The Toxicology of Mercury and Its Chemical Compounds

Abstract

This review covers the toxicology of mercury and its compounds. Special attention is paid to those forms of mercury of current public health concern. Human exposure to the vapor of metallic mercury dates back to antiquity but continues today in occupational settings and from dental amalgam. Health risks from methylmercury in edible tissues of fish have been the subject of several large epidemiological investigations and continue to be the subject of intense debate. Ethylmercury in the form of a preservative, thimerosal, added to certain vaccines, is the most recent form of mercury that has become a public health concern. The review leads to general discussion of evolutionary aspects of mercury, protective and toxic mechanisms, and ends on a note that mercury is still an "element of mystery."

Daily mercury intake in fish-eating populations in the Brazilian Amazon

“…Based primarily on the results of large longitudinal neurodevelopmental toxicity studies conducted in New Zealand, the Seychelles and the Faroe Islands, and using varying interpretations of the epidemiological evidence, recommended intake without appreciable risks currently range from 0.1 to 0.3 mg/kg/day (Clarkson and Magos, 2006;Innis et al, 2006;Wijngaarden et al, 2006). In comparison, daily mercury intake of the Amazonian population in the present study averaged 0.92 mg/kg/day, ranging from 0 to 4.3 mg/kg/ day, with an outlier whose intake was 11.8 mg/kg/day.…”

“…The RfD is ''an estimate of a daily oral exposure to the human population (including sensitive subgroups) that is likely to be without appreciable risk of deleterious effects during a lifetime'' (US EPA, 1998). Even if for some authors, exceeding these guidelines by a small margin is meaningless in terms of actual risk because of so many uncertainties (Clarkson and Magos, 2006), given the wide range of variation of the daily intake in this Amazonian cohort, there is reason for concern about the potential for deleterious health effects that could be caused by high mercury intake. Indeed, almost 50% of the population surpassed the Benchmark dose (BMD) for blood-mercury (58 mg/l) that was used to calculate the US NAS/NRC reference dose (NRC, 2000), and over 50% surpassed the BMD for hairmercury (14 mg/g) used to determine the World Health Organization reference dose (WHO, 2003).…”

“…There has been much debate about how to address the risks of mercury exposure and the benefits of fish consumption with questions raised about the suitability of regulating human risk based either on controlling average daily intake, as recommended by the EPA, or excluding fish with high mercury levels from the diet as put forward by FDA (Stern et al, 2004;Clarkson and Magos, 2006). In the Amazon, because fish is a dietary mainstay and there is high mercury intake, there is a need for a suitable strategy that would reduce mercury exposure while maintaining fish consumption.…”

“…However, little attention has been given to the importance of mercury intake in these populations, although a limited number of studies have tried to estimate the rates of mercury intake Henshel, 1996, 2000;Bidone et al, 1997;Hacon et al, 1997;Kehrig et al, 1998;Fre´ry et al, 2001). Daily oral exposures are used in many countries as the basis for risk assessment (Clarkson and Magos, 2006). In the Amazon, mercury daily dose is particularly difficult to estimate due to the diversity of fish and ecosystems, as well as seasonal changes in fish availability.…”

Mercury in alpine fish from four rivers in the Tibetan Plateau

“…As one of the organic mercurial species, MeHg is the most toxic. Due to its lipophilicity, MeHg can penetrate the blood-brain barrier and finally harm central nervous system (Cheng et al, 2005Clarkson and Magos, 2006;Winship, 1986). MeHg constitutes more than 80% of THg in fish muscle (Akagi et al, 1995;Bloom, 1992;Campbell et al, 2005;Guentzel et al, 2007;Mohan et al, 2012).…”