EFFECTS OF CHLORPYRIFOS ON A MICROECOSYSTEM

Abstract

A recirculating aquatic microecosystem consisting of three subsystems and with a total volume of 7.5 L was used to study effects of the insecticide chlorpyrifos. The three subsystems represent the trophic levels of primary producers (algae), herbivores (Daphnia magna), and decomposers (bacteria on a sand filter). Two of four microecosystems were perturbed with chlorpyrifos 429 d after they were started. All subsystems were monitored weekly for several chemical and biological variables. The response of the systems was followed for 130 d after chlorpyrifos application. An immediate decrease of the Daphnia population could be explained from the mortality observed in single species tests. The population recovered within two weeks. Two weeks after the introduction of chlorpyrifos, the pH in all subsystems dropped by about two units. Concurrent with the pH changes, there were changes in the algal biomass, the Daphnia numbers, and the oxygen concentrations. The pH in the treated systems was comparable to the controls about 90 d after the treatment, but the other variables did not recover. These effects were not predicted by any single-species test and, therefore, represented ecosystem effects.