Heavy metals in tropical small catchments in the state of São Paulo, Brazil: A first step towards the establishment of regional "background" levels

Abstract
Concentration of metal (Al, Fe, Mn, Ci, Cd, Pb, Ni, Cu, V, and Hg) were evaluated in six rivers located in pristine small catchments in the State of São Paulo (Southeast, Brazil). This is a first step in order to determine regional "background" levels of heavy metals in the area. Intervales and Morro do Diabo reserves are characterized by the presence of tropical forest (Mata Atlântica), and Vassununga reserve, is a region of Brazilian Savanna (Cerrado). The rivers that have similar vegetation and soils showed a relative homogeneity in the metal concentrations. Although all these rivers drain undisturbed areas, we found a great variation in metal concentrations among these areas (18-65% ). This variability probably reflex differences in geology, vegetation, precipitation, and altilude that occur in these watersheds. We conclude that to assess heavy metal contamination the use of regional background values is necessary. Otherwise two land of error could happen: first, a rise in metal levels could not be notice (because the use of inappropriate high average values that do not reflect the local characteristics) or a natural variation could be interpreted as a contamination.