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 (PrP^CWD). PrP^CWD may be shed into the environment by infected cervids and remains infectious in soils for years, creating a persistent indirect transmission risk. PrP^CWD may also be transported through soil by water via processes such as infiltration. We sought to determine how soil and porewater properties affect downward PrP^CWD transport through experiments in saturated soil columns. We detected PrP^CWD 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. PrP^CWD concentration was higher in leachates from coarse soils than from fine soils, and soil PrP^CWD concentration remained highest at the soil surface in all soils. Increasing porewater ionic strength reduced PrP^CWD leachate concentration, and no PrP^CWD was leached under acidic conditions (pH ≈ 5). We concluded that in most soils, there is risk that PrP^CWD is both retained at the surface and transported downward, though the relative amount of PrP^CWD retained versus transported varies with soil and porewater properties. Deviations from the ADRE indicate that PrP^CWD may be most accurately conceptualized and modeled as a colloidal contaminant.