Comparative effects of sediments contaminated by carcinogenic and non-carcinogenic PAHs in Dicentrarchus labrax: a semi-quantitative histopathological approach

Dissertação para obtenção do Grau de Mestre em Engenharia do Ambiente

Polycyclic Aromatic Hydrocarbons (PAHs) are considered priority pollutants due to their high risk to environmental and human health. Due to their hydrophobic character, in aquatic environments, these substances tend to adsorb to the particulate fraction and accumulate in the sediments. Despite their division into carcinogenic, potentially carcinogenic and non-carcinogenic to humans, little is known about the differences between modes of action of carcinogenic and non-carcinogenic PAHs in aquatic organisms. In order to understand the toxicity mechanisms of these two classes, laboratory assays were performed with juvenile basses (Dicentrarchus labrax) exposed to contaminated artificial sediments for 28 days. Sediment were spiked with environmentally-relevant concentrations of benzo[b]fluoranthene (a carcinogenic PAH) and phenanthrene (non-carcinogenic), either isolated or in mixture. Exposure effects were analysed through an indice-based semi-quantitative histopathological approach in hepatic tissue, due to the role of liver in the accumulation and detoxification of xenobiotics. Overall, significant alterations in the hepatic tissue were detected relatively to control tests, either for isolated or mixture assays, despite the low levels of exposure. Individuals exposed to benzo[b]fluoranthene presented higher severity and number of hepatic lesions compared to phenanthrene. Furthermore different toxicants caused different patterns of histopathological lesions and alterations. The results also show that histopathological condition indices of mixture-exposed individuals do not match the expected additive effects, suggesting a possible synergistic interaction effect between the contaminants. This work allows the conclusion that, albeit considered low, environmentally-relevant concentrations of PAHs in sediments may cause adverse effects in organisms, in this case, a demersal fish. On the other hand, results also suggest that a non-carcinogenic PAH may be responsible for considerable toxic effects, even in moderate concentrations. Altogether, requalifying risk assessment for these substances becomes of the upmost importance since PAHs (as other pollutants) are usually present in the environment in complex mixtures.