Occurrence, Bioaccumulation, and Emission Fluxes of Short-Chain Chlorinated Paraffins (SCCPs) in the Xiaoqing River Ecosystem: Insights from a Sewage Treatment Plant Discharge

Short-chain chlorinated paraffins (SCCPs, C10–13Cl5–10) pose substantial ecological risks due to their persistence and toxicity. This study investigated the occurrence of SCCPs in a farmland ecosystem downstream of a sewage treatment plant (STP). The mean concentrations of SCCPs in soil, wheat, sediment, fish, and water samples were 340 ng/g dry weight (dw), 958 ng/g dw, 492 ng/g dw, 1736 ng/g dw, and 39.7 ng/L, respectively. Soil concentrations on the sewage-irrigated north coast (422 ng/g dw) were significantly higher (p < 0.05) than on the south coast (268 ng/g dw), directly implicating river water irrigation as a major contamination pathway. C10 and Cl6 were the primary congeners, and longer carbon chain and higher chlorinated congeners tend to be enriched in wheat and fish samples. Bioaccumulation factors (BAFs) for wheat–soil and fish–sediments systems were 2.3 and 3.5, respectively. The fish bioconcentration factor (BCF = 8745 L/kg wet-wt) far exceeded model predictions (1711–4328 L/kg wet-wt), indicating significant point-source pollution from the STP. Annual emission flux of SCCPs from STP into the river was 14.3 kg. Although direct wheat uptake via irrigation was limited, significant bioaccumulation occurred in organisms. These results underscore the impact of STP discharges and highlight the need for enhanced wastewater treatment technologies.