Assessment of the potential toxicity of a poison for rabbits, pindone (2-pivalyl 1, 3 indandione), to domestic animals

Biomarkers Potency to Monitor Non-target Fauna Poisoning by Anticoagulant Rodenticides

The widespread use of pesticides to control agricultural pests is a hot topic on the public scene of environmental health. Selective pest control for minimum environmental impact is a major goal of the environmental toxicology field, notably to avoid unintended poisoning in different organisms. Anticoagulant rodenticides cause abnormal blood coagulation process; they have been widely used to control rodents, allowing inadvertent primary and secondary exposure in domestic animals and non-target predatory wildlife species through direct ingestion of rodenticide-containing bait or by consumption of poisoned prey. To report toxic effect, the most common approach is the measurement of liver or plasma residues of anticoagulant rodenticides in dead or intoxicated animals showing clinical symptoms. However, one major challenge is that literature currently lacks a hepatic or plasma concentration threshold value for the differentiation of exposure from toxicity. Regarding the variation in pharmacology properties of anticoagulant rodenticides inter- and intra-species, the dose-response relationship must be defined for each species to prejudge the relative risk of poisoning. Beyond that, biomarkers are a key solution widely used for ecological risk assessment of contaminants. Since anticoagulant rodenticides (AR) have toxic effects at the biochemical level, biomarkers can serve as indicators of toxic exposure. In this sense, toxicological knowledge of anticoagulant rodenticides within organisms is an important tool for defining sensitive, specific, and suitable biomarkers. In this review, we provide an overview of the toxicodynamic and toxicokinetic parameters of anticoagulant rodenticides in different animal species. We examine different types of biomarkers used to characterize and differentiate the exposure and toxic effects of anticoagulant rodenticide, showing the strengths and weaknesses of the assays. Finally, we describe possible new biomarkers and highlight their capabilities.

Accidental chlorophacinone exposure of lactating ewes: Clinical follow-up and human health dietary implications

Anticoagulant rodenticides are widely used for rodent control in agricultural and urban settings. Their intense use can sometimes result in accidental exposure and even poisoning of livestock. Can milk, eggs or meat derived from such accidently exposed animals be consumed by humans? Data on the pharmacokinetics of chlorophacinone in milk of accidently exposed ewes were used to estimate the risk associated with its consumption. Three days after accidental ingestion, chlorophacinone was detected in plasma of 18 ewes, with concentrations exceeding 100 ng/mL in 11 animals. Chlorophacinone was detected in milk on day 2 post-exposure and remained quantifiable for at least 7 days in milk of these 11 ewes. Concentrations in milk were much lower than in plasma and decreased quickly (mean half-life of 2 days). This study demonstrated dose-dependent mammary transfer of ingested chlorophacinone. Variation in prothrombin time (PT) on Day 3 suggested that some of the ewes that ingested chlorophacinone may have been adversely affected, but PT did not facilitate estimation of the quantity of chlorophacinone consumed. Using safety factors described in the literature, consumption of dairy products derived from these ewes after a one-week withdrawal period would pose low risk to consumers.

Pindone residues in rabbit tissues: implications for secondary hazard and risk to non-target wildlife

Context Pindone is used to control rabbits in Australia and New Zealand, but the secondary non-target risks presented by pindone-poisoned rabbits are poorly known. Aims We aimed to generate new data on residual concentrations of pindone in poisoned rabbits for use in a review of the secondary poisoning risks posed to non-target animals in New Zealand. Methods Laboratory rabbits were offered pellet bait containing 0.25 g kg–1 pindone in three trials to simulate a range of bait uptake scenarios: single exposure and low or high chronic exposure. Residual pindone concentrations measured in body tissues of laboratory rabbits that had ingested known exposures of pindone were compared with those in wild rabbit carcasses collected after three pindone-baiting operations. Residues in the faeces of some laboratory rabbits were also measured. Key results Highest concentrations of pindone residues were in the liver and fat tissue of poisoned rabbits, with consistently lower concentrations in muscle tissue. A dose–response relationship between pindone exposure and liver residue concentrations was found only at the highest chronic exposures. Rabbit carcasses collected after field-baiting operations had generally higher pindone residue concentrations than did laboratory rabbits that had ingested known lethal amounts of bait. Unmetabolised pindone was excreted in rabbit faeces. Conclusions The occurrence of the highest residual pindone concentrations in rabbit liver was consistent with the known tissue distribution of anticoagulants in mammals; however, the co-occurrence of similar-range pindone concentrations in rabbit fat has not been previously described. Re-ingestion of soft faecal pellets (caecotrophy) in rabbits that have eaten pindone bait may function as a secondary exposure to increase or prolong their oral exposure to pindone. Some rabbits poisoned following field pindone-baiting operations are likely to have consumed well in excess of a lethal amount of bait. Implications Concentrations of residual pindone in fat and liver of poisoned rabbits suggest that secondary poisoning hazard to some non-target predators and scavengers is high. The lack of field-based assessments of the non-target impacts of pindone is a marked information gap that needs to be addressed.

Assessment of ruminal degradation, oral bioavailability, and toxic effects of anticoagulant rodenticides in sheep

OBJECTIVE

To assess the rate and extent of ruminal degradation of warfarin, chlorophacinone, and bromadiolone in vitro and determine the oral availability and clinical and hemostatic effects of each anticoagulant rodenticide in adult sheep.

ANIMALS

3 Texel sheep.

PROCEDURE

Samples of ruminal fluid were incubated with each of the anticoagulants to assess the kinetics of ruminal degradation over 24 hours. To determine the plasma kinetics of the anticoagulants, each sheep received each of the anticoagulants IV or via a rumenimplanted cannula at 2-month intervals (3 rodenticide exposures/sheep). At intervals during a 240- to 360- hour period after treatment, prothrombin time (PT) was measured, plasma anticoagulant concentration was assessed, and clinical signs of rodenticide poisoning were monitored. In plasma and rumen extracts, anticoagulant concentrations were determined via high-performance liquid chromatography.

RESULTS

In the rumen extracts, anticoagulants were slightly degraded (< 15%) over 24 hours. In vivo, oral availability of warfarin, chlorophacinone, and bromadiolone was estimated at 79%, 92%, and 88%, respectively. Although maximum PT was 80 seconds after chlorophacinone and bromadiolone treatments, no clinical signs of toxicosis were detected; PT returned to baseline values within 2 weeks.

CONCLUSIONS AND CLINICAL RELEVANCE

In sheep, warfarin, chlorophacinone, and bromadiolone were not degraded in the rumen but their bioavailabilities were high after oral administration; the kinetics of these compounds in sheep and other mammals are quite similar. These data suggest that the lack of susceptibility of ruminants to these anticoagulant rodenticides cannot be explained by either ruminal degradation or the specific toxicokinetics of these anticoagulants.

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 effect of sub-lethal doses of bromadiolone on the breeding performance of house mice (Mus domesticus)

Both laboratory and field strains of Mus were exposed to wheat containing 0.0001% bromadiolone under laboratory and outdoor conditions, respectively. While both strains readily consumed the poisoned wheat, ad libitum sub-lethal doses of this anticoagulant equating to between 20% and 70% of the acute LD50 per feed had little apparent effect on the breeding performance of these mice. The implications of these findings are discussed with respect to the use of anticoagulants as pesticides.