Geochemical mapping of potentially hazardous elements in surface waters and stream sediments of the Quadrilátero Ferrífero, Brazil.

Abstract

Geochemical mapping and the determination of baseline concentrations of potentially hazardous elements in the environment receive increasing attention. The need to know regional geochemical background data as well as the spatial allocation of areas with anomalous element concentrations and chances to identify their major sources motivate the interest. Here, results from a geochemical mapping exercise and derived related baseline values are presented. 541 stream sediment and surface waters samples have been collected across the Iron Quadrangle (IQ), Brazil, with a density of 1 sample per 13 km2. Geochemical maps were compiled using the inverse distance weighted (lDW) interpolation method. “Normal” background concentrations were distinguished from anomalies with the separation-by-concentrationrange technique, where positive anomalies were defined by the “boxplot” Upper Inner Fence (UIF) rule. The results demonstrate that more than 70% of the IQ area shows geogenic background concentration ranges for the elements studied. About 20% of the area represent positive anomalies, likely related to both near surface rock types and to human interference. Distinct anthropogenic anomalies, notably from mining activities are identified in 5– 10% of all samples. This first sampling in the IQ allows delineation of the role of lithology on the elemental composition of stream sediments, and to establish baseline values for the main river basins – thus pinpointing localities, cities and fluvial basins that are exposed to environmental risks and need to be protected.