以水蚤急毒性試驗研究有機磷農藥之定量結構-活性關係

Abstract

有機磷農藥被廣泛用於農作物生長，防治病蟲害，其施用後可能經由灌溉或降雨使得這些有毒物質流入河川、湖泊或地下水中，對水體環境生態系造成影響，故本篇研究十種有機硫代磷酸酯類物質對水蚤之急毒性影響。從單一急毒性結果來看，化合物Phoxim對水蚤最具毒性，從結構式來看Phoxim與其他化合物之差異為其帶有苯乙腈官能基，其電荷密度分布不同造成電子傳遞而產生較高毒性。 在QSAR分析方面，疏水性參數log Kow毒性值迴歸相關性佳(r2 = 84.5%)，此結果顯示化合物毒性機制主要貢獻來源為藉由通透細胞膜滲入到細胞體內造成毒性。增加反應性參數只些微提升了方程式r2值，顯示反應性參數並非反應中速率限制步驟。從結果得知有機硫代磷酸酯雖被分類為乙醯膽鹼酯酶抑制有機物，但其對於水蚤毒性機制偏向於麻醉性。 風險評估方面，蒐集文獻數據和本研究急毒性及推估慢毒性數據計算風險商數，大部分RQ＞1，顯示此類化合物具潛在風險。比較急慢毒性數據計算之RQ值，顯示急毒性數據有高估風險的可能。

This study present the toxicity data of ten organothiophosphorus compounds to Daphnia magna using 48-hours acute toxicity test. Results indicate that Phoxim is the most toxic compound, the reason caused higher toxicity of Phoxim is dependent on its higher charge density due to benzyl cyanide group. Quantitative structure-activity relationships (QSARs) were established between the EC50 values and various molecular descriptors, and a highly predictive two-variable QSAR models were obtained. According to QSAR models, the toxic mechanism was highly related to hydrophobicity of these compounds, and this result indicated that organothiophosphorus compounds caused toxicity to Daphnia magna mainly due to permeate through membrances, changing the components of the cell membrances. Adding reactive parameters slightly improve the r2 values indicated that the reaction rate of the organothiophosphate with AChE, the conversion of organothiophosphate to organophosphate and the molecule polarity are not rate-limiting steps. The preliminary environmental risk assessment was conducted following the European Union RQ model. Results point out that most of these compounds exist potential risks to aquatic environment. Risk quotient derived from acute and estimated chronic toxicity data were different, using acute toxicity data may overestimate the risk quotient value.