Occurrence and distribution of C₆-C₄₀ chlorinated paraffins in deep-sea sediments from the Indian Ocean basins

Chlorinated paraffins (CPs) are high-production-volume industrial chemicals, yet their occurrence and distribution in deep-ocean basins remain poorly understood. Here, this study investigated 771 homologues of CPs with various carbon chain lengths (i.e., C₆-C₄₀), including very short-chain (vSCCPs, C₆-C₉; semi-quantified), short-chain (SCCPs, C₁₀-C₁₃), medium-chain (MCCPs, C₁₄-C₁₇), long-chain (LCCPs, C₁₈-C₂₀), and very long-chain CPs (vLCCPs, C₂₁-C₄₀; semi-quantified) in surface sediment samples collected from 17 sites in the Indian Ocean basins using high-resolution mass spectrometry. CPs were detected in 65% of the samples, with total concentrations of 15-100 ng/g dry weight (dw) (mean: 40 ± 27 ng/g dw). MCCPs (51%) and SCCPs (43%) predominated the homologue profiles, while vSCCPs, LCCPs, and vLCCPs were also frequently semi-quantitatively detected, indicating the widespread dispersion of lesser-monitored CP classes into deep-sea sediments. A clear spatial fractionation was observed: Western sediments (Arabian Sea) were enriched in heavier CP groups (MCCPs, 64%; C₁₄-C₁₅ homologues), whereas eastern sediments showed higher proportions of lighter CP groups (SCCPs, 53%; C₁₀-C₁₁ homologues). The positive correlation between concentrations of CPs and total organic carbon suggests that organic matter and particle-associated transport play an important role in CP accumulation, whereas the lack of a depth trend indicates that overlying water depth alone is not a primary predictor of sedimentary CP burdens. This study provides first-hand baseline data on C₆-C₄₀ CPs in deep-sea sediments, revealing the previously unrecognized presence of vSCCPs and vLCCPs in remote basins, and highlighting the need to include homologue-specific transport and deep-sea sequestration in future CP monitoring and risk assessment frameworks.