Relationships between mercury body concentrations,standard metabolic rate,and body mass in eastern mosquitofish (Gambusia holbrooki) from three experimental populations

Eastern mosquitofish (Gambusia holbrooki) were sampled from three experimental populations (two Hg-exposed populations and one reference population) to determine whether transgenerational exposure (lifelong exposure of multiple generations) to Hg adversely affects standard metabolic rate (SMR). Mosquitofish subjected to lifelong Hg exposure accumulated significant concentrations of Hg in their tissues compared to fish from the reference population (mean: 3.89-4.13 vs 0.08 microHg/g wet mass, respectively). Less than 10% of the variability in Hg tissue concentrations could be explained by fish body mass, likely because of the short life span and/or dietary habits of this species. Despite the high body burdens of Hg in exposed fish, we found no significant difference in SMR among individuals from Hg-exposed or reference populations. Our findings contrast recent laboratory work describing elevated SMR in mosquitofish exposed to 100 microg/L dissolved inorganic Hg for 48 h. To account for contrasting results between studies, we hypothesize that acute exposure to dissolved inorganic Hg damages gill epithelium, resulting in increased metabolic rate, but that lifelong Hg exposure via trophic uptake of methyl mercury does not affect fish respiratory structures. Alternative hypotheses include the possibility that G. holbrooki is a species that can tolerate high body burdens of Hg or that more than four years of genetic isolation during Hg exposure (8-12 generations) resulted in selection for Hg-tolerant or -resistant individuals.     

Histochemical demonstration of mercury in the olfactory system of salmon (Salmo salar L.) following treatments with dietary methylmercuric chloride and dissolved mercuric chloride

The deposition of organic and inorganic mercury compounds was studied histochemically in the salmon (Salmo salar L.) olfactory system. One group of salmon was given fodder pellets containing methylmercuric chloride (CH3HgCl, 99 micrograms Hg/g) for 4 weeks. Other groups of fish were exposed to dissolved mercuric chloride (HgCl2, 270 micrograms Hg/liter) for 2, 6, and 12 hr, respectively. In both series of experiments, the radioisotope 203Hg was included in order to determine the accumulation of mercury in the olfactory system. Gamma-spectrometry showed that both mercury compounds accumulated in the olfactory rosettes and their nerves. Tissue sections from the rosettes and olfactory nerves were subjected to autometallographic silver enhancement, thereby rendering mercury deposits visible for light and electron microscopy. Microscopic analysis demonstrated an intense and comprehensive Hg deposition in the axons and Schwann cells of both methylmercury- and inorganic mercury-exposed fish. On the other hand, the two mercury compounds showed different staining patterns in the sensory epithelium. The silver grains evoked by methylmercury were localized predominantly in lysosome-like inclusions within the receptor cells, while those produced by HgCl2 exposure were situated mainly along the borders of neighboring cells. The present findings that organic and inorganic mercury compounds were deposited in the olfactory system along its whole length, from the receptor cell apices to the brain, support the electrophysiological results presented elsewhere (Baatrup et al., 1990, Ecotoxicol. Environ. Safety 20, 269-276).     

Histochemical demonstration of mercury in the olfactory system of salmon (Salmo salar L.) following treatments with dietary methylmercuric chloride and dissolved mercuric chloride

The deposition of organic and inorganic mercury compounds was studied histochemically in the salmon Salmo salar L. olfactory system. One group of salmon was given fodder pellets containing methylmercuric chloride (CH₃HgCl, 99 μg Hg/g) for 4 weeks. Other groups of fish were exposed to dissolved mercuric chloride (HgCl₂, 270 μg Hg/liter) for 2, 6, and 12 hr, respectively. In both series of experiments, the radioisotope ²⁰³Hg was included in order to determine the accumulation of mercury in the olfactory system. Gamma-spectrometry showed that both mercury compounds accumulated in the olfactory rosettes and their nerves. Tissue sections from the rosettes and olfactory nerves were subjected to autometallographic silver enhancement, thereby rendering mercury deposits visible for light and electron microscopy. Microscopic analysis demonstrated an intense and comprehensive Hg deposition in the axons and Schwann cells of both methylmercury- and inorganic mercury-exposed fish. On the other hand, the two mercury compounds showed different staining patterns in the sensory epithelium. The silver grains evoked by methylmercury were localized predominantly in lysosome-like inclusions within the receptor cells, while those produced by HgCl₂ exposure were situated mainly along the borders of neighboring cells. The present findings that organic and inorganic mercury compounds were deposited in the olfactory system along its whole length, from the receptor cell apices to the brain, support the electrophysiological results presented elsewhere (Baatrup et al., 1990, Ecotoxicol. Environ. Safety 20, 269–276).     

Comparative uptake, bioaccumulation, and gill damages of inorganic mercury in tropical and nordic freshwater fish

This paper reports comparative results on the bioaccumulation of inorganic mercury and resulting gill damages in the tropical fish, Trichomycterus zonatus, and a nordic species, Salvelinus alpinus, using radioisotope 203Hg techniques and scanning electron microscopy. Uptake of inorganic Hg from water was much more important in T. zonatus than in S. alpinus and the Hg concentration in S. alpinus increased at a slower rate in all tissues during the first 24 h of exposure. After 96 h, Hg concentration was 70 times higher in the kidney, 10 times higher in liver, intestine, skin, and brain, and 3 times higher in gills, muscle, and the rest of body of T. zonatus compared to S. alpinus. Gill damages in T. zonatus were more evident and occurred much earlier than for S. alpinus. According to our data, the high differences observed in the inorganic mercury uptake, bioaccumulation, and gills damages strongly suggest that T. zonatus is more sensitive to inorganic mercury pollution than S. alpinus. Further studies are urgently needed to determine whether the high sensitivity observed for T. zonatus to inorganic Hg is also present in the majority of tropical species or whether this species presents an isolated case.     

Epidemiologic confirmation that fruit consumption influences mercury exposure in riparian communities in the Brazilian Amazon

Since deforestation has recently been associated with increased mercury load in the Amazon, the problem of mercury exposure is now much more widespread than initially thought. A previous exploratory study suggested that fruit consumption may reduce mercury exposure. The objectives of the study were to determine the effects of fruit consumption on the relation between fish consumption and bioindicators of mercury (Hg) exposure in Amazonian fish-eating communities. A cross-sectional dietary survey based on a 7-day recall of fish and fruit consumption frequency was conducted within 13 riparian communities from the Tapajós River, Brazilian Amazon. Hair samples were collected from 449 persons, and blood samples were collected from a subset of 225, for total and inorganic mercury determination by atomic absorption spectrometry. On average, participants consumed 6.6 fish meals/week and ate 11 fruits/week. The average blood Hg (BHg) was 57.1 +/- 36.3 microg/L (median: 55.1 microg/L), and the average hair-Hg (HHg) was 16.8 +/- 10.3 microg/g (median: 15.7 microg/g). There was a positive relation between fish consumption and BHg (r = 0.48; P<0.0001), as well as HHg (r =0.34; P<0.0001). Both fish and fruit consumption entered significantly in multivariate models explaining BHg (fish: beta = 5.6, P<0.0001; fruit: beta = -0.5, P = 0.0011; adjusted model R2 = 36.0%) and HHg levels (fish: beta = 1.2, P<0.0001; fruit: beta = -0.2, P = 0.0002; adjusted model R2 = 21.0%). ANCOVA models showed that for the same number of fish meals, persons consuming fruits more frequently had significantly lower blood and HHg concentrations. For low fruit consumers, each fish meal contributed 9.8 microg/L Hg increase in blood compared to only 3.3 microg/L Hg increase for the high fruit consumers. In conclusion, fruit consumption may provide a protective effect for Hg exposure in Amazonian riparians. Prevention strategies that seek to maintain fish consumption while reducing Hg exposure in fish-eating communities should be pursued.     

Mercury and selenium in workers previously exposed to mercury vapour at a chloralkali plant.

The concentrations of total mercury (B-Hg), inorganic mercury (B-IHg), and methyl mercury (B-MeHg) in whole blood, urinary mercury (U-Hg), and selenium in urine (U-Se) and whole blood (B-Se) were determined in 74 chloralkali workers previously exposed to Hg vapour, and compared with 51 age matched referents. Dental amalgam state, fish consumption, and exposure related indices were studied with regard to the determined elements. A significant relation between the surface of dental amalgam and U-Hg (Pearson's r = 0.63, p < 0.001) was found among the referents. Mean U-Se was significantly lower (p < 0.001) among the subjects previously exposed to Hg (34.1 nmol/mmol creatinine) compared with that for the referents (42.6 nmol/mmol creatinine). A significant negative relation between the cumulative Hg dose and U-Se was also found. The mechanisms and the clinical significance of these findings are not clear. No relation between current U-Hg and previous occupational exposure to Hg was found among subjects in whom exposure had ceased more than one year before the study.     

Factors contributing to the difference of hair mercury concentrations between the sexes

Scalp hair samples were collected by mail from 97 married couples who were living in several places in Okinawa-prefecture and supposedly had no specific exposure to mercury compounds. They were selectively analysed for organic and inorganic mercury content and the difference of hair mercury concentration between the sexes was discussed in relation to the frequency of fish intake, fish species, drinking habits and permanent-wave hair treatment. Results obtained were as follows: 1) The increase in hair levels of organic and inorganic mercury concentrations was roughly proportional to the dietary intake of fish in the range from none or low to moderate frequencies for both husbands and wives. However, this increase was not proportional to the dietary intake of fish in the range from moderate to high frequencies, showing almost the same level irrespective of the frequency of fish intake. 2) Though husbands and wives had dietary consumption patterns quite similar to each other, husbands were found to have higher hair organic mercury levels than wives, the average values being 6.40 ppm with a standard deviation of 4.69 ppm for husbands and 2.86 ppm with a standard deviation of 1.97 ppm for wives, respectively. The difference was statistically significant. No significant difference between the sexes was detected for inorganic mercury concentrations. However, a highly significant positive correlation coefficient for organic mercury and also a significant positive correlation coefficient for inorganic mercury were found between husbands and wives. 3) Hair without permanent-wave treatment showed higher levels of organic mercury concentrations than hair with permanent-wave treatment for both husbands and wives. Drinkers also had higher levels of hair mercury as compared to non-drinkers. However, the lower levels of organic mercury concentrations in women's hair than in men's hair were not fully explained by these factors. 4) Both men and women who showed higher hair levels of organic mercury had a preference for highly predatory fish such as tuna and bonito, which probably contributed most to the human intake of mercury.     

Sexual differences in the excretion of organic and inorganic mercury by methyl mercury-treated rats

Adult male and female Long Evans rats received 1 mumole of methyl (203Hg) mercuric chloride per kilogram sc. Whole-body retention of mercury and excretion of organic and inorganic mercury in urine and feces were monitored for 98 days after dosing. Females cleared mercury from the body more rapidly than did males. The major route of mercury excretion was feces. By 98 days after dosing, cumulative mercury excretion in feces accounted for about 51% of the dose in males and about 54% of the dose in females. For both sexes, about 33% of the dose was excreted in feces as inorganic mercury. Cumulative excretion of organic mercury in feces accounted for about 18 and 21% of the dose in males and females, respectively. Urinary excretion of mercury was quantitatively a smaller route for mercury clearance but important sexual differences in loss by this route were found. Over the 98-day experimental period, males excreted in urine about 3.2% of the dose and females excreted 7.5%. Cumulative organic Hg excretion in urine accounted for 1.8% of the dose in males and 5.3% of the dose in females. These sexual differences in urinary and fecal excretion of organic and inorganic mercury following methyl mercury treatment were consistent with previous reports of sexual differences in mercury distribution and retention in methyl mercury-treated rats, particularly sexual differences in organic mercury uptake and retention in the kidney. Relationships between body burdens of organic or inorganic Hg and output of these forms of Hg in urine and feces were also found to be influenced by the interval after MeHg treatment and by sex. Relationship between concentration of Hg in liver and feces and in kidney and urine differed for organic and inorganic Hg and depended upon sexual status and interval after MeHg treatment. These findings emphasize that sexual differences in distribution, retention, and metabolism of methyl mercury are factors to be considered in estimations of hazards associated with exposure to this agent.     

Immunologic effects of exposure to low levels of inorganic mercury

OBJECTIVE: The immune system is a target for the toxic effects of inorganic mercury, both in humans and animals. In humans it has been observed that occupational and environmental exposure to inorganic mercury may cause both clinical (autoimmunity, hypersensitivity) and subclinical effects (cellular and humoral immunologic variable modifications). To obtain a better definition of these effects with respect to the exposure levels, a multicentre study was performed on 117 workers exposed to very low doses of inorganic mercury and 172 subjects from the general population of the same geographical area with environmental exposure to mercury from dental amalgams and dietary fish intake. RESULTS: The white blood cell count was included in the normality range for all subjects and there was no difference between exposed and non exposed subjects. The immunologic variables studied showed an increase of the CD4+ and CD8+ number in exposed workers compared to non-exposed subjects, with a statistically significance only for CD4+, while no difference was observed regarding CD4+, CD8+, NK+ percentage and CD4+/CD8+ ratio. A significative decrease of serum IL-8 and an inverse correlation between serum levels of this cytokine and HgU were observed in exposed workers compared to non exposed subjects. No association between immunologic variables and both dental amalgams and dietary fish intake was found in subjects not occupationally exposed to inorganic mercury. DISCUSSION: The decrease in IL-8 serum levels observed in exposed workers might suggest an immunosuppressive effect of occupational exposure to very low doses of inorganic mercury. This result suggests the need to revise of current HgU BEI after further definition of its prognostic significance.     

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.     

Barbiturate potentiation in mercury poisoning

Summary Barbiturate potentiation was observed in Japanese quail fed dietary levels of 4, 21, and 24 ppm Hg as methyl mercuric chloride. Gross symptoms of mercury poisoning were not observed until after BP was observed. After the initial increase in BP time was observed in the birds receiving 4 and 12 ppm mercury, there followed a plateau in response until those birds receiving 24 ppm Hg began to show gross symptoms of toxicity and the, BP time markedly rose again. Pronounced BP persisted 7 weeks after removal of mercury from the diet reflecting the long biological half-life of mercury as the methyl derivative. Selenium effectively prevented BP after 7 days exposure to toxic levels of methyl mercury chloride. Therefore, results suggest that early toxic effects of mercury can be observed readily by BP and that this environmental contaminant may influence drug activity or increase the sensitivity of the nervous system to sodium pentobarbital.Scientific Article No.A1993, Contribution No.4935 of the Maryland Agricultural Experiment Station.     

Sexual differences in the distribution and retention of organic and inorganic mercury in methyl mercury-treated rats

At 56 days of age, male and female Long-Evans rats received 1 mumole of 203Hg-labeled methyl mercuric chloride per kilogram sc and total, organic, and inorganic mercury contents and concentrations in tissues were determined for up to 98 days postdosing. Whole body clearance of mercury was faster in females than in males, and females attained higher peak percentages of the methyl mercury dose in kidney and brain than did males. Females had significantly higher mean percentages of the mercury dose present in the kidney and brain as organic or total mercury and in brain as inorganic mercury than did males. Males had significantly higher mean percentages of the dose present as organic or total mercury in pelt and whole body than did females. When expressed on a concentration basis, the only significant sexual difference was in the higher average concentration of organic mercury in the kidneys of females. When expressed on a tissue content basis, significant male-female differences in the kinetics (sex X time interactions) of organic mercury retention were found in kidney, brain, skeletal muscle, pelt, and whole body. Significant sex X time interactions in the concentrations of organic mercury were found in kidney, skeletal muscle, and whole body. Kinetics of retention and concentration of inorganic Hg in the pelt differed significantly for males and females. Discordance in degree of statistical significance of differences in mercury contents and concentrations reflected in part differences in relative body composition of males and females. Integrated exposures of tissues of males and females to organic or inorganic mercury were determined by fitting multiexponential retention functions to retention data. Differences in integrated exposure were estimated by the female-to-male ratio of areas under retention curves. Reconstruction of whole body organic and inorganic mercury burdens from constituent tissues indicated that integrated exposures of males and females to inorganic mercury were equal but females had a lower integrated exposure to organic mercury. Integrated exposure of liver to either form of mercury was about equal in males and females. However, the integrated exposure of the brain of females to inorganic mercury was 2.19 times that of males suggesting a sexual difference in accumulation or retention of inorganic mercury in the nervous system. These sexual differences in distribution and retention of organic and inorganic mercury after methyl mercury exposure may underlie reported sexual differences in sensitivity to the toxic effects of methyl mercury.     

Eating tropical fruit reduces mercury exposure from fish consumption in the Brazilian Amazon

This study aimed to examine the influence of the consumption of traditional foods on the relationship between fish consumption and mercury (Hg) exposure. A 12-month prospective dietary survey was carried out with 26 adult women from a fish-eating community in the Brazilian Amazon. Food ingestion was determined using a daily food diary, and total hair Hg levels were assessed for each month through sequential analyses using cold vapor atomic absorption spectrometry. Simple and multiple regression analyses showed that the strong relationship between fish consumption and Hg exposure was significantly modified by fruit consumption: for the same number of fish meals, those who ate more tropical fruits had lower hair mercury levels. The findings of this study indicate different ways of maintaining fish consumption while reducing Hg exposure in the Amazon. A number of phytochemicals and nutritional fibers present in fruits might be interacting with Hg in several ways: absorption and excretion, transport, binding to target proteins, metabolism, and sequestration. More studies are required on larger populations to further elucidate the extent and public health implications of the use of fruits to counteract the toxic action of methylmercury.     

Blood organic mercury and dietary mercury intake: National Health and Nutrition Examination Survey, 1999 and 2000

Blood organic mercury (i.e., methyl mercury) concentrations among 1,709 women who were participants in the National Health and Nutrition Examination Survey (NHANES) in 1999 and 2000 (1999-2000 NHANES) were 0.6 microg/L at the 50th percentile and ranged from concentrations that were nondetectable (5th percentile) to 6.7 microg/L (95th percentile). Blood organic/methyl mercury reflects methyl mercury intake from fish and shellfish as determined from a methyl mercury exposure parameter based on 24-hr dietary recall, 30-day food frequency, and mean concentrations of mercury in the fish/shellfish species reported as consumed (multiple correlation coefficient > 0.5). Blood organic/methyl mercury concentrations were lowest among Mexican Americans and highest among participants who designated themselves in the Other racial/ethnic category, which includes Asians, Native Americans, and Pacific Islanders. Blood organic/methyl mercury concentrations were ~1.5 times higher among women 30-49 years of age than among women 16-29 years of age. Blood mercury (BHg) concentrations were seven times higher among women who reported eating nine or more fish and/or shellfish meals within the past 30 days than among women who reported no fish and/or shellfish consumption in the past 30 days. Blood organic/methyl mercury concentrations greater than or equal to 5.8 microg/L were lowest among Mexican Americans (2.0%) and highest among examinees in the Other racial/ethnic category (21.7%). Based on the distribution of BHg concentrations among the adult female participants in 1999-2000 NHANES and the number of U.S. births in 2000, > 300,000 newborns each year in the United States may have been exposed in utero to methyl mercury concentrations higher than those considered to be without increased risk of adverse neurodevelopmental effects associated with methyl mercury exposure.     

The influence of age on the gastrointestinal absorption of mercuric chloride and methyl mercury chloride in the rat

The intestinal absorption of mercuric chloride and methyl mercury chloride was determined in neonatal (6-day-old) and mature (7-week-old) rats. No differences between the two age groups were observed in the absorption of methyl mercury chloride (0.08 μg Hg/ml) determined up to 2 hr after administration in vivo into closed segments of the duodenum or ileum. In contrast, the 1-hr duodenal absorption of mercuric chloride (8 μg Hg/ml) was significantly greater in neonatal animals (18.1%) as compared to 23-day-old weanling (7.3%) or mature (3.6%) animals. Ileal absorption of mercuric chloride was also higher in neonates than in mature animals, but the magnitude of the difference was less than that observed in the duodenum. GI absorption of mercuric chloride (46 μg Hg/kg) was also assessed in neonatal, weanling, and mature rats at 4 and 43 hr after gastric intubation. The percentage of the dose in the carcass, determined after removal of the GI tract, was significantly higher at both times in neonatal and weanling rats as compared to mature animals. Analysis of mercury content in the gastrointestinal tract of these animals also indicated age-dependent differences in mercury transit through the GI lumen. The extent of gastric emptying of mercury by 4 hr after dosing was significantly less in neonatal and weanling rats compared to mature animals. In addition, the small intestinal transit of mercury was markedly slower in neonates with 74.8% of the dose in the GI tract after 43 hr as compared to 5.2% and 3.0% in weanling and mature animals, respectively. These findings indicate that in the neonate, exposure to inorganic mercury by the oral route can be expected to result in higher systemic, as well as small intestinal, levels of mercury because of enhanced GI absorption and decreased luminal transit, respectively.     

Differential effects of mercurial compounds on the electroolfactogram (EOG) of salmon (Salmo salar L.)

The effects on the salmon (Salmo salar L.) electroolfactogram (EOG) of the two mercurials, mercuric chloride (HgCl2) and methylmercuric chloride (CH3HgCl), were studied. The EOG responses were evoked by stimulating the olfactory epithelium with 340 microM L-alanine for 10 sec every second minute during a 1-hr period. Each EOG response consisted of an initial peak component followed by a sustained component with an amplitude about 40% below the peak value. Three experimental series, each comprising six fish, were carried out. In the first series, the rosette was irrigated solely with artificial "fresh water." In the two other series, a 5-min exposure to mercury (HgCl2 or CH3HgCl, at 10(-5) M) was included after 10 min and a 15-min exposure after 45 min. The mercuric ion (Hg2+) eliminated the peak response within 2 min and suppressed the sustained response to about 35%. During the subsequent irrigation with mercury-free fresh water, both EOG components regained about 50% of their initial amplitudes. In contrast, methylmercury induced a steady and parallel decline of both the peak and the sustained responses, which were not reversed by rinsing the epithelium with fresh water. The results of this study demonstrate the vulnerability of the olfactory receptor function in fish to mercury exposure. Also, they show the very different effects of inorganic and organic mercurials upon the EOG.     

Control Devices

Mercury transport pathways through the gastrointestinal tract were investigated to explain preferential inorganic mercury excretion in feces after exposure to methyl mercury salts. Mercury is excreted in bile predominantly as methyl mercury cysteine. Protein-complexed methyl mercury and protein-bound inorganic Hg are found less extensively. Methyl mercury cysteine is rapidly reabsorbed, not adding significantly to fecal Hg. Protein-bound inorganic Hg is not reabsorbed and comprises about 15% total fecal Hg the first days after methyl mercury chloride injection. A corresponding fecal Hg amount derives from protein-bound methyl mercury from bile. Intestinal cell shedding is the main fecal Hg source. These cells, however, contain less than 5% inorganic Hg, compared to about 50% in feces. Methyl mercury bound to structural proteins in these cells releases inorganic Hg, probably by lower-intestinal microbiological action.     

Gold-mining activities and mercury contamination of native amerindian communities in French Guiana: key role of fish in dietary uptake

In 1994, the French National Public Health Network reported significant mercury exposure of native Amerindians in French Guiana. In 1997, a study was conducted in the Wayana community to quantify the dietary intake and to identify the fish species contributing the most to the contamination. The study was completed by an impregnation analysis based on Hg determination in hair samples. The methodology used was a detailed familial dietary study associated with Hg measurements in fish and some game. The study was conducted over 7 days in two different seasons in the four most populated Wayana villages on the upper part of the Maroni River (521 people; 70% of the Wayana population in French Guiana). Analysis was based on data on consumption obtained from 165 people in a 1-14 day period (i.e., 940 persons [times] days) and involved 270 fish samples from 48 species. Total Hg and monomethylmercury (MMHg) were also determined in hair samples (235 samples for total Hg). The results confirm mercury exposure of the Wayana population related to a diet rich in fish, which are relatively highly contaminated for certain species (up to 1.62 mg/kg fresh weight or 8.1 mg/kg dry weight in skeletal muscle). Results from hair samples showed that 57% of the Amerindians had Hg levels above the World Health Organization (WHO) safety limit (10 microg/g); all those over 1 year of age had a Hg intake greater than the WHO safety limit (200 microg MMHg/week for a 60-kg male). Hg concentrations in fish muscle were closely linked to the feeding regime and position of fish in the food webs. Overall, 14.5% of the fish collected exceeded the 0.5 mg/kg (fresh weight) safety limit. Four carnivorous species accounted for no less than 72% of the metal ingested by the Wayana families, although these represented only 28% of the consumed fish biomass. In conclusion, this study revealed excessive exposure to mercury in the Wayana population in French Guiana related to the consumption of contaminated fish.     

Neurotoxic effect of exposure to low doses of mercury

OBJECTIVES: To assess early effects on the Central Nervous System due to occupational exposure to low levels of inorganic mercury (Hg) in a multicenter nationwide cross-sectional study, including workers from chloro-alkali plants, chemical industry, thermometer and fluorescent lamp manufacturing. The contribution of non-occupational exposure to inorganic Hg from dental amalgams and to organic Hg from fish consumption was also considered. METHODS: Neuropsychological and neuroendocrine functions were examined in a population of 122 workers occupationally exposed to Hg, and 196 control subjects, not occupationally exposed to Hg. Neuropsychological functions were assessed with neurobehavioral testing including vigilance, motor and cognitive function, tremor measurements, and with symptoms concerning neuropsychological and mood assessment. Neuroendocrine functions were examined with the measurement of prolactin secretion. The target population was also characterized by the surface of dental amalgams and sea fish consumption. RESULTS: In the exposed workers the mean urinary Hg (HgU) was 10.4 +/- 6.9 (median 8.3, geometric mean 8.3, range 0.2-35.2) micrograms/g creatinine, whereas in the control group the mean HgU was 1.9 +/- 2.8 (median 1.2, geometric mean 1.2, range 0.1-33.2) micrograms/g creatinine. The results indicated homogeneous distribution of most neurobehavioral parameters among exposed and controls. On the contrary, finger tapping (p < 0.01) and the BAMT (Branches Alternate Movement Task) coordination test (p = 0.05) were associated with occupational exposure, indicating an impairment in the exposed subjects. Prolactin levels resulted significantly decreased among the exposed workers, and inversely related to HgU on an individual basis (p < 0.05). An inverse association was also observed between most neuropsychological symptoms and sea fish consumption, indicating a "beneficial effect" from eating sea fish. On the contrary, no effects were observed as a function of dental amalgams. CONCLUSIONS: In conclusion, this study supports the finding of early alterations of motor function and neuroendocrine secretion at very low exposure levels of inorganic Hg, below the current ACGIH BEI and below the most recent exposure levels reported in the literature.     

Cytochemical demonstration of mercury deposits in trout liver and kidney following methyl mercury intoxication: differentiation of two mercury pools by selenium

The amount and the ultrastructural distribution of mercury was studied in seven different organs of rainbow trout (Salmo gairdneri) fingerlings following exposure to methyl mercury (MeHg)-contaminated fodder for periods of 2 and 7 weeks. The amounts of mercury retained by the whole fish and the selected organs were determined by measuring the uptake of 203Hg-labeled MeHg. Spleen, liver, and kidney had the highest concentrations after both experimental periods, while the largest relative increases were found in brain, muscle, and kidney. The subcellular distribution of mercury accumulations was demonstrated cytochemically in liver and kidney using the silver enhancement method by which accumulations of mercury-sulfides and/or mercury-selenides are made visible for light and electron microscopy. When sections prepared from the liver and kidney from fish, injected with selenium 2 hr prior to being killed, were compared with those of fish not treated with selenium, two distinct pools of mercury could be demonstrated, the HgS pool, and the HgSe pool. The HgS pool, supposed to represent inorganic mercury, was found exclusively within lysosomes. The increase of this pool from 2 to 7 weeks was most pronounced in the kidney. The HgSe pool, supposed to represent methyl mercury, was shown by the presence of silver deposits at new locations as well as by an increase in the amount of deposits within lysosomes. The new locations included (1) secretory-like vesicles and the bile canaliculi of the liver, suggesting a biliary excretion of this mercury pool; (2) microvilli and endosomes of kidney tubular cells, suggesting a glomerular filtration and subsequent reabsorption; and (3) mitochondria of proximal tubule cells.