Formation of 1,3-, 2,4-, 1,6-, 1,8- and 1,7-dinitropyrenes in metallic oxides as soil components in the presence of indoor air with 1-nitropyrene and sodium chloride under xenon lamp irradiation

The reaction products obtained from the mixture of 1-nitropyrene (1-NP) and sodium chloride were investigated on three metallic oxides as soil components under xenon lamp irradiation in the presence of indoor air. These chemicals including 1-NP were extracted with benzene/ethanol (4/1, v/v) and analyzed by gas chromatography/ mass spectrometry (GC/MS). The amounts of 1-NP gradually decreased as irradiation time elapsed on all three metallic oxides (TiO2: titanium dioxide, anatase form; SIO2,: silicon dioxide, silicic anhydride form; and Al2O3: aluminum oxide). In TiO2 in particular, 1-NP showed a greater decrease than the other two metallic oxides for all irradiation times. Six types of dinitropyrenes (DNPs) were detected from the reaction products (1,3-, 2,4-, 1,2-, 1,6-, 1,8- and 1,7-DNP). In both TiO2 and Al2O3, all 6 DNPs were detected, while in SiO2, 5 DNPs were confirmed except for 2,4-DNP. In TiO2, 1,7-DNP was formed in especially rich amounts for all irradiation times in comparison with the other metallic oxides. We presumed that 4- and 2-NPs were generated from 1-NP by the photochemical reaction of OH radical, and that 2,4-, 1,2- and 1,7-DNPs were formed continuously by the nitration of these isomers. The formation of 2,4-, 1,2- and 1,7-DNPs was confirmed for the first time on the metallic oxides by the photochemical reaction system of the 1-NP-NOx-Cl ion. NOx in the indoor air was shown to be a source of nitrogen used in forming DNPs in these metallic oxides. The yields and formation patterns of DNPs differed in the 3 metallic oxides as the irradiation time was extended. Hence, the nature of the photochemical reaction in the formation of DNPs differed depending on the type of metallic oxide in question. In SiO2, mutagenicity increased gradually up to 6 hr of irradiation when mutagenic potency showed 2.6 million revertants/sample, and then decreased to 1.5 million revertants/ sample at 12 hr. In Al2O3, mutagenicity increased gradually as irradiation time elapsed to a maximum of 1.64 million revertants/sample. In TiO2, mutagenicity decreased rapidly to 60% at 10 min and thereafter decreased gradually to 22% at 12 hr.