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 upper reaches of the tidal river have 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 such as hydrophobicity and their octanol/water partition coefficients (KOW). In general, hydrophobic pesticides have very large partition coefficients favoring enrichment in the non-polar 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. The cores were dated using 210Pb and/or 137Cs dating methods in order to establish a timeline for both historical and current use of legacy and controversial pesticides. This concentration/depth profile was 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.

Pesticide profiles in marsh sediment cores obtained from the tidal Potomac River

256th National Meeting (2018)

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