ABSTRACT
Plastic additives such as bisphenol A (BPA) and phthalates are added to plastics during production processes in order to improve their properties. The aim of this study was to investigate the toxicity of bisphenol –a and phthalates on soil biological sentinel of a dumpsite. Five soil replicate samples were collected from different locations within the Kaduna State waste management site located at Kakau in Chikun local government area which were merged together to form a composite sample. One soil sample was collected from a farm land at Afaka-Mando community which served as the control soil sample. The soil was analysed for the presence of plasticizers using Hewlett-Packard HP 5890 series 11 Gas chromatograph. The leaves of Talinum triangulare was also analyzed for the presence of plastics contaminants using high performance liquid chromatography. Nitrobacter acute toxicity test was carried out. The median effective concentration (EC50) and the median lethal concentration (LC50) values were calculated using the probit analysis. The xiihysic-chemical analysis of the composted soil and the control soil showed electrical conductivity of 245.00, 61.00µs/ cm, Chloride content of 66.15, 16.00mg/ kg, Potassium content of 171.5, 4.25mg/ kg, Nickel content of 1.00, 0.25mg/ kg, Iron content of 17.40, 3.11mg/ kg, Zinc content of 2.90, 0.67mg/ kg, moisture content of 5.32, 7.21%, total organic Carbon content of 5.26, 0.71% and total Nitrogen content of 0.53, 0.07% respectively. The bacteriological analysis for composted soil and control soil growth ranged from 4.0 × 103 ± 0.12 to 3.5 × 103 ± 0.10 cfu/ g and 3.2 × 103 ± 0.40 to 2.8 × 103 ± 0.10 respectively. The toxicity analysis revealed higher percentage utilization of nitrite in the plastic composted soil 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. A continuous decreased in the percentage survival rate 75.47 – 20.93% with increase in plastic concentrations was observed for earthworm across various plastic enriched composting soil. There was also continuous decrease in the percentage germination rate, height and stem girth of Talinum triangulare with increase in plastic concentrations. 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 plasticizers as nitrification process will be reduced.
