|Dionysiou recently keynoted the third International Symposium on Environmental Nanotechnology in South Korea. (Photo submitted)|
“Some of the cyanobacterial toxins are even more toxic than the venom produced by many poisonous snakes,” says Dionysiou, associate professor of environmental engineering. “These toxins have even been included in the list of chemical or biological warfare agents.” He explains that the toxins produced by cyanobacteria include hepatotoxins, neurotoxins and dermatotoxins, which affect the liver, nervous system and skin, respectively. Among the most commonly found cyanobacterial toxins is a group called microcystins. Microcystin-LR, for example, is a potent hepatotoxin.
|Prof. Dionysiou observes post-doctoral student Aditya Rastogi.|
Large growths of algae, known as harmful algal blooms, and their released toxins can be extremely toxic if swallowed by wildlife, livestock or people who drink untreated water. Because of such high toxicity, the World Health Organization assigned a provisional concentration limit of one microgram per litre of microcystin-LR and other cyanobacterial toxins in water. In January 2007, an EPA panel suggested lowering the provisional level to 100 nanograms per litre, or 100 parts per trillion.
|Prof. Dionysiou and post-doc Jongjun Chen examine an immobilized TiO2 catalyst sample.|
“The water in the Valle de Bravo dam, close to Mexico City, has very large concentrations of cyanotoxins,” Dionysiou notes. He has collaborated with Erick Bandala and his group of The Mexican Institute of Water Technology for the treatment of water from the Valle de Bravo dam which was contaminated with large concentrations of microcystin-LR. The team used a chemical oxidation system that was very effective in destroying the toxin.
|PhD candidate Miguel Pelaez, from Mexico, also studies reactions in swimming pools from cleaning solutions.|
“Westrick samples water from the Great Lakes, especially at locations close to the water intake of drinking water treatment plants, screens this water for toxins and then coordinates with the other project collaborators to determine the proper method for destroying the toxins in such water.” Dionysiou explains. The role of the investigators from PBS&J is monitoring for cyanobacterial toxins in certain aquatic systems in Florida. “You develop methodologies but eventually you have to test the system in real water.”
Dionysiou emphasizes that algal cells must be removed early on in the process in a drinking water treatment plant “because they foul the equipment of the process train.” He continues, “However, proper technologies need to be applied for cyanobacteria cell removal since some types of treatment methods for removing the cells, such as those that apply mechanical force, make the situation worse because they break the cells and release the intracellular toxins in water.”
|Dionysiou calls Maria Antoniou, fifth-year PhD student, the 'heart of the work on toxins.'|
Dionysiou explains that also with longer study time, the researchers can now document what happens at different UV doses over time. “What happens to these toxins?” he asks rhetorically. “And what happens with the chemical intermediates generated?”
The researchers are now able to study the types of intermediate products formed, the reaction pathway, the toxicity of the intermediates and how long it takes to break them down. In addition, Dionysiou is now studying the cost of using ultraviolet light. For example, catalysts — materials that are used to initiate or speed up a reaction without being affected by the reaction itself — can be combined with solar light to develop environmentally friendly, green, sustainable processes.
The value to using a technique that relies on solar light is that many Third World countries have solar light in abundance, due to their proximity to the equator. “In several African countries, millions of people do not have access to clean and safe drinking water at all,” Dionysiou points out, “and millions of people, especially children, around the world die every year due to waterborne diseases.”
Titanium dioxide, a ceramic material frequently used in paints and powders, is being investigated by Dionysiou’s group as a catalyst to generate photochemical and chemical reactions that destroy the toxins in water. Dionysiou uses this catalyst fixed on a support to lengthen the effect of the catalyst and to keep the catalyst itself out of the water. The catalyst is made with very high surface area using nanotechnology methods and containing very small quantities of nonmetals that make the catalyst operate using visible light, taking advantage of the sun’s light.
Dionysiou, who has received his earliest training in chemical engineering in Greece, followed by a master’s degree in chemical engineering from Tufts University and a PhD in environmental engineering from UC, is also now in the third year of a CAREER award by the National Science Foundation. This project, one of several ongoing projects in Dionysiou’s group, also deals with mechanistic aspects of oxidation of toxins in water using different powerful oxidizing reactive species, known as radicals.
Dionysiou has dedicated his teaching and research to water quality and treatment using advanced physical and chemical processes. All members in his group are working on projects dealing with treatment of different types of water and using a variety of technologies.
|Dionysiou, conferring here with Pelaez and Emily Riley (PhD), says the bar is set high by his graduate student researchers.|
“Almost all of my students have won national awards,” he says proudly. “They are a very hard-working group. The bar is set very high — there is passion; there is talent; there is creativity; there is hard work— and there are rewards.”
He sums up, “It’s a very good environment here at UC for scientific research.”
About the University of Cincinnati
Ranked by the National Science Foundation among the top 25 public research universities in the United States, UC's faculty have distinguished themselves worldwide for their creative teaching and research. The University of Cincinnati serves a diverse enrollment of more than 36,500 students through a balance of educational excellence and real-world experience. Founded in 1819, UC is the largest employer in the Cincinnati region, with an economic impact of more than $3 billion.