Developmental selenomethionine and methylmercury exposures affect zebrafish learning.

Methylmercury (MeHg) is a ubiquitous environmental pollutant and has been shown to affect learning in vertebrates following relatively low exposures. Zebrafish were used to model long-term learning deficits after developmental MeHg exposure. Selenomethionine (SeMet) co-exposure was used to evaluate its role in neuroprotection. Embryos were exposed from 2 to 24h post fertilization to (1) MeHg without SeMet, (2) SeMet without MeHg and (3) in combination of MeHg and SeMet. In case (1), the levels of MeHg were 0.00, 0.01, 0.03, 0.06, 0.10, and 0.30 microM. In case (2), the levels of SeMet were 0.00. 0.03, 0.06, 0.10, and 0.30 microM. In case (3), co-exposure levels of (MeHg, SeMet) were (0.03, 0.03), (0.03, 0.06), (0.03, 0.10), (0.03, 0.30), (0.10, 0.03), (0.10, 0.06), (0.10, 0.10), and (0.10, 0.30) microM. Learning functions were tested in individual adults, 4 months after developmental exposure using a spatial alternation paradigm with food delivery on alternating sides of the aquarium. Low levels of MeHg (<0.1 microM) exposure delayed learning in treated fish; fish exposed to higher MeHg levels were unable to learn the task; SeMet co-exposure did not prevent this deficit. These data are consistent with findings in laboratory rodents. The dorsal and lateral telencephalon are the primary brain regions in fish involved in spatial learning and memory. Adult telencephalon cell body density decreased significantly at all MeHg exposures >0.01 microM MeHg. SeMet co-exposure ameliorated but did not prevent changes in telencephalon cell body density. In summary, MeHg affected both learning and brain structure, but SeMet only partially reversed the latter.

Selenomethionine reduces visual deficits due to developmental methylmercury exposures.

Developmental exposures to methylmercury (MeHg) have life-long behavioral effects. Many micronutrients, including selenium, are involved in cellular defenses against oxidative stress and may reduce the severity of MeHg-induced deficits. Zebrafish embryos (<4 h post fertilization, hpf) were exposed to combinations of 0.0-0.30 microM MeHg and/or selenomethionine (SeMet) until 24 hpf then placed in clean medium. Fish were tested as adults under low light conditions ( approximately 60 microW/m(2)) for visual responses to a rotating black bar. Dose-dependent responses to MeHg exposure were evident (ANOVA, P<0.001) as evidenced by reduced responsiveness, whereas SeMet did not induce deficits except at 0.3 microM. Ratios of SeMet:MeHg of 1:1 or 1:3 resulted in responses that were indistinguishable from controls (ANOVA, P<0.001). No gross histopathologies were observed (H&E stain) in the retina or optic tectum at any MeHg concentration. Whole-cell, voltage-gated, depolarization-elicited outward K(+) currents of bipolar cells in intact retina of slices adult zebrafish were recorded and outward K(+) current amplitude was larger in bipolar cells of MeHg-treated fish. This was due to the intense response of cells expressing the delayed rectifying I(K) current; cells expressing the transient I(A) current displayed a slight trend for smaller amplitude among MeHg-treated fish. Developmental co-exposure to SeMet reduced but did not eliminate the increase in the MeHg-induced I(K) response, however, I(A) responses increased significantly over MeHg-treated fish to match control levels. Electrophysiological deficits parallel behavioral patterns in MeHg-treated fish, i.e., initial reactions to the rotating bar were followed by periods of inactivity and then a resumption of responses.

Serum PCB profiles in Native Americans from Wisconsin based on region, diet, age, and gender: Implications for epidemiology studies.

BACKGROUND: Different PCB congeners and different mixtures of congeners have been demonstrated to have different biological actions. More complete characterization of congener profiles in exposure sources may assist in predicting health outcomes. METHODS: Thirty-six (36) polychlorinated biphenyl (PCB) congeners were measured by gas chromatography isotope-dilution mass spectrometry (IDMS) in 314 serum samples from Native Americans in Wisconsin, Michigan and Minnesota. Five dietary groups were established based on the quantity and species of fish consumed and the waters from which the fish were caught. Multivariate statistical methods were able to resolve gender and dietary differences in PCB homologue and PCB congener patterns. RESULTS: Females had higher proportions of lower chlorinated homologues, including a consistently higher proportion of pentaCB 118. The relative presence of the very labile and volatile PCB 18, above 1% of the total PCB in females from the minimal fish consumption and "other" groups, suggests possible exposure to PCBs in the atmosphere. The dietary group consuming predatory fishes from Lakes Michigan and Superior had the highest serum concentrations of total PCB (mean of 3.1 ng/ml) and the most distinct congener profile. The two dietary groups least dependent on fishing or fishing mostly from inland lakes (non-Great Lakes) had the lowest total PCB concentrations, both with means of 1.4 ng/ml. CONCLUSIONS: These serum PCB concentrations were less than those found in earlier studies of fish consumers in the Great Lakes region and may reflect the decrease in PCBs in these lakes.

Exposure assessment and initial intervention regarding fish consumption of tribal members of the Upper Great Lakes Region in the United States.

The Ojibwe Health Study (OHS) has concluded 10 years of data collection and exposure assessment. Eight hundred and twenty-two participants from tribes in the states of Wisconsin, Michigan, and Minnesota (USA) completed fish consumption and environmental risk perception questionnaires. Many participants provided hair and blood samples for mercury and polychlorinated biphenyl (PCB) residue analyses as body burden indicators of these persistent environmental pollutants. Fish were collected by the tribal organizations and contaminants were analyzed for numerous tribal reports and professional environmental journal articles, these data were used by the Great Lakes Indian Fish and Wildlife Commission to produce tribal-specific geographic information systems maps as part of a public health intervention strategy. These maps are currently available at for six Wisconsin tribes that regularly harvest walleye. To determine the health impacts (if any) of pollutants on cancer, diabetes, and reproduction, it was necessary to know the recent trends in key indicators such as cancer mortality ratios and birth gender ratios. The Great Lakes Inter-Tribal Council provided the OHS and each participating tribe in Wisconsin and Michigan with a health profile. Total fish consumption (estimated by recall) for 720 tribal participants was self-reported as 60 g/day, but the highest actual consumption was measured as 11.2 g/day in one of the tribal groups. The highest blood concentrations in tribal participants were 18.6 ppb total serum PCBs and 11.8 ppb total blood mercury. Ninety percent of the participants had less than 3.8 ppb total serum PCBs and 2.6 ppb total blood mercury. Compared to other studies of subsistence fishing populations, these exposures were only moderately elevated and not high enough to warrant widespread restrictions on diets. Furthermore, the benefits of eating a fish diet must be continually emphasized. However, sport fishermen and their families who consume larger and more contaminated fish should abide by their state fish consumption advisories to minimize their health risks.

PCBs, mercury, and organochlorine concentrations in lake trout, walleye, and whitefish from selected tribal fisheries in the Upper Great Lakes region.

The purpose of this study was to determine the concentrations of environmental contaminants in the edible portion of fish tissue consumed by Ojibwa residing in the Upper Great Lakes region. Lake trout, whitefish, and walleye were collected from Lake Superior, Lake Huron, Lake Michigan, and selected inland lakes. These fish were harvested by either commercial fishing or spearfishing techniques and analyzed for environmental contaminants. Samples were pooled by species and location of collection and were analyzed as composites. The concentrations of congener-specific polychlorinated biphenyl (PCB), total mercury, and 17 other organochlorine compounds of the pooled samples were determined using gas chromatographic and atomic absorption techniques. Differences were noted in both the concentration and composition of contaminants depending on the geographic location of collection and the species examined. Lake trout and whitefish contained higher concentrations of organochlorine compounds than did walleye; and samples from Lakes Michigan and Huron had much higher concentrations than did Lake Superior fish. Conversely, mercury was much higher in walleye (580 ppb) when compared with lake trout (117 ppb) and whitefish (10 ppb). Several PCB congeners were commonly found in all fish samples; these included PCBs 138 + 163, 153, 66 + 95, 118, 77 + 110, 180, and 101. Lake trout accumulated the highly chlorinated PCB congeners, whereas walleye and whitefish accumulated certain lower tri- and tetrachlorobiphenyl congeners. In conclusion, the fish harvested and consumed by Ojibwa tribal members contained both mercury and organochlorine compounds. The concentrations of contaminants found in fish tissue differed among species and sampling sites. Consequently, it is imperative to sample fish that best represent those being consumed by tribal members and to continue long-term monitoring of fish from ceded waters. Therefore, risk assessment and risk management strategies need to take into account geographic location of the fish and unique preparation methods and to be directed at the contaminant(s) of concern for given locations.

Multi-center retrospective evaluation of carbonyl iron ingestions.

There is limited published data concerning carbonyl iron ingestion and no data on overdose. A retrospective chart review of all patients with carbonyl iron ingestion reported to 5 regional poison information centers from January 1998 to April 2000 was done. Thirty-three patients with carbonyl iron ingestion were reported. Twenty-seven patients (82%) were managed without referral to a health care facility. The mean and median age of these patients was 3years and 20 months, respectively. The mean dose ingested was 11.2 mg/kg (range of 2.2 to 34.5 mg/kg) with no effects noted. Six patients evaluated in the emergency ingested a mean of 34 mg/kg (range of 12 to 72 mg/kg). The mean peak serum iron concentrations in 4/6 were 82 microg/dL (range of 36 to 177 microg/dL). One child with a history of flu-like symptoms reported diarrhea, fever and lethargy and had a serum iron concentration of 36 microg/dL; symptoms were believed unrelated to the exposure. In this limited first case series of iron carbonyl ingestion, serious toxicity did not occur.