In many countries, the fox (Vulpes vulpes), predator of small mammals, is particularly affected by
anticoagulant rodenticides such as
bromadiolone due to secondary
poisoning. Nevertheless, to date, no method of exposure monitoring is applicable in the field over large areas, and no toxicological data are available concerning sensitivity of foxes to
bromadiolone. The aim of this work was to compare excretion kinetics of
bromadiolone in fox faeces with clinical and haemostatic effects after repeated exposure to intoxicated voles. A sensitive method for the quantification of
bromadiolone excretion in fox faeces and plasma was developed, using liquid chromatography combined with electrospray ionisation mass spectrometry (LC/ESI-MS). The LoD was 0.9microg/kg and 0.15microg/L, and the LoQ was 3.0microg/kg and 0.5microg/L, in faeces and in plasma, respectively. Four captive foxes were fed for 2 or 5 days with water voles (Arvicola terrestris Sherman) spiked with
bromadiolone at concentrations close to those measured in the field. Faeces and blood were collected for
bromadiolone titration, and blood-clotting tests were performed to monitor fox health daily during 10 days and then every 3-4 days until the end of the experiment (D28). Then, after
euthanasia, a complete necropsy was performed, and levels of
bromadiolone residues in the liver were determined.
Bromadiolone residues were detected in faeces 15h after the first exposure. They increased dramatically during the exposure period and then gradually decreased, but they remained detectable at the end of the experiment, i.e., 26 days after the last exposure.
Bromadiolone residues in plasma showed a similar pattern but were no longer detectable 7-24 days after the last exposure. Two foxes presented very severe external haemorrhages, requiring the administration of the
antidote vitamin-K1.
Bromadiolone residues in faeces and their relationships with exposure and other direct-markers that were measured are discussed. Liver residues and the toxicity data of our study will help to interpret data from fox carcasses collected by wildlife disease surveillance networks. These findings provide a basis for programs aiming to monitor the exposure of wild fox populations to
bromadiolone using non-invasive methods based on standard sampling and analysis of residues in faeces.