Characteristics and potential health risk of rural Tibetans' exposure to polycyclic aromatic hydrocarbons during summer period

Biomass fuels remain main energy sources in many remote rural regions, but potential health hazards from exposure to biomass combustion fumes have not been adequately assessed. Combustion of biomass fuels generates abundant polycyclic aromatic hydrocarbons (PAHs); hence residential exposure to PAHs can be used to evaluate the potential health risk to remote rural populations. The present study selected rural Tibetans to address the above-mentioned issue. Samples of indoor air and dust, human urine and local foods (Tsampa flour and buttered tea) were collected from five rural households in Langkazi County, an agricultural and pasturing region in Tibet of China in the summer season, which represented the best-case scenario as no heating was required. Residential exposure to PAHs by adults amounted to benzo[a] pyrene equivalent (BaPeq) dosages of 110-760, 1.2-50 and 0.5-23 ng d(-1) for ingestion, inhalation and dermal contact, respectively. Daily intakes of naphthalene, fluorene, phenanthrene and pyrene estimated from urinary monohydroxy PAH metabolites and from diet and inhalation exposure to PAHs were comparable (3.9, 1.9, 12 and 3.3 mu g d(-1) versus 9.5, 2.5, 5.1 and 1.1 mu g d(-1)), indicating the utility of external exposure in assessing daily intake of PAHs. The median incremental lifetime cancer risk was 32 x 10(-6) (95% confidence interval: 0.7-73 x 10(-6)) for ingestion and 2.4 x 10(-6) (95% confidence interval: 0.02-12 x 10(-6)) for inhalation and dermal contact combined, indicating moderate to slight potential cancer risk. Diet is the dominant source of health hazards for rural Tibetans, but cooking fumes also present a meaningful concern. The present study demonstrates that the pristine lifestyles of remote rural residents may be of global health concern, and merit further investigations.