Contribution to bacterial mutagenicity from nitro-pah compounds in ambient aerosols

To demonstrate a method for the identification of mutagenic components in organic fractions of ambient aerosols, the mutagenic activity was studied in samples collected simultaneously for six consecutive days during the summer of 1931 at an urban site and a suburban site in southeast Michigan. The filter samples were extracted with dichloromethane and fractionated by thin layer chromatography (TLC) into sixteen fractions. The individual TLC fractions were then examined by the Ames test using tester strains TA98, TA98NR and TA98DNP₆. Similar daily variations in the activity and the mutagenicity profiles of the TLC fractions occurred at both sites. In samples collected from both locations, approximately half of the mutagenic activity was found in the four most polar fractions of the particulate extracts. The remaining mutagenic activity was distributed among the less polar fractions where PAH, nitro-PAH and dinitro-PAH would be eluted. The mutagenic activity in all fractions decreased sharply when tested with two nitroreductase deficient tester strains, TA98NR and TA98DNP₆, indicating that the mutagens (especially those in the polar fractions) were nitro-substituted polycyclic aromatic hydrocarbon compounds. Three nitro compounds, 1-nitropyrene, 1,6-dinitropyrene and 1,8-dinitropyrene were detected by high performance liquid chromatography (HPLC) but could account for no more than 3% of the total airborne mutagenicity. A National Bureau of Standards' Ambient Particulate Sample (SRM No. 1649), collected for a long sampling period of 18 months, differed markedly from the urban and suburban Michigan samples in its mutagenicity profile.