Concentration-dependent response of soil parameters and functions to trifluoroacetic acid

Abstract

Despite growing environmental concerns about perfluoroalkyl and polyfluoroalkyl substances (PFAS) worldwide, the ultra-short-chain PFAS, for example, trifluoroacetic acid (TFA), have been largely neglected in the context of soil pollution. Given the persistence and increasing occurrence of TFA in the soil environment, accumulated TFA could impact soil properties and functions. Therefore, we investigated the effects of a wide range of concentrations of TFA (0.001–100 μg g−1) on chemical, physical and biological indicators of soil health, using a six-week microcosm experiment. Our results showed that TFA treatments decreased soil pH, sulphate content, soil respiration, litter decomposition and bacterial abundance, and increased phosphate content (p < 0.05). These effects were observed for TFA concentrations ≥1 μg g−1. As expected, because of its strong acidity, TFA decreased soil pH, and this change likely contributed to effects on other soil parameters and functions, for example, reducing bacterial abundance and soluble nutrients. However, importantly, TFA clearly also affected soil parameters at concentrations at which soil pH was not changed. Soil aggregation, fungal abundance, and enzyme activities were not affected by TFA in this study. Considering the current reported environmental levels of TFA of <2.4 μg g−1, only litter decomposition would be affected under current field conditions. Our data also show that future accumulation of higher concentrations, or hotspots of TFA, will likely negatively affect soils with similar properties as our test soil. Thus, we demonstrated that microbial processes can be impacted by the accumulation of the ‘forever chemical’ TFA in the tested sandy, low organic matter soil. Highlights: Trifluoroacetic acid (TFA) decreased soil pH, respiration, litter decomposition and bacterial abundance. TFA affected soil soluble nutrients. TFA affected litter decomposition at 1 μg g−1 with no change in soil pH. Effects of TFA on soil enzyme activity and aggregation and fungal abundance were negligible.