Toxicological Indices of Crude Oil-Polluted Soil Ecosystem

Abstract

Assessment of the level of contaminations from possible impact of crude oil on soil ecosystem is imperative for the determination of environmental acceptability. This study investigated this impact ex-situ using a culture-dependent approach to evaluate the total microbial counts; physicochemical tools to determine the cation exchange capacity (CEC), metal leachates, exchangeable bases (Mg, Ca, Na and K), pH, total petroleum hydrocarbon (TPH) and the overall effects on plants as indices of toxicity. The experiment demonstrated that at 1.5 – 3.5% contamination across days-zero to -28, there was a significant (p<0.05) increase in total petroleum hydrocarbon (TPH) from 0.03 ± 0.00 to 0.07 ± 0.00 with increase in acidity from pH 5.2 ± 0.00 to 4.0 ± 0.00 and a reduction in cation exchange capacity (CEC) from 0.82 ± 0.05 to 0.70 ± 0.11mEq and exchangeable bases with an augmented increase in phytotoxic elements and metal leachates. A reduction in microbial biomass from control, 1.30 x 109, to 3.6 x 108 cfu on week one as contamination increased and induction of hydrocarbonclastic organisms thereafter across weeks two and four, 3.88 x 108 and 4.40 x 108 cfu respectively was an indication of a reduction in microbial diversity. Ecosystem dynamics and mineralization were impaired and disrupted and the entire soil biochemistry altered with adverse effects on plant health.