Abstract

The present study investigated the effects of soil amendment on the remediation of waste engine oil (WEO) polluted soil, as well as the eventual phytotoxic effects of remediated amended soil on some growth parameters of cowpea. There were over 50% reductions from the original concentrations of Fe, Mn, Zn, Cu, Cr, Cd, Pb, Ni and V in soil nine months after amendment. Significant reductions in polyaromatic hydrocarbons were also achieved. Total PAH reduced from 538.59 to 1.10 mg/l in 10% w/w oil polluted soil. Achromobacter spp. Clostridium spp. Sarcina spp. and Micrococcus spp. were prevalent bacteria species found in the polluted soils, while prevalent fungi species included Aspergillus niger, Penicillium, Geotrichum and Trichoderma. The Actinomycetenocardia spp. was prevalent as well. Ecological risk factor initially posed by the presence of heavy metals in the unamended soil was significantly reduced to safe levels. Phytoassessment of the polluted soil was carried out just before soil was amended with sawdust, and results showed that virtually all the cowpea seedlings died within 2 weeks; only those seedlings in unpolluted soils survived. Nine months after soil was amended, all cowpea plants survived up to fruiting. The present study also showed that cowpea was able to bioaccumulate heavy metals into harvestable parts, though bioaccumulation quotients calculated showed that these accumulations were not significant.

Key words: Phytotoxicity, waste engine oil, soil amendment, polyaromatic hydrocarbons.