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 reservoir for the 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 (I) on pathogenic prion protein (PrP Sc ) properties (viz. aggregation state and ζ-potential) and adsorption to quartz sand was investigated. The apparent average isoelectric point of PrP Sc aggregates was 4.6. PrP Sc aggregate size was largest between pH 4 and 6, and increased with increasing I at pH 7. Adsorption to quartz sand was maximal near the apparent isoelectric point of PrP Sc aggregates and decreased as pH either declined or increased. PrP Sc adsorption increased as suspension I increased, and reached an apparent plateau at I ∼ 0.1 M. While trends with pH and I in PrP Sc 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 (I ) 10 mM). Our findings suggest that disposal strategies that elevate pH (e.g., burial in lime or fly ash), may increase PrP Sc mobility. Similarly, PrP Sc mobility may increase as a landfill ages, due to increases in pH and decreases in I of the leachate.

Colloidal suspensions of C60, C70, and a derivative of C60, PCBM ([6,6]-Phenyl C61-butyric acid methyl ester)were produced by extended mixing in water. We examined the contribution of background solution chemistry (pH, ionic strength) on the formation of colloidal suspensions in terms of mass, aggregate size, and zeta potential. These parameters were also compared between free-settling and filtered treatments. Results indicated that all three fullerenes were highly negatively charged in aqueous systems, that it took a finite time to reach kinetically stable suspensions, and that suspension formation was pH and ionic strength dependent. With isoelectric points approaching zero, the suspensions were generally stable at pH > 3. The results indicate that it is critical to state the condition under which the formation of aqueous fullerene suspensions occurs when employing such suspensions to evaluate environmental toxicity or fate and transport of fullerenes.

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Aqueous colloidal suspensions of C60 (aqu/C60) and the C60 derivatives PCBM ([6,6]-phenyl C61-butyric acid methyl ester) and the corresponding butyl and octyl esters, PCBB and PCBO (aqu/PCB-R, where R is an alkyl group), were produced by stirring in double deionized water for 5 months. Kinetically stable fullerene aggregates were formed using this procedure that ranged in intensity-averaged hydrodynamic diameter (Dh) from 193 +/- 2 nm (95% C.L.) for aqu/C60 to 259 +/- 6 nm for aqu/PCBO. Measured zeta potentials (zeta) were < -50 mV, and the isoelectric points (p) were < 1.0 for all of the aqu/fullerenes. Time-resolved dynamic light scattering (TRDLS) was used to measure aqu/fullerene Dh change with time and as a function of background solution ionic strength. The critical coagulation concentration (CCC) values for the aqu/PCB-R fullerenes were significantly higher than that of aqu/C60, indicating that the phenyl alkyl ester moieties of the equ/PCB-R fullerenes were impeding the aggregation process.