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David M. DeMarini,¹ Lance R. Brooks,¹ Sarah H. Warren,¹ Takahiro Kobayashi,² M. Ian Gilmour,¹ and Pramila Singh¹

¹National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA; ²Environmental Health Sciences Division, National Institute for Environmental Studies, Tsukuba, Japan

Abstract
Many pulmonary toxicity studies of diesel exhaust particles (DEPs) have used an automobile-generated sample (A-DEPs) whose mutagenicity has not been reported. In contrast, many mutagenicity studies of DEPs have used a forklift-generated sample (SRM 2975) that has been evaluated in only a few pulmonary toxicity studies. Therefore, we evaluated the mutagenicity of both DEPs in Salmonella coupled to a bioassay-directed fractionation. The percentage of extractable organic material (EOM) was 26.3% for A-DEPs and 2% for SRM 2975. Most of the A-EOM (~55%) eluted in the hexane fraction, reflecting the presence of alkanes and alkenes, typical of uncombusted fuel. In contrast, most of the SRM 2975 EOM (~58%) eluted in the polar methanol fraction, indicative of oxygenated and/or nitrated organics derived from combustion. Most of the direct-acting, base-substitution activity of the A-EOM eluted in the hexane/dichloromethane (DCM) fraction, but this activity eluted in the polar methanol fraction for the SRM 2975 EOM. The direct-acting frameshift mutagenicity eluted across fractions of A-EOM, whereas > 80% eluted only in the DCM fraction of SRM 2975 EOM. The A-DEPs were more mutagenic than SRM 2975 per mass of particle, having 227 more polycyclic aromatic hydrocarbon-type and 8-45 more nitroarene-type mutagenic activity. These differences were associated with the different conditions under which the two DEP samples were generated and collected. A comprehensive understanding of the mechanisms responsible for the health effects of DEPs requires the evaluation of DEP standards for a variety of end points, and our results highlight the need for multidisciplinary studies on a variety of representative samples of DEPs. Key words: bioassay-directed fractionation, diesel particulates, Salmonella mutagenicity, SRM 2975. Environ Health Perspect 112:814-819 (2004) . doi:10.1289/ehp.6578 available via http://dx.doi.org/ [Online 31 October 2003]

Address correspondence to D.M. DeMarini, U.S. Environmental Protection Agency, B143-06, Research Triangle Park, NC 27711 USA. Telephone: (919) 541-1510. Fax: (919) 541-0694. E-mail: demarini.david@epa.gov

We thank R. Owen, R.J. Preston, L.D. Claxton, D.L. Costa, L.S. Birnbaum, M. Madden, and J.A. Dye for their comments on the manuscript. This article was reviewed by the National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, and approved for publication.

P.S. was supported by National Institutes of Health grant ES11245-01.

The authors declare they have no competing financial interests.

Received 21 July 2003 ; accepted 30 October 2003.