Exposure of stone marten (Martes foina) and polecat (Mustela putorius) to anticoagulant rodenticides: Effects of regulatory restrictions of rodenticide use.

When anticoagulant rodenticides (ARs) are used to control rodent populations there is also a widespread secondary exposure of non-target predators to ARs. To reduce secondary exposure, regulatory restrictions in AR usage were tightened in Denmark in 2011. The restrictions included the cessation of AR use for plant protection and any use away from buildings, as well as limitations in private consumers' access to ARs. To quantify and evaluate the efficiency of the regulatory measures to reduce secondary exposure, we analysed ARs in liver tissue from 40 stone martens (Martes foina) and 40 polecats (Mustela putorius) collected before and 31 stone martens and 29 polecats collected after the restrictions were imposed. No declines in the prevalence ARs were detected following the regulatory restrictions in either stone marten (Before: 98%, After: 100%) or polecat (Before: 93%, After: 97%). The total AR concentration was higher in stone martens than in polecats in both sampling periods. Between the two sampling periods, the total AR concentrations in the mustelids increased (P<0.001). The increase was significant for stone marten (Before: 419ng/g ww, After: 1116ng/g ww, P<0.001), but not for polecat (Before: 170ng/g ww, After: 339ng/g ww). Overall, the total AR concentration was positively correlated to the urban area and the area used for Christmas tree production in which ARs were regularly used before 2011. The regulatory restrictions in AR usage did not reduce exposure of non-target stone martens and polecats. The temporal and spatial patterns of AR concentrations in predators indicate that chemical rodent control in and around buildings is the dominant source for the exposure of non-target predators in intensively human-dominated landscapes in Denmark. The results suggest that non-chemical methods for rodents control at buildings are necessary to prevent widespread secondary AR exposure of predators in human modified landscapes.