|KIM, HYUNGJUNG - Chonbuk National University|
|TORKZABAN, SAEED - Commonwealth Scientific And Industrial Research Organisation (CSIRO)|
Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/2015
Publication Date: 12/31/2015
Citation: Bradford, S.A., Kim, H., Headd, B.J., Torkzaban, S. 2015. Evaluating the transport of bacillus subtilis spores as a potential surrogate for Cryptosporidium parvum Oocysts . Environmental Science and Technology. 50:1295-1303. doi: 10.1021/acs.est.5b05296.
Interpretive Summary: Regulations in the US to protect drinking water supplies from disease causing microorganisms have focused on the removal of the pathogen Cryptosporidium, but accurate determination of risk is hampered by methodological and financial constraints. The US EPA has recommended the use of aerobic spores as an indicator for Cryptosporidium transport in groundwater environments. A series of packed column studies were conducted to compare the transport behavior of aerobic spores and Cryptosporidium oocysts. Results indicate that aerobic spores served as a conservative surrogate of the transport behavior of oocysts over a range of environmentally relevant conditions. This information should be of interest to regulators, drinking water companies, and public health officials that need to assess risks of microbial contamination to drinking water supplies.
Technical Abstract: The USEPA has recommended the use of aerobic spores as an indicator for Cryptosporidium oocysts when determining groundwater under the direct influence of surface water. Surface properties, interaction energies, transport, retention, and release behavior of B. subtilis spores were measured over a range of physicochemical conditions, and compared with similar information for C. parvum oocysts (Kim et al., 2010). Interaction energy calculations on smooth and nanoscale rough surfaces predicted a much larger energy barrier to the primary minimum and a shallower secondary minimum for spores than oocysts when the solution ionic strength (IS) equaled 0.1, 1 and 10 mM. No energy barrier to the primary minimum was predicted for both microbes when the IS=100 mM. Spores and oocysts exhibited similar trends of increasing retention with IS (0.1-100 mM) and decreasing Darcy water velocity (qw=0.2 and 0.5 cm min-1), and the predicted setback distance to achieve a six log removal was always larger for spores than oocysts. This observation indicates that aerobic spores can serve as a conservative surrogate for oocyst transport and retention over a range of physicochemical conditions. However, low levels of spore and oocyst release were observed during steady-state conditions, and this release significantly influenced the predicted setback distance, especially when the fraction of reversibly retained microbes (Frev) was high. Large pulses of spore and oocyst release were observed following a reduction in initial IS to deionized water and flow interruption. The value of Frev increased with decreasing initial IS and increasing qw for spores. The value of Frev for oocysts exhibited a similar dependency with qw as spores, but an opposite effect with the initial IS. Some physicochemical conditions are therefore expected to produce larger values of release and Frev for oocysts than spores.