Feature

Old Pesticide -- New Data

Despite 40 years of use as a pesticide, 1080 is still the subject of considerable research.

By C. T. Eason

It's been almost 40 years since the pesticide sodium monofluoroacetate, better known as 1080, was introduced in New Zealand. It is still an essential tool for vertebrate pest control, particularly for possums, but, despite worldwide experience and studies confirming its utility, its use continues to be controversial.

New data on the environmental fate and impact of 1080 is being generated by the Forest Research Institute (FRI) in collaboration with Lincoln University's Animal Veterinary Sciences Department and the Hydrology Department of Bayreuth University, in Germany. In addition, a DSIR group has initiated field studies to examine the ecological impact of 1080 on invertebrates.

The toxicology laboratory at FRI is monitoring the fate of pesticides used in vertebrate pest control as well as developing improved control technology. In addition to looking for alternative "safer" toxins to 1080, further research is being conducted on the environmental fate of 1080. Updating of our information base on 1080 is needed if it is to be used for controlling possums and the tuberculosis they carry.

Environmental Effects

On-going research at FRI includes field and laboratory-based studies re-assessing the fate of 1080 in water, soil, plants, invertebrates and non-target vertebrates -- especially livestock -- exposed to sublethal doses. Recent work includes the monitoring of water samples for four months after the largest ever 1080 control operation in New Zealand.

In 1990, more than 100 tonnes of cereal baits were dropped over 17,000 hectares of forest to kill possums damaging one of the country's most botanically diverse forests at Waipoua, Northland. Surface and ground water samples were also collected for six months from Rangitoto Island in the Waitemata Harbour after a control campaign to protect pohutukawas.

Both these control operations were extremely successful -- 93% of possums on Rangitoto and 85% of possums in Waipoua were killed. The presence of 1080 in streams or rivers at Waipoua and in surface or ground water on Rangitoto could not be detected.

Laboratory studies at FRI are also examining the role of microbial degradation of 1080 in water. Aquariums containing 80 litres of water, common pond plants, and invertebrates were spiked with 0.1 ppm of 1080. The concentration of 1080 declined rapidly within a few days. In contrast, the 1080 concentration remained stable in an aquarium containing only distilled water spiked with 1080. These studies will continue into 1992. The first results appear to confirm that 1080 degrades readily in the presence of micro and macroflora and fauna.

Rapid Elimination

The potential consumption of a sublethal dose of 1080 by livestock has caused concern, with people asking "can 1080 occur in meat for export or home consumption?" Initial results from studies conducted by FRI scientists in collaboration with Dr Ravi Gooneratne, a veterinary toxicologist at Lincoln University, have shown that the toxin is rapidly eliminated in rabbits, goats and sheep; half the toxin levels are eliminated in rabbit blood in less than an hour.

Further experiments and tissue analysis will continue into next year. It seems most unlikely that measurable 1080 residues (down to 0.0003 ppm) would occur in any of these animals after one week. Coupled with the practice of destocking lands oversown with 1080, this clearly indicates a negligible risk of humans consuming meat containing residues if 1080 is used sensibly.

Soil experiments by Holger Hoff, a post-graduate from Bayreuth working at FRI, and Roger Parfitt from the DSIR, indicate that 1080 is extremely unlikely to persist in the soil after rainfall. It may linger for a few weeks in drier conditions, but Dr John Walker at Canterbury University has demonstrated that 1080 is readily degraded by bacteria and fungi to non-toxic metabolites.

Recent work by DSIR scientist Dr Valerie Orchard supports these findings, although degradation may be slightly slower in some soils than suggested by Walker. The fate of 1080 in soil, water, and target and non-target animals will continue to be studied over the next couple of years, and these studies should provide high-quality data in areas of concern.

An unresolved concern now being assessed is the potential effects of 1080 on invertebrates. Preliminary results from Mike Meads, a DSIR invertebrate expert, suggest there may be a short-term effect on some species of insects.

Meads will be joining forces with Dr Eric Spurr of FRI to address the key question of whether there is a significant detrimental effect on insect populations in the long-term after wide scale use of 1080. Spurr has monitored bird populations before and after 1080-poisoning operations. Although a number of individual birds have been killed by 1080, there has been no effect on populations.

Identifying Alternatives

The role of environmental scientists and those involved with wildlife management is to solve problems as well as identify them. This means reducing bait sowing rates and looking at better baits and lures, a research field being keenly pursued by Dave Morgan at FRI. He has been a driving force in reducing sowing rates of pellet baits for possum control from 30-40 kg/ha to 5-10 kg/ha, and is confident that lower sowing rates can be achieved.

FRI scientists are also spearheading research on alternative toxins, such as anticoagulants, and alternative control techniques. When alternative toxins are promoted, they must be subjected to the same level of scrutiny applied to 1080.

In the long-term, an integrated pest management scheme might include a variety of methods which would allow a further reduction in sowing rate. Biological controls, such as immunocontraception carried by a virus, could be coupled with the use of a target-specific toxin incorporated into baits made attractive with species-specific lures, for example. The goal of integrated pest management is a major challenge for FRI and other groups in this field, and can be achieved by biochemists, physiologists, toxicologists and ecologists working together.

Charles Eason is a scientist with Landcare Research.