This study used chemometric tools and a Geographic Information System (GIS) to determine the influence of organic matter and anthropogenic activity on the distribution of metal species between two major communities of the Middle Negro River Basin-AM. Higher concentrations of metal species were determined in flooded regions. The chemometric analysis showed the affinity of organic matter for potentially toxic metals, indicating its selectivity. GIS spatial analysis has shown that proximity to urban areas is a variable that is likely to influence the pattern of concentration of organic matter, and consequently the distribution of metal species between flooded and non-flooded areas.

The region of Aracá River (Middle and Upper Rio Negro-AM) has peculiar characteristics, having soils with atypical profile and high organic matter contents in great deep. The levels of aluminum and iron in the soil samples increased as a function of depth and concentrations of mercury ranged from 0.097 to 0.964 µg g-1. Statistical analysis showed the degree of similarity between soil samples collected. The highest concentrations of mercury in soil samples are directly related to soil higher content of organic matter, directly influencing the fate and bioavailability of mercury species to the environment.