ABSTRACT
The fate of the insecticide chlorpyrifos (as Dursban® 4E) was studied in macrophyte-dominated and macrophyte-free indoor microcosms (0.7 m3) and outdoor macrophyte-dominated experimental ditches (40 m length). The insecticide was applied to the surface of the test systems to achieve a nominal concentration of 35 µg/L−1. A comparison was made between the fate of chlorpyrifos in these different test systems. To study the stratification of chlorpyrifos in the water column, water samples were taken at three different depths. To investigate the partitioning and disappearance of chlorpyrifos, integrated-depth water samples, macrophytes and sediment samples were collected at several times post-application. Stratification of chlorpyrifos occurred in all test systems during the first 24 hours post-application. In the indoor microcosms, stratification was more pronounced than in the outdoor ditch. The duration of the stratification was dependent on the macrophyte biomass and its spatial structure. A large part of the dose of chlorpyrifos applied was sorbed to the macrophytes. In macrophyte-free systems the sediment compartment was the most important sink. For all test systems the rate of disappearance of chlorpyrifos was relatively fast in the water and macrophytes and relatively slow in the sediment. The partitioning and the rate of disappearance of chlorpyrifos in the macrophyte-dominated microcosms were comparable with the observations in the outdoor experimental ditches.
