Evaluation of metal contamination in mangrove ecosystems near oil refining areas using chemometric tools and geochemical indexes

The northern and northeastern portion of the Todos os Santos Bay (TSB) is known for the presence of an oil refinery in addition to the development of other activities with significant potential for impact on the environment. 30 samples of superficial mangrove sediment were collected in two different locations: on the banks of the São Paulo River near the Landulpho Alves Mataripe Refinery (RLAM) and at Caboto Beach, a place that was once a control point in studies of metal pollution. After the determination of potentially toxic elements (Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Ti, V, Zn), the quality of the sediment was evaluated using the concentrations of these elements associated with geochemical parameters (TOC, P, S, and granulometry). In this way, the pollution indexes (EF, Igeo, PN) were calculated in addition to the comparison with the guide values for the sediment quality (TEL, PEL, ERL, ERM). Among the elements analyzed, Cu also showed levels (92.71–97.54 mg kg−1) very close to PEL (108 mg kg−1). At 13 sampling points, Cr concentrations were higher (56.16–66.01 mg kg−1) than TEL (52.3 mg kg−1). Ba showed significant concentrations in 6 samples collected on the São Paulo River, a region close to the oil refining area. The enrichment factor (EF) showed that most elements did not show enrichment, except for Zn. Through Igeo there was a tendency towards serious pollution of Ba, Cu, and Zn; moderately polluted by Cr. Principal component analysis (PCA) and Spearman's classification showed a correlation greater than 70% between the variables. According to Nemerow Synthetic Pollution (PN), both areas are polluted by Al, Ba, Cr, Cu, Fe, Mn, Ni, Ti, V, and Zn.