Historical reconstruction of PFAS discharge into the Cooum River - before and after the great Chennai flood in 2015.

Despite widespread research on PFAS, less is known in developing countries like India. PFAS levels in sediment core samples from the Cooum River of Chennai City (India) in 2014 and 2016 were estimated to evaluate the effect of the major flood event in 2015. Among 22 target PFAS in this study, 11 and 12 of them were detected in the 2014 and 2016 samples, respectively. Total PFAS concentrations were 70-1402 pg/g dw (average: 503 pg/g dw) in 2014 and 188-3629 pg/g dw (average: 1103 pg/g dw) in 2016. PFBS, N-EtFOSA, and 6:2 FTUCA, which were not detected in any layers in 2014, exhibited a dramatic increase in DFs in 2016, showing 50%, 50%, and 88%, respectively. Hierarchical cluster analysis revealed that the subsurface to bottom sediment layers for both years were similar in PFAS pollution, suggesting originating from the same sources. In contrast, the PFAS pollution in the surface layers in 2014 (0-18 cm) was statistically different from that in 2016 (0-23 cm), likely due to significant disturbance of the sediment profile caused by a major flood event in 2015. Correlation matrix analysis indicates the industrial uses of C8-based PFAS and shorter-chain alternatives near the studied area can be the major source of PFAS in the sediment near the studied area. The present study evidenced the ongoing production and use of PFAS in India, warranting and recommending further environmental monitoring of PFAS. To our knowledge, this is the first report about the effect of a major flood event in India on historical reconstruction of PFAS dynamics in Cooum river..