Abstract: Earthworms as test animats,were exposed in different concentrations of two pesticides:1(6 chloro 3 pyridinylmthyl)N nitromidazoliding-2-ylideneamin and 2′benzoyi 1′ tert butylbenzoylhydrazinc.The acute toxicity of these two pesticides was measured as median lethal concentration values(LC₅₀)of earth worms.Tests of three different exposure systems were performed:the comact filter paper bioassay,the immersion bioassay and the artificial soil bioassay.The results indicated that the two new type pesticides showed vaious toxic effects through different exposure paths.The LC₅₀ of 1(6 chloro 3 pyridinymethyl)N nitromidazolidin-2-ylideneamine was 0.034 ug·cm^-2 for 48hr filter paper test,0.77mg·ml^-1 for 48hr inmersion test and 2.3mg·kg^-1 for 14d artiflcial soil test,respectively; while the 2′ benzoy 1′tert butylbenzoylhydrazine was>480 μg·cm^-2 for 48hr filter paper test. 2655 mg·ml^-1 for 48hr immersion test,and>10000mg·kg^-1 for 14d artificial soil test,respectively.These outcome led to a conelusion that 1(6 chloro 3 pyridinylmethyl)N nitromidazolidin-2-ylideneamine was far more toxic than 2′ benzoyl 1′tert butylbenzoylhydrazine with regard to acute toxicity to earthworm.However,the comprehensive assessment of the influence of both the two pesticides to soil ecosystem could not be made only by acute toxic tests because we were not aware of the mechanism acted on organisms.

Key words: bottom trawl survey, index of relative importance (IRI), dominant species, ecological niche, Yangtze River estuary.