Why is exposure to PAH relevant to health?
PAH are a large and diverse group of chemical products of incomplete combustion of organic matter typically found in polluted air and water, and in foods prepared by grilling or barbecuing, or preserved by smoke curing. They are also found in unprocessed foods such as vegetables that may have been contaminated with PAH from the atmosphere. Tobacco smoke is also a significant source of PAH exposure. Dietary intake of PAH is considered to be the major route of exposure for a large proportion of the non-smoking, non-occupationally exposed population.
Airborne PAH exposures, often associated with automobile exhaust and typical in highly polluted and urban regions, have been associated with asthma prevalence, inflammation, and exacerbation. Prenatal PAH exposure has been associated with a range of problems including cancer, developmental delay, reduced IQ, symptoms of anxiety and depression, and attention-deficit hyperactivity disorder (ADHD).
Many PAH are well-established potent carcinogens, the best example of which is benzo[a]pyrene (BaP), considered carcinogenic to humans by the International Agency for Research on Cancer. Exposure to PAH represent one of the earliest examples of carcinogenesis by chemicals.
What types of questions can be answered?
Exposure to PAH can be measured by determining levels of their metabolites in urine or blood, or by measuring them in dust or air samples. All humans have these metabolites in their urine or blood; potentially higher exposures can be assessed by comparison to databases such as the National Health and Nutrition Examination Survey (NHANES). Elevated levels of these compounds might be expected in situations in which people live in highly polluted areas, consume diets containing high levels of PAH contamination, or are exposed to significant amounts of tobacco smoke or smoke from other sources of incomplete combustion.
How can exposure to PAH be measured?
- Analytes: PAH can be analyzed by measurement of well-accepted surrogate compounds in urine (e.g., 1-hydroxypyrene, hydroxylated phenanthrene) that serve as biomarkers for overall PAH exposure. Plasma and serum also can be used as a matrix for PAH exposure assessment, but the levels are expected to be much lower in blood than in urine.
- Methods: Analytical methods comprise chromatography coupled with mass spectrometry. All methods require preliminary purification steps to remove interfering substances from the matrix.
- Types of biospecimens: Urine, plasma, and serum are used. Urine is the preferred matrix, and typical concentrations of hydroxynaphthalenes and hydroxyphenanthrenes (major PAH metabolites in U.S. urine) are between 1 and 10 µg/L and 0.13-0.2 µg/L, respectively.
- Types of environmental samples: Dust, air, and silicone wristbands are the most common media analyzed, but other media have been used.
How does HHEAR ensure the quality of its analyses?
All assays are well validated with respect to accuracy and precision. All assays have embedded positive and negative controls. The positive controls are used to check assay accuracy within each set of samples. The negative controls are generally included to assess the possibility of any cross contamination in the assay procedure. HHEAR laboratories participate in international and national proficiency testing programs.
What sample quality and quantity are necessary?
This is highly dependent on the assay to be run, but in general, a few milliliters of urine, serum, or plasma, or one gram of dust is required. In general, PAH metabolites are quite stable, so multiple freeze-thaw cycles should not be a significant problem. Exposure of samples to light or heat is be avoided. Sunlight or UV light can degrade PAH and their metabolites, so samples are to be collected in amber (opaque) containers.
Centers for Disease Control and Prevention. National Biomonitoring Program Factsheet: Polycyclic Aromatic Hydrocarbons (PAHs).
Jedrychowski WA, Perera FP, Majewska R, et al. Depressed height gain of children associated with intrauterine exposure to polycyclic aromatic hydrocarbons (PAH) and heavy metals: the cohort prospective study. Environmental Research. 2015;136:141-147.
Karimi P, Peters KO, Bidad K, et al. Polycyclic aromatic hydrocarbons and childhood asthma. European Journal of Epidemiology. 2015;30:91-101.
Moorthy B, Chu C, Carlin DJ. Polycyclic aromatic hydrocarbons: from metabolism to lung cancer. Toxicological Sciences. 2015;145(1):5-15.
Perera FP, Chang HW, Tang D, et al. Early-life exposure to polycyclic aromatic hydrocarbons and ADHD behavior problems. PLOS One. 2014;9:e111670.