An Experiment With Outdoor Aquatic Microcosms:the Study Of Chlorpyrifos

With the prohibiting of high toxic pesticides, chlorpyrifos has gradually become the important substitute. The safety of chlorpyrifos to the environment is therefore getting more and more attention. As a valuable unit for ecological toxicology studies, microcosm is more and more commonly applied in assessment of pesticides and other environmental pollutants. On the basis of indoor single-species toxicity test, the inhibition and recovery of zooplankton community under various concentrations (0.1～1968.3μg/L) of chlorpyrifos and the effect of the insecticide application on water quality were studied in this paper with macrophyte-dominated outdoor microcosms of500L each.Research showed that:the sensitivity of the five zooplanktons towards chlorpyrifos was Simocephalus vetulus> Daphnia manga> Dolerocypris sinensis Sars> Eucyclops serrulatus> Brachionus calyciflorus.In the treatment of five lower concentrations, i.e.0.1μg/L,0.3μg/L,0.9μg/L,2.7μg/L and8.1μg/L, the actual concentrations were all lower than0.1μg/L after1d. In the treatment of five higher concentrations, i.e.24.3μg/L,72.9μg/L,218.7μg/L,656.1μg/L and1968.3μg/L, the actual concentrations of chlorpyrifos in microcosm changed over time, but they were significantly lower than expect(?)es. For the concentration of656.1μg/L and1968.3μg/L, the actual concentrations of chlorpyrifos could be detected till the end of the experiment.The principal component analysis (PCA) of the water quality parameters indicated that chlorpyrifos had no obvious impact on pH and TOC content of water within the microcosms, whereas it showed off the sign to alter the level of N and P. This suggested necessity to pay attention to the extent and mechanism of eutrophication caused, directly or indirectly, by the insecticide applications.The result showed that for cladocera, the no observed effect concentration (NOEC) of chlorpyrifos was found to be2.7μg/L, and when the concentration was increased to8.1μg/L, the community was restrained and the inhibition effect did not disappear till7d after the dose administration. When the concentration of chlorpyrifos was increased to72.9μg/L, the inhibition effect was also detected and it was found last for42d, and when the concentration was further increased to656.1μg/L, the inhibition effect did not disappear till end of the study (i.e.150d after the dose administration). As for copepoda, the NOEC of chlorpyrifos was determined to be24.3μg/L, and when the concentration was increased to72.9μg/L, the community was restrained and the inhibition effect did not disappear till end of the study. Compared with the cladocera and the copepoda, the rotifer was the most insensitive to the exposures of chlorpyrifos. Stimulation was detected with respect to the community at the relative low concentrations (i.e.0.1μg/L). Along with the increase of the administrative concentrations, the community was restrained at several time points, and in spite of that, no "dose-effect" relation was found between the rate (or the persistence) of the restrains and the concentrations applied, and therefore the NOEC of chlorpyrifos could not be determined for this community within the scope of concentrations to be tested.