Spent Lubricating Oil Decreased Vegetative Growth Parameters and Rhizosphere Microbial Abundance of Groundnuts (Arachis hypogea) and Maize (Zea mays)

Research Gap: there are little or no information on effect of oil pollution on groundnuts and maize.

Aim: to ascertain effect of spent engine oil (SEO) on plants’ growth, chlorophyll content, growth and survival of rhizosphere microorganisms in the contaminated soil.

Study Design: experiment was laid out as a completely randomized design in 3 replications.

Place and Duration of Study: Department of Environmental Management and Toxicology, Federal University of Petroleum Resources, Effurun/six months.

Methodology: farm top soil was collected and physico-chemical analysis was done. Viable seeds were determined by flotation method. Four treatments of SEO (5, 10, 15, 20ml) were applied to soil with plants at 2 weeks after planting. Shoot length, dry matter, leaf area, chlorophyll content of uprooted plant samples, rhizosphere bacterial and fungal counts were estimated biweekly using standard methods.

Results: different responses to SEO concentrations were observed. Leaf area was most affected (20ml SEO) at week 6 for groundnuts (0.0075±0.002m2) and maize (0.583±0.006m2). Application of SEO to soils had reductive effects on dry matter content of all plants; content values for groundnuts and maize at week 6 were 167±0.006g and 368±0.004g while controls were 0.567±0.007g and 0.860±0.002g, respectively. Bacterial counts increased in groundnuts from 1.21 ×105 CFU/g to 1.69×105 CFU/g (5ml), 0.7 x 105 CFU/g to 1.19 ×105 CFU/g (20ml), 2.03×105CFU/g to 2.56 ×105CFU/g (control) at weeks 2 and 6. Counts in maize were 1.35 ×105 CFU/g to 2.25×105 CFU/g (5ml), 0.8 ×105 CFU/g to 1.19×105 CFU/g (20ml), 2.15×105CFU/g to 2.96×105 CFU/g (control), respectively at weeks 2 and 6. There were statistical differences between the monitored parameters and treatments with respects to days.

Conclusion: study revealed plants may suffer great growth inhibition and perform poorly when exposed to SEO at early stages of growth. Therefore, enforcement of strict disposal regulations and legislations against irregular and indiscriminate disposal of spent engine oil into the environment is imperative.