Perfluoroalkyl substances (PFASs) have attracted attentions all around the world. However, little is known about their distribution among water, suspended particulate matter (SPM), and sediment phases in rivers, especially for the short-chain PFASs. In this work, the Yellow River, the largest turbid river in the world, was selected as a case to study eleven kinds of PFASs in the three phases of rivers. These PFASs included C4-C12 perfluorinated carboxylates (PFCAs), perfluorobutyl sulfonate (PFBS), and perfluorooctansulfonate (PFOS), among which C4-C7 PFCAs and PFBS belong to short-chain PFASs, while C8-C12 PFCAs and PFOS belong to long-chain PFASs. The results showed that the total PFAS concentration ranged from 44.7ngL(-1) to 1.52μgL(-1) in the water, from 8.19 to 17.4ngg(-1) in the sediment, and from 3.44 to 14.7ngg(-1) in the SPM. Short-chain PFASs predominated in the water and could reach up to 88.8% of the total PFAS concentration in water, while long-chain PFASs prevailed in the sediment and SPM. The PFAS concentration in SPM showed a significant negative correlation with SPM concentration in river water (p<0.01). The distribution coefficients (Kd) of PFASs between sediment/SPM and water increased with their chain length and there was a positive correlation between logKd and logKow (octanol-water partition coefficients). The total annual flux of all the eleven PFASs was estimated at 3.88tons for the Yellow River into the Bohai Sea, among which the PFOA flux was the highest (0.90tons). The widely occurrence and high concentrations of short-chain PFASs in the Yellow River indicates the shift of manufacturing focus of perfluoroalkyl chemicals from traditional long-chain ones to short-chain ones. Further studies should be conducted to evaluate the eco-environmental risks of these short-chain PFASs in water environments.

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Keywords:Bioavailability Polycyclic aromatic hydrocarbons (PAHs) Suspended sediment (SPS) Dams Water conservation project Water quality s u m m a r yThe water-sediment regulation of the Xiaolangdi Reservoir is conducted to control the relationship between riverine runoff and sediment transport of the Yellow River; however, there is no research about the effect of water-sediment regulation on the bioavailability and fluxes of hydrophobic organic compounds (HOCs). In this study, water and suspended sediment (SPS) samples were collected downstream of the Xiaolangdi Reservoir before, during, and after the water-sediment regulation in 2013. The 16 priority polycyclic aromatic hydrocarbon (PAH) concentrations of freely dissolved, total dissolved, and SPS-associated were determined. During water regulation, water discharged from the reservoir at a high flow rate led to the resuspension of downstream sediment. During sediment regulation, the sediment ejected from the reservoir resulted in higher SPS concentrations than that during water regulation. Both the freely and total dissolved PAH concentrations in river water during sediment regulation were the highest, followed by the concentrations during water regulation and before regulation. The freely dissolved PAH concentrations in river water during the water-sediment regulation were 2-11 times higher than those before water-sediment regulation. This was due to the fact that the resuspended sediment during water-sediment regulation could release PAHs into water phase, and more contaminants were released from the SPS during sediment regulation than during water regulation. The fluxes of sediment and the 16 priority PAHs (R 16 PAHs) during water-sediment regulation contributed to 32.4% and 35.7% of their annual fluxes, respectively, which were higher than the contribution (22.6%) of water discharge. This study suggested that the water-sediment regulation might reduce the long-term retention of sediment and PAHs in the reservoir. However, the environmental risk of PAHs as well as other contaminants downstream of the reservoir and in the estuary might increase during that period. Therefore, the effect of water-sediment regulation on the bioavailability and environmental risk of HOCs should be considered in the operation and management of the Xiaolangdi Reservoir in the future.

In natural waters, the equilibrium state of hydrophobic organic compounds among bottom sediment (BS), suspended sediment (SPS), and water is fundamental to infer their transfer flux and aqueous bioavailability. However, this type of information remains scarce and fragmented. This study systematically evaluated the equilibrium state of polycyclic aromatic hydrocarbons (PAHs) in the Yangtze River. Total and freely dissolved concentrations of the 16 priority PAHs in pore water and overlying water (including surface and near-bottom) of the Yangtze middle reaches were investigated, as were the concentrations of attached PAHs in SPS and BS. Results showed that concentrations of total/freely dissolved PAHs, dissolved organic carbon (DOC), and SPS in surface water were not statistically different from those in near-bottom water, and the DOC-water distribution coefficients of PAHs in pore water were not statistically different from overlying water. However, significant disequilibrium was found at the sediment-water interface; concentrations of total/freely dissolved PAHs in pore water were 1 to 2 orders of magnitude higher than those in overlying water. This study offers a complete analysis of the potential disequilibrium of PAHs in BS-water-SPS system of large rivers and suggests that distribution of hydrophobic organic compounds between BS and overlying water is essential in controlling their equilibrium state in the BS-water-SPS system of natural waters.

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