Sheep Dip – Update by Ceri Evans

Cypermethryn in sheep dip was identified some years ago as causing widespread pollution in rivers

Sheep Dip Update October 2007



Cypermethryn in sheep dip was identified some years ago as causing widespread pollution in rivers and its sale was suspended in February 2006. Since then only products already on-farm could be used.



As there was limited information available regarding sheep husbandry practices in controlling skin parasites the EA carried out target monitoring of rivers in sheep areas in England and Wales from May 2006 and February 2007 and also conducted a Q and A survey. A number of methods were used including water and moss sampling for both cypermethryn and diazinon dip chemicals and invertebrate kick sampling.



The interim results have been circulated.


  • The moss samples showed impacts by both chemicals.
  • The water sampling detected both chemicals in the sheep areas and in wool processing areas.
  • Diazinon was detected more often (more widely used) but where cypermethryn was found the level was most likely to exceed the Maximum Allowable Concentration. The MAC has since been reduced in the Water Framework Directive.
  • The invertebrate sampling showed few areas with very low BMWP scores but scores above 50 were not subdivided so it is not possible to distinguish between ‘fair’ and ‘good’ population rivers.



Although the use of cypermethryn declined after it was withdrawn most farmers had already changed to pour-on well before this date. A quick improvement in invertebrate numbers is being observed in most areas.



A survey of sheep farms in 2006 showed that 22% dipped their sheep, 53% used pour-on, 16% injected, 13% jetted and 14% (small farms) did not treat. In Wales there was an increase in the use of diazinon in 2006 and a fall in the use of cypermethryn to some 3% of farms.


The above uses EA data.



The report is yet to be discussed but paints quite a bleak outlook for cypermethryn in particular. We can only hope that the WFD will enforce greater care in the use of farm chemicals and ensure cleaner rivers and a healthier environment