Banca de DEFESA: LUCAS CINTRA ALMEIDA

Sediment; Toxic chemical elements; Geochemical indices; Ecological indices; Principal component analysis.

In this work, samples of surface sediments were collected in the Joanes River, Bahia, Brazil, during the rainy and dry periods. Initially, the dry sediment was subjected to granulometric analysis to determine the concentration of organic matter. Subsequently, the samples were digested using nitric acid in a microwave oven, and the metals cadmium, copper, chromium, nickel, lead, and zinc were determined using inductively coupled plasma optical emission spectrometry (ICP OES). The levels found ranged from 0.30 to 0.90 µg g-1 for cadmium, from 6.0 to 105.0 µg g-1 for copper, from 8.0 to 64.4 µg g-1 for chromium, 1 .3 to 21.2 µg g-1 for nickel, 3.5 to 44.1 µg g-1 for lead and 21.5 to 1415.9 µg g-1. The geochemical and toxicological assessment was carried out using the enrichment factor (FE), potential ecological risk index (IR), potential contamination index (PCI), pollutant load index (PLI), and geoaccumulation index (Igeo). In the assessment of ecological risks, all sediment samples were below the limit established by the risk index (RI). Zinc showed moderately severe enrichment (6.78–11.83) in all collection stations in the dry and rainy periods, followed by cadmium, which showed moderate enrichment (2.23–4.17), whose values exceeded almost 1000 times the background value in a location. The principal component analysis correlated the contents of metals, organic matter, and silt and clay fractions. The environmental risk assessment revealed a significant increase in the risk associated with metals during the rainy season, probably due to the greater supply of organic matter leaching from the river banks.