BIODEGRADATION OF DIAZINON AND METHOMYL PESTICIDES BY WHITE ROT FUNGI FROM SELECTED HORTICULTURAL FARMS IN RIFT VALLEY AND CENTRAL PROVINCES, KENYA

Abstract

White rot fungi are robust organisms and are generally more tolerant to high concentrations of polluting chemicals than bacteria, they therefore present a powerful prospective tool in bioremediation. In this study, the potential for biodegradation of methomyl and diazinon by white rot fungi through enrichment and isolation of methomyl and diazinon biodegraders from horticultural soils was done. Five white rot fungal isolates WR1, WR2, WR4, WR9 and WR15 were cultured in a medium containing methomyl and diazinon as the only carbon source and incubated at 280C and monitored for biodegradation at intervals of 10 days for a period of 100 days. Using Gilson HPLC system with acetonitrile (75% sample: 25% acetonitrile) as the mobile phases.  The biodegradation of methomyl and diazinon overtime using fungal isolate mixtures, took 59 days while for individual isolates, it took a maximum of 100 days to biodegrade the pesticides. These proofs that fungal mixtures in soil fasten the rate of biodegradation of pollutants compared to individual isolates. The pesticide methomyl was eluted at 4.9 minutes while the methomyl metabolite was eluted at 4.1 minutes. Diazinon was eluted at 11 minutes while the diazinon metabolites; diazoxon and oxypyrimidine were eluted at 2.3 and 2.6 minutes. The HPLC method used enabled the separation and quantification of the pesticides in an HPLC run-time of 15 min. Results indicated that after 100 days all the isolates managed to biodegrade the respective pesticides. The rate of mineralization or disappearance of a pesticide was proportional to the concentration of the pesticide. White rot fungi are advantageous over bacterial systems since these fungi can grow rapidly when supply of nutrients is low/limited.