In the present study, one interquartile range increase in ambient air pollution concentrations is associated with a 2.5 – 3.2 ng/ml increase in osteocalcin and a 24.0 – 32.3 ng/L increase in CTx. These effect sizes are significantly associated with bone density loss, according to published papers in adults. Quantitative assessments between bone markers and bone mineral density are still lacking for children. It has nevertheless been reported that the odds of rapid bone loss increase by 1.8 (95% CI: 1.3 – 2.5) and 1.7 (95% CI: 1.24 – 2.40) for every 2.6 ng/ml increase in osteocalcin (Ross and Knowlton, 1998) and when serum CTx concentrations increase more than 50 ng/l (Okuno et al., 2005) in adults. In this case, we believe that the elevation of bone marker levels in our study might indicate rapid bone loss.