| dc.description.abstract | Disposal of Spent Engine Oil (SEO) on farmlands is one of the environmental problems
creating unsatisfactory conditions for plant growth and human health. Studies have shown
that SEO contain contaminants which can be absorbed by plants thus, constituting danger to
the health of consumers of such plant products. This study was conducted to assess the effect
of SEO on cowpea growth and toxicity.
Topsoil (0-15 cm depth) was obtained from teaching and research farm, University of
Ibadan. A representative grab sample of the soil and that of SEO were taken for baseline
heavy metal analysis. The soil was put into perforated polythene bag to a weight of 350 g.
The experiment was laid out as completely randomised design in 5 replicates. Seven
treatments of SEO (A: 5 ml, B: 10 ml, C: 15 ml, D: 20 ml, E: 25 ml, F: 50 ml, and G: 75 ml)
were applied to the soil while the 8th group devoid of SEO served as the control. Three
cowpea seeds were dipped into each bag and watered daily. Growth parameters including
plant height and leaf number were recorded weekly. After harvesting, seed weight and total
plant weight were obtained. The seeds and roots were also subjected to heavy metal analysis
through Atomic Absorption Spectrophotometry assessment (AAS). The grease and oil
content in soil samples were determined by obtaining the absorbance on AAS at 450 nm. The
data were analysed using ANOVA, while Duncan Multiple Range test was used for post-hoc
comparisons.
Baseline heavy metal analysis showed that only lead and cadmium were present in the SEO
at 0.003 ppm and 0.462 ppm but absent in the soil. There was significant reduction in plant height (control: 50.72 cm, A: 41.79 cm, B: 39.39 cm, C: 37.36 cm, D: 33.27 cm, E: 32.13
cm, F: 26.85 cm, G: 24.33 cm) and number of leaves (control: 25.91, A: 22.54, B: 22.38, C:
21.57, D: 19.06, E: 20.65, F: 17.61, G: 17.67) in contaminated soil with increasing SEO
concentration (p<0.05). There was also significant decrease (p<0.05) in the seed weight of
plant grown on contaminated soil (control: 24.40 g, A: 24.00 g, B: 22.94 g, C: 16.38 g, D:
15.95 g, E: 9.66 g, F: 5.44 g, G: 5.03 g). Similar pattern was observed in the total plant
weight (control: 171.60 g, A: 170.25 g, B: 167.60 g, C: 136.60 g, D: 135.00 g, E: 124.20 g,
F: 62.60 g, G: 54.70 g). Plants grown on contaminated soil contained more cadmium with increasing oil concentration as manifested in its higher values of cadmium in seeds (control:
0.000 ppm, A: 0.046 ppm, B: 0.056 ppm, C: 0.057 ppm, D: 0.078 ppm, E: 0.081 ppm, F:
0.102 ppm, G: 0.119 ppm) and roots (control: 0.000 ppm, A: 0.063 ppm, B: 0.070 ppm, C:
0.079 ppm, D: 0.091 ppm, E: 0.113 ppm, F: 0.163 ppm, G: 0.263 ppm) from contaminated
soil. Also, the concentration of grease and oil in the polluted soil increased with increasing
SEO (control: 1.81 mg/l, A: 8.13 mg/l, B: 8.92 mg/l, C: 10.30 mg/l, D: 11.36 mg/l, E: 11.69
mg/l, F: 14.88 mg/l, G: 17.47 mg/l).
Cowpea grown on polluted soil with spent oil had stunted growth, higher concentration of
cadmium as well as reduced crop yield and plant weight. Indiscriminate disposal of spent oil
should be controlled. | en_US |
