Waterborne diseases kill nearly 3800 children every day.1 Even today, water-related diseases are one of the leading causes of death of children in the developing world. Of these, a significant number of deaths can be attributed to contaminated drinking sources that house large numbers of microorganisms, including viruses, bacteria, and protozoa.
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Consuming water from such contaminated sources often leads to diarrhea which can prove fatal, particularly for young babies. Of the microorganisms that cause diarrhea, both rotaviruses and shigellosis are readily spread through fecal contact. This can arise from either poor hand hygiene or water source contamination through improper disposal of fecal waste.
Controlling the spread of such diseases does not just involve tackling sanitation and hygiene, but also limiting human-to-human transmission. One approach to this is water testing to identify water sources that have been contaminated with fecal material. This way large clusters of infections are avoided and correct purification measures can be taken for any water removed from the source.
Wastewater testing in water sanitation plants often makes use of online spectroscopic methods for content analysis.2 Certain chemical species can be used as a proxy for different types of contamination, such as high levels of nitrates being indicative of fertilizer runoff entering the water stream. A spectroscopic method can be selected that is sensitive to the chemical fingerprint of the contaminant and then used to perform a continuous assessment of the water quality.
Other methods for water testing include sampling and then chemical analysis of the water content. For assessment of microbiological contamination, cell cultures or agar growths are used to cultivate samples for analysis. Identification can then be carried out using methods such as PCR, fluorescence in situ hybridization, or some type of biosensor.3
The problem with the collection and cultivation of microbiological species is that the samples pose a biohazard in themselves, and it can be challenging to perform the cultivations and analysis correctly without extensive laboratory infrastructures. Some cultivation techniques require very skilled experimentalists and the microbiological growth process can also be very time-consuming.
Spectroscopic methods offer a near-instantaneous result that can be much more straightforward to interpret than microbiological methods. Of the available spectroscopic approaches for wastewater analysis, fluorescence spectroscopy has proved viable for online wastewater monitoring, though there are some challenges with signal congestion associated with debris and other fluorescent contaminants.4
Despite the challenges with its use for quality control in online water analysis at sanitation plants, recent work from scientists at University College London has shown that fluorescence spectroscopy is an ideal tool for the rapid detection of fecal matter in wastewater.
Water contaminated with fecal matter shows a greater natural organic matter content as, for organic matter that is from human or animal origins, it often contains larger concentrations of tryptophan. Tryptophan is an amino acid that shows a fluorescent signal around 350 nm upon excitation at 280 nm.
The team showed that, by looking at the amount of tryptophan-like fluorescence from various water samples, fluorescence spectroscopy can provide a rapid in situ diagnostic for water contaminated with fecal matter. The use of fluorescence spectroscopy proved a more resilient measure of the degree of contamination than measurements of the thermotolerant fecal coliforms.
The team used an immersive probe that could be submerged in a 150 ml sample of the potentially contaminated water and then left the fluorimeter in a dark, stainless steel container to perform the measurements. Any stray light present would have given rise to false readings.
Two fluorimeters were used to target different excitation and detection ranges (280 / 360 and 280 / 450 λex / λem respectively) for the detection of both tryptophan-like fluorescence and humic-like fluorescence. Elevated humic-like fluorescence levels have been thought to be indicative of the presence of bacteria such as E. coli, which is also associated with water contamination.
The team examined several different regions throughout different parts of the year, looking at both shallow and deeper waters for sampling. They also performed several complimentary analysis types to see if the results from the fluorescence were comparable to other more labor and time-intensive approaches.
The overall findings from the work were that both humic-like fluorescence and tryptophan-like fluorescence provide more reliable and robust detectors of fecal matter contamination. The ability to provide rapid, online diagnostics also has a significant advantage in providing crucial information for making decisions about targeted water intervention to improve public health outcomes.
Access to portable fluorescence spectrometers may be a powerful tool in helping limit the impact of water contamination that devastates thousands of lives each year.
References and Further Reading
- World Health Organisation (2017) Protecting and Promoting Human Health. [Online] Available at: https://www.who.int/
- Broeke, J. Van Den, Langergraber, G., & Weingartner, A. (2006) On-line and in-situ UV / vis spectroscopy for measurements : a brief review. Spectroscopy Europe, 18(4), 1–4. https://www.spectroscopyeurope.com/system/files/pdf/UV1_18_4.pdf
- Köster, W., Egli, T., Ashbolt, N., Botzenhart, K., Burlion, N., Endo, T., ... & Rust, A. (2003). Analytical methods for microbiological water quality testing. Assessing microbial safety of drinking water, 237. https://www.who.int/
- Carstea, E. M., Bridgeman, J., Baker, A., & Reynolds, D. M. (2016). Fluorescence spectroscopy for wastewater monitoring : A review. Water Research, 95, 205–219. https://www.sciencedirect.com/science/article/abs/pii/S0043135416301488?via%3Dihub
- J. P. R., Nayebare, J., Carr, A. F., Lyness, R., Campos, L. C., Ciric, L., Goodall, T., Kulabako, R., Rushworth, C. M., Macdonald, A. M., Owor, M., Read, D. S., & Taylor, R. G. (2021) In-situ fluorescence spectroscopy is a more rapid and resilient indicator of faecal contamination risk in drinking water than faecal indicator organisms. Water Research, 206(October), 117734. https://doi.org/10.1016/j.watres.2021.117734
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