Residues of anticoagulant rodenticides (AR) in non-target animals were studied in Finland. ARs are acting by effective blocking of the vitamin K cycle, resulting in death by internal bleeding. These effects are gradual, developing over several days. ARs are the primary method for rodent control in Finland and they can be transferred to non-target animals feeding on poisoned rodents. In particular, second generation ARs (SGARs) have been found in non-target animals in many countries but no AR screening has been conducted in Finland earlier.

This study focused mainly on species which feed either on rodents or their carcasses and in which ARs have been found in other countries. Samples were collected mainly from humanpopulated areas on southern Finland. The animals were either found dead or were shot or trapped for other purposes. ARs approved in Finland, i.e. bromadiolone, difenacoum, brodifacoum, flocoumafen, chlorophacinone, difethialone and coumatetralyl were analysed in 136 liver samples by an UHPLC-triple quadrupole mass spectrometric method.

One or more ARs were detected in 87% of the samples. ARs were commonly found in eagle owls, tawny owls, raccoon dogs, red foxes and mustelids (pine martens, least weasels and stoats). The most prevalent AR was bromadiolone (found in 70% of the samples) which was also found in the highest concentrations. Bromadiolone has been the most frequently used AR in Finland since the beginning of 2000s. The second most common AR present in the livers was coumatetralyl (56%) followed by difenacoum (44%), brodifacoum (23%) and flocoumafen (15%). Overall, the prevalence of ARs corresponded well with the sales of these substances in Finland. A high variation of concentrations was found within and between the animals. Overall, concentrations measured in avian species were far lower than those in mammalian species. Highest concentrations were found in raccoon dogs and red foxes. In general, coumatetralyl was found in lower concentrations compared to SGARs.

The prevalence found in this study (87% in overall and 100% in half of the species studied) is high compared to several previous studies conducted in other countries. On the other hand, the majority of the concentrations found were quite low and thus probably not lethal for the animals. However, about 12.5% of the animals studied here were found with concentration above 200 μg/kg. This means that ARs could have influenced the blood clotting in these individuals. It may be concluded that biocidal use of these substances causes frequent exposure of non-target animals, since these ARs are authorized only as biocides in Finland and the use for the crop protection is insignificant. In Finland a national strategy on risk management of ARs was adopted in 2011. Based on these results it appears that the risk mitigation measures (RMMs) either have not been followed or have not been effective in preventing secondary exposure of the non-target animals. Current RMMs are discussed and new RMMs along with further study questions are suggested.