Neurobehavioural test results and exposure to inorganic mercury: in search of dose-response relations.

The aim of the analysis was, in general, to find a way to summarise results of studies in search of exposure-response relationships and, in particular, to ask whether an exposure-response relationship can be ascertained for neurobehavioural studies on occupational mercury exposure. Eighteen studies dealing with human mercury exposure and examining 1,106 exposed and 1,105 control subjects were included in the analysis. Effect sizes were calculated for each of the single neuropsychological test results on cognitive and motor performance and were considered in relation to mean current concentrations of exposure. The total of effect sizes demonstrated a correlation to exposure in the range of r=0.50. Additional analyses showed that the influence of mercury on psychological functions was different and that results on motor performance compared with memory and attention revealed the greatest impairment in mercury-exposed workers. Implications for the reversibility of impairments could be discussed because three of the studies examined subjects whose exposure had ceased. Besides the usefulness of the approach, it became obvious that the available 18 studies are a small sample, even when non-dimensional effect-sizes are used; hence, not all psychological domains covered by tests could be analysed.