Short-, medium-, and long-chain chlorinated paraffins in human serum from South China: Evidence of LCCP exposure and...

Chlorinated paraffins (CPs) are widely used industrial chemicals of emerging concern, but human internal exposure to long-chain chlorinated paraffins (LCCPs) remains poorly characterized because of analytical challenges. In this study, we quantified different CP congener groups in serum samples from 571 adults residing in Shenzhen, a major manufacturing hub in South China, collected during 2021-2023. Ninety-three CP congener, including 24 short-chain chlorinated paraffins (SCCPs), 34 medium-chain chlorinated paraffins (MCCPs) and 35 LCCPs, were detected in nearly all samples. The ∑CPs concentrations in serum ranged from 29.1 to 4810 ng/mL (weight wet [ww]) with a median concentration of 189 ng/mL ww. SCCPs were the dominant CPs congener group with a median concentration of 148 ng/mL ww, followed by MCCPs (34.0 ng/mL ww) and LCCPs (0.668 ng/mL ww). The widespread detection of LCCPs indicates that this rarely monitored CP class contributes to human internal exposure. Demographic factors explained approximately 27% of the variability in serum SCCP concentrations, although most interindividual variability remained unexplained. Integration with published Chinese biomonitoring data suggested that serum SCCP concentrations declined after 2021, temporally consistent with regulatory restrictions, whereas MCCPs showed an increased contribution, consistent with their use as SCCP substitutes. These findings highlight the need to include LCCPs in human biomonitoring frameworks and to improve analytical standardization for CP exposure assessment.