Bioavailability and Toxicity of Plastic Contaminants to Soil and Soil Bacteria

Abstract

Aim: The bioavailability and toxicity of plastic contaminants to soil and soil bacteria was investigated to detect the presence of plastic contaminants in the soil and to evaluate the toxic effects of plastic contaminants to soil and soil bacteria.  Methodology: Five plastic composted soil samples were collected from different locations within the Edo State Waste Management site located at Iyowa in Benin City which were merged together to form a composite sample. The physico-chemical characteristics of the soil samples were analysed. The soil was analysed for the presence of plastic components using the Perkin Elmer Gas Chromatograph model Auto-system XL. Nitrobacter acute toxicity test was carried out. The median effective concentrations (EC50) and the median lethal concentration (LC50) values were calculated using the probit analysis.    Results: The gas chromatography revealed that the control soil sample had zero concentration for chlorobenzene, dichlorobenzene, and benzene. The physico-chemical analysis for the plastic composted soil and the control soil had electrical conductivity  245.00, 61.00 us/cm, chloride 66.15, 16.00 mg/kg, potassium 171.50, 4.27 mg/kg, nickel  1.00, 0.25 mg/kg,  vanadium 0.44, 0.23 mg/kg, and moisture 5.32, 7.21% and  total organic carbon 5.26, 71.0.% respectively. The bacteriological analysis for the plastic composted soil and the control soil had growth ranging from 1.0x 101±0.16 to 4.0 x 102±0.11 cfu/g and 2.0 x 103±0.20 to 11.0 x 103±0.86 cfu/g respectively. The average turbidity result showed a normal bacteria growth curve when plotted for the control soil. There was significant difference (P<0.05) in the bacterial counts from the control soil sample. The toxicity analysis revealed higher percentage utilization of nitrite with EC50 values of 52.00, 81.72, 111.31 and 123.13 and higher bacteria inhibition with LC50 values of 25.04, 23. 93, 15.94 and 13.39. Conclusion: The result obtained from this study suggest that autotrophic transformation by nitrifying bacteria which enhances soil fertility may be hindered in an ecosystem polluted with these plastics as nitrification process will be reduced.