Extraction and Quantification of Microplastics Contained Within Al, Fe and Ca Drinking Water Treatment Residuals

Drinking water treatment residuals (DWTRs) are waste products generated during drinking water treatment. DWTR composition is typically dominated by either aluminum (Al), calcium (Ca), or iron (Fe) compounds, depending on the coagulant used at the source facility. Most commonly disposed of via landfill, the beneficial reuse of DWTRs as soil amendments and construction materials is desired yet complicated by the potential presence of contaminants, including microplastics (MPs). Currently, very little data is available on the occurrence of MPs in DWTRs, creating uncertainty regarding the potential reuse of this material. Here, the MP concentration in representative Al, Ca, and Fe DWTRs was determined by a two-part oxidation and density separation method to extract MPs for quantification via fluorescent staining. MPs were detected in all three DWTRs examined, with Ca DWTR containing the smallest number of MPs and Al DWTRs containing the larger number of MPs, suggesting that Ca DWTRs may be the freest of concerns regarding MPs contamination among DWTR types.