Anthropogenic particles and microplastics (APs; < 5 mm; e.g., cotton and polyester fibers) are pervasive contaminants in aquatic habitats and biota worldwide. Terrestrial-aquatic interactions can move anthropogenic litter into aquatic habitats where litter items may fragment into APs and deposit in sediments or enter food webs. Estuaries are among the most biologically valuable yet widely diminished ecosystems in the world, making these systems an ideal target for AP mitigation efforts. Estuary sediments provide critical habitat and support numerous estuary ecosystem services, including water filtration, nursery and refugia for aquatic biota, and biogeochemical cycling. Shellfish are an important estuary resident that can serve as ecosystem engineers in estuaries and are known to be particularly susceptible to particulate pollution due to their filter-feeding behavior. We sought to understand the importance of watershed anthropogenic development (e.g., percent urban; dominant land-use) and estuary protection status (e.g., state marine conservation area) in connection with the abundance and characteristics of APs in estuarine mussels and sediments. Estuaries were sampled for sediments in autumn 2023 (n = 15 sites) and for shellfish in winter, spring, and summer 2024 (n = 7 sites/season). Preliminary results from the summer mussel samples indicated that AP contamination was present in mussels across all sites, with fibers contributing approximately 96-99% of all AP particles. There were significantly greater AP concentrations in mussels from unprotected sites compared to marine protected area sites (t = -3.02, df = 18, P = 0.004). Microplastic color patterns were distinct across both site (χ2= 121.09, df = 66, P < 0.001) and watershed land-use (χ2= 37.53, df = 22, P = 0.021). These findings are expected to inform management and policy decisions for crucial coastal environments that will mitigate or prevent harmful environmental impacts from AP pollution.