Distribution of heavy metals and hydrocarbon contents in an alfisol contaminated with waste-lubricating oil amended with organic wastes

Abstract

Contamination of soil and groundwater with mineral oil-based products is among the most common sources of pollution in Nigeria. This study evaluated the distribution of some heavy metals and hydrocarbon content in soil contaminated with waste-lubricating oil (spent oil), and the effectiveness of some abundantly available organic wastes from animal source as remediation alternative to the expensive chemical and physical methods. The main-plot treatments include control (C), cow dung (CD), poultry manure (PM) and pig waste (PW) applied at 10 Mg/ha each; while the sub-plot treatments were control (0%), 0.5%, 2.5% and 5% spent oil (SP) applied at 10, 50 and 100 Mg/ha, respectively arranged in a split-plot in Randomized Complete Block Design (RCBD) with four replications. These treatments were applied once each year for two consecutive years. Soil samples (0–20 cm) were collected at 3, 6 and 12 months each year and analyzed for Cr, Ni, Pb and Zn, while the residual total hydrocarbon content (THC) was determined at the end of the 2 years study. Results show significant ( p < 0.05) accumulation of these metals with spent oil pollution following the sequence 5%SP > 2.5%SP > 0.5%SP, indicating higher metal pollution with increase in oil pollution. General distribution of Cr, Ni, Pb and Zn, relative to sampling periods, followed 3 months > 6 months > 12 months in the 1st year indicating reduction in metal levels with time. The trend for 2nd year indicated higher accumulation of Cr and Ni in 12 months, while Pb and Zn decreased with time of sampling. The results further showed higher accumulation of Cr followed by Zn, relative to other metals, with oil pollution. However, addition of organic wastes to the oil polluted soils significantly ( p < 0.05) led to reduction in the levels of the metals and THC following the order PM > PW > CD.