Anticoagulant rodenticide poisoning confirmed by vitamin K1 depletion in raptors from Patagonia.

The use of second-generation anticoagulant rodenticides (SGARs) raises a dilemma regarding the regulation of persistent bioaccumulative toxic substances (PBTs), given that these products have applications in high demand by society, such as the control of zoonotic pests, for which there are no clear alternatives. In this work, we describe for the first time SGAR contamination in birds of prey from Argentina and South America. We found concerning levels in the liver and prevalence of SGAR (brodifacoum, bromadiolone, difenacoum, flocoumafen and difethialone) bioaccumulation (18.2%), particularly around urban areas of NW Argentine Patagonia, where the risk of Andes Virus infection is high and the use of SGARs for rodent control is common. Given the difficulty of diagnosing SGAR poisoning at the individual level, we developed a novel method to measure hepatic vitamin K1 concentration coupled with SGAR residue analysis. Using this method, we confirmed that birds with SGAR residues showed lower hepatic concentrations of vitamin K1, opening the possibility of using this biomarker to support the diagnosis of SGAR poisoning. This was the case for a Lesser Horned Owl (Bubo magellanicus) with signs of coagulopathy, 1.2 µg g-1 of total SGARs in the liver, and a complete depletion of vitamin K1 levels. The use of SGARs in areas at high risk of Andes Virus infection may be counterproductive in the long term, as SGAR-resistant rodents tend to be selected while their predators experience the expected adverse effects of PBTs, leading to a loss of the capacity to control rodent populations, both chemically and naturally.