Characterization of polycyclic aromatic hydrocarbons (PAH) in airborne particles and assessment of human exposure to PAHs.

摘要

Polycyclic aromatic hydrocarbons (PAH), a group of carcinogenic and mutagenic pollutants, are byproducts of incomplete combustions of organic materials such as wood, fossil fuels, meat, and tobacco, and are therefore distributed ubiquitously in the ambient air, soil and water environments. PAH in the atmosphere, especially in densely populated areas, is significantly affected by anthropogenic emissions, such as automobile exhaust, fossil fuel combustion, biomass burning, cigarette smoking, and industrial activities. Particulate matter (PM) air pollution, especially fine particles with aerodynamic diameters less than 2.5 mum (PM2.5), has been linked to increased morbidity and mortality rates, as well as various adverse health effects such as respiratory and cardiovascular diseases. The association of PM2.5 with toxic compounds such as PAHs could further increase the health effects. Human exposure to PAHs can occur through three routes, i.e. inhalation, ingestion and dermal absorption. For the general population, the main exposure routes are inhalation of polluted air or cigarette smoke and ingestion of food containing PAHs. Atlanta is a rapidly growing city with high PM air pollutant. However, little is known on PAHs levels, especially PM2.5-bound PAHs concentrations in this area. To characterize PM2.5-bound PAHs in Atlanta, a method was developed to provide sensitive and reliable measurements of 28 PAHs and methyl-PAHs (Me-PAH) in archived daily PM2.5 samples collected with low flow rate (16 L/min or 24 m3 air/sample). Then PM2.5 samples taken at three sampling sites (urban, suburban-highway and rural) in the metropolitan Atlanta area during 2003-2004 were analyzed and the levels, seasonal and spatial variation of PAHs were studied. Correlation analyses between PAHs and other air pollutants such as PM2.5, OC, EC and potassium ion (K+) were conducted and the results indicated that PAHs had common sources as other pollutants, but with a distinct seasonal effect. Retene, a proposed biomass burning tracer, captured both the high leaves-grasses-bushes-branches burning season and the high wood burning months, suggesting that it might be a more general indicator of biomass burning than potassium, which is more specific to wood burning. Assessment of human exposure to environmental chemicals such as PAHs can be accomplished either through environmental monitoring in which concentrations of PAHs in environmental samples (air, food, water, soil, etc.) are determined, or through biomonitoring in which internal levels of PAHs in human body (e.g. urinary hydroxy PAHs, or OH-PAHs) are measured as indicators for assessing overall exposure to PAHs. A lot of studies have been reported since the early 1990's to assess high occupational exposure to PAHs; however, limited information is available on non-occupational exposure of the general populations to PAHs in the environment. Even less information is available on the temporal, intra- and inter-subject variability of these biomarkers. A method was developed to measure hydroxyl PAH metabolites (OH-PAH) in urine samples. A study was carried out to study the variability of the urinary biomarker levels in a non-occupationally exposed non-smoking reference group. Levels of urinary PAH metabolites varied widely both within-subject and between-subjects and the within-day variance far exceeded the between-day variance. There were also considerable temporal correlations for these biomarkers. Sample size calculations were conducted and taking 24-hour voids would require the least number of subjects, which can be used for future epidemiological study design. Finally, a study was conducted to evaluate exposure to PAHs in an urban setting among a group of non-occupational exposed non-smokers employing both personal air sampling and urine biomonitoring. PAH levels varied largely in air samples taken at home, at work, and while driving or jogging. Monitoring urinary OH-PAH levels can capture both inhalation and dietary exposures. Total inhaled PAH was correlated with total excreted OH-PAHs, suggesting that by combining personal air sampling and biomonitoring, exposure to environmental PAHs can be well characterized even for low-level exposure.