Are the damaging effects of oil refinery effluents on Corbicula fluminea (mollusca) reversible after its transfer to clean water?

The effluent discharged by oil refineries is known for its toxicity caused by its inorganic and organic chemicals. The biological effects of the effluent from a treated oil refinery on the bivalve filter feeder of Corbicula fluminea were assessed. DNA damages were assessed through comet assay, the biochemical parameters were measured based on the activity of enzymes such as catalase (CAT) and glutathione S-transferase (GST). Animals were exposed to treatments with effluent for 6, 24 and 96 h. Test animals were allowed to recover from the exposure period for 24, 72 and 144 h. Although animals exposed to the effluent for 96 h presented genotoxicity, they were fully recovered 144 h after the exposure period was over. The CAT activity of animals exposed to the effluent significantly reduced after 24 h of exposure. However, GST activity increased after 96 h of exposure, and its rate remained high after 144 h of recovery; therefore, there was protective GST activity. The damage detected after 96 h of exposure could have been caused by the polycyclic aromatic hydrocarbons (PAH) herein described as DNA intercalating agents. Other compounds such as monoaromatic ethylbenzene, toluene and xylenes (BTEX) were also detected in the assessed effluent. Our study is the first to use the comet assay as genotoxicity cyto-genetic biomarker to evaluate the overall recovery ability of bivalve mollusks, mainly of C. fluminea, after their exposure to effluent discharged by oil refineries. Further studies can help better understanding the responses from such exposure and improve knowledge about the persistence of certain disturbances even after contamination is over.