2.1.1. Acute CNP Exposure Study Design

Details of the study design have been previously reported by our group [18]. Briefly, in the acute exposure study, nine young, healthy, and non-smoking volunteers were asked to spend 5–6 h/day in a copy center. Five subjects volunteered to repeat the experiment three times, whereas four volunteers only two times, two–three times, in random non-consecutive days, weeks to months apart. Each volunteer gave NL and urine samples before exposure (U₀), at the end of the exposure period (U₆), the morning the next day (U₂₄), and the next day at the end of their shift (U₃₀). The same volunteers were also asked to spend an equal amount of time (6 h) for a single day in an office environment with no photocopying activities. Urine and NL samples were also collected from these controls at the beginning and end of the exposure period using the same sampling protocol. Each volunteer donated 8–12 samples (4 samples/day × 2 or 3 days; n = 92 urine samples) as part of the controlled CNP exposure, and another 2 urine samples (2 × 1 × 9; n = 18) as part of the background exposure day. A total of 110 urine samples were analyzed.