BEHAVIORAL-EFFECTS OF LOW-LEVEL EXPOSURE TO HG-O AMONG DENTISTS

Exposure thresholds for health effects associated with elemental mercu ry (Hg degrees) exposure were examined by comparing behavioral test sc ores of 19 exposed (mean urinary Hg = 36 mu g/l) with those of 20 unex posed dentists. Thirty-six mu g Hg/l is 7 times greater than the 5 mu g Hg/l mean level measured in a national sample of dentists. To improv e the distinction between recent and cumulative effects, the study als o evaluated porphyrin concentrations in urine, which are correlated wi th renal Hg content (a measure of cumulative body burden). Subjects pr ovided an on-site spot urine sample, were administered a l-h assessmen t consisting of a consent form, the Profile of Mood Scales, a symptom and medical questionnaire, and 6 behavioral tests: digit-span, symbol- digit substitution, simple reaction time, the ability to switch betwee n tasks, vocabulary, and the One Hole Test. Multivariate regression te chniques were used to evaluate dose-effects controlling for the effect s of age, race, gender and alcohol consumption. A dose-effect was cons idered statistically significant below a p value of 0.05. Significant urinary Hg dose-effects were found for poor mental concentration, emot ional lability, somatosensory irritation, and mood scores. Individual tests evaluating cognitive and motor function changed in the expected directions but were not significantly associated with urinary Hg. Howe ver, the pooled sum of rank scores for combinations of tests within do mains were significantly associated with urinary Hg, providing evidenc e of subtle preclinical changes in behavior associated with Hg exposur e. Coproporphyrin, one of three urinary porphyrins altered by mercury exposure, was significantly associated with deficits in digit span and simple reaction time. The prophyrin pooled sums of rank scores were a s sensitive as the urinary Hg analyses within the cognitive and motor domains but were less sensitive for the: overall battery of tests. The reported effects were detected among dentists with a mean urinary Hg level of 36 mu g/l, which lies between the proposed biologic threshold s of 25 and 50 mu g Hg/creatinine, suggesting the need for a more comp rehensive study to determine the threshold of adverse biologic effects .