Sedimentary records of microplastic pollution from coastal Louisiana and their environmental implications

Microplastics are a growing concern in the natural environment as plastic production and improper disposal have greatly increased since the first widespread use of plastic in 1950. Previous studies have investigated the amount of plastic found within organisms, the water column, and surface sediments, but few studies are available that investigate microplastics within the sedimentary column. This study seeks to determine the abundance of microplastics and their rate of deposition in two coastal Louisiana estuaries (Bay Champagne and Little Lake) that are influenced by the petroleum, shipping, and commercial fishing industries. Samples from two short sediment cores were treated for microplastic analysis following NOAA removal techniques. Microplastics were identified visually and confirmed using FTIR spectroscopy. Three morphotypes of microplastic were found throughout the sediment column in the cores (fibers, fragments, and sheets), with a high concentration near the surface and a major decrease downcore. Of the two sites, Little Lake had a much higher total abundance of microplastics than Bay Champagne, likely due to its proximity to New Orleans and the active commercial fishery. Interestingly, both sites had trace amounts of microplastic in basal samples, in sediment much older than 1950. Their presence is likely attributable to bioturbation by burrowing organisms, although sediment reworking by high energy disturbance events (i.e., hurricanes) or human activity is also possible. Microplastic presence within these highly productive estuarine waters is a major ecological issue and understanding the possible sources and sinks of microplastics is critical in addressing this growing problem of environmental pollution.