ABSTRACT

The problem of bioaccumulation and biomagnifications of Paraeforce in food chain and the attendant health hazards to human and farm animals as well as the cumbersome nature of the existing physicochemical methods of its degradation culminated in this study. The study is aimed at exploring the biodegradation potential of fungi on Paraeforce-impacted soil and the analysis of the associated enzymes and metabolites. Soil samples were collected from an agrarian soil previously exposed to Paraeforce herbicide. Physicochemical analysis was done on the homogenized soil sample. Fungal isolation was done using traditional plate culture and molecular techniques. The biodegradation potential of the isolates was determined using titrimetric method. The enzymes activity and metabolite concentration were measured spectrophotometrically. Statistical analysis was done on generated data using one way analysis of variance. The physicochemical analysis of the treated soil samples recorded a range of pH (5.1 to 5.9), temperature (31.9 to 33.3 0C), moisture content (52.28 to 62.5 %), nitrate (13.8 to 23.2 mg/kg), total organic carbon (5.3 to 25.1 mg/kg) and conductivity (0.09 to 0.18 µScm-1). Fungi isolated from the soil sample were Pichia kudriavzevii, Hanseniaspora opuntia, Aspergillus, Pichia cecembensis, Rhizopus, Candida, Fusarium and Penicillium. Of the above isolated microorganisms, Pichia kudriazevii, Hanseniaspora opuntia, Aspergillus spinosus and Pichia cecembensis were the only isolates capable of growth in Paraeforce medium. The degradation rate measured showed that Aspergillus spinosus was a better degrader, breaking down 36.8mg/kg of the Paraeforce in 90 days. There was a synergy in the degradative capacity of the mixed culture degrading 46.3 mg/kg in 90 days. At the end of 90 days, the rate of Paraeforce degradation was also high in treatments with Pichia kudriavzevii (27.5mg/kg), Hanseniaspora opuntia (22.4mg/kg) and Pichia cecembensis (23.1mg/kg). Natural attenuation showed a degradation rate of 41.37mg/kg in 90 days One way analysis of variance done on degradation showed there was a significant difference in the mean concentration of Paraeforce (F[6,42] = 4.338, p = 0.002) over a period of 90 days at 5% level of significance. When the sample was optimized using poultry wastes, the degradation rate improved. The mixed culture achieved 50mg/kg degradation of Paraeforce in 56 days. Natural attenuation achieved 50mg/kg degradation in 70 days while Aspergillus spinosus had 50mg/kg degradation in 84 days. Pichia kudriavzevii, Hanseniaspora opuntia and Pichia cecembensis had 36.7mg/kg, 29.5mg/kg and 26.08mg/kg respectively at the end of 90 days. The growth of fungi was influenced by pH, temperature, nitrate, total organic carbon and the Biochemical oxygen demand of the growth medium. Catalase, laccase, lignin peroxidase and manganese peroxidase were identified in the degradation process with associated formate and oxalate production. These metabolites were used to monitor the degradation process. Aspergillus spinosus and mixed culture of the isolates proved a more efficient tool in this study. The study showed that living cells of the four test fungi have great potential for the degradation of Paraeforce in an impacted soil and should be explored.