Exploring indirect photolysis of 6:2 fluorotelomer sulfonate in landfill leachate under simulated sunlight: effect of humic acid and nitrate

Landfill leachate is exposed to sunlight through on- and off-site leachate treatment and disposal to surface water bodies. Very little is known about the potential phototransformation of fluorotelomer compounds in landfill leachates, which can undergo environmental oxidation and produce perfluorocarboxylic acids (PFCAs). This study investigated phototransformation of spiked 6:2 fluorotelomer sulfonate (FTS) (similar to 100 mu g/L) in leachate under simulated sunlight, using a metal halide lamp (wavelength, 390 to 750 nm). To understand the effects of nitrate and humic acid (HA), phosphate buffer (pH 7.1) containing nitrate and HA were spiked with 6:2 FTS and irradiated under simulated sunlight for 72 h. Following irradiation, 6:2 FTS and known transformation products (i.e., PFCAs) were quantified in the samples using LC-MS/MS. The results showed that 6:2 FTS was undergoing indirect photolysis in leachate (half-life of similar to 15 days), suggesting that indirect photolysis of 6:2 FTS is likely a relevant transformation pathway in sunlit aquatic environments. However, the spiked 6:2 FTS did not show any observable decrease in the presence of nitrate and HA over 72 h. Perfluorohexanoic acid (PFHxA) increased in irradiated leachate background samples (without 6:2 FTS spike) suggesting that phototransformation in sunlit leachate could lead to the formation of persistent PFCAs at environmental concentrations of the precursors. Future studies using probe compounds are recommended to better understand the roles of reactive species in phototransformation of 6:2 FTS.

Automated summary

This study found that 6:2 FTS undergoes indirect photolysis in landfill leachate, with a half-life of approximately 15 days, indicating that this is a relevant transformation pathway in sunlit aquatic environments. However, the presence of nitrate and humic acid did not lead to a significant decrease in 6:2 FTS over 72 hours. Additionally, the formation of perfluorohexanoic acid (PFHxA) in irradiated leachate samples suggests that phototransformation in sunlit leachate could result in the formation of persistent PFCAs at environmental concentrations.