Hidrocarbonetos policíclicos aromáticos, metais e foraminíferos em um estuário tropical: o caso do rio Serinhaém após um derrame de petróleo.

Abstract

Monitoring of areas impacted by various activities can be carried out through the analysis of chemical elements and hydrocarbons in sediments, given the capacity of this matrix to preserve continuous records of environmental changes. In addition, biomonitors are used to assess the environment. In 2019, the Brazilian coast was hit by an oil spill that resulted in significant environmental and socioeconomic impacts. The oil reached the estuary of the Serinhaém River, located in the Baixo Sul region of the State of Bahia. This tropical environment is part of the Pratigi Environmental Protection Area (APA) and is an area that is a little influenced by anthropogenic activities. The present research aimed to investigate the environmental condition of the Serinhaém River estuary after the oil spill that hit the Brazilian coast in 2019. Sediments were collected at 14 sampling points, of which five were sediment cores, and nine were surface sediments. Polycyclic aromatic hydrocarbons (PAHs) and metals (Al, Ba, Co, Cr, Cu, Fe, Mn, Ni, Pb, V, and Zn; semi-metallic As) were determined in the sediments. Granulometry, pH, total organic carbon (TOC), and total nitrogen (TN) analyses were also performed. Foraminifera were used as biomonitors because changes in the shells record environmental changes. For the 16 PAHs considered priority control pollutants, the maximum values in the surface sediments of ΣBHPAs (low molecular weight PAHs), ΣAHPAs (high molecular weight PAHs), and Σ16HPAs (sum of the 16 PAHs) were, respectively, 120.92, 152.56 and 273.48 ng g-1. Diagnostic ratios indicated the petrogenic origin of PAHs at points in the downstream part of the estuary. When comparing the PAH values, only the phenanthrene concentration (89.47 ng g-1) is above the TEL (Threshold Effect Level) at a point located in the middle estuary. Regarding the sedimentary cores, T3 (middle estuary) was the one that presented the highest Ω16PAHs (1508 ng g-1). A more significant presence of high molecular mass PAHs was observed, which was associated with a pyrogenic origin. The analyses of the diagnostic ratios showed that in T1, located near the city of Ituberá, no source of petrogenic origin was found. In T5, located downstream of the estuary, the BMM/AMM ratio indicates a petrogenic origin. For foraminifera, data from samples from 2022 were compared with samples collected in 2013, and an association was found between diversity and distribution along the estuary with physicochemical variables. In 2013 and 2022, the distribution of foraminifera was unrelated to the presence of chemical elements in the estuary. The concentrations of chemical elements did not differ between 2013 and 2022. Therefore, the area of the Serinhaém River estuary in the Pratigi APA, even after the 2019 oil spill, is preserved in terms of the concentrations of the analyzed chemical elements. As for the PAHs, there is an indication of petrogenic origin both in the core further downstream of the estuary and in the surface sediments of the downstream and middle estuary, indicating oil contamination from the downstream part of the estuary, which may be related to the 2019 spill.