Assessment of mercury levels in soils, waters, bottom sediments and fishes of acre state in Brazilian Amazon

Mercury in the aquatic biota and geologic materials in areas without anthropogenic sources has been stimulating the discussion about the possibility of natural Hg occurrence in the Amazon region. In this study the dispersion of Hg in different geologic materials as well as its relationship with high Hg levels, detected in some species of carnivorous fish consumed in the Rio Branco city, is evaluated. Bottom and suspended sediments, river water and fishes were sampled in the Acre and Purus Rivers and in some of their tributaries. Total mercury as well as physical and chemical characterization of the waters were done. Hg on top soil and upper horizons samples were also determined to evaluate the potential Hg accumulation in these materials. In addition, the dominant minerals were determined by X-ray Diffraction analysis. Furthermore, ten samples of fossilized material were analyzed. The Hg analysis were carried out by CVAAS. The Hg mean levels in the bottom and suspensed sediments were 0.042 and 0.060 mug g(-1), respectively. In the river water samples, the Hg levels were below the detection limit. The Hg mean values in the different soil samples were as follow: soil samples (0.077 mu g(-1)), lower (50-60 cm depth) horizons samples (0.117 mu g(-1)), ferruginous nodules within the clayey matrix (0.190 mu g(-1)) and fossilized material (0.379 mu g(-1)). In the fishes the Hg levels are high with mean of the 1.287 mu g(-1) in the carnivorous species. These levels indicate a possible bioaccumulation of Hg mostly in the carnivorous fishes. Although low concentrations of Hg were found in the river waters, it is assumed here that the bioavailable Hg can be originally large from the ferruginous nodules and fossilized materials.