除蟲菊精類殺蟲劑芬化利與其他四種殺菌劑對端足蟲 (Hyalella azteca) 之混合毒性效應

Abstract

To ensure the production and the quality of crops, the application of pesticides is necessary during agricultural activities. The fate of these sprayed compounds would inevitably enter the aquatic system. Hence, the sediment becomes the sink of pollutants. Acute toxicity test of non-target organisms are an important way to assess the environmental risk of pesticides. In this study, amphipods Hyalella azteca was selected as test organism to evaluate the toxicity of six pesticides. There are five commonly used pesticides in Taiwan: imidacloprid, fenvalerate, prochloraz, hexaconazole and difenoconazole, and including a frequently detected herbicide atrazine in ground water. The result showed that fenvalerate is the most toxic compound toward H. azteca during the 7 d acute toxicity test, demonstrating a 50% of lethal concentration (LC50) is 16.7 ng L-1. Compared with previous research, pyrethroids are more toxic to H. azteca than other types of pesticides. Some fish species are as sensitive as H. azteca to pyrethroids because of the slow metabolic rate of parent compound. Esterase is the main metabolic enzyme of pyrethroids in vivo. In this research, esterase was extracted from H.azteca. The maximum velocity of esterase (Vmax) was compared with other animals in literature. We found that the Vmax of H. azteca esterase extractions is slower than those from medaka, splittail, salmon and porcine. After 7d exposed to the fenvalerate, the esterase activity in H. azteca decreases with the increasing concentration of fenvalerate. It is known that esterase is an important detoxification enzyme in vivo. As the esterase can be inhibited by fenvalerate, the addition of other pesticides may exert higher toxicity to non-target organisms. Four fungicides: prochloraz, difenoconazole, iprodione and procymidone were selected and mixed with fenvalerate to exam the joint effect on H. azteca in 7d acute toxicity test. The results showed that under 1 and 2 ng L-1 fenvalerate, the LC50 of prochloraz is decreased from 0.25 to 0.05 and 0.04 mg L-1 respectively. Difenoconazole is decreased from 0.21 to 0.02 mg L-1. Iprodione is decrease from 6.32 to 3.97 and 5.58 mg L-1. The fenvalerate treatment with procymidone make no significant different in LC50 under 95% confident interval. This research indicated that under low concentrations of fenvalerate, the toxicity of other fungicides would be increased. Thus, when applying pyrethroids, we should consider the synergic toxicity effects of more than one pesticide rather than merely singular toxicity effects toward non-target organisms.