The effects of the disposal of organophosphate and synthetic pyrethroid sheep dips on non-target organisms on farmland
The 1998 Groundwater Regulations required spent organophosphate and synthetic pyrethroid sheep dip to be disposed to farmland. The effects of dip disposal on soil invertebrates and the possible consequences for their bird predators were investigated on farms across Britain between 1999 and 2002.A preliminary survey of dip disposal practice on 42 hill farms on, or adjacent to SSSls that support breeding waders, exposed a wide variety of practices and considerable deviation from the recommended procedures in many cases. Paired disposal and control sites were sampled on a subset of the surveyed farms. Invertebrate abundance was estimated by taking soil samples, followed by Berlese extraction (or hand sorting for worms), pitfall trapping and suction sampling. Invertebrate densities on disposal sites were significantly lower than on control sites in 7 out of 15 cases and the multivariate analysis indicated significant effects of dip disposal on carabid, but not spider, species composition six months after application. Density reductions were greatest on areas that had been used for dip disposal over many years. Plots were set up in a "Latin-square" design on two experimental farms, allowing comparison of the effects of the two insecticides at two dilutions under controlled conditions. The same sampling methods were used as on the farm sites and densities of all invertebrate groups, except linyphiid spiders and carabid beetles, were significantly reduced on the disposal plots on one or more sampling occasion after application. Soil surface invertebrates taken by suction sampling showed the most severe and consistent reductions. A risk assessment suggests that spring disposal could compromise upland wading chick survival. However, the current scale of dip disposal in Britain does not pose a threat to whole bird populations.