The degradation rates of fenpropathrin, phoxim and their mixture in un sterilized soil were much quicker than those in sterilized soil, which indicated that soil microorganisms played a significant role in the degradation process in soil. The half life (T 0.5 ) in un sterilized soil was 56.2 d for fenpropathrin, 57.8 d for mixed fenpropathrin, 48.2 d for phoxim, and 41.7 d for mixed phoxim. The corresponding half life (T 0.5 ) in sterilized soil was 135.1 d, 147.3 d, 123.6 d, and 126.2 d, respectively. There were no significant differences for degradation rates between single use and mixed use of fenpropathrin and phoxim.
The effect of 5% fipronil flowable formulation and 95% malathion pure chemical on topmouth gudgeon ( Pseudorasbora parva ) was studied. The toxicity of 0.08 mg/l fipronil and 7 mg/l malathion mixture to topmouth gudgeon was greatly improved compared to the single 0.08 mg/l fipronil or 7 mg/l malathion. The potentiation toxicity index was 1000,much greater than 20,the threshold. After 48 hours administration, the AChE activity from the 0.01 mg/l fipronil and 1 mg/l malathion mixture treatments was nearly the same as that from the single 1 mg/l malathion treated .During recovery period, the former was lower than the latter and after 144 hrs, 192 hrs, the difference was significant (p<0.05) respectively. This enhances the unsafety for fish to live in the environment where there is continuous or repeated AChE inhibitors. The significance of recovery study was also discussed.
