Radula-mediated feeding drives selective ingestion of elongated microfibers by a freshwater snail

Microfibers (MFs) are a prevalent form of microplastics in aquatic environments and are frequently ingested by aquatic organisms. In nature, individual fibers do not always remain straight but can bend, coil, or become partially self-entangled, potentially altering their biological interactions. However, how such morphological variability influences MF ingestion by benthic gastropods remains poorly understood. Here, we exposed the freshwater snail Sinotaia quadrata to 50 items/L, within the range reported for freshwater systems, of polyethylene terephthalate and polyamide MFs, including elongated single fibers and coiled forms derived from the same individual fibers of corresponding lengths but exhibiting smaller external dimensions. Regardless of food availability and across all tested size classes, snails ingested significantly more elongated single fibers than coiled MFs. Ingestion of both forms peaked within 6 h; however, elongated fibers exhibited longer retention times in the digestive tract, whereas coiled forms were largely egested within 24 h. Microscopic observations indicated that radula-mediated feeding interactions more effectively captured elongated, flexible fibers, whereas coiled MFs were more likely to undergo transient contact without sustained retention and be dislodged during repeated radula-mediated movements. Scanning electron microscopy and micro-Raman analyses further revealed localized surface irregularities on ingested fibers. Together, these results provide experimental evidence that feeding interactions may enhance the bioavailability of elongated MFs and may facilitate their physical alteration. Our findings underscore the importance of fiber morphology and feeding mode in shaping MF exposure pathways and fate in benthic freshwater ecosystems.