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

The insecticide endosulfan is extensively used in the Australian cotton growing industry. Irrigation tailwater contaminated with endosulfan is released onto floodplains to avoid direct entry into river systems where endosulfan 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 all 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 previously exposed to endosulfan. More than 7700 arthropods were collected from a total sample area of 0.336 m(2). The dominant groups were the prostigmatid and oribatid mites (35 species), collembolans and hemipterans. Our analyses 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 related to treatment applications. The study, therefore, made two important findings: (1) a diverse and abundant soil fauna persists on floodplains exposed to endosulfan contaminated tailwater, and (2) this diverse and abundant soil fauna were unaffected by the addition of endosulfan at concentrations common to tailwater run-off from cotton fields. There is clearly a need to determine whether these findings can be extended to soil arthropod biodiversity in areas previously unexposed to endosulfan. (C) 2001 Elsevier Science B.V. All rights reserved.