Comparative acute toxicity and oxidative stress responses in tadpoles of Amietophrynus regularis exposed to refined petroleum products, unused and spent engine oils

Abstract

The relative acute toxicity of refined petroleum (diesel, kerosene and petrol), unused and spent engine oils as well as their abilities to alter the activities of superoxide dismutase (SOD) and cause lipid peroxidation in tadpoles of the common African toad, Amietophrynus regularis were evaluated.  After 48 h of exposures, kerosene was found to be the most toxic (LC₅₀= 4930 mg/L) while the least toxic was unused engine oil (LC₅₀ = 7777 mg/L). However, by 96 h of exposure, spent engine oil was found to be the most toxic (LC₅₀ = 2915 mg/L) while unused engine oil remained the least toxic (LC₅₀= 7353 mg/L). Further, assessment of oxidative stress markers was conducted using sub lethal concentrations of the test compounds (1/100th 96 h LC₅₀). There was significant inhibition of SOD in exposed tadpoles compared to the control (P<0.05) with the least activity recorded in tadpoles exposed to petrol, while unused engine oil recorded the highest. The results of the lipid peroxidation assay, determined by measuring the levels of malondialdehyde (MDA) indicated significantly higher levels in the exposed individuals compared to the control. Unused engine oil caused the highest level of MDA production while diesel induced the least level. Tadpoles exposed to diesel, kerosene, petrol and spent engine oil exhibited consistent responses among the three test parameters, however inconsistent responses were observed in tadpoles exposed to unused engine oils. The relevance of the comparisons in biomarker selection and ecotoxicology were discussed.

Keywords: Petroleum products, toxicity indices, tadpoles, oxidative stress.

African Journal of Biotechnology, Vol 13(45) 4251-4258