Sequential analysis of hair mercury levels in relation to fish diet of an Amazonian population, Brazil

Several studies in the Amazonian Basin have shown that riverine populations are exposed to methylmercury through fish consumption. It has been suggest ed that seasonal variations in hair mercury observed through sequential ana lyses may be related to the changes in fish species ingested by the local c ommunities. The aim of the present study was to investigate the relationshi p between fish-eating practices and seasonal variation in mercury exposure. A group of 36 women from a village located on the banks of the Tapajos Riv er, a major tributary of the Amazon, comprised the present study population . An interview-administered questionnaire was used to gather information on socio-demographic characteristics, fish-eating practices and other relevan t information. The women also provided hair samples of at least 24 cm in le ngth for mercury analysis. Hair total and inorganic mercury concentration w as measured using a cold vapor atomic absorption analytical method. Trigono metric regression analysis was done to assess the seasonal variation of tot al mercury levels. Variations in inorganic mercury were examined by repeate d measures analysis of variance, and analysis of contrast variable with a p olynomial transformation. The results showed that hair mercury levels varie d with the season. Higher levels were observed in months corresponding to t he dry season, with lower levels in the rainy season. Herbivorous fish pred ominated the diet for 47.2% of the women during the dry season, but this ro se to 72.2% during the rainy season. Those who reported eating fish daily h ad higher mercury levels in hair compared to those who only ate fish a few times per week. Retrospective mercury analyses, evaluated by the quantity o f mercury present in each centimeter of hair, indicate that mean mercury le vel of the population decreased over the 2 years prior to the study. The pe rcentage of inorganic mercury over the total mercuryin hair increased towar ds the extremities of the hair strand. Higher percentages of inorganic merc ury were found for the group who ate more fish (on a daily consumption basi s). These results support the assumption that there are seasonal variations in methylmercury exposure and also a relationship between type of fish spe cies consumed and the resulting hair mercury levels. (C) 2001 Elsevier Scie nce B.V. All rights reserved.