Ecological and Human Health Hazards from Broadcast Application of 0.005% Diphacinone Rodenticide Baits in Native Hawaiian Ecosystems

Abstract

In the early 1990s, a coalition of federal and state agencies, NGOs, and private landowners in Hawaii agreed to pursue a Special Local Needs pesticide registration [24(c) FIFRA] for the aerial broadcast of a 0.005% diphacinone rodenticide for the control of rodents in native ecosystems. While there was recognition of the important role introduced rodents play in the decline and extinction of native species, there were concerns expressed about the potential non-target impacts of this technique. Over the next 10 years, numerous studies were undertaken to address specific non-target issues. This research, along with other published and unpublished research on diphacinone and its human pharmaceutical counterpart, Dipaxin, was compiled and analyzed in 4 hazard assessments (human dietary and drinking water consumption, aquatic and terrestrial non-target species) that comprise the foundation of Hawaii's registration application. Hazards to humans and other non-target terrestrial organisms were evaluated in terms of dietary intake of contaminated food or water required before lethal or sublethal effects might be anticipated. Hazard to aquatic organisms was assessed according to traditional risk quotient methods employed by the U.S. Environmental Protection Agency. These assessments indicate the greatest human health hazard is to pregnant women drinking untreated stream water; however, even this risk is low. With a few exceptions, such as the Hawaiian crow, the ecological assessments indicate the acute risks to terrestrial or aquatic non-target species are minimal, even under the most conservative risk scenarios. However, there could be detectable physiological effects in birds exposed at sublethal levels. We believe that under proper supervision, this technique can be safely used in Hawaii, and elsewhere, to protect native species from the impacts of introduced rodents.

Assessment of toxicity and potential risk of the anticoagulant rodenticide diphacinone using Eastern screech-owls (Megascops asio)

“…In an often cited trial by Savarie et al (1979), seven captive golden eagles (Aquila chrysaetos) were fed muscle for 5 or 10 days from sheep (Ovis aries) that had been dosed with DPN (30 mg/kg), and then the eagles were switched to untreated food for 11 days. Prothrombin time more than doubled at doses as low as 0.11 mg/kg/day (cumulative dose as low as 0.55 mg/kg) (Eisemann and Swift 2006). Two of the eagles (daily doses: 0.22 and 0.14 mg/ kg/day; cumulative doses: 1.08 and 1.38 mg/kg) exhibited muscular weakness and extreme ataxia, and one of these bled from wounds on the wings and feet.…”

“…A considerable effort has been expended on assessing the hazard of DPN to non-target wildlife as part of an application for a Special Local Needs pesticide registration for its broadcast application for control of rodents and other pests in Hawaii (Johnston et al 2005;Eisemann and Swift 2006). These assessments concluded that the risk associated with acute exposure to DPN would be minimal for several endangered species (e.g., black-faced honeycreeper, Melamprosops phaeosoma, Hawaiian short-eared owl, and Hawaiian hawk), although the Hawaiian crow (Corvus hawaiiensis) was identified as possibly being at risk of lethal effects from direct ingestion of bait (primary exposure).…”

“…Based upon responses (e.g., prolonged clotting time, reduced hematocrit, lethality) in the short-term dietary toxicity study, the lowest-observed-adverse-effect-level and the lowest lethal dose was estimated and used to predict potential risk thresholds using a deterministic exposure model (Eisemann and Swift 2006). In addition, a probabilistic-based exposure model was developed using Crystal Ball Software (Oracle Inc., Redwood City, CA) and used to estimate the quantity of rodent liver consumption that would be required to exceed various toxicological endpoints (Johnston et al 2005).…”

Improving reptile ecological risk assessment: Oral and dermal toxicity of pesticides to a common lizard species (Sceloporus occidentalis)

“…This toxicity database represents data that were used by USEPA in pesticide ecological risk assessments. This is common practice in ecological risk assessment when the only data available is survival at the highest dose (e.g., [27] for birds and rodenticides). We used a correlation analysis to determine if there was a significant relationship between the limited reptile and bird data that is currently available.…”

Rodent Eradication on Cocos Island, Guam: Integrating Wildlife Damage Management, Resort Operations, and Non-Target Concerns

“…or their parts are used by local fisherman as bait on their hooks. Tanner et al (2004) found diphacinone residue in coconut crab tissues after feeding bait and diphacinone-poisoned rats to coconut crabs, and although no recommendation for safe levels of consumption were given, Eisemann and Swift (2006) indicated that the residues in crab tissues were much lower than the residues used for risk measurements. Thus, risk from eating crabs was negligible.…”