| Summary: | 博士 === 高雄醫學大學 === 職業安全衛生研究所 === 97 === Leukemia is the most common cancer in childhood. Studies to date failed to firmly establish risk factors for childhood leukemia except for ionizing radiation, chemotherapy agents, and certain inherited genetic disorders. Benzene has been identified as a cause of leukemia. A number of studies have reported that childhood leukemia is associated with exposure to high levels of traffic-related air pollution. In Taiwan, petrochemical industry and road traffic are the major sources of ambient air pollution in urban areas. The evidence for an association between exposure to petrochemical- or traffic-related air pollutants and the development of childhood leukemia is still inconclusive. Matched case-control studies were conducted using childhood deaths that occurred in Taiwan. Data on all eligible childhood leukemia deaths were obtained from the Bureau of Vital Statistics of the Department of Health. The control group consisted of children who died from causes other than neoplasms or diseases which were not associated with respiratory complications. The controls were pair matched to the cancer cases by gender, year-of-birth, and year-of-death. Each matched control was selected randomly from the set of possible controls for each case. Three different exposure indicators were applied to evaluate the exposure-response relationship. (1) The proportion of a municipality’s total population employed in the petrochemical industry in a municipality was used as an indicator of a resident''s exposure to air emissions from the petrochemical industry. The subjects were divided into three levels (≦25th percentile; 25th–75th percentile; >75th percentile) according to the levels of the indicator. After controlling for possible confounders, results showed that children who lived in the group of municipalities characterized by the highest levels of petrochemical air pollution had a statistically significant higher risk of developing leukemia than the group that lived in municipalities with the lowest petrochemical air pollution levels. (2) Air quality data for recorded concentrations of nitrogen dioxide (NO2) from study municipalities for 1995–2005 were obtained as an indicator of a subject''s exposure to air emissions from motor vehicles. The subjects were divided into tertiles according to the levels of NO2 in their residential municipality. The results showed that there was a significant exposure-response relationship between exposure to traffic exhaust pollutants and the risk of leukemia among young children after controlling for possible confounders. (3) Data on the number of petrol stations in study municipalities were collected from the two major petroleum supply companies, Chinese Petroleum Corporation (CPC) and Formosa Petrochemical Corporation (FPCC). The petrol station density (per square kilometer) (PSD) for study municipalities was used as an indicator of a subject’s exposure to benzene and other hydrocarbons present in evaporative losses of petrol or to air emissions from motor vehicles. The subjects were divided into tertiles according to PSD in their residential municipality. The results showed that there was a significant exposure-response relationship between PSD and the risk of leukemia development in young children after controlling for possible confounders. In conclusion, the findings of our studies suggest that further investigation is warranted in establishing the association between petrochemical or traffic-related air pollution exposure and childhood leukemia.
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