Exposure to genotoxins present in ambient air in Bangkok, Thailand — particle associated polycyclic aromatic hydrocarbons and biomarkers

Abstract

Exposure to genotoxic compounds in ambient air has been studied in Bangkok, Thailand, by analysis of polycyclic aromatic hydrocarbons (PAHs) associated with particles and using different biomarkers of exposure. Eighty-nine male, non-smoking Royal Thai police officers were investigated. The police officers were divided into a high exposure group (traffic police) and low exposure (office duty). Particulate matter was collected using personal pumps (2 l/min) and the eight carcinogenic PAHs were analysed by standard procedures. The traffic police was exposed to a 20-fold higher level of total PAHs than office police (74.25 ng/m³ vs. 3.11; P=0.001). A twofold variation was observed between the different police stations. The major PAHs in all groups was benzo[g,h,l]pyrelene. Large inter-individual differences in biomarker levels were observed, but the level of all markers was statistically significantly higher in the traffic police group than in the office group. The level of 1-hydroxypyrene (1-HOP) was 0.181±0.078 (range 0.071–0.393) μmol/mol creatinine in the traffic group and 0.173±0.151 (P=0.044) in the office group. The bulky carcinogen DNA-adduct level, determined by P³²-post-labelling, was 1.6±0.9 (range 0.4–4.3) adducts/10⁸ nucleotides in the traffic group and 1.2±1.0 (0.2–4.9) in the office group (P=0.029; Mann–Whitney U-test). The serum PAH–albumin adduct level was 1.76 (0.51–3.07) fmol adducts/μg albumin in the traffic group and 1.35±0.77 (0.11–3.45; P=0.001) in the office group. Lower biomarker levels were observed during the period when the traffic police officers were wearing a simple facemask, indicating that these masks protect against particle-associated PAHs. No statistically significant correlations were observed between biomarker levels and the level of individual PAHs or total PAH. Our data show, that people in Bangkok, who spend most of the day outside air-conditioned offices, are exposed to high levels of genotoxic PAHs. However, for people who spend their working day in offices, the exposure is similar to people living in other metropolitan areas.

Introduction

Atmospheric pollution has generally been recognised as a health hazard and substantial evidence exists for increased rates of morbidity and mortality from respiratory diseases following severe air pollution episodes. A number of epidemiological studies have indicated that people living in urban areas have an increased risk of lung cancer compared to people living outside metropolitan areas. However, the extent to which urban air pollution contributes to an excessive risk remains unknown (Katsouyanni and Pershagen, 1997). Urban air pollution mainly originates from incomplete fossil fuel combustion, the composition of which is very complex as it contains more than 500 different chemicals, some of which are carcinogenic in experimental animals. The carcinogenic polycyclic aromatic hydrocarbons (PAHs) can either be bound to the particulate matter (PM) or be in a volatile form. The lower molecular weight PAHs are mostly found in the volatile fraction, e.g. pyrene, whereas heavier PAHs are mostly bound to the PM. Exposure for air pollutants has mostly been assessed by measurement of the pollutants at fixed monitoring stations, e.g. nitrogen oxides, volatile and particle bound organic compounds. The exposure can then be estimated using time-activity patterns or by modelling, e.g. operational street pollution models (Berkowicz et al., 1996). Most of the studies on exposure for air pollutants have been conducted in temperate and sub-tropical countries, e.g. western Europe and the USA. In temperate climates, the amount and type of PAHs in urban areas exhibit seasonal fluctuations, the level generally being higher in the winter season (Cotham and Bidleman, 1995, Harrison et al., 1996). In tropical environments, like Thailand, very little is known about seasonal variations in environmental PAH levels (Garivait, 1999).

In the past decade, biomarkers have been introduced to assess human exposure to genotoxic compounds in ambient air in urban areas. Polycyclic aromatic hydrocarbons are a major group of carcinogenic compounds in ambient urban air and most biomarker studies have been focused on assessing PAH exposure. Urinary 1-hydroxypyrene (1-HOP) has served as a marker of exposure for volatile PAHs mostly in occupational environment and in smokers, whereas the level was generally low in people only exposed for ambient air pollution (Øvrebø et al., 1995, Pastorelli et al., 1999). Polycyclic aromatic hydrocarbons in ambient air are metabolised into metabolites that react with cellular macromolecules to form adducts, e.g. carcinogen DNA and protein adducts. Measurement of adducts in lymphocyte DNA and blood proteins has served as biomarkers of exposure for PAHs present in ambient air (Hemminki et al., 1995). DNA adducts represent a reliable biological marker widely used to identify health hazards and evaluate dose response relationships. Furthermore, it has been shown that peripheral blood DNA adducts have been reported to be an acceptable surrogate for target tissues and are predictive for the risk of lung cancer (Vineis and Perera, 2000, Rundle et al., 2000). An increased level of adducts has been seen in people who are occupationally exposed to high levels of ambient air pollution, e.g. bus drivers (Nielsen et al., 1996a), workers in bus garages (Hou et al., 1995), street vendors (Pastorelli et al., 1999) and traffic police officers (Merlo et al., 1998). The objective of the present study was to assess the exposure for genotoxic compounds present in the ambient air in a tropical city using the same biomarkers that has previously been used in studies in the Northern hemisphere. Bangkok is a large city with more than 8 million people. The city is considered highly polluted mostly due to its extensive traffic. In addition, the traffic profile is quite different from western cities, cars (2.3 million) and small motorcycles (1.6 million) the latter being a major means of transportation. Traffic police officers were selected as the high exposure group as they are spending at least 8 h every day at road intersection regulating the traffic, whereas police officers with office duty were selected as the low exposure group.