5.6 Effects on people
Human exposure to 1080 may arise from drinking contaminated water, direct contact with baits or 1080 solution, or by consuming food, particularly meat from animals that may have consumed 1080. Each of these potential exposure routes is discussed in the following sections.
Exposure to contaminated water
The most significant potential exposure route for the general public is likely to be the contamination of surface water in water supply catchments13. As indicated in Chapter 5.5, 1080 has been detected in surface water only occasionally during an extensive sampling programme of water bodies within or adjacent to operation areas, where contamination is most likely to be found. Still, potential contamination of water supplies remains one of the most cited public concerns about 1080 operations, particularly aerial operations.
However, based on an LD50 of 2.0 mg/kgbw for humans, a 60 kg person would need to drink 60,000 litres of water containing 2 ppb of 1080, in one sitting, to absorb a fatal dose. Even allowing a significant safety margin (typically applied to allow for sensitivity in the general population and uncertainty in the toxicological studies), a safety factor of 1000 would still require a person to drink at least 60 litres of water containing 2 ppb of 1080 before being considered at risk. Given that the daily intake of water of an average person is typically estimated to be around two litres per day, it is clear that the risk of ingesting a lethal dose of 1080 at these concentrations is negligible.
The No Observable Effect Level (NOEL) for toxicity in rats (of 0.075 mg/kg-day11, Chapter 4.1) however, does indicate that regular intake of 1080 contaminated water could cause sub-lethal effects. Based on this NOEL, a 60 kg person would need to drink 2,300 litres of water containing 2 ppb of 1080 per day, for an extended period of time, for sub-lethal effects to occur. Allowing a safety margin of 1000, a person would need to drink their entire daily intake of two litres per day of water from a contaminated source, for a period of weeks, to be considered potentially at risk. Similarly, a 60 kg pregnant woman would need to drink at least three litres per day, all of her daily intake, during the first 90 days of pregnancy, to receive a daily intake one thousand times less than the NOEL (of 0.1 mg/kg-day13, Chapter 4.1) for developmental toxicity in rats.
It is for this reason that the Ministry of Health has specified a concentration of 2 ppb 1080 in water as the level above which water should not be used for human supply. The results of the extensive analysis carried out to date, and the solubility and biodegradability of 1080, which means that it does not persist in water, mean that it is highly unlikely that ingestion of contaminated water would pose a risk to the public.
Direct poisoning from baits
Direct contact with or ingestion of any poison baits obviously poses a risk to any person. 1080 operation planning includes public advertisements, notices, visits to schools, and other public awareness initiatives. Every attempt is made to ensure people who enter a treatment area are able to identify and avoid contact with 1080 baits.
Notwithstanding this, the amount of bait that an adult would need to ingest to receive a lethal dose is reasonably large. A person weighing 60 kg would need to eat about thirteen 6-gram baits or seven 12- gram baits (containing 0.15% 1080) to receive a fatal dose of 1080. Heavier people would need to eat more baits. A child weighing 20 kg would need to eat about four 6-gram baits or two 12-gram baits (containing 0.15% 1080) to receive a fatal dose. Sub-lethal effects could occur if significantly less bait was eaten, based on the toxicity studies on rats (Chapter 4.1), and for this reason all attempts are made to eliminate the potential for the public to accidentally come into contact with 1080 baits.
Exposure of workers in 1080 manufacture and application
The people with the greatest potential to be exposed to 1080 are the workers involved in manufacturing and distributing 1080 baits. Potential exposure routes for workers are ingestion, inhalation (of dust for example) and absorption through skin. Ingestion and inhalation are the most direct exposure routes that must be eliminated or minimised when handling 1080. Dermal (skin) absorption is a less significant exposure route, as studies conducted on rabbits in the USA showed that 1080 is poorly absorbed through the skin10, but appropriate controls to minimise skin exposure are required.
Monitoring of worker exposure has been conducted to assess the level of exposure of workers in New Zealand. In January 2002, the Occupational Safety and Health Service (OSH) adopted a Biological Exposure Index (BEI) for the presence of 1080 in human urine. This is a more sensitive measure of exposure than using blood tests. The BEI was set at 15 ppb (0.015 mg/L). This level includes a large precautionary safety factor that ensures a conservative threshold level. As such it is more a measure of exposure to 1080, since health risks at this exposure level will be extremely low. Comparisons of worker BEI results can be used as a process to ensure worker exposure to 1080 is always minimised by appropriate handling practices and the use of protective equipment.
Workers were monitored between September 1998 and December 2000, in two factories making 1080 cereal pellet baits, during three aerial carrot operations, four aerial cereal pellet operations and one ground operation spreading 1080 paste bait47. None of the urine samples were above the BEI for the workers involved in the ground operation or in the aerial cereal pellet operation. Some of the workers monitored during the manufacture of 1080 baits and during the carrot bait operations were found to have some results above BEI exposure levels to 1080. Monitoring of workers involved with 1080 has now been expanded to ensure that 1080 handling practices and use of protective equipment minimise worker exposure levels to acceptable levels.
Meat from poisoned animals
Studies have shown that when animals such as sheep, goats and rabbits were given sub-lethal amounts of 1080, the 1080 levels in their blood peaked 2.5 hours after dosing, and were at negligible levels four days after dosing27. All traces of 1080 were eliminated within one week. DOC has set a precautionary period of four months following an aerial 1080 operation, during which time meat from feral animals should not be eaten. This is a conservative precautionary period, but it is set to ensure that animals that may have eaten baits some time after an aerial drop are no longer a hazard.
There may be occasions when domestic stock accidentally encounter baits and consume a sublethal amount of 1080. As a standard precaution, a withholding period is then followed. If none of the poisoned animals die, then a withholding period of five days should be applied before any meat is consumed. If some animals die after eating baits, it is standard practice to extend this period to 10 days and move the surviving stock to a 1080-free pasture.
Game packhouses that process game animals procured by hunters are required to operate systems to exclude animals from processing if there is risk of them having been exposed to 1080 baits in the field. Carcass samples from game packhouses are regularly tested for 1080 residues. Residue testing is carried out much less frequently for conventionally farmed red meats, due to the lower risk of exposure to 1080. Residue monitoring is the responsibility of the New Zealand Food Safety Authority.
Plants of cultural importance
The uptake and persistence of 1080 in two plants of cultural importance to Maori were recently examined in preliminary research by Landcare. The plants were the fern pikopiko (Asplenium bulbiferum) used for kai (food), and karamuramu (Coprosma robusta) used for rongoa (medicine). There was no evidence of pikopiko taking up 1080. Some 1080 was taken up by karamuramu, but at such low levels that there was negligible risk of people being poisoned by consuming the plant material. As for the recent research on eels (see section 5.2), these preliminary findings are subject to the Animal Health Board's peer review protocol. The full reports of both research projects will then be available. There is ongoing research, funded by the AHB, on the use, application and effects of 1080.
An unlikely worst-case scenario
As a way of estimating the risk to human health, consider the concentration of 1080 that was detected in a water sample during the last 13 years of monitoring after 1080 aerial operations. That one sample, out of the 1649 taken during this period, had the highest recorded level of 1080 at four parts per billion. It was not taken from a water supply, but from a small, shallow stream just two hours after an aerial 1080 operation. A second sample from the same site 24 hours after the operation had only one part per billion. This rapid drop in concentration reflects the very high solubility of 1080 in water. Although it was a small stream, the dilution property of 1080 had quickly diminished the level of 1080 at this site.
What were the potential health risks? Imagine a 60kg person was camped next to the stream at the time of the operation and was relying only on this stream for water supplies. Assume the camper drank from the same place and at the same time that the first water sample was taken. The risk of acute lethal effects would require the person to drink, in one sitting, about 20,000 to 30,000 litres (if it was possible to do so - see Chapter 5.6 for exposure risks). (Daily average intake of water is about 2 litres.)
What about more realistic risks of sub-lethal health effects? These could possibly occur only if a person has access to water with a significant level of contamination for weeks at a time. Recall that the water at this site lost 75% of its 1080 concentration in just one day. The dilution of 1080 would have continued at a similar rate in the following days. Within a week any remaining 1080 would probably have been below the level of detection.
In the Drinking-Water Standards for New Zealand, issued in 2000 by the Ministry of Health, the Provisional Maximum Acceptable Value (PMAV) for 1080 in drinking water is 3.5 parts per billon. The PMAV is one that is not considered to cause any significant risk to health of the consumer over a lifetime consumption of the water. However, to be on the safe side, exposure to water that might be contaminated with 1080 should be avoided whenever possible, which is the aim of the public notification procedures, safety measures and water monitoring that takes place during and after aerial operations.
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