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United States Environmental Protection Agency Office of Water 4305 EPA-823-F-01-011 June 2001 Fact Sheet Mercury Update: Impact on Fish Advisories Mercury is distributed throughout the environment from both natural sources and human activities. Methylmercury is the main form of organic mercury found in the environment and is the form that accumulates in both fish and human tissues. Several instances of methylmercury poisoning through consumption of contaminated food have occurred; these resul
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  1 United StatesEnvironmental ProtectionAgencyOffice of Water4305EPA- 823-F-01-011 June 2001 Fact SheetMercury Update: Impact on Fish Advisories Mercury is distributed throughout the environment from both natural sources and human activities. Methylmercury is the main form of organic mercury found in the environment and is the form that accumulates in both fish and human tissues. Several instances of methylmercury poisoning through consumption of contaminated food have occurred; these resulted in central nervous system effects such as impairment of vision, motor in-coordination,loss of feeling, and, at high doses, seizures, very severe neurological impairment, and death. Methylmercury has also been shown to be a developmental toxicant, causing subtle to severe neurological effects. EPA considers there is sufficient evidence for methylmercury to be considered a developmental toxicant, and to be of concern for potential human germ cell mutagenicity. As of December 2000, 41 states have issued 2,242 fish advisories for mercury. These advisories inform the public that concentrations of mercury have been found in local fish at levels of public health concern. State advisories recommend either limiting or avoiding consumption of certain fish from specific waterbodies or, in some cases, from specific waterbody types (e.g., all freshwater lakes or rivers). Sources of Mercury in the Environment Mercury is found in the environment in the metallicform and in different inorganic and organic forms.Most of the mercury in the atmosphere is elementalmercury vapor and inorganic mercury; most of themercury in water, soil, plants, and animals isinorganic and organic mercury (primarily methyl-mercury).Mercury occurs naturally and is distributedthroughout the environment by both naturalprocesses and human activities. Solid wasteincineration and fossil fuel combustion facilitiescontribute approximately 87% of the emissions ofmercury in the United States. Other sources ofmercury releases to the air include mining andsmelting, industrial processes involving the use ofmercury such as chlor-alkali production facilitiesand production of cement.Mercury is released to surface waters from naturallyoccurring mercury in rocks and soils and fromindustrial activities, including pulp and paper mills,leather tanning, electroplating, and chemicalmanufacturing. Wastewater treatment facilities mayalso release mercury to water. An indirect source ofmercury to surface waters is mercury in the air; it isdeposited from rain and other processes directly towater surfaces and to soils. Mercury also may bemobilized from sediments if disturbed (e.g.,flooding, dredging).Sources of mercury in soil include direct applicationof fertilizers and fungicides and disposal of solidwaste, including batteries and thermometers, tolandfills. The disposal of municipal incinerator ashin landfills and the application of sewage sludge tocrop land result in increased levels of mercury insoil. Mercury in air may also be deposited in soil andsediments. Fate and Transport of Mercury The global cycling of mercury is a complex process.Mercury evaporates from soils and surface waters tothe atmosphere, is redeposited on land and surfacewater, and then is absorbed by soil or sediments.After redeposition on land and water, mercury iscommonly volatilized back to the atmosphere as agas or as adherents to particulates.Mercury exists in a number of inorganic and organicforms in water. Methylmercury, the most commonorganic form of mercury, quickly enters the aquaticfood chain. In most adult fish, 90% to 100% of theThe purpose of this fact sheet is to summarize current information on sources, fate and transport, occurrencein human tissues, range of concentrations in fish tissue, fish advisories, fish consumption limits, toxicity, andregulations for mercury. The fact sheets also illustrate how this information may be used for developing fishconsumption advisories. An electronic version of this fact sheet and fact sheets for dioxins/furans, PCBs,and toxaphene are available at http://www.epa.gov/OST/fish . Future revisions will be posted on the web asthey become available.  2mercury is methylmercury. Methylmercury is foundprimarily in the fish muscle (fillets) bound toproteins. Skinning and trimming the fish does notsignificantly reduce the mercury concentration in thefillet, nor is it removed by cooking processes.Because moisture is lost during cooking, theconcentration of mercury after cooking is actuallyhigher than it is in the fresh uncooked fish.Once released into the environment, inorganicmercury is converted to organic mercury(methylmercury) which is the primary form thataccumulates in fish and shellfish. Methylmercurybiomagnifies up the food chain as it is passed froma lower food chain level to a subsequently higherfood chain level through consumption of preyorganisms or predators. Fish at the top of theaquatic food chain, such as pike, bass, shark andswordfish, bioaccumulate methylmercuryapproximately 1 to 10 million times greater thandissolved methylmercury concentrations found insurrounding waters.In 1984 and 1985, the U.S. Fish and Wildlife Servicecollected 315 composite samples of whole fish from109 stations nationwide as part of the NationalContaminant Biomonitoring Program (NCBP). Themaximum, geometric mean, and 85 th percentileconcentrations for mercury were 0.37, 0.10, and 0.17ppm (wet weight), respectively. An analysis ofmercury levels in tissues of bottom-feeding andpredatory fish using the data from the NCBP studyshowed that the mean mercury tissue concentrationof 0.12 ± 0.08 ppm in predatory fish species (e.g.,trout, walleye, largemouth bass) was significantlyhigher than the mean tissue concentration of 0.08 ±0.06 ppm in bottom feeders (e.g., carp, white sucker,and channel catfish).Mercury, the only metal analyzed as part of EPA’s1987 National Study of Chemical Residues in Fish(NSCRF), was detected at 92% of 374 sitessurveyed. Maximum, arithmetic mean, and medianconcentrations in fish tissue were 1.77, 0.26, and0.17 ppm (wet weight), respectively. Mean mercuryconcentrations in bottom feeders (whole bodysamples) were generally lower than concentrationsfor predator fish (fillet samples) (see Table 1). Mostof the higher tissue concentrations of mercury weredetected in freshwater fish samples collected in theNortheast.In 1998, the northeast states and eastern Canadianprovinces issued their own mercury study, includinga comprehensive analysis of mercuryconcentrations in a variety of freshwater sportfishcollected from the late 1980s to 1996. Top levelpredatory fish such as walleye, chain pickerel, andlarge and smallmouth bass were typically found toexhibit the highest concentrations, with mean tissueresidues greater than 0.5 ppm and maximumresidues exceeding 2 ppm. One largemouth basssample was found to contain 8.94 ppm of mercury,while a smallmouth bass sampled contained 5ppm. Table 2 summarizes the range and the meanconcentrations found in eight species of sportfishsampled.Table 3 provides national ranges and meanconcentrations for several species of freshwater fishcollected by states from the late 1980s to early 2001.43 states have provided EPA with 90,000 records ofchemical contaminant fish tissue data. These dataare available in the online National Listing of Fish and Wildlife Advisories  (U.S. EPA 2001b) atwww.epa.gov/ost/fish. Table 1. Mean Mercury Concentrations inFreshwater Fish a SpeciesMeanconcentration (ppm) b Bottom Feeders Carp0.11White sucker0.11Channel catfish0.09 Predator Fish Largemouth bass0.46Smallmouth bass 0.34Walleye0.52Brown trout0.14 a EPA National Study of Chemical Residues in Fish 1987; b Concentrations are reported on wet weight basis Source: Bahnick et al., 1994  . Table 2. Mercury Concentrations for Selected FishSpecies in the NortheastSpeciesMeanconcentration a (ppm)Minimum-maximumrange a (ppm)  3Largemouthbass0.510-8.94Smallmouthbass0.530.08-5.0Yellow perch0.400-3.15Eastern chainpickerel0.630-2.81Lake trout0.320-2.70Walleye0.770.10-2.04Brownbullhead0.200-1.10Brook trout0.260-0.98 a Concentrations are reported on a wet weight basis. Source: NESCAUM, 1998. Table 3. Mercury Concentrations for Selected FishSpecies in the U.S.SpeciesMeanconcentration a (ppm)Range Largemouthbass0.520.0005 - 8.94Smallmouthbass0.320.005 - 3.34Yellow perch0.250.005 - 2.14Easternchainpickerel0.610.014 - 2.81Lake trout0.270.005 - 2Walleye0.430.005 - 16NorthernPike0.360.005 - 4.4 a Concentrations are reported on a wet weight basis. Source: NLFWA, 2000. Because of the higher cost of methylmercuryanalysis, EPA recommends that total mercury ratherthan methylmercury concentrations be determined instate fish contaminant monitoring programs. EPAalso recommends that the assumption be made thatall mercury is present as methylmercury in order tobe most protective of human health. Potential Sources of Exposure andOccurrence in Human Tissues Potential sources of human exposure to mercuryinclude food contaminated with mercury, inhalation ofmercury vapors in ambient air, and exposure tomercury through dental and medical treatments.Dietary intake is by far the dominant source ofexposure to mercury for the general population. Fishand other seafood products are the main source ofmethylmercury in the diet; studies have shown thatmethylmercury concentrations in fish and shellfishare approximately 1,000 to 10,000 times greaterthan in other foods, including cereals, potatoes,vegetables, fruits, meats, poultry, eggs, and milk.Individuals who may be exposed to higher thanaverage levels of methylmercury include recreationaland subsistence fishers who routinely consumelarge amounts of locally caught fish andsubsistence hunters who routinely consume themeat and organ tissues of marine mammals.Analytical methods are available to measuremercury in blood, urine, tissue, hair, and breast milk. Fish Advisories  4The states have primary responsibility for protectingtheir residents from the health risks of consumingcontaminated noncommercially caught fish. They dothis by issuing consumption advisories for thegeneral population, including recreational andsubsistence fishers, as well as for sensitivesubpopulations (such as pregnant women/fetus,nursing mothers and their infants, and children).These advisories inform the public that highconcentrations of chemical contaminants, such asmercury, have been found in local fish. Theadvisories recommend either limiting or avoidingconsumption of certain fish from specific waterbodiesor, in some cases, from specific waterbody types(such as lakes or rivers).As of December 2000, mercury was the chemicalcontaminant responsible, at least in part, for theissuance of 2,242 fish consumption advisories by 41states. Almost 79% of all advisories issued in theUnited States are at least partly due to mercurycontamination in   fish and shellfish. Advisories formercury have increased steadily, by 149% from 899advisories in 1993 to 2,242 advisories in 2000. Thenumber of states that have issued mercuryadvisories also has risen steadily from 27 states in1993 to 41 states in 2000. Advisories for mercuryincreased nearly 8% from 1999 (2,073 advisories) to2000 (2,242 advisories).Thirteen states have issued statewide advisories formercury in their freshwater lakes and/or rivers:Connecticut, Kentucky, Indiana, Maine,Massachusetts, Michigan, Minnesota, NewHampshire, New Jersey, North Carolina, Ohio,Vermont and Wisconsin. Another nine states(Alabama, Florida, Georgia, Louisiana, Maine,Mississippi, North Carolina, and Texas) havestatewide mercury advisories in effect for their coastalmarine waters. Figure 1 shows the total number offish advisories for mercury in each state in 2000 (U.S.EPA, 2001a). Fish Consumption Limits   —EPA indicated in the Mercury Study Report to Congress  (U.S. EPA, 1997)that the typical U.S. consumer was not in danger ofconsuming harmful levels of methylmercury from fishand was not advised to limit fish consumption on thebasis of mercury content. This advice is appropriatefor typical consumers who eat less than 10 grams offish and shellfish per day with mercuryconcentrations averaging between 0.1 and 0.15 ppm.At these rates of fish intake, methylmercuryexposures are considerably less than the referencedose (RfD) of 1 x 10 -4 mg/kg-d. However, eating morefish than is typical or eating fish that are morecontaminated, can increase the risk to a developingfetus.Two groups of women of childbearing age are ofconcern: (1) those who eat more than 10 grams offish a day and (2) those who eat fish with highermethylmercury levels. Ten grams of fish is a littleover one-quarter cup of tuna per week or about onefish sandwich per week. Based on diet surveys,10% of women of childbearing age eat five times ormore fish than does the average consumer. If thefish have average mercury concentrations of 0.1 to0.15 ppm, the women’s mercury exposures rangefrom near or slightly over the RfD to about twice theRfD.The second group of women of concern are thosewho eat fish with higher mercury concentrations(e.g., 0.5 ppm and higher). Examples of fish withabove average mercury levels are king mackerel,various bass species, pike, swordfish, and shark.Even women eating average amounts of fish (i.e., <10g/d) have mercury exposures near the RfD, if themercury concentration is 0.5 ppm. If women eatthese fish species and their average fish intake isbetween 40 and 70 grams/day (or about a quartercup per day), their mercury exposures would rangefrom three to six times the RfD. Consumers who eatfish with 1 ppm mercury (e.g., swordfish and shark)at the level of 40 to 70 g/d have intakes that rangefrom 6 to nearly 12 times the RfD.Some women of childbearing age in certain ethnicgroups (Asians, Pacific Islanders, and NativeAmericans) eat much more fish than the generalpopulation. Because of the higher amounts of fish intheir diets, women in these ethnic groups need tobe aware of the level of mercury in the fish they eat.The RfD is not a “bright line” between safety andtoxicity; however, there is progressively greaterconcern about the likelihood of adverse effectsabove this level. Consequently, people are advisedto consume fish in moderate amounts and beaware of the amount of mercury in the fish they eat.For some populations, such as pregnant women,nursing mothers, and young children, some stateshave issued either no consumption advisories or restricted consumption advisories for methyl-mercury. Additional information on calculatingspecific limits for these sensitive populations isavailable in EPA’s Guidance for AssessingChemical Contaminant Data for Use in FishAdvisories, Volume 2, Section 3 (U.S. EPA 2000).Table 4 shows the recommended monthly fishconsumption limits for methylmercury in fish for fishconsumers based on EPA’s default values for riskassessment parameters. States may select otherscientifically defensible values for developing fish
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