By Nirit Ulitzur
The drinking water community is placing emphasis and urgency on security. An early or real-time warning system (EWS) is critical to address both naturally occurring and purposeful contamination of drinking water supplies. This became especially true after the 9.11 tragedy that raised major concerns about possible terror attacks on water supply systems.
According to the Organization for Economic Cooperation and Development (OECD), there is a need for enhancing the efficiency and effectiveness of water monitoring by reducing monitoring costs and by improving monitoring benefits. US EPA’s statement that in 2003, millions of people were effected by failures to meet monitoring requirements of various chemical contaminations strengthens this notion.
Apart from security issues, water is prone to contaminations from spills, accidents and negligence – an Assessment of Tap Water Quality investigation has recently revealed that more than 140 contaminants with no enforceable safety limits were found in US drinking water (1).
The goal of an EWS is to reliably identify low probability / high impact contamination events (chemical, microbial, radioactive) in source water or distribution systems in time to allow an effective local response that reduces or avoids entirely the adverse impacts that may result from the event. Such an EWS needs to be capable of continuous, accurate and reliable real-time detection of contaminants (which are not normally present in water). Further, it must be affordable and easy to operate and maintain, even remotely (2).
The identification of chemicals by sophisticated chemical and instrumental methods is conditioned by the presence of a reference sample. Such methods are unable to estimate possible biological synergistic or antagonistic interactions between chemicals; their routine use is limited due to their high cost and the requirement for skilled personal. While there are several different organisms that can be used to monitor for toxicity (including bacteria, invertebrates and fish), bacteria-based biosensors are ideal for use as early warning screening tools for drinking water security because bacteria usually respond to toxics in a matter of minutes.
Most luminescent bacteria strains are found in the sea. They emit visible (blue-green) light as a by-product of their respiration. The use of intact luminescent bacteria for analytical purposes has some clear advantages: one can use a simple luminometer to detect light generated by a few hundred cells/ml. Chemo-physical and biological factors that affect cell respiration, the rate of protein or lipid synthesis, promptly alter the level of luminescence. In 1979, Bulich first showed that luminescent bacteria used for toxicity testing could be freeze-dried and provided to testing laboratories in a convenient reagent configuration. Freeze-dried (lyophilized) luminescent bacteria can be stored for years at -18°C (-0.4°F). Upon hydration, freeze-dried cultures of luminescent bacteria can yield 95–98 percent of their original viability, as well as their original level of in vivo luminescence. Thus, the use of these preparations for analytical purposes is not different, in practice, from other biochemical tests.
New advances in testing
A suitable test for drinking water toxicants should be rapid and sensitive enough to detect very low concentrations of diverse groups of toxic agents. Additional requirements from such a test include simple operation, minimal false positive or negative responses, affordability and the capability to run the test outside the laboratory. An innovative toxic screening test now utilizes a marine luminescent bacterium (Photobacterium leiognathi) and applies unique assay buffers that markedly increase the sensitivity of the test and also enable the preliminary discrimination between organic and metalloids and cationic metals toxicants.
The operation principle is simple: changes in the level of bioluminescence indicate potential toxicity (see example in Figure 1). Cationic heavy metals and metalloids can be detected at sub-mg/L levels, many of them were detected at 10-50 µg/L range. Similarly, herbicides, pesticides, polyaromatic hydrocarbons (PAHs) and chlorinated hydrocarbons were detected in a parallel test, all within 15 minutes. For most of the tested toxic agents, this new test was found to be markedly (over 10-100 fold) more sensitive than other bioluminescence-based tests. A practical feature of the new bioassay is the option of running the test at ambient temperatures (18-33°C). In addition, the stability of the freeze-dried bacterial reagent preparation precludes the need for refrigeration or freezing during shipment.
These features, together with its simple operation procedure, suggest that it has potential applications as a cost-effective pre-screening tool to appraise chemical toxicity in various water sources. The higher sensitivity and simplicity of the new test has been recently confirmed by US EPA’s Environmental Technology Verification (ETV) program of rapid toxicity technologies. (3)
Recently, this test was integrated into a novel automatic online monitor. Freeze-dried luminescent bacteria are hydrated and kept in the device at 4°C to maintain a stable luminescent culture. The instrument is re-supplied with newly hydrated luminescent bacteria and a fresh inventory of liquid assay every four weeks. Automatic safeguards have been engineered into the system to assure reagent and data quality and appropriate instrument functioning. The instrument is also equipped with auto-calibration features to assure reliable instrument performance; microprocessor based system controls provide for data storage, data downloading, real time communication with a remote PC and user adjustable alarm levels.
This advanced bioluminescence-based instrument will reliably identify low probability/high impact chemical contamination events in source water or distribution systems, in time to allow an effective local response that reduces or avoids entirely the adverse impacts that may result from the event. It will provide continuous, accurate, and reliable real-time information and will enable remote operation and control.
- National Technology Alliance 2004; http://www.nta.org/docs/WaterMonitoring.pdf
Photo 1- Luminescent bacteria colonies on an agar plate
About the product
The product described above is the ToxScreen test by CheckLight Ltd. CheckLight’s mission is to enable global water utilities to supply clean and safe drinking water by developing, manufacturing and marketing cost effective, wide spectrum, automatic bioluminescence-based water quality tests and monitors. Contact the company directly at P.O.B 72 Tivo’n 36000, Israel. T- 972 4 9930530; fax 972 4 9533176 or visit the website http://www.checklight.co.il
About the author
Nirir Ulitzur is the founder and CEO of CheckLight Ltd (Israel).. contact her via email, firstname.lastname@example.org.