Exposure of non-target vertebrates to second-generation rodenticides in Britain, with particular reference to the polecat Mustela putorius

In Britain, the use of "second-generation'' rodenticides has become widespread on agricultural premises. The high toxicity and relatively long half-lives of these compounds has raised concerns over potential secondary exposure and poisoning of non-target predators. Over the last 15 years, exposure has been extensively documented in the barn owl Tyto alba but relatively little is known about mammalian terrestrial predators. This paper reviews recent studies and demonstrates that there is evidence of both secondary exposure and secondary poisoning in a variety of non-target, terrestrial mammals in Britain. It also presents new data on rodenticide levels in the polecat Mustela putorius which preys on farmyard rats in winter in Britain and ist therefore, considered to be highly vulnerable to exposure to rodenticides. The new data demonstrated that 26% of polecats in the sample contained difenacoum or bromadiolone and that exposure was geographically widespread and occurred in several years. The possible effects of secondary exposure on populations of polecats and other predators are discussed.