Transformation, leaching and plant uptake simulations of 6:2 and 8:2 polyfluoroalkyl phosphate diesters (diPAPs) and related transformation products under near-natural conditions

In response to the growing concern over PFAS contamination, employing models to simulate PFAS behavior in the environment becomes necessary. This facilitates evaluating risks tied to leaching into groundwater, adsorption in soil, plant uptake, entry into the food chain, and the conversion of precursors into persistent PFAS. We utilized the MACRO model to simulate the behavior of the precursors 6:2 diPAP and 8:2 diPAP using data from a 2-year lysimeter experiment, key compound parameters were optimized via the caRamel evolutionary algorithm. We assumed that the transformation of both diPAP precursors into stable PFAAs is influenced by temperature and soil moisture, similar to pesticide degradation by microorganisms. Results reveal that the model accurately represents transformation, leaching, soil retention, and plant uptake of diPAP and transformation products. A comparison with a lab-based soil column study supports the slower natural degradation of precursors, affirming our modeling approach. Temperature and soil moisture could indicate that a worst-case scenario for transformation product leaching into groundwater could occur during a mild summer with moderate evapotranspiration and heavy rainfall. Plant uptake involves multiple elements: PFAS availability in the root zone depends on prior degradation or presence. Increased moisture in the root zone favors PFAS uptake combined with temperatures high enough for prior biotransformation. The calculation of temperature and moisture-based conversion rates was adopted directly from MACRO. It is recommended to further investigate these effects to validate and possibly modify them.