Review of the health effects of methylmercury

Exploring developmental MeHg impact on extraembryonic and cardiac vessels and its effect on cardiomyocyte contractility

The toxicity of methylmercury (MeHg) during embryonic development is a relevant issue that remains unclear and deserves investigation. In this sense, there is evidence that links the intake of contaminated food with cardiovascular pathologies in human adults and children. Thus, this study aimed to verify the impact of MeHg on the structure and integrity of extraembryonic and cardiac blood vessels and the contractile function of cardiomyocytes, also evaluating embryonic weight and the cardiosomatic index (CSI). Thus, chicken embryos, used as an experimental model, were exposed to a single dose of 0.1 μg MeHg/50 μl saline at E1.5 and analyzed at E10. After exposure, an increase in the number of extraembryonic blood vessels and the veins of the cardiac tissue was observed. These increases were accompanied by a reduction in the content of VEGF and VCAM proteins related to vessel growth and adhesiveness. Together, these results were related to reduced nitrite (NOx) levels. Furthermore, MeHg reduces the number of sarcomeres and increases the content of cardiac troponin I (cTnI), a protein that regulates contraction. In general, exposure to MeHg affected the integrity of extraembryonic and cardiac vessels and the contractile function of cardiomyocytes, which had a systemic impact evidenced by the reduction in embryonic weight gain and CSI.

Total mercury, methylmercury, and selenium concentrations in blue marlin Makaira nigricans from a long-term dataset in the western north Atlantic

Mercury in seafood is a neurotoxicant that threatens human health. Dynamic rates of mercury emission, re-emission, and atmospheric deposition warrant studies into mercury concentrations in fish because many are consumed by humans and can serve as sentinels of mercury levels in the environment. We modeled trends in total mercury content in an apex marine fish predator, Atlantic blue marlin Makaira nigricans, whose muscle tissues were opportunistically sampled from North Carolina (USA) sportfishing tournaments over a discontinuous time period: between 1975 and 77 and 1998-2021 (n = 148). The model-estimated influence of marlin weight on total mercury concentration was constant across years (shared slope) allowing for comparisons of weight-corrected mercury concentrations among years. Weight-corrected total mercury concentrations revealed an inter-decadal decline of approximately 45 % between the 1970s and late 1990s and then variable but relatively stable concentrations through 2021. The mean (SD) wet weight concentration of total mercury was 9.47 (4.11) from 1975 to 77 and 4.17 (2.61) from 2020 to 2021. Methylmercury and selenium were measured on a subset of fish to address questions related to human health and consumption. Methylmercury levels (mean = 0.72 μg/g) were much lower than total mercury (mean = 4.69 μg/g) indicating that total mercury is not a good proxy for methylmercury in Atlantic blue marlin. Selenium, examined as a Se:Hg molar ratio and as a selenium health benefit value (HBV_Se), showed high protective value against mercury toxicity. Long-term trends in the concentration of mercury in blue marlin should continue to be monitored to determine whether policies to mitigate anthropogenic contributions to global mercury are achieving their intended goals and to provide information to inform safe human consumption.

Scyliorhinus canicula (Linnaeus, 1758) metal accumulation: A public health concern for Atlantic fish consumers?

One of the most landed sharks in Portuguese fisheries is the lesser-spotted dogfish (Scyliorhinus canicula), which is ever-present in Portuguese fish markets and consumed as cheap fish protein source. The focus of this study was to evaluate element contamination in consumed tissues of Atlantic S. canicula, with the intent of safeguarding possible public health issues. A total of 74 specimens were analysed for metals and metalloids in the deeper white muscle and skin. Arsenic, zinc, iron and aluminium were the elements with higher mean values. There was a tendency for higher levels in the skin, with differences between life-stage and gender. Many individuals surpassed stipulated guideline limits for mercury and arsenic, posing a risk for human consumption (according to the health risk assessment performed for the average Portuguese fish consumption) or even for use in feed production. Besides the public health concern, this study also evidences troubling signs on marine contamination status.

Mercury Pollution in the Arctic from Wildfires: Source Attribution for the 2000s

Atmospheric mercury (Hg) is a global environmental pollutant, with wildfire emissions being an important source. There have been growing concerns on Hg contamination in the Arctic region, which is largely attributed to long-range transport from lower latitude regions. In this work, we estimate the contributions of wildfire emissions from various source regions to Hg pollution in the Arctic (66° N to 90° N) using a newly developed global Hg wildfire emissions inventory and an atmospheric chemical transport model (GEOS-Chem). Our results show that global wildfires contribute to about 10% (15 Mg year^-1) of the total annual Hg deposition to the Arctic, with the most important source region being Eurasia, which contribute to 5.3% of the total annual Hg deposition followed by Africa (2.5%) and North America (1%). The substantial contributions from the Eurasia region are driven by the strong wildfire activity in the boreal forests. The total wildfire-induced Hg deposition to the Arctic amounts to about one-third of the deposition caused by present-day anthropogenic emissions. We also find that wildfires result in significant Hg deposition to the Arctic across all seasons (winter: 8.3%, spring: 7%, summer: 11%, and fall: 14.6%) with the largest deposition occurring during the boreal fire season. These findings indicate that wildfire is a significant source for Arctic Hg contamination and also demonstrate the importance of boreal forest in the global and regional Hg cycle through the mobilization of sequestered Hg reservoir.

Mercury and lead blood concentrations in pregnant women from 10 caribbean countries

Maternal mercury (Hg) and lead (Pb) blood concentrations were measured in a total of 442 samples taken from pregnant and delivering women in 10 Caribbean countries. Hg was detected in all 10 countries with the geometric mean ranging from a low of 0.83 μg L(-1) (Jamaica) to a high of 3.13 μg L(-1) (Grenada). When compared to comparable U.S. and Canadian data, Hg concentrations in Caribbean women are on average more than 2 times higher. With the exception of St. Kitts & Nevis, Pb was detected in at least one of the samples taken from the other 9 countries with two countries-Grenada and St. Vincent - having Pb detected in ≥60% of those sampled. In these two countries, the Pb concentrations ranged from a low of 1.17 μg dL(-1) (Grenada) to a high of 1.98 μg dL(-1) (St. Vincent). Compared to comparable U.S. and Canadian data, Pb concentrations in Caribbean women are generally higher than that measured in North America. This study confirms that neonates in the Caribbean are being exposed to both Hg and Pb and highlights the need to implement surveillance programs that continuously monitor, intervene, and evaluate the levels of these toxic elements to ensure that they are reduced as far as possible.

An evaluation of mercury concentrations in three brands of canned tuna

There is widespread concern over the presence of Hg in fish consumed by humans. While studies have been focused on determining the Hg concentration in sport fish and some commercial fish, little attention has been directed to canned tuna; it is widely held that concentrations are low. In the present study, the amount of Hg present in canned tuna purchased in Las Vegas, Nevada, USA, was examined, and the brand, temporal variation, type, and packaging medium impacts on Hg concentrations in tuna were explored. A significant (p < 0.001) brand difference was noted: Brand 3 contained higher Hg concentrations ($\bar x$ standard deviation (SD) (0.777 +/- 0.320 ppm) than Brands 1 (0.541 +/- 0.114 ppm) and 2 (0.550 +/- 0.199 ppm). Chunk white tuna (0.619 +/- 0.212 ppm) and solid white tuna (0.576 +/- 0.178 ppm) were both significantly (p < 0.001) higher in mean Hg than chunk light tuna (0.137 +/- 0.063 ppm). No significant temporal variation was noted, and packaging had no significant effect on Hg concentration. In total, 55% of all tuna examined was above the U.S. Environmental Protection Agency's (U.S. EPA) safety level for human consumption (0.5 ppm), and 5% of the tuna exceeded the action level established by the U.S. Food and Drug Administration (U.S. FDA) (1.0 ppm). These results indicate that stricter regulation of the canned tuna industry is necessary to ensure the safety of sensitive populations such as pregnant women, infants, and children. According to the U.S. EPA reference dose of 0.1 microg/kg body weight per day and a mean Hg value of 0.619 ppm, a 25-kg child may consume a meal (75 g) of canned chunk white tuna only once every 18.6 d. Continued monitoring of the industry and efforts to reduce Hg concentrations in canned tuna are recommended. Environ.

Assessment of total mercury levels in Clarias gariepinus from the Sagua la Grande River, Cuba

Total mercury levels (Thg) were quantified in Clarias gariepinus captured from the Sagua la Grande River (Cuba) in the vicinity of an active chlor-alkali plant, and relationships among place of capture; fish size, weight, and sex; and THg levels were assessed. THg levels ranged from 67 to 375 ng/g ww in collected fish, never exceeding the Cuban recommended maximum limit for fish consumption of 500 ng/g ww. No significant correlation was observed between mercury levels and fish allometric characteristics (p < 0.05); however, levels were significantly higher in fish captured below the chlor-alkali facility, suggesting a connection between mercury bioaccumulation and plant discharges.

Thyroid hormones and methylmercury toxicity

Thyroid hormones are essential for cellular metabolism, growth, and development. In particular, an adequate supply of thyroid hormones is critical for fetal neurodevelopment. Thyroid hormone tissue activation and inactivation in brain, liver, and other tissues is controlled by the deiodinases through the removal of iodine atoms. Selenium, an essential element critical for deiodinase activity, is sensitive to mercury and, therefore, when its availability is reduced, brain development might be altered. This review addresses the possibility that high exposures to the organometal, methylmercury (MeHg), may perturb neurodevelopmental processes by selectively affecting thyroid hormone homeostasis and function.

Reduced exposure to mercury in patients receiving enteral nutrition

The exposure to mercury (Hg) of various groups of people with different dietary backgrounds has been assessed because of its hazardous effects, but little is known about that in patients receiving enteral nutrition. Therefore, we studied the Hg exposure in 25 patients with severe motor disabilities, who received liquid enteral feedings for more than one year, by determining total mercury (T-Hg) in their hair samples with inductively coupled plasma-mass spectrometry. The geometric mean of the T-Hg level in hair from the patients was 88 ng/g hair (+/- 1 geometric standard deviation [GSD], 34 - 228 ng/g), whereas that for the control group on a normal diet was 1,900 ng/g (+/- 1 GSD, 1,022 - 3,531 ng/g). The T-Hg levels in the patients' hair were far lower than those in the controls (p < 0.001). The T-Hg levels in the enteral feedings used were below the detection limit of cold-vapor atomic absorption spectrophotometry (< 10 ng/g). The present study has shown that Hg exposure is low in patients receiving enteral nutrition, indicating that food is a primary source of Hg exposure.

Perinatal and lifetime exposure to methylmercury in the mouse: behavioral effects

This project was undertaken to more completely understand the consequences of lifetime exposure to methylmercury. A series of experiments examined how perinatal or lifetime exposure to methylmercury affected behavioral performances in the adult mouse at different ages. One hundred female B6C3F1/HSD mice were assigned to one of three dose groups, 0 ppm, 1 ppm, or 3 ppm methylmercury chloride administered in a 5 nM sodium carbonate drinking solution. Four weeks after initiating dosing, the females were bred with male CBA/J HSD mice to produce the trihybrid offspring B6C3F1/HSD x CBA/J HSD. The methylmercury-treated litters were split into two subgroups, one exposed throughout its lifetime to the original dose, the other exposed through postnatal day 13. Altogether, then, five groups were studied: Control, 1 ppm perinatal, 1 ppm lifetime, 3 ppm perinatal, and 3 ppm lifetime. Three neurobehavioral indices were evaluated: (1) delayed spatial alternation (a test of memory) and (2) running in a wheel to earn food pellets (schedule-controlled operant behavior) were assessed starting at 5 and 15 months of age; (3) hindlimb splay, a measure of motor function, was assessed at 5, 15, and 26 months of age. Subjects tested at one age were littermates of those tested at the other ages. MeHg altered the hindlimb splay distance; control mice differed from methylmercury-exposed mice, the 1 ppm lifetime and 3 ppm lifetime groups differed from each other, and the analysis yielded an age by dose interaction. MeHg exposure altered different measures of wheel running under the 3 ppm lifetime condition. In the delayed alternation procedure, the mouse was required to respond to one of two locations in a strictly alternating sequence. More mice from the treated groups, except for the 1 ppm perinatal group, failed to meet the criterion at longer delay values. Overall, the results show that exposure to low levels of methylmercury produces behavioral effects that depend on the test procedure, the dose, the duration of exposure, and the age. Lifetime evaluations of exposure to toxicants, beginning with early development, should be a component of the risk assessment process for neurotoxicity.

Environmental mercury exposure in children: South China's experience

BACKGROUND

Environmental mercury levels significantly increased in the past decades following its increase in industrial applications. In spite of an increasing concern on the potential harmful effects of mercury on children, there is no reported data for the Chinese population. The relationship between dietary habit and environmental mercury exposure in Chinese children was studied.

METHODS

The hair and blood mercury levels of Chinese children aged above 3 years in 2000 March to September, were studied. Sociodemographic data, dietary habits of the past 6 months, and other risk factors for environmental mercury exposure were collected. Those children with blood mercury levels above the toxic range (i.e. > 45 nmol/L) and their family members were further evaluated and their blood and hair mercury levels were monitored before and after Fishing-Moratorium period (June to August 2000) in South China Sea.

RESULTS

Altogether, 137 Chinese children (mean age, 7.2 years) were recruited. The mean hair mercury level was 2.2 p.p.m and the mean blood mercury level was 17.6 nmol/L. There was a strong correlation (r = 0.88) between hair and blood mercury levels in our cohort. Frequency of fish consumption correlated with hair (r = 0.51) and blood (r = 0.54) mercury levels. For those children who consumed fish more than 3 times/week, hair and blood mercury levels were twice as high as those who consumed fish l-3 times/week and threefold of those who never consumed fish. Five children and 12 family members had toxic blood mercury levels. Their blood (P < 0.0001) and hair (P = 0.02) mercury levels dropped significantly after reducing fish consumption during Fishing-Moratorium period.

CONCLUSION

Both blood and hair (i.e. Tissue) mercury levels of children in Hong Kong was elevated and correlated with the frequency of fish consumption.

Developmental neuropathology of environmental agents

The developing central nervous system (CNS) is more vulnerable to injury than the adult one. Although a great deal of research has been devoted to subtle effects of developmental exposure, such as neurobehavioral changes, this review instead focuses on a number of chemicals that have been shown, in several experimental models as well as humans, to cause morphological changes in the developing nervous system. Chemicals that are discussed include methylmercury (MeHg), lead (Pb), antiepileptic drugs, and ethanol. Additionally, the issue of silent neurotoxicity, i.e., persistent morphological and/or biochemical injury that remains clinically unapparent until later in life, is discussed.

Perinatal and lifetime exposure to methylmercury in the mouse: blood and brain concentrations of mercury to 26 months of age

Chronic, low-level exposures to environmental toxicants, because they often begin prenatally and then persist throughout the individual's lifetime, pose challenging issues to risk assessment. Exposure to low levels of methylmercury through the diet, based largely on consumption of fish and sea mammals, follows this pattern. Early development is considered to be a period of heightened vulnerability during which even low-level exposures may produce undetected, "silent", damage that is revealed only under conditions that challenge the functional capacities of the individual. Aging, with its diminished functional capacities and compensatory reserves provides such a challenge, but, to explore this possibility, requires basic information about blood and brain levels under conditions of chronic lifetime exposure. The current research was undertaken to provide such information. One hundred female B6C3F1/HSD mice were assigned to one of three dose groups, 0, 1, or 3 ppm methylmercury chloride administered in a 5 nM sodium carbonate drinking solution. They were bred with male CBA/J HSD mice to produce the trihybrid offspring B6C3F1/ HSD x CBA/J HSD. Dosing of the females began 4 weeks prior to breeding and continued for the two methylmercury-exposed groups throughout breeding and gestation. The methylmercury-treated litters were split into two subgroups, one exposed throughout its lifetime (set at 26 months) to the original dose, the other exposed through postnatal day 13 (PND 13). Brain and blood concentrations were assayed by cold-vapor atomic absorption. Samples were obtained on PND 4 and 21, and then at the end of months 14 and 26. On PND 4, brain and blood levels closely reflected maternal dosing. In all groups, concentrations fell sharply from PND 4 to 21, but to a greater extent in the perinatal groups. Blood levels in the 1 ppm lifetime group remained unchanged between months 14 and 26, but brain levels rose modestly. In the 3 ppm lifetime group, both brain and blood levels rose significantly between months 14 and 26, suggesting an interaction between dose and age.

Excretion of methyl mercury in human feces

Fecal excretion of methyl mercury was confirmed in four Japanese male subjects. Perhaps the methyl mercury detected in feces is dependent on (a) the unabsorbed methyl mercury in diet, (b) exfoliation of intestinal cells, (c) hepatic bile, and (d) intestinal methylation of inorganic mercury. The calculated amounts of methyl mercury excreted daily in feces were similar to those found in urine.

Cree leukoencephalopathy: neuroimaging findings

PURPOSE

To describe the computed tomographic (CT) and magnetic resonance (MR) imaging findings in Cree leukoencephalopathy.

MATERIALS AND METHODS

The authors retrospectively reviewed the medical records and neuroimaging studies in 12 infants with Cree leukoencephalopathy (CT in 12 infants, MR in six). The diagnosis was established clinically in six patients and at autopsy in the other six.

RESULTS

At CT, extensive, diffuse, and symmetric hypoattenuation was seen in the cerebral and cerebellar white matter in all 12 patients. Hypoattenuation was also seen in the corpus callosum in 11 (92%), internal capsule in 10 (83%), globus pallidus in nine (75%), brainstem in nine (75%), and thalamus in four (33%). The caudate nucleus and putamen were spared. On T2-weighted MR images in six patients, the cerebral and cerebellar white matter, including the subcortical arcuate fibers, was hyperintense as were the internal capsule, corpus callosum, corticospinal tracts, and globus pallidus. The thalamus was affected in four (67%) patients, pons in five (83%), and medulla in four (33%). The caudate nucleus and putamen were not affected.

CONCLUSION

Cree leukoencephalopathy causes striking symmetric and diffuse involvement of the cerebral and cerebellar white matter and brainstem with sparing of the caudate nucleus and putamen.

Are metals dietary carcinogens?

Humans have been in contact with metals almost since the beginning of our existence. In fact, one cannot even think on human evolution without considering the great role played by metals in mankind's development. Metals are common moieties of molecules involved in a wide variety of biological processes, and hence are found in virtually all living organisms. Some metals are essential for human nutrition; others are found as contaminants in foodstuffs. One feature of the normal human diet which is frequently found is the simultaneous presence of both essential and toxic metals. Other factors important in the risk-evaluation analysis of metals are their pharmacokinetics, interactions among them and with other major components of the diet, and, especially, the great differences in the dietary habits of different populations and in the regional distribution of metals. In attempting to understand the role which dietary metals could play in human carcinogenesis, we found that the many factors involved and the lack of specific information made it difficult to reach firm conclusions on the hazards of dietary metals. We hope that this paper will raise the interest of genetic toxicologists in the subject and will consequently facilitate a risk analysis of the carcinogenic potential of dietary metals.

Lead, mercury, and organochlorine compound levels in cord blood in Québec, Canada

We conducted this study to evaluate blood levels of lead, mercury, and organochlorine compounds in newborns in the Province of Quebec. During 1993 to 1995, we carried out a survey in 10 hospitals located in southern Quebec. During that time, umbilical cord blood samples were obtained from 1109 newborns, and we analyzed each for lead, mercury, 14 polychlorinated biphenyl congeners, and 11 chlorinated pesticides. We used the geometric mean and 95% confidence interval (CI) to describe the results. Mean concentrations of lead and mercury in cord blood were 0.076 micromol/l (95% CI = 0.074, 0.079) and 4.82 nmol/l (95% CI = 4.56, 5.08), respectively. The mean concentrations of total polychlorinated biphenyls (Aroclor 1260) and dichlorodiphenyl dichloroethylene were 0.514 microg/I (95% CI = .493, 0.536) and 0.412 microg/l (95% CI = 0.390, 0.435), respectively. We observed a statistically significant relationship between maternal age and cord blood concentrations of (a) lead, (b) mercury, (c) polychlorinated biphenyls, and (d) dichlorodiphenyl dichloroethylene. In addition, maternal smoking during pregnancy was associated with cord blood lead levels. The cord blood concentrations of lead, mercury, polychlorinated biphenyls, and dichlorodiphenyl dichloroethylene we measured in our study were the lowest levels recently reported in industrialized countries. The results of this study underline the role of public health authorities in the evaluation of biological levels of environmental contaminants among children for the assessment of risk of adverse health effects.

Neurotoxic effects of low-level methylmercury contamination in the Amazonian Basin

Many studies have demonstrated mercury contamination in the Amazonian ecosystem, particularly in fish, a dietary mainstay of populations in this region. The present study focused on potential health effects of this low-level methylmercury exposure. The study was carried out in a village on the Tapajós River, a tributary of the Amazon, on 91 adults inhabitants (15-81 years), whose hair mercury levels were inferior to 50 mu/g. Performance on a neurofunctional test battery and clinical manifestations of nervous system dysfunction were examined in relation to hair mercury concentrations. Near visual contrast sensitivity and manual dexterity, adjusted for age, decreased significantly with hair mercury levels (P < 0.05), while there was a tendency for muscular fatigue to increase and muscular strength to decrease in women. For the most part, clinical examinations were normal, however, hair mercury levels were significantly higher (P < 0.05) for persons who presented disorganized movements on an alternating movement task and for persons with restricted visual fields. These results suggest dose-dependent nervous system alterations at hair mercury levels below 50 micrograms/g, previously considered a threshold for clinical effects. The profile of dysfunction in this adult population is consistent with the current knowledge on methyl-mercury poisoning. The long-term implications of these findings are unknown and need to be addressed.

Alterations in immune parameters associated with low level methylmercury exposure in mice

Methylmercury (MeHg) is a known toxicant and continues to be a significant environmental contaminant. While the neurotoxicity and developmental toxicity of MeHg are well established, the immunotoxic effects of MeHg are just now being studied and described. This study evaluated strain and gender specific effects of low level, prolonged MeHg exposure in mice. Mice were exposed to MeHg in the drinking water (0, 3 or 10 ppm) for 4 weeks. Splenocytes and thymocytes were evaluated for alterations in immunophenotype, GSH levels, and intracellular Ca2+ flux after mitogen stimulation. MeHg exposure resulted in alterations in splenocyte and thymocyte subsets and a dose dependent decrease in GSH levels (as measured by monochlorobimane fluorescence and flow cytometry) of all splenocyte subsets. This decrease in GSH was further confirmed by biochemical assay in splenocytes. In addition, there was a dose response related decrease in mitogen stimulated Ca2+ flux and in the percentages of CD4+ splenocytes and CD8+ splenocytes from mice exposed to 10 ppm of MeHg. These results suggest that low-level chronic MeHg exposure may cause immune disfunction by disturbing thiol redox balance, transmembrane signaling and splenic cellularity.

Systemic transfer of mercury from amalgam fillings before and after cessation of emission

In 29 volunteers with a low amalgam load, the number of amalgam-covered tooth surfaces and the occlusal area of the fillings were determined. Concentrations of total mercury were measured in plasma and erythrocytes as well as in urine together with the excretion rate. Absorbed daily doses were estimated from intraoral Hg emission by two separate methods. The transfer of Hg from the fillings via the oral cavity and blood to urinary excretion was evaluated according to the most representative combination of parameters. This consisted of urinary excretion (1), Hg concentration in plasma (2), absorbed dose (3), and occlusal area (4). Pairwise correlation coefficients were 0.75 for parameters 1 vs 2 and 2 vs 3 and 0.49 for parameters 3 vs 4. Within 9 days after removal of the fillings, a transient increase was observed in plasma Hg levels only. This was reduced in those volunteers to whom a rubber dam had been applied during removal. Peak plasma Hg was 0.6 ng/ml on average and decreased with halftimes between 5 and 13 days. A significant decrease in Hg excretion was noted not before 100 days after removal. Being relatively insensitive to dietary mercury, the determination of total mercury in plasma and of its urinary excretion rate appears, under practical aspects, most suitable for the investigation of Hg uptake from amalgam.

Compartmental transfer of mercury released from amalgam

The number of amalgam-covered surfaces and the occlusal area of the fillings, the concentrations of total mercury in plasma, erythrocytes and urine, the urinary excretion rate, and the absorbed daily doses estimated by two separate methods from intra-oral Hg emission were determined in 29 volunteers with a low amalgam load. The transfer of Hg from the fillings via the oral cavity and blood to urinary excretion was evaluated by multiple correlations between these variables. In addition, the combination of variables most representative of the entire compartmental transfer of amalgam Hg was determined. Urinary excretion (1), Hg concentration in plasma (2) and absorbed dose (3) were most closely correlated to each other, followed by correlations with the variables of the fillings (4). Correlation coefficients were 0.75 for variables 1 vs 2 and 2 vs 3, and 0.49 for variables 3 vs 4. It was concluded that variables 1-3 best reflected the transfer of mercury from amalgam fillings throughout the organism and that they were relatively insensitive to dietary mercury. The determination of total mercury in plasma and of its urinary excretion rate appears, under practical aspects, most suitable for the investigation of Hg uptake from amalgam.

Concentrations of blood and hair mercury and serum PCBs in an Ojibwa population that consumes Great Lakes region fish

OBJECTIVE

This paper describes an exposure assessment of an American Indian population using blood and hair samples as indicators of mercury and polychlorinated biphenyl exposure from the consumption of fish taken from the Great Lakes region.

METHODS

Questionnaires regarding fish consumption were completed by 89 Ojibwa tribal members. Mercury concentrations were determined in human hair and blood samples, and polychlorinated biphenyl concentrations were determined in serum.

RESULTS

Fish were consumed at the highest rates in April, May, June, and July. Lake trout, whitefish, and walleye were the preferred fish consumed by 91.4% of the respondents. Concentrations of blood mercury were all below 55 micrograms/L (ppb), while concentrations of mercury in hair were all less than 3 mg/L (ppm). Hair mercury concentrations were correlated with the previous year's fish consumption (p = .05). Dental amalgams and blood mercury concentrations were also significantly correlated (p < .002). Serum polychlorinated biphenyl concentrations, determined as the sum of 89 congeners, were all below 9.6 ppb total polychlorinated biphenyls. Subject age and total serum polychlorinated biphenyls were correlated (p < .001).

CONCLUSIONS

The concentrations of mercury and polychlorinated biphenyls in this Ojibwa population were relatively low, but several individuals were identified as having elevated concentrations and additional testing may be warranted. Since the accumulation of contaminants was related to fish consumption and age, a long-term monitoring program that assesses chronic exposure to fish diets would be beneficial.

Fixed interval/fixed ratio performance in adult monkeys exposed in utero to methylmercury

Previous studies in monkeys and rodents have shown the fixed interval/fixed ratio (FI/FR) schedule to be a sensitive indicator of neurotoxicity. In the present study, monkeys (Macaca fascicularis) were exposed in utero to methylmercury (MeHg). Maternal doses of MeHg of 50, 70, or 90 micrograms/kg b.wt./day resulted in infant blood mercury levels at birth ranging from 1.04 to 2.45 ppm. Monkeys were tested on a multiple FI/FR schedule of reinforcement at 8-10 years of age. Four FI/FR cycles were run per session. Pause time and run rate were calculated for FI and FR components, as well as FI quarter-life and local FI response rates. MeHg treatment and sex effects were investigated by fitting a linear orthogonal polynomial regression to each monkey's profile across sessions and performing two-way ANOVAs on the resulting linear and intercept terms. There were no treatment-related effects on either the FI or FR component for pause time or run rate. Analysis of the quarter-life revealed a significant treatment by sex effect as well as a main effect for sex. Post hoc t-tests revealed a significant difference in quarter-life of treated male and female monkeys and a marginal difference between treated and control males. The FI run rate of the male monkeys was significantly greater than that of the female monkeys whereas the FR run rate of the males was marginally greater. These results indicate that there may be a differential effect of MeHg on male and female monkeys, which could be interpreted as an effect on temporal discrimination. Overall, adult monkeys exposed to in utero MeHg exhibited a very limited sex-related effects on the FI/FR intermittent schedule of reinforcement.

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.

Risk assessment and management of chemical contaminants in fishery products consumed in the USA

In the USA a small proportion of fishery products are contaminated with appreciable amounts of potentially hazardous contaminants. However, risks to consumers are not generally high. Inorganic contaminants with the greatest potential for toxicity are antimony, arsenic, cadmium, lead, mercury, selenium and sulfites. Among organic compounds, polychlorinated biphenyls, dioxins, several chlorinated hydrocarbon insecticides, certain processing-related and aquaculture-related contaminants pose potential risks for consumers. Log-normal distributions appear to provide good descriptions of the pattern of variation of contaminant concentrations among different geographic areas, and some contaminants (mostly organic) appear to be much more variable than others. This variability offers a solution for reduction of exposure through restricting the harvest of aquatic organisms from specific sites, and by excluding certain species. It is recommended that: (i) existing State and Federal regulations and environmental monitoring be strengthened and enforced to minimize contamination of the aquatic environment; (ii) a program of shared responsibility be instituted, where Federal agencies develop a set of monitoring and inspection practices and state agencies assume responsibility for primary control, site closures and advisories issue; (iii) research and public education by government agencies and health professionals be expanded to determine actual risks and approaches to manage them; (iv) mandatory labeling be considered for specific contaminants; (v) a better system requiring international agreements be developed in order to minimize the differences among various national regulatory approaches.

Mercuric chloride affects protein secretion in rat primary hepatocyte cultures: a biochemical ultrastructural, and gold immunocytochemical study

The toxicity of mercury on hepatocytes was studied at the ultrastructural, biochemical, and immunocytochemical levels. Albumin metabolism was examined because it is a representative liver-specific function. A novel cytochemical method using the protein A-gold technique for the in situ localization of albumin in hepatocyte cultures was applied. Primary rat hepatocyte cultures were exposed to increasing HgCl2 concentrations. Cytotoxicity was assessed by measuring the release of lactic dehydrogenase from the cells. At the highest exposure concentration tested (50 microM), Hg was found to be significantly cytotoxic in contrast to what occurred at 5.0 and 0.5 microM. The level of albumin secreted, as measured by ELISA, was decreased by approximately 38% at 5.0 microM HgCl2 and was found not to be different from that of controls at lower concentrations. The ultrastructural analysis showed that hepatocytes treated with 5.0 microM HgCl2 undergo drastic morphological changes such as a decreased number of ribosomes associated with the rough endoplasmic reticulum, and the disappearance of the latter organelle, proliferation of the smooth endoplasmic reticulum, and dilatation of both the Golgi apparatus and the biliary canaliculus-like structures. Immunocytochemical detection of albumin-immunoreactive sites using protein A-gold labeling further revealed that these were less abundant in hepatocytes treated with 5.0 microM HgCl2 (-64%) as compared to control preparations. These results suggest that one of the effects of mercury on hepatocytes is to affect liver-specific functions such as albumin production, possibly through interference with ribosomal function. This study also demonstrates for the first time the applicability of the high-resolution protein A-gold technique for toxicological investigations on hepatocytes in vitro.

Combined effects of low-level methylmercury and x-radiation on the developing mouse cerebellum

The effects of low-level methylmercury and x-radiation in combination on the developing mouse cerebellum were studied. Pregnant BALB/cJcl mice were divided into two groups. Dams of a group were orally given 9 micrograms Hg/g body weight of methylmercuric chloride on d 17 of pregnancy. The other dams were not treated. They were allowed to give birth, and the male pups were exposed to a single x-radiation at doses of 0.125 or 0.5 Gy on the day following birth. Sham-exposed pups were also prepared. The pups were killed at various postexposure periods, and their cerebella were removed and processed for microscopy and mercury analysis. Mercury was retained in the pup cerebellum at levels of 4-8 micrograms/g for 4 d and then lowered. Appearance and incidence of cell death in the external granular layer (EGL) were similar in groups exposed to 0.125 Gy alone or 0.125 Gy and methylmercury in combination. Fourteen percent of cells in the EGL were killed by exposure to 0.5 Gy with or without methylmercury. Restoration of the EGL from the damage was slightly retarded by methylmercury, but by 10 d of age these cerebella overtook the normal ones in development. These findings indicate that methylmercury does not modify the apoptotic cell death caused by x-radiation in the EGL but retards the tissue restoration from the damage.

Mercury compounds: lipophilicity and toxic effects on isolated myocardial tissue

Lipophilicity is suggested to modulate the diffusion and the cytotoxic effects of mercury compounds. To investigate this, the positive inotropic effect of four Hg compounds (HgCl2, CH3HgCl, chlormerodrin, bromomercurihydroxypropane) was studied in catecholamine-depleted isolated heart muscle preparations. The rate of development of the positive effect was inversely correlated to the concentration in the case of HgCl2 and chlormerodrin, i.e. the product of concentration (c) and time to half-maximal effect (t50) remained constant. This was in accordance with the assumption of a permeation-controlled rate of action, as was shown earlier for p-chloromercuriphenyl-sulfonic acid. In addition, the c X t50 values of the individual mercurials decreased hyperbolically with the increase in lipophilicity as measured by the octanol/water partition. The results support the view that the toxicity of mercurials increases with their lipid solubility. In conjunction with the previously reported negative inotropic effect of Hg compounds, a model is proposed allocating thiol groups responsible for the negative inotropic action to lipid compartments within the cell membrane, while SH groups conveying the increase in contraction force are thought to be situated at the internal surface of the sarcolemma.

Methylmercury developmental neurotoxicity: a comparison of effects in humans and animals

A qualitative and quantitative comparison of the neuropathological and neurobehavioral effects of early methylmercury (MeHg) exposure is presented. The focus of the qualitative comparison is the examination of how specific end-points (and categories of behavioral functions) compare across species. The focus of the quantitative comparison is the investigation of the relationship between MeHg exposure, target-organ dose and effects in humans and animals. The results of the comparisons are discussed in the context of the adequacy of the proposed EPA neurotoxicity battery to characterize the risk of MeHg to humans. The comparisons reveal several qualitative and quantitative similarities in the neuropathological effects of MeHg on humans and animals at high levels of exposure. Reports of neuropathological effects at lower levels are available for animals only, precluding any comparison. At high levels of exposure, specific neurobehavioral end-points affected across species are also similar. Effects at lower levels of exposure are similar if categories of neurobehavioral functioning are compared. Changes in the EPA test battery consistent with the results of the comparisons are discussed.

Methylmercury effects on the social behavior of Macaca fascicularis infants

Observations of the social behavior of Macaca fascicularis exposed in utero to methylmercury (MeHg) and nonexposed control infants were performed as part of a study of the toxic, reproductive and developmental effects of maternal MeHg intake. Infants were tested twice weekly from 2 weeks to 8 months of age. Data were summarized into 6 categories of social behavior and 7 categories of nonsocial behavior. Analysis of the most prevalent behavior indicated that MeHg-exposed offspring exhibited a decrease in social play behavior and a concomitant increase in nonsocial passive behavior. The MeHg effect on social play behavior tended to decrease with age, while the group differences in nonsocial passive behavior tended to increase. The results indicate that maternal intake of MeHg during pregnancy can affect the social development of infant primates by suppressing social interactions and increasing nonsocial behavior.

Kinetics of methyl mercury in blood and brain during chronic exposure in the monkey Macaca fascicularis

The disposition parameters derived from a compartmental model kinetic analysis of blood Hg levels in nonpregnant, adult female Macaca fascicularis given daily doses of MeHg did not vary with either dosage level (50, 70 or 90 micrograms MeHg/kg b.wt.day) or duration of exposure (up to 507 day). In contrast, blood clearance of Hg in pregnant females was dose-dependent; it being higher at the 90 micrograms MeHg/kg b.wt.day than at the lower dosage levels. Hg levels in the brain of adult fascicularis relative to blood Hg also increased at the highest level of exposure. Blood Hg half-life in neonate fascicularis was similar to half-life in their mothers (adults). Finally, the regional distribution of mercury in the brains of adult and neonate fascicularis exposed to low and intermediate levels of MeHg resembles the reported distribution of mercury in the brains of adult and neonate humans environmentally exposed to MeHg. Consequently, M. fascicularis may be an especially appropriate animal model for studying the neurotoxic mechanisms of chronic methyl mercury exposure.

Mercury concentration in organs of contemporary Japanese

Concentrations of inorganic mercury (IHg), methylmercury (MeHg), and total mercury (THg) were determined for autopsy samples from 46 Japanese subjects. Two laboratories (Labs A and B) participated in Hg analyses: Lab A for THg and IHg and Lab B for THg and MeHg. Total mercury concentration values were in good agreement between the two laboratories: the averages were several hundreds of ng/g in kidney cortex, kidney medulla, and liver, and were several tens of ng/g in cerebrum, cerebellum, heart, and spleen. Inorganic mercury accumulated more in kidney and liver: its percentage THg was 81-84% in the kidney, 67% in the liver, 25% in the heart, 22% in the spleen, 20% in the cerebrum, and 14% in the cerebellum. Methylmercury levels in tissues were uniform through all organs except the liver. Approximately 80% was in the form of MeHg in the cerebrum, cerebellum, heart, and spleen, whereas the values were 33%, 15%, and 11% in the liver, kidney medulla, and kidney cortex, respectively. Age was a significant factor in increased IHg concentrations in the cerebrum and heart, decreased values of %MeHg in the cerebrum, cerebellum, and heart, and increased values of %IHg in the cerebrum and heart.

New aspects on the distribution and metabolism of essential trace elements after dietary exposure to toxic metals

Under present environmental conditions, an increase in pollution owing to metals such as cadmium (Cd), lead (Pb), and methylmercury (MeHg) must be expected. The resulting effects would be seen particularly in the food chain. The daily intake of toxic metals in various parts of the world is different and depends on both the dietary habits and the concentration in foodstuffs. Oral ingestion of these toxic metals perturbs the metabolism of essential elements, especially zinc (Zn), copper (Cu), iron (Fe), and selenium (Se). The elemental composition of body tissues and fluids is an indicator of the nutritional and pathological status of humans. This review will describe the dietary intake and gut absorption of essential and toxic elements. Furthermore, it will discuss threshold values, toxic effects in relation to body burden of toxic metals, the biological indices of exposure, and the interaction between toxic and essential elements. The overall ratio of Cu, Zn, Fe, and Se concentration to Cd in the human kidney is the lowest in comparison to Hg and Pb. Increased kidney copper and urinary losses may be common denominators in the manifestation of renal toxicity induced by heavy metals. Factors affecting availability and loss of copper should be identified and measured. The critical kidney concentration for Cd, Pb, and MeHg should be revised in relation to essential elements.