Challenges in the interpretation of anticoagulant rodenticide residues and toxicity in predatory and scavenging birds

Abstract

Anticoagulant rodenticides (ARs) are part of the near billion‐dollar rodenticide industry. Numerous studies have documented the presence of ARs in nontarget wildlife, with evidence of repeated exposure to second‐generation ARs. While birds are generally less sensitive to ARs than target rodent species, in some locations predatory and scavenging birds are exposed by consumption of such poisoned prey and, depending on dose and frequency of exposure, exhibit effects of intoxication that can result in death. Evidence of hemorrhage in conjunction with summed hepatic AR residues >0.1–0.2 mg kg−1 liver wet weight are often used as criteria to diagnose ARs as the likely cause of death. In this review focusing on birds of prey and scavengers, we discuss AR potency, coagulopathy, toxicokinetics and long‐lasting effects of residues, and the role of nutrition and vitamin K status on toxicity, and identify some research needs. A more complete understanding of the factors affecting AR toxicity in nontarget wildlife could enable regulators and natural resource managers to better predict and even mitigate risk. Published 2020. This article is a U.S. Government work and is in the public domain in the USA

Endangered Australian top predator is frequently exposed to anticoagulant rodenticides

“…The use of AR concentration thresholds to interpret the likely physiological result has limitations due to inter-and intra-specific variation in susceptibility to toxicity (Rattner and Harvey, 2021 ;Thomas et al, 2011). That said, concentrations in 22% of the birds we studied were well above the potentially lethal range reported for European barn owls (Tyto alba; > 0.1 mg/kg; Newton et al 1999).…”

“…We used total SGAR concentrations to estimate the effects of over-all SGAR contamination due to their similar mode of action (Rattner and Harvey, 2021). FGARs were not included in the summed concentrations due to large differences in molecular weight, potency and half-life compared to SGARs (Rattner and Harvey, 2021).…”

“…We used total SGAR concentrations to estimate the effects of over-all SGAR contamination due to their similar mode of action (Rattner and Harvey, 2021). FGARs were not included in the summed concentrations due to large differences in molecular weight, potency and half-life compared to SGARs (Rattner and Harvey, 2021). To estimate potential toxicological effects of the total SGAR concentrations detected, we used published contamination thresholds (see Lohr, 2018) as follows: (i) 0.001-0.01 mg/kg ww, probably no toxicity; (ii) 0.01-0.1 mg/kg ww, unlikely lethal / possible toxicity; (iii) 0.1-0.5 mg/kg ww, possibly lethal / likely toxicity;…”

Anticoagulant rodenticide exposure and toxicosis in bald eagles (Haliaeetus leucocephalus) and golden eagles (Aquila chrysaetos) in the United States

“…The diagnosis of AR toxicosis in raptors and other wildlife has numerous challenges [36]. The specific concentrations of individual AR compounds that cause coagulopathy in bald eagles and golden eagles have not been determined due to the inability to perform experimental studies to determine lethal doses.…”

In Focus: vertebrate management and risk mitigation

“…However, it is often unclear what thresholds are for lethal and sub‐lethal effects in non‐target species. A review presented in this In Focus is dedicated to the assessment of AR potency, coagulopathy, toxicokinetics and long‐lasting effects of residues on toxicity in birds of prey and scavengers 14 . Better knowledge of the mechanisms of these factors helps to forecast risk and optimally align risk mitigation measures.…”