Simulation of diPAP Transformation and Related Metabolite Leaching Under Near-Natural Conditions

Per- and polyfluoroalkyl substances (PFAS) are organic contaminants which are ubiquitous in the environment and anthropogenically manufactured. The presence of PFAS in the environment is connected to their production, use and disposal, i.e. the whole life cycle. Contact with organisms can have adverse effects such as toxicity, bioaccumulation and carcinogenicity depending on the specific compound. There are several thousands of different PFAS with different structures and properties, which differ in their environmental behaviour as well. One example is biotransformation, which is not observed for all PFAS, such as the persistent group of perfluoroalkyl acids (PFAAs). Other PFAS, such as polyfluoroalkyl phosphate diesters (diPAP), act as precursors which are transformed into the stable PFAAs. When released to the environment, it is important to have information about the relevant processes such as adsorption, transformation and formation of non-extractable residues (NER).

In this study, leaching simulations were performed using a multi-objective parameter optimization algorithm (caRamel) in R connected to the MACRO 5.2 model. The simulation is based on a lysimeter study with two transformable precursors (6:2 diPAP and 8:2 diPAP) under near-natural conditions and a duration of two years. Objective functions of masses in the percolation water, in the soil and in the grass, planted on the lysimeter, were optimized simultaneously for diPAPs and related persistent PFAA metabolites. The model setup was based on past leaching simulations of soil columns with similar soils, the same substances and the same study duration. A comparison of lysimeter and soil column simulations indicates temperature-affected transformation kinetics, which could be related to the microbial activity. In further studies, the influence of environmental parameters on the transformation of diPAPs should be focussed to evaluate the results of this study.