Characterizing the temporal trends in the concentration and composition of microplastics over the 20th century to present in the Chesapeake Bay region

Plastic production first began in the early 20th century, with production rapidly growing from the mid-20 century to present day. Intertidal ecosystems, such as wetlands and estuaries, serve as significant sinks for microplastics (particles < 5 mm) due to daily tidal inundation, natural sediment accumulation processes, and inputs from atmospheric, marine and freshwater sources. Despite documented microplastics in coastal waters and sediments, quantitative studies on how their concentration and composition has changed over time are scarce. Here, we analyzed sediment cores from intertidal wetlands on both the bayside and seaside of the Chesapeake Bay to quantify microplastic concentrations and characterize polymers. We collected two 50-cm sediment cores from a bayside wetland in the Saxis Wildlife Management Area and a seaside wetland on Wallops Island National Wildlife Refuge. Microplastics were isolated, enumerated, and characterized in 1-cm intervals. Polymer characterization was conducted using a µRaman mass spectrometer. 210Pb and 137Cs analyses provided a chronology of the sediment sequences, showing that ~40 cm core depth corresponds to 1900 and ~15 cm corresponds to 1963. Data from bayside marsh revealed an increase in microplastics concentrations from the bottom (~0.47 particles/g and 5.7 fibers/g) to the top (~2.3 particles/g and 10.8 fibers/g) of the core. Dominant polymers shifted from polystyrene and nylon at the bottom to polyethylene terephthalate at the top. At the seaside marsh, preliminary data shows an overall lower concentration of microplastics (<1 particle/g) with no discernable pattern throughout the core. Dominant polymers shifted from polyethylene terephthalate, polyethylene, and polyamide at the bottom to polystyrene at the top. At both sites, microplastics were present in sediments from the early 20th century, however, at the bayside location, early microplastics are consistent with polymers in use during that period, while at the seaside location, the microplastic concentration and composition suggest possible sediment mixing due to bioturbation. Future work will aim to explore the potential relationship between microplastics and geochemical cycling in both the bayside and seaside marshes, as well as work to constrain the amount of microplastics entering both locations via atmospheric deposition.