Background

Childhood exposure to lead and urban air pollution remains a significant public health concern, yet evidence linking contemporary low blood lead levels (BLLs) to clinically diagnosed neurobehavioral disorders is limited. In addition, emerging evidence suggests that long-term exposure to ambient air pollution may increase the risk of ADHD. Further, low-income, urban neighbors are disproportionately affected by lead and air pollution exposures.

Methods

This was a clinical retrospective cohort including 14,127 children residing in Philadelphia, PA who visited the Temple University Health System (TUHS) between 2010-2020. Associations between BLLs and ADHD were evaluated using multivariable logistic regression, with BLLs modeled continuously and dichotomized at 3.5 µg/dL; sex-stratified analyses assessed effect modification. Associations between long-term ambient air pollution and ADHD were examined using a matched case-control design matching on age and index time and using conditional logistic regression models. Both models adjusted for individual- and neighborhood-level sociodemographic factors.

Results

Higher continuous BLLs were associated with increased odds of ADHD (adjusted OR 1.51; 95% CI 1.37, 1.67). Children with BLLs ≥3.5 µg/dL had higher odds of ADHD (adjusted OR 1.84; 95% CI 1.56, 2.16) compared with those with BLLs <3.5 µg/dL, with stronger associations observed among males than females. Associations between long-term exposure to PM2.5 or NO2 and ADHD were positive but not statistically significant (PM2.5: adjusted OR 1.19; 95% CI 0.77, 1.83; NO2: adjusted OR 1.02; 95% CI 0.91, 1.15).

Conclusions

Childhood lead exposure, and to a lesser extent long-term ambient air pollution, was associated with increased risk of ADHD in this urban clinical population, underscoring persistent neurodevelopmental risks and the need for continued prevention efforts.