Blog Literature 2 - Values and Limits of Correlation with Microbial Indicators

LITERATURE 2 - Values and Limits of Correlation with Microbial Indicators

Source:  Payment, Pierre. Locas, Annie. (2011). Pathogens in Water: Values and Limits of Correlation with Microbial Indicators. National Ground Water Association. Ground Water Volume 49, No. 1. 01 Dec 2016.
http://info.ngwa.org/gwol/pdf/110184396.pdf

This literature review focuses on the use of microbial indicators and its ability to predict the presence of pathogenic organisms that can be found in ground water supplies. This report mainly focuses on ground water supplies, as "in sewage, even with very high levels of microorganisms, no mathematical correlation can predict the type or concentration of any pathogen...In surface waters, advanced statistical methods such as logistic regression have provided some level of predictability of the occurrence of pathogens but not specific counts. In groundwater, the continuous absence of indicators indicates an improbable occurrence of pathogen. In contrast, when these indicators are detected, pathogen occurrence probability increases significantly" (Payment and Locas, 2011). The main parameter being used as a microbial indicator will be fecal coliform, based on what is presently known.

There were several criteria that had to be fulfilled in order to use an indicator for pathogenic occurrence probability, some of which include the inability of the indicator to not multiply in the environment, a display of similar behavior to external or natural reactions with the environment as in the pathogen being analyzed, and its ability to be easily isolated, identified and enumerated (Payment and Locas, 2011). An important practice done by the authors of this report is that they reduced "inter-laboratory differences" by testing at the same lab site. It is important to know this because one must understand that at different labs, equipments are calibrated differently, different lab practices are performed both because of the location and because of the experimenters performing the tests, and data collection as a result will be different. By keeping the testing in a single location, errors were greatly reduced. Samples were taken from the Saint-Lawrence River, as well as from local wells in the area.

Two viruses particularly being analyzed are Giardia and Cryptosporidium, because these viruses are known to be detrimental to human health if they are not eliminated from drinking water during water treatment. Scattergrams were performed, and compared to E. coli in order to determine the validity of the results. It was found that more viruses were found in the fall season, which makes sense because of how easily people normally get sick during the summer-to-winter transition. Figure 1 below shows the scattergram results.

Figure 1: Scattergram Results for Sanitary Water Samples in Saint-Lawrence River Area

Similar testing was then done for the river samples obtained from the Saint-Lawrence River. Surprisingly enough, the river water tested negative for the virus, with 55% containing fecal coliforms and 58% containing C. perfringens (Payment and Locas, 2011). These samples did, however, contain the indicator that was supposed to determine the probability of the water containing a pathogenic organism; therefore, based on this observation, other statistical models had to be used to determine whether the water contained viruses. Table 1 shows the results for the river water samples.

Table 1: Results for Saint-Lawrence River Water Samples

Finally, groundwater samples were tested for the two viruses. Interesting to note from the report is that people were seeing an increase in illness due to viruses coming from apparently clean groundwater sources, which means that the water was not being effectively treated for microorganism removal. Since these water normal do not contain fecal coliform, other indicators were necessary to be found. Figure 2 and Table 2 below show the results from the testing of the groundwater.

Figure 2: Scattergram Results for Ground Water Samples in Saint-Lawrence River Area

Based on their research, it was found that fecal indicators are the best predictor but it is still perfect tool for water quality and human health analysis. It is extremely difficult to pinpoint a single indicator that can directly identify what kind of pathogenic organisms are in the water, or if the water is even consumable. Other indicators will have to be used in combination with fecal coliform in order to properly determine how safe the water really is for consumption.