Prion Transport in Soils Varies with Soil and Porewater Properties

Chronic wasting disease (CWD) is a neurodegenerative disease affecting cervids that is caused by infectious prion protein (PrPCWD). PrPCWD may be shed into the environment by infected cervids and remains infectious in soils for years, creating a persistent indirect transmission risk. PrPCWD may also be transported through soil by water via processes such as infiltration. We sought to determine how soil and porewater properties affect downward PrPCWD transport through experiments in saturated soil columns. We detected PrPCWD in leachates and soils using the real-time quaking-induced conversion (RT-QuIC) assay and determined best-fit transport parameters with the one-dimensional advection-dispersion-reaction equation (ADRE) for solute transport. PrPCWD concentration was higher in leachates from coarse soils than from fine soils, and soil PrPCWD concentration remained highest at the soil surface in all soils. Increasing porewater ionic strength reduced PrPCWD leachate concentration, and no PrPCWD was leached under acidic conditions (pH ≈ 5). We concluded that in most soils, there is risk that PrPCWD is both retained at the surface and transported downward, though the relative amount of PrPCWD retained versus transported varies with soil and porewater properties. Deviations from the ADRE indicate that PrPCWD may be most accurately conceptualized and modeled as a colloidal contaminant.