Microplastic pollution has become a growing concern in urban coastal ecosystems, where seawater, sediment, and benthic organisms may jointly reflect environmental contamination and biological exposure. This study investigated microplastics in seawater, sediment, and the clam Ruditapes philippinarum along the Qingdao coast, China. All samples contained microplastics, with mean abundances of 635.67 ± 247.94 items m-3 in seawater, 262.74 ± 147.80 items kg-1 DW in sediment, and 20.28 ± 15.72 items ind.-1 in clams. Microplastic abundances showed clear spatial and seasonal variation, with relatively high levels in highly urbanized and recreational areas during summer and autumn. Fibres were the dominant shape across seawater, sediment, and clam samples, while polyethylene (PE), polypropylene (PP), and polyamide (PA) were the major polymers. Multivariate analyses indicated partial compositional overlap among seawater, sediment, and clam samples, supporting possible compartmental connectivity. Exposure experiments showed that R. philippinarum could ingest, retain, and depurate ingested microplastics, with rapid early accumulation and slower clearance under controlled high-exposure concentrations. Overall, this study provides regional evidence of microplastic contamination and bioaccumulation potential in an intensively used coastal ecosystem, highlights shellfish as important biological receptors of coastal microplastics, and supports cautious interpretation of ecological risks and transfer-related processes.