By applying the HYDRUS computer code to model the leaching of historical PFOS contamination and the infiltration of water contaminated with PFOA. The study considered various soil profiles with different SOC distributions, including no SOC, a realistic SOC distribution decreasing with depth, and a uniform SOC equal to the content measured in topsoil. Additionally, three root distributions (bare soil, grassland, and forest) and three soil textures (sand, sandy loam, and loam) were examined. 

The study found that the way organic carbon is distributed in the soil affects how fast PFOS moves. When organic carbon is distributed realistically PFOS moves twice as slow compared to when there is no SOC and even three times as slow compared to uniformly high SOC content in. Furthermore, the root distribution in soil plays a significant role in PFAS migration. Including the root zone in the simulations showed that it slows down the movement of PFAS primarily due to increased evapotranspiration and reduced downward water flux. Another effect of water uptake by plant roots is an increase in PFAS concentrations in soil water, known as evapoconcentration. This evapoconcentration and the slowdown of PFAS movement due to root water uptake are more pronounced in fine-textured soils than in sand. 

Want to learn more about how these findings can improve our understanding of PFAS movement through soil? Read the full article “Numerical modelling of PFAS movement through the vadose zone: Influence of plant water uptake and soil organic carbon distribution” by Biesek et al. for an in-depth analysis.