MeHg In Fish Research Articles

Blank correction considerations for isotope dilution and reverse isotope dilution calibration: Determination of methylmercury in fish tissue

A mathematical approach to the accurate correction of the blank when applying isotope dilution (ID) and reverse ID is presented. The manner in which blank correction is undertaken is critical to the quality of the final results. Direct subtraction of a procedural blank from the gross analyte concentration is only valid when the blank contributes to the primary ID process and not to the reverse ID process. When the blank contributes to both processes, typically only a fraction of this blank concentration should be subtracted. The approach developed here was illustrated and validated by the determination of MeHg in tuna fish using ID and reverse ID SPME GC-ICP-MS and an enriched Me198Hg spike. Despite a 150-fold higher blank (equivalent to 7% of the analyte concentration in the sample) arising from use of a 1 M NaOAc/HOAc buffer solution compared to that obtained with use of a 0.5 M NH4OAc/HOAc buffer, final concentrations of 19.90 ± 0.34 and 19.88 ± 0.10 μmol kg−1 (one standard deviation, n = 3) respectively, were derived. These data are in good agreement with the assigned value of 19.91 ± 0.82 μmol kg−1 (as 95% confidence interval, derived from an international intercomparison exercise). The methodology was also applied to the determination of a 50-fold lower concentration of MeHg in a salmon fish. A method detection limit (3SD) of 0.9 nmol kg−1 based on processing of a 0.40 g subsample was obtained.

Thiols in wetland interstitial waters and their role in mercury and methylmercury speciation

Organic sulfhydryl compounds, or thiols, are ligands that strongly complex class B metals such as Hg and methylmercury (MeHg). We determined the concentration profiles of five low‐molecular‐weight thiols (cysteine, thioglycolic acid, glutathione, N‐acetyl‐L‐cysteine, and 3‐mercaptopropionic acid) in sediment interstitial waters, at a vertical resolution of 1 cm, in three contrasting freshwater and brackish wetlands in Canada. All five thiols were detected in the porewaters, with concentrations ranging from nanomolar to submicromolar. In one of the wetlands (Baie St. Francois) the profiles of Hg and MeHg were also obtained at the same vertical resolution. Thermodynamic calculations revealed that at these levels thiols play a negligible role in inorganic Hg speciation in sediment interstitial waters, but they can dominate the MeHg speciation. Consistent with recent findings that intracellular MeHg in fish is dominated by MeHg‐thiol complexes, this suggests that thiols also play a significant role in MeHg speciation in the extracellular environment.

Current Hair Mercury Levels in Japanese for Estimation of Methylmercury Exposure

Methylmercury (MeHg) is an environmental pollutant with neurotoxic effects on the central nervous system. The major exposure route of MeHg to humans is via consumption of fish and shellfish which accumulate the chemical through the food web in an aquatic environment. We have been conducting a survey on hair mercury contents among general populations from different districts to estimate the current Japanese MeHg exposure level. In Japan, a provisional regulatory standard of mercury and MeHg in fish and shellfish was determined in 1973 based on the assumption of a safe intake limit of 0.17 mg/person/week (0.48 μg/kg/day). On the other hand, the US EPA issued a revised reference dose based on a cohort study conducted in the Faroe Islands. Recently, a provisional tolerable weekly intake (PTWI) of MeHg was revised to 1.6 μg/kg/week in 61st Joint FAO/WHO Expert Committee on Food Additives (JECFA), which was about half that of the Japanese standard. The distribution of hair mercury levels in Japanese populations currently obtained from 10 districts indicated that 25% of the Japanese females of child-bearing age were estimated to be exposed to MeHg over the PTWI level. This would reflect the high Japanese consumption of marine products. Not only mercury contamination, but also the nutritional benefit may have to be considered when discussing the risk involved in the current level of fish and shellfish consumption in Japan.

Predicted Mercury Concentrations in Hair From Infant Immunizations: Cause for Concern

Mercury (Hg) is considered one of the world’s most toxic metals. Current thinking suggests that exposure to mercury occurs primarily from seafood contamination and rare catastrophic events. Recently, another common source of exposure has been identified. Thimerosal (TMS), a preservative found in many infant vaccines, contains 49.6% ethyl mercury (EtHg) by weight and typically contributes 25 μg. of EtHg per dose of infant vaccine. As part of an ongoing review, the Food and Drug Administration (FDA) announced in 1999 that infants who received multiple TMS-preserved vaccines may have been exposed to cumulative Hg in excess of Federal safety guidelines. According to the centers for disease control (CDC) recommended immunization schedule, infants may have been exposed to 12.5 μg Hg at birth, 62.5 μg EtHg at 2 months, 50 μg EtHg at 4 months, 62.5 μg EtHg at 6 months, and 50 μg EtHg at approximately 18 months, for a total of 237.5 μg EtHg during the first 18 months of life, if all TMS-containing vaccines were administered. Neurobehavioral alterations, especially to the more susceptible fetus and infant, are known to occur after relatively low dose exposures to organic mercury compounds. In effort, to further elucidate the levels of ethyl mercury resulting from exposure to vaccinal TMS, we estimated hair Hg concentrations expected to result from the recommended CDC schedule utilizing a one compartment pharmacokinetic model. This model was developed to predict hair concentrations from acute exposure to methymercury (MeHg) in fish. Modeled hair Hg concentrations in infants exposed to vaccinal TMS are in excess of the Environmental Protection Agency (EPA) safety guidelines of 1 ppm for up to 365 days, with several peak concentrations within this period. More sensitive individuals and those with additional sources of exposure would have higher Hg concentrations. Given that exposure to low levels of mercury during critical stages of development has been associated with neurological disorders in children, including ADD, learning difficulties, and speech delays, the predicted hair Hg concentration resulting from childhood immunizations is cause for concern. Based on these findings, the impact which vaccinal mercury has had on the health of American children warrants further investigation.

Development of a single-meal fish consumption advisory for methyl mercury.

Methyl mercury (meHg) contamination of fish is the leading cause of fish consumption advisories in the United States. These advisories have focused upon repeated or chronic exposure, whereas risks during pregnancy may also exist from a single-meal exposure if the fish tissue concentration is high enough. In this study, acute exposure to meHg from a single fish meal was analyzed by using the one-compartment meHg biokinetic model to predict maternal hair concentrations. These concentrations were evaluated against the mercury hair concentration corresponding to the U.S. Environmental Protection Agency's reference dose (RfD), which is intended to protect against neurodevelopmental effects. The one-compartment model was validated against blood concentrations from three datasets in which human subjects ingested meHg in fish, either as a single meal or multiple meals. Model simulations of the single-meal scenario at different fish meHg concentrations found that concentrations of 2.0 ppm or higher can be associated with maternal hair concentrations elevated above the RfD level for days to weeks during gestation. A single-meal fish concentration cutoff of > or = 2.0 ppm is an important consideration, especially because this single high exposure event might be in addition to a baseline meHg body burden from other types of fish consumption. This type of single-meal advisory requires that fish sampling programs provide data for individual rather than composited fish, and take into account seasonal differences that may exist in fish concentrations.

Does Human Exposure to Mercury in Fish Cause Neurodevelopmental Problems?

Article| February 01 1999 Does Human Exposure to Mercury in Fish Cause Neurodevelopmental Problems? AAP Grand Rounds (1999) 1 (2): 14–15. https://doi.org/10.1542/gr.1-2-14 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation Does Human Exposure to Mercury in Fish Cause Neurodevelopmental Problems?. AAP Grand Rounds February 1999; 1 (2): 14–15. https://doi.org/10.1542/gr.1-2-14 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search toolbar search search input Search input auto suggest filter your search All PublicationsAll JournalsAAP Grand RoundsPediatricsHospital PediatricsPediatrics In ReviewNeoReviewsAAP NewsAll AAP Sites Search Advanced Search Topics: fishes, fluorescent in situ hybridization, mercury Source: Davidson PW, Myers GJ, Cox C, Axtell C, et al. Effects of prenatal and postnatal methylmercury exposure from fish consumption on neurodevelopment. Outcomes at 66 months of age in the Seychelles Child Development Study. JAMA. 1998;280:701–707. Neurodevelopment up to 66 months of age was evaluated after prenatal and postnatal exposure to methylmercury (MeHg) in 711 mother and child pairs living in the Republic of Seychelles (a westernized archipelago in the Indian Ocean) and ingesting fish almost daily. Inorganic mercury (Hg) discharged into water is converted to MeHg by microorganisms and bioaccumulated up the aquatic food chain. Levels of total Hg (THg) in 350 samples of fish were similar to those in fish sold in US markets. Maternal and infant hair levels of THg were 6.8 and 6.5 parts per million respectively (the lowest toxic level in hair for Hg is 50 ppm in adults). Frequent consumption of ocean fish can lead to MeHg levels as high as 50 ppm in hair samples. Maternal and child levels were not highly associated and were typical of populations that depend on fish as a major source of protein and calories. Polychlorinated biphenyls (PCBs) were measured in 49 children and found to be absent. Six age-appropriate neurodevelopment tests were administered to the children: Bender Gestalt, Child Behavior Checklist, Woodcock-Johnson Applied Problems and Word Recognition Tests of Achievement, McCarthy Scales of Children’s Abilities, and the Preschool Language Scale. No adverse outcomes were found. The delivery of heavy metals to the developing brain of the fetus or infant may adversely affect this organ because it is more sensitive than that of the adult brain to neurotoxic effects. Prenatal exposure to very high levels of MeHg in fish is associated with cerebral palsy, deafness, microcephaly, mental retardation, and seizures. Hg toxicity, like lead exposure, probably follows a dose response relationship. The questions that need to be answered are, how much Hg exposure is too much and at what time during development is the exposure most harmful. MeHg, like lead and aluminum, is easily absorbed by the human gut. The increased levels of MeHg in the Seychelles population (10–20 times higher than that in the USA) is not the result of ingesting an excessively high concentration of MeHg in a few fish, but the continued ingestion of more fish. In contrast to the above study, neurodevelopment studies involving children from the Faroe Islands (an archipelago situated between the British Isles, Norway, and Iceland) demonstrate cognitive defects in children tested at 7 years of age after prenatal exposure to Pilot Whales whose meat MeHg content is 10 times higher than that of the ocean fish consumed by the Seychelles and whose blubber concentration of PCBs is elevated.1 Prenatal ingestion of PCBs is also known to be neurotoxic to the developing brain.2 The Faroe Island study utilized more sensitive tests for neurodevelopment and demonstrated subtle deficits in language, attention, and memory. Maternal hair mercury levels in the Faroe Island study were similar... You do not currently have access to this content.

Bioaccumulation of mercury in pelagic freshwater food webs

Current paradigms regarding the bioaccumulation of mercury are rooted in observations that monomethyl mercury (meHg) biomagnifies along pelagic food chains. However, mechanisms regulating the formation of meHg, its initial incorporation at the base of pelagic food chains, and its subsequent trophic transfer remain controversial. Here we use field data from 15 northern Wisconsin lakes, equilibrium aqueous speciation modeling, and statistical modeling to revisit several hypotheses about the uptake, distribution, and fate of inorganic Hg (Hg II) and meHg in aquatic biota. Our field data comprise determinations of total Hg (Hg T) and meHg in surface waters, sediments, microseston, zooplankton, and small fish in each of the study lakes. For these lake waters, strong positive correlations between DOC and aqueous concentrations of mercury along with negative correlations between DOC and the seston–water partitioning of mercury indicate that organic ligands bind Hg II and meHg strongly enough to dominate their apparent aqueous speciation. In the microseston, zooplankton and fish, meHg concentrations and bioaccumulation factors (BAFs) increased with increasing trophic level while biotic concentrations of Hg II decreased — indicating that meHg was indeed the biomagnified species of mercury. For all trophic levels, meHg concentrations varied positively with the calculated aqueous concentration of meHg + (free ion), especially when coupled with pH, or meHgOH (hydroxide) species but not with meHgCl 0, the neutral chloride complex. These findings suggest that: (1) the passive uptake of meHg does not control bioaccumulation at the base of aquatic food webs in nature (i.e. phyto- and bacterioplankton); (2) correlation with pH and DOC largely reflect the supply and bioavailability of meHg to lower trophic levels; and (3) meHg concentrations at higher trophic levels reflect uptake at low trophic levels and other factors, such as diet and growth. Low concentrations of meHg in surficial sediments indicate that the fates of biotic Hg II and meHg are different. Most biotic meHg is demethylated rather than buried in lake sediments.

ECOLOGICAL RISK OF MERCURY IN THE ENVIRONMENT: THE INADEQUACY OF “THE BEST AVAILABLE SCIENCE”

ECOLOGICAL RISK OF MERCURY IN THE ENVIRONMENT: THE INADEQUACY OF “THE BEST AVAILABLE SCIENCE”

Certified reference materials (CRMs 463 and 464) for the quality control of total and methyl mercury determination in tuna fish

Determinations of total mercury and methyl mercury (MeHg) are currently performed by a number of laboratories to control the level of contamination of fish samples. The need to improve the quality control of MeHg in fish has justified the organisation of a series of interlaboratory studies in the frame of the BCR-Programme (now renamed Measurements and Testing Programme) of the European Commission, which were successfully concluded by the certification of total mercury and MeHg in two tuna fish materials (CRMs 463 and 464). These materials were collected in the Adriatic Sea, carefully prepared (controlled freeze-drying) and their homogeneity and stability were verified. This paper presents the certification work performed by 14 laboratories from 8 Member States of the European Union. The certified values for total mercury and MeHg are 2.85 ± 0.16 μg/g and 3.04 ± 0.16 μg/g (as MeHg +) in the CRM 463, and 5.24 ± 0.10 μg/g and 5.50 ± 0.17 μg/g (as MeHg +) in the CRM 464, respectively.

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.