Current Status of the Toxicology of Diesel Engine Exhaust — and the ACES Project

Summary A clear understanding of the health risks of DE has been elusive, because exposures of the workers and general populations studied epidemiologically have not been accurately measured. Experimental exposures of humans and animals can be measured and these have suggested potential health hazards, but results of experimental exposures have been difficult to place in a realistic human exposure context. Experimental human exposures must be of only short duration and relatively high concentrations of DE have been necessary to produce short-term effects. Short-term and long-term animal studies have been conducted and significant progressive health effects have been produced at extreme exposure concentrations, but it is difficult to translate those results into risk factors for humans with acceptable confidence. Diesel technologies have advanced markedly over the past few decades, and emissions have been reduced and altered in composition. No published epidemiological or toxicological study has used exhaust produced by recent diesel technologies. The ACES program in the United States was created to conduct animal studies of the potential health hazards of recent technology diesel exhaust. Rats and mice are exposed to different dilutions of exhaust from a heavy-duty engine meeting the 2007 on-road emission standards and operated on a variable-duty cycle. The study is underway and early results will be available in early 2011. Final results from the long-term study of the hazards of cancer and progressive non-cancer disease will be available in late 2013.