Risk-benefit considerations in evaluating commensal anticoagulant rodenticide impacts to wildlife

Abstract

Evaluation of the possible impacts of rodenticides on wildlife must be conducted in the context of riskbenefit considerations. Harmful introduced pests (e.g ., commensal rats and mice) historically have required management around human habitation for economic and public health reasons. Disparate views of limited data have accumulated concerning the wildlife impacts resulting from commensal rodent control activities. The founding of the Rodenticide Registrants Task Force (RRTF). a trade association that includes all the major manufacturers and importers of anticoagulant rodenticide products (and bromethalin, a non-anticoagulant rodenticide) in the U.S., is described. The potential for anticoagulant dispersion in wildlife via primary and secondary routes is considered. Toxicology and pharmacokinetic studies are analyzed to obtain a better understanding of the biological and toxicological significance of low levels of rodenticide in animal tissue. A framework to address rodenticide impact to wildlife is presented. It is based upon the example of long-tenn cooperative efforts in England involving government, environmental, and manufacturer groups.

Anticoagulant Residues in Non-Target Wildlife – Assessing Sublethal Exposure to Brodifacoum without Lethal Sampling

“…Brakes and Smith (2005) demonstrate that routine commensal rat control using an anticoagulant reduced local populations of some non-target small mammals, demonstrating a significant route of secondary anticoagulant exposure for predators and scavengers. While the toxicological significance of apparently sublethal brodifacoum residues in wildlife remains uncertain (Kaukeinen et al 2000), the potential for cumulative or chronic toxicosis needs further investigation. It may be that single or infrequent sublethal exposures do not significantly compromise long-term survival or reproductive fitness, but because the effects of cumulative or longterm exposure are not known, the ability to characterize field exposure profiles would be of great value in a proactive approach to identifying and minimizing risks to non-target wildlife.…”

Environmental Monitoring for Brodifacoum Residues after Aerial Application of Baits for Rodent Eradication

“…For example, Littin et al (2002) measured concentrations as low as 0.33 ppm in livers of lethally poisoned possums, but sublethally exposed chickens (Gallus gallus) had liver residues of 0.45-1.00 ppm (Fisher 2009). Rather than estimating a threshold liver concentration definitive of lethal brodifacoum exposure (e.g., Kaukeinen et al 2000), it is more valid to attribute increasing certainty of lethal exposure with increasing liver concentration -as did Myllymäki et al (1999), who estimated that survival probability in voles (Microtus sp.) started decreasing at 0.20 ppm in liver.…”

Concerns Regarding Proposed Restrictions in the Use of Second-Generation Anticoagulant Rodenticides for Commensal Rodent Control

“…Pest rodents cause extensive economic damage and risk to public health (Kaukeinen et al 2000). The environmental impacts and economic costs in the U.S. have been estimated at $19 billion per year, far more than any other invasive animal species (Pimentel et al 2000).…”

“…As a primary control technique, rodenticides constitute about 60% to 80% of control purchases to manage these harmful species, with the remainder primarily for traps (USEPA 2006). Homeowners purchase about 40 to 50 million containers or placements of rodenticides yearly (Kaukeinen et al 2000).…”

“…The resulting so-called 'second-generation' anticoagulants (SGARs) provided greater efficacy than the first-generation anticoagulant rodenticides (FGARs) (Kaukeinen and Rampaud 1986). In particular, they were more effective against house mice, controlled rodents resistant to warfarin and other older anticoagulants, and were effective in limited feedings, which was helpful in controlling sporadically-feeding commensal rodents as well as limiting the duration that baits had to be exposed to achieve control (Kaukeinen et al 2000). During the past three decades, the SGARs have been used to control commensal rats and mice in and around structures by homeowners, business personnel, and pest management professionals (PMPs).…”