Why is childhood exposure to PAH relevant to health?
PAH are a large and diverse group of 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 nonsmoking, non-occupationally exposed population.
Airborne PAH exposures, often associated with automobile exhaust and typical in highly polluted regions, have been associated with childhood asthma prevalence and exacerbation. Prenatal PAH exposure has been associated with a range of problems including developmental delay, reduced IQ, symptoms of anxiety and depression, depressed height gain, 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 represents 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. 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 in children might be expected in situations in which the children lived in highly polluted areas, consumed diets containing suspected high levels of PAH contamination, or were 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, phenanthrene tetraol) that serve as biomarkers for overall PAH exposure. Plasma and serum also can be used as sample sources for phenanthrene tetraol measurement.
- Methods: Methods that couple chromatography with either mass spectrometry or fluorescence detection are used. All methods require preliminary purification steps that remove interfering substances.
- Types of biospecimens: Urine, plasma, and serum are used. As noted above, the PAH biomarkers detected in blood products are limited.
How does CHEAR 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 water blanks that are included to assess the possibility of any cross contamination in the assay procedure.
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 are required. In general, PAH metabolites are quite stable, so multiple freeze-thaw cycles should not be a significant problem.
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.
Perera FP, Chang HW, Tang D, et al. Early-life exposure to polycyclic aromatic hydrocarbons and ADHD behavior problems. PLoS One. 2014;9:e111670.