Liver and fecal samples suggest differential exposure of red fox (Vulpes vulpes) to trans- and cis-bromadiolone in areas from France treated with plant protection products

Highlights: • Commercial bromadiolone is a mixture of 70% trans-isomer and 30% cis-isomer. • cis-Bromadiolone is rarely found in liver and scats of red foxes after bromadiolone poisoning. • cis-Bromadiolone does not seem to be persistent in the food chain. • Water voles and/or red foxes eliminate cis-bromadiolone more rapidly than trans-bromadiolone. • Monitoring of rodenticides should differentiate diastereoisomers in non-target species. Bromadiolone, a second generation anticoagulant rodenticide (SGARs), is authorized in France to control water voles (Arvicola scherman) outbreaks. SGARs enter the food chain and their persistence in rodents is responsible for secondary exposure or poisoning of predators and scavengers. Bromadiolone commercial formulations are a mixture of two diastereoisomers of bromadiolone: 70–90% is trans-bromadiolone and 10–30% is cis-bromadiolone. Both diastereoisomers were reported to inhibit coagulation function with similar potency. On the other hand, cis-bromadiolone has been shown to be less tissue-persistent than trans-bromadiolone in rats. Furthermore, cis-bromadiolone was not found in liver of red kites after bromadiolone poisonings of water voles. In this study, a multi-residue LC-MS/MS method for the quantification of the diastereoisomers of SGARs was used to investigate their proportions in field samples of another vole's predator, the red fox. Red fox livers (n = 48) and scats (n = 160) were collected in a pesticide use zone within a few months of bromadiolone application. We reported the concentrations of bromadiolone diastereoisomers in the livers and scats. Accumulation of bromadiolone was apparent in 81% (n = 39) of the livers with mean and max concentrations of 355 and 2060 ng/g, and in 23% of the faeces with mean and max concentrations of 78.5 and 593 ng/g. However, cis-bromadiolone was not detected in the liver of 35 of 39 exposed red foxes and was present at very low concentrations (below 24.6 ng/g) in 4 of 39 exposed red foxes. It was not detected in 11 of the positive scats and represented only 4.2% of the bromadiolone residues in scats. This demonstrated differential persistence of trans- and cis-bromadiolone in the food chain. The results suggest that a change of the proportions of bromadiolone diastereoisomers in baits could reduce the risk of secondary poisoning of predators, but retain primary toxicity for control water voles outbreaks.