A team of University of Maine chemists has reported that exposing pesticide-contaminated water to natural light and a mineral known as a zeolite can dramatically speed up the break down of the pesticide. The finding could be useful in developing technologies for protecting drinking water supplies or improving environmental quality.
Among the pesticides studied was malathion which has been shown to kill lobsters in laboratory studies by other researchers at UMaine and is suspected of being a contributing factor in the recent deaths of lobsters in Long Island Sound. Malathion had been sprayed in the New York area to control mosquitoes thought to be carrying the West Nile virus.
The team, led by Howard H. Patterson, professor of chemistry, reported its findings to the annual meeting of the American Chemical Society in August. Other scientists participating in the research are Sofian Kanan, a former Ph.D. student of Patterson's and currently a post-doctoral researcher in the Laboratory for Surface Science and Technology at UMaine, and Marsha C. Kanan, a master's student. Marsha Kanan is continuing research to determine if the zeolite technology can also speed decomposition of pesticides in gaseous form.
Zeolites are naturally occurring volcanic minerals. Because of their honeycomb structure, they can absorb other materials much as a sponge absorbs water. They are currently used in a variety of industrial processes and products such as cat litter, shoe deodorizers, and aquarium and pond filters.
In laboratory experiments at UMaine, the team tested insecticides that are commonly used in agriculture and have been detected in rivers and drinking water supplies in the United States. Each compound breaks down naturally in sunlight, but the decomposition process showed “astonishing increases in the rate of each reaction” when an A-type zeolite was present, the team reported.
The reaction rates for malathion, carbofuran and carbaryl were 35, 120 and 164 times faster respectively than the rates for those compounds when the zeolite was not present. Zeolites have well-defined pore and channel structures, and they work by capturing pesticide molecules and enabling light to disrupt chemical bonds.
“It's important to find the zeolite with the right size channels and surface chemistry,” says Patterson. “You want it tailored to the size of the molecule that you want to break down. A pesticide molecule enters a zeolite channel and fits snuggly like a hand in a glove. When you expose it to light, a reaction occurs, and the pesticide molecule breaks apart.”
Sofian Kanan, a native of Jordan, came to the U.S. in 1996 after working as a teaching assistant at Yarmouk University in Amman. Marsha
Kanan is a native of Mechanic Falls, Maine and the recipient of a prestigious Congressionally authorized Goldwater Scholarship.
Zeolites are commonly used in the petroleum industry, but the UMaine team may be the first to study the technology for reducing pesticide concentrations in water, Patterson notes.
The decomposition process is consistent with a conceptual model proposed by Sofian Kanan, Patterson and other researchers to explain the break down of another compound in a zeolite. According to an article published this year in The Journal of Physical Chemistry B, light affects the chemical bonds that hold nitric oxide within a zeolite and lead to the release of oxygen and nitrogen gas.
The model predicts that compounds with a certain size and surface charge can be degraded by this method. Further laboratory observations have confirmed the model, they note.
Participating in the nitric oxide research were Mohammad A. Omary of UMaine and Masaya Matsuoka and Masakazu Anpo of the University of Osaka Prefecture in Japan.
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