Comparing the fate and transport of MS2 bacteriophage and sodium fluorescein in a karstic chalk aquifer

Groundwater flow and contaminant migration tracing is a vital method of identifying and
characterising pollutant source-pathway-receptor linkages in karst aquifers. Bacteriophages are an
attractive alternative tracer to non-reactive fluorescent dye tracers, as high titres (>10¹² pfu mL−¹) can be safely released into the aquifer, offering improved tracer detectability. However, the interpretation
of bacteriophage tracer breakthrough curves is complicated as their fate and transport are impacted
by aquifer physicochemical conditions. A comparative tracer migration experiment was conducted
in a peri-urban catchment in southeast England to characterise the behaviour of MS2 bacteriophage
relative to sodium fluorescein dye in a karstic chalk aquifer. Tracers were released into a stream sink
and detected at two abstraction boreholes located 3 km and 10 km away. At both sites, the loss of MS2
phage greatly exceeded that of the solute tracer. In contrast, the qualitative shape of the dye and phage
breakthrough curves were visually very similar, suggesting that the bacteriophage arriving at each
site was governed by comparable transport parameters to the non-reactive dye tracer. The colloid
filtration theory was applied to explain the apparent contradiction of comparable tracer breakthrough
patterns despite massive phage losses in the subsurface. One-dimensional transport models were also
fitted to each breakthrough curve to facilitate a quantitative comparison of the transport parameter
values. The model results suggest that the bacteriophage migrates through the conduit system
slightly faster than the fluorescent dye, but that the former is significantly less dispersed. These
results suggest that whilst the bacteriophage tracer cannot be used to predict receptor concentrations
from transport via karstic flow paths, it can provide estimates for groundwater flow and solute
contaminant transit times. This study also provides insight into the attenuation and transport of
pathogenic viruses in karstic chalk aquifers.