Superabsorbent polymers in soil: The new microplastics?

Abstract The extensive use of synthetic polymers in our everyday lives has resulted in significant plastic pollution. Superabsorbent polymers (SAPs) are yet another class of anthropogenic materials with uncertain environmental implications. SAPs, like polyacrylates (PAA) or polyacrylamides (PAM), find applications in personal care products, construction, wastewater treatment, agriculture and soil remediation. However, when SAPs enter the soil, weathering may change their intended properties, potentially forming plastic-like solid residues over time. This review aims to evaluate the current scientific understanding of the application and environmental fate of SAPs in soil, focusing on the processes driving their potential transformation into solid residues. We explore analytical techniques for the qualitative and quantitative characterization of SAPs and solid SAP residues. Our research provides first insights into the potential mechanisms and conditions governing SAP aging and transformation, advancing our understanding of the fate of SAPs in soil and their impact on soil properties and functioning. There are specific knowledge gaps regarding the influence of climate change on the application and transformation of SAPs in soil. To facilitate future research, we suggest scrutinizing relevant processes of SAP transformation in the field, critically (re)evaluating SAP application to the soil and establishing robust monitoring methods.