Determining the Temperature-Dependent Air–Water Partitioning of Ether- and Thioether-Alcohol Perfluoroalkyl and Polyfluoroalkyl Substances Using a Modified Static Headspace Method

TL;DR

The study measures how a new type of PFAS interacts with water and air at different temperatures using a modified lab method.

Contribution

A modified static headspace method was used to determine temperature-dependent air–water partitioning of ether- and thioether-alcohol PFAS.

Findings

Log K_aw values ranged from −2.6 to −1.0 at 25 °C for the tested PFAS.

Increasing perfluorinated carbon chain length increased K_aw by about 1.5 log units.

COSMOtherm provided the most accurate in silico predictions of air–water partitioning.

Abstract

The temperature-dependent air–water partitioning
behavior
of a novel class of perfluoroalkyl and polyfluoroalkyl substances
(PFAS) was assessed both experimentally and via in silico prediction. These PFAS contain ether or thioether linkages and are
transformation products of an alternative PFAS surfactant. A modified
version of the static headspace method with variable headspace/solution
ratios was used to determine the dimensionless air/water partition
coefficients (K
aw) over a wide range of
temperatures (25–80 °C). The samples were analyzed through
the aqueous phase instead of the headspace because of their relatively
low volatility. The obtained log K
aw values
of the tested chemicals ranged from −2.6 to −1.0 at
25 °C. No differences in K
aw were
observed between ether and thioether congeners with the same perfluorinated
carbon chain length. Increasing the length of the perfluorinated carbon
chain from CF3- to C3F7- increased K
aw by about 1.5 log units. The obtained K
aw of a well-studied fluorotelomer alcohol,
4:2 FTOH, matched those of previous studies, indicating the appropriateness
of the method used. The temperature dependence of K
aw, as quantified by the molar internal energy change
of air–water partitioning, ΔU, ranged
from 20 to 37 kJ/mol and was not substantially influenced by the structure
of the chemicals. Among five in silico tools to predict
air–water partitioning, the quantum chemistry-based COSMOtherm ensured the most reliable and accurate prediction
as compared to the experimental results.

Figures