EnvironmentalToxicityStudiesUsingChickensasSurrogatesforWildlife:Effects ofVehicleVolume Jamie C. DeWitt, 1 Erin B. Meyer, 2 Diane S. Henshel 3 1 Curriculum in Toxicology, University of North Carolina, Chapel Hill, North Carolina 27599, USA 2 ICF Consulting, Fairfax, Virginia 22031, USA 3 School of Public and Environmental Affairs, Indiana University, Bloomington, Indiana 47405, USA Received: 29 November 2003/Accepted: 23 June 2004 Abstract. Domestic chicken embryos are frequently used for avian developmental toxicity studies of polyhalogenated aro- matic hydrocarbons, which are often injected into eggs with oil-basedvehicles.Thevolumeoftoxicantandvehicleinjected ranges from relatively low volumes (0.1–0.5 ll/g egg) to rel- atively high volumes (1.0 ll/g egg and above). Previous re- search from our laboratory suggested that high volumes of vehicle oil may disrupt normal growth of chicken embryos, possibly from hypoxia-like effects. This analysis explored the potential effects of vehicle volume on developing chicken embryos. We assessed standard measures of mortality, organ growth, body growth, and behavior from chickens develop- mentally exposed in ovo prior to incubation to low (0.1 ll/g egg) or high volumes (1.0 ll/g egg) of corn oil injected into airsacsortonoinjection.Thechickensreceivinghighvolumes of oil showed increases in overall embryonic mortality and early embryo mortality compared to chickens receiving low volumes of oil or no injection. The chickens receiving high volumes of oil showed decreased activity during righting reflex, running time, visual discrimination, and olfactory aversion tests, and increased activity during an open-field activity test compared to chickens receiving low volumes of oil or no injection. Somatic endpoints do not appear to be affected by high volume injections. These results suggest that high volumes of vehicle injected into airsacs of eggs may lead to hypoxia-like conditions that increase embryonic mortality and disrupt simple behaviors. However, some effects of vol- ume may diminish when injections are performed later in incubation. The statement ÔÔthe dose makes the poisonÕÕ engenders the idea that all that is required for toxicity is exposure to an effective dose of a toxicant. This statement does not address that an organismÕs overall health, age, sex, and genetic makeup influence the effects of dose, as do the exposure scenario, environmental factors, and the physical characteristics of the toxicant itself. Researchers take these factors into consider- ationwhenstudyingtheeffectsofdose,andtrytocontrolthese factors by comparison to effects in similarly treated control groupssothatthedosereallydoesmakethepoison.However, as much as researchers try to control these factors, differences between studies exist, especially in exposure scenarios, or the ways in which organisms are exposed to toxicants. According to Eaton and Klaassen (2001), the route of administrationandthedurationandfrequencyofexposuretoa chemical are major factors that influence toxicity as it relates totheexposurescenario.Indevelopmentaltoxicitystudies,the durationandfrequencyofexposurearefairlyconsistentacross studies examining similar endpoints and chemicals. It is the route of administration that varies most commonly, even among studies with similar endpoints and chemicals. In mammalian developmental toxicity studies, developing organisms are exposed to toxicants in utero, lactationally, or even directly after parturition. Mammalian studies often in- volve maternal exposure, which complicates developmental exposure as maternal systems influence the route of adminis- tration as well as the delivered dose to the offspring. Con- trolled avian developmental toxicity studies may involve maternal exposures, but because the egg is a self-contained entity, avian studies often involve directly exposing the developing bird to the toxicant. This methodology leads to more consistent in ovo exposures relatively uncomplicated by maternal influences. Therefore, controlled avian developmen- tal toxicity studies allow for a more controlled exposure sce- nario than many mammalian toxicity studies. However, such studies still use various routes of administration to expose the developing bird to a toxicant. Avian studies typically involve injection of a toxicant into the airsac, the yolk sac, or the albumin of an egg, or coating of the egg externally with the toxicant. According to Eaton and Klaassen (2001), toxic effects by any route of exposure can be influenced by the concentration ofatoxicantinitsvehicle,thetotalvolumeofthevehicle,and the properties of the vehicle itself. Depending on the class of toxicant under study, the vehicle can be oil, a solvent, or even water, each of which can potentially influence the organism Correspondence to: Jamie DeWitt; email: dewittjamie@hotmail.com Arch. Environ. Contam. Toxicol. 48, 260–269 (2005) DOI: 10.1007/s00244-004-1006-2