[ESE-NUST Degradation of Methyl Parathion using Indigenous Soil Microorganism

Abstract

In Pakistan, detoxification of pesticide contanoinated sites requires developnoent of biodegradation system for treating high concentration of various pesticides. Present research work was a lab scale study, conducted to investigate the degradation of methyl parathion in nutrient broth, using indigenous soil culture and to deternnine optimal pesticide concentration, pH and tenlperature for bacterial growth that cause subsequent breakdown of noethyl parathion. As pure culture of Pseudcnnonas IES-Ps-l is reported to have the potential to degrade low concentration of malathion, nnethanlidophos, cartap and cypermethrin so for this study, sallie culture was isolated fronl soil, Inorphologically identified and chem ical ly characterized. The results of initial acclilnatization experilnents with low concentration (1 00, 150 and 150 Ing/L) of nnethyl parathion showed that IES-Ps-l culture is able to grow in nutrient broth containing methyl parathion at 25 oc and pH 7. Therefore higher concentrations of noethyl parathion (such as 400, 600, 800, 1000 and 1200 Ing/L) in nutrient broth were preliminarily investigated to determine optinnum utilization potential of Inicroorganislns, shown by increase in Optical Density (OD) at 600 nm. Little increase in initial OD values were observed for 1000 and 1200 nog/L after 96 hrs of incubation compared to other concentrations of 400, 600 and 800 nog/L, which exhibited significant increase in OD. Therefore detailed studies were conducted using concentrations of 400 and 800 mg/L. Decrease in concentration of organic Inatter svas noeasured indirectly by t\V0 techniques i.e. Total Organic Carbon (TOC) and Chemical Oxygen Deinancl (COD) for xvi

selected methyl parathion concentrations of 400 and 800 mg/L in nutrient broth at various pH values, i.e., 6, 7 and 9, and tenlperatures of 25, 30 and 35 oc respectively. The 0 hr value of COD and TOC for 400 nog/L of noethyl parathion in nutrient broth at pH value of 7 was 444 and 235.62 mg/L, respectively. After 96 hrs of incubation period these values decreased to 234 mg/L for COD and 1 19.38 Ing/L för TOC, which represented maxinnum degradation compared to the other pH values of 6 and 9. Similarly, for 800 mg/L of Inethyl parathion in nutrient broth, the ma,xinoun1 decrease in values of COD and TOC were also achieved at pH value of 7. Almong three different telnperatures, 0 hr values of COD and TOC for 400 mg/L of Inethyl parathion in nutrient broth was 441.3 and 180.25 mg/L respectively, which decreased to 220.4 Ing/L for COD and 86.12 mg/L for TOC after 96 hrs of incubation. This decrease represented maximum renloval of COD (50.06 per cent) and TOC (52.2 1 per cent) at 30 o c. Sinnilar results were observed for 800 Ing/L, where 46.50 per cent COD rennoval and 49.66 per cent TOC renooval was achieved at 30 0 C. Overall this study denoonstrates that IES-Ps-l culture is able to grow effectively in higher concentrations of Inethyl parathion added to nutrient broth (up to 800 nog/L) at 30 o c and pH value of 7 resulting in significant rernoval of organic matter.