HUMAN EXPOSURE TO MERCURY - A CRITICAL-ASSESSMENT OF THE EVIDENCE OF ADVERSE HEALTH-EFFECTS

The ubiquitous nature of mercury in the environment, its global atmosp heric cycling, and its toxicity to humans at levels that are uncomfort ably close to exposures experienced by a proportion of the population are some of the current concerns associated with this pollutant. The p urpose of this review is to critically evaluate the scientific quality of published reports involving human exposures to mercury and associa ted health outcomes as an aid in the risk evaluation of this chemical. A comprehensive review of the scientific literature involving human e xposures to mercury was performed and each publication evaluated using a defined set of criteria that are considered standards in epidemiolo gic and toxicologic research. Severe, sometimes fatal, effects of merc ury exposure at high levels were primarily reported as case studies. T he disasters in Minamata, japan, in the 1950s and in Iraq in 1971-1972 clearly demonstrated neurologic effects associated with ingestion of methylmercury both in adults and in infants exposed in utero. The effe cts were convincingly associated with methylmercury ingestion, despite limitations of the study design. Several well-conducted studies have investigated the effects of methylmercury at levels below those in the Iraq incident but have not provided clear evidence of an effect. The lower end of the dose-response curve constructed from the iraq data th erefore still needs to be confirmed. The studies of mercury exposure i n the workplace were mainly of elemental or inorganic mercury, and eff ects that were observed at relatively low exposure levels were primari ly neurologic and renal. Several studies have investigated effects ass ociated with dental amalgam but have been rated as inconclusive becaus e of methodologic deficiencies. In our overall evaluation, 29 of 110 o ccupational studies and 20 of 54 studies where exposure occurred in th e natural environment provided at least suggestive evidence of an expo sure-related effect.