Study on the Mixture Toxicity of Organophosphorus (OP) Pesticides

Abstract

Organophosphorus (OP) pesticides have been largely produced and utilized in China and have been become ubiquitous contaminants in water. For single pesticides, their individual hazard has been well established. OP pesticides, however, frequently occur as mixtures, rarely as pure compounds, in most cases and have been detected as mixtures in the water bodies. Though the concentrations of single pesticides in the environment are less than their individual security control standards, the joint toxicities of the mixtures of organic pesticides have been attracted more and more attention. To examine the mixture toxicity with various compositions, the uniform design (UD) is employed to design the mixtures, which can explore the concentration variation with few experimental efforts. Two equivalent-effect concentration mixtures are also applied to build the whole concentration–response curves.. The mixture toxicities of OP pesticides are predicted by two models, concentration addition (CA) and independent action (IA). The results showed that the joint toxicity of all the OP mixtures could be well predicted by CA. However, the model of IA tends to underestimate the joint toxicity of all OP mixtures. The mixture toxicity based on SSD approach and the model of CA is applied to assess the mixture risk of five OP pesticides in Lake Taihu. The results show that the risk quotients of OP pesticide mixtures were greater than 1. The HC5-95 % values derived for five OP pesticides are much higher than the environmental quality standards for surface water set by China. It is suggested that the mixture toxicity of OP pesticides should be taken into account when setting the water quality criteria of OP pesticides.