PFAS in soils: decoding speciation to develop predictive modeling

Per- and polyfluoroalkyl substances (PFAS) are man-made chemicals of emerging concern due to their toxicity and ubiquitous presence in the environment. Soils serve as environmental reservoirs for PFAS, playing a significant role in pathways that lead to human exposure, e.g. through plant uptake and leaching to surface and groundwater. This project aims to unravel the mechanisms involved in PFAS partitioning (distribution) and speciation in the aqueous and solid phase, to ultimately model these interactions. Our experimental results will allow for the development of robust and risk-based regulatory measures for PFAS in the environment.

Background

Over 5000 types of PFAS have been produced over the past few decades, and their extensive use has resulted in widespread environmental PFAS contamination through wear and tear of PFAS-containing products. Due to their resistance to environmental degradation, PFAS persist in environmental media including surface and groundwater, as well as in soil and sediment. Considering their negative health impact, concerns have been mounting in the Netherlands, where PFAS have been detected at numerous locations, including publicly accessible areas such as airports and along the Dutch coast.

PFAS can enter soils through multiple sources and subsequently adsorb to reactive soil surfaces such as organic matter, iron/aluminum (hydr)oxides and clay minerals. Though few studies have looked at PFAS interaction with these soil mineral surfaces, a systematic and mechanistic understanding remains elusive.

Project description

This project aims to gain a mechanistic understanding of PFAS speciation in soil and sediment, i.e. their partitioning between different chemical forms in the aqueous and solid phase. Understanding PFAS speciation is crucial for predicting the mobility and bioavailability in the environment. We aim to study PFAS adsorption to different soil compartments (organic matter, iron/aluminum hydroxides and clay minerals) for a range of PFAS molecules, differing in functional group and carbon-fluorine chain length. In order to assess human PFAS exposure through plant uptake, a pot experiment will be conducted to relate the bioavailability of PFAS in soils to human health risks. The data obtained from the PFAS speciation experiments will ultimately be used for speciation and transport modelling, ultimately leading to improved risk-assessment of PFAS in soils and sediments.

Results

Preliminary findings indicate that PFAS adsorb to organic matter fractions and iron/aluminum (hydr)oxides. The results reveal distinct differences in the speciation of PFOS and PFOA, suggesting that variations in PFAS molecular structure significantly influence their binding behavior in soil and sediment. Moreover, soil properties play a crucial role in determining PFAS speciation. For PFOS, an additional reactive surface, such as clay minerals or humin, appears to be involved in its speciation.