Associations between emerging chlorinated polyfluoroalkyl ether sulfonic acids exposure and birth size

•PFOS alternative, 6:2 Cl-PFESA was found in 100% of the cord sera from Wuhan.•The mixture of emerging Cl-PFESA and legacy PFASs was associated with birth size.•6:2 Cl-PFESA was the highest contributor to the effect on small for gestational age.•The effect on large for gestational age was mainly driven by legacy PFOS. As an alternative to legacy perfluorooctane sulfonate (PFOS), the wide usage of chlorinated polyfluoroalkyl ether sulfonic acid (Cl-PFESA) in China has generated considerable concerns. The study aimed to investigate the associations between cord serum emerging Cl-PFESA (6:2 Cl-PFESA and 8:2 Cl-PFESA) levels and suboptimal birth size, including low birth weight (LBW), macrosomia, small or large for gestational age (SGA or LGA) among 1048 newborns in Wuhan, China. 6:2 Cl-PFESA and 8:2 Cl-PFESA were 0.76 ng/mL and 0.03 ng/mL, respectively, higher than previously reported levels in newborns from other cities in China. We did not find significant associations between the Cl-PFESAs and suboptimal birth size when considering each Cl-PFESA as a single exposure. However, when integrating emerging Cl-PFESAs and legacy PFASs (PFOS and perfluorooctanoate acid (PFOA)) as a mixture using Bayesian kernel machine regression (BKMR) models, we found that the mixture of legacy PFASs and emerging Cl-PFESAs had inverse associations with SGA and LGA. Two legacy PFASs and two Cl-PFESAs had similar contributions to the association with SGA, whereas the majority of the association with LGA was driven by PFOS. The results demonstrated these legacy PFASs were still the predominant PFASs associated with suboptimal birth size while emerging Cl-PFESAs had a less but nonnegligible contribution to the association with SGA. Further studies in different regions with varied Cl-PFESA levels are needed to replicate the associations. [Display omitted]