Impact of synthetic pyrethroid-sheep dip on the indigenous microflora of animal slurries

Abstract

The chemical constituents of sheep dip in the UK are currently changing from organophosphate-based to synthetic pyrethroid-based insecticides. As a result, changes are also being made to the methods of disposal of these chemicals in the environment, such that pyrethroid sheep dips must now be diluted in animal slurry or water. To date, there is a lack of quantitative information on the impact of the insecticide on the indigenous microflora of animal slurries. This paper investigated the impact of Bayticol (synthetic pyrethroid sheep dip) over a range of concentrations on selected populations of bacteria within animal slurry. It was found that, with increasing pesticide concentration, there was up to a four orders of magnitude increase in the numbers of faecal coliforms and pathogens, such as putative Salmonella spp. These findings have implications for the disposal of sheep dip-amended animal slurries to land from several aspects: (i) the longevity of putative pathogens in the field may require re-evaluation of the time required before the return of grazing livestock to a slurry-amended field; (ii) the potential for the transfer of pathogenic bacteria and faecal coliforms into human and animal foodchains, and (iii) the increased potential for faecal coliforms being washed into streams, rivers and coastal bathing waters. ß

Effects of organophosphate and synthetic pyrethroid sheep dip formulations on protozoan survival and bacterial survival and growth

“…It must be noted that our results cannot be directly extrapolated to slurry systems. In Semple et al [8], a concentration of 0.02% SP in animal slurry showed no effect on bacterial populations, despite being at or above the MICs of most protozoa tested in this study. At 1% SP, however, the dramatic increase in faecal coliform numbers correlates with the significant protozoan mortality found here.…”

“…In Thirup et al [19], the inhibition of protozoa by Corbel ® , a formulation containing the fungicide fenpropimorph, resulted in an increase in early‐colony‐forming bacteria. In animal slurries, bacterial populations may grow unchecked, as the exponential increase of faecal coliforms and faecal streptococcus populations in slurries containing fresh SP dip has shown [8]. The scale of the contamination is dependent upon microbial number and survival in the soil and water environments.…”

“…A study of the indigenous microflora of animal slurries containing Bayticol, an SP‐based sheep dip with 6% flumethrin, reported an increase in faecal coliforms, heterotrophic and protolytic bacteria as well as putative Salmonella sp. of up to four orders of magnitude compared to control slurries [8]. Two hypotheses were proposed for the observed increase in bacterial abundance.…”

Campylobacters in water, sewage and the environment

“…However, compared to the situation with sewage sludge, the lack of quality control on the disposal of farm slurries put to land is a cause of increasing concern (McCann 1999). Co‐disposal of spent, pyrethroid‐based sheep dip with farm slurry resulted in the disappearance of campylobacters from the slurry (Semple et al. 2000).…”

Mitigation and Current Management Attempts to Limit Pathogen Survival and Movement Within Farmed Grassland

“…The on farm practicalities associated with acid treatment, such as management requirements, safety precautions and potential corrosion of steel and concrete stores means that in reality only a specialist contractor would be able to facilitate this management option (Chambers, 2003) The use of sheep dips in the form of synthetic pyrethroid (SP) insecticides within UK agriculture replaced organophosphate (OP) insecticides after health risks to farmers were associated with the latter. As a result, SP's are now the most commonly used sheep dips within the UK (Semple et al, 2000). Ho wever, SP's are considerably more toxic than OP's for aquatic life-forms (Virtue and Clayton, 1997) and thus sheep dip contamination of watercourses can have detrimental effects on aquatic ecosystems (Hooda et al, 2000).…”