Adsorption of pathogenic prion protein to quartz sand

Management responses to prion diseases of cattle, deer, and elk create a significant need for safe and effective disposal of infected carcasses and other materials. Furthermore, soil may contribute to the horizontal transmission of sheep scrapie and cervid chronic wasting disease by serving as an environmental reservoirforthe infectious agent. As an initial step toward understanding prion mobility in porous materials such as soil and landfilled waste, the influence of pH and ionic strength (l) on pathogenic prion protein (PrPsc) properties (viz. aggregation state and zeta-potential) and adsorption to quartz sand was investigated. The apparent average isoelectric point of PrPsc aggregates was 4.6. PrPsc aggregate size was largest between pH 4 and 6, and increased with increasing l at pH 7. Adsorption to quartz sand was maximal near the apparent isoelectric point of PrPsc aggregates and decreased as pH either declined or increased. PrPsc adsorption increased as suspension l increased, and reached an apparent plateau at l approximately 0.1 M. While trends with pH and l in PrPsc attachment to quartz surfaces were consistent with predictions based on Born-DLVO theory, non-DLVO forces appeared to contribute to adsorption at pH 7 and 9 (l = 10 mM). Our findings suggest that disposal strategies that elevate pH (e.g., burial in lime or fly ash), may increase PrPsc mobility. Similarly, PrPsc mobility may increase as a landfill ages, due to increases in pH and decreases in l of the leachate.