Riverine inputs and source tracing of perfluoroalkyl substances (PFASs) in Taihu Lake, China

- PFHxS was the predominant PFAS compound in Taihu Lake and flow-in river waters.
- The ratio of 3 + 5m-/1m-PFOS was used as an index to distinguish the degradation of precursors.
- Degradation of precursors made an important contribution to PFOS in Taihu Lake.
- PFHxS mainly originated from the products containing it as active ingredient.
- The riverine flux of PFASs into the Lake was estimated to be 1255 kg/year.

The occurrence, riverine inputs and sources of perfluoroalkyl substances (PFASs) in Taihu Lake, one of the largest lakes in China, were investigated by measuring PFASs including the isomers of perfluorooctanesulfonate (PFOS), perfluorooctanoate (PFOA) and perfluorohexanesulfonate (PFHxS) in the Lake and its main flow-in rivers. It was found that PFHxS, instead of PFOS or PFOA, was predominant both in the Lake and rivers (45.9-351 ng/L), reflecting increasing demand of PFHxS in recent years. The riverine flux of PFASs into the Lake was estimated to be 1255 kg/year. The percentage of linear (n-) PFOS and the ratio of 3 + 5m-/1m-PFOS were combined to indicate indirect source due to biodegradation of PFOS-precursors. The percentage order of n-PFOS was: the Lake (48.7%) < the flow-in rivers (59.2%) < ECF product (70.3%). While the ratio of 3 + 5m-/1m-PFOS was in reverse order: the Lake (11.9) > the rivers (8.99) > ECF (electrochemical fluorination) product (6.76). These suggested that degradation of PFOS-precursors made distinct contribution to PFOS load in the waters, particularly in the Lake. The Lake and river waters had a consistent proportion of n-PFHxS (89.0%), which was slightly lower than the ECF product (96.0%), indicating it was mainly due to the release from production and application of PFHxS as an active ingredient.

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