RESUMO
The geochemical processes involved in the Amazon soils formation are not totally understood because its geological and pedological features were formed during different geological events and different times. The Southwestern region of Amazonas State is an example of a region where the soils were developed from rocks formed by sedimentary processes and, nowadays, the soils continue receiving seasonal inputs from the Andes sediments. Data on geochemical patterns of this region are scarce, and there is no information about the possible effects of the natural or unnatural enrichment of potentially toxic elements (PTEs). Thus, this study represents the first research into the geochemical patterns of PTEs in soils of Southwestern Amazonas State. Further, we carried out a human health risk assessment and a proposal for Quality Reference Values (QRV) for thirteen PTEs (As, Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, Ti, V, Zn and Zr). Our findings showed that the PTEs contents in soil samples collected in the lowland areas are strongly influenced by sediments inputs, while samples localized in the highland areas are weakly influenced by sediments inputs and present depletion of PTEs. Barium, Cr, Cu, Ni and Pb were the PTEs most influenced by sediment's deposition. The soil contamination assessment showed the existence of enrichment of the potentially toxic elements in soil samples, which may be a consequence of the natural inputs of the Andean sediments. Furthermore, Co and Cr exceed the safety zone for carcinogenic risk assessment, which indicates the need to monitor these elements and their possible effects on the health of the population in this region.
