The Risk Assessment Of Butachlor And Chlorpyrifos On Plankton In Aquatic Ecosystem

Butachlor and chlorpyrifos are the pesticides currently being used in a large-scale in paddy fields of China. Due to the characteristics of irrigation and drainage of rice cultivation, pesticides can easily enter the surrounding waters ecosystems of paddy fields, posing a threat towards various organisms in the aquatic ecosystem. As a starting point, the phytoplankton in channels surrounding farmland were firstly surveyed in the paper, and10species of algae easily expanding and cultivating were isolated, and then the toxicology effect and the Species Sensitivity Distribution (SSDs) of two pesticides butachlor and chlorpyrifos on the10species of algae were also assessed. Accordingly, the indoor standardized aquatic microcosm (SAM) and typical microcosm were builded using6species of algae easily counting and other common zooplankton for assessment of the risks of butachlor, chlorpyrifos in the aquatic ecosystem.The results of single species toxicity test showed that, the toxicity of butachlor on10species of algae were, Monoraphidium sp.> Selenastrum bibraianum>Scenedesmus obliquus> Chlamydomonas> Asterococcus Scherffel> Navicula> Chlorella vulgaris> Scenedesmus> Synedra> Spirogyra, in which the medium toxicity was observed on the Synedra and Spirogyra, while the high toxicity level were observed on the remaining8species of algae. Chlorpyrifos showed high toxicity on Monoraphidium sp., Asterococcus Scherffel, Chlorella vulgaris and Scenedesmus obliquus, and the medium toxicity on Synedra, Selenastrum bibraianum, Navicula and Spirogyra, and the low toxicity on Chlamydomonas and Scenedesmus. By constructing the SSDs curve, the safety concentration of pesticides on algae was calculated. Then according to the measured environmental concentration of pesticides, ecological risk on algae was also assessed. The test results showed that, the hazardous concentration5%(HC5) of butachlor and chlorpyrifos on algae were9.3μg/L and27.9μg/L respectively.In the indoor standardized aquatic microcosm test, the PRC analysis results showed that butachlor exerted the greatest impact on the Selenastrum bibraianum and the less impact on Scenedesmus, Chlorella vulgaris and zooplankton, and the imapct of which on the Monoraphidium sp., Scenedesmus obliquus and Navicula didn’t reflect the does-dependent relationship. In the early stage (within14ds), the concentration0.1μg/L of butachlor showed stimulative effect, but then showed inhibitory effect later, and then showed stimulation effect again after24d. Within the concentrations of1-1000μg/L, butachlor showed different degrees of inhibition, which was stronger when the concentration was higher; the system began to recover after21d and the inhibitory effect was weakened after28ds. In terms of inhibition, it could be infered that the no observed effect concentration on algae was0.1μg/L in the indoor standardized aquatic microcosm after applcation of butachlor.In the indoor typical microcosm test, after the application of butachlor and chlorpyrifos, the pesticides were also considered as environmental factors, and then all the environmental factors as explanatory variables, to analyze the effects of environmental factors on plankton. Both the results of the butachlor and chlorpyrifos microcosm tests showed that, the DO, pH and EC were positively correlated with the phytoplankton, and the nitrate nitrogen, ammonium nitrogen were negatively correlated with the phytoplankton. The difference was, the butachlor was negatively correlated with the phytoplankton while the chlorpyrifos was almost uncorrelated with the phytoplankton, the butachlor was somewhat negatively correlated with the zooplankton while the chlorpyrifos was much negatively correlated with the zooplankton. In terms of inhibition, it could be infered that the no observed effect concentration on algae was1μg/L in the indoor typical microcosm after application of butachlor, and the concentration on zooplankton was10μg/L. The no observed effect concentration on algae was10μg/L in the indoor typical microcosm after applying chlorpyrifos, and the concentration on zooplankton was10μg/L.