The short-term effects of endosulfan discharges on eucalypt floodplain soil microarthropods

The insecticide endosulfan is extensively used in the Australian cotton gro wing industry. Irrigation tailwater contaminated with endosulfan is release d onto floodplains to avoid direct entry into river systems where endosulfa n is highly toxic to fish. We examined the short-term effects of endosulfan , at levels likely to be present in tailwaters, on soil arthropods on such a floodplain near Moree, NSW. The study consisted of four treatments: a dry control (replicates untreated), wet control (replicates flooded with water only), 1 mug/l endosulfan and 10 mug/l endosulfan. Treatments were applied in the middle of summer and soil invertebrate samples were taken 1 week. 1 month and 2 months following treatment. Invertebrates were sorted to order level and oribatid mites to species. Endosulfan sulphate was detected in a ll treatments, including the two controls, most likely the result of spray drift. The focus of the experiment was therefore to explore the short-term impacts of endosulfan contaminated tailwater on communities that had been p reviously exposed to endosulfan. More than 7700 arthropods were collected f rom a total sample area of 0.336 m(2). The dominant groups were the prostig matid and oribatid mites (35 species), collembolans and hemipterans. Our an alyses did not detect any short-term effect of the endosulfan treatments on the number of individuals, spatial aggregations or community structure of the soil fauna. There were clear responses to changes in soil moisture rela ted to treatment applications. The study, therefore, made two important fin dings: (1) a diverse and abundant soil fauna persists on floodplains expose d to endosulfan contaminated tailwater, and (2) this diverse and abundant s oil fauna were unaffected by the addition of endosulfan at concentrations c ommon to tailwater run-off from cotton fields. There is clearly a need to d etermine whether these findings can be extended to soil arthropod biodivers ity in areas previously unexposed to endosulfan. (C) 2001 Elsevier Science B.V. All rights reserved.