Dissipation of chlorpyrifos, pendimethalin, and thiophanate-methyl pesticides in compost based- versus peatmoss based-biomixtures of biobeds

Biobeds is a simple and a cost effective way to treat point source pesticide’s contamina- tion. In this study, we replaced peat-moss (P) with compost (C) which is locally available to compare the effectiveness of both bio-mixtures (biomix) P and C on pesticide dissipation. Chlorpyrifos, pendimethalin, and thiophanate methyl were added separately (at three con- centrations 25, 50, and 75 mg/kg of both biomix P and C). Our results showed that biomix composition influenced the dissipation of pesticides. For chlorpyrifos, the highest dissipation rate was recorded in biomix P. This result was confirmed by the mineralization kinetics, since, 25% of 14C-chlorpyrifos initially added to biomix evolved to 14CO2 in biomix P while only 14% evolved to 14CO2 in biomix C. In addition, chlorpyrifos dissipation rate was found to be influenced by the initial concentration applied to biomix P and C. In contrary, highest rate of dissipation of pendimethalin was observed in biomix C. More than 76% of pendimethalin was dissipated in biomix C while only 67 % were dissipated in biomix P. The efficiency of both biomix (C and P) was similar in the dissipation of thiophanate-methyl but less efficient compared to other tested pesticides. The addition of the three tested pesticides as mixture at 25 mg/kg of biomix C had a positive effect on both chlorpyrifos and thiophanate-methyl dis- sipation, while pendimethalin dissipation was similar when applied separately or mixed. In both biomixtures, dehydrogenase activity of microorganisms was stimulated by the addition of pesticides