Plastic problem solved? Environmental implications of synthetic hydrophilic polymers across ecosystem boundaries

Synthetic hydrophilic polymers are an emerging yet overlooked class of anthropogenic substances. Unlike particulate plastics, synthetic hydrophilic polymers can interact with water, which complicates studying their fate and effects in the environment. This review discusses the sources, fate, and effects of these polymers across ecosystem boundaries. We identified households, agriculture, and mining as major sources. Despite wastewater treatment, synthetic hydrophilic polymers enter natural waterbodies. Agrochemical and sewage sludge applications release them to soil. Sorption and coagulation processes, influenced by polarity and molecular weight, likely define their fate through aquatic and terrestrial systems. Slow biodegradation may favor their accumulation. To advance our understanding of their fate, analytical techniques need improvement. Ecotoxicity studies found acute effects but long-term and field studies on mixtures and interactions with other pollutants are lacking. All in all, the prevailing literature emphasizes benefits of synthetic hydrophilic polymers while neglecting potential negative consequences; this calls for precaution. • Synthetic hydrophilic polymers interact with water via polar functional groups. • Polarity and high molecular weight favor sorption and accumulation in soil and sediment. • Their fate and effects are understudied and require further research. • Analytical methods are still under development. • Current research focuses on beneficial effects, disregarding negative consequences.