that during the course of that program water protection became a high-priority issue so the technology was applied to water and not air.

System Cost

Tom Dillion, of Science Applications International Corporation, asked about the cost of the AquaSentinel system.

Dr. Greenbaum responded that the system could be built for less than $20,000 per unit, perhaps even less than $10,000, based on the price of the components of the system. A fluorometer is also needed but the one used here was more sophisticated than necessary for these special measurements. He said that the entire system could actually be put on a chip. Estimating that 500 to 1,000 of these units would sell around the world, the price would probably be less than $10,000.

System Location

Mr. Dillion followed up by saying that it would be good to utilize this technology in individual buildings. He said that in terms of protecting a water supply, dilution phenomena make it unlikely that attacks will happen at a water supply area.

Dr. Greenbaum replied that this technology only works for primary-source drinking waters because once that water has been filtered and disinfected, the algae are removed. Without algae, the fluorescence signal one would want to monitor would not exist.

Purposeful Nutrient Enhancement

Vasilios Manousiouthakis, of the University of California at Los Angeles, wondered if there might be compounds that could be mixed with the maliciously placed toxin so that it would help the algae grow, and therefore have some kind of compensatory effect on the sensors and prevent the needed detection level being reached.

Dr. Greenbaum responded that it would not be possible to do this because the presence of the nutrients needed to grow the algae would not change the sensing signal of toxins such as cyanide, methyl parathion, or DCMU. He said that the chemistry and specific action of these toxins are independent of the nutrients present in the system in this case. However, he said that the kinetics of fluorescence decay is the difference between algae grown in a nutrient-rich lab environment versus the more nutrient-poor field conditions. He said that in the lab the kinetics of decay are slower because the algae are much healthier than those living in the river, but that even when they are very healthy the algae are still susceptible to the harmful effects of the toxins.

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