The California Department of Food and Agriculture holds registrations for four grain-based anticoagulant rodenticides used in agricultural areas in California to control the California ground squirrel. These rodenticides contain either chlorophacinone or diphacinone as the active ingredient at 0.005% or 0.01% by weight, and are applied by either broadcast or spot baiting techniques. Using residue data from recent field studies, an ecological risk assessment was performed for non-target species potentially receiving secondary exposure through consumption of squirrel carcasses. The species of concern included five birds (American kestrel, burrowing owl, common raven, golden eagle, red-tailed hawk) and one highly sensitive mammal, the coyote. Risks to nontarget species were estimated using a risk quotient (RQ) approach, with RQ values calculated using species-specific daily exposure estimates and levels of concern derived from subchronic toxicity studies. Exposure estimates for the birds of concern ranged from 0.05-0.21 mg/kg bw/day for chlorophacinone and from 0.04-0.16 mg/kg bw/day for diphacinone. For chlorophacinone uses, RQs for birds ranged from 0.172-0.724. RQ values for diphacinone were 16-18 times lower. Based on the methodology used and using EPA risk criteria, the RQ data indicate de minimus risks for all avian receptors of concern. Exposure estimates for adult and subadult coyotes spanned a range from 0.009-0.028 mg a.i./kg bw/day depending on the use pattern. RQs for mortality and blood coagulation were generally near, or slightly above, a value of 1.0 for all of the use patterns evaluated; however, because of the conservative exposure assumptions and other factors, it is highly unlikely that ecologically significant effects on coyotes does or could occur due to use of CDFA’s anticoagulant baits. Wildlife incidence data and population modeling studies corroborate this. Based on the weight of evidence, it is concluded that use of CDFA’s rodenticides for spot and broadcast baiting will not cause “unreasonable adverse effects” on coyote populations or those of other predators/scavengers that feed on squirrel carcasses.

After several years of reviewing study data and conducting risk assessments, in September of 1998 the U.S. Environmental Protection Agency (U.S. EPA) issued for comment a Reregistration Eligibility Decision (RED) document for pesticide products in the Rodenticide Cluster. The RED document covered 243 rodenticide products containing the following active ingredients: brodifacoum, bromadiolone, bromethalin, chlorophacinone, diphacinone and its sodium salt, and pival and its sodium salt. The U.S. EPA’s human health risk assessment in the RED document concluded that it was concerned about the risk to children due to accidental exposures to these chemicals through use in and around residences. With regard to ecological effects, the Agency concluded that there is a high risk of secondary poisoning, especially to mammals, from the use of these rodenticides outdoors in rural and suburban areas. In order to address the potential risks to children, the U.S. EPA initially required several mitigation measures designed to minimize exposure (e.g., addition of dye and bittering agent to formulations, labeling changes). The Agency also initiated implementation of a Rodenticide Stakeholder Process through which these and other risk mitigation measures would be discussed and required as needed. To help mitigate potential risks to non-target wildlife, the Agency initially determined that all uses of field-bait rodenticides containing more than 0.005% of chlorophacinone or diphacinone were ineligible for reregistration. The U.S. EPA also decided that all rodenticide products labeled for field use (except those limited to manual underground baiting) should be reclassified as Restricted Use pesticides. This paper reviews the regulatory process for the Rodenticide Cluster RED and discusses the response of the California Department of Food and Agriculture (CDFA) and other registrants to the requirements proposed in the RED document including formation of the Rodenticide Registrants Task Force (RRTF). It also outlines how an on-going dialogue with the Agency, both through the Rodenticide Stakeholder Process and in separate discussions, has diminished the RED requirements from those originally proposed. In addition, the paper discusses the implications and potential impacts of the current RED reregistration requirements for those applicators involved in agricultural and urban rodent control.