Methylmercury In Fish Research Articles

Aqueous phase ethylation atomic emission spectroscopy for the determination of methylmercury in fish using permeated dimethylmercury calibration.

Aqueous phase ethylation atomic emission spectroscopy for the determination of methylmercury in fish using permeated dimethylmercury calibration.

Human toxicology of Mercury

This article describes the health effects of the two principal forms of mercury to which humans are exposed, namely mercury vapor and methylmercury compounds. Mercury vapor is the monatomic gas that vaporizes from liquid metallic mercury. It has a long history of human exposure dating back to ancient times. The earliest life forms on this planet may have received substantial exposure and developed defense mechanisms that we inherit to this day. Severe forms of poisoning from inhalation of mercury vapor are now rare. More commonly observed in occupational exposures are subtle neurobehavioral effects and preclinical changes in biochemical markers of kidney function. Methylmercury compounds may also date back to Archean times. The methylation of inorganic mercury by methanogenic bacteria is believed to be a protective mechanism for these cells that appeared early in evolution. Unfortunately, for life forms dependent on a central nervous system, what is protective for simple cells becomes a threat to the more complex life forms. Today, the main source of human exposure is from methylation of inorganic mercury in bodies of fresh and ocean water, the ensuing bioaccumulation in the aquatic food chain, and the consumption of fish or sea mammals by humans. Methylmercury selectively damages the brain. In adult humans, damage is focal, affecting specific cell types in certain anatomical areas such as the visual cortex and the cerebellum. Prenatal exposure disrupts the normal developmental processes of the fetal brain. Indeed, the prenatal period is widely believed to be the most susceptible stage of the life cycle. At present, two large epidemiological studies are underway to determine human health risks from methylmercury in fish. J. Trace Elem. Exp. Med. 11:303–317, 1998. © 1998 Wiley-Liss, Inc.

Human toxicology of Mercury

This article describes the health effects of the two principal forms of mercury to which humans are exposed, namely mercury vapor and methylmercury compounds. Mercury vapor is the monatomic gas that vaporizes from liquid metallic mercury. It has a long history of human exposure dating back to ancient times. The earliest life forms on this planet may have received substantial exposure and developed defense mechanisms that we inherit to this day. Severe forms of poisoning from inhalation of mercury vapor are now rare. More commonly observed in occupational exposures are subtle neurobehavioral effects and preclinical changes in biochemical markers of kidney function. Methylmercury compounds may also date back to Archean times. The methylation of inorganic mercury by methanogenic bacteria is believed to be a protective mechanism for these cells that appeared early in evolution. Unfortunately, for life forms dependent on a central nervous system, what is protective for simple cells becomes a threat to the more complex life forms. Today, the main source of human exposure is from methylation of inorganic mercury in bodies of fresh and ocean water, the ensuing bioaccumulation in the aquatic food chain, and the consumption of fish or sea mammals by humans. Methylmercury selectively damages the brain. In adult humans, damage is focal, affecting specific cell types in certain anatomical areas such as the visual cortex and the cerebellum. Prenatal exposure disrupts the normal developmental processes of the fetal brain. Indeed, the prenatal period is widely believed to be the most susceptible stage of the life cycle. At present, two large epidemiological studies are underway to determine human health risks from methylmercury in fish. J. Trace Elem. Exp. Med. 11:303–317, 1998. © 1998 Wiley-Liss, Inc.

Capillary electrophoresis determination of methylmercury in fish and crab meat after extraction as the dithizone sulphonate complex

Dithizone sulphonate (DzS) is used in place of cysteine to separate methylmercury in the final stage of a simplified Westöö extraction procedure. The intensely absorbing methylmercury DzS complex is then separated by CE using a coated capillary and determined by direct absorption measurement at 480 nm. Good quantitative performance is demonstrated by spiking experiments and analysis of DORM-1 certified reference material. Values found ranged from 218 μg kg −1 for a tuna fish to 2.8 μg kg −1 for a crab sample. The very stable baseline and lack of interfering peaks meant that a low detection limit of 2 μg kg −1 could be achieved for a 10 g sample.

Methylmercury in fish from Owyhee Reservoir in southeast Oregon: scientific uncertainty and fish advisories

Data collected during 1987–1994 showed elevated levels of mercury (Hg) in fish tissue from the Owyhee Reservoir in southeastern Oregon. Sixty-five percent of the samples analyzed had total Hg levels exceeding the US Environmental Protection Agency's (EPA) health screening value of 0.6 mg/kg. Eighteen out of 89 (20%) fish tissue samples also had total Hg levels greater than the US Food and Drug Administration's (FDA) mercury action level of 1.0 mg/kg. The overall mean Hg content for all fish collected from the reservoir was 0.75 mg/kg wet weight (wet wt.). Fish muscle taken from largemouth bass ( Micropterus salmoides), smallmouth bass ( Micropterus dolomieu) and channel catfish ( Ictalurus punctatus) had the highest mean Hg levels of 0.92, 0.87 and 0.82 mg/kg, respectively. In contrast, rainbow trout ( Salmo gairdneri) had the lowest mean Hg content of 0.37 mg/kg. Increases in total Hg concentrations were found to be positively correlated with size for rainbow trout and yellow perch. A weak but significant correlation was also observed between total mercury content and age for smallmouth bass. Based on these data, in 1994 the Oregon Health Division (OHD) issued a fish consumption advisory for the Owyhee Reservoir using a conservative risk-based approach. The process of defining and communicating these consumption limits is the subject of this paper.

Importance of dose‐response model form in probabilistic risk assessment: A case study of health effects from methylmercury in fish

We compared the effect of uncertainty in dose‐response model form on health risk estimates to the effect of uncertainty and variability in exposure. We used three different dose‐response models to characterize neurological effects in children exposed in utero to methylmercury, and applied these models to calculate risks to a native population exposed to potentially contaminated fish from a reservoir in British Columbia. Uncertainty in model form was explicitly incorporated into the risk estimates. The selection of dose‐response model strongly influenced both mean risk estimates and distributions of risk, and had a much greater impact than altering exposure distributions. We conclude that incorporating uncertainty in dose‐response model form is at least as important as accounting for variability and uncertainty in exposure parameters in probabilistic risk assessment.

Uptake, Toxicity, and Trophic Transfer of Mercury in a Coastal Diatom

The primary mechanisms controlling the accumulation of methylmercury and inorganic mercury in aquatic food chains are not sufficiently understood. Differences in lipid solubility alone cannot account for the predominance of methylmercury in fish because inorganic mercury complexes (e.g., HgCl2), which are not bioaccumulated in fish, are as lipid soluble as their methylmercury analogs (e.g., CH3HgCl). Mercury concentrations in fish are ultimately determined by methylmercury accumulation at the base of the food chain, which is governed by water chemistry, primarily pH and chloride concentration. Our studies of mercury speciation, toxicity, and phytoplankton uptake demonstrate that passive uptake of uncharged, lipophilic chloride complexes is the principal accumulation route of both methylmercury and inorganic mercury in phytoplankton. The predominance of methylmercury in fish, however, is a consequence of the greater trophic transfer efficiency of methyl- mercury than inorganic mercury. In particular, methylmercury in phytoplankton, which accumulates in the cell cytoplasm, is assimilated by zooplankton four times more efficiently than inorganic mercury, which is principally bound in phytoplankton membranes. On the basis of these results, we constructed a simple model of mercury accumulation in fish as a function of the overall octanol−water partition coefficient of methylmercury. Our model can explain the variability of mercury concentrations in fish within, but not among, different lake regions.

Photodegradation of methylmercury in lakes

METHYLMERCURY can accumulate in fish to concentrations that threaten human health1. Fish methylmercury concentrations are high in many reservoirs2 and acidic lakes3, and also in many remote lakes4,5—a fact that may be related to increased atmospheric deposition of anthropogenically mobilized mercury during the past few decades6. Although sources of methylmercury to lakes and reservoirs are known7, in-lake destruction has not been demonstrated to occur at the low concentrations found in most water bodies. Here we report in situ incubations of lake water that show that methylmercury is decomposed by photo- degradation in surface waters. This process is abiotic and the rate is first-order with respect to methylmercury concentration and the intensity of solar radiation. In our study lake, the calculated annual rates of methylmercury photodegradation are almost double the estimated external inputs of methylmercury from rain, snow, streamflow and land runoff, implying the existence of a large source of methylmercury from bottom sediments. Photodegradation could also be an important process in the mercury cycle of other aquatic systems. This discovery fundamentally changes our understanding of aquatic mercury cycling, and challenges the long-accepted view that microbial demethylation dominates methylmercury degradation in natural fresh waters.

Mercury and methylmercury in fish and human hair from the Tapajós river basin, Brazil

Mercury is being released in the Amazon in an abusive way due to goldmining activities. The Tapajós river basin was the first to be intensively exploited in the modern Amazon gold rush. Fish and hair samples as the best indicators of human methylmercury contamination were investigated in the main cities and villages along the Tapajós river basin. The upper basin has typical fish fauna with much larger carnivorous fish with higher mercury levels reaching an average value of 0.69 μg·g −1 wet wt. in 43 fish. This was accompanied by high levels in hair of the human population living in the same area. The maximum hair value reach 151 μg·g −1 dry wt. with two villages presenting an average value close to 25 μg·g −1 dry wt. An analytical laboratory intercalibration exercise was performed between Japanese and Brazilian laboratories for total mercury analysis. Critical fish, areas, and more exposed human groups are identified.

Determination of methylmercury in fish and river water samples using in situ sodium tetraethylborate derivatization following by solid-phase microextraction and gas chromatography-mass spectrometry

A solid-phase microextraction (SPME) analytical procedure is described for the quantitative determination of methylmercury and labile Hg 2+ in fish and river water matrices, The analytical procedure involves aqueous-phase derivatization of ionic mercury species with sodium tetraethylborate in a sample vial and subsequent extraction with a silica fiber coated with poly(dimethylsiloxane). The mercury derivatives are desorbed in the splitless injection port of a gas chromatograph and subsequently analyzed by electron impact mass spectrometry. Both headspace SPME and aqueous-phase SPME are studied, and the linear range of the method spans several orders of magnitude for both procedures. The detection limits of the headspace SPME procedure for a 20-ml sample are 7.5 and 3.5 ng/l as Hg for CH 3Hg + and Hg 2+, respectively. The detection limits of aqueous-phase SPME for a 1.5-ml sample are 6.7 and 8.7 ng/l as Hg for CH 3Hg + and Hg 2+, respectively. Analyses of standard reference materials and river water sample demonstrate the suitability of this method for the determination of methylmercury and labile Hg 2+.

Determination of Methyl Mercury in Fish and Shellfish.

A simple and rapid method for the determination of methyl mercury in fish and shellfish using a gas chromatograph with electron capture detection (GC/ECD) was developed. Lipids and other organic interference in the test materials were eliminated by pretreatment with acetone and benzene, and then the methyl mercury extracted with the acidified benzene was analyzed by GC/ECD. Good recoveries (tuna, 90.3±2.3% ; shark, 105.5±3.2% ; sail-fish, 87.5±2.7% ; and shrimp meat, 88.4±2.6%) were obtained from samples spiked with 1 ppm of methyl mercury. The detection limit of methyl mercury was approximately 0.0016 ppm.

Fish Consumption Patterns and Blood Mercury Levels in Wisconsin Chippewa Indians

Methylmercury is a known neurotoxin at high blood levels (> 400 micrograms/l) and is thought to cause neurologic symptoms at substantially lower levels in susceptible adults and infants. Given that levels of methylmercury in fish in northern Wisconsin lakes can be high (> 1 ppm, FDA standard) and Chippewa Indians take large amounts of fish from these lakes, the extent of their exposure to methylmercury was investigated. Using tribal-maintained registries, 465 Chippewa adults living on reservation were selected randomly and were invited to participate; 175 (38%) participated in the study. In an effort to characterize nonrespondents, 75 nonrespondents were selected randomly and were followed up aggressively. An additional 152 volunteers who were selected nonrandomly also participated in the study. Subjects completed a questionnaire about fish consumption patterns and had blood drawn for mercury determination. Sixty-four persons (20%) had blood mercury levels in excess of 5 micrograms/l (i.e., upper limit of normal in nonexposed populations); the highest level found was 33 micrograms/l. Fish consumption was higher in males and the unemployed. Blood mercury levels were highly associated with recent walleye consumption (p = .001). Methylmercury levels in some Wisconsin Chippewa were found to be elevated, but were below the levels associated with adverse health effects. We recommend a continuation of efforts to limit exposures in this high-risk population.

Toxicity, bioavailability and metal speciation.

1. Environmental toxicology emphasizes the difference from traditional toxicology in which pure compounds of interest are added to purified diets, or injected into the test animals. When the objective is to study the fate and effects of trace elements in the environment, knowledge of the speciation of the elements and their physico-chemical forms is important. 2. Cadmium salts such as the sulfides, carbonates or oxides, are practically insoluble in water. However, these can be converted to water-soluble salts in nature under the influence of oxygen and acids. Chronic exposure to Cd is associated with renal toxicity in humans once a critical body burden is reached. 3. The solubility of As(III) oxide in water is fairly low, but high in either acid or alkali. In water, arsenic is usually in the form of the arsenate or arsenite. As(III) is systemically more poisonous than the As(V), and As(V) is reduced to the As(III) form before exerting any toxic effects. Organic arsenicals also exert their toxic effects in vivo in animals by first metabolizing to the trivalent arsenoxide form. Some methyl arsenic compounds, such as di- and trimethylarsines, occur naturally as a consequence of biological activity. The toxic effect of arsenite can be potentiated by dithiols, while As has a protective effect against the toxicity of a variety of forms of Se in several species. 4. Selenium occurs in several oxidation states and many selenium analogues of organic sulfur compounds exist in nature. Selenium in selenate form occurs in alkaline soils, where it is soluble and easily available to plants. Selenite binds tightly to iron and aluminum oxides and thus is quite insoluble in soils. Hydrogen selenide is a very toxic gas at room temperature. The methylated forms of Se are much less toxic for the organism than selenite. However, the methylated Se derivatives have strong synergistic toxicity with other minerals such as arsenic. 5. Aquatic organisms absorb and retain Hg in the tissues, as methylmercury, although most of the environmental Hg to which they are exposed is inorganic. The methylmercury in fish arises from the bacterial methylation of inorganic Hg. Methylmercury in the human diet is almost completely absorbed into the bloodstream. The nervous system is the principal target tissue affected by methylmercury in adult human beings, while kidney is the critical organ following the ingestion of Hg(II) salts.

Rapid determination of inorganic and methyl mercury in fish

A method has been developed that uses a mixed solution of NaOH, NaCl and cysteine to digest fish. Inorganic Hg and MgHg were determined by cold vapor atomic absorption (CVAAS) using a selective reduction step with SnCl2 and SnCL2-solutions. Ethyl alcohol was satisfactorily used to prevent excessive foaming. Two optimum digestion procedures were established: (1) using a dry block heater at 90 °C for 1 hr and (2) overnight digestion at 25 to 30 °C. Differences between both were not significant (95%) in the range of 30 to 500 ng g−1 Hg (II) and MeHg in fish. Reduction of the Hg signal due to matrix effects in different fish species was evaluated (95 to 60%). Oily fish, shrimp and lobsters gave the highest reduction. Internal calibration by addition of Hg standards are strongly recommended when exact determinations are needed. The detection limit obtained was near 10 ng g−1. Signals were linear in the concentration range studied (30 to 500 ng g−1). Accuracy of analyses was in the order of 5% or better, with a relative standard deviation of 5%. The method could be applied to other environmental matrices: hair, urine and blood, with some modifications.

Projects for the improvement of the quality of chemical speciation analyses in environmental matrices

The release of organometallic compounds and other chemical forms of elements in the environment has caused great concern because of their possible high toxicity. To validate the analytical techniques, the Community Bureau of Reference (BCR) has undertaken a series of projects for the improvement of the quality of determinations of chemical species in environmental matrices. The implementation of these projects follows a stepwise approach involving intercomparisons to detect and remove sources of errors in different phases of the analytical methods and the certification of the compounds in various matrices. The current projects deal with the determination of the extractable content of trace metals in soils (single extraction) and sediment (sequential extraction), forms of aluminium in water, elements with different oxidation states (e.g. As, Cr and Se) and organic forms (e.g. methylated forms of As in solution, methyl-mercury in fish, arseno-betaine and -choline in solutions, triethyl- and trimethyl-Pb compounds in solution, and butyltin compounds in sediment).

Sulfate stimulation of mercury methylation in freshwater sediments

The relationship between bacterial sulfate reduction and mercury methylation, as well as the in situ distribution of methylmercury in sediments, was studied in Quabbin Reservoir, MA. Fish methylmercury levels in Quabbin and other lakes affected by acid deposition are often elevated. However, the cause of acceleration of net methylmercury production or bioaccumulation in these lakes is poorly understood. Experimental additions of sulfate to either anoxic sediment slurries or lake water above intact sediment cores resulted in increased microbial production of methylmercury from added inorganic mercury

Determination of methylmercury in fish by headspace-gas chromatography with microwave-induced-plasma detection

Some additional experiments checking out the extraction method recently developed for the determination of MeHg in biological samples by Headspace Gas Chromatography with Microwave Induced Plasma atomic emission spectroscopy detection were performed. In this method, the MeHg is cleaved from the biological tissue by H2SO4 and by addition of iodoacetic acid converted to the iodide form. These reaction steps take place in a closed headspace vial. The H2SO4 concentration and the sample matrix have an important influence on the recovery of the MeHg from the sample and these effects are discussed. The method was then applied to the determination of MeHg in cod fish caught in the North Sea. Levels found ranged from 0.13 to 0.63 μg g−1 dw with a mean of 0.33 μg g−1 on the 25 samples analyzed. The total Hg content of these samples was also determined by Cold Vapour Atomic Absorption Spectrometry, and all data pooled ranged from 0.19 to 0.90 μg g−1 with a mean of 0.40 μg g−1. A study of the ratio MeHg/total Hg revealed that MeHg always constituted more than 60 % of the total Hg level, with a mean of 83 % on the 25 samples. The percentage MeHg did not increase or decrease markedly when the total Hg content increased. It could be concluded that these North Sea samples are not much contaminated by Hg and are surely suitable for consumption.

Mercury contamination-what we have learned since Minamata

Atmospheric cycling of mercury and other pollutants has become a major concern as industrialized countries have eliminated point discharges, sometimes by relocating the industries to underdeveloped and developing countries where point sources have become problems. Such circumventions may be to no avail in the long run as pollution continues to elevate levels of methylmercury in fish in waterways that are remote from direct contamination as well as where the source can be readily identified. Much has been learned about the cycling of mercury in the environment since human disabilities and deaths at Minamata, Japan, initially drew attention to the problem of methylmercury poisoning from the consumption of contaminated seafood in the 1950s. In that instance, methylmercury produced industrially concentrated to toxic levels in fish. As this manufacturing process was not used outside Japan, concern did not become immediate in other developed nations until the 1960s when it was established that mercury was not only biomethylated by microorganisms but also biomagnified through the food chain. Point sources to the waterways may have been eliminated too late to return the levels in fish to background because of the geochemical cycling of mercury through the environment. Despite decreases in domestic, industrial and agricultural point source releases over the last two decades, large quantities from non-point sources such as fossil fuel combustion, smelters, and incinerators are still being released. Much of this mercury is transported from the atmosphere to aquatic ecosystems and stored in sediments until it is again released to the water and atmosphere.

Human health risks from methylmercury in fish

AbstractHuman health risks from methylmercury in fish are evaluated in terms of dose‐response relationships for both adult and prenatal human exposures. Specifically, information has become available from three independent epidemiological studies indicating that methylmercury levels in the mother during pregnancy predict the probability of adverse effects in her offspring. The mercury levels in the mother are measured as concentration in head hair which in turn is an excellent predictor of blood concentration. The adverse effects in the offspring take the form of psychomotor retardation. These dose‐response relations along with a one‐compartment kinetic model for methylmercury accumulation in humans will be used to estimate minimum toxic daily intakes; these are, for nonpregnant adults, 4,300 ng Hg/kg body weight/d and about 600 to 1,100 ng Hg/kg/d for pregnant adults. These values assume continuous exposure until the individual has attained steady state balance with respect to the body burden of methylmercury. This will take up to one year in most cases.

Mercury in women exposed to methylmercury through fish consumption, and in their newborn babies and breast milk.

The presence of methylmercury in fish is a major environmental problem. During the major epidemics of methylmercury poisoning through sea food in Minamata in Japan, and through dressed seed in Iraq, there was a high prevalence of infants, who developed cerebral palsy. This was generally assumed to be due to intrauterine methylmercury poisoning, as it is well known, that methylmercury is transferred through the placenta into the fetus. There is also a possibility that exposure occurred through breast milk, as high levels of mercury in breast milk have been reported in mothers from Minamata. Information on the relationship between methylmercury exposure, mercury levels in blood of mothers and their babies, and levels in breast milk are reported here.