The impact of synthetic pyrethroid and organophosphate sheep dip formulations on microbial activity in soil

Sheep dip formulations containing organophosphates (OPs) or synthetic pyrethroids (SPs) have been widely used in UK, and their spreading onto land has been identified as the most practical disposal method. In this study, the impact of two sheep dip formulations on the microbial activity of a soil was investigated over a 35-d incubation. Microbial utilisation of [1-14C] glucose, uptake of 14C-activity into the microbial biomass and microbial numbers (CFUs g−1 soil) were investigated. In control soils and soils amended with 0.01% sheep dip, after 7 d a larger proportion of added glucose was allocated to microbial biomass rather than respired to CO2. No clear temporal trends were found in soils amended with 0.1% and 1% sheep dips. Both sheep dip formulations at 0.1% and 1% concentrations resulted in a significant increase in CFUs g−1 soil and [1-14C] glucose mineralisation rates, as well as a decline in microbial uptake of [1-14C] glucose, compared to control and 0.01% SP- or OP-amended soils. This study suggests that the growth, activity, physiological status and/or structure of soil microbial community may be affected by sheep dips.