Covariation between serum cotinine and blood lead levels among US pediatric populations: Trends from 1999 to 2018

Background: Tobacco smoke, including both active and passive smoke, can be an important source of lead exposure. However, the relationship between passive tobacco smoke exposure (PTSE) and blood lead levels (BLL), especially in vulnerable populations, needs to be further explored. The present study was to assess the covariation between serum cotinine, a measure of PTSE, and BLL in a pediatric population during 1999–2018. Methods: Data on 21,817 children, aged 3–19 years, was extracted from the biennial nationally representative surveys. The trends of the prevalence of lead exposure (BLL ≥ 3.5 µg/dL) and PTSE (cotinine ≥ 1 ng/mL but < 10 ng/mL) were determined, and the covariation between BLL and cotinine was assessed. The population attributable fraction (PAF) of PTSE to the BLL was proxied using the partial R² of the hierarchical linear regression. The association between PTSE and lead exposure was estimated using multivariate logistic regression. Results: A parallel decreasing trend in the prevalence of lead exposure and PTSE was observed. Similarly, the means of both BLL and cotinine declined simultaneously. Overall, the PAF from PTSE towards blood lead was 7 %, doubling the PAF from race/ethnicity and family income combined. Stratified by race/ethnicity, PAF from PTSE was 8 % in Blacks and Whites and 4 % for Hispanics. The odds ratio of PTSE with lead exposure was 2.45 (95 % CI, 1.75, 3.44), 2.00 (1.21, 3.33), and 1.16 (0.64, 2.13) for Black, White, and Hispanic children, respectively. Cotinine mean remained two times higher in Blacks than non-Black children at the end of the study period. Conclusion: Serum cotinine and BLL may have a significant association in children that persists even as both have been steadily declining in recent years. The contribution from PTSE to blood lead variations could be greater than that from socioeconomic factors. Further reducing lead exposure might be achieved by eliminating PTSE, particularly for the Black pediatric population.