Relationship of mercury bioaccumulation with seasonality and feeding habits of fish species caught upstream and downstream of the Curuá-Una hydroelectric dam in the Brazilian Amazon.

Hydroelectric plants impact the dynamics of mercury accumulation and transfer to aquatic ecosystems and organisms. This study aimed to determine total mercury (THg) concentration in filtered water, aquatic macrophytes, and fish and assess the influence of fluvial regime (low-water, rising-water, and high-water) and the feeding habits of fish species caught upstream and downstream of the Curuá-Una hydroelectric dam in the Brazilian Amazon. THg levels were determined by cold-vapor atomic fluorescence spectrometry. THg concentration in filtered water was higher (5.3-11.2 ng L^-1) during the low-water period. THg concentration in fish ranged from 0.075 to 1.160 µg g^-1 in specimens caught downstream and from 0.014 to 1.036 µg g^-1 in specimens caught upstream of the dam. The highest THg concentrations were detected in specimens of the piscivorous species Acestrorhynchus falcirostris (1.161 µg g^-1) caught at downstream sites. There were significant correlations of THg concentration with the trophic level (Analysis of Variance; p ≤ 0.001) of fish species and fluvial regime (Analysis of Variance; p ≤ 0.001). The macrophyte Utricularia foliosa contained the highest THg levels in leaf tissues in the low-water period (71.4 µg g^-1). It is concluded that THg concentration varies between fish trophic levels and fluvial regimes. Macrophytes contribute to enhancing mercury transfer and availability along the aquatic trophic chain.