Determination of geochemical background values on a tropical estuarine system in a densely urban area. Case study: Capibaribe estuary, Northeastern Brazil.

This study aims to infer the background values of several metals in the Capibaribe estuary and to identify the likely impact of anthropic activities during 200-years of sedimentation. Two cores were sampled, with subsamples at intervals of 2cm. Sedimentation rates and metal concentrations were analyzed. The Al-normalized method was used to infer the background values, and to identify anthropic influences, the enrichment factor, the contamination factor and the geoaccumulation index were employed. The background values showed concentrations for Mn of 292.2, for Co of 10.4, for Ni of 22.3, for Cu of 60.8, for Zn of 105.5, for As of 106.0, for Pb of 52.9 (all in mgkg) and for Fe of 2.7%, The higher values, mainly for As, Zn and Pb, are associated with the influence of the Barreiras Formation. The geogenic inputs are significantly greater than the anthropic activities, masking the contamination.