Long-distance transport of bacteriophages MS2 and phiX174 in karst aquifers

Waterborne pathogens pose a particular threat to aquifers with low retention capacity, such as karst aquifers. To date, particle transport in groundwater is typically studied using tracer tests with microspheres or natural sediments, which might be unsuitable to derive transport characteristics of pathogenic bacteria or viruses. This study investigated the transport and attenuation behavior of two bacteriophages, MS2 and phiX174, as surrogates for pathogens in a karst aquifer in South-West Germany. Both bacteriophages and the solute reference tracer uranine were recovered within five days at a 9.1 km distant spring. Only a small proportion of infectious bacteriophages was recovered compared to uranine. Breakthrough curves indicated no observable retardation but major attenuation of bacteriophages during transport. The modeled transport parameters of bacteriophages were subject to high uncertainty relative to uranine due to insufficient analytical accuracy at the low concentrations observed. However, it was demonstrated that visual inspections of the breakthrough curves alone might lead to incorrect assumptions regarding dominating transport processes. The high attenuation of bacteriophages was attributed to attachment processes rather than inactivation, which affected the removal of bacteriophages only little in this study. Yet, the fast breakthrough of infectious bacteriophages at the spring indicates the high contamination potential of karst springs. Findings further suggest that only surrogates relevant to the specific requirements and injected at appropriate locations can accurately simulate the transport behavior of particles of interest. The results highlight the need for suitable experimental sites, tracer materials, and analytical methods for risk assessment studies concerning pathogens.