NIWA scientists alleviate concern over 1080 in drinking water

NIWA scientists have found little cause for concern about the possibility of 1080 contamination in streams. This finding was part of a detailed investigation on the West Coast, during August last year. The study, which coincided with planned aerial bovine tuberculosis (TB) control operations in the area, tested whether 1080 was likely to leach from possum baits.

“Under the worst-case scenario of rainfall after an aerial bait drop, the tests found the amount of 1080 leached and detected in a stream during and following rainfall was extremely small. If leaching does occur, it is likely to be within the first few hours of rainfall and will result in concentrations less than the prescribed Ministry of Health drinking water standards,” says NIWA scientist Dr Alastair Suren.

Exposure to 1080 from contaminated drinking water supplies following an aerial operation continues to concern some people. However, 1080 is very soluble in water and is used by DoC and the Animal Health Board (AHB) to control pests throughout New Zealand.

The New Zealand drinking water standard, or Provisional Maximum Acceptance Value (PMAV) for 1080, is set by the Ministry of Health. The standard protects water users from any risk to their health when consuming drinking water over a lifetime. The PMAV for 1080 is 3.5 micrograms per litre (3.5 parts per billion). As a further precautionary measure, the concentration of 1080 in water taken from 1080 bait-treated catchments must be below 2 micrograms per litre if it is to be used for human water supply.

Regulatory boards also stipulate that toxic baits must not be laid in any catchment that provides water for human consumption except where approved by a medical officer of health.

When aerial 1080 operations are planned, regional councils can request buffer zones around larger waterways to prevent baits from entering them. They are designed to eliminate 1080 contamination. Smaller streams may become contaminated after an aerial operation and there is ongoing concern that 1080 left in uneaten baits, which have been exposed to rain, may enter streams that feed into drinking water supplies.

NIWA scientists detailed investigations of 1080

This detailed study took place in a small West Coast stream, during mid-August 2009. NIWA scientists tested whether 1080 was likely to leach from baits left uneaten in the catchment and exposed to rain. To find out what happens, the scientists installed equipment to measure rainfall and stream discharge. The bait was applied across the catchment by helicopter as close as possible to forecast heavy rain.

Stream water samples were collected at the base of the catchment to ensure that the sampled water had flowed through the catchment area and, therefore, may have potentially been exposed to the 1080 baits on the ground.

Water samples were also collected after the baits were applied - but before the rain started - to check if any contamination had occurred from baits landing in the stream. The stream was sampled every hour for 12 hours after the onset of rain, then every two to three hours after that.

Further additional samples were collected throughout the rainfall event, which lasted for three days. By that time a total of 61mm of rain had fallen. A final sample was collected nine days after the baits were applied across the catchment. A further 68mm of rain had fallen within the study area during that time.

“No 1080 was detected in the samples collected over a 12-hour period immediately after application, before the rain began. This means that baits were unlikely to have fallen into the stream or were not present in amounts sufficient to cause contamination,” says Dr Suren.

Of the 15 samples collected after the rain started, only one contained detectable 1080. This had a concentration of 0.1 micrograms per litre and was collected two hours after rain began to fall.

“It is likely that the short lived pulse of 1080 residue in the stream reflected 1080 leaching from baits and entering the stream through either overland flow or via soil water moving into the stream. No 1080 was detected in any of the other samples including the sample collected on day nine, when further significant rain had fallen.

“The concentration of 1080 found in the stream water under this ‘worst case scenario’ was 20 times less than the precautionary drinking water value of 2 micrograms per litre, set by the Ministry of Health,” says Dr Suren.

Scientists have been monitoring 1080 in waterways for 20 years

Between 1990 and now, waterways throughout New Zealand have been monitored after major aerial pest control operations. In total, 1950 water samples have been collected and analysed for 1080 residues.

Findings from this show there has been no significant or prolonged contamination of surface water within catchments. No 1080 was detected in 96.3 per cent of samples. Of the 72 samples with positive traces, 65 (90 per cent) had concentrations of less than 1 microgram per litre - less than half of the Ministry of Health guidelines.

The remaining seven samples contained between 1 and 9 micrograms per litre. The sample containing 9 micrograms per litre has been attributed to accidental contamination by a worker. The other six samples contained less than this and repeated sampling from four of these sites showed decreasing 1080 concentrations over time. More importantly, no quantifiable 1080 contamination has been found in samples taken from drinking water supplies between 1990 and 2006.

From these results, scientists have concluded that prolonged contamination of waterways is not likely to occur if pest control operators follow the correct operating procedures.

ENDS

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