Total Mercury and Methylmercury Residues in River Otters (<Emphasis Type="Italic">Lutra canadensis</Emphasis>) from Wisconsin

The Wisconsin Department of Natural Resources (WDNR) collected trapper-caught river otter (Lutra canadensis) from 3 distinct areas of Wisconsin (north, central, and south). Otter carcasses were collected from a total of 12 counties during the trapping seasons of 2003 and 2004. Liver, kidney, muscle, brain, and fur tissue was collected for mercury (Hg) analysis. Analysis of variance identified collection zone as the significant factor for differences in tissue Hg levels, with a pattern of decreasing Hg concentrations from north to south (p < 0.0001). This trend was apparent in all tissue types analyzed. Strong relationships were observed between Hg concentrations in all tissues. Likewise, highly significant (p < 0.0001) relationships were found to exist between Hg concentrations in otter fur and Hg concentrations of internal organs (brain, muscle, kidney, and liver). Although these data suggest that Hg concentrations are related among tissues, they do not suggest uniform distribution of Hg throughout the tissues. The results suggest that Hg accumulates at higher concentrations in fur followed by liver, kidney, muscle, and brain. Analysis of a subset of samples for methylmercury (MeHg) revealed that MeHg made up a greater percentage of total Hg in brain and muscle compared to liver and kidney tissue. Although a gradient in tissue concentrations was observed from north to south, none of the tissue concentrations reached levels known to cause toxicity in either otter or mink.     

Dose-Dependence of Methylmercury Metabolism

The distribution and excretion of different body burdens of methylmercury (MeHg) have been investigated in the squirrel monkey. In monkeys given weekly 0.8 mg/kg doses, orally, of ²⁰³MeHg, a linear correlation was observed between the concentrations of radioactive Hg in the blood and brain to as much as a blood concentration of 1μg/gm. Above this level, the ratio of concentration in the brain and blood was increased.

The total Hg concentration in bile collected from the bile duct was 10% to 30% of that in blood, while the concentration in bile from the gallbladder approached that in blood. The total Hg concentration in feces was always more than ten times that in urine.

Biotransformation of MeHg to inorganic mercury has been demonstrated; in the liver about 20% of the total mercury was inorganic, in the kidney 50%, and in the bile 30% to 85%. In the brain<5% of the total mercury was inorganic. After a single 0.8 mg/kg dose, orally, of ²⁰³MeHg, the halftime for total Hg in blood was 49±2.8 days, and in the whole body 134±2.7 days. During the first four days after dosing, the decrease in blood concentration was more rapid than that occurring later, due to a redistribution within tissue compartments. A differential distribution of MeHg within the brain has been demonstrated in animals that showed clinical signs of intoxication.     

High exposure of Chinese mercury mine workers to elemental mercury vapor and increased methylmercury levels in their hair

Objective The aim of this study was to determine the level of exposure of mercury (Hg) miners and smelter workers to elemental mercury (Hg⁰) vapor in China, who work in Hg mines without using protective equipment against Hg⁰ vapor. In addition, the level of methylmercury (MeHg) intake by the workers was estimated from the MeHg concentration in their hair. Methods Urinary total mercury (THg) and hair THg and MeHg concentrations were measured in 26 Hg miners and smelter workers (i.e., exposed group), and 48 unexposed people (unexposed group). Results The exposed group showed high geometric mean THg concentrations in urine (258 ng/ml, 226 μg/g creatinine) and hair (20.0 μg/g). The urinary THg concentration of the smelter workers in particular was extremely high (338 μg/g creatinine in urine). The highest urine THg concentration reached 4577 μg/g creatinine. THg concentrations in urine and hair showed a significant correlation in the exposed group (r=0.62), indicating the adhesion of Hg⁰ vapor to hair. However, no such significant correlation was found in the unexposed group. Hair MeHg concentration in the exposed group (1.97 μg/g) was about threefold higher than that in the unexposed group (0.60 μg/g). Conclusions This study shows that smelter workers in a Chinese Hg mine are exposed to extremely high levels of Hg⁰ vapor, and that Hg miners are exposed to higher levels of MeHg than the unexposed subjects. Further study is needed to determine the cause of the higher hair MeHg concentration in the exposed group.     

Methylmercury Concentrations in Fish from Tidal Waters of The Chesapeake Bay

Striped bass (Morone saxatilis), white perch (Morone Americana), and largemouth bass (Micropterus salmoides) were collected in the Chesapeake Bay mainstem and tributaries and analyzed for total mercury (Hg) and methylmercury (MeHg) content. Striped bass are anadromous, whereas white perch and largemouth bass are resident species, and the largemouth bass are also restricted to the tidal fresh portion of the Bay. Total Hg and MeHg concentrations in striped bass increased with fish size, and large fish (>7.5 kg wet weight) tended to have MeHg concentrations of 300 ng g⁻¹ or greater. On average, the striped bass MeHg concentration was 120 ± 100 ng g⁻¹ and the fraction of the total Hg as MeHg was 65 ± 22%. Reasons for the lower relative MeHg content are discussed. Otolith strontium/calcium ratios were also determined to examine whether migration had a significant impact on MeHg content in striped bass. Resident fish did appear to have a higher MeHg burden than the more migratory fish of similar size. Largemouth bass and white perch tended to have low MeHg content (respectively, 14 ± 7 and 13 ± 11 ng g⁻¹; all fish <1 kg wet weight), and the white perch also had a low %MeHg (28 ± 14%), reflecting their mostly planktivorous lifestyle. A comparison of largemouth bass and striped bass MeHg concentrations for the estuarine fish with those of fish in Maryland reservoirs of similar size showed that the estuarine fish have much lower MeHg burdens. Differences in MeHg concentration in the estuarine waters compared to the reservoir waters likely account for much of this difference, although the importance of other factors is also discussed.     

Comparative Experimental Study of Cadmium and Methylmercury Trophic Transfers Between the Asiatic Clam Corbicula fluminea and the Crayfish Astacus astacus

Cadmium (Cd) and methylmercury (MeHg) trophic transfers were analyzed between the Asiatic clam Corbicula fluminea and the crayfish Astacus astacus. Metal bioaccumulation in crayfish was quantified after 5, 10, and 15 days of exposure via daily ingestion of soft bodies of C. fluminea, previously exposed during 7 days to Cd (20 μg · L⁻¹) and MeHg (4 μg · L⁻¹). Bioaccumulation kinetics in the predator were investigated at organ and tissue levels: hemolymph, tail muscle, hepatopancreas, gills, stomach/mesenteron, intestine, green gland, carapace. Trophic transfer rates were estimated at the whole organism level. Results showed marked differences (1) in assimilation efficiencies, mean transfer rates being 5% for Cd and 16% for MeHg; and (2) in the metal distribution within the different tissue compartments of the crayfish: for Cd, the trophic uptake leads to high concentrations in the hepatopancreas and small accumulation in the muscle tissue; for MeHg, the highest levels of bioaccumulation occur in the green gland and in the tail muscle. From an ecotoxicological point of view, these experimental data suggest a small risk of Cd transfer between the crayfish and predators, humans included; on the other hand, Hg distribution in the muscle and accumulation trends in this tissue represent an obvious risk of transfer. Received: 7 April 1999/Accepted: 9 September 1999     

Accumulation and Elimination of Cadmium by the Nile Tilapia (Oreochromis niloticus) in differing Temperatures and Responses of Oxidative Stress Biomarkers

The aims of this study were to investigate the accumulation (15 days) and elimination (15 and 30 days) of cadmium (Cd) in the liver, gill, kidney and muscle of Oreochromis niloticus following exposures to different concentrations (1 and 2 mg/L) of Cd at different water temperatures (20, 25, 30 ^oC). Additionally, responses of oxidative stress biomarkers (superoxide dismutase, SOD; catalase CAT; glutathione peroxidase, GPx and malondialdehyde, MDA) of the liver were determined following Cd exposures. In accumulation period, Cd levels increased significantly in all the tissues at all temperatures and tissue accumulation order was kidney?>?liver?>?gill. All tissues, except the muscle, accumulated Cd in relation to exposure concentrations and water temperatures. There was no measurable level of Cd accumulation in the muscle, except in fish exposed to 2 mg Cd/L at 30 ^oC. Likewise, elimination of Cd from the tissues also increased in depends on periods and water temperatures. The order of Cd elimination from the tissues was gill?>?liver?>?kidney. The oxidative stress biomarkers also responded to both Cd exposure and temperature increases. The activities of antioxidant enzymes such as SOD, CAT, GPx and MDA levels in the liver increased in relation to increases in Cd concentrations and water temperatures.

     

Differences in Methylmercury and Inorganic Mercury Biomagnification in a Tropical Marine Food Web

Methylmercury (MeHg), inorganic mercury (Hg_inorg) and their biomagnification factors (BMF) were evaluated along a non-degraded Brazilian bay food web. Highly significant differences (p < 0.0001) were found between MeHg and Hg_inorg concentrations among all organisms (microplankton, shrimp, fish and dolphin). MeHg increased with increasing trophic position while Hg_inorg did not present the same pattern. BMF values for MeHg were higher than 1 for all trophic interactions from source to consumer, indicating that MeHg was transferred more efficiently and biomagnified over the entire web. Only one BMF exceeding one was observed for Hg_inorg (27) between microplankton and their consumer, planktivorous fish. BMF values for Hg_inorg were significantly different than those found for MeHg (20) at the base of the food web.     

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.     

Cadmium Accumulation and Antioxidant Responses in <Emphasis Type="Italic">Sparus aurata</Emphasis> Exposed to Waterborne Cadmium

Cadmium (Cd), a nonessential trace element, is rapidly accumulated by most living organisms and subsequently exerts its toxicity at different molecular levels. This study exposed gilthead sea bream (Sparus aurata) to waterborne 0.1 mg/l Cd for 11 days and investigated the Cd accumulation pattern, lipid oxidation, and response of antioxidant defences. At the end of the experiment, mean Cd concentrations in gills and liver, the organs most prone to metal accumulation, were 209.4 and 371.7 ng/g ww, respectively. Muscle did not show any Cd retention during the 11 days of exposure. In liver, the cytosolic fraction of the metal was chelated into the nontoxic form by metallothionein (MT), a specific Cd-inducible protein. Zn and Cu concentrations were not influenced by Cd exposure. Glutathione (GSH) concentrations and the antioxidant enzyme activities of GSH reductase and GSH peroxidase showed an overall decreasing trend. In addition, lipid and aqueous hydroperoxide levels did not show any significant variation. Oxidative stress indirectly generated by Cd seems to be compensated for by the different biochemical systems tailored to decrease cellular damage. In particular, the negative effects of Cd accumulation in tissues were probably counteracted by the induction of MT.     

Distribution, biomagnification, and elimination of butyltin compound residues in common cormorants (Phalacrocorax carbo) from Lake Biwa, Japan

Concentrations of butyltin compounds (BTs) were determined in various body tissues of common cormorants (Phalacrocorax carbo) collected from the Lake Biwa, Japan. Elevated concentrations of butyltins were detected in the feathers of cormorants. Among other organs and tissues, butyltin levels were also higher in the kidney (290±150 ng/g) and liver (270±260 ng/g), ranging from 115 to 544 ng/g and 142 to 1007 ng/g (wet wt basis), respectively. The accumulation of BTs in cormorant bodies was in the order of MBT > DBT > TBT and their organ specific burdens were in the order of muscle feathers > skin > liver > rest of the tissues and organs. The higher levels of BTs residues in feather suggested the excretion of about one fourth of their body burden during a complete molting cycle, which has been a natural detoxification mechanism in these birds. Based on the whole body concentrations of BTs in cormorants (42–160 ng/g wet wt) and fish (10–55 ng/g wet wt) biomagnification factors were assessed to be in the range of 1.1–4.1. To our knowledge, this is the first fundamental study to substantially indicate the contamination and kinetics of BTs in wild birds.     

Tissue Distribution of Polychlorinated Biphenyls and Organochlorine Pesticides and Potential Toxicity to Alaskan Northern Fur Seals Assessed Using PCBs Congener Specific Mode of Action Schemes

The fur seal (Callorhinus ursinus) population has decreased in their primary breeding grounds in the Bering Sea; contamination is among suspected causes. Our goal was to better understand the extent of contamination of seal tissues with certain organochlorine compounds by measuring the concentrations of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in fur seal tissues from St. Paul Island, to gain a better perspective of tissue congener distribution and to evaluate the observed PCB levels against toxicologically significant levels for modes of action. Concentrations of 145 PCB congeners (∑₁₄₅PCBs) and 12 OCPs were measured with gas chromatography–ion trap mass spectrometry in 8 different tissues of 10 male northern fur seals. The mean concentrations of ∑OCPs [in ng/g lipid weight (lw)] were 1180 in blubber, 985 in the heart, 1007 in the liver, 817 in the kidney, 941 in muscle, 660 in reproductive tissues, 204 in the brain, and 322 in the lung. The mean concentrations of ∑₁₄₅PCBs (in ng/g lw) were 823 in blubber, 777 in the liver, 732 in the heart, 646 in reproductive tissues, 638 in muscle, 587 in the kidney, 128 in the lung, and 74.3 in brain tissues. Concentrations of PCBs affecting the aryl hydrocarbon receptor expressed as total PCB toxic equivalents (∑PCB-TEQs) ranged from 0.3 to 545 pg/g lw for the various tissues. The major contributors to ∑PCB-TEQs are CB-118 in muscle, brain, lung, kidney, and liver, CB-126 in blubber, and CB-118 and CB-126 equally in the heart and reproductive tissues. Concentrations of PCBs affecting Ca²⁺ homeostatsis expressed as the neurotoxic equivalent (NEQ) showed ∑PCB-NEQs ranged from 17.7 to 215 ng/g lw in all tissues. Although no composite measure of perturbation of thyroid function is available, sufficient amounts of congeners with high binding to the thyroxine transport system were present to warrant consideration of this mode of action in future studies. Analyses of 145 PCBs and mode of action evaluation suggest that PCB contamination could potentially exert an effect on the Alaskan northern fur seal population although the PCB concentrations have been decreasing in the fur seals over the last decade.     

Metal interactions within the kidney,gill, and digestive gland of the clam,Mercenaria mercenaria,following laboratory exposure to cadmium

Mercenaria mercenaria were exposed to 0.1 g Cd/ml seawater (¹⁰⁹Cd + stable carrier) for either (1) periods of 1 hr to 31 days, or (2) a period of 3 days followed by depuration in clean seawater for 2 to 64 days. Cd accumulated at increasing rates in the kidney, but at decreasing rates in all other organs of the clam during the laboratory exposure period. Measurement of total Cd levels confirmed that¹⁰⁹Cd was accumulated by the clam tissues and not simply exchanged. The overall rate of Cd accumulation was significantly greater (P < 0.05) for the kidney than for the gill, mantle, digestive gland, pericardial gland, adductor, or remaining viscera, but not significantly different among the other organs (P > 0.05). No loss of Cd or other detectable metals occurred even after 64 days depuration. The degree to which Cd accumulated in the kidney, gill, and digestive gland did not correlate with the concentrations of other metals already present in these organs (except with Zn in the digestive gland). Negative correlations between different metal concentrations were never observed. Comparison of metal interaction patterns between the kidney, gill, and digestive gland indicates that each organ relies on different mechanisms for sequestering metals.     

Accumulation of Lead,Zinc, and Cadmium in a Wild Population of <Emphasis Type="Italic">Clethrionomys glareolus</Emphasis> from an Abandoned Lead Mine

Lead, zinc, and cadmium were determined in a range of tissues from wild populations of bank voles (Clethrionomys glareolus) trapped on an abandoned metalliferous mine site and a reference site. Estimated dietary intakes indicated that animals were exposed to elevated levels of all three metals at the mine site, and this was generally reflected in metal residues in body tissues. Lead concentrations were significantly higher in all tissues of animals from the mine compared to the reference site, while Cd was higher only in the kidney. There was evidence of age-accumulation (using total body weight as an index of age) of Cd in both the liver and kidney of mine site animals but no evidence of such accumulation of lead in bone. In contrast to Cd and Pb, Zn was lower in the tissues of mine site animals compared to the reference site. Based on critical tissue concentrations, the ecotoxicological risk to a wild population of bank voles (Clethrionomys glareolus), associated with total substrate levels of 1 μg g⁻¹ dry weight Cd and 700 μg g⁻¹ dry weight Zn at this mine site is negligible, but that associated with 4000 μg g⁻¹ dry weight Pb may be considered significant. Received: 28 January 2002/Accepted: 29 July 2002     

Methylmercury and selenium speciation in different tissues of beluga whales (Delphinapterus leucas) from the western Canadian Arctic

Monitoring data have shown that the total monomethylmercury (CH(3) Hg(+) and its complexes; collectively referred as MeHg hereafter) concentrations in Arctic marine mammals have remained very high in recent decades. Toward a better understanding of the metabolic and toxicological implications of these high levels of MeHg, we report here on the molecular forms of MeHg in the muscle, brain, liver, and kidneys of 10 beluga whales from the western Canadian Arctic. In all tissues analyzed, monomethylmercury was found to be dominated by methylmercuric cysteinate, a specific form of MeHg believed to be able to transport across the blood-brain barrier. Another MeHg-thiol complex, methylmercuric glutathionate, was also detected in the muscle and, to a much lesser extent, in the liver and brain tissues. Furthermore, a profound inorganic Hg peak was detected in the liver and brain tissues, which showed the same retention time as a selenium (Se) peak, suggesting the presence of an Hg-Se complex, most likely an inorganic Hg complex with a selenoamino acid. These results provide the first analytical support that the binding of MeHg with glutathione and Se may have protected beluga whales from the toxic effect of high concentrations of MeHg in their body.     

Mercury Distribution and Methylmercury Mobility in the Sediments of Three Sites on the Lebanese Coast,Eastern Mediterranean

Mercury (Hg) contamination in coastal sediments has been widely studied in clay deposits; however, equivalent results on carbonated sediments are scarce. This article aims to study Hg distribution in Lebanese carbonate coastal marine sediments (Eastern Mediterranean) in order to characterize their contamination level and to explore the postdepositional mobility of methylmercury (MeHg) in the deposits. Vertical distribution profiles of total (HgT) and MeHg have been established for the solid phase of sediment cores collected in various near-shore environments chosen for their hypothetical various degrees of anthropization. In addition, dissolved MeHg was determined in sediment pore waters to test its mobility and potential availability for biota. Three sites on the Lebanese coasts—Akkar, Dora, and Selaata—were selected. Akkar is far from any direct contamination source, whereas Dora, located near the Beirut harbor, is a heavily urbanized and industrialized zone including a huge dump site, and Selaata is near a chemical plant that produces phosphate fertilizers. Particulate HgT concentrations in the sediments varied between <0.04 and 0.65 μg/g, with a proportion of MeHg lower than 1%. Based on a sediment quality guideline (MacDonald et al. 2000), we concluded that Dora bay sediments are heavily contaminated by Hg, with concentrations exceeding the “consensus-based threshold effect” level (0.17 μg/g) and almost reaching the “effects range-medium” level (0.71 μg/g). In spite of the low HgT concentration in Akkar and Selaata sediment (similar to natural carbonated sediment: 0.04 μg/g according to Turekian and Wedephol (1961), a closer analysis of the sediment core vertical profile allows one to observe an anthropogenic impact. This impact might be toxicologically insignificant; however, it allows tracing the time increase of Hg diffuse deposition. On the other hand, dissolved MeHg concentrations ranged from 0.04 to 0.09 and from 0.04 to 8.76 ng/l in the Selaata and the Dora sediments, respectively; MeHg vertical profiles in interstitial water enabled us to calculate diffusive fluxes of MeHg from the sediment varying from 0.3 to 1.0 ng/m²/day. Thus, the deposited sediments constitute a measurable source of bioavailable Hg for epibenthic organisms.     

Factors Controlling Mercury and Methylmercury Concentrations in Largemouth Bass (Micropterus salmoides) and Other Fish from Maryland Reservoirs

The concentration of mercury (Hg) and methylmercury (MeHg) was determined for largemouth bass (Micropterus salmoides), bluegill (Lepomis macrochirus) and black crappie (Pomoxis nigromaculatus) from Maryland reservoirs. Overall, there was a large difference in normalized bass MeHg concentration (for fish of ∼370 mm) between the reservoirs, ranging from <100 ng g⁻¹ to almost 800 ng g⁻¹. Furthermore, the relationship between fish weight and MeHg concentration varied substantially between lakes, and showed no geographical relationship. The concentration of Hg, MeHg and ancillary parameters were determined in the water and correlations were sought between the normalized concentration of MeHg in bass and both physical and chemical parameters of the reservoirs, as well as the concentration of MeHg in the prey of the largemouth bass. Bass MeHg concentration correlated with dissolved MeHg and dissolved organic carbon, but not with other chemical parameters. There was no relationship to physical characteristics that varied over orders of magnitude for these reservoirs. Dissolved MeHg did not correlate with any chemical or physical attributes. Overall, this study suggests that water column MeHg is a good predictor of fish concentration but that the water column MeHg cannot be predicted based on usually measured chemical and physical characteristics of fresh water bodies.     

Occurrence of methylated mercury in a terrestrial food chain

The presence and transfer of methylated mercury (MeHg) in a terrestrial food chain were determined by radiotracer laboratory experiments and chemical analyses of field-collected organisms. [²⁰³Hg]MeHg-tagged fescue grass (Festuca sp.) at 0.65 μg MeHg/g grass (wet wt) was fed to cotton rats (Sigmodon hispidus). The rats had an assimilation efficiency (A_e) for MeHg of 99% and a biological half-life (t_b) of 9.5 days. Control S. hispidus and Festuca collected from the same populations as the experimental organisms were analyzed for MeHg and found to have, for the S. hispidus, 1.4 ± 0.2 ng/g, 1 SE, and 1.3 ± 0.3 ng/g, 1 SE, in skeletal muscle and liver, respectively; and, for Festuca (composite sample) 0.6 ng/g. Total mercury (ΣHg) for the same tissues was 119.4 ± 39 ng/g, 1 SE, 34.6 ± 8.9 ng/g, 1 SE; and 71 ng/g (composite sample), respectively. Calculations with the experimental and analytical MeHg values indicated that the feral S. hispidus would, at equilibrium, have a whole-body MeHg concentration of 1.89 ng/g. These results, compared with literature reports, indicate that feral rodents have concentration ranges of ～50 to ～160 ng/g for ΣHg, and ～1 to ～7 ng/g for MeHg. Environmental levels of mercury are likely to increase significantly; further environmental measurements and especially appropriate toxicity tests are warranted to assess the importance of MeHg in terrestrial ecosystems.     

Effects of Heavy Metals (Hg2+, Cd2+, Pb2+) During the Embryonic Development of Acridid Grasshoppers (Insecta, Caelifera)

Heavy metals present in the soil get differently accumulated in organisms and show different rates of toxicity at different stages of the life cycle of any organism living there. To see whether such toxicants get accumulated during the embryonic development and/or change the normal developmental processes of organisms exposed to heavy metals, freshly laid eggs and egg pods of two acridids, Aiolopus thalassinus and Eyprepocnemis plorans, were tested against different concentrations of Hg²⁺, Cd²⁺, and Pb²⁺. At increasing Hg²⁺ concentration in the substrate, an increased egg mortality and reduced nymphal hatching in A. thalassinus were observed, yet no change in the normal duration for embryonic development was noticed. A higher hatching rate of E. plorans nymphs than that of A. thalassinus could possibly be due to the higher tolerance, contributed by larger egg volume and thicker foam around the egg pods of the former. Treated concentrations of Hg²⁺ could be of sublethal (0.121 μg Hg²⁺/g substrate) to lethal (0.605 μg and more Hg²⁺/g substrate) doses. The mortality of eggs did not always increase with increasing substrate concentration of Cd²⁺ and Pb²⁺, and the hatching rates of both grasshopper species in many cases were even higher than that in the control. Still, lower accumulation factors of Cd²⁺ and Pb²⁺ than that of Hg²⁺ were found coupled with not increased mortality. The tested concentrations of Cd²⁺ and Pb²⁺ in the substrates, thus, could be of subacute doses. The embryonic development was found prolonged due to Cd²⁺ and Pb²⁺. During parallel egg and egg pod treatments, higher metal concentrations were found in not developed eggs than that in fresh nymphs hatching from the same substrates. This indicated the role of foam around the egg pods as “protective filter” against the toxic substances in the soil. Received: 31 May 1998/Accepted: 12 November 1998     

Organic and Inorganic Mercury in Neonatal Rat Brain after Prenatal Exposure to Methylmercury and Mercury Vapor

Background

Many populations are exposed to multiple species of mercury (Hg), predominantly organic Hg as methylmercury (MeHg) from fish, and inorganic Hg as Hg vapor from dental amalgams. Most of our knowledge of the neurotoxicity of Hg is based on research devoted to studying only one form at a time, mostly MeHg.

Objectives

In this study we investigated the effects of prenatal exposure to MeHg and Hg vapor on Hg concentrations in the brain of neonatal rats.

Methods

Female Long-Evans hooded rats were exposed to MeHg (0, 3, 6, or 9 ppm as drinking solution), Hg vapor (0, 300, or 1,000 μg/m³ for 2 hr/day), or the combination of both, from 30 days before breeding through gestational day 18. On postnatal day 4, whole brains were taken from one male and one female from each of four litters in each treatment group to assess organic and inorganic Hg in the brain by cold vapor atomic absorption spectrometry.

Results

Statistical analysis using linear mixed effects models showed that MeHg dose was the primary determinant of both organic and inorganic brain Hg levels. For both outcomes, we also found significant interactions between MeHg and Hg vapor exposure. These interactions were driven by the fact that among animals not exposed to MeHg, animals exposed to Hg vapor had significantly greater organic and inorganic brain Hg levels than did unexposed animals.

Conclusion

This interaction, heretofore not reported, suggests that coexposure to MeHg and Hg vapor at levels relevant to human exposure might elevate neurotoxic risks.     

Assessment of White Blood Cell Phagocytosis as an Immunological Indicator of Methylmercury Exposure in Birds

White blood cell (WBC) phagocytosis was investigated as a potential immunological indicator of methylmercury (MeHg) exposure in birds. The assay was first assessed using chicken WBCs dosed with MeHg in vitro either in whole blood or as isolated cells and later using blood of wild common loons exposed in vivo to a range of dietary MeHg and having a range of blood-Hg concentrations. Whole blood and isolated WBCs from captive chickens were exposed to a range of MeHg concentrations for 3 h. After MeHg exposure, cells were incubated with fluorescent latex microbeads (diameter = 1.75 μm), fixed, and analyzed for size, complexity, and fluorescent intensity by flow cytometry. MeHg significantly depressed phagocytic activity when added to isolated WBCs at concentrations > 0.01 μg/ml, but not when added to whole blood up to 50 μg/ml. Similarly, no significant relationship between the concentration of Hg in whole blood and phagocytic capacity of WBCs in free-living loons was observed. Our results suggest that the phagocytosis assay, although rapid and convenient for use in field studies with wildlife species, is not a responsive immunological indicator of MeHg exposure at environmentally realistic concentrations of blood-Hg in wild loons. Assays that measure other immunologic endpoints (e.g., bacterial killing assay, PHA skin test, and mitogen-induced lymphocyte proliferation) should be assessed with respect to their ability to detect MeHg immunotoxicity in wild birds. Received: 3 May 2002/Accepted: 11 November 2002