Defra says sheep dip research can continue - with fundamental changes

A landmark study into the human health effects of organophosphate (OP) chemicals used in sheep dip will resume, according to the UK’s Department of environment food and rural affairs (Defra). 

Defra commissioned the study four years ago, but in June this year the lead scientists were told that the project may be shut down after a review panel working for the Veterinary Medicines Directorate (VMD) questioned their research protocol.

OPs are nerve toxins used in sheep dips to combat sheep scab, caused by a particularly resilient parasite that lives in the sheep’s fleece. But many farmers have reported symptoms, including cognitive effects, fatigue and muscle paralysis, which they attribute to the continued use of OPs. 

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Organophosphate sheep dips are still a cause for concern

  Still, there is substantial scientific uncertainty about this connection. Defra’s study, led by Sarah Mackenzie-Ross of University College, London, is unique in combining a psychological assessment of farmers with blood tests that should pin down the links between OPs and these symptoms. However, the VMD’s review panel had raised concerns about the study’s selection of a control group - people who had never been exposed to OPs.   

’The experts on the [review panel] took issue with this study as they were not satisfied that a suitable control group had been found,’ a spokesperson for Defra told Chemistry World. ’Since there is a large amount of public money being spent on this work, it is right and proper that the study be scrutinised for scientific validity.’     

Reprieves and caveats   

’Defra have now told us that they want the study to continue and that it was never their intention to close it down,’ Mackenzie-Ross told Chemistry World. ’But that was clearly the intention of the VMD.’     

McKenzie-Ross has been instructed by Defra that she must make some changes to her study, including the addition of an epidemiologist to her research team.   

’We are going to carry on working, but to ask an epidemiologist to join at this late stage is going to be difficult,’ she said. ’Why would someone want to join a study that is near completion?’   

The study must also identify an acceptable control group. But Mackenzie-Ross told Chemistry World  that she has already presented the VMD with twelve options for possible control groups, which they rejected without offering advice on a more suitable selection.   

McKenzie-Ross added that after more than five months of delay, some of the 160 farmers who were participating in her research have pulled out. Her next task is to produce a follow-up report for Defra detailing how she has met their requirements.   

Victoria Gill