Long-term inactivation of bacteriophage PRD1 as a function of temperature, pH, sodium and calcium concentration.

The two most significant processes controlling virus mobility in the subsurface environment are virus attachment and inactivation. In particular, models that predict subsurface virus transport are highly sensitive to inactivation. Virus inactivation is known to depend on temperature as well as hydrochemical conditions. The aim of the current work was to study the effects of temperature and hydrochemical conditions on the inactivation of bacteriophage PRD1 as a model virus, and to develop a quantitative relation for these effects. Series of batch experiments under controlled temperature were conducted, for a range of conditions: 9.5 °C and 12 °C, pH4 - pH8, sodium concentrations of 1, 10 and 20 mM, and calcium concentrations of 0.5, 1.5, and 3 mM. By multivariate regression analysis, a joint log-square model was developed that describes the inactivation rate of PRD1 as a function of these hydrochemical conditions. This model approximates two rate and Weibull models and accounts for the observed non-linear inactivation at increased pH and salt concentrations. Model predictions are within ±0.4 log10 (0.4-2.5 times) virus concentration reduction. The nature of the log-square model does not allow extrapolation of virus inactivation beyond the experimental conditions. Inactivation rate of PRD1 was found to increase with increasing temperature and increasing sodium and calcium concentrations, and to be lowest between pH 6.5 and pH 7.5. Within the studied conditions, the developed log-square model may be applied at field scale for predicting inactivation during subsurface transport of viruses.