Acumulação de mercúrio em Tucunarés da Amazônia

In the water, the transformation to methylmercury takes place mostly due to the action of microorganisms. The formation of methylmercury increases the dispersion and bioavailability of the element in the aquatic environment. The methylmercury can be assimilated by plankton and enters the food chain. The concentration of the metal increases further up in the trophic levels of the chain and reaches the highest values in carnivorous fish, like tucunare. Thus, mercury emissions cause the contamination of natural resources and enhance the health risks of regular fish consumers. The aim of this work is to study the bioaccumulation of mercury in tucunare fish (Cichla sp.), top predator of the food chain, through mathematical model. Total mercury concentrations in tucunares collected in two representative regions of the Amazonian fluvial ecosystem in the state of Para, in the years 1992 and 2001 are compared. The model calculates concentrations in top predators of the food chain and can be used as a tool for the management of aquatic ecosystems potentially contaminated by mercury. This objective was accomplished through the combination of the Trudel mass balance and Wisconsin bioenergetics models, applied to tropical species of the Cichla (tucunare) genre of the Tapajos river basin. The Wisconsin bioenergetics model was utilized to determine the rates of food consumption from estimated fish growth data. The parameters used in the models were found in the literature. The ability of the models to predict mercury contents in tucunares was evaluated by comparison with field data, obtained in 1992 and 2001, in the Tapajos River and in Maica lakes. The best results were attained for specimens collected in 1992, which seems to be related to a better estimate of mercury concentration in the food in this year.