Monitoring The Hepatic Residues Of Cis- And Trans-Diastereoisomers Of Second Generation Anticoagulant Rodenticides Reveals A Different Bioaccumulation Of Diastereoisomers In The Food Chain Of The Reunion Harrier (Circus Maillardi)

The Reunion harrier is an endangered raptor and endemic species to the Reunion Island. Second generation anticoagulant rodenticides (SGARs) are widely used pesticides on the island in order to control rodent populations. The latter are responsible for the transmission of leptospirosis to humans, the damage of sugarcane crops, and the decline of endemic endangered birds. SGARs are very persistent chiral pesticides and consequent secondary exposure or poisoning of the Reunion harrier has been observed (73% of prevalence in a group of 58 harriers). Commercial formulations of SGARs are a mixture of trans-and cis-diastereoisomers. Both diastereoisomers of all SGARs have been shown to inhibit coagulation function with the same potency. On the other hand, they have been shown to have a significant difference in terms of tissue-persistence. This difference has led to residue levels in rats with a significantly lower proportion of one of the isomers compared to the bait composition. In this study, residue levels of the diastereoisomers of all SGARs were evaluated in the livers of 58 harrier carcasses. The respective concentrations and proportions of cisand trans-diastereoisomers of all SGARs are presented. cis- Brodifacoum and trans-bromadiolone had the highest concentrations (up to 438 and 573 ng/g ww respectively), while trans-brodifacoum was less than 46 ng/g and cis-bromadiolone was barely detected. cis-Difenacoum showed the highest prevalence and the highest concentration was 82 ng/g ww, while trans-difenacoum was never detected. This study demonstrated that only cis-brodifacoum and trans-bromadiolone (and cisdifethialone, but with a low prevalence) had hepatic concentrations above a toxic threshold. The cisand trans-diastereoisomers of SGARs had differential bioaccumulation in the food chain of the R & eacute;union harrier com-pared to commercial baits. This suggests that a change of the proportions of SGARs diastereoisomers in baits could reduce the risk of secondary poisoning of predators, but maintain primary toxicity.(c) 2021 Elsevier B.V. All rights reserved.