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Prevalence of anticoagulant rodenticides in non-target predators and scavengers in Finland

Schematic illustration for how poisons intended to control one trophic level of the food chain (rodents) can accumulate to higher levels (predators and scavangers)

Read the report

The report (in English with a Finnish summary) can be downloaded here

Media features of the report

What did we do and find?

Target species

We focused mainly on non-target species which feed either on rodents or their carcasses and in which ARs have been found in other countries. Samples were collected mainly from human-populated areas on southern Finland. ARs approved in Finland, i.e. bromadiolone, difenacoum, brodifacoum, flocoumafen, chlorophacinone, difethialone and coumatetralyl were analysed in 136 liver samples.
 

Findings

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. The most prevalent AR was bromadiolone (found in 70% of the samples) which was also found in 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 species studied. Highest concentrations were found in raccoon dogs and red foxes, which is probably due to their habitat and diet preferences. Both species occur regularly in urban environments and can take an advantage of feeding from garbage bins when given the chance, making also direct exposure via bait eating a possibility especially for these species.


The red fox. One species were AR rodenticides accumulated most strongly

Conclusion

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. 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. In the report current RMMs are discussed and new RMMs along with further study questions are suggested.
 

Reference:

Koivisto E, Koivisto P, Hanski IK, Korkolainen T, Vuorisalo T, Karhilahti A, Välttilä V, Loivamaa I, Koivisto S (2016): Prevalence of anticoagulant rodenticides in non-target predators and scavengers in Finland. Report of the Finnish Safety and Chemicals Agency (Tukes).
 

11.3.2016,
Elina Koivisto
 
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