near the breathing zone of study subjects. As for ambient air sampling, badges were hung on poles or walls at a height of approximately 150 cm off the ground. Sampling time was 8 h, after which samples were capped, transported to the laboratory, and stored at −20 ◦C until analysis. Urine samples were collected in the morning (prior to the start of the school day) and afternoon (at the end of the school day), and stored frozen until analysis. All air samples were collected between January and March (dry season).