Species sensitivity distributions ( SSD ) method was used to assess the acute ecological risk of four commonly-used organophosphorus pesticides ( diazinon, parathion , fenitrothion and malathion) to freshwater organisms. The acute toxicity data ( LC50 ) were collected from ECOTOX database and SSD curves were fitted based on BurrⅢ function. The acute ecological risks of the organophosphorus pesticides and the sensitivity of vertebrate and invertebrate (including fish, crustaceans, insects and spiders) to these pesticides were compared by the hazardous concentrations for 5% of the species ( HC5 ) and the potential affected fraction (PAF). The joint ecological risks of the organophosphorus pesticides in the Yellow River, Jiulongjiang River, and Wuxiaochuan River were also analyzed. The following results were obtained: 1 ) by comparing the HC5 and PAF values, the toxicities and ecological risks of the organophosphorus pesticides to invertebrates were significantly higher than those to vertebrates, and the largest toxicities and ecological risks were found to crustaceans, while the minimum to fish. 2) It was found by comparing the SSD curves that, in case of the log-transformed concentration less than 3. 5 μg/L, the ecological risks of four organophosphorus pesticides to invertebrates were significantly higher than those to vertebrates; on the contrary, in case of the log-transformed concentration larger than 4. 5μg/L, those to vertebrates were higher. 3 ) In the vast majority of exposure concentrations, invertebrates were more sensitive to the organophosphate pesticides than vertebrates. Under lower exposure concentrations, crustaceans were more sensitive to the organophosphate pesticides; while, under higher exposure concentrations, insects and spiders were more sensitive. 4) The PAFs and multisubstance PAFs(msPAFs) of parathion and malathion to the freshwater organisms in the Yangtze River, Jiulongjiang River, and Wuxianchuan River were less than 0.5% , which imply that their ecological risks wcre very low.%构建了4种常用有机磷农药(二嗪磷、对硫磷、杀螟硫磷和马拉硫磷)对淡水生物的物种敏感性分布(SSD)曲线,计算了4种有机磷农药对不同淡水生物的5％危害浓度(HC5)及其不同暴露浓度对淡水生物的潜在影响比例(PAF),分析了4种有机磷农药的急性生态风险,比较了脊椎动物和无脊椎动物(包括鱼类、甲壳类以及昆虫与蜘蛛类)对4种有机磷农药的敏感性,评估了3个典型水体中常用有机磷农药的联合生态风险.结果表明:1)通过HC5和PAF值的比较发现,4种有机磷农药对无脊椎动物的毒性与生态风险明显高于脊椎动物,对甲壳类的毒性与生态风险最大,对鱼类的毒性与生态风险最小.2)通过SSD曲线的对比发现,当对数暴露浓度小于3.5 μg/L时,4种有机磷农药对无脊椎动物的生态风险明显高于脊椎动物；而当对数暴露浓度大于4.5 μg/L时,其对脊椎动物的生态风险较大.3)在绝大多数暴露浓度下,无脊椎动物比脊椎动物对4种有机磷农药更敏感；在较低暴露浓度下,甲壳类对4种有机磷农药的敏感性较高；而在较高暴露浓度下,昆虫和蜘蛛类对其敏感性较高.4)长江、九龙江和五小川流域水体中对硫磷与马拉硫磷对淡水生物的PAF以及它们的复合潜在影响比例(msPAF)均小于0.5％,生态风险很低.
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