Skip directly to search Skip directly to A to Z list Skip directly to site content
CDC Home

Biomonitoring Summary

Polycyclic Aromatic Hydrocarbons Overview

General Information

Polycyclic aromatic hydrocarbons (PAHs) are a class of more than 100 chemicals generally produced during the incomplete burning of organic materials, including coal, oil, gas, wood, garbage, and tobacco. PAHs are composed of up to six benzene rings fused together such that any two adjacent benzene rings share two carbon bonds. Examples include phenanthrenes, naphthalene, and pyrene. Important PAH sources include motor vehicle exhaust, residential and industrial heating sources, coal, crude oil and natural gas processing, waste incineration, and tobacco smoke. The emitted PAHs can form or bind to particles in the air, and particle size depends in part on the source of the PAHs. The smaller or fine particulates (e.g., PM2.5 or smaller) have higher concentrations of PAHs than the larger or coarse particulates (Bostrom et al., 2002; Rehwagen et al., 2005). Ambient air PAH concentrations show seasonal variation (IPCS, 1998; Rehwagen et al., 2005). Smoking, grilling, broiling, or other high temperature processing leads to PAH formation in meat and in other foods, as well. Uncooked foods and vegetables generally contain low levels of PAHs but can be contaminated by airborne particle deposition or growth in contaminated soil. With the exception of naphthalene, the PAHs described here are not produced commercially in the U.S.

Human exposure usually occurs to PAH mixtures rather than to individual chemicals, and PAH mixture composition varies with the combustion source and temperature (ATSDR, 1995). For persons without occupational exposure, important sources of PAHs include ambient air pollution (especially motor vehicle exhaust), smoke from wood or fossil fuels, tobacco smoke, and foods. PAH exposure can occur in workplaces where petroleum products are burned or coked, such as coke production, coal gasification and gas refining, iron or steel production, roofing tar and asphalt application, waste incineration, and aluminum smelting. Coal tar ointments containing PAHs are used to treat several inflammatory skin conditions.

PAHs are lipid soluble and can be absorbed through the skin, respiratory tract, and gastrointestinal tract. PAH metabolism is complex and occurs primarily in the liver, and to a lesser extent, in other tissues. PAH elimination occurs via urine and feces, and urinary metabolites are eliminated within a few days (Ramesh et al., 2004). PAHs and their urinary hydroxylated metabolites measured in at CDC are shown in the table. The metabolic pathways and enzyme-inducing effects of specific PAHs, such as benz[a]pyrene, have been actively studied to elucidate cancer potential and causal mechanisms (Ramesh et al., 2004). Although immunologic, kidney and brain toxicity have been seen in animals after high doses were administered, it is unclear if similar effects may occur in humans. Lung, bladder, and skin cancers have been reported in occupational settings following high PAH exposures (Bosetti et al., 2007; Bostrom et al., 2002; Lloyd, 1971). Exposure to fine particulates has been associated with fetal growth retardation, respiratory disorders, and cardiovascular disease, but it is unknown whether PAHs contained within fine particulates are etiologic (ATSDR, 1995; Choi, 2006).

IARC classifies naphthalene as a possible human carcinogen. NTP determined that naphthalene is reasonably anticipated to be a human carcinogen. Many other PAHs are considered to be probable or possible human carcinogens. IARC and NTP have classified specific PAH-containing chemical mixtures (e.g., soot, coke oven emissions, coal tars and coal tar pitches) as human carcinogens. OSHA has developed criteria on the allowable levels of these chemicals in the workplace.

Information about external exposure (i.e., environmental levels) and health effects is available in reviews (Bosetti et al., 2007; Bostrom et al., 2002; Brandt and Watson 2003) and from ATSDR at

PAH Metabolites in the National Biomonitoring Program
Polycyclic Aromatic Hydrocarbon (CAS number) Urinary hydroxylated metabolite (CAS number)
Fluorene (86-73-7) 2-Hydroxyfluorene (2443-58-5)
3-Hydroxyfluorene (6344-67-8)
9-Hydroxyfluorene (484-17-3)
Naphthalene (91-20-3) 1-Hydroxynapthalene (90-15-3)
2-Hydroxynapthalene (135-19-3)
Phenanthrene (85-01-8) 1-Hydroxyphenanthrene (2433-56-9)
3-Hydroxyphenanthrene (605-87-8)
4-Hydroxyphenanthrene (7651-86-7)
Pyrene (129-00-0) 1-Hydroxypyrene (5315-79-7)

Biomonitoring Information

Measurement of urinary metabolites reflects recent exposure to PAHs. Some of the parent PAHs can produce more than one measurable urinary metabolite, as shown in the Table. The hydroxylated metabolites of PAHs are excreted in human urine both as free hydroxylated metabolites and as hydroxylated metabolites conjugated to glucuronic acid and sulfate. Urine metabolite profiles can vary depending on the PAH source(s), but also have been found to vary between individuals experiencing similar exposures within the same workplace (Grimmer et al., 1997; Jacob and Seidel 2002).

Finding a measurable amount of one or more metabolites in the urine does not imply that the levels of the PAH metabolites or the parent PAH cause an adverse health effect. Biomonitoring studies of urinary PAHs provide physicians and public health officials with reference values so that they can determine whether or not people have been exposed to higher levels of PAHs than are found in the general population. Biomonitoring data can also help scientists plan and conduct research on exposure and health effects.


CAS No. 86-73-7

Fluorene can be an intermediate in several chemical processes, and it is used to form polyradicals for resins and in manufacturing dyestuffs. Fluorene is frequently detected in the vapor phase of various PAH emission sources, including coal tar pitch, petroleum refineries, diesel exhaust fumes, and tobacco smoke, where it is the second most abundant PAH (Ding et al., 2005). Fluorene is present in air particulates resulting from vehicle emissions and combustion of coal and petroleum-based fuels (Fang et al., 2006). IARC determined that fluorene was not classifiable with respect to human carcinogenicity.

Biomonitoring Information

Urinary levels of 2-hydroxyfluorene, 3-hydroxyfluorene, and 9-hydroxyfluorene reflect recent exposure. Mean levels of 2-hydroxyfluorene were significantly higher in Japanese smokers than non-smokers in one small study (Toriba et al., 2003). By comparison, geometric mean and median urinary 2-hydroxyfluorene levels in adults in NHANES 2003-2004 and 2005-2006 were similar to the mean levels in the smokers and somewhat higher than those in the non-smokers.

Finding a measurable amount of one or more urinary fluorene metabolites does not imply that the level causes an adverse health effect. Biomonitoring studies of urinary fluorene metabolites can provide physicians and public health officials with reference values so that they can determine whether or not people have been exposed to higher levels of fluorene than levels found in the general population. Biomonitoring data can also help scientists plan and conduct research on exposure and health effects.


Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological profile for polycyclic aromatic hydrocarbons 1995 [online]. Available at URL: 12/28/12

Bosetti C, Boffetta P, La Vecchia C. Occupational exposures to polycyclic aromatic hydrocarbons, and respiratory and urinary tract cancers: a quantitative review to 2005. Ann Oncol 2007;18:431-446.

Bostrom CE, Gerde P, Hanberg A, Jernstrom B, Johansson C, Kyrklund T, et al. Cancer risk assessment, indicators, and guidelines for polycyclic aromatic hydrocarbons in the ambient air. Environ Health Perspect 2002;110Suppl 3:451-488.

Brandt HCA, Watson WP. Monitoring human occupational and environmental exposures to polycyclic aromatic compounds. Ann Occup Hyg 2003;47(5):349-378.

Choi H, Jedrychowski W, Spengler J, Camann DE, Whyatt RM, Rauh V, et al., International studies of prenatal exposure to polycyclic aromatic hydrocarbons and fetal growth. Environ Health Perspect 2006;114(11):1744-1750.

Ding YS, Trommel JS, Yan Xj, Ashley D, Watson CH. Determination of 14 polycyclic aromatic hydrocarbons in mainstream smoke from domestic cigarettes. Environ Sci Technol 2005;39:471-478.

Fang G-C, Wu Y-S, Chen J-C, Chang C-N, Ho T-T. characteristic of polycyclic aromatic hydrocarbon concentrations and source identification for fine and coarse particulates at Taichung Harbor near Taiwan Strait during 2004-2005. Sci Tot Environ 2006;366:729-738.

Grimmer G, Jacob J, Dettbarn G, Naujack K-W. Determination of urinary metabolites of polycyclic aromatic hydrocarbons (PAH) for the risk assessment of PAH-exposed workers. Int Arch Occup Environ Health 1997;69:231-239.

International Programme on Chemical Safety (IPCS). Selected non-heterocyclic policyclic aromatic hydrocarbons. Environmental Health Criteria 202. 1998 [online]. Available at URL: 12/28/12

Jacob J, Seidel A. Biomonitoring of polycyclic aromatic hydrocarbons in human urine. J Chromatogr B 2002;778(1-2):31-47.

Lloyd J. Long-term mortality study of steelworkers. V. Respiratory cancer in coke plant workers. J Occup Med 1971;13:53-68.

Ramesh A, Walker SA, Hood DB, Guillen MD, Schneider K, Weyand EH. Bioavailability and risk assessment of orally ingested polycyclic aromatic hydrocarbons. Int J Toxicol 2004;23(5):301-333.

Rehwagen M, Muller A, Massolo L, Herbarth O, Ronco A. Polycyclic aromatic hydrocarbons associated with particles in ambient air from urban and industrial areas. Sci Tot Environ 2005;348:199-210.

Toriba A, Chetiyanukornkul T, Kizu R, Hayakawa K. Quantification of 2-hydroxyfluorene in human urine by column-switching high performance liquid chromatography with fluorescence detection. Analyst 2003;128(6):605-610. The U.S. Government's Official Web PortalDepartment of Health and Human Services
Centers for Disease Control and Prevention   1600 Clifton Road Atlanta, GA 30329-4027, USA
800-CDC-INFO (800-232-4636) TTY: (888) 232-6348 - Contact CDC–INFO
A-Z Index
  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #