Pindone residues in rabbit tissues: implications for secondary hazard and risk to non-target wildlife

Abstract

Context Pindone is used to control rabbits in Australia and New Zealand, but the secondary non-target risks presented by pindone-poisoned rabbits are poorly known. Aims We aimed to generate new data on residual concentrations of pindone in poisoned rabbits for use in a review of the secondary poisoning risks posed to non-target animals in New Zealand. Methods Laboratory rabbits were offered pellet bait containing 0.25 g kg–1 pindone in three trials to simulate a range of bait uptake scenarios: single exposure and low or high chronic exposure. Residual pindone concentrations measured in body tissues of laboratory rabbits that had ingested known exposures of pindone were compared with those in wild rabbit carcasses collected after three pindone-baiting operations. Residues in the faeces of some laboratory rabbits were also measured. Key results Highest concentrations of pindone residues were in the liver and fat tissue of poisoned rabbits, with consistently lower concentrations in muscle tissue. A dose–response relationship between pindone exposure and liver residue concentrations was found only at the highest chronic exposures. Rabbit carcasses collected after field-baiting operations had generally higher pindone residue concentrations than did laboratory rabbits that had ingested known lethal amounts of bait. Unmetabolised pindone was excreted in rabbit faeces. Conclusions The occurrence of the highest residual pindone concentrations in rabbit liver was consistent with the known tissue distribution of anticoagulants in mammals; however, the co-occurrence of similar-range pindone concentrations in rabbit fat has not been previously described. Re-ingestion of soft faecal pellets (caecotrophy) in rabbits that have eaten pindone bait may function as a secondary exposure to increase or prolong their oral exposure to pindone. Some rabbits poisoned following field pindone-baiting operations are likely to have consumed well in excess of a lethal amount of bait. Implications Concentrations of residual pindone in fat and liver of poisoned rabbits suggest that secondary poisoning hazard to some non-target predators and scavengers is high. The lack of field-based assessments of the non-target impacts of pindone is a marked information gap that needs to be addressed.