Chlorpyrifos degradation in a Biomix: Effect of pre-incubation and water holding capacity

Biobed system is a simple method to minimize point source contamination during manipulation of pesticides and is based on the adsorption and degradation potential of a biomix composed by top soil, peat, and straw and covered with a grass layer. In our study, the biomix was prepared with Andisol, peat and straw in a volumetric pro-portion of 1:1:2, and adsorption and degradation studies were done. Degradation of chlorpyrifos (160 mg a.i. kg-1) and formation of TCP (3, 5, 6-trichloro-2-pyrinidol) at different pre-incubation times (0, 15 and 30 days) and with different moisture contents (40, 60 and 80 % of water holding capacity) were evaluated, ligninolytic enzyme activity and microbial respiration in the biomix were periodically analyzed. Adsorption isotherms were fitted using Freundlich and linear models for Andisol and the biomix. The adsorption assays demonstrated that biomix has a higher ca-pacity to retain chlorpyrifos than top soil. The pre-incubation period, WHC and the concentration of the chlorpyrifos of the biomix influenced the degradation of the contaminant and TCP formation as well as the biological activities in the biomix. The TCP was formed during the first steps of chlorpyrifos degradation and was later degraded in the biomix under all studied conditions. In conclusion, biomix with Andisol, peat and straw (1:1:2), pre-incubated by 15 days and incubated with 60% of WHC is capable to degrade chlorpyrifos efficiently