First evidence of the suitability of hair for assessing wildlife exposure to anticoagulant rodenticides (ARs)

Anticoagulant rodenticides (ARs) are potent pesticides acting as vitamin K epoxide reductase inhibitors causing haemorrhaging or external bleeding from orifices and/or skin lesions in intoxicated rodents. However, their non-selective mode of action makes them particularly harmful for non-target wildlife, which may be exposed to ARs via ingestion of AR-containing baits (primary exposure), feeding on AR-intoxicated rodents and carrions (secondary exposure), consuming AR-contaminated necrophagous species (tertiary exposure), and exposure to surface waters receiving baited sewer systems and ARs from outdoor-placed traps after heavy rain events. In the present study, we assessed the suitability of hairs as a non-invasive matrix for monitoring the possible exposure of mammals to ARs with a focus on the first-generation anticoagulant rodenticides (FGARs) warfarin, coumatetralyl, and chlorophacinone and the second-generation anticoagulant rodenticides (SGARs) brodifacoum, bromadiolone, difenacoum, flocoumafen, and difethialone. The Red fox (n = 24) was selected as the species representing the potentially exposed non-target wildlife in a littoral area of Northern Italy along the Adriatic coast (Cavallino-Treporti municipality). Half (n = 12) of the analysed hair samples were positive for at least one of the targeted ARs, with a higher prevalence of SGARs (n = 11; 46%) compared to FGARs (n = 1; 4%). The most frequently quantified ARs were brodifacoum (25%), difethialone (13%), and flocoumafen (13%), with concentrations ranging from 0.08 ng g⁻¹ (difethialone) to 0.96 ng g⁻¹ (brodifacoum). These data documented that a relevant part of the Red foxes living in the study area were exposed to ARs and, most importantly, provided the first evidence that hair residues can be used as a non-invasive matrix for assessing the possible exposure of mammals to ARs.