Characterization and evaluation of the ecotoxicity of petroleum refinery effluents using a battery of bioassays

Abstract

This study aimed to characterize and evaluate the ecotoxicity of petroleum refinery effluents using a battery of bioassays. A laboratory scale study was conducted on Port Harcourt (PH) and Warri petroleum refinery effluent samples using standard methods of physicochemical, and microbiological analysis, dehydrogenase inhibition test, Allium cepa test, and fish toxicity test. Five treatments and the control designs were set up in triplicates containing 6.25%, 12.5%, 25%, 50%, 100%, and 0% petroleum effluent concentrations and incubated at 25 ± 1°C for 2 h and 96 h, respectively. The results revealed that the Port Harcourt refinery effluent contained higher quantities of physicochemical parameters than the Warri effluent sample, with lower counts of hydrocarbons using bacteria and fungi in both samples. The results of Bacillus sp. dehydrogenase inhibition and Clarias batrachus toxicity revealed that the PH sample had the most harmful effects with EC50 values of 17.01%, LC50 values of 75.86 at 24, 48, and 72 h, and LC50 of 50.12 at 96 h. The Warri sample had the most harmful effect on Allium cepa root with an EC50 value of 94.7%, while the positive control (potassium dichromate (K2Cr2O7) had the most harmful effect on S. cerevisiae dehydrogenase with an EC50 value of 25.00% and LC50 values of 11220.18 at 24 and 48 h, as well as LC50 of 7079.46 at 72 and 96 h. Inhibition (%), aberration (%), and mortality (%) correlated significantly (P < 0.05) positively with concentration. The toxicity threshold concentration values of < 1 EC50/LC50/TUa < 100 observed and recorded in the present study align with the toxicity data on untreated refinery industrial effluents, indicating probable toxic effects on the microbial community, plants, and animals. Therefore, the outcomes of this study suggest the deployment of strict measures to avoid future escalation in order to preserve our ecosystems.