Benzo[a]pyrene

Description

Benzo(a)pyrene (BaP) is bioactivated to its carcinogenic form by phase 1 and phase 2 metabolism. As with other polycyclic aromatic hydrocarbons (PAHs), the presence of the ‘bay region’ contributes greatly to the carcinogenicity of BaP. This region is sterically constrained, allowing the formation of diol epoxides, which subsequently react with intracellular molecules such as DNA. Human exposure to BaP and other PAHs occurs primarily from smoking or from secondhand smoke, air polluted with combustion products, or food and water polluted with combustion products, such as those cooked over charcoal or broiled.
BaP has been extensively studied for its toxicities in children and during pregnancy. A study of pregnant active smokers showed that BaP crossed the human placenta and was bound to fetal hemoglobin at levels significantly higher than in pregnant nonsmokers.

Chemical properties

B(a)P, is yellowish needles, crystals or powder. Odorless. PAHs are compounds containing multiple benzene rings and are also called polynuclear aromatic hydrocarbons.

Physical properties

Odorless, yellow, orthorhombic or monoclinic crystals from ethanol. Solution in concentrated sulfuric acid is orange-red and fluoresces green under exposure to UV light (quoted, Keith and Walters, 1992).

The Uses of Benzo[a]pyrene

Benzopyrene is a polyaromatic hydrocarbon (PAH) found in coal tar. Benzopyrene is a known carcinogen. The metbolism of Benzopyrene results in diol epoxides that react and bind to DNA forming adducts which in turns leads to mutations and eventually cancer.

The Uses of Benzo[a]pyrene

BaP is not commercially produced; it is a by-product of combustion. Its primary uses include toxicological mechanistic studies and cancer studies, as a positive control in carcinogenicity studies. There is no known commercial use for BaP.

The Uses of Benzo[a]pyrene

Extensively used in cancer research and for GC (Gas Chromatography) and LC (Liquid Chromatography) Analysis. It is also a multipurpose intermediate.

Definition

ChEBI: An ortho- and peri-fused polycyclic arene consisting of five fused benzene rings.

Definition

A cyclic aromatic hydrocarbon with a structure consisting of five fused benzene rings. It occurs in coal tar and tobacco smoke and has strong carcinogenic properties.

General Description

A liquid. Presents a threat to the environment. Immediate steps should be taken to limits its spread to the environment. Easily penetrates the soil and contaminates groundwater or nearby waterways.

Air & Water Reactions

Insoluble in water.

Reactivity Profile

BENZO[A]PYRENE undergoes photo-oxidation after irradiation in indoor sunlight or by fluorescent light in organic solvents. Incompatible with strong oxidizing agents including various electrophiles, peroxides, nitrogen oxides and sulfur oxides. Oxidized by ozone, chromic acid and chlorinating agents. Readily undergoes nitration and halogenation. Hydrogenation occurs with platinum oxide .

Hazard

Highly toxic, confirmed carcinogen by inhalation.

Health Hazard

The acute oral toxicity of benzo[a]pyrene islow. This may be due to the poor absorption of this compound by the gastrointestinal tract.The lethal dose in mice from intraperitonealadministration is reported as 500 mg/kg(NIOSH 1986).
Animal studies show sufficient evidence ofits carcinogenicity by all routes of exposureaffecting a variety of tissues, which includethe lungs, skin, liver, kidney, and blood.
Dasenbrock et al. (1996) have investigatedthe carcinogenic potency of carbon particles,diesel soot and benzo[a]pyrene in rats fromrepeated intracheal administration in a 16-week study. A total dose of 15 mg purebenzo[a]pyrene caused lung tumor in theexperimental animals at a rate similar tothat caused by diesel soot and carbon blackparticles.
Lodovici et al. (1998) measured the levelsof PAHs and benzo[a]pyrenediol epoxideDNA adduct in autoptic lung samples ofsmokers and non-smokers. Benzo[a]pyrenediol epoxide resulting from metabolic activation of benzo[a]pyrene binds to DNA to forman adduct, the levels of which can be used as abiomarker to evaluate the exposure of humansto benzo(a)pyrene.
Benz[a]pyrene exhibited teratogeniceffects in test species. It is a mutagen.It showed positive in a histidine rever-sion–Ames test, cell transform mouse embryotest, and in in vitro sister chromatid exchange(SCE)–human lymphocytes..

Fire Hazard

Literature sources indicate that BENZO[A]PYRENE is nonflammable.

Toxicology

benzo[a]pyrene (BP) is a reasonably potent contact carcinogen, and therefore has been subjected to extensive carcinogenic testing. A diet containing 25 ppm of benzo[a]pyrene (BP) fed to mice for 140 days produced leukemia and lung adenomas in addition to stomach tumors. Skin tumors developed in over 60% of the rats treated topically with approximately 10 mg of benzo[a]pyrene three times per week. The incidence of skin tumors dropped to about 20% when treatment was about 3 mg  3 per week. Above the 10 mg range, however, the incidence of skin tumors increased dramatically to nearly 100%. benzo[a]pyrene (BP) is also carcinogenic when administered orally. In one experiment, weekly doses of greater than 10 mg administered for 10 weeks induced stomach cancers, although no stomach cancers were produced at the dose of 10 mg or less. At 100 mg doses, nearly 79% of the animals had developed stomach tumors by the completion of the experiment. When 15 ppm of benzo[a]pyrene (BP) in feed was orally administered to mice, production of leukemia, lung adenomas, and stomach tumors were observed after 140 days.

Safety Profile

Confirmed carcinogen withexperimental carcinogenic, neoplastigenic, andtumorigenic data. A poison via subcutaneous,intraperitoneal, and intrarenal routes. Experimentalteratogenic and reproductive effects. Human mutation data reported. A skin irritant.

Potential Exposure

Benzopyrene (BP) is a PAH that has no commercial-scale production. B(a)P is produced in the United States by one chemical company and distributed by several specialty chemical companies in quantities from 100 mg to 5 g for research purposes. Although not manufactured in great quantity, B(a)P is a by-product of combustion. It is estimated that 1.8 million pounds per year are released from stationary sources, with 96% coming from: (1) coal refuse piles, outcrops, and abandoned coal mines; (2) residential external combustion of bituminous coal; (3) coke manufacture; and (4) residential external combustion of anthracite coal. Human exposure to B(a)P can occur from its presence as a by-product of chemical production. The number of persons exposed is not known. Persons working at airports in tarring operations; refuse incinerator operations; power plants, and coke manufacturers, may be exposed to higher B(a)P levels than the general population. Scientists involved in cancer research or in sampling toxic materials may also be occupationally exposed. The general population may be exposed to B(a)P from air pollution, cigarette smoke, and food sources. B(a) P has been detected in cigarette smoke at levels ranging from 0.2 to 12.2:g per 100 cigarettes. B(a)P has been detected at low levels in foods ranging from 0.1 to 50 ppb.

First aid

If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifting upper and lower lids. Seekmedical attention immediately. If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water. Seek medical attention immediately. Ifthis chemical has been inhaled, remove from exposure,begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR ifheart action has stopped. Transfer promptly to a medicalfacility. When this chemical has been swallowed, get medical attention. Give large quantities of water and inducevomiting. Do not make an unconscious person vomit. Keepvictim quiet and maintain normal body temperature. Effectsmay be delayed; keep victim under observation.

Source

MCLG: zero; MCL: 0.2 μg/L (U.S. EPA, 2000).
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.
Particle-phase tailpipe emission rates from gasoline-powered automobiles with and without catalytic converters were 0.021 and 41.0 μg/km, respectively (Schauer et al., 2002).
Under atmospheric conditions, a low rank coal (0.5–1 mm particle size) from Spain was burned in a fluidized bed reactor at seven different temperatures (50 °C increments) beginning at 650 °C. The combustion experiment was also conducted at different amounts of excess oxygen (5 to 40%) and different flow rates (700 to 1,100 L/h). At 20% excess oxygen and a flow rate of 860 L/h, the amount of benzo[a]pyrene emitted ranged from 39.4 ng/kg at 650 °C to 690.7 ng/kg at 850 °C. The greatest amount of PAHs emitted were observed at 750 °C (Mastral et al., 1999).

Environmental Fate

The main natural sources of Benzo[a]pyrene(BaP) are forest fires and erupting volcanoes. Anthropogenic sources include the combustion of fossil fuels, coke oven emis- sions, and vehicle exhausts. In surface waters, direct deposition from the atmosphere appears to be the major source of BaP. Benzo[a]pyrene is moderately persistent in the environment. It readily binds to soils and does not readily leach to groundwater, though it has been detected in some groundwater. If released to water, it sorbs very strongly to sediments and particulate matter. In most waters and sediments, it resists breakdown by microbes or reactive chemicals, but it may evaporate or be degraded by sunlight. In water supply systems, it tends to sorb to any particulate matter and be removed by filtration before reaching the tap. In tap water, its source is mainly from PAH-containing materials in water storage and distribution systems.

storage

Color Code—Blue: Health Hazard/Poison: Storein a secure poison location. Store in tightly closed containers in a cool, well-ventilated area away from oxidizing chemicals (such as chlorates, perchlorates, permanganates, andnitrates). A regulated, marked area should be establishedwhere this chemical is handled, used, or stored in compliance with OSHA Standard 1910.1045.

Purification Methods

A solution of 250mg of benzo[a]pyrene in 100mL of *benzene is diluted with an equal volume of hexane, then passed through a column of alumina, Ca(OH)2 and Celite (3:1:1). The adsorbed material is developed with a 2:3 *benzene/hexane mixture. (It showed as an intensely fluorescent zone.) The main zone is eluted with 3:1 acetone/EtOH, and is transferred into 1:1 *benzene-hexane by adding H2O. The solution is washed, dried with Na2SO4, evaporated and crystallised from *benzene by the addition of MeOH [Lijinsky & Zechmeister J Am Chem Soc 75 5495 1953]. Alternatively it can be chromatographed on activated alumina, eluted with a cyclohexane-*benzene mixture containing up to 8% *benzene, and the solvent evaporated under reduced pressure [Cahnmann Anal Chem 27 1235 1955], and crystallised from EtOH [Nithipatikom & McGown Anal Chem 58 3145 1986]. [Beilstein 5 III 2517, 5 IV 2687.] CARCINOGENIC.

Toxicity evaluation

BaP is purposely synthesized solely for laboratory studies. The primary source of BaP and many PAHs in air is the incomplete combustion of wood, gasoline, and other fuels; in industrial settings where coal is burned; and in natural burns such as forest fires. BaP can bind to particulate matter, and inhalation is a common route of exposure. BaP is poorly water soluble, partitioning strongly to the sediment, and does not readily bioaccumulate. BaP is found in fossil fuels, crude oils, shale oils, and coal tars, and is emitted with gases and fly ash from active volcanoes. If released to air, an extrapolated vapor pressure of 5.49×10^-9 mm Hg at 25°C indicates BaP will exist solely in the particulate phase in the atmosphere. Particulate-phase BaP is usually removed from the atmosphere by wet or dry deposition. BaP contains chromophores that absorb at wavelengths >290 nm and therefore is expected to be susceptible to direct photolysis by sunlight; after 17 h irradiation with light >290 nm, 26.5% of BaP adsorbed onto silica gel was degraded. If released to soil, BaP is expected to have very low to no mobility based on measured soil Koc values of 930–6300. Volatilization from moist soil surfaces is not expected to be an important fate process based on a Henry’s Law constant of 4.57×10^-7 atm m3 mol1. The stability of BaP in soil is expected to vary depending on the nature of compounds accompanying it and the nature and previous history of the soil; biodegradation half-lives of 309 and 229 days were observed in Kidman and McLaurin sandy loam soils, respectively. BaP is expected to adsorb to suspended solids and sediment based on the measured Koc values, when released into water. Biodegradation of BaP is possible in aquatic systems. Volatilization from water surfaces is not expected to be an important fate process based on this compound’s Henry’s Law constant. Measured bioconcentration values ranging from 8.7 to 1×1010⁵ suggest bioconcentration in aquatic organisms can be low to very high. Hydrolysis is not expected to be an important environmental fate process since this compound lacks functional groups that hydrolyze under environmental conditions.

Incompatibilities

Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoacids, epoxides, nitrogen dioxide and ozone.

Waste Disposal

Incineration in admixture with a flammable solvent.