Microplastic in Dredged Sediments: From Databases to Strategic Responses

Microplastics (MPs) accumulate in sediments, yet guidelines for evaluating MP risks in dredged sediments are lacking. The objective of this study was to review existing literature on MPs in sediments to improve fundamental knowledge of MP exposures and develop a publicly available database of MPs in sediments. Twelve percent of the reviewed papers (nine studies) included sediment core samples with MP concentrations generally decreasing with depth, peaking in the top 15 cm. The remaining papers evaluated surficial grab samples (0 to 15 cm depth) from various water bodies with MPs detected in almost every sample. Median MP concentrations (items/kg dry sediment) increased in this order: lakes and reservoirs (184), estuarine (263), Great Lakes nearshore areas and tributaries (290), riverine (410), nearshore marine areas (487), dredge activities (817), and harbors (948). Dredging of recurrent shoaling sediments could be expected to contain MPs at various depths with concentrations influenced by the time elapsed since the last dredging event. These results offer key insights into the presence and variability of MPs in dredged sediments, informing environmental monitoring and risk assessment strategies.