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

Stereoselective bioaccumulation of chiral anticoagulant rodenticides in the liver of predatory and scavenging raptors

Second-generation anticoagulant rodenticides (SGARs) are persistent chiral pesticides used to control rodent populations. Raptors are protected species and may be exposed through the ingestion of rodents contaminated with SGARs. Commercial formulations of SGARs are a mixture of four stereoisomers (E1, E2, E3, E4): the cis- and trans-diastereoisomers are each a racemic mixture of two enantiomers. In this study, the residue levels of all SGARs (bromadiolone, difenacoum, brodifacoum, difethialone, flocoumafen) were evaluated in the liver of 529 raptor carcasses. All species (n = 18) and 75 % of individuals (n = 396) were SGAR positive and 29 % (n = 154) had summed hepatic concentrations above 100 ng/g ww. Concentrations were higher for predators with facultative scavenging behaviors than for predators and obligate scavengers. Bromadiolone, brodifacoum and difenacoum had equivalent hepatic prevalence (between 48.9 and 49.9 %), and difethialone was detected less frequently (31.7 %). Concentrations and enantiomeric fractions of the four stereoisomers of all SGARs are described in to demonstrate the biological enantioselectivity of these chiral pesticides in the food chain. A difference was observed between the proportions of SGARs diastereoisomers and stereoisomers in the liver of all raptor species and in commercial baits. The enantioselective bioaccumulation of E1-trans-bromadiolone, E3-cis-brodifacoum, E1-cis-difenacoum and E3-cis-difethialone was characterized and represented 96.8 % of total SGARs hepatic residues. While hepatic concentrations were heterogeneous, the proportions of stereoisomers and diastereoisomers were homogeneous with no inter-individual or inter-species differences (only E1-trans-bromadiolone is present in hepatic residues). However, proportions of brodifacoum stereoisomers and diastereoisomers were more scattered, probably due to their slower elimination. This could provide an opportunity to date the exposure of individuals to brodifacoum. We highlight the need to consider each SGAR as four molecular entities (four stereoisomers) rather than one. These findings suggest new commercial formulations with the less persistent stereoisomers could reduce secondary exposure of non-target species.

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.

Enantiomer fraction evaluation of the four stereoisomers of second-generation anticoagulant rodenticides in biological matrices with polysaccharide-based chiral selectors and liquid chromatography tandem mass spectrometry

Numerous cases of wildlife exposure to five second-generation anticoagulant rodenticides have been reported worldwide, and residues of these chiral pesticides in biological matrices are still quantified by achiral liquid chromatography methods. However, they are a mixture of cis- and trans-diastereomers, thus a mixture of four stereoisomers. Their persistence must be evaluated in a differentiated way in the food chain of concerned predator species in order to reduce the environmental impact. This article presents an evaluation of the chiral selectivity of five polysaccharide-based chiral selectors for the four stereoisomers of bromadiolone, difenacoum, brodifacoum, flocoumafen and difethialone. Different chromatographic parameters, influencing the chiral separation, such as organic modifier (acetonitrile, methanol), percentage of formic acid and water content in the mobile phase are systematically tested for all columns. It was shown that little amount of water added to the acetonitrile mobile phase may influence the retention behaviors between reversed phase and HILIC-like modes, and consequently the enantiomer elution order of the four stereoisomers. On the contrary, reversed phase is always the observed mode for the methanol water mobile phase. A suitable combination of all these parameters is presented for each second-generation anticoagulant rodenticide with a description of the enantioresolution, the enantiomer elution order and the retention times of the respective stereoisomers. A method is validated for all stereoisomers of each second-generation anticoagulant rodenticide with chicken liver and according to an official bioanalytical guideline. As an example, the enantiomer fraction is evaluated in the liver of a raptor species (rodent predator) exposed to bromadiolone and difenacoum. The results showed that only one enantiomer of trans-bromadiolone and one enantiomer of cis-difenacoum is present in hepatic residues, although all four stereoisomers are present in bromadiolone and difenacoum rodenticide baits.

Exposure of predatory and scavenging birds to anticoagulant rodenticides in France: Exploration of data from French surveillance programs

Wild raptors are widely used to assess exposure to different environmental contaminants, including anticoagulant rodenticides (ARs). ARs are used on a global scale for rodent control, and act by disruption of the vitamin K cycle that results in haemorrhage usually accompanied by death within days. Some ARs are highly persistent and bioaccumulative, which can cause significant exposure of non-target species. We characterized AR exposure in a heterogeneous sample of dead raptors collected over 12 years (2008-2019) in south-eastern France. Residue analysis of 156 liver samples through LC-MS/MS revealed that 50% (78/156) were positive for ARs, with 13.5% (21/156) having summed second-generation AR (SGAR) concentrations >100 ng/g ww. While SGARs were commonly detected (97.4% of positive samples), first-generation ARs were rarely found (7.7% of positive samples). ARs were more frequently detected and at greater concentration in predators (prevalence: 82.5%) than in scavengers (38.8%). Exposure to multiple ARs was common (64.1% of positive samples). While chlorophacinone exposure decreased over time, an increasing exposure trend was observed for the SGAR brodifacoum, suggesting that public policies may not be efficient at mitigating risk of exposure for non-target species. Haemorrhage was observed in 88 birds, but AR toxicosis was suspected in only 2 of these individuals, and no difference in frequency of haemorrhage was apparent in birds displaying summed SGAR levels above or below 100 ng/g ww. As for other contaminants, 17.2% of liver samples (11/64) exhibited Pb levels compatible with sub-clinical poisoning (>6 μg/g dw), with 6.3% (4/64) above the threshold for severe/lethal poisoning (>30 μg/g dw). Nine individuals with Pb levels >6 μg/g dw also had AR residues, demonstrating exposure to multiple contaminants. Broad toxicological screening for other contaminants was positive for 18 of 126 individuals, with carbofuran and mevinphos exposure being the suspected cause of death of 17 birds. Our findings demonstrate lower but still substantial AR exposure of scavenging birds compared to predatory birds, and also illustrate the complexity of diagnosing AR toxicosis through forensic investigations.

Chiral liquid chromatography-tandem mass spectrometry analysis of superwarfarin rodenticide stereoisomers - Bromadiolone, difenacoum and brodifacoum - In human plasma

Superwarfarins are second-generation long-acting anticoagulant rodenticides that can cause unintended human and wildlife toxicity due, in part, to their prolonged half-lives. Commercially available superwarfarin rodenticides are synthesized as racemates with two asymmetric carbons, producing four stereoisomers. To support studies of human plasma half-lives of individual superwarfarin stereoisomers, a method was developed based on LC-MS/MS to separate and quantify stereoisomers of the commercially important superwarfarins bromadiolone, difenacoum and brodifacoum. Human plasma samples were prepared using protein precipitation and centrifugation. Chiral-phase HPLC separation was carried out on-line with tandem mass spectrometric quantitative analysis of the eluting stereoisomers using selected-reaction monitoring with positive ion electrospray on a triple quadrupole mass spectrometer. All four stereoisomers of each superwarfarin were resolved within 12.5 min with calibration curves spanning 2-3 orders of magnitude and lower limits of quantitation between 0.87 and 2.55 ng/mL. This method was used to determine the half-lives of superwarfarin stereoisomers in plasma from patients who had inhaled synthetic cannabinoid products contaminated with superwarfarins. These data may be used to guide the development of safer next generation anticoagulant rodenticides stereoisomers.

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.