5.8 Disposal of waste 1080
Occasionally, quantities of baits may need to be disposed of if they are damaged or unusable. In 1996/1997, 12,000 kilograms of 1080 cereal pellets and pastes were buried in a purpose-dug pit at the Winton landfill in Southland, after they had deteriorated in storage. Water samples were taken from two boreholes, 5 and 13 metres from the disposal pit, for 13 months. The 1080 concentrations in those samples were either below or close to the Ministry of Health PMAV for 1080 in drinking water. No 1080 was detected from the bore samples after 10 months.
The waste material was also sampled to find out how quickly it would break down. Sampling showed that 1080 concentrations decreased to less than 10% of their original level within 12 months. It appeared that the active bacterial processes operating in the landfill provided an ideal environment for the rapid natural breakdown of 1080. The conclusion was that, by following approved procedures and by not disturbing the site, the 1080 waste materials did not appear to pose any significant risk to public safety or the environment50.
In a second example, 20 tonnes of cereal baits were buried in a West Coast landfill in March 2000. The baits were 8-20 years old and had lost some of their original toxicity during storage (manufacture strength was 0.15%, but a 1996 bait test was 0.11%). In the landfill, baits were mixed with a starter of organic material and buried about 2.5 metres deep. Water samples were taken one month after burial and every four months after that. Water samples were taken from surface water, 10 metres, 100 metres and 2 km from the dump site. No detectable levels of 1080 were discovered in any of the water samples. When concerns were raised about the safety of the landfill, the baits and surrounding soil were excavated in October 2000 (seven months after burial) and trucked to a Christchurch chemical waste disposal plant. Samples from the bait were taken in July 2000 and testing showed between 0.024% and 0.053% 1080. This was a 52-78% reduction in 1080 strength in seven months. After treatment at Christchurch, the bait was tested at 0.004%, and finally buried at a Canterbury landfill.