Neurobehavioural tests were performed by 98 dentists (mean age 32, range 24-49) exposed to elemental mercury vapour and 54 controls (mean age 34, range 23-50) with no history of occupational exposure to mercury. The dentists were exposed to an average personal air concentration time weighted average (TWA) of 0-014 (range 0-0007-0-042) mglm3 for a mean period of 5-5 (range 0 7-24) years and had a mean blood mercury concentration of 9-8 (range 0-6-57) pgIl. In neurobehavioural tests measuring motor speed (finger tapping), visual scanning (trail making), visuomotor coordination and concentration (digit symbol), verbal memory (digit span, logical memory delayed recall), visual memory (visual reproduction, immediate and delayed recall), and visuomotor coordination speed (bender-gestalt time), the performance of the dentists was significantly worse than that of the controls. The dentists scored 3-9 to 38-9% (mean 13-9%) worse in these tests. In trail making, digit span, logical memory delayed recall, visual reproduction delayed recall, and bender-gestalt time test scores were more than 10% poorer. In each of the tests in which significant differences were found and in the block design time, the performance decreased as the exposed dose (product of the TWA of air mercury concentrations and the years of exposure) increased. These results raise the question as to whether the current threshold limit value of 0 050 mg/m3 (TWA) The organs most frequently affected by metallic mercury in chronically exposed subjects are the nervous system, kidney, and mucosal surfaces of the mouth.'2 The central nervous system is probably the most sensitive organ."5 Many studies on the neurotoxic effects of mercury have been reported."3 The earlier ones were usually on subjects exposed to high concentrations (more than 0 05 mg/m3) of mercury.57 Some of the more recent studies generally lack adequate measurements on exposure to mercury.4 12Neurobehavioural performance tests are sensitive methods used to detect subclinical effects.9'0 The purpose of this study was to measure early changes in performance of motor speed, manual dexterity, visual scanning, and visual and verbal memory among dentists exposed to mercury vapour at concentrations of less than 0-05 mg/m' in their work environment. Materials and methods STUDY POPULATIONA cross sectional study of 98 dentists (representing 32% of active dentists in Singapore), 38 women and 60 men exposed to a time weighted average (TWA) concentration of air mercury vapour below 0-05 mg/ m3was undertaken. The dentists typically worked 10 hours a day for a six day work week in air conditioned rooms. A control group of 54 persons (27 women and 27 men) with no history of occupational exposure to mercury were selected from staff at the National University of Singapore. Questionnaires were used to select subjects (dentists and controls) that did not have a history of neuropathy from diabetes, renal diseases and excessive alcohol use, disease of the central or peripheral nervous system or psychiatric d...

Hair samples from three groups of occupationally exposed subjects were analyzed for their lead (Pb), manganese (Mn) and mercury (Hg) contents. For lead (number of subjects, n = 209), the hair Pb ranged from 0.93 to 3527 micrograms/g (geometric mean, GM = 641) and blood Pb from 33.3 to 774 micrograms/l (GM = 341); for manganese (n = 38), the hair Mn ranged from 0.20 to 52.97 micrograms/g (GM = 2.66) and urine Mn ranged from 1.70 to 17.9 micrograms/l (GM = 5.56); and for mercury (n = 85), the hair Hg from 1.79 to 12.8 micrograms/g (GM = 5.09) and the blood Hg from 0.63 to 57.3 micrograms/l (GM = 10.9). The hair Pb was significantly (P < 0.0001) correlated to blood Pb (r = 0.85); the hair Mn to urinary Mn (r = 0.45); and the hair Hg to blood Hg (r = 0.53). The average metal content at the distal end was not significantly (P > 0.05) different from that of proximal end. The GM levels for the distal end were 223 micrograms/g (95% CI 152-347) and 2.26 (95% CI 0.97-5.29); and those for the proximal end were 186 (95% CI 97-261) and 1.18 (95% CI 0.54-2.58) for Pb and Mn respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

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