Microplastics, defined as plastic particles less than 5mm in size, are an emerging environmental concern due to their pervasive and persistent presence in aquatic environments. As the scope of the problem evolves, global research efforts seek to obtain baseline information on microplastics, their presence, and factors that may influence abundance and persistence. To support these efforts, standardized protocols for sampling, isolating, and quantifying microplastics in environmental samples have been published. However, methodologies for marine water samples have largely focused on open ocean environments, limiting their utility with higher sediment loads or turbidity. With an estimated 80% of marine plastics originating from land-based sources, estuaries are critical ecosystems of concern due to their position at the intersection of terrestrial and aquatic environments. The lack of established microplastic analytical protocols for this habitat underscores the need for innovation. A pilot study was conducted in the Hampton-Seabrook Estuary (HSE), NH during the summer of 2021 to assess the utility of published protocols, and to explore innovations to adapt these approaches (if needed) to better suit application in estuarine systems. A series of surface water samples were collected over three months during neap and spring conditions on the outgoing tide at twelve locations across the estuary. Water temperature, salinity, precipitation, and sea-state were recorded at each sampling interval. High organic matter and suspended sediment in samples across all locations demonstrated that significant modifications to both the field collection (sampling location, duration, and collection method) and laboratory/analytical (sub-sampling, digestion, and density separation) methodologies were required to obtain quantifiable microplastic counts and characterizations in estuarine waters. Through this study, we have developed a reliable methodology to isolate and quantify microplastics from waters with moderate to high organic matter and sediment loads that may be applicable to estuarine systems in New Hampshire and across the region.
