Impact of biodegradation on the potential bioaccumulation and toxicity of refinery effluents

Whole effluent assessments (WEA) are being investigated as potential tools for controlling aqueous industrial discharges and minimizing environmental impact. The present study investigated how toxicity and the presence of potentially bioaccumulative substances altered when refinery effluents were subjected to biodegradation tests. Three petrochemical effluents were assessed, two freshwater and one saline, and subjected to two different types of biodegradation tests, resembling either a ready style (dissolved organic carbon (DOC)-die away) or an inherent style (Zahn-Wellens) test and the toxicity and potential to bioaccumulate parameters were re-analysed during and after biodegradation. A high proportion of the potentially bioaccumulative substances (PBS) in these effluents was easily biodegradable. Biodegradation not only lowered the PBS concentration but also toxicity. Appropriate controls are required however, as some increases in toxicity were observed after 4 h. In the present study, six other petrochemical effluents were also assessed for their PBS content and toxicity to increase the understanding of the relationship between PBS and toxicity. The results showed that the PBS concentrations in these samples were lower than the estimated benchmarks of acute toxicity for algae, fish and crustacean, although two samples were above the critical PBS values for chronic narcotic toxicity for Daphnia magna, which support the assumption that narcotic effects are mainly responsible for the observed toxicity in refinery effluents. It can be concluded that for facilities processing petroleum products that the measurement of PBS is a suitable surrogate for toxicity tests at the screening stage. Finally, the combination of persistency, bioaccumulation, and toxicity tests was shown to have additional value compared to an approach using only toxicity tests.