Congener-specific C_(10)-C_(13) and C_(14)-C_(17) chlorinated paraffins in Chinese agricultural soils: Spatio-vertical distribution, homologue pattern and environmental behavior

Abstract

A comprehensive spatio-vertical survey of short-chain (SCCPs, C_(10-13)) and medium-chain (MCCPs, C_(14-17)) chlorinated paraffins (CPs) was performed in surface and core soils from Chinese nation-wide agricultural lands in 2016, and a total of 48 congener groups were measured. The shorter carbon chain C_(10-11) in SCCP and C_(14-15) in MCCP homologue groups, and the lower chlorinated congeners (Cl_(5-7)) for both CP groups were predominant. The ∑SCCP and ∑MCCP concentrations in surface soils ranged from 39 to 1609 ng/g and 127–1969 ng/g, dry weight (dw), respectively. The spatial distribution trend showed that SCCP congener groups with relatively low octanol-water partition coefficient (K_(OW)) and octanol-air partition coefficient (K_(OA)) are uniformly distributed across surface soils compared to MCCP congener groups. Significant relationships were observed between the spatial variation of SCCP concentrations and the driving factors responsible for dispersion and deposition. The distribution behavior of SCCPs and MCCPs in highland and plain surface soils showed an increasing trend of MCCP concentrations with elevation, indicating the “mountain cold-trapping effect”. Vertical distribution profile revealed similar homologue group composition patterns of SCCP and MCCP congener groups as those of surface soils. Furthermore, the penetration potential ratios (r) of chlorine and carbon atoms of CPs demonstrated that the lower chlorinated (Cl_(5-7)) and the shorter carbon chain (C_(10-13)) congener groups are more prone to vertical movement into deeper soil layers compared to the longer carbon chain (C_(14-17)) and highly chlorinated (Cl_(8-10)) congener groups.