The distribution of sodium fluoroacetate within 1080 egg-baits used for canid control

Abstract

Egg-baits prepared by the insertion of a 1080 (sodium fluoroacetate)-treated rhodamine-dyed oat-grain into each egg are used for controlling foxes (Vulpes vulpes) in Australia. However, the diffusion pattern of 1080 from the inserted oat into the egg and the distribution of 1080 within the egg are unknown. As both factors will influence whether the target species needs to consume the oat to receive a lethal dose, and also the withholding period required before the baits can be laid, we examined the rate of diffusion and the ultimate distribution of 1080 within these baits. Rhodamine oats containing 4.5 mg of 1080 were inserted into the white of intact eggs, or into eggs where the white and yolk was mixed (scrambled). 1080 rapidly dispersed into the eggs (but not the yolk of intact eggs) irrespective of which technique was used: 72–88% (3.22–3.96 mg 1080) of the recovered 1080 was found in the scrambled egg fraction or in the egg-whites within 1–2 h. Most of the remaining 1080 was found in the rhodamine oats, with the yolks containing only 2–8% of the nominal amount. The rapid diffusion of 1080 into the egg fraction, together with the very low levels of 1080 remaining in the rhodamine oats, indicate that: (1) target species such as foxes would not need to consume the oat to ingest a lethal dose, (2) providing a 2–3 h withholding period is allowed before baits are laid, any rhodamine oats not ingested would contain minimal amounts of 1080 and therefore pose little potential risk to non-target species, and (3) foxes would not need to ingest an entire egg-bait to receive a lethal dose. However, in preparing these baits, we recommend that the eggs be scrambled before the insertion of the rhodamine oats (to reduce the potential for operator error) and that a 2–3-h withholding period be allowed (to ensure that most 1080 is within the egg fraction) before these baits can be consumed by foxes or other target species.