Less brodifacoum in baits results in greater accumulation in the liver of captive Rattus norvegicus in a no-choice trail

Anticoagulants are widely used as potent cumulative rodenticides; however, they are also associated with adverse environmental effects, such as intoxication of non-target animals. To ensure user safety, in the EU the use of anticoagulants containing active substances of > 30 ppm is restricted to professionals as these substances are toxic to reproduction Kat.1 A or B. Therefore, new products with < 30 ppm anticoagulant substance have been developed and registered. While the biological efficacy of these new products has been evaluated, the effect of their application on liver residues in targeted rodents was not examined before product introduction to the market. Our laboratory no-choice study on wild brown rats ( Rattus norvegicus ) showed that baits with high (50 ppm) and low (25 ppm) brodifacoum concentrations (with identical nontoxic cereal-based food components) presented 100% efficacy, although the 25 ppm bait exhibited significantly higher palatability and 4.5 times higher liver residues. Rats consumed 13.6 and 167.7 g of the 50 and 25 ppm baits, respectively, which corresponded to 3.16 and 14.91 μg/g of brodifacoum liver residues at their time of death. The experiments demonstrated that a decreased concentration of brodifacoum anticoagulant in rodenticide baits may lead to greater accumulation in rodent liver, thus indicating the urgent need to perform a detailed study of the environmental risks of low-concentration anticoagulant baits.