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Bitter pill

1080 poison helps control the possum plague. But are the risks too great?

New Zealand, a global biodiversity hotspot, is a world leader in conservation management. We also consume about 90 percent of the world's production of 1080 poison. Perhaps these two facts are related, but there's a controversy raging in paradise.

The Environmental Risk Management Authority (ERMA) has invited public submissions on the use of 1080, with a closing date of January 31. Is this poison the key to salvation for our biological diversity? Or is it a weapon of mass destruction?

Caught in the crossfire is the possum, the main target for 1080 poisoning.

When we make an omelette, we have to break a few eggs, but inevitably we must decide which eggs to sacrifice. The Department of Conservation is between the egg and the frying pan over this issue and is probably nervous about the review's outcome (unless this policy omelette is already cooked). The Animal Health Board and local authorities are also part of the team at war with the possum terror. The stakes are high: our agriculture industry does not want bovine tuberculosis to rampage through the national beef and dairy herd, and protecting unique biodiversity on the last major landmass to be populated by humans is a monumental task.

But opponents of 1080 are significant in number and growing in political strength and purpose. What is broken that needs fixing?

Opponents argue that non-target animals (including people) are paying too high a price for the gains made and are seeking redress. But what kind of science lies behind the skull and crossbones?

Toxins can be grouped into acute and chronic categories. Exposure to 1080 can produce acute or chronic effects, depending on the dose.

Acute toxicity: 1080 causes cardiac or respiratory failure if consumed in lethal doses. The lethal dose differs for different species. According to the US Environmental Protection Agency (EPA), the "probable oral lethal dose in humans is less than 5mg/kg, or a taste (less than 7 drops) for a 150lb [68kg] person".

Chronic toxicity: the EPA classifies 1080 as a male reproductive toxin. Several other studies suggest that consuming 1080 at less-then-lethal doses can cause abnormalities in the reproductive system, and birth defects.

The vast majority of studies on 1080 focus on death rates in animals. Chronic toxicity is more difficult to study but no less important. The disruption of reproductive hormone systems is an example; studies of rats, mustelids, birds and skinks have provided evidence that 1080 is a reproductive hormone disrupter - hence the EPA classification.

Proponents of 1080 often point out that it is biodegradable, which basically means that bacteria eat it. Bacteria are more active in warm conditions and logic suggests that biodegradation rates may be slower at colder temperatures. Studies into the biodegradation rates of 1080 have confirmed this. Laboratory studies conducted at warm temperatures show rapid biodegradation rates for 1080. In one experiment, the laboratory water was 21°C. But 1080 tends to be used in winter when the possums are hungry. Stream temperatures at these times are likely to be much lower - less than 10°C in many mountain areas.

People will need to decide for themselves what they do with this kind of information because there is not space here to explore the options in any detail. But either way, it seems appropriate that there is room for some movement in 1080 policy in New Zealand, given the evidence of harm now available. This may mean using it in some areas but not others, with trappers being used in areas close to human settlement.

What remains certain, though, is that we cannot afford to allow possums to munch our forests with impunity and spread pestilence among our cattle. Getting the different groups together to talk this through will produce far better results than a win-lose political battle. Perhaps ERMA could facilitate this kind of dialogue as part of its review.

That would certainly help build mutual understanding, help us move past the polarised situation that has developed, and in the process help build a stronger community that cares about our land, our economy and our people.

Dr Sean Weaver is a senior lecturer at the School of Geography, Environment and Earth Sciences, Victoria University of Wellington.