Oak Ridge National Laboratory researchers have refined a method for detecting contaminants in municipal water supplies. Their work shows that the technology, which uses algae, has broader applications than expected.
Miguel Rodriguez Jr. and Elias Greenbaum found that under real-world operating conditions, the sensitivity of algae to toxins occurs in 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, like when the algae are starved for nutrients. "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.
The researchers used a fluorometer to measure the fluorescence signal of algae that grow naturally in Tennessee's Clinch River. They exploited the known characteristics of Photosystems I and II, which convert light energy into chemical energy, to detect any changes in the process of photosynthesis.
"Recent advances in optoelectronics and portability make this a powerful technology for monitoring the in situ physiology of aquatic photosynthetic organisms such as green algae and cyanobacteria," they said. Even low levels of toxins quickly alter fluorescence patterns.
The researchers looked at five classes of chemical agents in water: Diuron, atrazine, paraquat, methyl parathion, and potassium cyanide. 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 Photosystem II 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."
Discussions for commercialization of this technology, to be marketed under the name AquaSentinel, are under way.