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 This research, along with other published and unpublished research on diphacinone and its human pharmaceutical counterpart, Dipaxin, was compiled and analyzed in 4 hazard assessments (human dietary and drinking water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.