Intrinsic Qualities of a Naturally Attenuated Petroleum Hydrocarbon-polluted Seed Bed Exposed to Different Kinds of Mulching Materials

As materials that help in the conservation of soil moisture, improvement of soil health and fertility, mulches also improve microbial activity, which is sin qua non to successful intrinsic bioremediation. The study investigated the effects of mulching with selected materials on the natural attenuation of waste engine oil (WEO)-polluted soil. Top soil was mixed with WEO to obtain 5% w/w oil- in-soil concentration. The soil was made into beds and covered separately with 5 different mulching materials [aluminum foil, polyethylene materials (transparent and black), granite and tarpaulin] for 3 months. Results showed that efficiency of heavy metal reductions was decreased by application of the various mulches. Percentage reduction in total heavy metal content (Cu, Mn, Ni, V, Cr and Pb) was 18.77% in the transparent polyethylene-covered bed and 62.61% in the aluminum foil-mulched soil, compared to 83.65% in the control. Total PAH content in the uncovered soil was 336.80mg/kg, indicating a 67.14% bioremediation efficiency, compared to 79.08% in the black polyethylene-covered seed bed and 74.75% in the aluminum foil-mulched bed. Total bacterial count in both treatment and control soils was highest in the tarpaulin-mulched soil (6.8 x 105 cfu/g), compared to 1.8 x 105 cfu/g in the control (uncovered). Prominent bacteria species were Bacillus subtilis and Micrococcus luteus whereas predominant fungus species were Aspergillus niger and Penicillium sp. Phytoassessment of the treatment and control soils using transplants of Amaranthus hybridus showed highest yield and biomass accumulation in the tarpaulin-mulched soils.