UNLABELLED

Organophosphate esters (OPEs), widely used as alternative flame retardants and plasticizers, have been recognized for their bone toxicity. However, evidence linking OPE exposure to bone health in children and adolescents remains limited. We analyzed data from the 2011-2018 National Health and Nutrition Examination Survey, including 1576 participants aged 8-19 years. Five urinary OPE metabolites were measured-dibutyl phosphate (DBUP), bis(1-chloro-2-propyl) phosphate (BCPP), bis(2-chloroethyl) phosphate (BCEP), bis(1,3-dichloro-2-propyl) phosphate (BDCPP), and diphenyl phosphate (DPHP)-to examine their associations with BMD at the total body, lumbar spine, trunk, and pelvis. Weighted multivariable linear regression and restricted cubic spline models examined individual associations, while Bayesian kernel machine regression (BKMR) assessed mixture effects. Subgroup analyses were conducted by gender. DBUP was negatively correlated with BMD at multiple sites, total body BMD β =  - 0.016 (95% CI: - 0.030, - 0.002), trunk BMD β =  - 0.019 (95% CI: - 0.032, - 0.005), and pelvis BMD β =  - 0.028 (95% CI: - 0.048, - 0.007). BCPP, BCEP, BDCPP, and DPHP exhibited site-specific associations. DPHP showed a nonlinear dose-response with total-body and trunk BMD. BKMR confirmed a negative mixture effect, with DBUP contributing most. Subgroup analyses suggested that its effect on BMD was more significant in males.

CONCLUSIONS

Individual and combined OPE exposure in children and adolescents was inversely associated with bone mineral density, with gender differences. However, due to the cross-sectional research design, these findings should be interpreted with caution and need to be verified in future longitudinal studies.

WHAT IS KNOWN

• OPEs, widely used as flame retardants and plasticizers, have been recognized both as potential endocrine disruptors and for their bone toxicity. • Prior studies on the association between OPE exposure and BMD have mainly focused on adult populations, with limited evidence in children and adolescents.

WHAT IS NEW

• This study is the first to investigate the association between urinary OPE metabolites and BMD across multiple skeletal sites among U.S. children and adolescents aged 8-19 years using NHANES data. • Individual and combined OPE exposures were inversely associated with BMD, with site- and gender-specific variations; DBUP showed the strongest effect. These findings suggest that early-life OPE exposure may impair bone health, highlighting the need for longitudinal studies.