Residual crude oil concentrations and ecotoxicity of polluted tropical soils after phytoremediation

Changes in residual crude oil concentrations and soil ecotoxicity during the phytoremediation assessment of tropical plants growing on crude oil-polluted soils were evaluated in a greenhouse study. The plants (Panicum maximum, Zea mays, Centrosema spp. and Pueraria spp.) were grown in weathered polluted soil samples in microcosms for 10?weeks. Residual crude oil in soil was quantified colorimetrically, while the ecotoxicity of the vegetated and control soil samples were evaluated using earthworms’ percentage survival and crop seeds’ germination bioassays. It was observed that planting of 1% (w/w) polluted soil samples reduced crude oil in the rhizosphere soils of P. maximum and Centrosema spp. by 71.6?±?1.4 and 55.3?±?4.3%, respectively. These are in contrast with 37.5?±?2.5% reduction in non-vegetated control soil samples. The ecotoxicity assays indicated that planting also effected reduction of crude oils’ toxicity positively. There were 100, 40?±?28.3 and 50?±?21.1% survival of test earthworms, respectively, after 24?h in 1% w/w polluted soil samples phytoremediated with P. maximum, Centrosema spp. and Pueraria spp. as against 0% survival in non-vegetated control samples. The observed sensitivity of the test organisms to chemical stress bodes well for providing rapid information on effectiveness of remediation programmes.