Biodegradability and ecotoxicity of bio-insulating oils in aqueous and soil environments in Douala, Cameroon

Abstract

This work focuses on the analysis of the deleterious effects in case of spills in aqueous and soil environments of palm kernel oil methyl esters (PKOME) and castor oil methyl esters (COME) prototyped to substitute mineral oils in power transformers. Two main properties were investigated according to the Organization for Economic Cooperation and Development (OECD) standards. Biodegradability based on the OECD-301B guideline for CO2 release in biological media; and acute toxicity, analysed according to the OECD-203 guidelines for fish and OECD-207 guidelines on earthworms. At the end of 28 days of incubation, the PKOME samples showed a biodegradation rate of 92.6% in Wouri water and 74.93% in Douala soil. COME samples showed a biodegradation rate of 67.4% in aqueous medium and 57.64% in soil medium. Whatever the biological medium, the degradation rates of the PKOME prototypes were better than that of COME, and both were higher than those of mineral oils. The acute toxicity test was carried out on Arius africanus fish in an aqueous medium and earthworms type Eisenia foetida in soil medium at different doses of the substances. In both bioindicators, spills from the COME prototypes showed a moderate toxic effect. In aqueous medium, they caused 50% mortality at an LC50 concentration of 1.35 gl−1 and LC100 of 2.66 gl−1. In soil, the LC50 obtained were 1958.4 ppm (PKOME) and 541.73 ppm (COME).