Microplastic polymer accumulation, distribution, and toxicity in sediment of a freshwater tidal marsh, USA.

Microplastics (MPs) persistence in the environment leads to exposure to both wildlife and humans, which is a concern globally. However, understanding MP sources, transport pathways, and environmental risks from exposure remains limited in many environments. Identifying polymer types provides crucial information to address this knowledge gap. This study examines MP distribution and polymer composition in sediment from the John Heinz National Wildlife Refuge at Tinicum, PA, USA, a freshwater tidal marsh. We identified 4590 MP particles and 29 polymer types using laser direct infrared spectroscopy across five sediment cores from four sampling sites. The most abundant polymers were polypropylene (PP), polyurethane (PU), and tire rubber. To evaluate toxicity, we focused on six common polymers produced internationally: polyethylene, PP, polyvinyl chloride, polyethylene terephthalate, PU, and polystyrene. MP concentrations, polymer diversity, and risks increased downstream based on the polymer hazard index and potential ecological risk index, indicating environmental danger. We observed higher MP concentrations and risks in recent depositional sediments. Interestingly, MP concentrations in sediment reported from estuaries located across five continents (18 countries) showed no significant differences, suggesting shared sources of contamination in global estuarine sediments. The global MP burial flux was estimated at approximately 0.2 Mt. yr^-1. Our findings highlight that MPs primarily originate from polymers commonly used to produce single-use plastic products, emphasizing the need for stricter waste management and reduction efforts aimed at disposable plastics.