Mutagenicity of nitro derivatives induced by exposure of aromatic compounds to nitrogen dioxide

Abstract

Mutagenic nitro derivatives were readily induced when 6 kinds of chemicals were exposed to 10 ppm of nitrogen dioxide (NO 2). Single nitro derivatives were formed from pyrene, phenathrene, fluorene of chrysene. Carbazole and fluoranthene each produced 2 derivatives substituted with nitro groups at different positions. The formation of nitro derivatives was enhanced by exposure of pyrene to NO 2 containing nitric acid (HNO 3,>100-fold enhancement) or sulphur dioxide (SO 2, >15-fold enhancement). After 24 h of exposure the yields of the nitro derivative were 0.02% with 1 ppm of NO 2 in air and 2.85% with NO 2 (1 ppm) containing traces of HNO 3. The nitro derivatives from all but phenanthrene and carbazole were chemically identified by means of gas chromatography (GC) and mass spectrometry (MS), and the mutagenicity of the 4 kinds of authentic nitro derivatives was tested by using Salmonella strains TA98 and TA1538 with or without the S9 fraction from rat liver treated with Aroclor 1254. The nitro derivative induced from pyrene was determined to be 1-nitropyrene; that of chrysene was 6-nitrochrysene; that of fluorene was 2-nitrofluorenel and those of fluoranthene were 3-nitrofluoranthene, and 8-nitrofluoranthene. Tested with strain TA98 in the absence of the S9 fraction, the first 4 of these derivatives yielded, respectively, 3050, 269, 433 and 13 400 revertants per nmole. Thus, each nitro derivative formed was potentially a direct-acting frameshift-type mutagen. Each compound exposed to NO 2 showed a decreased mutagenic activity when tested in the presence of S9 mix. A possible explanation comes from experiments in which 1-nitropyrene was incubated with the S9 mix at 37°C for 10 min, and 1-aminopyrene was formed. The mutagenic activity of 1-aminopyrene was appreciable, but only about one-tenth of that of 1-nitropyrene in the Ames test. Many nitro-containing compounds including nitrofurans (Cohen et al., 1973, 1976; Nomura, 1975) and nitro-aromatics (Yahagi et al., 1975), are mutagenic and carcinogenic (Nomura, 1975; Takemura et al., 1974). The mutagenicity of nitro derivatives, however, has been shown for only some of these compounds in the Salmonella typhimurium (Ames et al., 1975; Rosenkranz and Poirier, 1979), Escherichia coli (Kadam 1973) and Saccharomyces cerevisiae (Simmon, 1979) test systems. In previous studies, we (Ohnishi et al., 1980; Tokiwa et al., 1977, 1980) and others (Ames et al., 1973b; Dehnen et al., 1977; Löfroth, 1980; McClellan, 1979; Pitts et al., 1977; Talcott and Wei, 1977; Teranishi et al., 1978; Wang et al., 1978; Wei et al., 1980) have demonstrated the mutagenicity of airborne particulate matter and automobile exhaust. They noted that direct-acting mutagens were found and suggested that they might include nitro derivatives (Pitts et al., 1977, 1978; Tokiwa et al., 1980). Because nitro derivatives can be induced by the nitration of polycyclic aromatic hydrocarbons (PAH) in pollutant gases (Pitts et al., 1978), and because volatile or gaseous compounds, including NO 2 and SO 2, are widespread air pollutants (Wade et al., 1375), we wondered whether non-mutagenic chemicals might be converted to potent mutagens when exposed to NO 2 in the environment. This conjecture was strengthened when we detected (by high-pressure liquid chromatography) 1-nitropyrene, 3-nitrofluoranthene and 5-nitroacenaphthene in the neutral fraction extracted from air-polluting particulates and diesel exhaust (unpublished data). We have therefore exposed non-mutagenic aromatic or heterocyclic compounds, which are normally detectable in the environment (Ohnishi et al., 1980; Tokiwa et al., 1980), to NO 2, and have then investigated whether potent mutagenic nitro derivatives were produced.