Methylmercury In Fish Research Articles

Necrophagy by a benthic omnivore influences biomagnification of methylmercury in fish

Omnivory has an important role in the movement of energy, nutrients, and contaminants between benthic and pelagic food webs. While top-predator fish are known to supplement a mostly piscivorous diet with benthic organisms, a more obscure benthic–pelagic coupling occurs when benthic invertebrates forage on fish carcasses, referred to as necrophagy. The combination of these two benthic–pelagic links, top-predator fish feeding on benthic organisms that have fed on dead fish, can generate a trophic feedback cycle that conserves energy and nutrients and may have implications for biomagnification of methylmercury (MeHg) in fish. We investigated the role of necrophagy by crayfish ( Procambarus clarkii), via a trophic feedback cycle, on the biomagnification of MeHg in largemouth bass ( Micropterus salmoides), a cosmopolitan top predator fish known to feed on crayfish. Controlled laboratory tests quantified the uptake of MeHg by both organisms from artificial and natural food (whole crayfish or bass tissue). Assimilation efficiency (AE) of MeHg was greater for bass fed crayfish (79 ± 0.5%) than those fed artificial food (60 ± 3%). Furthermore, AE of MeHg was greatest for largemouth bass fed crayfish that fed on MeHg-dosed dead fish (i.e., trophic feedback cycle; 94 ± 17%). A model, parameterized with results of the laboratory experiments, was used to make steady-state projections of MeHg biomagnification factors. Model projections also indicate that MeHg biomagnification would be greatest for largemouth bass from a trophic feedback cycle. These results suggest that food web ecology has an important role in determining MeHg levels in predatory fish and underscore the need for further investigation into the magnitude that necrophagy may affect MeHg biomagnification in aquatic systems.

Awareness and knowledge of methylmercury in fish in the United States

In the 1970s several states in the Great Lakes region became concerned about mercury contamination in lakes and rivers and were the first to issue local fish consumption advisories. In 2001, the Food and Drug Administration (FDA) advised pregnant women, nursing mothers, young children, and women who may become pregnant not to consume shark, swordfish, king mackerel, and tilefish and recommended that these women not exceed 12 ounces of other fish per week. In 2004, FDA reissued this advice jointly with the U.S. Environmental Protection Agency (EPA) and modified it slightly to provide information about consumption of canned tuna and more details about consumption of recreationally caught fish. Though several studies have examined consumers' awareness of the joint FDA and EPA advisory as well as different state advisories, few used representative data. We examined the changes in awareness and knowledge of mercury as a problem in fish using the pooled nationally representative 2001 and 2006 Food Safety Surveys (FSS) with sample sizes of 4482 in 2001 and 2275 in 2006. Our results indicated an increase in consumers' awareness of mercury as a problem in fish (69% in 2001 to 80% in 2006, p<.001). In our regression models, we found that in both years, parents having children less than 5 years of age were more aware of mercury in fish and knowledgeable about the information contained in the national advisories about mercury in fish ( p<.01) than other adults. In both 2001 and 2006, women of childbearing age (aged 18–45) were less aware and knowledgeable about this information than other women. However, women of all age groups had larger gains in awareness and knowledge than their male counterparts during this time. Participants' race, education, income, region, fish preparation experiences, having a foodborne illness in the past year, and risk perceptions about the safety of food were significant predictors of their awareness and knowledge.

Tracing Sources and Bioaccumulation of Mercury in Fish of Lake Baikal− Angara River Using Hg Isotopic Composition

This study presents the determination and comparison of isotopic compositions of Hg in sediments, plankton, roach, and perch of two freshwater systems in the Lake Baikal-Angara River aquatic ecosystem: the man-made Bratsk Water Reservoir contaminated by Hg from a chlor-alkali factory and the noncontaminated Lake Baikal. Isotopic ratios of biota exhibit both significant mass-independent fractionation (MIF) (Δ(199)Hg from 0.20 to 1.87‰) and mass-dependent fractionation (MDF) (δ(202)Hg from -0.97 to -0.16‰), whereas sediments exhibit high MDF (δ(202)Hg from -1.99 to -0.83‰) but no MIF. δ(15)N and δ(13)C are correlated with methylmercury in organisms from both sites, indicating bioaccumulation and biomagnification through food webs of both regions. Combining this with isotopic composition of samples shows that δ(202)Hg increases with the trophic level of organisms and also with methylmercury in fish from Lake Baikal. This study demonstrates that MIF in fish samples from Bratsk Water Reservoir allow to trace anthropogenic Hg, since fish with the highest levels of Hg in muscle have the same isotopic composition as the sediment in which anthropogenic Hg was deposited. Less contaminated fish do not exhibit this anthropogenic signature accumulating relatively lower Hg amount from the contaminated sediments. This work reveals that Hg isotopic composition can be used to track the contribution of anthropogenic sources in fish from a contaminated lake.

Welfare Effects of Food Labels and Bans with Alternative Willingness to Pay Measures

AbstractThis paper integrates several areas of the literature by more fully developing the linkage between demand estimates and the welfare effects of food labels and bans for three common survey/experimental approaches used to elicit consumer preferences. We present empirical applications related to beef cloning and methylmercury in fish where, for the same data sets, we compare each value elicitation approach in terms of the consumer surplus changes that result from two regulations. Welfare measures vary significantly across the three methodologies, but the sign of the welfare change is invariant across method.

Risk and Regulation: Methylmercury Exposure and Fish Consumption

Exposure to organic mercury (methylmercury) occurs almost universally due to ingestion via &#x0D; contaminated fish and shellfish tissue. Ultimate sources of mercury consist of air release by domestic &#x0D; industrial combustion, mining, and international mercury emissions transported via a global cycle. &#x0D; Deposition of mercury from air to surface waters results in methylation to organic methylmercury and &#x0D; bioaccumulation in the aquatic food web.&#x0D; Health effects from methylmercury exposure consist mainly of neurological and &#x0D; neurodevelopmental effects, with fetuses particularly sensitive. Thus regulation of methylmercury &#x0D; exposure has concentrated on acceptable exposure levels and reference doses aimed toward protecting &#x0D; developing fetuses. &#x0D; The risk of methylmercury exposure in humans is regulated largely by the federal government, &#x0D; especially by the Environmental Protection Agency (EPA) and the Food and Drug Administration (FDA). The EPA imposes limits on mercury emissions and seeks to research methylmercury levels in fish and humans. The EPA sets a reference dose for methylmercury exposure. The FDA conducts uses date on methylmercury levels in fish to advise consumers on how to make informed decisions regarding fish consumption.&#x0D; There are numerous shortcoming to government regulation of this issue. Further scientific &#x0D; research, improved implementation of available data and scientific conclusions, and improved public &#x0D; communication of risk would all lead to more effective treatment of the risk of methylmercury &#x0D; exposure via ingestion of fish and shellfish. This could include more effective monitoring systems of &#x0D; human and fish methylmercury levels, research into the process of bioaccumulation, and &#x0D; implementation of stricter fish labeling standards, as well as research into higher-risk subpopulations &#x0D; allowing for targeted standards and recommendations.

How good is the evidence for a favourable effect of very long chain n‐3 polyunsaturated fatty acids on cardiovascular disease?

AbstractThe evidence for beneficial effects of very long chain (VLC) n‐3 polyunsaturated fatty acids (PUFA) on cardiovascular disease (CVD) is strong because it is based on the results of adequately powered intervention trials with disease endpoints. This contrasts with the evidence for a detrimental effect of saturated fat on CVD which is weak because such studies have not been carried out. Accordingly, any set of dietary recommendations which attaches more importance to saturated fat intakes than VLC n‐3 PUFA intakes can be questioned. Despite the strength of the evidence there are practical difficulties associated with implementing the recommendation to increase intake of VLC n‐3 PUFA to 1g per day which need to be overcome. These include the acceptability of fatty fish consumption, the presence of methyl mercury in fish at the top of the food chain and declining global fish stocks.

Urine Mercury Excretion Following meso-Dimercaptosuccinic Acid Challenge in Fish Eaters

Abstract Context.—Public awareness of methylmercury in fish has caused patients to seek testing for mercury poisoning. In some patients, the diagnosis of mercury poisoning has been made based on urine mercury excretions following oral dosing of meso-dimercaptosuccinic acid (DMSA), a metal chelator. However, studies comparing urine mercury excretion following DMSA in healthy non–fish eaters with healthy fish eaters could not be located. Objectives.—To describe urinary mercury excretion before and after DMSA in healthy fish eaters and non–fish eaters, and to determine whether urine mercury excretion after DMSA would rise above baseline levels to a greater extent in fish eaters. Design.—A total of 24 healthy physicians were assigned to 1 of 3 groups based on fish consumption: non–fish eaters; 1 to 2 fish servings per week; and 3 or more servings per week. Blood mercury concentrations and 12-hour urine mercury and creatinine excretions were measured before and after oral ingestion of 30 mg of DMSA per kilogra...

Using Empirical Likelihood to Combine Data: Application to Food Risk Assessment

This article introduces an original methodology based on empirical likelihood, which aims at combining different food contamination and consumption surveys to provide risk managers with a risk measure, taking into account all the available information. This risk index is defined as the probability that exposure to a contaminant exceeds a safe dose. It is naturally expressed as a nonlinear functional of the different consumption and contamination distributions, more precisely as a generalized U-statistic. This nonlinearity and the huge size of the data sets make direct computation of the problem unfeasible. Using linearization techniques and incomplete versions of the U-statistic, a tractable "approximated" empirical likelihood program is solved yielding asymptotic confidence intervals for the risk index. An alternative "Euclidean likelihood program" is also considered, replacing the Kullback-Leibler distance involved in the empirical likelihood by the Euclidean distance. Both methodologies are tested on simulated data and applied to assess the risk due to the presence of methyl mercury in fish and other seafood.

INNOVATIVE TECHNOLOGIES: Fluorescent Probe Detects Mercury

Mercury is toxic to the nervous system and may cause memory loss, cognitive and behavioral disturbances, headaches, insomnia, peripheral nerve damage, tremors, and motor dysfunction—all problems that have been observed to disappear upon removing the source of mercury exposure, according to the International Programme on Chemical Safety. Removing the source may now become easier with a new chemical probe that gives off a bright green glow when it reacts with mercury in fish and dental amalgams. Eventually the probe could be used to detect contaminated fish at home or mercury in wastewater at dental offices. Developer Kazunori Koide, an associate professor in the University of Pittsburgh Department of Chemistry, based the probe on a simple principle taught in undergraduate organic chemistry classes: Mercury converts alkynes into ketones. Koide’s team synthesized an alkyne-based compound from commercial dichlorofluorescein. When mercury converts the alkyne into a ketone, the reaction generates a green fluorescent signal whose intensity corresponds to the amount of mercury present. “It’s a very straightforward approach,” Koide says, “yet no one ever thought to do this.” The probe performed well in real-life tests described in the 10 December 2008 issue of the Journal of the American Chemical Society. A piece of salmon about the size of a dime was first treated with an oxidizing agent to release mercury bound up as methylmercury, then was soaked in the alkyne test solution. Within 30 minutes, mercury in the sample had converted the test solution to a ketone, which produced a strong fluorescent signal. Next, the researchers soaked a thin cloth with saliva and pressed it against an extracted tooth filled with silver amalgam (which may contain up to 50% mercury) obtained from a dental clinic. When the solution was applied to the cloth, its green fluorescent signal was substantially brighter than that of a control cloth also treated with saliva but not held against the tooth. Because the sulfur-containing amino acid cysteine is known to bind tightly to mercury in fish, Koide wondered whether cysteine in sulfur-rich foods such as onions and eggs would react with mercury in dental amalgams. In another experiment, two extracted teeth containing amalgams were soaked for an hour in a cysteine solution. The filled teeth released a significant amount of mercury into the cysteine solution as compared with teeth that had been soaked in water at a temperature of 35oC. Other probes for mercury reported in the scientific literature are largely based on chemical reactions between mercury and sulfur groups. However, sulfur-based tests are prone to oxidation during storage, making them impractical for environmental testing. The standard method for detecting mercury in environmental samples—atomic absorption spectrometry—is expensive. “We’re not trying to compete with atomic absorption spectrometry,” says Koide. “We want to fill a gap by making a probe that the general public can use.” Koide’s fluorescent probe “provides a clever chemical approach for detecting mercury in complex samples,” says Chris Chang, an assistant professor of chemistry at the University of California, Berkeley. “The simplicity and sensitivity of this assay are promising for further application.” Koide and colleagues hope to turn this chemical tool into a kit, and are modifying the method to make it consumer-friendly, such as finding safe chemicals to transform extremely toxic methylmercury in fish into less toxic mercury species before testing.

Urine Mercury Excretion Following meso-Dimercaptosuccinic Acid Challenge in Fish Eaters

Public awareness of methylmercury in fish has caused patients to seek testing for mercury poisoning. In some patients, the diagnosis of mercury poisoning has been made based on urine mercury excretions following oral dosing of meso-dimercaptosuccinic acid (DMSA), a metal chelator. However, studies comparing urine mercury excretion following DMSA in healthy non-fish eaters with healthy fish eaters could not be located. To describe urinary mercury excretion before and after DMSA in healthy fish eaters and non-fish eaters, and to determine whether urine mercury excretion after DMSA would rise above baseline levels to a greater extent in fish eaters. A total of 24 healthy physicians were assigned to 1 of 3 groups based on fish consumption: non-fish eaters; 1 to 2 fish servings per week; and 3 or more servings per week. Blood mercury concentrations and 12-hour urine mercury and creatinine excretions were measured before and after oral ingestion of 30 mg of DMSA per kilogram of body weight. A total of 24 subjects completed the study, and 2 subsequently were excluded. No difference in baseline urinary mercury excretion was detected between groups. All groups demonstrated an increase in urinary mercury excretion following DMSA, which was higher in fish eaters (P = .04). Multiple linear regression found that the best predictor of a rise in urine mercury excretion following DMSA challenge was the prechelation blood mercury concentration. In this study of healthy physicians, oral DMSA produced a rise in urine mercury excretion both in non-fish eaters and fish eaters. The increase in chelated mercury excretion was higher in fish eaters. A simple rise in chelated mercury excretion over baseline excretion is not a reliable diagnostic indicator of mercury poisoning.

Determination of methylmercury in fish and seafood using optimized digestion and derivatization followed by gas chromatography with atomic emission detection

Mercury is an environmental contaminant that appears in different chemical forms. Organic forms of mercury, such as methylmercury, can occur in marine organisms like fish and shellfish and are far more toxic than the inorganic form. It is therefore vital to have refined analytical methods for the different mercuric species in order to evaluate the potential risk for seafood consumers. The aim of our investigations was to develop a simple, robust and valid method for differentiation of the mercury species in marine organisms. Different alkaline and acidic digestion procedures were evaluated. The best performing methodology consisted of digestion of 0.5 g sample in methanolic potassium hydroxide solution. After derivatization with sodium tetraethylborate and extraction of the ethylated mercury species using n-hexane, a quantitative determination of the extract using gas chromatography, combined with atomic emission detection, was possible. The procedure was shown to be selective and sensitive with a limit of detection of 6.1 μg/kg for methylmercury. The average recovery for the full procedure was 91 ± 19%. A preliminary survey of seafoods confirmed the previous observation that the proportion of methylmercury in the total mercury can vary widely, up to a complete occurrence as methylmercury.

Poor psychometric scores of children living in isolated riverine and agrarian communities and fish–methylmercury exposure

Because of heavy dependence on fish, Amazonian riparian communities are chronically exposed to high levels of methylmercury (MeHg). We studied fish–MeHg exposure (total hair-Hg, HHg) as a determinant of neurocognitive scores of children living in two geographically distant, culturally distinct and isolated poor communities of non-urban environments: Amazonian riverines (Riparians, n = 38) of the Puruzinho Lake community in the Rio Madeira Basin and rural agrarians from Iúna, Espírito Santo (Agrarians, n = 32). Nutritional status was estimated by anthropometry (Z-scores) and individual cognitive abilities were assessed by the Wechsler Intelligence Scale for Children-III (WISC-III) and the Human Figure Drawings (HFD), both validated versions for Brazilian children. Anthropometric assessment showed slightly elevated Z-scores for the Agrarian children (not statistically significant) but median HHg concentrations were 14.4 and 0.25 μg g −1 respectively for Riparian and Agrarian children ( p = 0.000). Despite paradoxical MeHg exposures, both groups showed comparable HFD scores but very poor performance in WISC-III test battery; median of sum of WISC-III subtests scores (ΣTOT) were 17.9 and 28.6 ( p < 0.000) for Riparian and Agrarian children, respectively (percentage scale). Spearman correlation between nutritional status (attained growth) and psychometric scores were statistically significant between height-for-age Z-score and Object Assembly subtest ( r = 0.269; p = 0.043), ΣTOT ( r = 0.319; p = 0.016), Performance-IQ ( r = 0.311; p = 0.019) and Perceptual Organization Index scores ( r = 0.302; p = 0.023). In these isolated communities there are stronger determinants of neurocognitive poor performance than MeHg exposure. Global strategies for reducing human exposure to MeHg by curtailing fish consumption are unrealistic options for riverine subsistence populations and are not justifiable to prevent low cognitive scores.

Rapid determination of trace methylmercury in natural crude medicine of animal origin

A rapid and simple method to determine methylmercury in natural crude medicine of animal origin was developed using gas chromatography electron capture detection (GC-ECD). Methylmercury, one of the forms of organomercury in nature, is much more toxic than inorganic and elemental mercury due to its lipid soluble property. The method is based on acidic digestion in hydrochloric acid solution following the extraction with toluene. The following parameters for the determination of methylmercury with GC-ECD were established: limit of detection 2 μg kg−1, limit of quantification 8 μg kg−1, linearity 10–300 ng mL−1, reproducibility as relative standard deviations 11.8%, 10.7% and 1.7% for 300, 150, and 20 ppb solutions, respectively, and recovery 87.1–112.4%. The results on animal-origin natural medicines using the method developed in this study were assured by comparison with those obtained by the method derived for measuring methylmercury in fish.

Methylmercury in a predatory fish ( Cichla spp.) inhabiting the Brazilian Amazon

This research tested whether limnological conditions, biological characteristics of fish and anthropogenic impacts influenced the assimilation of methylmercury into the muscle of a sedentary piscivorous fish, Cichla spp., from three rivers (Negro, Madeira, Tapajós) and two hydroelectric reservoirs (Balbina, Tucuruí) within the Brazilian Amazon. Methylmercury in this fish ranged from 0.04 to 1.43 μg g −1 w.w. across sites. No significant differences were observed in the methylmercury concentrations between males and females, or for different morphotypes of this species. Positive correlations were found between methylmercury and fish body weight. No differences were found between the weight normalized methylmercury (MeHg) concentrations or its percent of total mercury in fish from the three rivers; weight normalized MeHg was highest in one of the two reservoirs. In Rio Tapajós, where gold mining and deforestation cause high water turbidity, fish showed the highest MeHg and concentrations were different across the four sites examined. In all sampling areas, the %MeHg was found to be higher than 70.

Negative Confounding in the Evaluation of Toxicity: The Case of Methylmercury in Fish and Seafood

In observational studies, the presence of a confounding factor can distort the true association between an exposure and a toxic-effect outcome, if the confounding variable is not controlled for in the study design or analysis phase. While confounding is often assumed to occur in the same direction as the toxicant exposure, the relationship between the benefits and risks associated with fish and seafood consumption is a classic example of negative confounding: the exposure to methylmercury occurs with fish and seafood, which are also associated with beneficial nutrients, and the signs of mercury toxicity are thereby counteracted. Mercury and nutrients may affect the same epidemiological outcomes, but most studies addressing one of them have ignored the potential for negative confounding by the other. This article reviews the existing evidence of effects of both nutrient and contaminant intakes as predictors of neurodevelopmental and cardiovascular outcomes. Substantial underestimation of the effects of mercury toxicity and of fish benefits occurs from the lack of confounder adjustment and imprecision of the exposure parameters. Given this inherent bias in observational studies, regulatory agencies should reconsider current dietary advice in order to provide better guidance to consumers in making prudent choices to maintain a nutritious diet with seafood that is low in mercury concentrations. Attention should also be paid to the occurrence of negative confounding in other connections.

Determination of inorganic and methylmercury in fish by cold vapor atomic absorption spectrometry and inductively coupled plasma atomic emission spectrometry

Simple and rapid analytical procedures for the determination of Hg 2+ and methylmercury in fish were proposed after careful optimization of chemical and instrumental parameters for Hg measurement by cold vapor (CV)/hydride generation (HG) atomic absorption spectrometry (AAS) and CV/HG inductively coupled plasma atomic emission spectrometry (ICP-AES). Quantitative extraction of Hg species avoiding any inter-species conversion was achieved by fast microwave assisted solubilization of fish tissue with relatively low amount of tetramethylammonium hydroxide (TMAH) or 6 mol L − 1 HCl. After careful optimization of chemical parameters selective determination of Hg 2+ in the presence of excess of methylmercury is attained by using continuous flow CV AAS, 1% m/V SnCl 2 as reductant and 0.1 mol L − 1 HCl as reaction medium. Simple calibration curve prepared with aqueous standard of Hg 2+ is recommended for its quantification. Both Hg 2+ and methylmercury could be determined simultaneously with equal sensitivity by CV/HG ICP-AES directly in the diluted TMAH solution obtained after extraction with 1% m/V NaBH 4 as reductant. Quantification of the sum of Hg 2+ and methylmercury against calibration curve prepared with aqueous standard of methylmercury is suggested. It should be mentioned that batch hydride generation system with quartz tube heated in air/acetylene flame could also be used for simultaneous determination of both Hg species in fish extracts, with standard additions calibration. The validity of the developed analytical procedures for selective determination of Hg 2+ and methylmercury (by difference between the total Hg and Hg 2+) is confirmed by the analyses of certified reference material DOLT-1 and reference material IMEP-20. Very close agreement between certified values and analytical results was found.

Whole-ecosystem study shows rapid fish-mercury response to changes in mercury deposition

Methylmercury contamination of fisheries from centuries of industrial atmospheric emissions negatively impacts humans and wildlife worldwide. The response of fish methylmercury concentrations to changes in mercury deposition has been difficult to establish because sediments/soils contain large pools of historical contamination, and many factors in addition to deposition affect fish mercury. To test directly the response of fish contamination to changing mercury deposition, we conducted a whole-ecosystem experiment, increasing the mercury load to a lake and its watershed by the addition of enriched stable mercury isotopes. The isotopes allowed us to distinguish between experimentally applied mercury and mercury already present in the ecosystem and to examine bioaccumulation of mercury deposited to different parts of the watershed. Fish methylmercury concentrations responded rapidly to changes in mercury deposition over the first 3 years of study. Essentially all of the increase in fish methylmercury concentrations came from mercury deposited directly to the lake surface. In contrast, <1% of the mercury isotope deposited to the watershed was exported to the lake. Steady state was not reached within 3 years. Lake mercury isotope concentrations were still rising in lake biota, and watershed mercury isotope exports to the lake were increasing slowly. Therefore, we predict that mercury emissions reductions will yield rapid (years) reductions in fish methylmercury concentrations and will yield concomitant reductions in risk. However, a full response will be delayed by the gradual export of mercury stored in watersheds. The rate of response will vary among lakes depending on the relative surface areas of water and watershed.

Trading Off Fish Health and Safety: Female Decision‐Making Processes toward the Risk of Methylmercury in Fish

This study takes a qualitative, point‐in‐time look at 26 females’ decision‐making processes toward trading off the risks of mercury and the health benefits of a seafood diet. The data revealed five different decision‐making processes, with 17 of the 26 participants indicating their fish consumption patterns did not change. Of the nine who changed their fish consumption in some way, six specifically reduced the amount of tuna they ate. Similarly, participants who were most at risk—women of childbearing age and those with young children—expressed fish consumption changes more frequently than others, especially in the amount of tuna they consumed.

A review of dioxins/furans and methyl mercury in fish from the Penobscot river, located near Lincoln, Maine

The Agency for Toxic Substances and Disease Registry (ATSDR) was requested to review the analytical results of tissue samples from fish caught in the Penobscot river in Maine, calculate fish consumption limits and provide a public health opinion regarding the health implications associated with eating the contaminated fish. Fish consumption limits were calculated to provide guidance on the amount of fish that a person may eat monthly that would probably not pose a public health threat. Earlier, in 1987, the Maine Bureau of Health (BOH) issued a fish consumption advisory for portions of the Penobscot river to protect the public from exposures to dioxins/furans and methyl mercury-contaminated fish. From 1988 to 2003 the state of Maine conducted fish surveys at four locations along the Penobscot river to monitor the levels of dioxins/furans and methyl mercury contamination. In 2005, ATSDR reviewed the sampling results for two fish species (i.e., bottom feeders and predators) collected from the Penobscot river that revealed various levels of dioxins/furans and methyl mercury. The United States Environmental Protection Agency's (US EPA) guidance for evaluating potential health threats associated with contaminated fish recommends that a minimum of two target species be sampled including one predatory and one bottom feeding species. Target species are chosen to meet the following criteria: (1) known to accumulate high concentrations of target contaminants in their tissues; (2) normally populate the freshwater system being studied; (3) are routinely caught and consumed by anglers; (4) nonmigratory; (5) pollutant-tolerant; (6) easily identified; (7) abundant and easy to collect and (8) of sufficient size to provide adequate tissue samples for analyses of contaminants (US EPA, 2000). The analytical results of these fish tissue samples appear to indicate that toxic equivalency quotients concentrations of dioxins/furans have slightly decreased since 1988. In contrast, fish tissue levels of methyl mercury appear to have increased slightly since 1988. Dioxins/furans and methyl mercury levels detected in fish tissue samples caught in the Penobscot river located near Lincoln, Maine, may continue to pose a public health hazard to persons who consume the fish daily, depending on the amount consumed. The ATSDR concurred with Maine BOH's fish advisory for dioxins/furans and methyl mercury, that is, currently in place for portions of the Penobscot river near Lincoln.

Risk assessment of dietary exposure to methylmercury in fish in the UK

Risk assessment of chemicals in food is generally based upon the results of toxicological studies in laboratory animals, allowing for uncertainties relating to interspecies differences, human variability, and gaps in the database. Use of quantitative human data is preferable if available, as in the example of methylmercury. Methylmercury is a neurotoxic environmental contaminant, for which fish is the main source of dietary exposure. Human data from poisoning incidents and epidemiological studies have been used by expert committees to derive a guideline intake level for methylmercury, based on the susceptibility of the most sensitive lifestage, the developing fetus. In the UK, an expert group of nutritionists and toxicologists was formed to review the benefits and risks associated with fish consumption. A formal risk-benefit analysis was not possible because the nutritional data were not sufficiently quantitative. The Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (COT), therefore, modified the risk assessment approach to derive different guideline intake levels for different subgroups of the population. The COT opinion was used to provide targeted advice on how much fish can be consumed without undue risk from the contaminants. Consumption by adults of one weekly portion (140 g) of shark, swordfish or marlin, would lead to an exceedance of the guideline intake for methylmercury of 40-90%, set to protect the developing fetus, without considering intake from the rest of the diet. Pregnant women and women who may become pregnant within 1 year were, therefore, advised to avoid consumption of these species. Intakes in other adults would be within a higher guideline intake, set to protect groups of the population other than the developing fetus. However, consumption by children of one weekly portion of these species could lead to an exceedance of this guideline intake by up to 60%, without considering intake from the rest of the diet. It was, therefore, advised that consumption of these species by children should be avoided.