Geochemical base for As, Co, Cu, Ni, P, Pb, S, V and Zn in road dust collected in areas of oil industry activity in the Metropolitan Region of Salvador, Bahia, Brazil

Abstract

Road dust collection was carried out in Salvador and some municipalities in the Metropolitan Region of Salvador (MRS), such as Simões Filho, Candeias, Madre de Deus and São Francisco do Conde, situated within an area of oil activity. In the chemical-physical characterisation of the road dust collected, the average fractions of coarse sand (17.44 %), medium (27.15 %), fine (32.63 %) and very fine (15.54 %) were found in the 17 samples collected. The samples underwent an acid extraction procedure in a closed digester block, with the mixture HCl + HNO3 + H2O2. The extract was analysed and concentrations of Al, As, Co, Cu, Fe, Ni, Pb, P, Sb, V and Zn were determined. Linear regression analysis was applied to the concentrations of As, Co, Cu, Ni, Pb, P, V and Zn, generating the equations of the straight lines, which served as a geochemical baseline for the region of road dust samples. For the enrichment factor (EF), most chemical elements showed values lower than < 1 at the collection points, except for Cu, Mn, and P (10 < EF < 25) and for Co, Cu, P and Ni (5 < EF < 10), in the regions of Candeias and Simões Filho. On the other hand, the geoaccumulation index (Igeo) of most points were evaluated as uncontaminated (class 0) and moderate or uncontaminated (class 1) for Igeo, except for P (class 4) and Mn (class 5). Principal component analysis (PCA) showed accumulated total variance corresponding to 76.45 %. For the hierarchical cluster analysis (HCA), the results agree with those found in the PCA. Points P3 (Candeias) and P16 (Simões Filho) were the points that showed less dissimilarity with the other points analysed, indicating possible enrichment of the chemical elements found at these points, confirmed by the EF values.