Human-cell mutagens in respirable airborne particles in the northeastern United States. 1. Mutagenicity of fractionated samples.

Few studies have characterized the regional scale (300−500 km) variability of the mutagenicity of respirable airborne particles (PM_(2.5)). We previously collected 24-h PM_(2.5) samples for 1 year from background, suburban, and urban sites in Massachusetts (MA) and rural and urban sites in upstate New York (NY) (n = 53−60 samples per site). Bimonthly composites of these samples were mutagenic to human cells. The present report describes our effort to identify chemical classes responsible for the mutagenicity of the samples, to quantify spatial differences in mutagenicity, and to compare the mutagenicity of samples composited in different ways. Organic extracts and HPLC fractions (two nonpolar, one semipolar, and one polar) of annual composites were tested for mutagenicity in the h1A1v2 cells, a line of human B-lymphoblastoid cells that express cytochrome P450 CYP1A1 cDNA. The mutagenic potency (induced mutant fraction per μg organic carbon) of the semipolar fractions was the highest at all five sites, accounting for 35−82% of total mutagenic potency of the samples, vs the nonpolar (4−38%) and polar (14−32%) fractions. These results are consistent with previous studies. While unfractionated extracts exhibited no spatial variations, the mutagenicity of semipolar fractions at the NY sites was ∼2-fold higher than at the MA sites. This suggests there may be significant regional differences in the sources and/or transport and transformation of mutagenic compounds in PM_(2.5). In addition, mutagenic potency was sensitive to whether samples were fractionated and how they were composited:  unfractionated annual composite samples at the NY sites were significantly less mutagenic than their semipolar fractions and the annual average of bimonthly composites; spatial differences in the mutagenic potency of bimonthly composites and the semipolar fractions were not apparent in the annual composites.