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-(14)C] glucose, uptake of (14)C-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 7d a larger proportion of added glucose was allocated to microbial biomass rather than respired to CO(2). 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-(14)C] glucose mineralisation rates, as well as a decline in microbial uptake of [1-(14)C] 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.

Influence of plants on the chemical extractability and biodegradability of 2,4-dichlorophenol in soil.

This study investigated the fate and behaviour of [UL-(14)C] 2,4-dichlorophenol (DCP) in planted (Lolium perenne L.) and unplanted soils over 57 days. Extractability of [UL-(14)C] 2,4-DCP associated activity was measured using calcium chloride (CaCl(2)), acetonitrile-water and dichloromethane (DCM) extractions. Biodegradability of [UL-(14)C] 2,4-DCP associated activity was assessed through measurement of (14)CO(2) production by a degrader inoculum (Burkholderia sp.). Although extractability and mineralisation of [UL-(14)C] 2,4-DCP associated activity decreased significantly in both planted and unplanted soils, plants appeared to enhance the sequestration process. After 57 days, in unplanted soil, 27% of the remaining [UL-(14)C] 2,4-DCP associated activity was mineralised by Burkholderia sp., and 13%, 48%, and 38% of (14)C-activity were extracted by CaCl(2), acetonitrile-water and DCM, respectively. However, after 57 days, in planted soils, only 10% of the [UL-(14)C] 2,4-DCP associated activity was available for mineralisation, whilst extractability was reduced to 2% by CaCl(2), 17% by acetonitrile-water and 11% by DCM. This may be due to the effect of plants on soil moisture conditions, which leads to modification of the soil structure and trapping of the compound. However, the influence of plants on soil biological and chemical properties may also play a role in the ageing process.

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

Sheep dipping with organophosphate or synthetic pyrethroid-based formulations is still widely used by farmers in the UK to control ectoparasites and results in 175-220 million litres of spent sheep dip produced each year. Spent sheep dip may be diluted in animal slurry or water prior to disposal onto land. However, the effects of this practice on the microbial ecology of animal slurries, soil and aquatic systems are still relatively unknown. This paper investigated the effect of Bayticol (synthetic pyrethroid sheep dip) and Ectomort (organophosphate sheep dip) concentrations on (i) the survival of 15 protozoan species, (ii) the recovery of the four species of amoebae, and (iii) bacterial survival and growth. This investigation found that overall Bayticol was less toxic to protozoa than Ectomort, with minimum inhibitory concentrations ranging from 0.01 to 0.03% (v/v) and 0.005 to 0.06% (v/v), respectively. Amoebic cysts remained viable and emerged from dormancy, thereby pointing to the potential for recovery of protozoan communities in contaminated environments. The presence of sheep dips did not affect bacterial survival and growth on agar; however, the five test bacteria were not able to utilise the sheep dips as sole carbon sources. These findings have implications for the contamination of animal slurries, soil and aquatic systems, in that there is the potential for significant increases in microbial numbers, containing putative pathogens due to the diminution of bacteriophagous protozoan populations.