TOXICITY OF SOIL POLLUTED WITH SPENT ENGINE OIL ON THE GROWTH OF TOMATO (Lycopersicon esculentum M.) AND AFRICAN SPINACH (Amaranthus hybridus L.).

Abstract

Toxicity from Spent Engine Oil (SEO) contamination due to its indiscriminate disposal is a prevalent problem in Nigeria. This could lead to build up of heavy metals in plants which in turn cause cancer or mutation in humans due to biomagnifications in food chain and also reduces growth parameters in plants. Therefore a field investigation was carried out in a screen house beside the Academic building, School of Science, Federal University of Technology, Akure, Nigeria to determine the effect of spent engine oil contaminated soil on growth parameters and heavy metals contents of Tomato (Lycopersicon esculentum M.) and African Spinach (Amaranthus hybridus L.). Five treatments (0.0, 10, 20, 30, and 40ml/1.5kg of soil) of the spent oil were applied to 1.50kg of soil samples collected from the vegetation behind the new security unit at The Federal University of Technology, Akure and fill into a perforated pots arranged in a Randomized Complete Block Design (RCBD) with five replications. Seeds of L. esculentum and A. hybridus were collected from International Institute of Tropical Agriculture (IITA), Ibadan were planted in the polluted soil. The percentage germination of the plants were determined four weeks after planting (4WAP). Plant height, leaf number and diameter of the stem of the plants were taken weekly for eight weeks (8weeks) after five weeks of planting the seeds. The leaf of the plants were harvested 12WAP and taken to Institute of Agricultural Research and Trainning (IAR&T), Ibadan for analysis of the following metals; Arsenic (As), Zinc (Zn), Lead (Pb), Mercury (Hg) and Cadmium (Cd) using Atomic Absorption Spectrophotometry. Significant differences (p < 0.05) were observed in shoot height, leave number and stem diameter of L. esculentum from the treatments. There were decrease in shoot height, number of leaves and stem diameter of L. esculentum as the volume of SEO in the soil increased. At 0.0ml, 10ml, 20ml, 30ml, and 40ml of SEO/1.50kg of soil, the mean height of L. esculentum 12 weeks after planting were 17.28cm, 17.33cm, 7.95cm, 7.37cm and 10.76cm respectively and the mean height of A. hybridus at 0.0ml, 10ml, 20ml, 30ml, and 40ml of SEO/1.50kg 12 weeks after planting were 22.50cm, 11.56cm, 9.09cm, 8.82cm and 7.40cm respectively. This same trend was also observed in the stem diameter, leaf numbers and percentage germination of the plants. There were no significant difference (p < 0.05) observed in the percentage germination L. esculentum and A. hybridus. At 0.0ml, 10ml, 20ml, 30ml, and 40ml of SEO/1.50kg of soil, the percentage germination of L. esculentum and A. hybridus were: 80.25% and 76.70%; 65.30% and 57.80%; 48.85% and 49.60%; 40.50% and 37.50%; and 28.68% and 25.80% respectively. There was significant differences (p < 0.05) in heavy metal concentration in the plants at different treatment levels as the mean heavy metals increased with increase in volume of SEO in the soil. However arsenic has the lowest concentration as no value was detected in soil treated with 10ml, 20ml and the control while zinc has the highest mean concentration (1667x104 and 1467 x104 for L. esculentum and A. hybridus respectively at 40ml of SEO/1.50kg of soil). The concentrations of heavy metals investigated in this research at different treatments levels of spent engine oil were below the permissive limits recommended by WHO/FAO but the bioaccumulation of this heavy metals may be detrimental to human health. It is therefore imperative to inform and enlighten the local farmers and the consumers on the danger of planting on soil polluted with spent engine oil and using water which pollutant level has not been detected for irrigation of agricultural crops in order to ensure safety, hence there is need to avoid planting crops in polluted soils.