Methylmercury exposure affects motor performance of a riverine population of the Tapajos river, Brazilian Amazon

Gold mining and deforestation in the Brazilian Amazon are increasing mercur y pollution of the extensive water system, exposing riverine populations to organic mercury through fish-eating. The aim of the present study was to e valuate the effect of such exposure on motor performance. This cross-sectio nal study was carried out in May 1996, in a village located on the banks of the Tapajos river in the Amazonian Basin, Brazil. Information concerning s ociodemographics, health, smoking habits, alcohol drinking, dietary habits and work history were collected using an interview-administered questionnai re. Mercury concentrations were measured by cold vapor atomic absorption in blood and hair of each participant, of whom those aged between 15 and 79 y ears were assessed for motor performance (n = 84). Psychomotor performance was evaluated using the Santa Ana manual dexterity test, the Grooved Pegboa rd Fine motor test and the fingertapping motor speed test. Motor strength w as measured by dynamometry for grip and pinch strength. Following the exclu sion of 16 persons for previous head injury, working with mercury in the go ld-mining sites, or for diabetes, the relationship between performance and bioindicators of mercury was examined using multivariate statistical analys es, taking into account covariables. All participants in the study reported eating fish, which comprised 61.8% of the total meals eaten during the pre ceding week. The median hair total mercury concentration was 9 mu g/g. Orga nic mercury accounted for 94.4 +/- 1.9% of the total mercury levels. Multiv ariate analysis of variance indicated that hair mercury was inversely assoc iated with overall performance on the psychomotor tests, while a tendency w as observed with blood mercury. Semipartial regression analyses showed that hair total mercury accounted for 8% to 16% of the variance of psychomotor performance. Neither hair nor blood total mercury was associated with the r esults of the strength tests in women and men. Although dose-effect relatio nships were observed in this cross-sectional study, they may reflect higher exposure levels in the past. The findings of this study demonstrated neuro behavioral manifestations of subtle neurotoxic effects on motor functions, associated with low-level methylmercury exposure.