Fate of sodium monofluroacetate (1080) following disposal of pest bait to a landfill

The results of a programme to monitor the containment and natural breakdown of approximately 12 000 kg of toxic vertebrate pest bait, containing compound 1080 (sodium monofluroacetate), in a landfill site are reported. The baits were buried in a purpose-dug pit in a managed solid waste disposal site at Winton in central Southland, New Zealand, in August 1996. Compound 1080 is used extensively in a bait form to control a range of introduced vertebrate pests, (e.g., European rabbit, Australian brush tailed possum), which cause considerable economic and environmental damage in New Zealand. Two shallow monitor bores, sited 5 and 13 m from the disposal pit, were sampled weekly for five weeks and thereafter monthly for 13 months. Analyses detected 1080 in 5 of the 28 groundwater/leachate samples. The 1080 concentrations in those samples, except for one result, were low. These were either below or close to the Ministry of Health provisional maximum acceptable value standards (PMAV) for drinking water, currently 0.005 mu g ml(-1). The concentrations of 1080 in groundwater in the more distant bore (13 m) were markedly lower than those in the nearer bore (5 m). 1080 was first detected in the near bore after 5 weeks and the more distant bore after 16 weeks. The level and frequency of incidence of 1080 in both holes decreased over the sampling period until none was detected after 10 months. In situ sampling of the residual waste material indicated the 1080 concentration in the disposal pit decreased to less than 10% of its original level in 12 months. The active anaerobic bacterial processes operating in the organic refuse pile appear to provide an ideal environment for the rapid natural breakdown of 1080. The findings will assist with the setting of conditions for resource consents concerning the disposal of materials containing 1080 in landfill sites.