Water safe after 1080 drop

Aerial dispersal of 1080 pellets from helicopters is the most efficient and cost-effective way of deploying the pesticide in inaccessible areas, but public concerns persist. One concern is over potential contamination of water supplies following aerial drops, despite 20 years of research that shows this is very unlikely.

The pesticide known as 1080 is a key weapon in the battle against New Zealand’s plague of possums, helping to control bovine tuberculosis and protect native biodiversity.

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Transport of unconsumed 1080 from cereal baits in rainfall-runoff and rainfall-recharge were sampled in two separate field studies in the West Coast of South Island. Less than 5 percent of samples were tested positive and the 1080 concentration even in those did not exceed Ministry of Health drinking water standards.

Between 1990 - 1998, Landcare Research tested 2098 water samples following aerial 1080 operations. Taken during the subsequent 24 hours, just three per cent were found to contain traces of 1080 and, apart from one test suspected of contamination, levels averaged 0.2 parts per billion. This is well below the Ministry of Health’s precautionary drinking water standard of two parts per billion. Importantly, no 1080 has been detected in drinking water supplies.

In a study for the Animal Health Board, NIWA intensively sampled a West Coast stream after an aerial drop of cereal 1080 baits in August 2009. The study was aimed at investigating the potential for short-term contamination from baits landing directly in the stream, and rainfall leaching 1080 from baits.

“Even in a worst-case scenario, the amount of 1080 detected in the stream was extremely small and transient, with levels well below the drinking water standard set by the Ministry of Health,” says NIWA freshwater ecologist Dr Alastair Suren, who led the research.

Reducing risks of contamination

Because it is highly water soluble, 1080 (sodium fluoroacetate) readily leaches from cereal baits exposed to rain. 1080 from uneaten baits could get into streams and rivers via soil water (the moisture held in soil) and runoff, or directly from baits falling into streams.

Although 1080 is rapidly diluted, some regional councils require a bait-free buffer around larger streams during aerial drops to reduce the risk of contamination. The Department of Conservation and the Animal Health Board also avoid aerial 1080 drops in water-supply catchments, and time their operations to coincide with dry spells.

Designing a worst-case scenario

“For the NIWA study, we deliberately tested 1080 levels under a worst-case scenario: in a small stream in steep country after rain and in cool temperatures,” says Dr Suren. Laboratory studies by Landcare Research have shown that 1080 is broken down into harmless components by microorganisms and aquatic plants, with faster breakdown in warmer temperatures. Regardless of temperature, dilution has a much greater and quicker effect than biological breakdown in reducing 1080 levels in water.

The 150-hectare study site was chosen because it was steep (to maximise potential runoff), had a relatively shallow soil profile (to maximise the flow of soil water towards the stream), and was drained by a single small stream, less than a metre wide (to minimise the dilution effect). The study was conducted soon after a much larger bait drop in the area. With most of the possums in the area already poisoned, there would presumably be more uneaten baits lying around.

What the scientists did

The scientists set their instruments to measure rainfall and stream flow every 15 minutes during the experiment, and took frequent water samples from the stream at the base of the catchment to ensure their sampling represented flow from the entire area covered by 1080 baits.

They tested intensively for 1080 in stream samples when it was most likely to be found – after significant rainfall. Samples were tested at frequent intervals during the first day after rainfall began. They also analysed a sample taken nine days after the 1080 drop to test the persistence of 1080 in the stream.

Water from the stream was also tested once before the 1080 drop, to determine if there was any 1080 present before the study, and once between the 1080 drop and the first rain, to check if any contamination had arisen from baits landing in the stream. All water samples were analysed by Landcare Research in a specialised laboratory.

What they found

Of 17 samples tested, only one contained a measurable amount of 1080. It was collected two hours after rain began to fall (38 hours after the aerial drop) and had a 1080 concentration of 0.1 parts per billion. This is 20 times less than the Ministry of Health’s precautionary drinking water standard and no detectable 1080 was found in the stream one hour later.

“We can be confident that, if the tests didn’t detect 1080, it wasn’t there in significant levels,” says Dr Suren. “It’s a very sensitive test, able to detect 1080 concentrations as small as 0.1 parts per billion. That’s the equivalent of finding a single gram of 1080 in one hundred 10-tonne dump trucks.

“The concentrations we’re talking about are very, very small. Some plants, such as tea, naturally contain 1080 in detectable quantities. Despite a worst-case scenario, the quantity of 1080 we found in the stream was only a very small fraction of what you’d naturally find in plants, and didn’t persist,” says Dr Suren. “This study further supports past research where no significant 1080 contaminations were reported.”

Although there was no buffer zone around the stream, the scientists found no evidence of baits in the stream. “It’s likely that the short-lived pulse of 1080 residue in the stream reflected 1080 leaching from baits and entering the stream through runoff or via soil water,” says Dr Suren. “The reason you get peaks and then no more is because 1080 is highly soluble and probably moves quickly through soil water. Once it’s leached, it’s gone.”

 

More information

Dr MS Srinivasan
MS.Srinivasan@niwa.co.nz 

 
Helicopters are used to apply 1080-dosed cereal pellets across large tracts of native forest to kill introduced possums, helping to control bovine tuberculosis and protect native biodiversity. (The Southland Times)
 

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Archived on 30 October 2018