Seasonal and Spatial Variations in Human Cell Mutagenicity of Respirable Airborne Particles in the Northeastern United States

Samples of respirable airborne particles (similar in size to PM_(2.5)) were collected at five sites in the northeastern United States every sixth day during 1995 and tested in a mutagenicity assay based on human cells. Three sites were located in Massachusetts:  in downtown Boston, in a suburban area 20 km to the north, and in a rural area 100 km west of Boston. The other two sites were located in downtown Rochester in upstate New York and in a rural area 35 km to the west. Bimonthly composite samples (10−11 sampling days per composite) were extracted in organic solvents and tested for mutagenicity at the thymidine kinase locus in h1A1v2 cells, a line of human B-lymphoblasts that constitutively expresses P450 CYP1A1 cDNA. Mutagenicity levels were significantly higher in winter than in summer at all sites, both per microgram of airborne particulate organic carbon (OC) and per cubic meter of air. Mutagenicity per microgram of OC was significantly inversely correlated with air temperature (r = −0.95 in NY, r = −0.40 in MA) and ambient concentrations of OC (r = −0.4). Annual averages of mutagenicity per microgram of OC in upstate New York were roughly 2-fold higher than in Massachusetts; however, no clear intrastate spatial variations were evident. Mutagenicity per cubic meter of air showed an increase of roughly 1.5−2-fold from rural areas to urban centers within each state. This increase was influenced by higher OC concentrations in the urban locations (up to 2-fold) but not by higher mutagenicity per microgram of OC. These results indicate that cold weather is significantly correlated with the human cell mutagenicity of respirable particles in the northeastern United States and further show that populations of urban centers in this region are exposed to higher levels of airborne human cell mutagens than in nearby rural areas.