Sodium monofluoroacetate and alternative toxins for possum control

Efficacy of cholecalciferol rodenticide to control wood rat, Rattus tiomanicus and its secondary poisoning impact towards barn owl, Tyto javanica javanica

Studies were conducted on the potential use of cholecalciferol as an alternative to anticoagulant rodenticides to control common rat pest in oil palm plantations, i.e., wood rats, Rattus tiomanicus, and the secondary poisoning impact of cholecalciferol on barn owls, Tyto javanica javanica. The laboratory efficacy of cholecalciferol (0.075% a.i.) was compared with commonly used first-generation anticoagulant rodenticides (FGARs): chlorophacinone (0.005% a.i) and warfarin (0.05% a.i). The 6-day wild wood rat laboratory feeding trial showed cholecalciferol baits had the highest mortality rate at 71.39%. Similarly, the FGAR chlorophacinone recorded a mortality rate of 74.20%, while warfarin baits recorded the lowest mortality rate at 46.07%. The days-to-death of rat samples was in range of 6-8 days. The highest daily consumption of bait by rat samples was recorded for warfarin at 5.85 ± 1.34 g per day while the lowest was recorded in rat samples fed cholecalciferol, i.e., 3.03 ± 0.17 g per day. Chlorophacinone-treated and control rat samples recorded consumption of about 5 g per day. A secondary poisoning assessment on barn owls in captivity fed with cholecalciferol-poisoned rats showed after 7 days of alternate feeding, the barn owls appeared to remain healthy. All the barn owls fed with cholecalciferol-poisoned rats survived the 7-day alternate feeding test and throughout the study, up to 6 months after exposure. All the barn owls did not show any abnormal behavior or physical change. The barn owls were observed to be as healthy as the barn owls from the control group throughout the study.

Combining aspirin with cholecalciferol (vitamin D3)--a potential new tool for controlling possum populations

The introduced Australian brushtail possum is a major vertebrate pest in New Zealand, with impacts on conservation and agriculture being managed largely through poisoning operations. Cholecalciferol (vitamin D3) is registered for use in controlling possums and despite its many advantages it is expensive and relatively inhumane. Combination of a high proportion of aspirin with a low proportion of cholecalciferol was effective in killing high proportions of groups of acclimatised, caged possums: this is attributed to both an unexpectedly high toxicity of the type of cholecalciferol used, and a proposed synergistic mechanism between the two compounds. Death was caused by localised damage to heart ventricles by aspirin, and inhibition of tissue repair by both aspirin and cholecalciferol. The observed toxicosis had lower impact on the welfare of possums than either compound administered alone, particularly aspirin alone. Residue analyses of bait remains in the GI tract suggested a low risk of secondary poisoning by either compound. The combination of cholecalciferol and aspirin has the potential to meet key requirements of cost-effectiveness and humaneness in controlling possum populations, but the effect of the combination in non-target species has yet to be tested.

Toxicity and persistence of sodium fluoroacetate (1080) in the land crab (Gecarcinus lagostoma) on Ascension Island

An eradication program for introduced feral cats, using sodium fluoroacetate (1080) bait, was planned on Ascension Island to help breeding seabird populations to recover. We investigated the likelihood of mortality and the occurrence of residual 1080 in the ‘non-target’ Ascension land crab (Gecarcinus lagostoma) through simulating ‘realistic’ and ‘worst case’ exposure to 1080 bait. Crabs feeding on 1080 baits ingested an estimated maximum of 9–56 mg 1080 (kg bodyweight)–1 and although two of 32 treatment crabs died, this mortality was not attributed to 1080 poisoning but to other, unknown, causes. Our results suggest that G. lagostoma has relatively low susceptibility to acute toxic effects of 1080. Most residual 1080 was eliminated rapidly from crab tissue, with concentrations of 0.006–0.070 mg (kg bodyweight)–1 measured in crab claw/leg tissue 9–11 days after exposure. Concentrations of 0.200 and 0.650 mg (kg bodyweight)–1 were measured in the claw tissue of two crabs that died from other causes on the third day of exposure to 1080, indicating potential for secondary exposure of sensitive scavengers or predators of 1080-exposed crabs. We recommend a moratorium on human consumption of all crabmeat for a withholding period following the eradication program. The withdrawal period should be defined by further research on the longevity of 1080 in crab tissues, and be confirmed by monitoring of residues in crabs after baiting.

Tissue distribution of cytochrome P450 3A (CYP3A) in brushtail possums (Trichosurus vulpecula) exposed to Eucalyptus terpenes

We evaluated the distribution pattern of a specific xenobiotic metabolizing enzyme, cytochrome P450 3A (CYP3A) in the common brushtail possum (Trichosurus vulpecula). Western blot studies using CYP3A antibodies were used to compare CYP3A levels in the intestine, liver, kidney, brain, testes and adrenal gland in possums fed diets with and without a mixture of terpenes. Possums appear to produce at least 3 different CYP3A-like isoforms that are differentially expressed in various tissues. The liver and duodenum produce all three isoforms (CYP3A P1, P2, P3), the jejunum only produces CYP3A P1, the ileum, kidney, testes and adrenal only produce CYP3A P2 and the brain only produces CYP3A P3. Terpene treatment did not alter relative levels of isoforms present in any tissue type. This study is the first to identify the presence and differential expression of several CYP3A-like isoforms in a variety of tissues of a wild mammalian herbivore. Data suggest that CYP3A-like enzymes are not induced by terpenes. However, the wide distribution of CYP3A-like isoforms in a variety of tissues, suggests that these enzymes are an important mechanism for metabolism in possums and may contribute to the high tolerance possums have to a wide range of xenobiotics.

The use of myocardial and testicular end points as a basis for estimating a proposed tolerable daily intake for sodium monofluoroacetate (1080)

This paper presents the development of a tolerable daily intake (TDI) for sodium monofluoroacetate (1080) using the quantal myocardial and testicular toxicity end points derived from the traditional NOAEL and newer benchmark dose (BMD) methods. 1080 is a highly toxic vertebrate pesticide that has been proven to be effective in controlling possums and other pests. By convention, the TDIs are derived using the traditional no-observed-adverse-effect-level (NOAEL) and applying appropriate default uncertainty factors (UF). In addition to the default UF, a statistically derived UF was also employed in deriving the TDI. The TDIs derived from the NOAEL and BMD approach, 0.075 and 0.10 mg/kg bw/day, respectively, were compared. The resulting TDI estimates using the BMDL, a statistical lower confidence bound on the BMD, were generally consistently slightly higher than those derived using the NOAEL approach. Based on the best fit of modelled dose-response data, a TDI of 0.03 micro g/kg bw/day is proposed for human health risk assessment of 1080.

Effect of the anticoagulant, pindone, on the breeding performance and survival of merino sheep, Ovis aries

The effect of the anticoagulant, pindone, on the breeding performance and survival of relatively free-ranging merino sheep was assessed. Pindone (2-pivalyl-1, 3-indandione) was administered orally as a single (10, 3, or 2 mg pindone kg(-1) over three consecutive days) or multiple exposure (dosing regime repeated after a further 8 days). Prothrombin times (PT) increased up to 4-fold in treated sheep, and haemorrhage occurred in some instances, particularly with the double dose treatment. Deaths of sheep also occurred, usually when the sheep were placed under added stress, particularly that associated with shearing. The breeding performance of pregnant ewes dosed with pindone was reduced, mainly due to an increase in stillborn and nonviable lambs (i.e. deaths within 2 days of birth). The motility of sperm in treated rams was also affected. Pindone persisted in the blood (maximum, 13.2 mg L(-1)) for up to 14 days after the last dose, and the half-life (t1/2) was estimated at approximately 5 days depending upon the dosing regime. Other tissue residues ranged from 17 (fat) to 39 (liver) mg kg(-1). The implications of these findings for ongoing responsible use of pindone (anticoagulants) in pest control programs are also discussed.

The mode of toxic action of the pesticide gliftor: the metabolism of 1,3-difluoroacetone to (-)-erythro-fluorocitrate

The biochemical toxicology of 1,3-difluoroacetone, a known metabolite of the major ingredient of the pesticide Gliftor (1,3-difluoro-2-propanol), was investigated in vivo and in vitro. Rat kidney homogenates supplemented with coenzyme A, ATP, oxaloacetate, and Mg2+ converted 1,3-difluoroacetone to (-)-erythro-fluorocitrate in vitro. Administration of 1,3-difluoroacetone (100 mg kg(-1) body weight) to rats in vivo resulted in (-)-erythro-fluorocitrate synthesis in the kidney, which was preceded by an elevation in fluoride levels and followed by citrate accumulation. Animals dosed with 1,3-difluoroacetone did not display the 2-3 hour lag phase in either (-)-erythro-fluorocitrate synthesis or in citrate and fluoride accumulation characteristic of animals dosed with 1,3-difluoro-2-propanol. We demonstrate that the conversion of 1,3-difluoro-2-propanol to 1,3-difluoroacetone by an NAD+-dependent oxidation is the rate-limiting step in the synthesis of the toxic product, (-)-erythro-fluorocitrate from 1,3-difluoro-2-propanol. Prior administration of 4-methylpyrazole (90 mg kg(-1) body weight) was shown to prevent the conversion of 1,3-difluoro-2-propanol (100 mg kg(-1) body weight) to (-)-erythro-fluorocitrate in vivo and to eliminate the fluoride and citrate elevations seen in 1,3-difluoro-2-propanol-intoxicated animals. However, administration of 4-methylpyrazole (90 mg kg(-1) body weight) to rats 2 hours prior to 1,3-difluoroacetone (100 mg kg(-1) body weight) was ineffective in preventing (-)-erythro-fluorocitrate synthesis and did not diminish fluoride or citrate accumulation in vivo. We conclude that the prophylactic and antidotal properties of 4-methylpyrazole seen in animals treated with 1,3-difluoro-2-propanol derive from its capacity to inhibit the NAD+-dependent oxidation responsible for converting 1,3-difluoro-2-propanol to 1,3-difluoroacetone in the committed step of the toxic pathway.