5.5 Monitoring waterways after 1080 operations

Because 1080 is water soluble, extensive water sampling programmes have been conducted following aerial operations, throughout the country. Over a 14 year period (1990-2003), Landcare Research has analysed 1649 water samples collected from streams on the days following application of 1080, and also after subsequent heavy rain, following 230 possum control operations⁴⁶. The results are shown in Figure 7.

Figure 7: Results of water monitoring after aerial 1080 operations (1991-2003)

Concentration in 1080 sample

0.3%	5 samples >2.0 ppb
3.2%	53 samples 0.1-0.2 ppb
96.5%	1591 samples no 1080 detected ( < 0.1 ppb)

Ministry of Health recommended maximum concentration of 1080 in drinking water: 2.00 ppb. At this concentration of 1080 a 60 kg person would have to consume:

• 60,000 litres of water for a lethal dose of 1080
• 2,300 litres of water per day to suffer adverse sub-lethal effects.

In 96.5% of the samples (1591 samples) there was no trace of 1080, that is, no 1080 could be detected above the level of detection of 0.1 parts per billion (ppb). 1080 was detected in 3.5% of samples (58 samples). Figure 7 shows the proportion of samples with no detectable 1080, those where less than 2 ppb were present, and the five samples where 1080 levels exceeded 2ppb. However, in 51 of those 58 samples the 1080 recorded was less than 1 ppb. Those samples where 1080 was found to be present were mostly taken from small streams, and 1080 baits were present in the water. Other samples from the same streams did not contain detectable concentrations of 1080, which showed that continuous contamination of the waterway did not occur.

Of the 1649 samples analysed, 107 were taken from reticulated town water supplies. All of these samples were free of detectable1080.

When 1080 was detected, it was present only for a matter of days. The solubility of 1080 and experiments demonstrating its degradation by micro-organisms indicate that, on the few occasions it is present in water after aerial operations, it has a transient presence only. It is also important to note that samples have been taken predominantly from within or adjacent to operational areas, where there would be the greatest chance of detecting 1080 in water.

While it is preferable to treat all possum habitat, including riverbanks, to ensure as few possums as possible survive the operation, the current practice by Medical Officers of Health requires that 1080 baits are not deposited within at least 20 metres of major waterways during aerial applications. This is achieved by using airborne navigation systems, and planning flight paths to avoid water supply reservoirs and feeder rivers. Where appropriate, contingency plans are made with urban and private water supply operators in case of accidents.

The potential risk posed by the occasional presence of 1080 in water is discussed in more detail in the following section. However, as a broad indication, the concentration of 1080 detected in all but three of the 1649 samples analysed was less than the provisional maximum acceptable value (PMAV) for 1080 in drinking water of 3.5 ppb, set by the Ministry of Health (Ministry of Health, 2000). The current standard was lowered from the previous PMAV, set in 1995, of 5 ppb. This new standard is a very protective value that incorporates a large safety factor. The Ministry has also set guidelines recommending that water taken from catchments in which 1080 has been applied should not be used for human supply until tests show that the concentration is below 2 ppb, approximately 50% of the PMAV. Only five of the 1649 samples analysed contained 1080 concentrations greater than 2 ppb.

There has been no evidence of 1080 presence in reticulated water to urban or rural water supplies in New Zealand. Clearly, however, it is most important to follow all specified safety procedures in any 1080 operation, and to use control methods that are appropriate to the risks needing to be managed.

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