This study examined the cytotoxic response, germination, survival, morphological deviations as well as enzyme activities of Arachis hypogaea and Sorghum bicolor in crude oil contaminated soil. Crude oil spillage was simulated to achieve 1%, 2%, 3% (w/w) contamination levels in pot experiments. Treatments without crude oil were used as control. Cytotoxicity, germination and survival were determined by using percentages while enzyme activity was measured by using spectrophotometric methods and standard curves. S. bicolor had lower mitotic index (3.7) with higher percentage aberrations (65.56%) compared to A. hypogaea. However, difference in mitotic index and percentage aberration between A. hypogaea and S. bicolor was not significant at P≥0.05. Percentage germination and survival of both plants were not different. Enzyme study showed that enzyme activity in A. hypogaea and S bicolor were the same in control but increased with crude oil contamination. Laccase activity was significantly higher (P≤0.05) in A. hypogaea than in S. bicolor in 1% and 2% crude oil concentrations. The same applies to soluble methane monoxygenase activity in all crude oil concentrations. Tyrosinase activity was not significantly different in both plants in all concentrations. The study shows A. hypogaea to have better tolerance in crude oil contaminated soils than S. bicolor. © JASEM https://dx

The need to reclaim contaminated soils is important in ensuring the sustainability of life and biodiversity. Food crops grown in heavy metal contaminated soils have the risk of passing the accumulated metals to man and such has been demonstrated to cause various diseases in man. In this study, we investigated the potentials to reclaim heavy metal contaminated soil using Eudrilus euginae and Lumbricus terrestris. The contaminated soils were obtained from mechanic, welder and metallic workshops and were grouped individually and as combinations. The soils were incubated with the earthworms and the quantities of heavy metals in soil were determined before and after the growth of the earthworms. The percentage of the heavy lost from soils at the end of the study was calculated to evaluate the ability of the earthworm to enhance the remediation of heavy metal contaminated soil. The presence of the earthworms led to more reduction of the levels of the heavy metals in the soils than natural attenuation. The presence of L. terrestris led to a lower reduction of Cd, Cr and Pb in the combined soil from the three sites but a greater reduction of Zn and Ni from such soil. The presence of E. euginae led to greater loss of all the heavy metals in the soil from the welder workshop and greater loss of Cd, Pb, Ni and Zn in the soil the mechanic workshop than L. terrestris. The presence of E. euginae led to more loss of Cr, Pb, and Ni in combined soils of mechanic and welder workshops and mechanic workshop and metallic dumpsite. The findings of this study show that although the presence of both earthworms enhanced the remediation of heavy metals from the soils, the efficiency of the remediation is organism-specific and site-specific. Study on detailed mechanisms of enhancing heavy metals by earthworms is recommended.