microLAN On-line Biomonitoring Systems

Detecting Chemical Contaminants in Drinking Water Using Bacteria-Based Biosensors

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A continuous supply of clean drinking water is something that most Americans take for granted. Even those of us in the environmental profession, who know the effort and engineering it takes to provide clean drinking water, rarely go to the tap doubting that the water will be clean and safe.

Things Have Changed

Since September 2001, the general population and water supply professionals have been concerned about the safety and protection of drinking water supplies. It seems like every day since then, there have been advisories from federal and local government agencies issued to water utilities to take every precaution against a possible terrorist attack. Many important steps have been taken by drinking water utilities in the past months to prevent possible attacks on water utility infrastructure and to prevent any attempts to contaminate reservoirs or treated water supplies.

One of the principles repeated by security professionals is “Delay, Detect and Respond.” This means that anything that can be done to slow down or delay an intruder trying to access a water utility increases his or her chances of being detected and of getting caught, which allows the utility to respond — by arresting the intruder and, if needed, preventing that source water from entering the distribution system.

An intruder who tries to physically break in to a water utility can be detected by the type of security devices that we are all accustomed to — motion detectors, alarms, cameras, etc. But what devices are being used to detect the chemical agents that might be introduced into a water system?

Biotoxicity Detection Technology

One of the technologies being used is biotoxicity monitoring. Toxicity testing is based on exposing an organism to a water or a wastewater sample and measuring the effect. The sensing element can include a variety of biological elements that can range from antibodies to complex whole organisms. Standard methods involve exposing species of freshwater invertebrates or fish (Fathead minnows) to the water sample.

Another type of system, bacteria-based biosensors, combine a bacterial species with an electronic measuring device producing a sensitive and rapid test method in a single instrument. This has demonstrated the potential to quickly detect a broad range of toxic agents. The metabolism of bacterial cells, like all living cells, is supported by a broad range of continuous biochemical reactions that can be disrupted by toxic chemicals. By coupling a cell suspension with the appropriate instrument that can measure the metabolic rate of the cells, an operational biosensor can be developed.

Bacteria-based biosensors are also unique in that they produce a very rapid response to toxicity in water. While toxicity methods using higher-level organisms, such as fish, may take many days to produce a measurable result, bacteria-based biosensors can usually produce measurable acute toxicity data in as little as 15 minutes. This makes these types of instruments uniquely suited as an early warning screening tool for drinking water systems. Also, bacteria-based biosensors can be incorporated into a portable instrument making rapid response and field-testing practical, something not possible with toxicity test formats using other organisms.

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