BENZO[a]PYRENE

Yalkowsky, 1998) Environmental fate: Biological. Benzo[a]pyrene was biooxidized by Beijerinckia B836 to cis-9,10-dihydroxy9,10-dihydrobenzo[a]pyrene. Under nonenzymatic conditions, this metabolite monodehydroxylated to form 9-hydroxybenzo[a]pyrene (quoted, Verschueren, 1983). Under aerobic conditions, Cunninghanella elegans degraded benzo[a]pyrene to trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (Kobayashi and Rittman, 1982), 3-hydroxybenzo[a]pyrene, 9-hydroxybenzo[a]pyrene, and vicinal dihydrols including trans-9,10-dihydroxy-9,10-dihydrobenzo[a]pyrene (Cerniglia and Gibson, 1980; Gibson et al., 1975). The microorganisms Candida lipolytica and Saccharomyces cerevisiae oxidized benzo[a]pyrene to trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene, 3-and 9-hydroxybenzo[a]pyrene (Cerniglia and Crow, 1980; Wiseman et al., 1978) whereas 3-hydroxybenzo[a]pyrene was the main degradation product by the microbe Neurospora crassa (Lin and Kapoor, 1979). After a 30-d incubation period, the white rot fungus Phanerochaete chrysosporium converted benzo[a]pyrene to carbon dioxide. Mineralization began between the third and sixth day of incubation. The production of carbon dioxide was highest between 3-18 d of incubation, after which the rate of carbon dioxide produced decreased until the 30th day. It was suggested that the metabolism of benzo[a]pyrene and other compounds, including p,p′-DDT, TCDD, and lindane, was dependent on the extracellular lignin-degrading enzyme system of this fungus (Bumpus et al., 1985). In activated sludge, <0.1% mineralized to carbon dioxide after 5 d (Freitag et al., 1985). Contaminated soil from a manufactured coal gas plant that had been exposed to crude oil was spiked with benzo[a]pyrene (400 mg/kg soil) to which Fenton’s reagent (5 mL 2.8 M hydrogen peroxide; 5 mL 0.1 M ferrous sulfate) was added. The treated and nontreated soil samples were incubated at 20 °C for 56 d. Fenton’s reagent greatly enhanced the mineralization of benzo[a]pyrene by indigenous microorganisms. The amounts of benzo[a]pyrene recovered as carbon dioxide after treatment with and without Fenton’s reagent were 17 and 2%, respectively (Martens and Frankenberger, 1995). Ye et al. (1996) investigated the ability of Sphingomonas paucimobilis strain U.S. EPA 505 (a soil bacterium capable of using fluoranthene as a sole source of carbon and energy) to degrade 4, 5 and 6-ringed aromatic hydrocarbons (10 ppm). After 16 h of incubation using a resting cell suspension, 33.3% of benzo[a]pyrene had degraded. In the presence of 5 ppm benzo[b]fluoranthene, biodegradation was reduced about 30%. It was suggested that biodegradetion occurred via ring cleavage resulting in the formation of polar metabolites and carbon dioxide. Soil. Lu et al. (1977) studied the degradation of benzo[a]pyrene in a model ecosystem containing Drummer silty clay loam. Samples were incubated at 27.6 °C for 1, 2, and 4 wk before extraction with acetone for TLC analysis. After 4 wk, only 8.05% of benzo[a]pyrene degraded forming one polar compound and two unidentified compounds. The reported half-lives for benzo[a]pyrene in a Kidman sandy loam and McLaurin sandy loam are 309 and 229 d, respectively (Park et al., 1990). Surface Water. In a 5-m deep surface water body, the calculated half-lives for direct photochemical transformation at 40 °N latitude, in the midsummer during midday were 3.2 and 13 d with and without sediment-water partitioning, respectively (Zepp and Schlotzhauer, 1979). The volatilization half-life of benzo[a]pyrene from surface water (1 m deep, water velocity 0.5 m/sec, wind velocity 1 m/sec) using experimentally determined Henry’s law constants is estimated to be 1,500 h (Southworth, 1979). Photolytic. Coated glass fibers exposed to air containing 100-200 ppb ozone yielded

after 1 and 4 h, respectively (Pitts et al., 1990). In a similar study, kiln-fired glass fiber filters were coated with a mg of benzo[a]pyrene and exposed to oxygen containing 2 ppm ozone for 1 h. Degradation products identified using LC-atmospheric pressure chemical ionization-MS were benzo[a]pyrene-1,6-dione, benzo[a]pyrene-3,6-dione, benzo[a]pyrene-6,12-dione, benzo[a]pyrene-4,5-dione, and 4-oxabenzo[d,e,f]chrysene-5-one (Letzel et al., 1999). Free radical oxidation and photolysis of benzo[a]pyrene at a wavelength of 366 nm yielded the following tentatively identified products: benzo[a]pyrene-1,6-quinone, benzo[a]pyrene-3,6-quinone, and benzo[a]pyrene-6,12-quinone (Smith et al., 1978). In a solution containing oxygen, photolysis yields a mixture of 6,12-, 1,6-, and 3,6-diones. Nitration by nitrogen dioxide forms 6-nitro-, 1-nitro-, and 3-nitrobenzo[a]pyrene. When benzo[a]pyrene in methanol (1 g/L) was irradiated at 254 nm in a quartz flask for 1 h, the solution turned pale yellow. After 2 h, the solution turned yellow and back to clear after 4 h of irradiation. After 4 h, 99.67% of benzo[a]pyrene was converted to polar compounds. One of these compounds was identified as a methoxylated benzo[a]pyrene (Lu et al., 1977). A carbon dioxide yield of 26.5% was achieved when benzo[a]pyrene adsorbed on silica gel was irradiated with light (λ >290 nm) for 17 h (Freitag et al., 1985). In a 5-m deep surface water body, the calculated half-lives for direct photochemical transformation at 40 °N latitude, in the midsummer during midday were 3.2 and 13 d with and without sediment-water partitioning, respectively (Zepp and Schlotzhauer, 1979). Behymer and Hites (1985) determined the effect of different substrates on the rate of photooxidation of benzo[a]pyrene using a rotary photoreactor. The photolytic half-lives of benzo[a]pyrene using silica gel, alumina, and fly ash were 4.7, 1.4, and 31 h, respectively. Matsuzawa et al. (2001) investigated the photochemical degradation of five polycyclic aromatic hydrocarbons in diesel particulate matter deposited on the ground and in various soil components. The photochemical degradation by artificial sunlight was accomplished using a 900-W xenon lamp. Light from this lamp was passed through a glass filter to eliminate light of shorter wavelengths (λ <290 nm). The intensity of this light was about 170 mW/cm2. In addition, a solar simulator equipped with a 300-W xenon lamp was used to provide the maximum sunlight intensity observed in Tokyo (latitude 35.5 °N). The half-lives of benzo[a]pyrene in diesel particulate matter using 900-and 300-W sources were 1.63 and 6.59 h, respectively. The following half-lives were determined for benzo[a]pyrene adsorbed on various soil components using 900-W apparatus: 1.62 h for quartz, 1.01 h for feldspar, <0.5 h for kaolinite, 1.04 h for montmorillonite, 0.51 h for silica gel, and 0.35 h for alumina. Benzo[a]pyrene (2.5 mg/L) in a methanol-water solution (3:7 v/v) was subjected to a high pressure mercury lamp or sunlight. Based on a rate constant of 3.22 x 10-2/min, the corresponding half-life is 0.35 h (Wang et al., 1991). Chemical/Physical. Ozonolysis to benzo[a]pyrene-1,6-quinone or benzo[a]pyrene-3,6-quinone followed by additional oxidation to benzanthrone dicarboxylic anhydride was reported (IARC, 1983). In a simulated atmosphere, direct epoxidation by ozone led to the formation of benzo[a]pyrene4,5-oxide. Benzo[a]pyrene reacted with benzoyl peroxide to form the 6-benzoyloxy derivative (quoted, Nikolaou et al., 1984). It was reported that benzo[a]pyrene adsorbed on fly ash and alumina reacted with sulfur dioxide (10%) in air to form benzo[a]pyrene sulfonic acid (Nielsen et al., 1983). Benzo[a]pyrene coated on a quartz surface was subjected to ozone and natural sunlight for 4 and 2 h, respectively. The compounds 1,6-quinone, 3,6-quinone, and the 6,12-quinone of benzo[a]pyrene were formed in both instances (Rajagopalan et al., 1983). When benzo[a]pyrene adsorbed from the vapor phase onto coal fly ash, silica, and alumina was exposed to nitrogen dioxide, no reaction occurred. However, in the presence of nitric acid, nitrated compounds were produced (Yokley et al., 1985). Chlorination of benzo[a]pyrene in polluted humus poor lake water gave 11,12-dichlorobenzo[a]pyrene and 1,11,12-, 3,11,12-or 3,6,11-

1989). When an aqueous solution containing benzo[a]pyrene (53.14 µg/L) was chlorinated for 6 h using chlorine (6 mg/L), the concentration was reduced 98% (Sforzolini et al., 1970). Benzo[a]pyrene will not hydrolyze in water because it does not contain a hydrolyzable functional group (Kollig, 1993). At influent concentrations of 1.0, 0.1, 0.01, and 0.001 mg/L, the GAC adsorption capacities were 34, 12, 4.5, and 1.6 mg/g, respectively (Dobbs and Cohen, 1980). Exposure limits: Potential occupational carcinogen. No individual standards have been set; however, as a constituent in coal tar pitch volatiles, the following exposure limits have been established (mg/m3): NIOSH REL: TWA 0.1 (cyclohexane-extractable fraction), IDLH 80; OSHA PEL: TWA 0.2 (benzene-soluble fraction); ACGIH TLV: TWA 0.2 (benzene solubles). Toxicity: LC50 (96-h) for Daphnia pulex 5 µg/L (Trucco et al., 1983), Xenopus laevis >13.2 µM (Saka, 2004). Acute LC50 for Neanthes arenaceodentata >50 µg/L (Rossi and Neff, 1978). LD50 for mice (subcutaneous) 50 mg/kg (quoted, RTECS, 1985). LD50 for mice (intraperitoneal) 232 mg/kg (Salamone, 1981). Drinking water standard (final): MCLG: zero; MCL: 0.2 µg/L (U.S. EPA, 2000). Source: Identified in Kuwait and South Louisiana crude oils at concentrations of 2.8 and 0.75 ppm, respectively (Pancirov and Brown, 1975). Emitted to the environment from coke production, coal refuse and forest fires, motor vehicle exhaust, and heat and power (utility) generation (Suess, 1976). Benzo[a]pyrene is produced from combustion of tobacco and fuels. It is also a component of gasoline (133-143 µg/L), fresh motor oil (20 to 100 g/kg), used motor oil (83.2 to 242.4 mg/kg), asphalt (≤0.0027 wt %), coal tar pitch (≤1.25 wt %), cigarette smoke (25 µg/1,000 cigarettes), and gasoline exhaust (quoted, Verschueren, 1983). Detected in asphalt fumes at an average concentration of 14.72 ng/m3 (Wang et al., 2001). Benzo[a]pyrene was also detected in liquid paraffin at an average concentration of 25 µg/kg (Nakagawa et al., 1978). Benzo[a]pyrene was reported in a variety of foodstuffs including raw and cooked meat (ND to 12 ppb), fish (0.3-6.9 ppb), vegetables oils (ND-4), fruits (ND to 6.2 ppb) (quoted, Verschueren, 1983). The concentration of benzo[a]pyrene in coal tar and the maximum concentration reported in groundwater at a mid-Atlantic coal tar site were 3,600 and 0.0058 mg/L, respectively (Mackay and Gschwend, 2001). Based on laboratory analysis of 7 coal tar samples, benzo[a]pyrene concentrations ranged from 500 to 6,400 ppm (EPRI, 1990). In three high-temperature coal tars, benzo[a]pyrene concentrations ranged from 5,300 to 7,600 mg/kg (Lehmann et al., 1984). Benzo[a]pyrene was identified in a U.S. commercial creosote at an approximate concentration of 0.3% (Black, 1982). Nine commercially available creosote samples contained benzo[a]pyrene at concentrations ranging from 2 to 160 mg/kg (Kohler et al., 2000). Identified in high-temperature coal tar pitches used in roofing operations at concentrations ranging from 4,290 to 13,200 mg/kg (Arrendale and Rogers, 1981; Malaiyandi et al., 1982). Lee et al. (1992a) equilibrated 8 coal tars with distilled water at 25 °C. The maximum concentration of benzo[a]pyrene observed in the aqueous phase was 1 µg/L. Schauer et al. (2001) measured organic compound emission rates for volatile organic compounds, gas-phase semi-volatile organic compounds, and particle phase organic compounds from the residential (fireplace) combustion of pine, oak, and eucalyptus. The particle-phase emission rates of benzo[a]pyrene were 0.712 mg/kg of pine burned, 0.245 mg/kg of oak burned, and 0.301 mg/kg of eucalyptus burned.