Silent killer stopped by science

Cefas research has led to a ban on the sale of cypermethrin sheep dips throughout the UK. Cypermethrin sheep dips are powerful chemicals based on synthetic pyrethroids. These have a toxic effect on the reproductive systems of certain fish, particularly salmon. Research from several countries also shows that carp and other river life are similarly affected.

Dr Andy Moore, based at Cefas' Lowestoft laboratory, said: "These chemicals are seriously toxic: one part per billion has a serious effect on fish reproduction. The chemical significantly reduces the sperm produced by the spawning male salmon, and the chances for egg survival. Such harm has serious implications for the survival of salmon, seas trout and wild brown trout populations."

Sheep dips routinely enter watercourses from numerous pathways including disposal on fields, "washing off" the wet fleece of sheep, and waste from fleece processing. As long ago as 1997, when these dips became widely used, the Salmon and Trout Association (S&TA) and the Anglers' Conservation Association (ACA) jointly called for a ban.

The Veterinary Medicines Directorate (VMD) acknowledged that the toxicological information showing the serious damage the sheep dips have on the environment was too overwhelming to ignore. Chemical manufacturers were unable to provide adequate information or guidance on the pollution risk so the VMD took the action of banning the sale of cypermehrin sheep dips.

"This ban is a notable victory, for flylife, fisheries and the environment," says Paul Knight, Director of S&TA. "All contributors should feel proud."