EVIDENCE OF EARLY NERVOUS-SYSTEM DYSFUNCTION IN AMAZONIAN POPULATIONSEXPOSED TO LOW-LEVELS OF METHYLMERCURY

There is increasing concern about the potential neurotoxic effects of exposure to methylmercury in Amazonian populations due to mercury (Hg) release from gold-mining activities. A preliminary study was undertak en in two villages on the Tapajos River, an effluent of the Amazon, si tuated over 200 km downstream from the extraction areas. The study pop ulation included 29 young adults (less than or equal to 35 years), 14 women and 15 men, randomly chosen from a previous survey. Hair analyse s were conducted with cold vapor atomic fluorescence spectrophotometry . Total hair Hg (THg) varied between 5.6 mu g and 38.4 mu g/gl, with M eHg levels from 72.2% to 93.3% of the THg. A quantitative behavioural neurophysiological test battery, designed for use under standard condi tions, in an area without electricity and for persons with minimal edu cation was administered to all participants. The results of visual tes ting showed that although all participants had good near and far visua l acuity, color discrimination capacity (Lanthony D-15 desaturated pan el) decreased with increasing THg (F = 4.1; p = 0.05); near visual con trast sensitivity profiles (Vistech 6000) and peripheral visual field profiles (Goldman Perimetry with Targets I and V) were reduced for tho se with the highest levels of THg. For the women, manual dexterity (Sa nta Ana, Helsinki version) decreased with increasing THg (F = 16.7; p < 0.01); this was not the case for the men. Although the women showed a tendency towards reduced grip strength, muscular fatigue did not var y with THg for either sex. The findings of this study demonstrate that it is possible, using a sensitive test battery, to detect alterations in nervous system functions, consistent with knowledge on Hg toxicity , at levels below the currently recognized threshold of 50 mu g/g THg. (C) 1996 Inter Press, Inc.