while two schools situated in Chonburi (provincial area located approximately 110 km from Bangkok) were used as control sites. All study subjects were 9–13-year old male students. Children with a known history of medical problems that could affect physiological function, or that may make them susceptible to possible iatrogenic expo- sures to radiation sources, were excluded. Parents had to sign a consent form for all student subjects participating in the study. Students also completed a questionnaire to allow assessment of eating habits, food, residence, health status, play behavior, and cigarette smoke exposure, and therefore allow determi- nation of confounding factors that may influence biomarker levels.