Toxicology studies involving optimization of soil contaminated with spent engine oil using leaves of maize

Abstract

The effect of spent engine oil-contaminated soil on morphological and biochemical properties of Zea mays (maize) was investigated. Thirty polythene pots with drainage holes at the bottom, each containing 10 kg of surface soil, were randomly placed on a table in the greenhouse in a factorial combination of five treatment levels (5 ml, 10 ml and 15 ml) of spent engine oil and additional three variants of each with pH adjustment to 5.5, 7 and 8.5 and were designated S0 for Control, S5 for soil containing 5 ml engine oil with no pH adjustment and S5A, S5B and S5C for pH adjustment to 5.5, 7.0 and 8.5 respectively. Three seeds of maize per pot were planted. Growth parameters (plant height, stem girth, relative water content (RWC), selected leaf properties (chlorophyll content (SPAD value) and soluble protein content (SPC)) and antioxidant indices were determined in the corn over a period of eight weeks after planting (WAP). The maize planted in contaminated soil with pH adjustment recorded significantly higher height than their corresponding contaminated soil without pH adjustment (p<0.05). The girth of plant decreased with increased concentration of contaminant (spent engine oil). SPC of Control (S0) is significantly higher (p<0.05) than any of the maize planted in soil contaminated with spent engine oil. Generally, activities of antioxidant enzymes of Control were significantly lower (p<0.05) than those of maize planted in soil contaminated with spent engine oil. It could be inferred that spent engine oil in soil hindered the growth and development of maize, it created artificial water deficit to cellular system of maize and induced a condition of oxidative stress. However, maize planted in soil amended to pH 5.5 recorded favourable biochemical indices.