Trifluoroacetate is formed when fluorinated gases, such as refrigerants and fluorinated pesticides, are partially degraded in the environment. Water flowing through air and soil picks up trifluoroacetate, transporting the persistent and mobile compound to groundwater aquifers. However, drinking groundwater sources have not been widely tested for trifluoroacetate because there is no regulatory limit for it beyond the European Environment Agency (EEA) limit for total PFAS in drinking water of 0.5 parts per billion (ppb). Therefore, Christian Albers and Jürgen Sültenfuss wanted to thoroughly assess groundwater in Denmark for this contaminant, looking for potential changes over the past 60 years.

The researchers collected samples from 113 groundwater monitoring wells across Denmark. They analyzed the samples for trifluoroacetate and, using an established tritium and helium isotope method, calculated how long ago the water entered the underground aquifers. Overall, their data showed a trend of increasing trifluoroacetate concentrations since the 1960s. In particular, groundwater from:

• Before 1960 the level was unmeasurable.
• In the years 1960–1980 the average content was 0.06 ppb.
• In the years 1980–2000 the average content was 0.24 ppb.
• Between 2000 and 2020, the average PFAS content in drinking water was 0.6 ppb, which is above the EEA limit for PFAS in drinking water.

The researchers attribute the differences in concentrations over time to changing atmospheric concentrations, plant uptake, and local pesticide use. For example, pesticides that may be precursors to trifluoroacetate have been used in agricultural areas in Denmark since the late 1960s. Based on these observations, the researchers say trifluoroacetate concentrations can be used to categorize when groundwater entered aquifers, such as after 1985 or before 2000, rather than using more sophisticated and tedious dating methods that require isotopes. In addition, Albers says that some particularly high concentrations of trifluoroacetate in groundwater that are less than 10 years old could suggest that local sources have recently become more important, such as the use of fluorinated pesticides.

The authors confirm funding from the Danish Environmental Protection Agency and the Danish Groundwater Monitoring Programme.