Liver and fecal samples suggest differential exposure of red fox (Vulpes vulpes) to trans- and cis-bromadiolone in areas from France treated with plant protection products

Greater predisposition to second generation anticoagulant rodenticide exposure in red foxes (Vulpes vulpes) weakened by suspected infectious disease

Anticoagulant rodenticide (AR) exposure in wild carnivores is a current and global concern due to continuous and widespread use worldwide. We studied the prevalence of ARs in liver samples of 25 red foxes (Vulpes vulpes), 3 European badgers (Meles meles) and 2 genets (Genneta genneta) from Alicante (Spanish Levante region) obtained in 2021 and 2022. In addition to trauma, poisoning by pesticides is the most frequent cause of death in wild carnivores in this region. The present research aims to explain a possible association between the fact of suffering from an infectious disease and the increase in ARs concentrations in the affected animals. Both first- and second-generation ARs were analysed by HPLC/MS/TOF in liver samples. Apart from the cause of death, the influence of other variables such as age, sex and body weight were also assessed on AR liver concentrations. Potential health risks for individuals and populations in the study area have also been studied. Our research detected higher AR concentrations in the group of red foxes clinically diagnosed with infectious disease compared to the group of apparently healthy red foxes, mostly killed by trauma. Furthermore, our results lead us to suggest that red fox could be considered a good sentinel species for the risk of exposure to ARs in other wild mammals. All the livers analysed contained ARs and the most detected compounds in red fox were difenacoum, bromadiolone, brodifacoum, present in all the samples analysed, and flocoumafen (in 96 %). Additionally, 53 % of the animals had at least one second generation anticoagulant rodenticide (SGAR) above the threshold value reported as triggering adverse health effects (200 ng/g). Regarding this, the level of risk in red fox in this area might be classified as high and worrying. Moreover, we suggest that individuals and populations with weakened health due to other diseases (for example, infectious or parasitic diseases) might be more prone to high exposure to anticoagulant rodenticides and, very probably, would be more sensitive to suffering serious effects at lower doses of ARs.

Interest of the faecal and plasma matrix for monitoring the exposure of wildlife or domestic animals to anticoagulant rodenticides

Anticoagulant rodenticides (ARs), particularly second-generation compounds (SGAR), are known to be a potential threat to unintended species due to their tissue persistence. The liver is the storage tissue of ARs and is a matrix of choice in diagnosing exposure and intoxication of non-target fauna. However, it is only available on dead animals. Blood and faeces can be used on living animals. These two biological matrices were compared in terms of their relevance to exposure to ARs. In addressing this question, we compared the faecal, plasma and liver concentrations of bromadiolone, one of the SGAR frequently implicated in wildlife exposure. We studied this comparison at the individual level and at the population level, considering three influencing factors: dose, sex and time. Our findings demonstrate that faecal analyses are more valuable than plasma analyses for monitoring AR exposure of domestic and wild animals, even if faecal concentrations cannot be correlated with liver concentrations.

Weasel exposure to the anticoagulant rodenticide bromadiolone in agrarian landscapes of southwestern Europe

Bromadiolone is an anticoagulant rodenticide (AR) commonly used as a plant protection product (PPP) against rodent pests in agricultural lands. ARs can be transferred trophically to predators/scavengers when they consume intoxicated live or dead rodents. ARs exposure in weasels Mustela nivalis, small mustelids specialized on rodent predation, is poorly known in southern Europe. Moreover, in this species there is no information on bioaccumulation of AR diastereomers e.g., cis- and trans-bromadiolone. Trans-bromadiolone is more persistent in the rodent liver and thus, is expected to have a greater probability of trophic transfer to predators. Here, we report on bromadiolone occurrence, total concentrations and diastereomers proportions (trans- and cis-bromadiolone) in weasels from Castilla y León (north-western Spain) collected in 2010-2017, where bromadiolone was irregularly applied to control outbreaks of common voles Microtus arvalis mainly with cereal grain bait distributed by the regional government. We also tested variables possibly associated with bromadiolone occurrence and concentration, such as individual features (e.g., sex), spatio-temporal variables (e.g., year), and exposure risk (e.g., vole outbreaks). Overall bromadiolone occurrence in weasels was 22% (n = 32, arithmetic mean of concentration of bromadiolone positives = 0.072 mg/kg). An individual showed signs of bromadiolone intoxication (i.e., evidence of macroscopic hemorrhages or hyperaemia and hepatic bromadiolone concentration > 0.1 mg/kg). All the exposed weasels (n = 7) showed only trans-bromadiolone diastereomer in liver, whilst a single analyzed bait from those applied in Castilla y León contained trans- and cis-bromadiolone at 65/35%. Bromadiolone occurrence and concentration in weasels varied yearly. Occurrence was higher in 2012 (100% of weasels), when bromadiolone was widely distributed, compared to 2016-2017 (2016: 20%; 2017: 8.33%) when bromadiolone was exceptionally permitted. The highest concentrations happened in 2014 and 2017, both years with vole outbreaks. Our findings indicate that specialist rodent predators could be exposed to bromadiolone in areas and periods with bromadiolone treatments against vole outbreaks.

Anticoagulant rodenticide use in oil palm plantations in Southeast Asia and hazard assessment to non-target animals

Anticoagulant rodenticides (ARs) are used worldwide for the control of rodent pests and are the main method of control of rat pest populations in agricultural areas. The main aim of this review is to discuss the risk of ARs to non-target wildlife in oil palm areas in Southeast Asia, mainly Indonesia and Malaysia. We discussed AR use in oil palm areas and toxicities of ARs on target and non-target animals. We also reviewed published literature on wildlife species reported in oil palm areas in Southeast Asia and utilizing this information, we assessed the hazard risk of ARs to non-target wildlife in oil palm plantations. ARs are a secondary exposure hazard to rodent-consuming mammalian carnivores, such as leopard cats and civets, and rodent-consuming raptors, such as barn owls. Consumption of dead poisoned prey puts scavengers, such as water monitors, at high risk for AR exposure. Domestic livestock and granivorous birds are at high risk for AR exposure via primary exposure to toxic bait, while omnivores such as macaques and wild pigs are at moderate risk for both primary and secondary exposure to ARs. The effects of ARs on barn owls have been well studied in the field and in laboratory secondary toxicity studies. Thus, the nest-box occupancy and reproductive parameters of local barn owl populations can be monitored as an indicator of the AR exposure level in the area. CLINICAL TRIALS REGISTRATION: No clinical trials were involved in this study.

Asymptomatic Anticoagulant Rodenticide Exposure in Dogs and Cats—A French and Belgian Rural and Urban Areas Study

Anticoagulant rodenticides (ARs) are important tools for controlling rodent pests, but they also pose a health threat to non-target species. ARs are one of the most common causes of pet poisoning. However, exposure of domestic animals to subclinical doses of ARs is poorly documented. To study the random exposure of dogs and cats to ARs, feces from animals showing no clinical signs of rodenticide poisoning were collected from a network of French and Belgian veterinarians. We analyzed fresh feces from 304 dogs and 289 cats by liquid chromatography-tandem mass spectrometry. This study showed a limited prevalence of AR exposure in dogs and cats of 2.6 and 4.5% respectively. In both species, access to the outdoors is a risk factor for ARs exposure. In contrast, the sex of the animals did not affect the ARs exposure status. The observation of the ratio of cis and trans isomers suggested primary exposure in dogs, but also in some cats. While primary exposure in dogs appears to be related to the use of ARs as plant protection products, primary exposure in cats may be malicious, as warfarin, an anticoagulant formerly used as a rodenticide and now used only in humans, was found in 4 of 13 exposed cats. Secondary exposure may also occur in cats.Our study showed reduced exposure in dogs and cats, compared to wildlife, which often has high exposure, especially in areas where rodent control is important.

Endangered Australian top predator is frequently exposed to anticoagulant rodenticides

Anticoagulant rodenticides (ARs) used to control mammalian pest populations cause secondary exposure of predatory species throughout much of the world. It is important to understand the drivers of non-target AR exposure patterns as context for assessing long-term effects and developing effective mitigation for these toxicants. In Australia, however, little is known about exposure and effects of ARs on predators. We detected AR residues in 74% of 50 opportunistically collected carcasses of the Tasmanian wedge-tailed eagle (Aquila audax fleayi), an endangered apex predator. In 22% of birds tested, or 31% of those exposed, liver concentrations of second generation ARs (SGARs) were >0.1 mg/kg ww. Eagles were exposed to flocoumafen, a toxicant only available from agricultural suppliers, at an exceptionally high rate (40% of birds tested). Liver SGAR concentrations were positively associated with the proportion of agricultural habitat and human population density in the area around where each eagle died. The high exposure rate in a species not known to regularly prey upon synanthropic rodents supports the hypothesis that apex predators are vulnerable to SGARs. Our results indicate that AR exposure constitutes a previously unrecognized threat to Tasmanian wedge-tailed eagles and highlight the importance of efforts to address non-target AR exposure in Australia.

Seasonal diet-based resistance to anticoagulant rodenticides in the fossorial water vole (Arvicola amphibius)

Anticoagulant rodenticides (AR) resistance has been defined as "a major loss of efficacy due to the presence of a strain of rodent with a heritable and commensurately reduced sensitivity to the anticoagulant". The mechanism that supports this resistance has been identified as based on mutations in the Vkorc1 gene leading to severe resistance in rats and mice. This study evaluates the validity of this definition in the fossorial water vole and explores the possibility of a non-genetic diet-based resistance in a strict herbivorous rodent species. Genetic support was explored by sequencing the Vkorc1 gene and the diet-based resistance was explored by the dosing of vitamins K in liver of voles according to seasons. From a sample of 300 voles, only 2 coding mutations, G71R and S149I, were detected in the Vkorc1 gene in the heterozygous state with low allele frequencies (0.5-1%). These mutations did not modify the sensitivity to AR, suggesting an absence of genetic Vkorc1-based resistance in the water vole. On the contrary, vitamin K1 was shown to be 5 times more abundant in the liver of the water vole compared to rats. This liver concentration was shown to seasonally vary, with a trough in late winter and a peak in late spring/early summer related to the growth profile of grass. This increase in concentration might be responsible for the increased resistance of water voles to AR. This study highlights a non-genetic, diet-related resistance mechanism in rodents to AR. This diet-based resistance might explain the different evolution of the Vkorc1 gene in the fossorial water vole compared to rats and mice.

Monitoring the hepatic residues of cis- and trans-diastereoisomers of second generation anticoagulant rodenticides reveals a different bioaccumulation of diastereoisomers in the food chain of the Réunion harrier (Circus maillardi)

The Réunion harrier is an endangered raptor and endemic species to the Réunion Island. Second generation anticoagulant rodenticides (SGARs) are widely used pesticides on the island in order to control rodent populations. The latter are responsible for the transmission of leptospirosis to humans, the damage of sugarcane crops, and the decline of endemic endangered birds. SGARs are very persistent chiral pesticides and consequent secondary exposure or poisoning of the Réunion harrier has been observed (73% of prevalence in a group of 58 harriers). Commercial formulations of SGARs are a mixture of trans- and cis-diastereoisomers. Both diastereoisomers of all SGARs have been shown to inhibit coagulation function with the same potency. On the other hand, they have been shown to have a significant difference in terms of tissue-persistence. This difference has led to residue levels in rats with a significantly lower proportion of one of the isomers compared to the bait composition. In this study, residue levels of the diastereoisomers of all SGARs were evaluated in the livers of 58 harrier carcasses. The respective concentrations and proportions of cis- and trans- diastereoisomers of all SGARs are presented. cis-Brodifacoum and trans-bromadiolone had the highest concentrations (up to 438 and 573 ng/g ww respectively), while trans-brodifacoum was less than 46 ng/g and cis-bromadiolone was barely detected. cis-Difenacoum showed the highest prevalence and the highest concentration was 82 ng/g ww, while trans-difenacoum was never detected. This study demonstrated that only cis-brodifacoum and trans-bromadiolone (and cis-difethialone, but with a low prevalence) had hepatic concentrations above a toxic threshold. The cis- and trans-diastereoisomers of SGARs had differential bioaccumulation in the food chain of the Réunion harrier compared to commercial baits. This suggests that a change of the proportions of SGARs diastereoisomers in baits could reduce the risk of secondary poisoning of predators, but maintain primary toxicity.

Risk of Anticoagulant Rodenticide Exposure for Mammals and Birds in Parc National des Pyrénées, France

The extensive use of anticoagulant rodenticides (ARs) to control rodent populations poses intoxication risks for wildlife: persistence of ARs in rodents can cause secondary exposure and poisoning of predators or scavengers. We investigated risk factors for wildlife exposure to ARs in the Parc National des Pyrénées (PNP), France, using a multivariable logistic regression analysis. A total of 157 liver samples were collected from carcasses of 10 mammal and three bird species found in the PNP between 2010 and 2018 and screened for presence of AR residues. First- and second-generation ARs were detected in more than 60% of red fox (Vulpes vulpes) and stone marten (Martes foina) samples and in around 40% of wild cat (Felis silvestris), European pine marten (Martes martes), American mink (Neovison vison), and Eurasian Buzzard (Buteo buteo) samples. Wildlife exposure to ARs was significantly associated with species having a regular consumption of small mammals (odds ratio [OR]: 2.5, 95% confidence interval [CI]: 1.1-5.8) being collected in the Ossau valley (OR: 2.5, 95% CI: 1.1-6.1) and between 2013 and 2015 (OR: 4.8, 95% CI: 2.0-11.7). We identified wild species that could be targeted for risk-based surveillance program for AR secondary exposure and determined high risk areas in which alternative measures should be applied for rodent control.

Water vole management - Could anticoagulant rodenticides stereochemistry mitigate the ecotoxicity issues associated to their use?

Cyclic water vole population explosions can be controlled in some European countries with anticoagulant rodenticides leading sometimes to wildlife poisonings due to the toxin's tissue persistence. Here, we analyzed the pharmacokinetics of rodenticide residues in voles and we explored potential ways of improving the mass application of these agents based on the concept of stereoisomers. We demonstrated the dramatic persistence of bromadiolone in vole tissues with a hepatic half-life of about 10-30 days, while the tissue persistence of chlorophacinone is rather short with a hepatic half-life of about one day. The dramatic persistence of bromadiolone is due to the trans-isomer group (the major compound in bromadiolone), while the cis-isomer group has a short half-life. Because of resistance to chlorophacinone, the cis-bromadiolone isomers may constitute an excellent compromise between efficacy and ecotoxicological risk to control voles. A mathematical model is proposed to favor the development of baits mixed with cis-isomer groups.

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.

Feces are Effective Biological Samples for Measuring Pesticides and Flame Retardants in Primates

The habitats of wild primates are increasingly threatened by surrounding anthropogenic pressures, but little is known about primate exposure to frequently used chemicals. We applied a novel method to simultaneously measure 21 legacy pesticides (OCPs), 29 current use pesticides (CUPs), 47 halogenated flame retardants (HFRs), and 19 organophosphate flame retardants in feces from baboons in the U.S.A., howler monkeys in Costa Rica, and baboons, chimpanzees, red-tailed monkeys, and red colobus in Uganda. The most abundant chemicals were α-hexachlorocyclohexane (α-HCH), β-hexachlorocyclohexane (β-HCH), and hexachlorobenzene among OCPs across all sites, chlorpyrifos among CUPs in Costa Rica and Indiana, decabromodiphenylethane (DBDPE) in Costa Rica and Indiana and 2, 2', 4, 4'-tetrabromodiphenyl ether (BDE-47) in Uganda as HFRs, and tris(2-butoxyethyl) phosphate (TBOEP) as OPFRs across all sites. The detected chemical concentrations were generally higher in red-tailed monkeys and red colobus than in chimpanzees and baboons. Our methods can be used to examine the threat of chemical pollutants to wildlife, which is critical for endangered species where only noninvasive methods can be used.

Comparison of anticoagulant rodenticide concentrations in liver and feces from apparently healthy red foxes

Exposure of wildlife and domestic animals to anticoagulant rodenticides (ARs) is a worldwide concern, but few methods exist to determine residue levels in live animals. Traditional liver detection methods preclude determining exposure in live wildlife. To determine the value of assessing AR exposure by fecal analysis, we compared fecal and liver residues of ARs in the same animals. We collected liver and fecal samples from 40 apparently healthy red foxes (Vulpes vulpes) potentially exposed to ARs, and quantified brodifacoum, bromadiolone, coumatetralyl, difenacoum, difethialone, and flocoumafen residues by liquid chromatography-tandem mass spectrometry. Residues of ARs were detected in 53% of the fecal samples and 83% of the liver samples. We found good concordance between AR residues in feces and liver for coumatetralyl, difenacoum, and difethialone. Bromadiolone occurred in significantly greater frequency in livers compared to feces, but no significant difference in concentration between feces and liver in individual foxes could be detected. Brodifacoum displayed a significant difference in concentration and occurrence of positive samples between liver and feces. Our findings demonstrate that fecal analysis of ARs provides a feasible and valuable non-lethal means of determine AR exposure in live wildlife.

Comparative biological properties of the four stereoisomers of difethialone, a second-generation anticoagulant rodenticide, in rats: development of a model allowing to choose the appropriate stereoisomeric ratio

The current management of rodent pest populations is based on second-generation anticoagulant rodenticides (SGAR). These molecules, of which difethialone is part, are much more efficient than the first generation. Nevertheless, this efficiency comes with a major drawback, SGARs are tissue persistent that increases the exposure of rodent predators to them. According to its chemical structure, difethialone has four stereoisomers, whose specific inhibition potency and pharmacokinetic have never been described and might be useful to design new eco-friendly rodenticides. The study aimed to investigate the ability to inhibit anticoagulant target enzyme (VKORC1) and the pharmacokinetics in rats of the four difethialone stereoisomers in rats. We show that stereoisomers are all highly efficient to inhibit VKORC1 activity, but they have distinct initial half-life with 6.0 h, 25.4 h, 69.3 h, and 82.3 h for, respectively, E4-trans, E2-cis, E1-trans, and E3-cis stereoisomer. These results open the way of the development of eco-friendly and efficient rodenticide by mixing some of these stereoisomers. Preferential incorporation of the E4-trans stereoisomer (high inhibitory VKORC1 potency, relatively shorter liver half-life) into difethialone rodenticides baits might result in a more eco-friendly product than current commercially available difethialone formulations. In addition, we put forward modelling to help design bait according to the circumstance of use (presence of non-target species, food competition, etc.) by modulating the theorical AUC and and the theorical concentration of the product at the death of the rodent pest. Thus, this modeling might allow to diminish the use of laboratory animal in assay.

The stereoisomerism of second generation anticoagulant rodenticides: a way to improve this class of molecules to meet the requirements of society?

Second generation anticoagulant rodenticides (SGAR) are generally highly efficient for rodent management even towards warfarin-resistant rodents. Nevertheless, because of their long tissue-persistence, they are very associated with non-target exposure of wildlife and have been identified as 'Candidates for Substitution' by the European Union's competent authority. A promising way to reduce ecotoxicity issues associated to SGAR could be the improvement of SGAR based on their stereoisomery, and due to this improvement, positioning about SGAR might be reconsidered. © 2018 Society of Chemical Industry.

Anticoagulant rodenticide exposure in an Australian predatory bird increases with proximity to developed habitat

Anticoagulant rodenticides (ARs) are commonly used worldwide to control commensal rodents. Second generation anticoagulant rodenticides (SGARs) are highly persistent and have the potential to cause secondary poisoning in wildlife. To date no comprehensive assessment has been conducted on AR residues in Australian wildlife. My aim was to measure AR exposure in a common widespread owl species, the Southern Boobook (Ninox boobook) using boobooks found dead or moribund in order to assess the spatial distribution of this potential threat. A high percentage of boobooks were exposed (72.6%) and many showed potentially dangerous levels of AR residue (>0.1 mg/kg) in liver tissue (50.7%). Multiple rodenticides were detected in the livers of 38.4% of boobooks tested. Total liver concentration of ARs correlated positively with the proportions of developed areas around points where dead boobooks were recovered and negatively with proportions of agricultural and native land covers. Total AR concentration in livers correlated more closely with land use type at the spatial scale of a boobook's home range than at smaller or larger spatial scales. Two rodenticides not used by the public (difethialone and flocoumafen) were detected in boobooks indicating that professional use of ARs contributed to secondary exposure. Multiple ARs were also detected in recent fledglings, indicating probable exposure prior to fledging. Taken together, these results suggest that AR exposure poses a serious threat to native predators in Australia, particularly in species using urban and peri-urban areas and species with large home ranges.