August 28, 2009 By Blake Harris
Photo: Tennessee's Clinch River where latest research was carried out.
A new method to detect toxins and contaminates in municipal water supplies has undergone further refinements by two Oak Ridge National Laboratory (ORNL) researchers according to a news announcement today.
The approach uses algae as "sentinels" to detect toxins and contaminants. Using a fluorometer to measure the fluorescence signal of algae that grow naturally in source water such as Tennessee's Clinch River, which was used in this study, any changes in the process of photosynthesis - the natural process of converting light energy into chemical energy - can be detected, indicating the presence of a toxin.
Recent advances in optoelectronics and portability make this approach a powerful technology for monitoring the in situ physiology of photosynthetic organisms such as green algae and cyanobacteria. Even low levels of toxins alter fluorescence patterns within minutes.
The new work demonstrates that the technology that uses algae as sentinels has broader applications than previously reported, according to authors Miguel Rodriguez Jr. and Elias Greenbaum of the Department of Energy's ORNL. For example, under real-world operating conditions, the sensitivity of the algae to toxins has a natural daily cycle that tracks the sun.
"When the sun is overhead and shining brightly, the algae are less sensitive to the toxins," Greenbaum said. "The new work shows that keeping the water sample in darkness for about 30 minutes prior to testing for toxins restores full sensitivity to the test."
The new results also show that the technology can be applied to many different water quality environments such as when the algae are starved for nutrients. As well, based on statistically data, it has been shown that the threshold for detection levels for broad classes of toxins such as blood and nerve agents and agrochemicals are at or near Environmental Protection Agency regulatory guidelines, according to Greenbaum.
"Our key result is that despite real-world conditions that create challenges, free-living microalgae combined with 'work-around' strategies can be used as broad-spectrum automated biosensor systems for continuous monitoring of source drinking water," Greenbaum said.
For their study, the researchers looked at five classes of chemical agents in water: Diuron, atrazine, paraquat, methyl parathion and potassium cyanide. All are known to be harmful to human health. In the case of Diuron, used in agriculture for 50 years, Greenbaum and Rodriguez were able to detect 1 part per million. This was indicated by a 17 percent decline in the algae's photosynthetic efficiency.
"We have shown that microalgae in source drinking water can be used as broad-spectrum, robust sentinel sensors to detect relatively low concentrations of toxins," Greenbaum said. "We have also shown that the microalgae do not need to be in an optimized state for this technology to be effective."
This story was compiled from news reports. Photo of Tennessee's Clinch River by J. Stephen Conn. CC Attribution-Noncommercial 2.0 Generic