Charles Eason

Assessment of Risks of Brodifacoum to Non-target Birds and Mammals in New Zealand

The risks to non-target birds and other wildlife from the use of vertebrate pesticides, including anticoagulant rodenticides, are determined to a significant extent by species intrinsic susceptibility, and the toxicokinetics of the compounds used. Brodifacoum is highly toxic to birds and mammals. The acute toxicity of brodifacoum to birds in New Zealand varies from <1 mg/kg in pūkeko (Porphyrio p. melanotus), the native swamp hen, to >20 mg/kg in the paradise shelduck (Tadorna variegata). Like other second-generation anticoagulants brodifacoum is strongly bound to vitamin K epoxide reductase and will persist, apparently for at least 6 months, in organs and tissue containing this enzyme, e.g., liver, kidney, and pancreas. The unique toxicokinetics of this class of compound exacerbates the risk of primary and secondary poisoning of non-target species. Vertebrate pest control programmes in New Zealand using bait containing brodifacoum have resulted in the primary and secondary poisoning and sub-lethal contamination of non-target species. These include native raptors, such as the Australasian harrier (Circus approximans) and morepork (Ninox novaeseelandiae), other native birds such as the pūkeko, weka (Gallirallus australis), southern black-backed gull (Larus dominicanus), and kiwi (Apteryx spp.), and introduced mammals, including game animals. There are increasing numbers of reports worldwide of wildlife contamination and toxicosis after the use of second-generation anticoagulants. All pest control activities require careful risk–benefit assessment in view of their potential to cause adverse environmental impact. Monitoring of wildlife for pesticide residues will provide data that can be used to reduce the risk of anticoagulant bioaccumulation and mortality in non-target species.

Review of the toxicity and impacts of brodifacoum on non‐target wildlife in New Zealand

Abstract Brodifacoum, an anticoagulant used in cereal‐based baits for the control of vertebrate pests, especially rodents, may be accidentally ingested by non‐target species. In birds, its acute toxicity varies from an LD50 of 20 mg/kg in paradise shelduck. Fourteen indigenous and eight introduced bird species have been reported killed by field use of brodifacoum in New Zealand. Populations of three species (western weka, Stewart Island weka, and pukeko) have been severely reduced in poisoned areas. There are no published data on the acute toxicity of brodifacoum in bats, reptiles, or amphibians. Invertebrates are unlikely to be killed by anticoagulants. Because of the high toxicity of brodifacoum, all vertebrates that eat baits or poisoned prey are at risk. Brodifacoum is only slowly eliminated from the liver, and therefore accumulates in vertebrates if there are repeated exposures to the toxin, which increases the risk of death. In New Zealand, indigenous non‐target species most ...

The use of biomarkers in ecological risk assessment: recommendations from the Christchurch conference on Biomarkers in Ecotoxicology

S. MARSHALL ADAMS1, JOHN P. GIESY 2, LOUIS A. TREMBLAY3 and CHARLES T. EASON3* 1 Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 USA 2 Aquatic Toxicology Laboratory, Department of Zoology, Institute of Environmental Toxicology, National Food Safety and Toxicology Center, Michigan State University, East Lansing, MI 48824 USA 3 CENTOX (Centre for Environmental Toxicology), Landcare Research, PO Box 69, Lincoln, New Zealand.

Sodium monofluoroacetate (1080) risk assessment and risk communication

Sodium monofluoroacetate (1080) is a vertebrate pesticide widely used for possum control in New Zealand. Fluoroacetate is also a toxic component of poisonous plants found in Australia, South Africa, South America, and India. Because of its importance and effectiveness in pest control and the highly toxic nature of this compound, its acute sub-lethal and target organ toxicity have been extensively studied. In relation to its use as a pesticide its environmental fate, persistence, non-target impacts and general toxicology have been and continue to be extensively studied. Toxic baits must be prepared and used with extreme care, otherwise humans, livestock, and non-target wildlife will be put at risk. The high risk of secondary poisoning of dogs is a cause for concern. 1080 acts by interfering with cellular energy production. Possums die from heart failure, usually within 6-18 h of eating baits. Long-term exposure to sub-lethal doses can have harmful effects and strict safety precautions are enforced to protect contractors and workers in the bait manufacturing industry. Considerable care is taken when using 1080 to ensure that the risks of using it are outweighed by the ecological benefits achieved from its use. When its use is controversial, risk communicators must take care not to trivialise the toxicity of the compound. The benefits of 1080 use in conservation, pest control, and disease control should be weighed up alongside the risks of using 1080 and other techniques for pest control.

Biomarkers in toxicology versus ecological risk assessment

Toxicity testing of drugs, pesticides, and hazardous compounds has evolved into a battery of standardized tests conducted in a range of surrogate test organisms. The toxicity of these xenobiotics in terms of their LD(50) and LC(50) (Dose or concentration lethal to 50% of the test population), ED(50) and EC(50) (Dose or concentration producing a specified response in 50% of the test population), MATC (Maximum acceptable toxicant concentration), LOEL (Lowest observable effects level), LOEC (Lowest observable effects concentration), NOEL (No observable effects level) or NOEC (No observable effects concentration) is extrapolated to humans and wildlife. Historical failures in the risk assessment process have been largely due to over reliance on regulatory toxicology and an assembly line mentality to toxicology. The importance of toxicokinetics, receptor studies and biomarkers are reviewed, firstly, with reference to toxicological incidences in drug development programmes, and secondly, with reference to improved environmental risk assessment of pesticides and other contaminants. Ecological risk assessments also require multidisciplinary skills to study the entry, distribution, and biological effect and fate of chemicals to fully characterise and understand the potential adverse implications of contamination. Optimum integration of chemical measurements and biomarker responses is a challenge that will lead to an improved understanding of adverse effects and their significance in both human and ecological risk assessment.

Anticoagulant effects and the persistence of brodifacoum in possums (Trichosurus vulpecula)

Abstract Brodifacoum was administered to possums at a sub‐lethal dose of 0.1 mg/kg to assess its persistence in blood, muscle, and liver. Only 1 of 68 possums died at this dose level. However, significant increases in one‐stage prothrombin (OSP) and activated partial prothrombin times (APP) confirmed that the possum is susceptible to the anticoagulant effects of brodifacoum. Trace amounts of brodifaooum were detected in plasma for 35 days. Substantial concentrations of brodifacoum were retained in the liver for 8 months. Much lower concentrations were also retained in muscle tissue. The persistence of brodifacoum raises concerns about the possible transfer of this compound through the food chain to humans, dogs, or wildlife.

Persistence of Sodium Monofluoroacetate in Livestock Animals and Risk to Humans

1 Sodium monofluoroacetate (1080), a vertebrate pesticide widely used in New Zealand, was administered orally to sheep and goats at a dose level of 0.1 mg kg-1 body weight to assess risk to humans of secondary poisoning from meat. Blood, muscle, liver, and kidney were analysed for 1080 residues. 2 The plasma elimination half-life was 10.8 h in sheep and 5.4 h in goats. Concentrations of 1080 in muscle (0.042 ?g g-1), kidney (0.057 ?g g-1), and liver (0.021 ?g g-1) were substantially lower than those in plasma (0.098 ?g m-1) at 2.5 h after dosing. 3 Only traces of 1080 (<0.002 to 0.008 ?g g-1) were found in sheep tissues after 96 hours. 4 Livestock are normally excluded from areas where 1080 is being used for pest control, reducing the risk of secondary poisoning. Even with accidental exposure to a sublethal dose 1080 would not persist in tissues for more than a few days because it is cleared rapidly from the body. Therefore the occurrence of 1080 in meat intended for human consumption is highly unlikely.

Sodium monofluoroacetate and alternative toxins for possum control

Abstract Sodium monofluoroacetate (1080) is still an essential tool for possum control. We have reassessed the fate of this compound in the environment, and found no evidence of water contamination after large-scale possum control operations. The toxin is biodegradable in all living systems and will not accumulate in the food chain. Nevertheless, overreliance on a single toxin for a particular pest, such as 1080 for possum control, is unwise, and we are evaluating alternatives. Possums are susceptible to some non-anticoagulant toxins, including gliftor, cholecalciferol, calciferol, and alpha-chloralose. Of the anticoagulant toxins, brodifacoum is more effective than pindone. Integrated pen and field trials will determine the most cost-effective alternatives to 1080 for use in bait stations and for aerial application. Any alternative toxin will need to be subjected to the same scrutiny as 1080 for its environmental fate and impact on non-target species.

Fluoroacetate content of some species of the toxic Australian plant genus, gastrolobium, and its environmental persistence

Gas chromatography confirmed the relatively high concentrations of fluoroacetate found in toxic Gastrolobiums, a genus of indigenous Australian plants. Fluoroacetate concentration in these plants ranged from 0.1 to 3875 micrograms/g (ppm) dry weight, with young leaves and flowers containing the highest concentrations. However, there was considerable intrastand variation between individual plants of at least two species with coefficients of variation ranging from 94% to 129%. Despite the high concentrations of fluoroacetate in many species, only one of nine soil samples collected from beneath these plants contained fluoroacetate. None of the 16 water samples collected from nearby streams and catchment dams contained fluoroacetate. This suggests that fluoroacetate does not persist in this environment. Fluoroacetate was also found in the genus Nemcia, and very low levels of fluoroacetate (ng/g) were detected in the foodstuffs, tea and guar gum. The latter indicates that other plant species may produce biologically insignificant amounts of fluoroacetate.

Persistence of sodium monofluoroacetate (1080) in baits under simulated rainfall

Abstract The rate of leaching of sodium monofluoroacetate (1080) by simulated rainfall was determined for carrot and possum pellet baits containing 0.08 and 0.15% 1080. Carrot baits were highly water‐resistant and showed no decline in 1080 concentration after 200 mm of rain. It is therefore inadvisable to use carrot bait in arid areas when rapid restocking of land is required after a control operation, but they may be particularly suitable for forest habitats. Of the two types of pellet (Wanganui No. 7 and RS5) tested, RS5 pellets were the less water‐resistant and started to disintegrate after only 5 mm of rain. The 1080 concentration also declined more rapidly in these pellets. So that toxicity is retained for the maximum length of time, RS5 pellets should be used in arid areas and Wanganui No. 7 pellets in wetter environments, when pellets are the bait of choice. RS5 pellets should be used if rapid return of stock to the land is required,.