Anticoagulant rodenticides on the menu of urban and peri-urban wild boars

    An investigation reveals that urban and peri-urban populations of wild boar have a high prevalence of anticoagulant rodenticides in internal tissues and evaluates the derived risks for food safety


    The constant increase in the abundance of wild boars (Sus scrofa) in the Iberian Peninsula over the last decades has become a growing cause of socio-environmental conflicts. Months ago, this species of wild ungulate became the protagonist of news related to the health and environmental consequences of its overabundance in certain natural spaces and its growing presence in urban centers. Now, a new investigation carried out in Barcelona and its metropolitan area has revealed that the urban and peri-urban populations of the suido present a high prevalence of second generation anticoagulant rodenticides.

    Anticoagulant rodenticides are synthetic chemical compounds that we have actively spread throughout our agricultural fields and cities to control commensal populations of rodents. The second generation (known as SGARS: Second-Generation Anticoagulant Rodenticides) were introduced in the 70s after discovering the resistance developed by rodents to the first generation, so they provide a more effective single lethal dose, but are much more persistent. As their name suggests, these biocides, which are highly toxic, cause lethal haemorrhage in rodents exposed to high enough acute doses.

    However, its toxic action not only affects rodents, and as they are very persistent substances, its bioaccumulation in the internal tissues of exposed animals facilitates its transfer along the food chain, generating a risk of secondary poisoning in non-target species that occupy the upper trophic links, such as wild boar.

     

    As an omnivorous and opportunistic animal, the wild boar (Sus scrofa) can be exposed to second-generation anticoagulant rodenticides directly, through the consumption of poisoned baits, or indirectly, through the ingestion of rodent carcasses or other animals killed by poisoning (Photo: SEFaS).

    The study, which has been developed by the Research Group in Wildlife Toxicology of the Instituto de Investigación en Recursos Cinegéticos (IREC – CSIC, UCLM, JCCM), the Wildlife Ecopathology Service (SEFaS) of the Autonomous University of Barcelona (UAB) and the Higher Technical School of Agricultural Engineering of the University of Lleida, shows that wild boar exposure to SGARs depends on the degree of anthropization of the habitat, being higher in the areas most densely occupied by humans.

    Thus, 61 and 40% of the wild boars that inhabit the city of Barcelona and its metropolitan area, respectively, have residues of SGARs in the liver and muscle, mainly from bromadiolone and brodifacoum. The accumulation of these biocides is especially noticeable in the liver, where levels above the threshold associated with the appearance of internal bleeding are reached in almost 14% of the animals analyzed.

    In areas that are home to high human population densities, such as Barcelona and its peri-urban environment, SGARs are used intensively to control populations of commensal rodents, so these results suggest that wild boars inhabiting urban and peri-urban areas they could be relatively frequent consumers of poisoned baits and the carcasses of poisoned rodents or even their predators, like cats.

     

    The researchers analyzed 10 types of SGARs in the liver and muscle of 3 different wild boar populations: (1) the urban population of the city of Barcelona; (2) the peri-urban population of the Sierra de Collserola Natural Park, which is part of the Barcelona Metropolitan Area; and (3) a non-urban population close to the Cabañeros National Park, in the province of Ciudad Real, which was used as the reference population.

    This job has a special relevance in the field of food safety, since the wild boar is a hunting species whose meat is intended for human consumption. In this sense, only 12% of the meat samples (muscle) accumulate detectable levels of rodenticides, and in all cases they are low enough not to pose a risk derived from their consumption. On the contrary, the results obtained advise against the use of wild boar liver as a food product when it comes from areas subject to intensive use of SGARs, requiring a more in-depth assessment of the public health risk.

    The research also compares the proportions of the chemical forms accumulated in the tissues of wild boars with respect to those found in commercial baits, since each chemical form of a SGAR (called diastereomers Are you there- y trans-) may have different toxicokinetic properties that determine its greater or lesser metabolism and persistence. Unlike what happens in rodents, in which one of the diastereomers accumulates more than the other, in wild boar liver both are found in proportions similar to those present in commercial formulations. This information could be of great relevance to improve the formulation of SGARs through the selection of the least persistent chemical forms and therefore less harmful to non-target species and trophic chains, although this will require more research.

    The scientific publication of this research is available at: