ABSTRACT
Methylmercury is one of the most toxic forms of mercury to humans.17’36 Its use as a fungicide and indiscriminate disposal as a byproduct of chemical manufacture has been responsible for human mortality and morbidity of near epidemic proportions in Japan,75’129 Iraq, Pakistan, Guatemala, Ghana, and the former Soviet Union, and isolated incidents have been reported elsewhere.3’36’45 Environmental application and overt dumping appear to have subsided and, currently, biotic and abiotic methylation of inorganic mercury to methylmercury in aquatic sediments appears to be the major source of environmental contamination by methylmercury.18’46’75’82’129’133
Methylmercury is readily bioaccumulated and biomagnified in food chains/webs.71’133 It is accumulated by aquatic species from the water and their diet.61’106 130 Biomagnification in food chains/webs can result in high-dose exposure to top predators as exemplified by the Minamata (Japan) disaster.75’129 Indeed, substantial concentrations of methylmercury are still found in freshwater and marine fishes and, via consumption, may adversely affect humans, especially the fetus and young child.107’133 However, as stated by Kevorkian et al.:56 “[Although] knowledge of mercury levels in fishes is doubtlessly important as a potential source of humans ills ... it is analysis of human tissues which will determine with finality whether environmental mercury pollution is of sufficient magnitude to pose a real human threat, all other biological hosts not withstanding.” In addition, knowledge of regional trends in the mercury concentration of human tissues is the ultimate sentinel of localized environmental
contamination of potential human consequence. Unfortunately, information on the mercury content of human tissues is limited.10’21’35’39’41’49,54’56’59’67’68’76’84’100’104’114’116’138
If the Kevorkian et al.56 statement is axiomatic, it would be useful to have sufficient data on human tissue mercury to establish a no-observed-effect level (as a function of chemical compound, if possible) for at least the irreplaceable organs most susceptible to irreversible damage. In addition, since knowledge of long-term, low-level exposure is limited and recent evidence on lead suggests deleterious effects of such exposure,50,57 alteration of human tissue mercury levels should be monitored as a function of time, especially in areas in which significant environmentally available mercury levels have been detected. Litde systematic information is available on long-term trends in human tissue mercury levels and, for the foreseeable future, it does not appear that there will be.
