Influence of the natural Rio Negro water on the toxicological effects of a crude oil and its chemical dispersion to the Amazonian fish Colossoma macropomum.

The increment in crude oil exploitation over the last decades has considerably increased the risk of polycyclic aromatic hydrocarbon (PAH) contamination to Amazonian aquatic environments, especially for the black water environments such as the Rio Negro. The present work was designed to evaluate the acute toxicity of the Urucu crude oil (CO), the chemically dispersed Urucu crude oil (CO + D), and the dispersant alone (D) to the Amazonian fish Colossoma macropomum. Acute toxicity tests were performed, using a more realistic approach, where fish were acclimated to both groundwater (GW), used as internal control, and natural Rio Negro water (RNW) and exposed to CO, CO + D and D. Then, biomarkers such as ethoxyresorufin-O-deethylase (EROD), superoxide dismutase (SOD), lipid peroxidation (LPO), serum sorbitol dehydrogenase (s-SDH) in liver, DNA damage in blood cells, and the presence of the benzo[a]pyrene-type, pyrene-type, and naphthalene-type metabolites in fish bile were assessed. Fish exposed to CO and CO + D, at both water types tested, presented increased biomarker responses and higher PAH-type metabolites in the bile. However, fish exposed to these treatments after the acclimation to RNW increased the levels of LPO, s-SDH (hepatotoxicity), DNA damage in blood cells (genotoxicity), and benzo[a]pyrene-type metabolites when compared to fish in GW. Our data suggests that some physicochemical properties of Rio Negro water (i.e., presence of natural organic matter (NOM)) might cause mild chemical stress responses in fish, which can make it more susceptible to oxidative stress following exposure to crude oil, particularly to those chemically dispersed.