A landmark study will resume

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 could be shut down after a review panel working for the Veterinary Medicines Directorate (VMD) questioned their research protocol (see Chemistry World November 2006, p8). 

OPs are nerve toxins used in sheep dips to combat sheep scab, caused by a 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. 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 [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.’ 

MacKenzie-Ross has been instructed by Defra to make changes to the study, including the addition of an epidemiologist to her research team. ’We are going to carry on, 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. She 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