Our findings do not support an association between total mercury exposure and the risk of coronary heart disease, but a weak relation cannot be ruled out.
A study was conducted to evaluate toenail arsenic concentrations as a biologic marker of drinking water arsenic exposure. Study subjects were controls in a US population-based case-control study of nonmelanoma skin cancer, randomly selected from drivers' license records (those < 65 years of age) and Medicare enrollment files (those > or = 65 years of age). Between 1994 and 1997, a total of 540 controls were interviewed and toenail samples of sufficient weight were collected from 506 (93.7%) of these. Beginning in 1995, a sample of tap water was taken from the participants' homes; a total of 217 (98.6%) water samples were obtained from the 220 subjects interviewed. Arsenic determinations were made from toenail samples using neutron activation analysis. Water samples were analyzed using hydride-generation magnet sector inductively coupled mass spectrometry. Among 208 subjects with both toenail and water measurements, the correlation (r) between water and nail arsenic was 0.65 (p < 0.001) among those with water arsenic concentrations of 1 microg/liter or higher and 0.08 (p = 0.31) among those with concentrations below 1 microg/liter (overall r = 0.46, p < 0.001). Our data suggest that toenail samples provide a useful biologic marker for quantifying low-level arsenic exposure.
The ability of selenium (Se) to moderate mercury (Hg) toxicity is well established in the literature. Mercury exposures that might otherwise produce toxic effects are counteracted by Se, particularly when Se:Hg molar ratios approach or exceed 1. We analyzed whole body Se and Hg concentrations in 468 fish representing 40 species from 137 sites across 12 western U.S. states. The fish samples were evaluated relative to a published wildlife protective Hg threshold (0.1 sg Hg x g(-1) wet wt.), the currenttissue based methylmercury (MeHg) water quality criterion (WQC) for the protection of humans (0.3 microg Hg x g(-1) wet wt) and to presumed protections against Hg toxicity when Se:Hg molar ratios are >1. A large proportion (56%) of our total fish sample exceeded the wildlife Hg threshold, whereas a smaller, but significant proportion (12%), exceeded the MeHg WQC. However, 97.5% of the total fish sample contained more Se than Hg (molar ratio >1) leaving only 2.5% with Se: Hg ratios <1. All but one of the fish with Se:Hg <1, were of the genus Ptychochelius (pikeminnow). Scientific literature on Se counteracting Hg toxicity and our finding that 97.5% of the freshwater fish in our survey have sufficient Se to potentially protect them and their consumers against Hg toxicity suggests that Se in fish tissue (Se:Hg molar ratio) must be considered when assessing the potential toxic effects of Hg.
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