Exposure to genotoxins present in ambient air in Bangkok, Thailand — particle associated polycyclic aromatic hydrocarbons and biomarkers
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.
Section snippets
Study subjects and collection of samples
The study participants were selected in collaboration with the Royal Thai Police. All were males, non-smokers for at least 1 year, and had been working in the traffic police for at least 1 year. The participants were healthy at the time of entry into the study based upon a complete medical examination. A total of 89 traffic police officers were recruited for the study. The group was divided into two subgroups according to expected exposure. The high exposure group consisted of 44 officers (mean
Results
The exposure for genotoxic compounds present in ambient air in the city of Bangkok was assessed by determination of the eight carcinogenic PAHs in the breathing zone and by using different biomarkers. Bangkok is considered a highly polluted city, the major contribution of pollutants originating from the traffic.
Discussion
Most studies on the use of biomarkers to assess exposure for genotoxins in ambient air have been conducted in non-tropical areas. In tropical countries, meteorological conditions, higher temperature and higher level of UV radiation may influence the atmospheric transformation of the PAH and the rate of association of the PAH with particles and thus the exposure. In this paper, we present data from a study conducted in Bangkok, Thailand. Polycyclic aromatic hydrocarbons are a major group of
Acknowledgements
The project was supported by a grant from the Chulabhorn Research Institute, Thailand.
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