6-Nitrobenzo(a)pyrene

6-Nitrobenzo[a]pyrene was emitted in the exhaust from a modern day EURO IV heavy duty diesel engine as a result of formation of 6-nitrobenzo[a]pyrene by nitration of pre-existing PAH(1). 6-Nitrobenzo[a]pyrene was detected in the particulate material emitted from the exhaust of 1978 Volkswagen Rabit diesel engine(2). 6-Nitrobenzo[a]pyrene has been detected in diesel soot (14 mg/kg), diesel-powered car exhaust particulates (50 mg/kg) and gasoline-powered car emissions (0.21-32.8 mg/kg)(3). The rates of emission of 6-Nitrobenzo[a]pyrene in automobile exhaust have been reported to be 1.46 ug/mile for a gasoline-powered car with a precatalyst engine running on leaded fuel, 0.45 ug/mile for an engine with the catalyst removed running on unleaded fuel and 0.012 ug/mile for a gasoline-powered engine with a catalytic converter(4). A production model diesel engine emitted <0.15 ug/mile and a diesel trap model, 0.01 ug/mile(4). 6-Nitrobenzo[a]pyrene has been detected in stack gases from aluminium smelters(4). A fireplace in which red oak was burned yielded emissions of 0.11 and 0.12 mg/kg particles(4).

Using a structure estimation method based on molecular connectivity indices(1), the Koc of 6-nitrobenzo[a]pyrene can be estimated to be 9.5X10+5(SRC). According to a classification scheme(2), this estimated Koc value suggests that 6-nitrobenzo[a]pyrene is expected to be immobile in soil.

URBAN/SUBURBAN: 6-Nitrobenzo[a]pyrene was detected in airborne particulate matter collected in Newark, NJ during Jan 1985 to Feb 1986 monitoring at concentrations ranging from 13 to 6400 pg/cu m(1). 6-Nitrobenzo[a]pyrene was identified in 2 of 17 urban aerosol samples collected in New Jersey, but was not identified in 5 rural aerosol samples at a detection limit of 1 pg/cu m(2). Air samples collected in downtown Baltimore MD in January and July 2001 contained mean 6-nitrobenzo[a]pyrene concentrations of 1.7 (range of 0.01-3.8) and 1.4 (range of 0.4-2.8) pg/cu m respectively(3); air samples collected in suburban Fort Meade MD in January and July 2001 contained mean 6-nitrobenzo[a]pyrene concentrations of 4.1 (range of 3.8-4.4) and 0.26 (range of 0.13-0.40) pg/cu m respectively(3); 100% of the 6-nitrobenzo[a]pyrene was detected in particulate material with 0% detected in the gas-phase(3). 6-Nitrobenzo[a]pyrene has been detected in airborne particles in Prague, Czechoslovakia(4). Ambient particles collected in the area of Detroit, MI during the spring and summer of 1981 contained levels of 0.9-2.5 mg/kg, corresponding to airborne concentrations of 0.04-0.28 ng/cu m(4). Air monitoring at a traffic site in the summer of 2010 and at suburban site in the summer of 2009 in Paris France, detected 6-nitrobenzo[a]pyrene in particulates samples(5); at the suburban site, 100% of 6-nitrobenzo[a]pyrene occurred in particulates <2.5 um in size(5); at the traffic site, about 70% of 6-nitrobenzo[a]pyrene occurred in particulates <2.5 um in size(5).

RURAL/REMOTE: Gaseous and pariculate samples collected in late autumn of 2010 from Wanqingsha, a rural site in the Pearl River Delta region, China, contained an average 6-nitrobenzo[a]pyrene concentration of 63 pg/cu m in the particule samples and 0 pg/cu m in the gaseous samples(1). 6-Nitrobenzo[a]pyrene was detected in air samples collected in two French alpine valleys(2).

/GENOTOXICITY/ Metabolism of 6-nitrobenzo[a]pyrene led to DNA adduct formation in ...explanted human tissues and animals. 6-Nitrobenzo[a]pyrene caused transformation of ...human cultured cells...

/OTHER TOXICITY INFORMATION/ Questionable carcinogen.

6-Nitrobenzo[a]pyrene's limited production and use in laboratory applications(1) may result in its release to the environment through various waste streams. 6-Nitrobenzo[a]pyrene and other nitrated-polycyclic aromatic hydrocarbons (nitro-PAHs) may be present in the atmosphere due to direct emission from sources such as diesel and gasoline exhaust and through atmospheric reaction of parent PAHs with nitrogen oxides and nitrate radicals(2). Nitro-PAHs are formed through incomplete combustion of fossil fuels like coal and oil and through pyrolysis of organic materials and may be emitted from cars, factories and oil and coal stoves(3). 6-Nitrobenzo[a]pyrene is emitted in the exhaust of modern day EURO IV heavy duty diesel engines via formation of 6-nitrobenzo[a]pyrene by nitration of pre-existing PAH(4). In laboratory chamber studies conducted at room temperatures and atmospheric pressure, 1-, 3- and 6-nitrobenzo[a]pyrene were identified as reaction products of benzo[a]pyrene exposed to NO2, NO3/N2O5 and OH radicals(5).

PURE CULTURE: Incubation of 6-nitrobenzo[a]pyrene with the fungus Cunninghamella elegans for periods ranging from 1 to 7 days resulted in degradation of the 6-nitrobenzo[a]pyrene to metabolites identified as glucoside and sulfate conjugates of 1- and 3-hydroxy 6-nitrobenzo[a]pyrene(1); 62% of initial 6-nitrobenzo[a]pyrene was metabolized within 168 hours(1). Nitro-substituted PAHs are only slowly degraded by indigenous microorganisms and may persist in soils and sediments(2); the recalcitrance of high molecular weight nitro-PAHs is due in part to the strong adsorption to soil organic matter, low solubility, large molecular size and the polar character of the nitro group(2).

6-Nitrobenzo[a]pyrene

Group 3: Not classifiable as to its carcinogenicity to humans

Volume Sup 7: Overall Evaluations of Carcinogenicity: An Updating of IARC Monographs Volumes 1 to 42, 1987; 440 pages; ISBN 92-832-1411-0 (out of print)

1989

1988

An estimated BCF of 1800 was calculated in fish for 6-nitrobenzo[a]pyrene(SRC), using a log Kow of 5.44(1) and a regression-derived equation(2). According to a classification scheme(3), this BCF suggests the potential for bioconcentration in aquatic organisms is very high(SRC), provided the compound is not metabolized by the organism(SRC).

The Henry's Law constant for 6-nitrobenzo[a]pyrene is estimated as 3.2X10-9 atm-cu m/mole(SRC) using a fragment constant estimation method(1). This Henry's Law constant indicates that 6-nitrobenzo[a]pyrene is expected to be essentially nonvolatile from water surfaces(2). 6-Nitrobenzo[a]pyrene's Henry's Law constant indicates that volatilization from moist soil surfaces is not expected to occur(SRC). 6-Nitrobenzo[a]pyrene is not expected to volatilize from dry soil surfaces(SRC) based upon an estimated vapor pressure of 1.0X10-10 mm Hg(SRC), determined from a fragment constant method(1).

/LABORATORY ANIMALS: Acute Exposure/ A series of environmentally occurring nitro-polycyclic aromatic hydrocarbons (nitro-PAHs) including those containing nitro-groups oriented coplanarly to the aromatic rings, such as 1- and 3-nitrobenzo[a]pyrene (1- and 3-NBAP), 6-nitrochrysene, and 1- and 4-nitropyrene, and those with a molecular orientation of the nitro-groups perpendicular to the aromatic moieties, such as 7-nitrobenz[a]anthracene and 6-nitrobenzo[a]pyrene (6-NBAP), were used to study the induction of certain rat hepatic phase II conjugating enzymes. Effects of these two different classes of nitro-PAHs on microsomal UDP-glucuronyltransferase (UDPGT), cytosolic glutathione S-transferases (GSTs) and sulfotransferases (STs) were investigated. After three consecutive daily i.p. injections, 1- and 3-NBAP and 6-nitrochrysene significantly increased the activities of UDPGT and GST, whereas their parent PAHs did not induce UDPGT (and GST activity was also unaltered by benzo[a]pyrene). UDPGT and GST activities were also significantly increased by 1-nitropyrene. In contrast, the sulfotransferases directed to 2-naphthol were not significantly induced by any PAH or nitro-PAH when assayed at either pH 5.5 or 7.5; however, the activities of aryl STs III and IV (pH 5.5) were significantly decreased following treatment with pyrene and two nitro-compounds, 6-NBAP and 7-nitrobenz[a]anthracene, in which the nitro-group is oriented perpendicular to the aromatic moiety. These results indicate that a coplanar orientation of the nitro-group of certain nitrated PAHs facilitates the induction of hepatic phase II enzymes by these compounds in rats, and the comparable induction patterns for P450IA1, UDPGT, and GST provide further evidence supporting the coordinate regulation (through the Ah receptor) of these phase I and phase II activities.

/LABORATORY ANIMALS: Chronic Exposure or Carcinogenicity/ 6-Nitrobenzo[a]pyrene was tested for carcinogenicity in a two-stage initiation-promotion study in mouse skin and by intraperitoneal injection into newborn mice. The study by skin application was inadequate for evaluation. An increased incidence of liver-cell tumors was observed in male mice after intraperitoneal injection.

/GENOTOXICITY/ Metabolism of 6-nitrobenzo[a]pyrene led to DNA adduct formation in bacteria... and animals. 6-Nitrobenzo[a]pyrene caused transformation of animal ...cultured cells and was mutagenic to cultured animal cells. It induced mutations in bacteria in the presence of an exogenous metabolic system.

/GENOTOXICITY/ The mononitro-substituted isomers of benzo[a]pyrene (B[a]P), 1-, 3- and 6-nitrobenzo[a]pyrene (NB[a]P), are environmental pollutants and are metabolized to mutagens in Salmonella by rat-liver homogenate postmitochondrial supernatant (S9) fractions. In this study, activation of these compounds to mutagens was investigated using the hepatocyte-mediated Salmonella mutagenicity assay. Hepatocytes from rats treated with Aroclor 1254 activated both 3-NB[a]P and 1-NB[a]P to mutagens, while 6-NB[a]P was not mutagenic. The positive mutagenicity responses were functions of both the chemical dose and the hepatocyte concentration. By using a nitroreductase-deficient strain (TA98NR) and a transesterificase-deficient strain (TA98/1,8-DNP6), it was verified that the direct-acting mutagenicities of 1- and 3-NB[a]P primarily were due to metabolic processes involving nitroreduction while the S9- and hepatocyte-mediated mutagenicity responses were also dependent on transesterification. When compared with the mutagenic responses produced with S9, the mutations induced by 1- and 3-NB[a]P in the presence of hepatocytes were relatively more dependent upon nitroreductase metabolism and less on transesterification. Thus, intact hepatocytes were capable of activating 1- and 3-NB[a]P to mutagenic metabolites and some of these metabolites appeared to be different from those produced by S9.

For more Non-Human Toxicity Excerpts (Complete) data for 6-Nitrobenzo[a]pyrene (9 total), please visit the HSDB record page.