Sorption of novel side-chain fluorinated polymers to sediment - the impact of pH

Abstract: Fluorinated compounds are produced on a large scale and their releases are contaminating the environment. Among these are side-chain fluorinated polymers found in technical mixtures of Scotchgard™, which are used as surfactants in fabric coating. Today, the knowledge about these Scotchgard products (Pre-2002 and Post-2002, formulations used in Scotchgard products before and after 2002) and side-chain fluorinated polymers, in general, are limited, and more studies need to be performed to increase the understanding of the behaviour of the compounds and their fate in the environment. This study performed sorption tests in liquid to sediment ratio of 100:1, with sediment from Lake Hjälmaren, Sweden, and water spiked with Pre-2002 and Post-2002. The waters were Milli-Q water, containing CaCl2, adjusted to different pHs (range between 4.4 and 11.2) with NaOH, and on water from Lake Hjälmaren. The solutions were shaken for 0.5, 1, 2, 4, 8, 12, 24 and 168 h. Liquid-liquid extraction with tert-butyl methyl ether (MTBE) was used to extract the remaining target compounds in the aqueous phase and analysed using ultra-performance liquid chromatography (UPLC). For the different pH solutions, the result showed both Pre-2002 and Post-2002 readily sorbed to the sediment with close to 0 % remaining in the aqueous phase after 4 hours. For the first time point, 0.5 h, more than 7 % remained in the aqueous phase with a pH of 11.2, while under 1 % remained with a pH of 4.4 for both Pre-2002 and Post-2002, showing that the sorption capacity was dependent on pH. In water from Lake Hjälmaren, neither of the target analytes were under the limit of detection (LOD) until the time point of 168 h. In contrast to the result of the pH solutions, Post-2002 were shown to be more prone to sorb to the sediment in the water from Lake Hjälmaren than Pre-2002. This might be due to particles, ions and competing per- and polyfluoroalkyl substances (PFAS) present in the water. However, the pH of Lake Hjälmaren was around 5; when comparing the data, the amount sorbed, somewhat aligned with what would be expected based on the sorption test with different pHs, indicating that the sorption capacity might be more dependent on pH than water chemistry.