PFAS in Sediments: A Dynamic Reservoir
PFAS contaminating water bodies do not remain exclusively dissolved in the water column—they partition between water, suspended particles, and bottom sediments based on compound-specific sorption coefficients. Understanding PFAS sediment dynamics is important for water utilities because sediment resuspension and desorption from bed sediments can affect source water PFAS concentrations in ways that treatment systems must accommodate.
Chain Length and Sediment Sorption
Long-chain PFAS (PFOA, PFOS) sorb more strongly to organic-rich sediments than short-chain variants, accumulating in bed sediments near contamination sources. Sediment-bound PFOS concentrations can significantly exceed overlying water concentrations, creating a reservoir that slowly releases PFAS to the water column through desorption and bioturbation.
Sediment Disturbance Events
Storm events, floods, dredging operations, and boat traffic can resuspend PFAS-laden sediments, causing temporary spikes in water column PFAS concentrations. Water utilities drawing from surface water sources should anticipate PFAS concentration increases following storm events and design treatment systems with sufficient capacity to handle peak loads without compliance exceedances.
Sediment Management Implications
Water reservoir management practices that minimize sediment disturbance—controlling boat traffic, monitoring sediment PFAS concentrations, managing watershed inputs—can reduce source water PFAS variability. Sediment remediation through capping or dredging may provide long-term source water quality improvement but requires careful management to avoid short-term PFAS release during remediation activities.