Trait-Linked Bioaccumulation of Microplastics in Lanistes carinatus: Selective Ingestion and Ecological Risk Assessment in the Nile River, Egypt

Freshwater habitats are increasingly recognized as major sinks and sources of microplastic (MP) pollution, yet data on their bioavailability and transfer through food webs remain scarce. This study provides the first comprehensive assessment of MPs in sediments and the freshwater gastropod Lanistes carinatus from two Nile River sites in Sohag Governorate, Egypt, influenced by residential and industrial activities. MPs were extracted from sediments and gastropod tissues using density separation and digestion, identified via stereomicroscopy and Fourier-transform infrared spectroscopy, and characterized by type, size, color, and polymer composition. Mean MP concentrations in sediments were 445 ± 111 items/kg, with no significant difference between sites. MPs occurred in 83% of gastropods, with higher abundance at the industrial site, and were positively correlated with body size. Fibers were the dominant type, with polyethylene terephthalate, polyethylene, and polypropylene as the most common polymers. L. carinatus exhibited selective ingestion of specific shapes, colors, and size ranges, as indicated by the Target Group Index. Ecological risk assessment showed moderate contamination, with higher risk at the residential site. These findings identify L. carinatus as a promising bioindicator species and provide essential baseline data to inform monitoring and mitigation strategies for MP pollution in the Nile River’s freshwater ecosystems.