Avaliação da contaminação de ostras por óleo diesel através de análises in situ e in vitro utilizando hidrocarbonetos policíclicos aromáticos e isótopos estáveis como marcadores

Abstract

Oil is a crucial energy source and serves as the foundation for the production of countless items utilized by human society. However, it poses a persistent environmental risk, inflicting harm on marine biological communities. As a toxic compound with unique physical and chemical properties, oil can induce both lethal and sublethal effects, as well as biochemical changes in marine organisms. Investigating these changes through bioindicators and biomarkers can yield valuable insights for assessing the consequences of oil introduction into the environment. Oysters are excellent bioindicators due to their filter-feeding behavior and sessile nature. The present study aims to employ techniques for quantifying polycyclic aromatic hydrocarbons (PAHs) and stable isotopes ( 13 C and 15 N) in oyster tissues to investigate the impacts of oil on these organisms. To achieve the established objectives, field sampling was conducted alongside laboratory bioassays. In the first stage (Chapter 1), oysters were collected from two locations in Arraial do Cabo, each exhibiting different levels of anthropogenic impact. The stable isotopes 13C and 15N in their tissues were analyzed. The isotopic signatures in the oyster tissues did not reveal significant differences between the sampling sites. Conversely, the seston displayed variations, indicating a greater terrigenous contribution at the Praia do Forno station, although the influence of petrogenic sources could not be identified. These findings underscored the necessity of conducting bioassays to evaluate the direct effects of oil on these bivalves. Aiming at developing these bioassays, Chapter 2 presents a comparative test between two oil-in-water dispersion techniques: “oil-in-water dispersion” (OWD) and “water accommodated fraction” (WAF). This test demonstrated that both techniques were effective in terms of oil dispersion, with the WAF technique achieving a higher concentration of PAHs, while the OWD method produced greater homogeneity among the replicates. Consequently, OWD was selected for the bioassays due to its efficiency and simpler logistical requirements. In Chapter 3, an experiment was conducted exposing the oyster Crassostrea brasiliana to diesel oil dispersed in water using the OWD technique. PAHs were quantified in both the water and the total tissues of the oysters, along with stable isotopes δ 13 C and δ 15 N, and the nitrogen and carbon percentages in the gills, hepatopancreas, and muscles over a seven-day period. The primary results indicated that the concentration of PAHs in the water decreased rapidly, with bioaccumulation observed in the oysters within the first 48 hours. After seven days, the concentrations in the tissues also diminished, demonstrating the depuration of the tested PAHs. These findings confirmed diesel oil as an extremely volatile substance and highlighted the capacity of Crassostrea brasiliana as a bioindicator. Regarding the stable isotopes, no significant differences were observed between control and treatmentsamples, suggesting that the slow recycling rate and rapid reduction of contaminants in the water hindered the detection of any isotopic changes. In Chapter 4, oysters were exposed to oil-water dispersions (OWDs) created with five concentrations of diesel oil (1:5, 1:10, 1:100, 1:1.000, and 1:10.000) to evaluate bioaccumulation and mortality rates in these varying conditions. Overall, the results indicated very low mortality across all treatments, with no difference observed between the experimental groups and the control. The bioaccumulation levels recorded were similar among the three highest concentrations, likely due to the rapid degradation of the most abundant polycyclic aromatic hydrocarbons (PAHs), particularly the lighter compounds such as naphthalene. Consequently, the species Crassostrea brasiliana demonstrated its effectiveness as a bioindicator, attributable not only to its inherent characteristics as a semi-sessile filter feeder but also to its resilience and capacity for bioaccumulation.