Despite evidence that exposure levels to mercury can produce neurological damage to the coastal communities of the Tapajos River basin, only a few clinical studies have assessed changes of neurological functions, especially somatosensory disturbance, considered as the initial manifestations of methylmercury poisoning. In this study we evaluated the current levels of exposure to mercury and sensory symptoms in adults from Riverside communities located in different river basins. Two in the Tapajós River basin and one in Tocantins basin. Participating in this study were 78 residents in Barreiras, 30 in São Luís do Tapajós (Tapajós River basin) and 49 in Furo do Maracujá (Tocantins basin), aged between 13 and 53 years, of both sexes. Total hair mercury concentrations were quantified by atomic absorption spectrophotometry and the neurological evaluation was carried out by conventional examination and by quantitative measures for tactile sensation by Semmes-Weinstein monofilaments, vibration sensation and two points discrimination. Concentrations of mercury in the Tapajós River basin communities were higher than that of Tocantins (p<0.0001). The evaluation of neurological changes showed no significant difference between the communities of exposed areas and control for the changes observed by conventional neurological examination, except for gait deviation (p<0.05). Thresholds for tactile sensation by Semmes-Weinstein monofilaments (except for the left chest), vibration sensation (except for the upper sternum) and discrimination of two points were higher in the subjects in the area of exposure when compared with those of the control area (p<0.05). On the correlation of the thresholds with current concentrations of Hgtotal in hair, directly proportional correlation was only observed for the thresholds of tactile sensation by Semmes-Weinstein monofilaments of lower lip (p-value<0.0001). It is concluded that mild changes in the sensitivity thresholds were predominant in the areas of exposure to methylmercury. Maintenance of exposure monitoring, guidance on public health measures and new clinical studies using somatosensory quantitative measures are required for clarification of the occurrence of clinical cases of poisoning in riparian areas contaminated by mercury.
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