28 August 2008

It's in the trees! (no it's not)

Many tonnes of bait containing the poison 1080 (sodium fluoroacetate) are dropped on native forests every year in New Zealand to control possum numbers. ERMA (the Environmental Risk Management Authority) has recently reassessed the use of this compound and found that it is still the most useful poison that we have to deal with our major pest problem in New Zealand. There are, however, still many concerns expressed about the use of 1080. One issue is that 1080 may leach into soil and then be absorbed by plants. Of particular concern is whether 1080 is being absorbed into native plants used by Maori for food and medicines, as these plants grow and are harvested in areas that may be included in 1080 drops.

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Lincoln University researchers Shaun Ogilvie and James Ataria, with collaborators from Ngai Tuhoe and Department of Conservation, have published in Ecotoxicology the results of experiments on 1080 uptake in plants. In association with Ngai Tuhoe (of the eastern central North Island), experiments were done in a forest block just south of Lake Waikaremoana. Two plant species were selected for the trials. Pikopiko (hen and chicken fern, Asplenium bulbiferum) is a species of fern where emerging shoots are used as food. Karamuramu (Coprosma robusta) is a small tree species used as an internal and external medicine. Ten healthy specimens of pikopiko were enclosed in wire mesh cages and a single cereal 1080 bait was placed at the base of all the plants of both species in a smaller mesh cage to prevent disturbance by rodents. Samples from each plant were taken several times from 0-56 days after the bait was placed. The samples were then analysed for 1080 concentrations using gas chromatography. No 1080 was found in any pikopiko samples. 1080 was detected in one karamuramu plant on days 7 and 14 at between 2.5 and 5 ppb (parts per billion), representing about 0.0004% of the 1080 present in the original bait. The researchers calculated that to reach a lethal dose of 1080 for a 70 kg human that the person would need to consume about 28 tonnes of karamuramu! It was concluded that the risk to humans from 1080 absorbed into these plant species was negligible.

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