Marshes in riverine estuaries provide an enhanced deposition zone for sediments, nutrients, and pollutants, such as pesticides. The watershed of the tidal Potomac River has many unique hydrologic and geologic characteristics that make it ideal for a spatial and temporal study on pesticides associated with aquatic geosolids. The tidal river has undergone an extensive transformation in land use over the past nine decades, primarily from the conversion of forested and agricultural land use to urban and suburban land use. Marshes play an important role as pesticide sinks through deposition and burial processes that occur in their sediments. As a result, marshes act as filters for particle-associated contaminants. Many pesticides partition between the organic matter (OM) component of total suspended solids (TSS) based upon their physicochemical properties. In general, hydrophobic pesticides have very large partition coefficients favoring enrichment in the nonpolar regions of TSS. Sediment cores (~1 m depths) were obtained from selected marshes along the tidal Potomac River and sectioned at approximately 2 cm intervals for geologic chronology and chemical analysis. The historical record of pesticides in sediment cores were determined using GC-MS, to identify and quantify the concentrations of the pesticides (including neonicotinoids, organochlorines, organophosphates, pyrazoles, and pyrethroids) present. Depth profiles for the cores were also developed based on total organic carbon (TOC), total nitrogen (TN), and particle size. The concentration/depth profiles fall into 3 main types: profiles that increase in concentration with age and depth, profiles that decrease concentration with age and depth, and profiles that remain consistent throughout the age and depth. The profiles were then used to compare the spatial and temporal distributions of these chemicals to determine the effect of watershed demographics, management practices, use statistics, restrictions, and changing land use (urbanization/reduction of farmland) patterns on the concentrations and sediment chronology of the pesticides.

Legacy pesticides in riverine marsh sediment cores from the tidal freshwater, oligohaline, and mesohaline zones of the Potomac River

2019 Spring National Meeting

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