1080 may be naturally present in pūhā
A team of researchers studying 1080 uptake in pūhā and watercress has uncovered some unexpected results.
In 2007, the Environmental Risk Management Authority approved the continued use of 1080, but placed stricter controls on its use. It also recommended further research on 1080 be undertaken, including into its impact on flora.
The Animal Health Board recently funded research by Lincoln University, Landcare Research, Tūhoe and Ngāi Tahu to look at the uptake and persistence of 1080 in pūhā and watercress.
The pūhā study was done on the southern side of Lake Waikaremoana, and the watercress study was done in Kaikoura.
At Lake Waikaremoana, a 1080 bait was laid on the ground at the base of each of eight pūhā plants, and a non-toxic bait laid below two further plants to allow comparison. At various time points before and after the baits were laid, a sample was taken from each plant, snap frozen on dry ice, and sent for laboratory analysis of 1080 content.
At Kaikoura, a 100-metre section of a spring-fed stream with abundant watercress was divided into 10 equal sections. In each section, a wire-mesh cage was anchored into the streambed and a 1080 bait was placed into the cage. Plant samples were taken, snap frozen and sent for 1080 analysis.
The results showed that both pūhā and watercress took up 1080 released from the bait. In pūhā, the maximum concentration was 15 parts per billion (ppb), three days after the baits were laid. By the end of the sampling, at day 38, the 1080 concentration had decreased to below the laboratory Method Detection Limit (MDL) of 3 ppb.
However, on closer scrutiny of the data, 59 of the 60 pūhā samples showed trace levels of 1080 near the MDL. This included samples from plants taken before the bait was laid, and from the plants with non-toxic baits.
This suggests that pūhā could naturally contain trace amounts of 1080.
Lincoln University Senior Lecturer Shaun Ogilvie says 1080 occurs naturally in other plant species around the world, but this is the first time it has been indicated in a plant species in New Zealand.
The researchers would now look for further funding to undertake a survey of plants throughout New Zealand to see if it occurs in other species.
The research team at one of the trial sites.
Dr Ogilvie says the finding has important implications for Māori, and the wider scientific community.
“Pūhā has been used as a food source for a very long time. While the amount of 1080 in pūhā is at extremely low concentrations, detecting 1080 in pūhā has caused the Māori researchers in the team to revisit thinking on 1080, and on 1080 use for possum control.”
“For the wider scientific community, the indication of 1080 in a New Zealand plant is an interesting discovery, worthy of further exploration into other plant species.”
The trace levels of 1080 were similar to those seen in common tea brands, in which 1080 occurs naturally.
The maximum 1080 concentration measured in watercress was 63 ppb on day 7. No further 1080 was detected after this, indicating that the 1080 was quickly eliminated from watercress. There was no evidence that 1080 naturally occurs in watercress.
At the maximum 1080 concentration of 15 ppb seen in pūhā, a 70 kg person would need to eat 9.3 tonnes of the affected pūhā in a single sitting to have a 50 per cent chance of dying of 1080 poisoning. For the maximum observed watercress concentration of 63 ppb, 2.2 tonnes would need to be eaten.
This led the research team to conclude that there was negligible risk of humans being poisoned by 1080 through the consumption of pūhā or watercress after an aerial 1080 operation.
Footnote: Dr Ogilvie was a member of ERMA New Zealand Māori advisory body Ngā Kaihautū Tikanga Taiao from 2004 to 2008. He has been involved in investigating the fate of 1080 in the environment and has published a number of articles in this area. In 2008, he was appointed to the Authority. He was not involved in the Authority’s reassessment of 1080 in 2007.