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Large numbers of individuals suffered severe neurological effects from poisoning with methyl mercury from the consumption of fish contaminated by industrial discharge in Minamata in the 1950s and 1960s and from bread made from fungicide-treated wheat in the early 1970s in Iraq. In both episodes, infants exposed in utero showed developmental delays. Data from Iraq permitted the estimation of dose-response relationships and provided evidence of greater sensitivity of the foetal brain compared to adult. Studies in a number of communities regularly consuming fish have sought to determine whether and at what level of prenatal exposure neurodevelopment defects may be detected, but the findings do not present a consistent picture. Benchmark analysis using data from Iraq and the three largest studies (New Zealand, Faroes, and Seychelles) suggest an overlap in estimated dose corresponding to a 10% increase in prevalence of adverse effects above background level. However, the Seychelles study, examining children up to 9 years of age, has not found a consistent pattern of adverse developmental effects; a possible explanation may be the presence of micronutrients in the ocean fish diet that enhance brain development and/or counter the toxic effects of methyl mercury.

Evidence from the Seychelles Child Development Nutrition Study suggests that maternal nutritional status can modulate the relationship between prenatal methylmercury (MeHg) exposure and developmental outcomes in children. The aim of this study was to investigate whether maternal PUFA status was a confounding factor in any possible associations between prenatal MeHg exposure and developmental outcomes at 5 y of age in the Republic of Seychelles. Maternal status of (n-3) and (n-6) PUFA were measured in serum collected at 28 wk gestation and delivery. Prenatal MeHg exposure was determined in maternal hair collected at delivery. At 5 y of age, the children completed a comprehensive range of sensitive developmental assessments. Complete data from 225 mothers and their children were available for analysis. Multiple linear regression analyses revealed Preschool Language Scale scores of the children improved with increasing maternal serum DHA [22:6(n-3)] concentrations and decreased with increasing arachidonic acid [20:4(n-6)] concentrations, albeit verbal intelligence improved with increasing (n-6) PUFA concentrations in maternal serum. There were no adverse associations between MeHg exposure and developmental outcomes. These findings suggest that higher fish consumption, resulting in higher maternal (n-3) PUFA status, during pregnancy is associated with beneficial developmental effects rather than detrimental effects resulting from the higher concomitant exposures of the fetus to MeHg. The association of maternal (n-3) PUFA status with improved child language development may partially explain the authors' previous finding of improving language scores, as prenatal MeHg exposure increased in an earlier mother-child cohort in the Seychelles where maternal PUFA status was not measured.

Background Dental amalgams contain approximately 50 percent metallic mercury and emit mercury vapor during the life of the restoration. Controversy surrounds whether fetal exposure to mercury vapor resulting from maternal dental amalgam restorations has neurodevelopmental consequences. Methods The authors determined maternal amalgam restoration status during gestation (prenatal exposure to mercury vapor [Hg 0 ]) retrospectively in 587 mother-child pairs enrolled in the Seychelles Child Development Study, a prospective longitudinal cohort study of the effects of prenatal and recent postnatal methylmercury (MeHg) exposure on neurodevelopment. They examined covariate-adjusted associations between prenatal maternal amalgam restoration status and the results of six age-appropriate neurodevelopmental tests administered at age 66 months. The authors fit the models without and with adjustment for prenatal and recent postnatal MeHg exposure metrics. Results The mean number of maternal amalgam restorations present during gestation was 5.1 surfaces (range, 1–22) in the 42.4 percent of mothers who had amalgam restorations. The authors found no significant adverse associations between the number of amalgam surfaces present during gestation and any of the six outcomes, with or without adjustment for prenatal and postnatal MeHg exposure. Results of analyses with the secondary metric, prenatal amalgam occlusal point scores, showed an adverse association in boys only on a letter- and word-identification subtest of a frequently used test of scholastic achievement, whereas girls scored better on several other tests with increasing exposure. Conclusions This study’s results provide no support for the hypothesis that prenatal Hg 0 exposure arising from maternal dental amalgam restorations results in neurobehavioral consequences in the child. These findings require confirmation from a prospective study of coexposure to MeHg and Hg 0 .

Maternal consumption of fish during the gestational period exposes the fetus to both nutrients, especially the long-chain polyunsaturated fatty acids (LCPUFAs), believed to be beneficial for fetal brain development, as well as to the neurotoxicant methylmercury (MeHg). We recently reported that nutrients present in fish may modify MeHg neurotoxicity. Understanding the apparent interaction of MeHg exposure and nutrients present in fish is complicated by the limitations of modeling methods. In this study we fit varying coefficient function models to data from the Seychelles Child Development Nutrition Study (SCDNS) cohort to assess the association of dietary nutrients and children's development. This cohort of mother-child pairs in the Republic of Seychelles had fish consumption averaging 9 meals per week. Maternal nutritional status was assessed for five different nutritional components known to be present in fish (n-3 LCPUFA, n-6 LCPUFA, iron status, iodine status, and choline) and associated with children's neurological development. We also included prenatal MeHg exposure (measured in maternal hair). We examined two child neurodevelopmental outcomes (Bayley Scales Infant Development-II (BSID-II) Mental Developmental Index (MDI) and Psychomotor Developmental Index (PDI)), each administered at 9 and at 30 months. The varying coefficient models allow the possible interactions between each nutritional component and MeHg to be modeled as a smoothly varying function of MeHg as an effect modifier. Iron, iodine, choline, and n-6 LCPUFA had little or no observable modulation at different MeHg exposures. In contrast the n-3 LCPUFA docosahexaenoic acid (DHA) had beneficial effects on the BSID-II PDI that were reduced or absent at higher MeHg exposures. This study presents a useful modeling method that can be brought to bear on questions involving interactions between covariates, and illustrates the continuing importance of viewing fish consumption during pregnancy as a case of multiple exposures to nutrients and to MeHg. The results encourage more emphasis on a holistic view of the risks and benefits of fish consumption as it relates to infant development.

The Seychelles Child Development Study was designed to test the hypothesis that prenatal exposure to MeHg from maternal consumption of a diet high in fish is detrimental to child neurodevelopment. To date, no consistent pattern of adverse associations between prenatal exposure and children's development has appeared. In a comprehensive review of developmental studies involving MeHg, a panel of experts recommended a more consistent use of the same endpoints across studies to facilitate comparisons. Both the SCDS and the Faeroe Islands studies administered the Bender Visual Motor Gestalt Test. However, the method of test administration and scoring used was different. We repeated the test on the SCDS Main Study children (mean age 10.7 years) using the same testing and scoring procedure reported by the Faeroe studies to obtain Copying Task and Reproduction Task scores. We found no association between prenatal MeHg exposure and Copying Task scores which was reported from the Faeroese study. However, our analysis did show a significant adverse association between MeHg and Reproduction Task scores with all the data (p = 0.04), but not when the single outlier was removed (p = 0.07). In a population whose exposure to MeHg is from fish consumption, we continue to find no consistent adverse association between MeHg and visual motor coordination.

Background:Both folate and betaine are important predictors of total homocysteine (tHcy) during pregnancy. However, studies to date have only been undertaken in populations with Western dietary patterns. Objective: We investigated the predictors of tHcy in pregnant women recruited in the Seychelles, a population where access to fortifiedfoodsislimitedandwherewomenhabituallyconsumediets rich in fish, eggs, rice, and fruit. Design: Pregnant women (n 226) provided blood samples at enrollment,atweek28ofgestation,andatdelivery.Cordbloodwas obtained from a subset of participants (n 135). Results: As in other studies, maternal tHcy was lower during pregnancy than at delivery, whereas folate and vitamin B-12 status declinedsignificantlytodelivery.Despitelowmaternalfolatestatusat delivery (median: 9.0 nmol/L), with 35% of women in the deficient range(serumfolate:6.8nmol/L),cordbloodfolatestatus(median: 40.2 nmol/L) was similar to concentrations reported in Western populations. Folate was a significant predictor of tHcy at all time points (P 0.001). In contrast with previous studies, betaine was only a significant predictor of maternal tHcy (P 0.001) when the essential amino acid methionine was low. Conclusions: The current study reports 2 important findings. First, fetal requirements for folate are paramount, such that cord blood folate statusismaintained,evenwhenmaternalstatusislow.Second,betaine is a significant predictor of tHcy in pregnant women with low serum folate and low serum methionine concentrations. Am J Clin Nutr 2008;87:391–7.

Several biological media have been used as indicators of the fetal body burden of methylmercury and the levels in the primary target tissue, the developing brain. These media include maternal hair and blood. The relative merits of these media will be considered both with regard to current knowledge of the physiology of mercury disposition in the body and also the practicality of field application with respect to sample, collection, transport, storage and processing.

Background: The Seychelles Child Development Study (SCDS) has been longitudinally following a cohort of over 700 children enrolled in 1989. Their mothers consumed a diet high in fish during pregnancy. Repeated examination of the SCDS cohort at six different ages through age 11 years has shown no pattern of adverse effects. Some early appearing beneficial associations between both prenatal and postnatal hair MeHg and several child development endpoints were noted. We hypothesized these might be related to micronutrients in the fish, but they were not found when the children reached middle school age. These findings suggest that the associations observed between MeHg and developmental outcomes may vary with developmental stage. Method: We examined the main cohort of the SCDS to determine if this might be true using a longitudinal multiple regression analysis design that focused on those endpoints that were repeatedly measured at different ages. The primary endpoint analyzed was global cognition, involving a measure of developmental quotient or IQ. Secondary analyses included other domains such as Reading and Mathematics scholastic achievement, social behavior, and memory. Analyses involved two different approaches, one including incorporation of a passage of time variable, the other including a difference of scores across time points. Results: No significant associations were found between prenatal MeHg exposure and any of the repeatedly measured endpoints. Conclusions: These results suggest that even when individual subject variance is controlled there was no consistent pattern of associations between child development outcomes and prenatal exposures to MeHg from maternal consumption of a diet high in fish. The Seychellois diet contains about 10 times more ocean fish than is typically consumed by US citizens. Our primary focus on IQ should further inform growing scientific interest in the analysis of the risks and benefits of fish consumption on overall cognitive ability.

Methyl mercury (MeHg) is highly toxic to the developing nervous system. Human exposure is mainly from fish consumption since small amounts are present in all fish. Findings of developmental neurotoxicity following high-level prenatal exposure to MeHg raised the question of whether children whose mothers consumed fish contaminated with background levels during pregnancy are at an increased risk of impaired neurological function. Benchmark doses determined from studies in New Zealand, and the Faroese and Seychelles Islands indicate that a level of 4-25 parts per million (ppm) measured in maternal hair may carry a risk to the infant. However, there are numerous sources of uncertainty that could affect the derivation of benchmark doses, and it is crucial to continue to investigate the most appropriate derivation of safe consumption levels. Earlier, we published the findings from benchmark analyses applied to the data collected on the Seychelles main cohort at the 66-month follow-up period. Here, we expand on the main cohort analyses by determining the benchmark doses (BMD) of MeHg level in maternal hair based on 643 Seychellois children for whom 26 different neurobehavioral endpoints were measured at 9 years of age. Dose-response models applied to these continuous endpoints incorporated a variety of covariates and included the k-power model, the Weibull model, and the logistic model. The average 95% lower confidence limit of the BMD (BMDL) across all 26 endpoints varied from 20.1 ppm (range=17.2-22.5) for the logistic model to 20.4 ppm (range=17.9-23.0) for the k-power model. These estimates are somewhat lower than those obtained after 66 months of follow-up. The Seychelles Child Development Study continues to provide a firm scientific basis for the derivation of safe levels of MeHg consumption.

Exposure to environmental mercury may be a factor that contributes to idiosyncratic autoimmune disease. Studies have demonstrated that inorganic, ionic mercury (i.e., Hg2+) modulates several lymphocyte signal transduction pathways, which may be a mechanism whereby Hg2+ dysregulates the immune response. The CD95/Fas apoptotic signaling pathway, which is of critical importance in regulating peripheral tolerance, is disrupted by low and environmentally relevant concentrations of Hg2+. Activation of the cysteine protease caspase-3 is a critical component of both CD95-mediated and TNF-alpha-induced apoptosis. The present work demonstrates that Hg2+ selectively disrupts death receptor mediated caspase-3 activation, where CD95-mediated caspase-3 activation is impaired in Hg2+ treated cells; whereas TNF-alpha-induced caspase-3 activation is not. Using the fluorogenic caspase-3 substrate, Ac-DEVD-7-amino-4-methyl coumarin, to measure caspase-3 enzyme activity as well as Western blotting to track processing of the caspase-3 proenzyme, we have considered the potential direct and indirect effects of Hg2+ on caspase-3. At relatively high concentrations and in a cell-free system, Hg2+ is capable of targeting the active site cysteinyl of caspase-3 resulting in enzyme inhibition. However, at more environmentally relevant exposures, Hg2+ does not gain access in appreciable quantities to the intracellular compartment where caspase-3 resides. Collectively, these data establish that Hg2+ impairs CD95-mediated apoptosis by targeting a plasma membrane proximal signaling event. By measuring the cellular Hg2+ content following various exposure conditions, we have determined that a cellular Hg2+ burden of approximately 50 ng/10(6) cells is sufficient to impair CD95-mediated caspase-3 activation. The present study furthers an understanding of the mechanism whereby relatively low and non-cytotoxic concentrations of Hg2+ may disrupt peripheral tolerance leading to sustained autoimmune disease.

Studies of the association between prenatal methylmercury exposure from maternal fish consumption and neurodevelopmental test scores in the Seychelles Child Development Study have not found adverse effects through age 9 years. The analysis for the most recent 9-year data (Lancet 361 (2003) 1686) employed conventional linear regression models. In this study we reanalyzed the same Seychelles 9-year data using semiparametric additive models with different degrees of smoothing to explore whether nonlinear effects of prenatal exposure were present. Of 21 endpoints in the linear analysis, we chose only those with a two-tailed P value less than 0.2 for the effect of prenatal exposure. Six endpoints met the criterion. A nonlinear effect was identified with the more smooth model for only one endpoint. The test for an overall effect of prenatal exposure was also significant, with a P value of 0.04, while the corresponding P value in the linear regression analysis was 0.08. The nonlinear curve appeared to be nearly flat when the level was below approximately 12 ppm in maternal hair, with a linear trend above that level, suggesting a possible adverse effect in the uppermost range of prenatal exposure included in this cohort. Because of the descriptive nature of semiparametric additive models, the P values are not precise, and certainly there are fewer data above 12 ppm. We conclude that this reanalysis supports the primary linear analysis, showing little evidence for a prenatal adverse effect.

Studies of the effects of environmental exposures on human health typically require estimation of both exposure and outcome. Standard methods for the assessment of the association between exposure and outcome include multiple linear regression analysis, which assumes that the outcome variable is observed with error, while the levels of exposure and other explanatory variables are measured with complete accuracy, so that there is no deviation of the measured from the actual value. The term measurement error in this discussion refers to the difference between the actual or true level and the value that is actually observed. In the investigations of the effects of prenatal methylmercury (MeHg) exposure from fish consumption on child development, the only way to obtain a true exposure level (producing the toxic effect) is to ascertain the concentration in fetal brain, which is not possible. As is often the case in studies of environmental exposures, the measured exposure level is a biomarker, such as the average maternal hair level during gestation. Measurement of hair mercury is widely used as a biological indicator for exposure to MeHg and is the only indicator that has been calibrated against the target tissue, the developing brain. Variability between the measured and the true values in explanatory variables in a multiple regression analysis can produce bias, leading to either over or underestimation of regression parameters (slopes). Fortunately, statistical methods known as measurement error models (MEM) are available to account for measurement errors in explanatory variables in multiple regression analysis, and these methods can provide an (either “unbiased” or “bias-corrected”) estimate of the unknown outcome/exposure relationship. In this paper, we illustrate MEM analysis by reanalyzing data from the 5.5-year test battery in the Seychelles Child Development Study, a longitudinal study of prenatal exposure to MeHg from maternal consumption of a diet high in fish. The use of the MEM approach was made possible by the existence of independent, calibration data on the magnitude of the variability of the measurement error deviations for the biomarker of prenatal exposure used in this study, the maternal hair level. Our reanalysis indicated that adjustment for measurement errors in explanatory variables had no appreciable effect on the original results.

Summary Introduction Exposure to methylmercury (MeHg) before birth can adversely affect children's neurodevelopment. The most common form of prenatal exposure is aternal fish consumption, but whether such exposure harms the fetus is unknown. We aimed to identify adverse neurodevelopmental effects in a fish-consuming population. Methods We investigated 779 mother-infant pairs residing in the Republic of Seychelles. Mothers reported consuming fish on average 12 meals per week. Fish in Seychelles contain much the same concentrations of MeHg as commercial ocean fish elsewhere. Prenatal MeHg exposure was determined from maternal hair growing during pregnancy. We assessed neurocognitive, language, memory, motor, perceptual-motor, and behavioural functions in children at age 9 years. The ssociation between prenatal MeHg exposure and the primary endpoints was investigated with multiple linear regression with adjustment for covariates that affect child development. Findings Mean prenatal MeHg exposure was 6·9 parts per million (SD 4·5ppm). Only two endpoints were associated with prenatal MeHg exposure. Increased exposure as associated with decreased performance in the grooved pegboard using the non-dominant hand in males and improved scores in the hyperactivity index of the Conner's teacher rating scale. Covariates affecting child development were appropriately associated with endpoints. Interpretation These data do not support the hypothesis that there is a neurodevelopmental risk from prenatal MeHg exposure resulting solely from ocean fish consumption.

The historical record of clinical cases of methyl mercury poisoning dates back to the 19th century when the first chemical synthesis occurred. The potent fungicidal properties of both methyl and the closely related ethyl mercury compound were subsequently discovered, which led to widespread agricultural application for prevention of fungal infection in seed grain. Several catastrophic outbreaks of poisoning occurred in the mid-20th century when the treated seed grain was mistakenly used to prepare homemade bread. The largest outbreak took place in rural Iraq in the early 1970s. Human poisonings also occurred in Japan due to the release of methyl mercury into bodies of fresh and ocean water. The most infamous outbreak occurred in the area of Minamata Bay: methyl mercury, which was unwittingly discharged into the ocean water, avidly accumulated in the aquatic food chain to such an extent that people who consumed fish were severely poisoned. Today, human exposure to methyl mercury occurs from consumption of fish and sea mammals. Inorganic mercury that is present in aquatic sediments is methylated by microorganisms and accumulates in the aquatic food chain. Although no cases of clinical poisoning have been reported, a number of epidemiological studies have been carried out that raise the possibility of prenatal damage. Previous studies (especially the Iraq outbreak) indicate that the prenatal stage of the life cycle is the most vulnerable. However, ongoing epidemiological studies of heavy fish consumers of the Seychelles Islands in the Indian Ocean do not reveal adverse effects. To the contrary, the results of some developmental tests that were conducted on prenatally exposed children indicate beneficial outcomes that correlate with mercury levels during pregnancy. This article discusses the potential role of micronutrients in fish as a plausible explanation for these findings.

Mechanisms of methylmercury (MeHg) and inorganic mercury (Hg) uptake were examined in HepG2 cells, a human hepatoma-derived cell line. MeHg uptake was faster when it was present as the l -cysteine complex, as compared to the glutathione (GSH), CysGly, γ-GluCys, d -cysteine, N-acetylcysteine, l -penicillamine, or albumin complexes. Uptake of MeHg- l -cysteine was independent of Na+, stereoselective, and was inhibited by the amino acid transport system l substrates l -leucine, l -valine, and l -phenylalanine (5 mM). Moreover, [3H] l -leucine uptake was inhibited by MeHg- l -cysteine, suggesting that MeHg- l -cysteine is transported into HepG2 cells by an l -type amino acid carrier. Uptake of MeHg as the GSH complex (MeHg-SG) was dependent on the extracellular GSH concentration, and was diminished when cellular γ-glutamyl transpeptidase activity was inhibited. Inorganic mercury uptake was slower than that of MeHg, but was also sensitive to the type of thiol ligand present. These findings demonstrate that mercury uptake by HepG2 cells is dependent on the chemical structure of the mercury compound, the thiol ligand, and the activity of γ-glutamyl transpeptidase. γ-Glutamyl transpeptidase appears to play a key role in the disposition of MeHg-SG by facilitating the formation of MeHg- l -cysteine, which is readily transported into the cells on an amino acid-type carrier.

Methylmercury (MeHg) is a neurotoxicant whose high-dose effects first became known following a number of poisoning outbreaks that occurred worldwide. The primary human exposure is low dosage from fish consumption. Studies of fish-eating populations have not found a consistent pattern of association between exposures and outcomes. Therefore, examining specific areas of cognitive functioning has been suggested as an important approach to determine whether more subtle effects of MeHg exposure are present. In the Seychelles longitudinal study of prenatal and postnatal MeHg exposure from fish consumption and development, the McCarthy Scales of Children's Abilities (MSCA) were administered to children at age 66 months. No association between MeHg exposure and performance on the MSCA General Cognitive Index was identified. We analyzed these data further to determine whether associations were present on specific subscales of the MSCA. The standard MSCA subscales were analyzed. Then, more specific subscales of the MSCA were defined and analyzed utilizing a neuropsychological approach. The subscales were recombined to approximate the domains of cognitive functioning evaluated in the Faroes and New Zealand studies. Analyses of both the standard and the recombined MSCA subscales showed no adverse associations with MeHg exposure and neuropsychological endpoints. A positive association between postnatal MeHg exposure and performance on the MSCA Memory subscale was found. These findings are consistent with previous reports from the Seychelles study in that no adverse effects of MeHg exposure from fish consumption can be detected in this cohort.

To reach its target tissue, methylmercury must traverse brain capillary endothelial cells, the site of the blood-brain barrier. Methylmercury uptake from blood plasma into these cells is mediated in part by an amino acid carrier that transports the methylmercury-L-cysteine complex; however, the mechanism by which it is released from the endothelial cells into brain interstitial space is unknown. Using bovine brain capillary endothelial cells in culture, the present study examined the hypothesis that methylmercury is transported out of these cells as a glutathione (GSH) complex. GSH concentration in cultured bovine brain capillary endothelial cells was 13.1 +/- 3.3 nmol/mg protein. Depletion of intracellular GSH in [203Hg]methylmercury-preloaded cells by exposure to 1-chloro-2,4-dinitrobenzene or diethyl maleate decreased the rate of [203Hg]methylmercury efflux. Incubation of [203Hg]methylmercury-preloaded cells with high concentrations of S-methylglutathione, S-ethylglutathione, S-butylglutathione, and sulfobromophthalein-glutathione inhibited [203Hg]methylmercury efflux. The GSH analogs gamma-glutamylglycylglycine and ophthalmic acid also inhibited [203Hg]methylmercury efflux, but to a lesser degree than the glutathione S-conjugates, whereas L-leucine, L-methionine, and L-alanine had no effect. Efflux was not affected by depletion of intracellular ATP with 2-deoxyglucose or antimycin A. These results indicate that complexation with GSH and subsequent transport of the complex by an ATP-independent mechanism may be involved in the transport of methylmercury out of brain capillary endothelial cells.

Both terrestrial and aquatic food chains are capable of accumulating certain environmental contaminants to toxic concentrations. This article focuses on the aquatic food chain because we have less control over contaminant entry into this chain than we have for the terrestrial chain. In general, at least three special properties are required for a contaminant to bioaccumulate in an aquatic food chain: 1) a high octanol-water partition coefficient, 2) chemical and metabolic stability in water and in organisms in the food chain, and 3) a low toxicity to organisms in the chain so that the chain is not broken by loss of an intermediate species. Few of the thousands of chemicals produced by human industry meet these requirements. In terms of organic chemicals, the best known examples of bioaccumulation in aquatic food chains are the polychlorinated biphenyls (PCBs), dioxins, and organochlorine pesticides such as dichlorodiphenyltrichloroethane (DDT). Few examples exist of bioaccumulation of metal compounds. Methylmercury is arguably the most dramatic and best documented example of high bioaccumulation.

Rat pheochromocytoma PC12 cell sublines with increasing resistance to methylmercury (MeHg) were isolated by exposure to MeHg in two sequential steps. The strongest resistance (PC12/TM) among the clones obtained by the first cloning was characterized. PC12/TM cells exhibited about an 8- to 10-fold increase in resistance compared with parent PC12 cells on the bases of the concentration required for 50% inhibition of growth and colony-forming activity. PC12/TM cells accumulated smaller amounts of MeHg (one-half to one-fifth) than parent PC12 cells. This reduced MeHg accumulation in PC12/TM cells resulted from the slow uptake and rapid efflux. A close correlation between reduced MeHg accumulation and MeHg resistance was found among seven sublines of PC12 cells with different sensitivity to MeHg. The reduced retention of MeHg in PC12 sublines was also well correlated with the sensitivity to MeHg. Phenol-3,6-dibromophthalein disulfonate inhibited MeHg efflux from PC12/TM cells and increased its accumulation. These results suggest that efflux of MeHg from PC12/TM cells is associated with glutathione.

Due to its ability to avidly accumulate methyl mercury from blood, scalp hair has been widely used as a biological monitor for human exposure. The question arises that hair may also be an important route of elimination of methyl mercury from the body. Taking original publications and reviews on the physiology of hair (including growth by weigh and density) and on the deposition parameters for methyl mercury in the body (including the hair to blood concentration ratio of methyl mercury), one can calculate the rate of elimination of methyl mercury in hair. The result indicates that hair accounts for only a small fraction, less than 10%, of the total elimination of methyl mercury from the body. This relationship is expected to be maintained at every level when the dominant form of mercury is methyl. Other species of mercury I eliminated by hair even at a lower rate.

Corrigendum to ‘‘Habitual fish consumption does not prevent a decrease in LCPUFA status in pregnant women (The Seychelles Child Development Nutrition Study)’’ [Prostaglandins, Leukotrienes and Essential Fatty Acids 78 (2008) 343–350] M.P. Bonham, E.M. Duffy , J.M.W. Wallace , P.J. Robson , G.J. Myers , P.W. Davidson , T.W. Clarkson , C.F. Shamlaye , J.J. Strain a,n a Northern Ireland Centre for Food and Health (NICHE), Department of Biomedical Sciences, University of Ulster, Cromore Road, Coleraine BT52 1SA, Northern Ireland, UK b University of Rochester, School of Medicine and Dentistry, Rochester, NY 14642, USA c Ministry of Health, Box 52, Republic of Seychelles

In the article cited above, it has recently come to the authors’ attention that there were errors in the calculation of Docosahexaenoic acid (DHA), Arachidonic acid (AA), Eicosapentaenoic acid (EPA), Alpha-linolenic acid (ALA), Linoleic acid (LA), V-3 and V-6 concentrations. These errors resulted from applying an incorrect conversion factor to account for sample dilution. As a result, the values for these longchain polyunsaturated fatty acid (LCPUFA) concentrations in Table 2 were incorrectly reported. More specifically, the means, standard deviations and ranges of the reported LCUPFA values are overestimated and should be divided by 6.25. Reported values for the AA/DHA ratio and V-6/V-3 ratio in Table 2 are not affected. The estimated regression coefficients for DHA, AA, EPA + DHA, V-3 and V-6 shown in Table 4 are underestimated and should be multiplied by 6.25, while the p-values are unchanged. Estimated regression coefficients for AA/ DHA ratio and V-6/V-3 in Table 4 are not affected. Results presented in Table 3 and Fig. 1 are not affected. Further details are available from the first author upon request. The conclusions of this article remain unchanged. The authors regret the errors. A R T I C L E I N F O

We conducted a population-based pharmacokinetic study to assess blood levels and elimination of mercury after vaccination of premature infants born ator =32 and37 weeks of gestation and with birth weightor =2000 but3000 g.Blood, stool, and urine samples were obtained before vaccination and 12 hours to 30 days after vaccination from 72 premature newborn infants. Total mercury levels were measured by atomic absorption.The mean +/- standard deviation (SD) birth weight was 2.4 +/- 0.3 kg for the study population. Maximal mean +/- SD blood mercury level was 3.6 +/- 2.1 ng/mL, occurring at 1 day after vaccination; maximal mean +/- SD stool mercury level was 35.4 +/- 38.0 ng/g, occurring on day 5 after vaccination; and urine mercury levels were mostly nondetectable. The blood mercury half-life was calculated to be 6.3 (95% CI, 3.85 to 8.77) days, and mercury levels returned to prevaccination levels by day 30.The blood half-life of intramuscular ethyl mercury from thimerosal in vaccines given to premature infants is substantially shorter than that of oral methyl mercury in adults. Because of the differing pharmacokinetics, exposure guidelines based on oral methyl mercury in adults may not be accurate for children who receive thimerosal-containing vaccines.

The assertion in the Case Report by Roger Ho and colleagues (Jan 24, p 352) that methyl mercury (MeHg) exposure from a daily diet of tuna is responsible for amnesia is problematic toxicologically and clinically. The lowest level reported for adult manifestations of MeHg exposure is 200 μg Hg per L whole blood. That level is used by most national regulatory committees. The blood Hg level of the patient in the Case Report was 28 μg/L. This is equivalent to a hair level of about 5·5 μg/g (ppm). In populations that consume fi sh regularly, this level is commonly seen: one study in the Seychelles found the mean maternal hair level to be 6·9 μg/g. There were no reports of memory loss. Additionally, neurological defi cits from MeHg poisoning are permanent, yet Ho and colleagues’ patient improved. The concomitant reduction of blood Hg by 9 μg/L in 2 months is consistent with the reported 44-day half-time in the blood. In Iraq, the fi rst symptoms of MeHg poisoning were paraesthesias and ataxia. Memory loss has not been a part of clinical reports in the past. Tremor, gingivitis, and erythism are typical of inorganic Hg poisoning. The absence of any of the typical fi ndings of MeHg poisoning, the presence of an atypical fi nding, amnesia, and the patient’s improvement make the conclusion that the patient suff ered from MeHg poisoning from consuming tuna untenable.

Evidence is presented that exposure of rats to elemental mercury vapor results in increased amounts of a metallothionein-like protein in kidney tissue but not in liver. After three or more daily exposures, each of 2 h duration, to elemental mercury vapor, more than 50% of the mercury in kidney tissue is bound to a protein having a molecular weight (mol. wt.) of about 10 000 as determined by Sephadex G-75 gel filtration chromatography. Cystine is incorporated into a 10 000 mol. wt. protein fraction from kidneys of rats which were injected with [U-14C]cystine after five daily 2-h exposures to mercury vapor. In contrast, no significant incorporation of [U-14C] cystine into this protein fraction was observed in kidneys of control rats or in livers of both control and mercury vapor-exposed rats. The in vivo incorporation of109Cd into the fraction followed the same pattern as that of [14C] cystine in rats injected with tracer doses of CdCl2 labeled with radioactive109Cd isotope. This 10 000 mol. wt. protein, newly synthesized in response to repeated exposures to mercury vapor, exhibited identical properties to metallothionein, namely in its subcellular localization, molecular weight, heat stability and isoelectric points. A significant incorporation of [U-14C]-cystine into this protein in rat kidney alone on exposure to mercury vapor confirms its induced biosynthesis in the kidney.

A new method of estimating fetal exposure is used in a dose-response analysis of data from the 1971 outbreak of methyl mercury poisoning in rural Iraq. An X-ray fluorescence instrument for the measurement of single strands of human hair was employed to obtain longitudinal profiles recapitulating fetal exposure. Logit and hockey-stick models as well as nonparametric smoothing are used to describe data on delayed development and central nervous system abnormality.

As bile is the main route of elimination of many metals, a large number of studies have been directed toward the characterization of the hepatobiliary transport of both endogenous and exogenous metals. Although some progress has been made, we still know little of the basic mechanisms involved in the hepatocellular uptake of metals, in their intracellular translocation and metabolism, or in their transport into bile. Our recent studies have focused on the last step in the hepatobiliary transport of mercury, namely, the secretion of the metal from liver cells into bile. The rate of secretion of methyl and inorganic mercury into bile was low in suckling rats and rapidly increased to adult rates soon after weaning. These changes closely followed similar developmental changes in the biliary secretion of reduced glutathione (GSH). When GSH secretion into bile was completely inhibited, without changing hepatic levels of GSH or mercury, mercury secretion was also completely blocked. Mercury secretion paralleled individual and sex-related differences in GSH secretion. At the same time, the secretion of mercury was independent of bile flow, of the thiol and mercury concentration gradients between bile and liver cells, and of those between bile and plasma. Our results, therefore, indicate a close coupling between the secretion of mercury and that of GSH. These in vivo findings, along with in vitro studies by others in vesicles isolated from the canalicular membrane of the liver cell, indicate a carrier-mediated transport system for GSH, but the nature of the linkage of this transport system with mercury secretion is not yet fully established. Our data and those in the literature are consistent with the involvement of at least two steps in the movement of mercury from liver cells to bile--the formation of a mercury-glutathione complex in the liver cell, followed by the secretion of this complex through a process closely linked to GSH secretion. The identification of GSH as an endogenous complexing agent in the transport of metals between tissues and body fluids now permits the design of therapeutic strategies aimed at exploiting this transport vehicle to effect the removal of metals via physiological routes of excretion. The present discussion considers the role of GSH in the hepatobiliary transport of metals. In doing so, a brief review is given of current understanding of hepatic GSH metabolism and transport.

The interrelation between the biliary transport of glutathione (GSH) and of inorganic mercury was investigated in suckling and adult male and female rats. The 14-day-old rat secreted inorganic mercury into bile at one-seventh the rate of the 28-day-old rat. Development of the ability to secrete mercury paralleled development of the ability to secrete GSH. The inability of the 14-day-old rat to secrete mercury and GSH occurred despite hepatic tissue concentrations of both of these compounds which were similar to those of adult rats. In adult rats, inhibition of GSH secretion by sulfobromophthalein (BSP) administration resulted in a parallel inhibition of mercury secretion. Conversely, the increase in the rate of GSH secretion into bile after cysteine or GSH administration was accompanied by an increase in the rate of mercury secretion into bile. The changes in the biliary secretion of mercury and of GSH after treatment with cysteine or GSH were not closely parallel, probably because of the tissue redistribution of mercury effected by these sulfhydryl-containing compounds. Mercury secretion into bile was independent of the changes in bile flow produced by dehydrocholate (DHC) or hypertonic sucrose, but it was closely related to the rate of GSH secretion. Further, sex differences and individual variability in the biliary secretion of inorganic mercury were correlated with differing abilities to secrete GSH into bile. These results suggest that the biliary secretion of inorganic mercury is in large part dependent on the biliary transport of GSH.

This study was undertaken to see whether the decreased pulmonary absorption of mercury vapor in alcohol-treated animals was due to decreased pulmonary transport or to decreased in vivo oxidation of the metal in the red blood cells. Metallic mercury dissolved in a phosphate buffer was introduced iv into alcohol-treated and untreated animals. The untreated animals exhaled 14% of the injected mercury as compared to 22% in the 34 treated animals. Furthermore, exhalation of mercury vapor continued for a much longer period in 17 treated animals. Alcohol also reduced the lung content of mercury by a factor of 10 and, to a less extent, the mercury content of heart, brain and blood. It was concluded that the primary effect of alcohol is on the rate of the in vivo oxidation of metallic mercury.

Observations are reported on the effects of administration of 2,4-dinitrophenol (DNP), probenecid, sodium fluoroacetate, sodium fluoride and sodium malonate on the ability of the rat kidney to accumulate inorganic mercury. Mercury was injected into female rats, body wt. 240 g, as mercuric chloride or mercuric cysteine (100 μg Hg per animal, i.m.) and the metabolic inhibitors were given subcutaneously in doses approaching the ld 50 dose. Mercury levels were measured in urine, blood and kidney. DNP inhibited the renal accumulation of mercury. The other inhibitors were ineffective. DNP was effective only when given just prior to the injection of mercury. The dose of DNP capable of inhibiting renal uptake or mercury was without effect on renal hemodynamics and either did not influence, or only slightly influenced, the excretion of various urinary solutes and water. DNP did not increase the urinary excretion of mercury. It was concluded that the selective accumulation of mercury by kidney is because of energy-dependent processes and that most of this accumulation took place directly into renal tissue from the peritubular capillaries and not by way of glomerular filtration.

The nature of the biliary metabolites of three phenanthridinium salts—3,8-diamino-6- p -aminophenyl-5-methylphenanthridinium chlori (150C47), 3,8-diamino-6-phenyl-5-ethylphenanthridinium bromide (ethidium), and 2-amino-6- p -carbethoxyaminophenyl-5-methylphenanthridinium sulfate (carbidium) —has been investigated in rats with ligated renal pedicles. Up to 50 per cent of a small intravenous dose of each of these compounds may be excreted in the bile of rats with ligated renal pedicles in 1 hr depending on the dose and individual variation. At the dose selected, about 15 per cent of the dose was excreted in the first hour after injection. Sixty-five percent of a 15 mg/kg dose of 150C47 was recovered in the bile in 11–21 hr; 85 percent of this total was excreted within 5 hr. Of the material recovered, approximately 15 per cent was unchanged 150C47. The major metabolite present in bile was a monoacetyl amino conjugate and this accounted for about 50 per cent of the material recovered. Two other metabolites were also shown to be present and these are also believed to be acetyl conjugates. One of these is probably a diacetylated compound and accounted for about 25 per cent of the material recovered. The other accounted for the remaining 10 per cent. During the first hour after injection, the material was almost entirely in the form of the major metabolite plus the unchanged compound. After injection of the major monoacetyl metabolite, only the injected monoacetyl compound and the diacetylated one could be detected in bile, and the rate of excretion exceeded the rate of excretion of all forms of 150C47 in control rats given the same dose of 150C47. Of a 15 mg/kg dose of ethidium, 50–55 per cent was recovered in the bile in 16–18 hr. Unchanged ethidium accounted for 20–25 per cent of the material present. Two metabolites were found and these are both believed to be monoacetyl amino conjugates. They accounted for 65–70 per cent and 10 per cent of the material recovered; 85–90 per cent of this total was excreted within 5 hr. Carbidium is excreted in bile as the unchanged compound and its acetyl conjugate. Only one acetyl conjugate is possible for this compound and it was the only metabolite found in bile. Of a dose of 15 mg/kg, 60–65 per cent was recovered in 10–16 hr. About 20 per cent of the material recovered was unchanged carbidium; the remaining 80 per cent was the acetyl derivative. During the first hour after injection, 55 per cent of the material excreted was unchanged carbidium.

The biliary excretion of phenanthridinium salts has been investigated in rats with ligated renal pedicles. The biliary excretion of the four phenanthridinium compounds investigated took place against large bile-blood concentration gradients and became constant with increasing dose. 150C47 (3, 8-diamino-6- p -aminophenyl-5-methylphenanthridinium chloride) was investigated in detail to determine if it is excreted into bile by the specific metabolically dependent transport system that has been proposed for a number of other quaternary ammonium compounds, including certain phenanthridinium compounds. The excretion of total diazotizable material in bile reached a maximum at a dose of about 20 mg/kg and then remained constant as the dose was increased further. This maximum was not a result of either decreased bile flow or a limited ability of the liver to accumulate 150C47. The excretion of free 150C47 increased with dose over the entire dose range investigated (0–50 mg/kg), whereas its monoacetyl metabolite reached a maximum rate of excretion at 15–20 mg/kg and then decreased as the dose was increased further. The excretion of both forms was directly proportional to dehydrocholate-induced bile flow, but independent of the decrease in flow caused by the intravenous administration of hypertonic sucrose. The possible role of bile salts in the excretion of phenanthridinium compounds is discussed, and data in vitro on the binding of 150C47 to plasma proteins and liver homogenates and its complexing with bile are presented in connection with this point. The behavior of this compound is compared with that of procaineamide ethobromide, a quaternary compound for which a specific metabolically dependent transport system has been proposed.