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A new method for detecting fecal matter in water
When it comes to drinking water safety, many new innovations are focused on emerging contaminants. One new testing method, however, focuses on something that has plagued drinking water for ages — contamination by fecal matter. Water Quality Products Managing Editor Kate Cline recently spoke with Vladislav V. Yakovlev, developer of the technology, about the new testing method and its potential benefits.
Kate Cline: Briefly describe the new detection method procedure.
Vladislav V. Yakovlev: Conventional methods of detection based on optical sensing are usually based on tight focusing light to a small volume. In the proposed and experimentally validated new approach, a large sample volume can be utilized, allowing a significantly larger number of molecules to be involved in the generated optical signal. An integrated cavity serves several purposes: It utilizes a larger excitation volume, helps utilize non-absorbed photons, and directs the generated light (in our particular implementation, it is a fluorescent signal) to the detector. As a result, a much greater sensitivity is achieved. In a practical implementation for fecal contamination detection, we used the known fact that a certain molecule, urobilin, is a signature of the contamination’s presence. When zinc ions are added into a solution containing urobilin, a light-emitting complex is formed, making it possible to optically excite this compound and collect a specific fluorescent signal, which is significantly enhanced by the new experimental arrangement.
Cline: What are some of the limitations of the detection method?
Yakovlev: The detection sensitivity reached in our experiments is better illustrated using the following example. If light is focused using a conventional microscopic arrangement, less than 0.001 of a molecule on average is present in the excitation volume at the concentration level we were able to record. In those experiments, we used a relatively inexpensive spectrometer and a cheap LED light source bought at a local RadioShack store. A better light source and better detection arrangement should further improve the sensitivity of detection by an additional two to three orders of magnitude.
Cline: How can contamination by animal or human waste affect water sources? What dangers does this type of contamination pose to human health?
Yakovlev: There is an excellent book published by the World Health Organization, [available at] www.who.int/water_sanitation_health/publications/2012/animal_waste/en/, which describes all the known possible dangers of animal/human waste. In brief, there is a danger from microorganisms, which are sparsely distributed and do not diffuse as rapidly as small molecules like urobilin, and there is a danger from, for example, ammonia contained in manure, which can affect fish population, etc.
Cline: What are some potential applications of the new detection technology?
Yakovlev: The new detection technology is not limited to fluorescence, as demonstrated in the published report. We have already demonstrated that the same approach is applicable to other spectroscopic methods of chemically specific detection, making it possible to detect and distinguish chemicals identified by the U.S. Environmental Protection Agency as compounds affecting human health, at the critical concentration level. It makes it possible to provide real-time quality control of water. The same approach can be also extended to air quality control, breath analyzers, etc. Considering a very low acquisition cost and simplicity of use, it provides a simple and adequate solution both for developed and developing countries.
Cline: How might the new technology benefit homeowners or public water systems?
Yakovlev: In short, it is possible, and we are currently working on several licensing agreements for the simplest implementation of the proposed technology to animal/human waste detection in water.