Chiang Mai Journal of Science

A biomixture is a principal element controlling the pesticide degradation efficiency of a biobed. In this study, a biomixture containing peat, as in the original Swedish design (Biomix-1), was compared with two biomixtures containing a spent mushroom substrate (SMS) (Biomix-2) and SMS inoculated with the ligninolytic fungus (Biomix-3) on their degradation of Chlopyrifos, 2,4-D, Cartap, and Cypermethrin and microbial activity. The residual concentration of pesticides was identified by the QuEChERS method. Ligninolytic activity was determined using the MBTH/DMAB assay, and the microbial respiration was assessed by CO2 evolution via alkaline trap method. Detoxification of Chlopyrifos, 2,4-D, Cartap, and Cypermethrin in the optimal biomixture was also evaluated by the ecotoxicity test. A test for the emergence and growth of higher plants was performed according to ISO 11269-2:2012. The acute toxicity test for earthworms was conducted following ISO 11268-1:2012 and OECD-207:1984. The results showed that the pesticide degradation efficiency and microbial activities of the biomixtures followed the decreasing trend: Biomix-3 > Biomix-2 > Biomix-1. Germination showed a non-significant decreasing trend with increasing applied spent Biomix-3 concentrations, while plant fresh weight values increased significantly up to certain concentrations of spent Biomix-3 compared to the respective control. Similarly, no significant mortality of earthworms was observed between the control and any treatments with spent Biomix-3. However, earthworms in treatments with high spent concentrations (>50 g/kg dry soil) had higher wet biomass reduction rates than earthworms in the controls. Therefore, it was recommended to use Biomix-3 to improve the performance of biobeds and the reuse of spent biomixture in Vietnam due to the availability of substrates.