t emperatu res (Armstrong 1979), at lower oxygen content (Sloof et al. 1991),and at reduced salinities in marine environments (McKenney and Costlow 1981).Site-specific factors (such as TOC) affect the bioavail abili ty and toxicit y of mercury-contaminated sediment (Langston 1990). Even though correlations exist betweentoxicological observations and sediment pollution gradients, Langston (1990)recommends collecting site-specific data because biological responses can notalways be satisfactori ly predicted from chemical data or modelin g resul ts.

The sensiti vity of aquatic organisms to either inorganic or methylm ercury variesconsiderably between species —more than the difference in sensit ivity of aparticular species to variou s mercury compou nds (EPA 1985). Methylmercury ismore acutely toxic to aquatic organisms than inorganic mercury , but the range

25



among dif ferent species in sensitivi ty to either compound is quite large. Forexample, the concentration of i norganic mercury inducing acute toxicity wasobserved to range over almost t hree orders of magnit ude from 0.1 µg/l t o moreth an 200 µg/l wh en results from tests with different species were compared (Eisler

1987). Tests on the same freshwater species wi th both i norganic andmethy lmercury showed th at methylmercury was more than 30 ti mes more acutelytoxic than inorganic m ercury (EPA 1985).

The general m echanism of action for toxic effects for inorganic mercury which hasthe form Hg (II), the divalent mercury cation , is believed to be the high affinity forth iol or sulfhydryl groups of prot eins (Clarkson 1972; Hughes 1957, Passow et al.1961) result ing in altered protein produ ction or synthesis (Syversen 1977).Methylmercury is lipid soluble, allowing rapid penetration of the blood-brainbarrier (Feltier et al. 1972, Giblin and M assaro 1973; McKim et al. 1976; Olson et al.1978; Beijer and Jernelov 1979). Injury to the cent ral nervou s system resul ts fromaccumu lation of methylmercury in the cerebellu m and cerebral cortex where itbinds tight ly to sulfh ydryl groups resul tin g in pathological changes (Sastry andSharma 1980). Inside th e cell , meth ylmercury inhibi ts protein synth esis/RNAsynthesis (Yoshino et al. 1966; Chang et al. 1972).

Zil lioux et al. (1993) suggest that, prior to th e mid-1980s, few data are avail able on

the biological effects of mercury at environmental concentrations becauselaboratory studies used exposure concentrations that were much higher than actualconcentrations in the field. Thi s was in part du e to contamination during samplecollection and analysis. Improvements in t race-metal-free clean protocols duringsample collection, handl ing, and processing as well as lower analytical detectionlimi ts have resul ted in l ower envi ronm ental concentrations of mercury and lowerconcentrations reported to elicit adverse effects. Alt hough pre-1980 data are usefulin identi fying modes of effect and relative toxicity of the various mercurycompounds, these data should be used with caution.

The following sections review available literature on the toxicity of mercury inwater, toxicity in sediment , and toxicity associated wi th m ercury in ti ssues. A widerange of toxic concent rations have been reported.

26



Toxici ty of Mercury in WaterNearly all of th e studies evaluating the toxicity of mercury compounds where theroute of exposure is th rough water h ave been condu cted u nder laboratorycondi tions. Due to th e natu re of laboratory studies and differences in experimental

design and techniqu e, a wide range of toxic concentrations have been reported fora given species (Table 1). For example, toxici ty tests using flow-th rou gh systemsgenerally show higher toxicity at lower concentrations than static-renewal systemsusing th e same (nominal) concentrations and th e same species. This difference isprobably due to loss of mercury from the test container in the static-renewal tests(Birge et al. 1979; Biesinger et al. 1982; WHO 1989).

Fish

Fish tend to be more sensitive to sublethal effects from chronic exposure to bothinorganic and organic mercury than invertebrates, bu t fi sh are less sensit ive toacute effects (EPA 1985; Hansen 1989). The early li fe stages of fish are generallyth e most sensitive to mercury. Birge et al. (1979) conducted several tests designedto evalu ate embryo surv ival, hatching success, teratogenic effects, and the effects of mercury on six species of freshwater fish. The sensit ivity of th e embryo-larval stagefor various species was correlated wit h t he length of ti me for eggs to develop andhatch and the duration of exposure. Trout eggs treated in a flow-thr ough systemexperienced approximately 40% mortality after a five-day exposure and 100%mortality after an eight-day exposure to an average mercury concentration of 0.12 µg/l .

Birge et al. (1979) also evaluated the long-term effects of mercury exposure on f ishreproduction by conducting chronic bioassays with rainbow trout . Their resul tssuggest that exposure of adult f ish to m ercury can h ave signifi cant adverse effectson their offspring, wi th th e effects enh anced if th e embryos are also reared in amercury-contaminated environment. Their data show a dose-dependent response

in both bioaccumu lation of mercury in gonadal ti ssues and toxic effects onembryos. Shor t-term exposures of embryos to high concentrations of mercury canalso elicit significant adverse effects (Sharp and Neff 1980) and such exposuresshou ld be taken into account in the evaluation of potential long-term impacts toreceiving environments. Althou gh ti me-integrated concentrations may be withinaccepted guidelines, a shor t-term exposure to an elevated mercury concentration

27



T a b

l e 1 . T o x

i c i t y r e s u l

t i n g

f r o m

e x p o s u r e

t o m e r c u r y i n w a t e r .

F i s h S p e c i e s

H g

( µ g / l )

H g

F o r m

E x p o s u r e

E f f e c t ( s )

R e f e r e n c e

B r a c h y d a n i o r e r i o

Z e b r a f i s h

( a d u l t s & f e r t i l i z e d e g g s )

0 . 1 , 1 , 5 ,

1 0 , & 2 0

p h e n y l m e r c u r i c

a c e t a t e

2 5 d a y s

8 3 % s p a w n i n g i n h i b i t i o n a t

5 u g / l ;

9 9 % i n h i b i t i o n a t 2 0 u g / l ; s i g n i f i c a n t

d e c r e a s e i n h a t c h i n g

f r e q u e n c y a t

0 . 2 a n d

1 u g / l .

K i h l s t r o m e t a l .

1 9 7 1

B r a c h y d a n i o r e r i o

Z e b r a f i s h

( f e r t i l i z e d e g g s )

1 0 , 2 0 & 5 0

p h e n y l m e r c u r i c

a c e t a t e

~ 6 d a y s

i n c r e a s e d h a t c h i n g s u c c e s s a t

1 0 u g / l ; i n c r e a s e

d t i m e

t o h a t c h a n d

r e d u c e d h a t c h i n g s u c c e s s a t

2 0 u g / l ; n o

h a t c h a t

5 0 u g / l

K i h l s t r o m a n d H u l t h

1 9 7 2

P o e c i l i a r e t i c u l a t a

M e d a k a g u p p i e s

1 . 8


3 m o n t h s

i m p a i r e d s p e r m a t o g e n e s i s

W e s t e r 1 9 9 1

O r y z i a s l a t i p e s

M e d a k a


1 5 2 0 & 3 0

m e r c u r i c c

h l o r i d e

1 6 d a y s

8 0 % e g g m o r t a

l i t y ; c a r d i o - v a s c u l a r

a b n o r m a l i t i e s i n e g g s

( h e m o r r h a g i n g ,

b l o o d v e s s e l

d e t e r i o r a t i o n , l o s s o f c i r c u l a t i n g

b l o o d c e l l s a n d

b l o o d v e s s e l s ) ,

t e r a t o g e n i c e f f e c t s

i n f r y ( i . e .

, n o n -

f u n c t i o n i n g c a u

d a l f i n s , s k e l e t a l

d e f e c t s , s p i n a l c u r v a t u r e )

1 0 0 % e g g m o r t a l i t y

H e i s i n g e r a n d G r e e n

1 9 7 5

F u n d u l u s h e t e r o c l i t u s

K i l l i f i s h


0 , 4 , 1 0 , 2 0 , 3 0 ,

4 0 , 6 0 , 8 0 &

1 0 0

m e r c u r i c c

h l o r i d e

3 2 d a y s

d e c r e a s e d h a t c h i n g a t

[ H g ] > 1 0 u g / l ;

l a t e r a l c u r v a t u r e o f t h e s p i n e

i n

l a r v a e a t

[ H g ] 3 0 u g / l .

S h a r p a n d

N e f f 1 9 8 0

F u n d u l u s h e t e r o c l i t u s

K i l l i f i s h


3 0 & 4 0

m e t h y l m e r c u r i c

c h l o r i d e

u p t o 4 8

d a y s

r e d u c e d a x i s f o r m a t i o n ,

d e v e l o p m e n t o f c y c l o p i a ,

d e f e c t i v e

c a r d i o v a s c u l a r s y s t e m , s k e l e t a l

m a l f o r m a t i o n s

W e i s a n d

W e i s 1

9 7 7

P i m e p h a l e s p r o m e l a s

F a t h e a d M i n n o w

0 . 2 6

1 . 0 2 2 . 0 1

m e r c u r i c c

h l o r i d e

4 1 d a y s

d e c r e a s e d g r o w

t h i n f e m a l e s a n d

r e d u c t i o n i n n u m

b e r o f s p a w n i n g

p a i r s c e s s a t i o n o f s p a w n i n g

s e v e r e s t u n t i n g a n d s c o l i o s i s

S n a r s k i a n d O l s o n

1 9 8 2

O n c o r h y n c h u s m y k i s

R a i n b o w t r o u t


0 . 1 2

m e r c u r i c c

h l o r i d e

5 & 8 d a y s

4 0 % m o r t a l i t y i n

f e r t i l i z e d e g g s ;

1 0 0 % m o r t a l i t y a f t e r 8

d a y s

B i r g e e t a l .

1 9 7 9



T a b

l e 1 . c o n

t i n u e d

M o l l u s c s / B i v a l v e s

S p e c i e s

H g

( µ g / l )

H g

F o r m

E x p o s u r e

E f f e c t ( s )

R e f e r e n c e

C r e p i d u l a f o r n i c a t a

L i m p e t

> 0 . 2 5

0 . 4 2

1 . 0

m e r c u r i c c

h l o r i d e

1 6 w e e k s

g r o w t h i m p a i r m e n t ,

d i m i n i s h e d

c o n d i t i o n

s u p p r e s s e d f e c u n d i t y , r e d u c t i o n s

i n

l a r v a l s e t t l e m e n t

s i g n i f i c a n t g r o w

t h r e d u c t i o n s

T h a i n 1 9 8 4

M e r c e n a r i a m e r c e n a r i a

C l a m s

1 5

m e r c u r i c c

h l o r i d e

8 & 1 0

d a y s

r e d u c e d g r o w t h

C a l a b r e s e e t a l . 1 9 7 7

C r a s s o s t r e a v i r g i n i c a

O y s t e r s

1 2


M y t i l u s e d u l i s

M u s s e l s

0 . 3

> 1 . 6

m e r c u r i c c

h l o r i d e

1 0 - 2 2 d a y s

> 3 d a y s


c e s s a t i o n o f g r o w t h

S t r o m g r e n

1 9 8 2

E c h i n o d e r m S p e c i e s

A n t h o c i d a r i s c r a s s i s p i n a

S e a u r c h i n

1 0

m e r c u r i c c

h l o r i d e

N o t a v a i l a b l e

f e r t i l i z a t i o n a n d

d e v e l o p m e n t

i n t e r f e r e n c e

K o b a y a s h i 1 9 8 4

C r u s t a c e a n S p e c i e s

C a l l i n e c t e s s a p i d u s

B l u e c r a b

( m e g a l o p a e

t h r o u g h

2 n d c r a b s t a g e )

1 0 t o 2 0

m e r c u r i c c

h l o r i d e

2 2 d a y s

r e d u c e d s u r v i v a

l i n m e g a l o p a e

M c K e n n e y a n d

C o s t l o w

1 9 8 1

M y s i d o p s i s

b a h i a

M y s i d s

1 . 6 2 . 5

m e r c u r i c c

h l o r i d e

f u l l l i f e

c y c l e

d e l a y e d s e x u a l m

a t u r a t i o n , d e l a y e d

b r o o d r e l e a s e ,

d e c r e a s e d b r o o d

p r o d u c t i o n

i n c r e a s e d b r o o d d e v e l o p m e n t

t i m e ;

a b o r t e d d e v e l o p i n g j u v e n i l e s

G e n t i l e e t a l . 1 9

8 3



could resul t in inh ibi tion of hatching, teratogenic development, and possiblepopulation effects.

Low concentrations of mercury in f reshwater reportedly resul t in ol factory and

chemoreceptor impairment i n salmonids and other fish, which may in terfere withnormal m igratory behavior (Hara et al. 1976; Rehnberg and Schreck 1986). Forexample, Hara et al. (1976) reported that rainbow trout exposed to inorganicmercury concentrations as low as 0.1 mg/l for two hours showed reduced olfactoryresponses. Further physiological and behavioral studies by Rehnberg and Schreck(1986) showed that mercury exposure reduced the ability of coho salmon to detectnatural odors and disrupted simple upstream movement i n laboratory experiments.

Weis and Weis (1989) suggest that pr ior exposure to mercury may producepopulations that are more tolerant to the toxic effects of mercury contamination.Differences in tolerance to th e effects of methylmercury were observed betweenorganisms from mercury-contaminated and clean environments. Eggs collectedfrom killifish in a contaminated area were mostly resistant to the teratogenic effectsof methylmercury, while eggs of fi sh f rom th e clean area showed a range of sensit ivity. The susceptible eggs from th e clean area also accumul ated higher levelsof mercury th an did th e eggs from th e contaminated area (Weis et al. 1981; 1982).Offspring from fish previously exposed to mercury contamination were more

tolerant to environmental mercury concentrations than offspring from cleanenvironments (Weis and Weis 1984).

The situation is complicated by the fact that some fish that bui ld u p a tolerance tolow concentrations of mercury can also detoxify the free metal wi th in cells via theproduction of metalloth ioneins (MTs) and other metal-binding proteins. Brown etal. (1983) proposed that t oxic effects occur as th e binding capacity of MT becomessaturated, due to the interaction of excess free metal in the cell with the enzymepool.

Invertebrates

Calabrese et al. (1977) suggest that marine bivalves embryos are more sensitivethan the larvae in th eir susceptib ili ty to mercury. They further indicated thatgrowth of fu lly-developed larvae may be retarded at concentrations too low to elicit

30



significant mortality, thus prolonging the pelagic stages and increasing the risk of predation, disease, and di spersion. Several endpoi nt s have been used to measurethe effect of m ercury exposure on bivalves, inclu ding biomarkers. The prophyr inprecursor ∂-aminolevulinic acid (ALA) may be useful as a biomarker of mercury

exposure in bivalves (Brock 1993).

The effects of salinit y on the toxicity of mercury have been demonstrated in a studyconducted wi th the megalopae of th e blue crab, Cal li nectes sapi du s (McKenney andCostlow 1981). Their results indicated that as salinity was reduced below 20 parts-per-thousand, less mercury was required to produce equivalent toxicity amongmegalopae. This is significant for blue crab and ot her estu arine species wh ichinhabit, migrate through, and use areas of lower salinity for foraging, spawning, andnursery grounds. Their data imply th at th e impact to a given population of fish orinvertebrates is highly dependent on the li fe stage and surrounding environmentalconditions.

The significance of experimental design and exposure period on evaluating thetoxicity of mercury was demonstrated in a series of studies conducted by Biesingeret al. (1982). In acute flow-th rough toxi city tests with Daphnia magna ,methy lmercuri c chloride was about 10 times more toxic th an in organic mercury,but onl y about 4 t imes as toxic under static-renewal condit ions. In the static-

renewal tests with methylmercury, it was discovered that about 90 percent of themercury h ad been converted to inorganic mercury dur ing the testin g period. Inchronic flow-through toxicity t ests with Daphnia m agna , methy lmercuric chloridewas about 30 times more toxic than inorganic mercury.

Plants

Chronic toxicity (as demonstrated by reduced population growth) in a marin ediatom (Thal assi osi ra weissflogi i ), exposed to inorganic mercury, methylmercury,

dimethylmercury, and elemental mercury , was related to the aqueousconcentration of a single mercury species, (th e chlor ide species HgCl 2 or CH3HgCl),

not to th e total mercury or free mercury ion concentr ation (Mason et al . 1996).Approxim ately t he same concentration of CH 3HgCl and HgCl2 reduced growth in

th e diatom by 50 percent. Mason et al . (1996) explain the apparently highertoxicity of methylmercury compared to inorganic mercury (expressed as a total

31



concentration of all inorganic forms) observed by numerous authors as a result of the low percentage of th e chloride form (HgCl 2) in the inorganic mercury fraction

of seawater (3.3 %) compared to the hi gh percentage of the meth yl m ercuricchl ori de species (CH 3HgCl), which forms 100% of the methy lmercury in seawater.

Elemental and dimethylmercury, even thou gh more hydrophobic than HgCl 2 andCH3HgCl respectively, were neither accumu lated nor toxic to the diatom. The

hypothesis by Fisher et al . (1984), th at the metals that are most bi oaccumulated byphytoplankton are the most toxic, may also be tru e about in divi dual mercuryspecies.

Toxicity of Mercury in SedimentThe complex behavior of mercury in th e environment makes it di fficult to predicttoxic effects based on bulk sediment total mercury concentrations. All the availabledata for effects of mercury in sediment are based on measurements of eitherinorganic mercury or total mercury.

The concentrations of mercury in sediment associated wit h toxicity are primaril yderived from field studies, in contrast to th e large number of laboratory toxicitytests for water exposure. The results from on ly two spiked sediment bioassays areavail able. Birge et al. (1979) reported reduced survi val (70% and 45%) of rainbowtrou t eggs exposed to sediment contamin ated wit h inorganic m ercury (mercuri c

chloride) for 20 days at concentrations of 1.05 and 0.18 mg/kg respectively. Swartzet al. (1988) reported an LC50 of 13.1 mg/kg for the marine amph ipod ( Rhepoxynius

sp .).

Considerable data are available, however, from field-collected samples th at includeboth measurements of mercury concentrations in sediment and adverse biologicaleffects. Long and M acDonald (1992) reviewed th e concent rations of mercury thatwere associated with measures of adverse biological effects in 169 studies thatincluded both marine and estu arine systems. Data from those stu dies were used tocalculate Effects Range-Low (ERL) and Effects Range-Median (ERM) concent rationsof 0.15 mg/kg and 0.71 mg/kg, respectively . The ERL and ERM concentrations arethe lower (10 percentile) and median (50 percentile) of the study concentrationsassociated with toxic effects. Of the tot al number of studies in th e data set, 8.3%had biological effects below the ERL (Long et al. 1994). The incidence of effectsbetween the ERL and ERM concentrations was 23.5%. The in cidence of effects

32



above the ERM concentration was 42.3% for mercury, whi le for oth er metals (e.g.,chromi um , copper, lead and silver) the incidence of adverse effects above the ERMwas in th e range of 75%. The low accuracy of the ERL and ERM m ercury guidelinesin predict ing adverse effects compared to th ese oth er metals hi ghl ights the need for

site-specific effects-based data for determining sediment mercury concent rationsthat are a threat t o aquatic bi ota.

The Washington State Department of Ecology uses Apparent Effects Threshold(AET) concentrations as th e basis for sedim ent cri teria for mercury. The AETs,based on laboratory bioassays and benth ic commun ity studies, represent theconcentration of a contami nant above wh ich signi ficant adverse effects were alwaysobserved for a specific biological indi cator (PTI 1988). The AETs for mercury wereempirically derived from studies conducted wi th contaminated and referencemarine sediments collected from Puget Sound. AETs for total mercury are0.41 mg/kg for the Microtox™bacterial luminescence bioassay, 0.59 mg/kg foroyster larvae abnorm alit y, 2.1 mg/kg for amphipod ( Rhepoxyniu s abroni us ) lethality,and 2.1 mg/k g for reductions in th e abun dance of major taxa of benth icmacroinvertebrates.

A laboratory study by McGreer (1979) demon strated th at clams, M acoma balthi ca ,avoided burrowing into field-collected sediment containing a sui te of metals. Theconcentrations of both cadmium (1.4 ppm) and mercury (0.46 ppm) best explainedth e behavioral responses. Avoidance of mercury-contaminated habit ats by aquaticspecies may be important ecologically . Inhi bit ed burrowing response, relocation,and l ack of l arval sett lement can decrease population sizes and reduce overallcommun ity compositi on. Species th at avoid contact wi th contaminated sedimentand do not burrow into the sediments are more vulnerable to predators and adverseenvironmental condi tions (e.g., temperatu re extremes, wave action, andcontaminants in the water colum n).

Toxicity Associated with Mercury in TissuesFew stu dies report both ti ssue residues and effects in either short - or long-termexposure to low concentrations of mercury (Table 2). It i s important to stress th atboth the tissue concentration and the exposure time and route (i.e. water, food,

33



maternal transfer) are criti cal factors in producing toxic symptoms in aquaticreceptors.

According to Wiener and Spry (1996), mercury transferred from the female to theeggs during oogenesis may pose a greater r isk to embryos than exposure tomercury i n the water colum n. For rainbow trou t, mercury residu es in ovaries of 0.5mg/kg were associated wit h a significant reduction in larval survival and abnormaldevelopment (Birge et al. 1979). Wh itney (1991) reported that hatchin g success andembryonic survival in walleye were inversely correlated wit h mercuryconcentrations in th e egg (range 0.002 to 0.058 mg/kg). How ever, only one of 12samples had h atching success or embryonic survival less th an 90%, and th ere wasno apparent dose-response relationship.

Mercury concent rations in brain t issue associated with l ethal effects appear to showless variation than that of other tissues (e.g., mu scle, wh ole body). For example,mercury concentrations in most types of ti ssues of brook trou t k ill ed by exposureto 2.9 µg/l of mercury in the water column varied among individu als, whereasconcentrations in the brain showed lit tl e variation (McKim et al. 1976). Theseresults are consistent wi th th e hypothesis that the central nervous system, ratherthan mu scle tissue or other organs, is the site of t he most harmfu l t oxic action infish exposed to mercury (Wiener and Spry 1996). In their review of the li terature,Wiener and Spry (1996) concluded that m ercury concentrations of 7 mg/kg or

greater in fish brain probably cause severe, potent ially leth al effects. In sensitivespecies such as the walleye, brain ti ssue concentrations of 3 mg/kg or greaterprobably indicate significant toxic effects.

Based on a review of t he li terature, Ni imi and Kissoon (1994) suggest that a totalmercury body burden of 1-5 mg/k g represents a threshold concentration forchronic adverse effects in aquatic organisms. Wiener and Spry (1996) reviewed th e

li teratu re and provided guidance for in terpreting mercury residu es in the axialmu scle tissue in adult fish associated wit h toxicity; both field and l aboratory studiesindicate that residu es of 6 to 20 mg/kg are toxic. Whole body mercuryconcentrations of about 5 mg/kg in brook trou t and 10 mg/kg in rainbow troutwere associated wi th sublethal and l ethal effects. Both of these papers are recentexampl es of attempts to identi fy a th reshol d of mercury in ti ssue th at is associated

34



T a b l e

2 . T o x i c i t y a s s o c i a t e d

w i t h m e r c u r y

i n t i s s u e s

( µ g / g ) w e t w e i g h

t .

F i s h S p e c i e s

T i s s u e T y p e

T i s s u e H g

( µ g / g , w w )

H g F o r m

E x p o s u r e

E f f e c t ( s )

R e f e r e n c e



o v a r y

0 . 5

m e r c u r i c c h l o r i d e

4 0 0

- 5 2 8

d a y s

s i g n i f i c a n t r e d u c t i o n

i n a l e v i n s u r v i v a l ( 4 -

d a y

p o s t h a t c h ) ; s i g n i f i c a n t i n c r e a s e i n

t e r a t o g e n i c e f f e c t s

B i r g e e t a l .

1 9 7 9



w h o l e b o d y

1 0 - 3 0

3 0 - 3 5


c h l o r i d e

8 4

d a y s

d e c r e a s e d g r o w t h a n d a p p e t i t e

d a r k e n e d s k i n a n d

l e t h a r g y

R o d g e r s a n d

B e a m i s h 1 9 8 2



b r a i n l i v e r

m u s c l e

w h o l e b o d y

1 6 - 3 0

2 6 - 6

8

2 0 - 2 8 1 9

t o t a l m e r c u r y

i n f o o d

2 7 0 d a y s

d a r k e n e d s k i n ; l o s s

i n a p p e t i t e , v i s u a l a c u

i t y ,

a n d g r o w t h ; l o s s o f e q u i l i b r i u m

M a t i d a e t a l .

1 9 7 1



m u s c l e

1 2 - 2 3


c h l o r i d e ( 4 - 2 4 p p m

i n

f o o d )

1 0 5 d a y s

h y p e r p l a s i a o f g i l l e p i t h e l i u m

W o b e s e r

1 9 7 5



b r a i n l i v e r

m u s c l e

7 - 3 2

3 2 - 1 1 4

9 - 5 2


c h l o r i d e ( 4 µ g / l i n w a t e r

c o l u m n )

3 0 - 9 8

d a y s

d e c r e a s e d a p p e t i t e a n d a c t i v i t y , m o r t a l i t y

N i i m i a n d K i s s o o n 1 9 9 4



w h o l e b o d y

4 - 2 7


c h l o r i d e ( 9 µ g / l i n w a t e r

c o l u m n )

1 2 - 3 3

d a y s

d e c r e a s e d a p p e t i t e a n d a c t i v i t y , m o r t a l i t y

N i i m i a n d K i s s o o n 1 9 9 4

P i m e p h a l e s p r o m e l a s

F a t h e a d m

i n n o w

w h o l e b o d y

1 . 4

m e r c u r i c c h l o r i d e

6 0

d a y s

i m p a i r e d r e p r o d u c t i o n , r e t a r d e d

l a r v a l g r o w t h

S n a r s k i a n d

O l s o n 1 9 8 2

M u g i l c e p h a l u s

S t r i p e d m u l l e t

w h o l e b o d y

0 . 3

5 . 0


c h l o r i d e ( 0

. 0 0 1 m g / l i n

w a t e r c o l u m n )


c h l o r i d e ( 0

. 0 1 m g / l i n


7 , 1 1 , 1 4 d a y s

i n h i b i t i o n o f r e g e n e r a t i o n o f a m p u t a t e d

c a u d a l f i n

W e i s a n d

W e i s

1 9 7 8

S a l v e l i n u s

f o n t i n a l i s

B r o o k t r o u t

b r a i n l i v e r

o v a r i e s / e g g s

w h o l e b o d y

5 8 5 3


c h l o r i d e ( 0

. 2 7 µ g / l i n


2 7 3 d a y s

n o a p p a r e n t e f f e c t s

M c K i m e t a l .

1 9 7 6

S a l v e l i n u s

f o n t i n a l i s

B r o o k t r o u t

b r a i n l i v e r


w h o l e b o d y

1 7 2 4 1 0 5 -

7


c h l o r i d e ( 0

. 9 3 µ g / l i n


2 7 3 d a y s

i n c r e a s e d m o r t a l i t y ,

d e c r e a s e d g r o w t h ,

l e t h a r g y , a n d

d e f o r m i t i e s

M c K i m e t a l .

1 9 7 6

S a l v e l i n u s

f o n t i n a l i s

B r o o k t r o u t

b r a i n l i v e r


w h o l e b o d y

4 2 5 8 2 4 2 4


c h l o r i d e ( 2 . 9 µ g / l i n


2 7 3 d a y s

l o s s o f a p p e t i t e , m u s c l e s p a s m s , a n d

d e f o r m i t i e s ; m o r t a i l i t y

M c K i m e t a l .

1 9 7 6

S t i z o s t e d i o n v i t r e u m

v i t r e u m

W a l l e y e

b r a i n l i v e r

m u s c l e

3 - 6

6 - 1 4 5 - 8


( 5 - 1 3

p p m i n f o o d )

4 2 - 6

3 d a y s

m o r t a l i t y ; e m a c i a t i o n ; l o s s o f l o c o m o t i o n ,

c o o r d i n a t i o n a n d a p p e t i t e .

S c h e r e r e t a l .

1 9 7 5

S t i z o s t e d i o n v i t r e u m

v i t r e u m

W a l l e y e

b r a i n l i v e r

m u s c l e

1 5 - 4 0

1 8 - 5 0

1 5 - 4 5


( 5 - 1 3

p p m i n f o o d )

2 4 0

- 3 1 4

d a y s

h i g h e r m o r t a l i t y ; e m a c i a t i o n ; p o o r e r

l o c o m o t i o n , c o o r d i n a t i o n a n d a p p e t i t e .

S c h e r e r e t a l .

1 9 7 5



with adverse effects. The "thresholds" presented in these papers are based oneffects in adult fish and probably do not represent a tru ly protective level for allspecies and li fe stages, including maternal transfer. We begin to become concernedabout reproductive or early life stage effects when total Hg in whole bodies of fish

are between 0.5 and 1.0 ppm.

In te ract ions wi t h Other Meta l sThe effects on aquatic organisms due to interactions of mercury with cadmium ,copper, selenium, and zinc were found t o be dependent on exposure concentrations(Birge et al. 1979). In general, effects were less th an addit ive at lower exposureconcentrations and greater than additive (synergistic) at higher concentrations.Zinc and cadmium were reported to reduce the teratogenic effects of methy lmercury to k ill ifi sh (Weis et al. 1981). Cadmium added to methy lmercuryreduced the retardation effect on fin regeneration in mullet (Weis and Weis 1978).

The percentage of embryos affected and degree of malformation observed due toexposure of kil lif ish eggs to 20-50 µg/l methylmercury was reduced wh en cadmiumor zinc was added. Selenium was reported to reduce th e developmental effects of inorganic mercury to embr yos of the medaka (Japanese ricefish), but only after th eformation of th e embryonic liver (Bowers et al. 1980). Interactions betweeninorganic mercury and zinc, PCBs, and a PAH (fluoranthene) were observed to be

generally addit ive in sediment exposure to a marine amph ipod (Swartz et al. 1988).A mixtu re of an in organic form of mercury (mercuric chlor ide) and the chlorides of zinc and lead had a synergistic toxic effect on the water exposure of a marine ciliateUronema mar inu m (Parker 1979).

CRITERIA AND GUIDELINES

This section briefly discusses EPA’s AWQC for mercury in freshw ater and m arine

systems and variou s guidelines th at have been proposed for evalu ating thepotential toxicity of mercury in sediments.

Am bient Wat er Qual i t y Cr i t er ia (AWQC)The AWQC, promu lgated by th e U.S. EPA, are in tended neither as ru les norregulations, but present data and guidance on the effects of pollutants that can be

36



used to derive regulations based on considerations of water qu ality impacts (EPA1993). The AWQC consist of two concentrations: the Criterion M aximumConcentration (usually referred to as the acute AWQC) and the CriterionContinuou s Concentration (usually referred to as the chronic AWQC). The acute

AWQC are derived from short-term toxicity tests using statistical methods thatestimate th e LC 50 concentrations for the lowest 5 percent of the most sensitivespecies tested. Acute AWQC for mercury are 2.4 and 2.1 µg/l for freshwater andmarine organisms, respectively. They are based on inorganic mercury because it isthe predominant form of mercury released into the envi ronment (EPA 1985).

The chronic AWQC are defined by EPA as th e lowest (most protective)concentrations from th ree categories of tests: th e fin al chr onic value, derived fromchroni c toxicity tests with animals; the final plant value, derived from toxicity testsusing aquatic plants; and th e final residue value (FRV), derived from maximu mpermissible tissue concentrations (for protection of human health) andbioconcentration factors (BCF). For mercury, th e chronic AWQC of 0.012 µg/L forfreshwater species and 0.025 µg/l for marine species represent FRVs, which arebased on the Food and Drug Administration’s (FDA) action level of 1 mg/kg andBCFs for methylmercury.

The use of the FDA action level to derive the chronic AWQC assum es th at aquati c

organisms would not be adversely affected by methylmercury tissue concentrationsgreater than or equal to 1 mg/k g. Thi s is based on a study in wh ich long-termexposure of brook t rout to methylm ercury resul ted in ti ssue residu e concentrationsgreater than 1 mg/kg bu t no signif icant effects on survival, growth, or reproduction(McKim et al. 1976). However, oth er stu dies have demonstrated th at tissueconcentrations close to the FDA action level may eli cit adverse effects in somespecies (Birge et al. 1979; Snarski and Olson 1982).

Eisler (1987), in his review of the hazards of mercury to aquatic organisms, notedthat the AWQC do not appear to be protective of aquatic organisms whencompared to results from toxicity tests with sensitive species. Assum ing the BCFsaccurately reflect bioaccumu lation u nder field condit ions, the FDA action levelwou ld be the average concentration in mu scle tissue of exposed aquati c organisms.Thus, many aquatic organisms exposed to mercury concentrations equivalent to

37



the chronic AWQC would be expected to have tissue concentrations above 1 mg/kg(EPA 1985).

Sedim ent GuidelinesNo sediment criteria are cur rently available for either methylmercury or totalmercury. Several approaches have been proposed for developing guidelines forscreening contaminated sediments, but two of the more frequently used approachesare the National Status and Trends Effects Range approach (Long and MacDonald1992) and the AET (PTI 1988) approach developed for screening sediments in PugetSound, Washington. The State of Washington used the AET approach as th e basisfor marine sediment management standards in Puget Sound.

The ERL and ERM concent rations for mercury in marine and estu arine sediments

are 0.15 and 0.71 mg/kg (Long and MacDonald 1992), respectively, while the AETconcentrations for mercury range between 0.41 and 2.1 mg/kg (PTI 1988).

TissueNo standards that woul d be protective of aquatic organi sms have been establi shedfor mercury concentrations in tissues. The current FDA action l evel for th eprotection of human health , based only on methylm ercury in t he edible flesh of fish and shellfish, is 1 mg/kg (U. S. FDA 1984).

APPLICATIONSEcological assessments of hazardous waste sites with elevated concentrations of mercury in th e aquatic envi ronment are parti cularly challenging due to thecomplexity of the factors that affect the availability of mercury to aquaticorganisms. The distribut ion of total mercury in sediment , which in most cases ispredominantly inorganic mercury, may not provide sufficient information about thebioavail abili ty and toxicity of mercury to aquatic species. Because of theimportance of methylation in determining the availability of mercury to aquaticorganisms, the sampling design, evaluation of remedial alternatives, and monitoringprogram shoul d be based on an understanding of th e system-specific processes th atlead to increased methylation and the pathways to resources of concern. The effortrequired and detail of th is understanding shou ld be determin ed by the magnit udeof the problem and the scope of th e project. This section di scusses some special

38



considerations to assist in sampling, risk assessment, monitoring, and remedialdecisions.

Samp l ing and Moni t or ing Considera t ions

Target Species and Analysis

Mercury concentrations in resident aquatic organisms may provide the bestmeasure of the availability of mercury in a particular area, both because of potentialhu man h ealth concerns and because it is the best indicator of availabil ity of mercury u nder the specifi c condit ions present at a site. In selectin g target species,the trophic level, size, age, sex, life habit, metabolism, and life span of organisms areall important factors to consider. Hi gher troph ic-level fish species are useful fordetermi nin g whether a problem exists since mercury biomagnifi es, and for long-

term m oni tor ing, since mercury concentrations are slower to decrease. How ever,even fish occupying the same trophic level, with similar diets and feeding habits,may exhibi t di fferent temporal patterns of mercury accumu lation due to dif ferencesin habitat preferences, behavior , and metabolic rate causing dif ferent exposures(Jackson 1991). Mercury concentrations in biota may not correlate with sedimentmercury concentrations. Correlations between mercury concentrations in predatorand prey species may be useful in determining the food web pathways that connectthe mercury in th e sediment t o the biota.

Whole body analyses of fish are typically done to determine food chain exposure,wh ile fish fi llets are typically analyzed to assess hum an health exposure. Wh ole-body m ercury concentrations may be less than the concentration in the fil let;however the difference may not be statisti cally signi ficant . For example, althoughmethy lmercury concentrations were higher in fi llet th an in whole body samplesmeasured in four fi sh species (whi te perch, small mou th bass, blu egil l, and gizzardshad) in Onondaga Lake (New York), only concentrations in bluegill werestatistically different (Becker and Bigham 1995).

Invertebrates such as bivalve mol lu scs and mayflies ( Hexagenia sp.) have also beenused for assessing the availabili ty of mercury in a particular location. Dependi ngon the scope of the project, moni tor ing several di fferent species from differenttrophic levels may be appropriate.

39



In developing assessment endpoin ts and sampling objectives, the potential fordirect toxicity to aquatic organisms shou ld not be overlooked. Laboratory and in -situ toxicity t esting are usefu l approaches for assessing th e direct bi ological effectsof elevated mercury concentrations to aquatic organisms in sediment and water.

Toxicity testin g at mercury sites shou ld include standard toxicity tests. In addition,early l ife-stage tests (exposure of test species from post-fert il ization th rou ghembryonic, larval, and early juvenile development) or parti al li fe-cycle tests (early

ju venile th rough post-h atch of next generation wi th measurements of survi val,growth, and reproductive endpoints) are sensitive tests for mercury toxicity.Monitoring changes in abundance and diversity in macrobenthic communitycomposition may also provide useful information in assessing the toxicity of mercury in aquatic habitats.

Environmental Sampling

Investigations should be designed to include both spatial and temporal sampling.Seasonal and spatial variations in mercury concentrations, includin g its forms andpartitioning, within a single waterbody can be significant (e.g., Gill and Bruland1990; Parks et al. 1989). Mercury contents in mu ssels from different parts of th eGulf of St. Lawrence estu ary (normalized by shell length and soft-tissue dry weigh t)were highest in areas with the greatest freshwater influence and lower in regionswh ere the marine infl uence was greatest (Cossa and Rondeau 1985). All ard andStokes (1989) found t hat total mercury in two species of crayfish w as significantlyhigher in specimens from lake inlets than in t hose from the lake basin.Determini ng th ose envi ronm ental parameters that affect th e activi ty of methy latingmicrobes such as nu tr ients, temperature, and di ssolved oxygen, and th e factorsaffecting th e availability of inorganic mercury for methylation such as theresuspension of sediment , TOC, and sul fides, may be warranted for th e design of sampli ng and monitoring plans. Data on chloride concentration and pH may beused to determin e th e relative proportions of th e individu al inorganic and

methylmercury species and their overall partition coefficients (Mason et al . 1996).In addit ion to th e form of mercury , its parti tioning between di ssolved andparti culate forms has an important effect on both uptake and t ransport. Indetermi nin g the extent of contamination at a site, it is important to consider th atboth resuspended contaminated sediment and dissolved mercury may act asimportant sources.

40



Accurately m odeling the fate of mercury in aquatic environments and theavailabil ity of mercury to aquatic organisms requi res the collection of detailedinformation on th e forms of mercury and th eir relative concentrations in d ifferent

environmental compartments (e.g., the amounts of inorganic, methyl-, andelemental mercury in dissolved and parti culate forms in th e water column,sediment [particulate and pore water], and biota). The scope of a project l ike th is isenormous and th e effectiveness of this comprehensive approach has yet to bedemonstrated. The transfer of mercury through the food web was modeled using adescript ive approach t o explain the hi gh levels of mercury in Lavaca Bay fish andshell fish (Evans and Engel 1994). Tissue burdens for mul tiple food webcomponents are required. This approach was useful in identifying critical factorsresponsible for localized elevations in mercury concentrations, but alsodemonstrated the limi tations and l arge effort required for modeling.

Approaches to RemediationThe level of effort needed to characterize a mercury-contaminated site may rangefrom simple monit oring of mercury concentrations in biota and environmentalmedia at small sites, to biogeochemical modeling at major mercury sites (PTI 1991).Althou gh methylm ercury is the form of most concern in aquatic systems, it has notbeen routinely measured due to the lack of standard analytical methods and cost

considerations. Determi nin g which form of mercury to measure, and in wh ichmedia and organisms, depends on the nature of the contamination and theobjectives of th e study. Measur ing onl y total mercury concentrations in sedimentand biota may give a general picture of the extent of contamination and t hemagnitu de of the problem, but only provides minimal information on the fate,transport , and availabili ty of mercury in th e system. In order to select an effectiveremedial alternative, it may be necessary to characterize th e major pathways toreceptors of concern and the aspects of th e aquati c system th at enhancemethylation and influence mercury availability.

The role of speciation in determin ing concentrations in, and t oxicity to, biota mayneed to be understood pr ior to attempts to control the geochemical cyclin g of mercury withi n a waterbody. Remediation attempts have been unsuccessfu l at siteswh ere th ese factors have been ignored. However, this approach requi res analytical

41



techniqu es th at are selective and sensit ive enou gh to measur e ambientconcentrations of the different mercury species.

A primary goal of many remedial investigations is to establish cleanup

concentrations for mercury in variou s envi ronmental media that wi ll be protectiveof both h uman health and th e envi ronment . Establishing target cleanupconcentrations for mercury is extremely di fficult due to the many environmentalfactors that influ ence the transformation of inorganic mercury to methylmercury.Target cleanup concentrations shou ld be determined on a sit e-by-site basis due tothe variabili ty i n the bioavailabil ity of mercury and condi tions between sites.Determini ng a cleanup concentration requires knowing the effect t hreshold andtranslating that to a sediment concentration that is protective. Cleanupconcentrations shou ld be chosen t hat both reduce the source of total mercury toth e system and its bioavailabili ty to organisms. Confi rmation of the effectiveness of the target cleanup concentration requi res long-term monitoring of both sedimentand biota.

Removing hot spots (by dredging or capping) may eliminate important sources of inorganic mercury bu t may not provide substantial improvement in environmentalcondi tions if methylation rates are mu ch h igher in l ess contaminated areas, such asfreshwater wetlands (St. Louis et al. 1994). Oth er factors affecting the sit e also need

to be considered. Methylation of mercury left in sediments could be increased bydredgin g, increased organic loading (with out sulfi des), and in creased thermalloading (Rada et al. 1986).

Where source control has not been feasible due to the volume and extensivedistribu tion of th e mercury, remediation strategies that focus on li mi tin g thebioavail abili ty of mercury have been stu died. Dilution approaches, such as addinguncontaminated sediments, may reduce the supply of mercury by an order of magnitu de (Rudd and Tu rner 1983). Complexation of m ercury to “detoxify” (e.g.,addit ion of selenium to the water colum n) may be a valid approach. Researchindicates that selenium interferes wit h b ioaccumu lation efficiency of mercury infish since selenium concent rates in th e fish food source and exclu des mercury.This approach can yield up to a twofold decrease in mercury bioaccumulation rates.However, selenium toxicity may add a new problem. Liming to increase pH infreshwater lakes has also been attempted wi th variable resul ts, wi th posit ive effects

42



taking two or more years (Lindqvi st 1991; Meili 1995). The long-term effectivenessof these remedies and th e potential adverse effects on the environm ent have notbeen well-studied.

Analytical ConsiderationsDetection Limits in Water, Sediment, and Biota

Detection li mi ts shoul d be chosen based on the objective of th e stu dy. Analysis of mercury i n water samples is parti cularly d iffi cult due to the very low concentrations(parts per tr il lion) that need to be measured. Achieving low detection l imits isfurth er compli cated by the possibi lit y of external contamination of samples whichcan be a signifi cant probl em (Fitzgerald 1990).

The chronic AWQC for methylmercury are 0.012 and 0.025 µg/l for f reshwater andsaltwater, respectively. Using the AWQC as a detection l imit may be diff icult as fewlabs have analyti cal procedures th at can reach these low concentrations. Thedetection limit for the EPA standard contract lab program (CLP) method for analysisof total mercury in water is 0.2 µg/l . To achieve ecologically relevant detectionlimi ts it may be necessary to employ analyti cal methodologies other th an thosespecified under the CLP, or to modify the CLP meth ods. For example, mercurydetection limits to determine the mass balance of mercury in the Onondaga LakeSuperfun d site were establi shed as foll ows: 0.00001 µg/l for methylmercury inwater; 0.0001 µg/l for total mercury in water; and 0.01 mg/kg wet weight i n fi sh(PTI 1991).

These detection limits were achievable by modifying standard procedures.Unfil tered water samples are analyzed for comparison to criteria concentrations. Inthe EPA criteria document, the measurement of acid-soluble mercury (the mercurythat passes th rough a 45-µm fil ter foll owing acidi fication to a pH of 1.5 to 2.0) isrecommended, although no EPA-approved protocol has been establi shed (EPA

1985). Some recent analyti cal approaches for t he analysis of methylmercury aredescribed by the following auth ors: Bloom and Crecelius (1983), Gill and Fitzgerald(1987), Bloom (1989), Gil l and Brul and (1990).

Choosing appropriate detection lim its for sampli ng of sediment is parti cularlyimportant for mercury sit es because even low concentr ations can cause significant

43



accumulations in bi ota. Detection limi ts for sediments shou ld be below th e ERLvalue of 0.15 mg/kg developed by Long and MacDonald (1992).

Quality control is an important aspect of any testin g program but is parti cularly

important for t he analysis of mercury in environmental samples. It i s highlyrecommended that analyses of mercury in water, sediment , and ti ssue also inclu deanalyses of cert if ied standards for th e appropr iate matrix as part of the qualitycontrol plan to verify the extraction and analytical processes.

Difficulties in the extraction and analysis of mercury residues in tissues areapparently not uncomm on. For example, in three recent Superfund projects inthree different regions, methylmercury concentrations in fish tissue were reportedto be higher than total mercury concentrations. In another study of contaminantconcentrations in t issues of aquatic organisms, spike-recovery values for mercury intissue samples were in the range of 50 percent (Tetra Tech 1988).

The National Research Council of Canada has cert ifi ed standards formethylmercury and total mercury in animal tissue samples (e.g., dogfish liver anddogfish muscle), and for sedim ent and water samples. The U.S. Nati onal Bureau of Standards has comparable standards for total mercury.

SUMMARY

NOAA recomm ends a sit e-specific approach t hat focuses on determining theavailabil ity of mercury and th e potential for toxic effects. The accumulation of mercury in aquatic biota is often the prim ary concern at mercury sites and isuseful for assessing availabili ty . Bioaccum ul ation studies shou ld measur e ti ssueconcentrations in m ore than one resident and/or transplanted caged species,preferably with species representing different trophic levels or different food webpathways. It may not be possible to correlate sediment m ercury concentrationswit h concentrations in biota. However, correlations between mercuryconcentrations in predator and prey species may be useful in determiningpathways of mercury transfer.

Toxicity tests such as th e standard amph ipod tests shou ld also be conducted toassess mercury toxicity to aquatic organisms. At major mercury sites, chronic

44



toxicity endpoints shou ld be included in the assessment—in particular, fish early li festage or reproductive endpoin t t ests. Because of the persistence of mercury inaquatic systems, sour ce control alone may not be sufficient to permit recovery.Addit ional remedial actions may be required to reduce th e total mercury burden in

the system. Long-term monitoring of tissue concentrations of mercury in aquaticbiota is needed to assess remedial effecti veness.

REFERENCES

Alberts, J.J., M.T. Pri ce and M. Kania. 1990. Metal concent rations in ti ssues of Sparti na alterni flora (Loisel.) and sediments of Georgia salt marshes. Estuarine,

Coastal an d Shelf Science 30 : 47-58.

All ard, M. and P. Stokes. 1989. Mercury in crayfish species from th ir teen OntarioLakes in relation to water chemistry and smallmouth bass ( M icropteru s dolomi eui )

mercury. Can ad i an Jour na l of Fi sheri es an d Aqu ati c Sciences 46 .

Andersen, A., K. Julshamn, O. Ringdal, and J. Mork ore. 1987. Trace Elements Intakein the Faroe Islands, II: Int ake of Mercury and Other Elements by Consumption of Pilot Wh ales (Globicephalus meleanu s). Sci ence of the Total Envir onm ent 65 :63-68.

Andre, J. M., A. Boudou , and F. Ribeyre, and M. Bernh ard. 1991a. Comparativestudy of mercury accumulation in dolphins ( Stenell a coer ul eoal ba ) from FrenchAtlantic and Mediterranean coasts. Sci. Total Envir on. 104 :191-209.

Andre, J. M., A. Boudou , and F. Ribeyre. 1991b. Mercury accumulation inDelphinidae. Wat. Air Soil Pollu t. 56 :187-201.

Ari ma, S., and K. Nagaku ra. 1979. Mercury and selenium content of Odontoceti .Bul l. Jap an ese Soc. Scien ti fi c Fish. 45 (5):623-626.

Armstrong, F. A. J. 1979. Effects of mercury compounds on fish. In: J. O. Nriagu(Ed.), The Biogeochemi str y of M ercur y in the Envir onm ent . pp. 657-670. New York:Elsevier/North-Holland Biomedical Press.

45





Bloom , N.S. 1989. Determination of picogram levels of methy lmercury by aqueousphase ethylation, followed by cryogenic gas chromatography wit h cold vaporatomic flu orescence detection. Can ad i an Jour na l of Fi sheri es an d Aqu ati c Sciences

46 :1131-1140.

Bloom , N. S. 1992. On the chemical form of mercury in edible fish and marineinvertebrate t issue. Ca n. J. Fi sh. Aqu at . Sci . 49 :1010-1017.

Bloom, N.S., C.J. Watras, and J.P. Hurley. 1991. Impact of acidif ication on t hemeth ylmercury cycle of remote seepage lakes. Wat er , Ai r, Soi l Pollu t. 56 :477-491.

Bloom, N.S. and S.W. Effler. 1990. Seasonal variabil ity in the mercury speciation of Onondaga Lake (New York). Wat er , Ai r , Soi l Pollu t. 53 :251-265.

Bloom, N.S. and E.A. Crecelius. 1983. Determination of mercu ry in seawater atsubnanogram per l it re levels. M ari ne Chemi stry 14 :49-59.

Blu m, J. M. and R. Bartha. 1980. Effect of salinity on methylation of mercury.Bulletin of Envir onmental Contamin ation and Toxicology 25 :404-408.

Bonzongo, J.J., Heim, K.J., Y. Chen, W.B. Lyons, J.J. Warwick, G.C. Miller and P.J.Lechler. 1996. Mercury pathways in th e Carson River-Lahontan Reservoir System,Nevada, USA. Envir on. Toxi col. an d Chem. 15 (5):677-683.

Born, E. W., I. Kraul , and T. Kristensen. 1981. Mercury, DDT, and PCB in th eAtlant ic walrus (O dobenu s rosma r us r osma r us ) from the Thul e District, NorthGreenland. Ar cti c 34 :255.

Boudou , A., M. Delnomdedieu, D. Georgescauld, F. Ribeyre, and E. Saouter. 1991.Fundamental roles of biological barriers in mercury accum ulation and t ransfer infreshwater ecosystems (analysis at organism, organ, cell and molecular levels).Water, Ai r, and Soil Pollu ti on 56 :807-822.

Bowers, M. A., D. Dostal, and J. F. Heisin ger. 1980. Failure of selenit e to protectagain st mercur ic chl ori de in early developmental stages of the Japanese ri cefish(Or yzi as lati pes ). Compa ra ti ve Biochemi str y and Physi ology 66C :175-178.

47



Breteler, R.J., I. Valiela, and J.M. Teal. 1981. Bioavailabi li ty of mercur y in severalNorth-eastern U.S. Spartina ecosystems. Estu ar i ne, Coastal an d Shelf Science 12 :155-166.

Brock, V. 1993. Effects of mercury on th e physiological condi tion and content of the biomarker ALA in th e oyster O strea edu li s . M ar . Ecol. Prog. Ser i es. 96 :169-175.

Brown, D. A., R. W. Gosset, P. Hershelman, H. A. Schaefer, K. D. Jenkins, and E. M.Perkins. 1983. Bioaccumu lation and detoxi fication of contaminants in marin eorganisms from South ern Californ ia coastal waters. In: D. F. Soule and D. Walsh(Eds.), Waste D i sposal i n the Ocean s . p. 171. Boulder: Westview Press.

Bryan, G. W. and W. J. Langston . 1992. Bioavailabi li ty , accum ulation and effects of heavy metals in sediments with special reference to Uni ted Kingdom estu aries: areview. Envi ron . Pollu t. 76 : 89-131.

Calabrese, A., J. R. MacInnes, D. A. Nelson, and J. E. Mill er. 1977. Surv ival andgrowth of bivalve larvae under h eavy m etal stress. M ar . Biol. 41 :179-184.

Call ister, S. M. and Winfrey, M. R. 1986. Microbial methylation of mercury in u pperWisconsin River sediments. Water, Air and Soil Polluti on 29 : 453-465.

Choi, S.-C., and R. Barth a. 1994. Environmental factors affecting mercury

methylation in estuarine sediments. Bull. Envir on. Contam . Toxicol. 53 :805-812.

Clarkson, T. W. 1972. Recent advances in t oxicology of mercury with emphasis onthe alkyl mercurials. Cr i t. Rev. Toxi col. 203-234:.

Compeau, G. and R. Barth a. 1983. Effects of sea salt anions on the formation andstability of methylmercury. Bulletin of Envir onmental Contami nati on and

Toxi cology 31 :486-493.

Compeau, G. and R. Bartha. 1985. Sulfate-reducing bacteria: prin cipal m ethylatorsof mercury in anoxic estuarine sediment. Appl. Envir on. M i crobi ol. 50 : 498-502.

Cope, W. G., J. G. Wiener, and R. G. Rada. 1990. Mercury accumu lation in yellowperch in Wisconsin seepage lakes: relation to lake characteri sti cs. Environmental

Toxicology an d Chemi stry 9:931-940.

48



Cossa, D. and J. G. Rondeau. 1985. Seasonal, geographical and size-indu cedvariability in mercury content of M ytilus edul is in an estuarine environment: a re-assessment of mercury pollut ion level in th e Estu ary and Gul f of St. Lawrence.M ari ne Biology 88 :43-49.

Craig, P.J., and P.A. Moreton. 1983. Total mercury, meth yl m ercury and sul phi de inRiver Carron sediments. M ari ne Polluti on Bulletin 14 (11):408-411.

Craig, P.J., and P.A. Moreton. 1985. The role of speciation in mercury m ethylationin sediments and water. Environ mental Poll uti on Seri es B 10:141-158.

Darnell , D. W., B. Greene, M. T. Henzl, J. M. Hosea, R. A. McPherson, J. Sneddon, M.D. Alexander. 1986. Selective recovery of gold and other metal ions from an algalbiomass. Envi r on. Sci. Technol . 20: 206-208.

De Haan, H. 1992. Impacts of environm ental changes on the biogeochemistry of aquatic hu mic substances. Hydrobiologia 229:59-71.

Dukerschein, J. T., R. G. Rada, and M . T. Steingraeber. 1992. Cadmium and mercuryin emergent mayfl ies (Hexagenia bili neata) from th e upper Mississippi River. Arch.

Envir on. Contam . Toxi col. 23: 109-116.

Eganhouse, R.P. and D.R. Young. 1978. Total and organic mercury in benthic

organisms near a major subm arine wastewater outfall system. Bulletin of Envir onmental Contamin ation and Toxicology 19:758-766.

Eisler, R. 1987. M er cur y hazar ds to fi sh, wi ld li fe, an d i nver tebra tes: a synopti c r eview .U.S. Fish and Wildl ife Service Biology Report 85(1.10). Washin gton , D.C.: U.S.Department of the Interior. 90pp.

Evans, D.W. and D.W. Engel. 1994. M ercur y bi oaccum ul ati on in fi nfi sh and shellfi sh

fr om Lavaca Bay, Texas: descr i pti ve mod els an d an nota ted bibl i ograph y . NOAA

Technical Memorandum NMFS-SEFSC-348. Beaufor t, North Carol ina: Nati onalMarin e Fisheries Service, NOAA.

Faust, B.C. 1992. The octanol/water distribution coefficients of meth ylmercur icspecies: the role of aqueous-phase chemical speciation. Envir on. Toxicol. Chem.

11:1373-1376.

49



Felt ier, J. S., E. Kahn, B. Salick, F. C. Van Natta, and M. W. Whit ehouse. 1972. Ann.

In tern . M ed. 76:779-792.

Fisher, N.S., M. Bohé, and J.-L. Teyssié. 1984. Accumu lati on and t oxicity of Cd, Zn,Ag, and H g in four marine phytoplankters. M ar . Ecol. Pr og. Ser . 18 :201-213.

Fitzgerald, W.F. 1990. Mercury in seawater. In: M ercury i n the M ari ne

Environment . Workshop proceedings. U.S. Dept. Interior, Mineral ManagementService, Anchorage, Alaska. OCS Study M MS 89-0049.

Fowler, S. W., M. Heyraud, and J. La Rosa, 1978. Factors affecting methyl andinorganic mercury dynamics in mu ssels and shr imp. M ari ne Biology 46: 267-276.

Francesconi , K. and R. C. J. Lenant on 1992. Mercury contaminati on in a semi-

enclosed marine embayment: organic and inorganic mercury content of biota, andfactors inf luencing mercury levels in fish. M ar i ne Envi ronm ental Resear ch 33: 189-212.

Gadd, G. M. 1988. Accumul ation of metals by microorganisms and algae. In:Rehm H-J and G. Reed (eds) Biotechnology . Vol 6b, 401-433. Weinheim, Germany:VCH Verlagsgesellschaft.

Gentil e, J. H., S. M. Gentile, G. Hoffm an, J. F. Heltshe, and N. Hairston, Jr. 1983. The

effects of a chroni c mercury exposure on survival, reproduction and populationdynamics of M ysi dopsi s bahi a . Envir on. Toxicol. Chem. 2 :61-68.

Gibl in , F. J. and E. J. Massaro. 1973. Pharmacodynamics of methyl m ercury inrainbow trout (Salm o gai rd neri ): ti ssue upt ake, distr ibut ion and excretion. Toxicol.

Appl. Pharma col. 24 :81-91.

Gill , G. A. and K. W. Bru land. 1990. Mercury speciation in surface freshwatersystems in Cali forn ia and oth er areas. Envir onm enta l Sci ence an d T echnol ogy 24 (9):

1392-1400.Gill, G.A. and W.F. Fit zgerald. 1987. Picomolar mercury measurements in seawaterand other materials using stannous chloride reduction and two-stage goldamalgamation wi th gas phase detection . M ari ne Chemi stry 20 : 227-243.

50



Gilmour, C.C., E.A. Henry, and R. Mitchell. 1992. Sul fate stimu lation of mercurymethylation in freshwater sediments. Envi r on. Sci. Technol . 26 (11): 2281-2287.

Gilmour, C. C. and E. A. Henry. 1991. Mercury methylation in aquatic systemsaffected by acid deposit ion. E nvir onmental Pollu tion 71 (2-4): 131-169.

Gilmour, C. C. and Capone, D. G. 1987. Relationship between H g methylation andth e sul fur cycle in estu arine sediments. EO S 68 :1718.

Greib, T.M., C.T. Dri scoll, S. P. Gloss, C.L. Schofield, G.L. Bowie, and D.B. Porcella.1990. Factors affecting mercury accumu lation in fi sh in th e upper Michiganpeninsula. Envir onmental Toxi cology and Chemi stry 9 :919-930.

Hall, A.S., F.M. Teeny, and E.J. Gaugli tz. 1976a. Mercury in fish and shell fish of the

northeast Pacif ic. II . Sablefish, Anoplopoma fim bri a . Fisher y Bull eti n 74 :791-797.

Hall , A.S., F.M. Teeny, L.G. Lewis, W.H. Hardman, and E.J. Gaugl itz, Jr. 1976b.Mercury in fish and shell fish of the nor th east Pacific. I. Pacific Halibut ,H i ppogl ossus stenolepi s . Fisher y Bull eti n 74 :783-789.

Hansen, C. T., C. O. Nielsen, R. Dietz, and M. M. Hansen. 1990. Zinc, cadmium,mercury and selenium in Minke Wh ales, Belugas and Narwh als from WestGreenland. Polar Biology 10 :529-539.

Hansen, D. J. 1989. U.S. Environmental Protection Agency regulations and crit eriafor mercury in w ater. Sum mary presentation to the coordination t eam. In:M ercury in the M ari ne Envir onment . Work shop proceedings. U.S. Dept. Interi or,Min eral Management Service, Anchorage, Alaska. OCS Stu dy M MS 89-0049.

Hara, T.J., Y.M.C. Law, and S. McDon ald. 1976. Effects of mercury and copper onthe olfactory response in rainbow t rout ( O ncorhyn chus myk i ss ). J Fi sh Res Bd Ca n

33 :1568-1573.

Heisinger, F. J. and W. Green. 1975. Mercur ic chlori de uptake by eggs of th e ri cefish and resul ting t eratogenic effects. Bul l. Envir on. Conta m. Toxicol. 14 :665-673.

Hil l, W.R., A.J. Stewart, and G.E. Napoli tano. 1996. Mercury speciation andbioaccumu lation in loti c primary producers and pr imary consumers. Ca n. J. Fish.

Aqu at . Sci. 53 :812-819.

51



Hin es, M. E., S. L. Knollm eyer, and J.B. Tugel. 1989. Sulfate reduction and othersedimentary biogeochemistry in a northern New England salt marsh. Limnol .

O cean ogr. 34 (3): 578-590.

Hi ntelmann, H., P. M. Welbou rn, and R. D. Evans. 1995. Bindin g of meth ylmercurycompounds by h umic and fulvic acids. Water, Ai r, and Soil Pollu ti on 80 :1031-1034.

Hoff, R., H. Curl, Jr., J. Farr , and N. Beckvar. 1994. Empi r e Kn i ght: Assessi ng

envir onmental ri sk . NOAA Technical Memorandum NOAA ORCA 81. Seatt le:Hazardous Materials Response and Assessment Division, National Oceanic andAtmospheric Administration. 31pp.

Holden, A. V. 1978. Pollu tants and seals-A review. M amm al Rev. 8 (1-2):53-66.

Horvat, M. 1991. Determi nation of methylmercury in biological certi fied referencematerials. Water, Ai r, and Soil Pollu ti on 56 :95-102.

Huckabee, J., J. Elwood, and S. Hildebrand. 1979. Accumu lati on of mercu ry infreshwater biota. In: Nriagu (ed.) The Biogeochemi str y of M ercur y i n th e

Environment . pp 277-302. New York: Elsevier/North-Holland Biomedical Press1979.

Hu ghes, W. L. 1957. A physicochemical rationale for th e biological activ ity of

mercury and it s compoun ds. An n. N ew Yor k Acad. Sci . 65 : 454-460.

Jackson, T.A. 1991. Biological and environm ental cont rol of mercury accumu lationby f ish in lakes and reservoirs of nor th ern Manitoba, Canada. Ca n. J. Fi sh. Aqu at .

Sci . 48 :2449-2470.

Jackson, T. A. 1986. Methyl mercury l evels in a pollut ed prair ie river-lake system:seasonal and site specific variations, and the dominant influence of trophicconditions. Can ad i an Jour na l of Fisher i es an d A quat i c Sci ences 43 :1873-1877.

Jackson, T. A. 1987. Methylation, demethy lation, and bio-accumu lation of mercur yin lakes and reservoirs of northern Manitoba, with particular reference to effects of environmental changes caused by th e Chu rchil l-Nelson River diversion. In:Sum mar y Report, Canad a-M ani toba Agreement on the Stud y and M oni tori ng of

M ercur y in the Chur chi ll Ri ver D i versi on . Ott awa: Governments of Canada andManitoba.

52



Jackson, T. A. 1988. Accumulation of mercury by plank ton and benthi cinvertebrates in riverine lakes of northern Manitoba (Canada): Importance of regionally and seasonally varying environmental factors. Canadi an Journal of

Fisher i es an d Aqu at i c Sciences 45 :1744-1757.

Jackson, T. A. 1989. The influence of clay minerals, oxides, and hu mic matter onthe methylation and demethylation of mercury by micro-organisms in freshwaterenvironments. Appli ed O rganom etall i c Chemi stry 3 :1-30.

Jernelov, A. 1968. Laboratory Experim ents regardi ng the conversion of mercuryinto i ts different forms of occurrence 1. Vatten 24 (1):53-56. Translation by CanadaDept . Sed. State Transl. Bur..

Joiri s, C. R., L. Holsbeek, J. M. Bouquegneau, and M . Bossicart . 1991. Mercurycontamination of the harbour porpoise Phocoena phocoena and other cetaceansfrom the North Sea and th e Kattegat. Wat. Air Soil Pollu t. 56 : 283-293.

Julshamn, K. O. Ringdal, and O. R. Braekkan. 1982. Mercury concentrati on in l iverand mu scle of Cod ( Gadu s morhua ) as an evidence of migration between waterswit h d ifferent levels of mercury. Bull. Envir onm. Contam. Toxicol. 29 :544-549.

Julshamn, K., A. Andersen, O. Ringdal, and J. Mork ore. 1987. Trace elements in takein th e Faroe Islands, I. Element levels in edible parts of Pilot Wh ales ( Globicephalus

meleanus ). Sci . Total Envir on. 65 :53-62.

Kelly , C.A., J.W.M. Rudd, V.L. St. Louis, and A. Heyes. 1995. Is total mercuryconcentration a good predictor of m ethyl mercury concentration in aquaticsystems? Water, Ai r, and Soil Pollu ti on 80 :715-724.

Kih lstrom, J. E. and L. Hu lth. 1972. The effect of phenylmercur ic acetate upon th efrequency of hatching in the zebrafish. Bull . Envir on. Conta m. Toxi col. 7 :111.

Kobayashi, N. 1984. Marine ecotoxicological testing wi th echinoderms. In : G.Persoone, E. Jaspers, and C. Claus (Eds.), Ecotoxi cologi cal Testi ng for the ma r i ne

Environment . Bredene, Belgium: State University Ghent and Insti tu te Mar. Scient.Res. pp. 341-381.

53



Kopfler, F. C. 1974. The accumu lation of organic and inorganic mercurycompounds by t he eastern oyster ( Cr assostr ea vi r gin i ca ). Bull. Envi ron. Contam.

Toxi col. 11 :275-280.

Korth als, E. T and M. R. Winfrey. 1987. Seasonal and spati al variati ons in mercurymethy lation and demethylation in an oligotrophic lake. Applied an d

Envir onmental M icrobiology 53 :2397-2404.

Langston, W. J. 1990. Chapter 7: Toxic effects of metals and the incidence of metalpol lu tion in marin e envi ron ments. In : R. W. Furness and P. S. Rainbow (Eds.),H eavy Metals i n the M ar i ne Environ ment. pp. 101-122. Boca Raton , Florida: CRCPress, Inc.

Langston, W. J. 1986. Metals in sediments and benthic organisms in the MerseyEstuary. Estu ar i ne, Coastal an d Shelf Science 23 :239-261.

Langston , W. J. 1982. The distr ibu tion of mercury in Briti sh estu arine sedimentsand its availability to deposit-feeding bivalves. J. M ar . Biol . Ass. U.K . 62 : 667-684.

Lasorsa, B. and S. Allen-Gil . 1995. The methylmercury to total mercury ratio inselected marine, freshwater, and terrestrial organisms. Water, Ai r, and Soil Poll uti on

80 :905-913.

Leah, R.T., S.J. Evans, and M.S. Johnson. 1992. Mercury in flounder (Platichthysflesus L.) from estuaries and coastal waters of the north-east Irish Sea.Envir onmental Polluti on 75 :317-322.

Lenka, M., K.K. Panda, and B. B. Panda. 1990. Stu dies on the abili ty of waterhyacinth (Eichlornia crassipes) to bioconcentrate and biomonitor aquatic mercury.Envir on. Pollu t. 66 : 89-99.

Leonzio, C., S. Focardi , and C. Fossi. 1992. Heavy metals and seleni um in stranded

dolph ins of the Northern Tyr rhenian (NW M editerranean).Sci . Total Envir on.

119 :77-84.

Lindberg, S. E. and R.C. Harri ss. 1974. Mercury-organi c matter associati ons inestu arine sediments and in tersti tial water. Envi r . Sci . Tech. 8 (5):459-462.

54



Lindqvist, O. ed. 1991. Mercury in th e Swedish environment: Recent research oncauses, consequences and corrective meth ods. Water, Ai r, and Soil Poll uti on 55 (1-2). Special Issue. 261pp.

Long, E. R., D. D. MacDonald, S. L. Smith, and F. D. Calder. 1995. Incidence of adverse biological effects within ranges of chemical concentrations in marine andestuarine sediments. Envir onmental M anagement 19 (1):81-97.

Long, E. R. and D. D. MacDonald. 1992. Nati onal Status and Trends ProgramApproach. In: Sedi ment Classi fi cati on M ethods Compendi um . EPA 823-R-92-006.EPA Office of Water (WH-556). Washin gton , DC.: U.S. Env ironmental ProtectionAgency.

Luoma, S.N. 1977. The dynamics of biologically available mercury in a smallestuary. Estu ar i ne Coast. M ar . Sci. 5 :643-652.

Major, M.A., D.H. Rosenblatt and K.A. Bostian. 1991. The octanol/water part it ioncoefficient of methylm ercuric chloride and methylm ercuric h ydroxide in purewater and salt solu tions. Envir on. Toxi col. Chem. 1 0:5-8.

Mason, R.P., J.R. Reinfelder, and F.M.M. Morel. 1996. Uptake, toxicity, and t rophictransfer of mercury in a coastal diatom. Envi r on. Sci. Techn ol. 30 :1835-1845.

Mason, R.P., K.R. Rolfhus and W.F. Fit zgerald . 1995a. Methylated and elementalmercury cycling in surface and deep ocean waters of the North Atlantic. Water, Ai r,

and Soil Polluti on 80 : 665-677.

Mason, R.P., J.R. Reinfelder, and F.M.M. Morel. 1995b. Bioaccumulation of mercur yand methylmercury. Water, Ai r, and Soil Poll uti on 80 :915-921.

Mathers, R. and P. Johansen. 1985. The effects of feeding ecology on mercuryaccumu lation in walleye ( Sti zostedi on vit r eum ) and pik e (Esox lu ci us ) in Lake Sim coe.Canad i an Jour nal of Z oology 63

: 2006-2012.Matida, Y., H. Kumada, S. Kimura, Y. Saiga, T. Nose, M. Yokote, and H. Kawatsu.1971. Toxicity of mercury compounds to aquatic organisms and accumu lation of the compounds by the organisms. Bul l. Freshw at er Fi sh. Res. La b. (Tok yo) 21 :197-227.

55



McGreer, E. R. 1979. Sublethal effects of heavy metal cont aminated sediments onthe bivalve M acoma balthi ca (L). M ar . Pollu t. Bull. 10 :259.

McKenney, C. L., Jr. and J. D. Costl ow, Jr. 1981. The effects of salin ity and m ercur yon developing megalopae and early crab stages of the blue crab Cal li nectes sapi du s

Rathbu n. In . F. J. Vernberg, A. Calabrese, F. P. Thurberg, and W. B. Vern berg (Eds.),Biological M onitori ng of M ari ne Pollutants . pp. 241-262. New York: Academic Press.

McKim, J.M., G. F. Olson, G. W. Hol combe, and E.P. Hunt . 1976. Long-term effectsof methylmercuri c chloride on three generations of brook t rout ( Salvelinus

font inal is ): Toxicity , accumu lation, distri but ion, and elim ination . Jour na l Fi sheri es

Resear ch Boar d of C an ad a 33 :2726-2739.

Meili , M.. 1995. Limi ng effects on mercury concentrations in f ish. In: L. Henr iksonand Y. W. Brodin (eds). Lim in g Acid ifi ed Sur . Waters . p. 383-398. Berli n: Spri nger.

Mierle, G., and R. Ingram. 1991. The role of hu mic substances in the mobi li zationof mercury from watersheds. Water, Ai r, and Soil Pollu ti on 56 :349-357.

Miskimmi n, B. M., J. W. M. Rudd, and C. Kelly. 1992. Influence of dissolved organiccarbon, pH, and microbial respiration rates on m ercury methylation anddemethylation in lake water. Can. J. Fi sh. Aqu at . Sci. 49 :17-22.

Møhlenberg, F. and H.U. Rii sgård. 1988. Partit ion ing of inorganic and organicmercury i n cockles Cardi um edule (L.) and C. Glaucum (Bruguiere) from achronically polluted area: in flu ence of size and age. Envir on. Pollu t. 55 :137-148.

Nicoletto, P. and A. Hendricks. 1987. Sexual differences in accumu lation of mercury i n four species of centrarchid f ishes. Canad i an Jour nal of Z oology 66 :944-949.

Ni imi, A.J. and G.P. Kissoon. 1994. Evaluation of th e crit ical body bur den concept

based on in organic and organic mercury toxicity to rainbow trout (Oncorhynchus

mykiss ). Ar ch. Envir on. Conta m. Toxicol. 26 :169-178.

Nishimura H., and M . Kum agai. 1983. Mercury poll ut ion of fi shes in M inamata Bayand surroundi ng water: analysis of path way of mercury. Water, Ai r, and Soil

Polluti on 20 :401-411.

56



Olson, B.H. and R.C. Cooper. 1976. Comparison of aerobic and anaerobicmeth ylation of mercuric chlor ide by San Francisco Bay sediments. Wa ter Res. 10 :113-116.

Olson, K R., K. S. Squ ibb, and R. J. Cousins. 1978. Tissue uptake, subcellulardistribu tion, and metabolism of 14 CH3HgCl and CH 3203 HgCl by rainbow trou t,

Salm o gair dn eri . J. Fi sh. Res. Boar d Ca n . 35 :381-390.

Parks, J. W., A. Lutz, and J. A. Sutton. 1989. Water column m ethylmercury in theWabigoon /English River-Lake System: Factors contr oll ing concentration, speciation,and net production . Can ad i an Jour na l of Fisher i es an d Aqua ti c Sci ences 46 :2184-2202.

Passow, H., A. Rothstein , and T. Clark son. 1961. The general pharmacology of th eheavy metals. Phar ma col. Rev. 13 :185-224.

Pentreath , R.J. 1976a. The accumul ation of organic mercury f rom sea water by th eplaice, Pleur on ectes pl at essa L. Journ al of Experi mental M ar i ne Biology and Ecology

24 :121-132.

Pentreath , R.J. 1976b. The accumul ation of inorganic mercury from sea water byth e plaice, Pleur on ectes pl at essa L. Jour nal of Experi mental M ar i ne Biology and

Ecology 2 4 :103-119.

PTI. 1991. Onondaga Lake RI/FS Work Plan. PTI Env ironmental Services, Bellevue,Washington.

PTI. 1988. Bri efi ng r eport to the EPA Sci ence Ad visory Board : The Appar ent Effects

Thr eshold a ppr oach . Seatt le: Env ironmental Prot ection Agency, Region 10, Office of Puget Sound. 57 pp.

Rada, R. G., J. G. Wiener, M. R. Winfrey, D. E. Powell . 1989a. Recent i ncreases in

atmospheric deposit ion of mercury to north -central Wi sconsin lakes inferred fromsediment analyses. Ar ch. Envir on. Conta m. Toxicol. 18 :175-181.

Rada, R. G., J. E. Fin dley, and J. G. Wiener. 1989b. Env ir onmental fate of mercurydischarged into th e upper Wisconsin River. Water, Air , and Soil Pollu ti on 29 :57-76.

57



Rada, R. G., J. E. Fin dley, and J. G. Wiener. 1986. Env ir onmental fate of mercurydischarged into th e upper Wisconsin River. Water Ai r Soil Pollu t. 29 :57-76.

Ramlal, P. S., J.W.M. Rudd, A. Furu tani, L. Xun. 1985. The effect of pH on m ethylmercury production and decompositi on i n lake sediments. Canadi an Journal of

Fisher i es an d Aqu at i c Sciences 4 2: 685-692.

Regnell , O. 1994. The effect of pH and dissolved oxygen levels on methylation andparti tioning of m ercury i n freshwater m odel systems. Envir onmental Polluti on 84 :7-13.

Rehnberg, B.C. and C.B. Schreck. 1986. Acute metal toxi cology of olfaction in cohosalmon: behavior , receptors, and odor-metal complexation. Bull. Envi ron . Contam.

Toxi col. 36 :579-586.

Reigel, D. V. 1990. The di stri buti on an d behavior of mercur y i n sedi ments and

ma r i ne or gani sms of Lavaca Bay, Texas . Coll ege Station, Texas: The Texas A&MUniversity. Masters Thesis.

Richardson, G.M. and D.J. Curr ie. 1996. Does acid precipit ation exacerbate th eproblem of fi sh m ercury contamination? SETAC N ews 16 (2): 14.

Riisgård , H.U. and P. Famme. 1988. Distr ibu tion and mobi li ty of organic and

inorganic m ercury in flou nder, Platichthys flesus, from a chronically pol lu ted area.Toxi col. Envi r on. Chem. 16 :219-228.

Riisgård , H. U. and P. Famme. 1986. Accumulation of in organic and organicmercury in shrimp, Cran gon crangon . M ari ne Polluti on Bulletin 17 :255-257.

Rii sgård, H.U., T. Kiorboe, F. Møhlenberg, I. Drabk , and P. Pheiffer Madsen. 1985.Accum ulation , elimination and chemical speciation of mercury in the bivalvesMytil us edul is and Macoma balth ica. M ar . Biol. 86 :55-62.

Riisgård , H. U. and S. Hansen. 1990. Biomagnification of mercury i n a marinegrazing food-chain: algal cells Phaeodactylu m tri corn utu m , mussels M ytilus edul is

and flou nders Plat i chthys fl esus stu died by m eans of a stepwise-reduction -CVAAmethod. M ar i ne Ecology Pr ogress Ser i es 62 :259-270.

58



Rodgers, D.W. and F.W.H. Beamish. 1982. Dynamics of dietary methylmercu ry inrainbow trout, Salmo gairdneri. Aquati c Toxicology 2 : 271-290.

Rodgers, D.W. and F. W. H. Beami sh. 1981. Uptake of waterborn e methylmercu ryby rainbow trou t (Salm o gair dn eri ) in relation to oxygen consum ption andmethylmercury concentration. Can ad i an Jour na l of Fi sher i es an d A quat i c Sci ences

38 (11): 1309-1315.

Roesijadi, G., A.S. Drum, and J.R. Bridge. 1981. Mercury in m ussels of Bell in ghamBay, Washi ngton (U.S.A.): th e occurrence of mercury-bindi ng proteins. In:Vernberg, F.J., Calabrese, A. Thurberg, F.P. and W.B. Vernberg (Eds.), Biological

M onitor ing of M ari ne Pol lutants . pp. 357-376. New York: Academy Press.

Rubinstein , N.I., E. Lores, and N.R. Gregory. 1983. Accumu lation of PCBs, mercuryand cadmiu m by N er ei s vir ens , M ercenar i a mercenar i a and Pala emon etes pu gi o fromcontaminated harbor sediments. Aquati c Toxicology 3 :249-260.

Rudd, J. W. M. and M. A. Turner. 1983. The Engl ish-Wabigoon River System:V. Mercury and selenium bioaccum ulation as a function of aquatic primaryproductivity. Can ad i an Jour na l of Fisheri es an d A quat i c Sciences 40 :2251-2259.

Rudd, J. W. M., M. A. Turn er, A. Furu tani , A. L. Swi ck, and B. E. Townsend. 1983.

The English-Wabigoon River System: I. A synth esis of recent research with a viewtowards mercury amelioration. Can ad i an Jour na l of Fi sher i es an d A quat i c Sciences

40 :2206-2217.

Saouter, E., L. Hare, P. G. C. Campbell, A. Boudou, and F. Ribeyre. 1993. Mercuryaccumu lation in th e burrowing mayfly H exageni a ri gida (Ephemeroptera) exposedto CH 3HgCl or HgCl2 in water and sediment . Wat . Res. 27 (6):1041-1048.

Saouter, E. F. Ribeyre, A. Boudou, and R. Maury-Brachet. 1991. H exageni a ri gida

(Ephemeroptera) as a biological m odel in aquatic ecotoxicology: experimentalstu dies on mercury transfers from sediment . Envir onmental Polluti on 69 :51-67.

Saroff, S. T. 1990. Proceedi ngs of the On ond aga La ke Remedi ati on Con fer ence .Bolton Landing, New York: New York State Department of Law and New York StateDepartment of Environmental Conservation. 193 pp.

59



Sastry, K. V. and K. Sharma. 1980. Effects of mercur ic chlori de on the acti vi ti es of brain enzymes in a freshw ater teleost, Ophi ocephalu s (Channa) pu nctatus . Arch.

Envir on. Conta m. Toxi col. 9 :425-430.

Scherer, E., F. A. J. Arm strong, and S. H. Nowak. 1975. Effects of m er cur y-

contam i nated di et u pon w all eyes Sti zostedi on vi treum vitr eum (M i tchell ) . Fish. Mar.Serv. Tech. Rep. No. 597. Win nipeg, Manitoba: Fisheries Marin e Service. 21 pp.

Schindler, D.W., S.E. Bayley, P.J. Curtis, B.R. Parker, M.P. Stanton and C.A. Kelly.1992. Natu ral and man-caused factor s affectin g the abundance and cycling of dissolved organic substances in precambrian shield lakes. H ydrobiologia 229 :1-21.

Schi ntu, M., F. Jean-Caurant , and J. C. Amiard . 1992. Organomercu rydetermi nation in biological reference material: application to a study on mercuryspeciation in marine mammals off the Faröe Islands. Ecotoxi cology an d

Envir onm ent al Safety 24 :95-101.

Sharp, J. R. and J. M. Neff. 1980. Effects of th e duration of exposure to mercu ricchloride on the embryogenesis of th e estu arine teleost, Fun du lus heteroclit us , M a r.

Envi r on . Res. 3 : 195-213.

Shoichi, O. and S. Sokichi . 1985. The 1-octanol/water part it ion coefficient of mercury. Bul l. Chem. Soc. Jap an . 58 :3401-3402.

Slooff, W., P.F.H. Bont, M. van Ewijk , and J.A. Janu s. 1991. Exploratory r eport

mercury . Report no. 710401006. Bil th oven, The Netherlands: National Institute of Public Health and Environmental Protection .

Snarski , V. M. and G. F. Olson. 1982. Chronic toxicity and bi oaccumulation of mercuric chloride in the fathead minnow ( Pim ephal es pr omelas ). Aquati c Toxicology

2:143-156.

Spry, D. J. 1991. Metal bioavailabili ty and toxi city to fish in low-alkalini ty lakes: acritical review. Environ . Pollu t. 71 :243-304.

Spry, D. J. and J. G. Wiener. 1991. Metal bioavailabili ty and toxicity to fi sh in low-alkalinity lakes: A critical review. Envir onmental Polluti on 71 :243-304.

60



St. Lou is, V.L., J.W.M. Rudd, C.A. Kell y, K.G. Beaty , N.S. Bloom and R.J. Flett . 1994.Importance of wetlands as sour ces of m ethyl m ercury to boreal forest ecosystems.Ca n. J. Fi sh. Aqu at . Sci. 51 :1065-1076.

Stromgren, T. 1982. Effect of heavy metals (Zn, Hg, Cu, Cd, Pb, Ni ) on the lengthgrowth of M ytilus edul is . M ar . Biol. 72 :69-72.

Surma-Aho, K. and J. Paasivir ta. 1986. Organic and inorganic mercury in th e foodchain of some lakes and reservoir s in Finland. Chemospher e 15 (3):353-372.

Swartz, R. C., P. F. Kemp, D. W. Schults, and J. O. Lamberson. 1988. Effects of mixtu res of sediment contaminants on th e marin e infaunal amphipod, Rhepoxynius

abronius . Envir onmental Toxi cology and Chemi stry 7 :1013-1020.

Syversen, T. 1977. Effects of methylmercury on in v ivo protein synthesis inisolated cerebral and cerebellar neurons. N eur opathol. Appl. Neurobi ol. 3 :225-236.

Szefer. P., W. Czarnowski , J. Pempkowiak, and E. Holm. 1993. Mercur y and majoressential elements in seals, penguins, and other representative fauna of th eAntarctic. Ar ch. Envir on. Conta m. Toxicol. 25 :422-427.

Tessier, L., G. Vail lancou rt , and L. Pazdern ik . 1994. Temperatu re effects oncadmium and mercury ki netics in freshwater moll uscs under laboratory conditi ons.

Ar ch. Envir on. Cont am . Toxi col. 2 6:179-184.

Tetra Tech, Inc. 1988. H ealt h r i sk a ssessment of chemi cal conta mi na ti on i n Puget

Sou nd seaf ood . Seatt le: Environmental Prot ecti on Agency, Region 10, Office of Puget Sound. 102 pp + appendices.

Thain, J. E. 1984. Effects of mercury on the prosobranch mol lu sc Crepidula

fornicata : Acute lethal toxicity and effects on growth and reproduction of chronicexposure. M ar . Envi r . Res. 12 :285-309.

Thompson, D. R. 1990. Metal levels in marin e vert ebrates. In: W. D. Furness andP. S. Rainbow (Eds.), H eavy Metals i n the M ar i ne Envir onment . pp. 144-182. BocaRaton , Flori da: CRC Press.

61



U.S. Environmental Protection Agency (EPA). 1985. A mbient wa ter quali ty cri teri a

for mercur y - 1984 . U.S. EPA 440/5-84-026. Washington, D.C.: Office of Water.136 pp.

U.S. Environmental Protection Agency (EPA). 1996. Update: National li sting of fi shand wi ldli fe consumption advi sories. EPA Fact Sheet EPA-823-F-96-006.Washi ngton, D.C.: Office of Water.

U.S. Food and Dru g Administration (FDA). 1984. Action level for methyl mercuryin fish. Federa l Regi ster 4 9 :45663- . November 19, 1984.

Wagemann , R., N. B. Snow, A. Lutz, and D. P. Scott. 1983. Heavy metals in ti ssuesand organs of the narwhal ( M onodon monoceros ). Ca n. J. Fi sh. Aqu at . Sci. 40 (Suppl.2):206-214.

Weber, J. H.. 1993. Review of possible path s for abiot ic methylation of m ercury (II)in t he aquatic envi ronm ent. Chemospher e 26 (11):2063-2077.

Weis, J. S. and P. Weis. 1977. Effects of heavy metals on development of thekillifish,Fund ul us heter ocli tus . J. Fi sh. Bi ol . 11 :49-54.

Weis, P., and J.S. Weis. 1978. Methylmercury inhi bit ion of fin renereration in fi shesand its in teraction with salin ity and cadmium. Estua r i ne Coastal M ar . Sci . 6 :327-

334.

Weis, J. S. and P. Weis. 1984. A rapid change in m ethylmercury tolerance in apopulation of k illi fish,Fun du lus heteroclit us , from a golf course pond. M a r i n e

Envir onm ent al Resear ch 13 :231-245.

Weis, J. S,. and P. Weis. 1989. Effects of env ironmental poll utants on early fi shdevelopment. Rev. Aqu at . Sci . 1 :45-73.

Weis, J. S., P. Weis, and M. Heber. 1982. Variation in response to methylmercu ry bykillifish (Fun du lu s heteroclitu s ) embryos. In : J.G. Pearson, R.B. Foster, and W.E.Bishop (eds.), Aqua ti c Toxi cology and H azar d Assessment: Fifth Con fer ence . ASTMSTP 766. pp. 109-119. Phil adelphia: American Society for Testi ng and Materials.

62





Xun, L., N.E.R. Campbell, and J.W.M. Rudd. 1987. Measurements of specific rates of net methy l mercury production in the water colum n and sur face sediments of acidified and circumneutral lakes. Ca n. J. Fi sh. Aqu at . Sci. 44 :750-757.

Zil li oux, E. J., D. B. Porcell a, and J. M. Benoit. 1993. Mercury cycli ng and effects infreshwater wetland ecosystems. Envi ron mental Toxicology and Chemi stry 1 2 :1-20.

Date post:	02-Jun-2018
Category:	Documents
Upload:	rgsir2014
View:	218 times
Download:	0 times

89 Rpt Mercury Aquatic Habitats

Documents