Progress in Understanding the Toxicity of Gasoline and Diesel Engine Exhaust Emissions

To help guide heavy vehicle engine, fuel, and exhaust after-treatment technology development, the U.S. Department of Energy and the Lovelace Respiratory Research Institute are conducting research not addressed elsewhere on aspects of the toxicity of particulate engine emissions. Advances in these technologies that reduce diesel particulate mass emissions may result in changes in particle composition, and there is concern that the number of ultrafine (<0.1 micron) particles may increase. All present epidemiological and laboratory data on the toxicity of diesel emissions were derived from emissions of older-technology engines. New, short-term toxicity data are needed to make health-based choices among diesel technologies and to compare the toxicity of diesel emissions to those of other engine technologies. This research program has two facets: 1) development and use of short-term in vitro and in vivo toxicity assays for comparing the toxicities of gasoline and diesel exhaust emissions; and 2) determination of the disposition of inhaled ultrafine particles deposited in the lung. Responses of cultured cells, cultured lung slices, and rodent lungs to various types of particles were compared to develop an improved short-term toxicity screening capability. To date, chemical toxicity indicators of cultured human A549 cells and early inflammatory and cytotoxic indicators of rat lungs have given the best distinguishing capability. A study is now underway to determine the relative toxicities of exhaust samples from in-use diesel and gasoline engines. The samples are being collected under the direction of the National Renewable Energy Laboratory with support from DOE's Office of Heavy Vehicle Technologies. The ability to generate solid ultrafine particles and to trace their movement in the body as particles and soluble material was developed. Data from rodents suggest that ultrafine particles can move from the lung to the liver in particulate form. The quantitative disposition of inhaled ultrafine particles will be determined in rodents and nonhuman primates.