Methylmercury In Fish Research Articles

Rapid Determination of Methyl Mercury in Fish and Shellfish: Collaborative Study

A modification of the official AOAC method for determining methyl mercury in fish and shellfish was studied in 8 laboratories. Methyl mercury is isolated from homogenized, acetone-washed tissue by adding HCl and extracting into toluene the methyl mercuric chloride produced. The extract is analyzed for methyl mercuric chloride by electron capture gas chromatography. Collaborators determined methyl mercury in blind duplicate homogenates at 2 levels in tuna and at 1 level in swordfish and oysters. Collaborators also analyzed single homogenates of swordfish and oysters containing methyl mercury at a second level. Both fortified and unfortified tissues were analyzed. Methyl-bound mercury in the commodities ranged from 0.50 to 2.30 micrograms Hg/g. Reproducibility coefficients of variation ranged from 4 to 15%. Accuracy, measured by comparison to reference values, ranged from 92 to 101%. Recovery from fortified homogenates ranged from 86 to 98%. Reference values and unfortified levels were determined in the author's laboratory by replicate analysis of fortified and unfortified commodities. The method has been approved interim official first action.

Rapid Determination of Methyl Mercury in Fish and Shellfish: Method Development

The AOAC official first action method for methyl mercury in fish and shellfish was modified to provide more rapid determination. Methyl mercury is isolated from homogenized, acetone-washed tissue by addition of HCl and extraction by toluene of the methyl mercuric chloride produced. The extract is analyzed by electron capture gas chromatography (GC) on 5% DEGS-PS treated with mercuric chloride solution. The quantitation limit of the method is 0.25 micrograms Hg/g. Swordfish, shark, tuna, shrimp, clams, oysters, and NBS Research Material-50 (tuna) were analyzed for methyl mercury by the AOAC official first action method. All products also were analyzed by the modified method and the AOAC official method for total Hg. In addition, selected extracts obtained with the modified method were analyzed by GC with Hg-selective, microwave-induced helium plasma detection. There was no significant difference between the results for the various methods. Essentially all the Hg present (determined as total Hg) was in the organic form. Coefficients of variation from analyses by the modified method ranged from 1 to 7% for fish and shellfish containing methyl mercury at levels of 0.50-2.30 micrograms Hg/g. The overall average recovery was 100.5%.

Determination of methylmercury in fish by gas chromatography--direct current plasma atomic emission spectrometry.

Gas chromatography (GC) has been interfaced very simply and inexpensively with a direct current plasma (DCP) atomic emission spectrometer in order to perform highly specific and selective determinations of methylmercury (MeHg) in fish samples. A simple, isothermal, low-cost GC was constructed which could be dedicated to the DCP, allowing routine qualitative and quantitative determinations of organomercury species in complex food matrices. Optimisation of the GC-DCP interface was accomplished, followed by a determination of the detection limits, the linearity of the calibration graph and comparison of the results with those obtained by GC-electron-capture detection (ECD) and total mercury by cold-vapour atomic absorption spectrometry. In most instances, qualitative and quantitative results for incurred and spiked levels did not agree for the GC-DCP and GC-ECD approaches. An additional extraction procedure has also been developed for MeHg from fish samples involving extraction with an organic solvent, concentration and injection on to the GC column. Depending on the particular organic solvent employed, artifact formation of MeHg can occur as a result of the extraction-GC conditions. Methods to avoid an artifact situation are suggested, and the possible implications of this for the currently accepted AOAC method involving GC-ECD.

Methylmercury in Fish: A Review of Residue Levels, Fish Consumption and Regulatory Action in the United States

The dangers associated with the consumption of large amounts of methylmercury in fish are well recognized, and there is some evidence to suggest that methylmercury may be the cause of subtle neurological impairments when ingested at even low to moderate levels, particularly the prenatal and early childhood periods. This concern has prompted a continuing assessment of the risk of methylmercury toxicity among fish consumers in the United States as well as other countries. The toxicokinetics of methylmercury in humans are reviewed and used to estimate body burdens associated with toxic effects. To determine seafood consumption patterns among the continental U.S. population the Food and Drug Administration (FDA) has analyzed data from a diary study commissioned by the Tuna Research Foundation. Mercury residue levels in domestic fish sampled by the FDA were used to determine the level of exposure to methylmercury. Until evidence is presented that substantially lowers the known body burden of methylmercury which causes toxicity, calculations indicate that the current 1.0 ppm regulatory level provides adequate protection for the average fish consumer, for young children, and for a significant number of consumers exceeding the acceptable daily intake. However, additional studies are being carried out in a continuing process to ensure that safe levels of prenatal exposure to mercury residues in fish are maintained.

Methylmercury in fish: a review of residue levels, fish consumption and regulatory action in the United States.

The dangers associated with the consumption of large amounts of methylmercury in fish are well recognized, and there is some evidence to suggest that methylmercury may be the cause of subtle neurological impairments when ingested at even low to moderate levels, particularly the prenatal and early childhood periods. This concern has prompted a continuing assessment of the risk of methylmercury toxicity among fish consumers in the United States as well as other countries. The toxicokinetics of methylmercury in humans are reviewed and used to estimate body burdens associated with toxic effects. To determine seafood consumption patterns among the continental U.S. population the Food and Drug Administration (FDA) has analyzed data from a diary study commissioned by the Tuna Research Foundation. Mercury residue levels in domestic fish sampled by the FDA were used to determine the level of exposure to methylmercury. Until evidence is presented that substantially lowers the known body burden of methylmercury which causes toxicity, calculations indicate that the current 1.0 ppm regulatory level provides adequate protection for the average fish consumer, for young children, and for a significant number of consumers exceeding the acceptable daily intake. However, additional studies are being carried out in a continuing process to ensure that safe levels of prenatal exposure to mercury residues in fish are maintained.

Elevation of mercury in human blood from controlled chronic ingestion of methylmercury in fish.

The relationship between the intake of methylmercury in fish and mercury in blood has been investigated in man. The intakes of methylmercury were carefully controlled and lay in the range 40-230 micrograms/day, the Provisional Tolerable Weekly Intake is equivalent to about 30 micrograms/day. The results indicate that a daily intake of 1 microgram methylmercury would, at equilibrium, produce a blood mercury concentration of 0.8 micrograms/kg. There is a good close-to-linear correlation between methylmercury intake and blood mercury concentrations within the wide range of intakes employed.

Electron Capture Gas-Liquid Chromatographic Determination of Methyl Mercury in Fish and Shellfish: Collaborative Study

A method for determining methyl mercury in fish and shellfish was collaboratively studied in 8 laboratories. Methyl mercury is isolated from acetone-washed, homogenized tissue by adding hydrochloric acid and extracting into benzene the methyl mercuric chloride that is formed. The benzene extract is concentrated and analyzed for methyl mercuric chloride by electron capture gas-liquid chromatography on 5% DEGS-PS treated with inorganic mercuric chloride solution. The quantitation limit for the method is 0.05 micrograms Hg/g. Each collaborator determined methyl mercury at 2 levels in blind duplicate samples of swordfish, tuna, oyster, and shrimp tissues. Both fortified and unfortified samples were analyzed. Methyl-bound mercury in the samples ranged from 0.15 to 2.48 micrograms Hg/g. The reproducibility coefficients of variation for the 8 samples ranged from 3 to 13%. The accuracy, measured by comparison to reference values, ranged from 99 to 120%. Reference values were determined in the Associate Referee's laboratory by replicate analyses of the fortified and unfortified samples. The method has been adopted official first action.

Determination of methylmercury in fish by high-performance liquid chromatography.

A method has been developed that uses a simplified sample preparation procedure and atomic absorption or electrochemical detection of HPLC eluents for the determination of methylmercury in fish. Methylmercury is isolated from the blended sample by chloroform elution from a diatomaceous earth-hydrochloric acid column. The organomercury compound is then extracted into a small volume of 0.01 N sodium thiosulphate solution. An aliquot of this solution is injected on to a Zorbax ODS column and eluted with methanol-ammonium acetate solution (3 + 2) buffer, pH 5.5 containing mercapto-ethanol. Detection can be accomplished by atomic-absorption spectrophotometry with the aid of a specially designed apparatus for the generation of mercury vapour. Alternatively, a commercially available electrochemical detector equipped with a dropping-mercury electrode may be used.

Gas Chromatographic- Atmospheric Pressure Active Nitrogen Method for Organomercury Speciation in Environmental Samples

Methods are presented for the determination of methylmercury in fish, water, urine, and sediments, and diorganomercury compounds in water. Two significant differences from previous methods are the use of methylene chloride extracting solvent which permits sample extracts to be concentrated to volumes as low as 0.1 mL, and use of a gas chromatograph interfaced to an atmospheric pressure active nitrogen (APAN) afterflow detector. Such a detector is very sensitive and selective for Hg at picogram levels. Thus, limits of detection were significantly enhanced.

The cumulation of methylmercury in fish (Poecilia reticulata).

Methylmercury labelled with mercury-203 was used for the investigation of the uptake and the release of methylmercury in fish. It has been found that methylmercury compounds adsorbed on fish food remain completely in fish and that they are released with the biological half-time of 110 +/- 20 days. The cumulation of methylmercury from water is very rapid: the cumulation constant is 237 +/- 67 days-1. Equations for the calculation of the concentration of methylmercury in fish were derived and compared with the uptake of phenylmercury and inorganic mercury.

Use of Background Correction to Improve the Accuracy of the Selective Reduction Method for Determining Methyl Mercury in Fish

Background correction is used with a previously published flameless atomic absorption method for the concurrent determination of inorganic and methyl mercury. The use of background correction simplifies the procedure, but, more importantly, eliminates errors in mercury readings due to broad band absorption by other volatile compounds produced during the determination.

Duplicate diet study on fishing communities in the United Kingdom: Mercury exposure in a “critical group”

Duplicates of a week's diet of 119 individuals from fishing communities in the areas around the northeastern Irish Sea, an area affected by the industrial discharge of mercury, have been examined for their total concentrations of mercury and selenium. (Fish consumption varied from 10–225 g/day with approximately 50% of each population having a consumption greater than 50 g/day.) Total weekly intakes of mercury varied between 4 and 443 μg/70 kg body wt, compared with intakes varying from 4 to 560 μg/70 kg body wt in 55 individuals from fishing communities in the southern reaches of the English Channel who acted as a reference group. Total weekly selenium intakes varied from 171 to 1272 μg/70 kg body wt in the northeastern Irish Sea, compared with 127 to 1685 μg/70 kg body wt in the reference area. The concentrations of total mercury in whole blood in the communities around the Irish Sea ranged from 0.04 to 2.58 μg/100 ml, compared with concentrations ranging from 0.04 to 1.21 μg/100 ml in the reference group. Concentrations of mercury in hair ranged from 0.1 to 11.3 mg/kg in the northeastern group (with the exception of a contaminated sample with a concentration of 60 mg/kg) and from 0.4 to 5.8 mg/kg in the reference group. On the basis of these studies it is concluded that there are unlikely to be any consumers of fish in the United Kingdom who are adversely affected by the presence of methyl mercury in fish.

Molecular activation analysis for methylmercury

The principle of molecular activation analysis is described, as well as its unsuccessful application to the species specific determination of methylmercury in fish. The reasons for the failure of the method were determined and are found to be of significance to hot atom chemistry and to possible future use of this principle. The reasons are: (i) a matrix dilution of the species sought, (ii) a scavenging, probably of methyl groups, by serine or related components of fish powder, and (iii) a methylation by some unidentified component associated with the fish fats.

Determination of methylmercury in fish of South Carolina.

Determination of methylmercury in fish of South Carolina.

Dr. Miller Replies

Pediatricians are well aware of the special susceptibility of the fetus and child to chemical pollutants.1 Methemoglobinemia may occur in infants exposed to nitrates from well water2; congenital Minamata disease (cerebral palsy) has occurred from intrauterine exposure to methylmercury in fish from contaminated seawater.3 There is no doubt about the need for safe water. In its statement, the Committee on Environmental Hazards considered the evidence then available on the carcinogenicity in man of chemical contaminants of water.

Determination of mercury and methylmercury in fish.

Determination of mercury and methylmercury in fish.

A Simplified Method for the Gas-Liquid Chromatographic Determination of Methyl Mercury in Fish and Shellfish

A simple acetone wash of the fish sample which removes lipids and other organic materials replaces the cystein cleanup specified in other methods. Methyl mercury is freed by hydrochloric acid, extracted into benzene, and determined with a gas-liquid chromatograph equipped with an electron capture detector. The method is quantitative for methyl mercury levels as low as 0.10 ppm in fish and shellfish. Ethyl mercury chloride may be used as an internal standard to detect unsuspected error or instrumental parameter variation.

Determination of Methyl Mercury in Fish by Flameless Atomic Absorption Spectroscopy and Comparison with an Acid Digestion Method for Total Mercury

A method for the concurrent determination of methyl mercury and inorganic mercury by flameless atomic absorption spectroscopy (AAS) is described. Fifty-seven samples of juvenile black marlin fish were analyzed for inorganic and methyl mercury, and total mercury was calculated by addition of the 2 values. The sensitivity of the method was estimated to be 0.029 mug for inorganic mercury and 0.033 mug for methyl mercury. The detection limit of the method was about 0.02 mug inorganic mercury or methyl mercury and the error of the method was found not to exceed 10% for samples giving about 10% deflection on the absorbance scale. Samples from the same fish were analyzed by a commonly accepted flameless AAS method for the determination of total mercury. When the results for total mercury from the 2 methods were statistically compared, using a paired t-test, the difference between the results obtained by the 2 methods was found to be insignificant at the 95% confidence level.

Studies on microbial synthesis and decomposition of organomercury compounds.

The studies conducted at Kumamoto University concluded that the Minamata disease is caused by methyl mercury. In the course of a nationwide survey made thereafter on environmental pollution by mercury, methyl mercury was detected in fish and human hairs which were supposedly free from artificial contamination by mercury. In particular, 60 to 70% of mercury found in tuna caught in oceans has been reported to be in the form of methyl mercury. An abnormally high mercury content in fish has also been reported in Sweden. Westoo carried out analyses of mercury in fish and other foodstuffs and claimed that 80 to 100% of mercury is present as methyl mercury.To elucidate the origin of such methyl mercury in nature and the effects of methyl mercury on mankind from the standpoint of public health, microbiological and ecological studies were undertaken on microbial conversion of inorganic mercury into organic mercury and of a process of the biological chain. A mercury-resistant bacterium belonging to Pseudomonas was separated from sewage water and biological synthesis and decomposition of organic mercury by this bacterium were investigated. Following this, microorganisms growing in a zone of mercury deposits, soils, rivers and seas and certain eumycetes were found to possess the ability to synthesize organic mercury. Hence, the possibility of conversion of inorganic mercury into organic mercury in nature was recognized. Furthermore, the extent of synthesis of organic mercury and the extent of accumulation of methyl mercury in fish by way of biological concentration were studied with the aid of ecological means. The microbially synthesized methyl mercury is concentrated by the food chain and an unusually high mercury content is sometimes found in fish. However, accumulation of methyl mercury in fish seldom proceeds to such a high level as to cause mercury poisoning, unless continual flow of methyl mercury in abnormally large quantities is present, as has been known in the case of the Minamata disease. Therefore, detection of an abnormally large amount of mercury in fish or shellfish suggests artificial contamination by mercury in one way or another, and a countermeasure must be worked out.

The rapid sub-picogram determination of volatile organo-mercury compounds by gas chromatography with a microwave emission spectrometric detector system

The applicability of a gas Chromatograph with a microwave emission spcctrometric detector (g.c.-m.e.s.) to the determination of trace amounts of volatile organo-mercury compounds in environmental samples is described. The high selectivity of the detector to mercury compounds allows the procedures to be drastically simplified. Thus, the total analysis time for methylmercury in fish is less than 15 min and more than 30 samples of CH 3HgCl (benzene extracts) can be analyzed per hour. The detection limit is 0.5 pg for CH 3HgCl (or C 2H 5HgCl) and 2 pg for (CH 3) 2Hg. The relative sensitivity for CH 3HgCl in water samples is 1 ng l −1 and for fish samples is 1 ng g −1. Direct determinations of CH 3HgCl and (CH 3) 2Hg in aqueous solutions arc also discussed.