Effects of Pesticide Mixtures on Zooplankton Assemblages in Aquatic Microcosms Simulating Rice Paddy Fields

The individual and combined effects of pesticides (chlorpyrifos, triadimefon and butachlor) on the zooplankton assemblages of microcosms were investigated. Laboratory microcosms were constructed with water and sediment to simulate aquatic conditions in China's rice paddy fields. Results from principal response curves analysis showed that butachlor and triadimefon had no significant impact individually on the population level in zooplankton assemblages. The deleterious effects of pesticide mixtures on the zooplankton were mainly caused by chlorpyrifos. In fact, assemblage succession only occurred in the treatments containing chlorpyrifos. There was no synergy effect on the microcosm from combinations of pesticides on the assemblages. The zooplankton assemblages affected by chlorpyrifos did not recover at the termination of the experiment, i.e., after 56 days.