Testing of water samples taken after the September 28 aerial application of 1080 at Russell Forest failed to find any trace of the toxin, according to the Department of Conservation.
Samples were taken 15 and 39 hours after the operation, and on October 25, following 10mm of rain over 24 hours, at two sites within the treatment area and eight outside it. One of the 30 samples at 15 hours produced detectable 1080, at 0.1 part per billion (ppb), well below the Ministry of Health's precautionary drinking water standard of 2ppb.
When that water was re-tested at 39 hours, no detectable 1080 was found, nor was the toxin detected in drinking water supplies.
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DOC's Northern North Island operations director Sue Reed Thomas said the results supported the department's contention that 1080 broke down very quickly in water.
"We can be confident that the water was not contaminated following the pest control operation," she said.
"The tiny detection in the first sample taken from the middle of the aerial drop is the equivalent of finding a single gram of 1080 in a 25m swimming pool, the size of the competition indoor pool in Whangarei.
"We know people have concerns about water quality after a 1080 operation, and we wanted to provide independent testing to show the water is safe and 1080 is not present in the awa in Russell Forest."
Ms Reed Thomas said DOC routinely had water tested by independent laboratories following 1080 operations. Samples were collected immediately when there was the greatest possibility of detecting contamination. The Ministry of Health's 2ppb precautionary standard had never been exceeded.
A further four samples, from Waikare streams, were tested to provide information for local iwi, and produced no detectable 1080.
Details of the pest species kill from the Russell and Cape Brett operations were due in coming weeks.