Rodenticide screening 2016–2018 Exposures in birds (raptors and gulls) and red foxes

Rodenticides are biocidal products that are used in order to control rats and mice. This screening study aims at investigating whether chemical substances belonging to the group anticoagulant rodenticides can be detected in Swedish non-target biota, and to investigate if the levels are different compared with the results from a previous study. The levels of anticoagulant rodenticides detected in the present screening study are similar to those found in earlier studies in Sweden and elsewhere. The literature indicates that toxic effects can occur in birds at levels > 100 ng/g (liver) whereas the level > 200 ng/g has been proposed to be a threshold level in foxes. Some individuals of raptors (n =2) and several foxes (n = 7) exceed these levels in the present study. These data suggest that anticoagulant rodenticides that are transferred in the food web may cause secondary toxicity in non-target mammals and birds in Sweden. However, no pathology has been performed for the individuals of the present study that can confirm any concentration-effect relationship or reason for mortality