Uptake and elimination kinetics of heavy metals by earthworm (Eudrilus eugenia) exposed to used engine oil-contaminated soil
Earthworm inoculation of petroleum hydrocarbon contaminated soil is thought to catalyze the bioremediation. Most bioremediation studies focus on the petroleum hydrocarbon content and not on the heavy metals. Here, the uptake kinetics of heavy metals by earthworm in used engine oil contaminated soil was investigated. The metals considered were zinc (Zn), copper (Cu), nickel (Ni), chromium (Cr), titanium (Ti) and manganese (Mn). Five different concentrations of used engine oil contaminated soil were considered: 12.5, 25, 50, 75 and 100 g/kg of soil. At the end of the 20 days study, the concentration of Zn, Cu, Ni, and Cr in the worms were found to have decreased (of which initial concentrations in the worms where higher than their concentrations in all used engine oil contaminated soils considered, that is, 12.5, 25, 50, 75, and 100 g/kg of soil), whereas Ti and Mn showed an increase (of which initial concentrations in the worms where lower than concentrations in all used engine oil contaminated soils considered, that is, 12.5, 25, 50, 75 and 100 g/kg of soil). The uptake and elimination rate constants of the metals were estimated using one-compartment model. The percentage drop in total petroleum hydrocarbon was also found to increase with increase in initial used engine oil concentrations.
Key words: Eudrilus eugenia, heavy metals, kinetics, one-compartment model, soil, used engine oil.