Secondary and tertiary poisoning risks associated with brodifacoum

The field use of brodifacoum baits (Talon(R) and Pestoff(R)) to control brushtail possums (Trichosurus vulpecula) has increased in recent years. This has raised concerns of secondary and tertiary poisoning, resulting from the transfer of this toxicant through the food chain. In New Zealand, feral pigs (Sus scrofa) are known to scavenge possum carcasses and and may also gain access to bait stations containing possum baits. We have determined the concentrations of brodifacoum in muscle and liver tissue from captive pigs after primary and secondary poisoning. Hight st concentrations were found in the liver. Pigs eating 500 to 1776 g of brodifacoum bait containing 20 mg kg(-1) had muscle concentrations ranging from 0.02 to 0.07 mg kg(-1) and liver concentrations ranging from 0.72 to 1.38 mg kg(-1). Both appeared to be independent of the amount of bait eaten. Possums fed 400 g of bait had similar liver concentrations (0.52-1.20 mg kg(-1)). Pigs that had eaten the soft tissue from eight poisoned possums had brodifacoum concentrations of 0.32 to 0.80 mg kg(-1) present in the liver and the concentration increased in a dose-dependent manner. Brodifacoum was detected in muscle from only one of these animals. In a preliminary field survey, 11 of 21 wild pigs sampled from areas where possum control had been undertaken were contaminated with brodifacoum concentrations in the liver ranging from 0.007 to 1.7 mg kg(-1). In view of the potential impact on pig hunters and dogs consuming wild pig meat and offal, some restrictions on the wide-scale field use of brodifacoum baits appears to be warranted.