University Park, Pa. --- A new analytic approach pioneered by Penn State researchers is helping to pile up evidence about why and how composting's product, humus, can control pollution.
Dr. Jean-Marc Bollag, director of Penn State's Center for Bioremediation and Detoxification (CBD) and the project leader says, "Forty to 50 percent of chemicals applied to the soil, including pesticides and other potentially harmful compounds, stay in the soil." They remain there bound to humus, the brown or black organic portion of soil formed from the partial decomposition of vegetable or animal matter.
This binding, which is a natural process, can be considered beneficial since bound chemicals are unavailable to be taken up by plants or to leach into ground water. However, until now, data on the nature of the bonds and the ultimate stability of the bound chemicals has been limited.
Over the last six years, Bollag and his research team have pioneered the use of carbon-13 nuclear magnetic resonance spectroscopy (C-13 NMR) to characterize these bonds. Their work has shown C-13 NMR to be a valuable new tool in the soil biochemist's arsenal.
Speaking at the American Chemical Society (ACS) National Meeting in San Francisco, Calif., April 13-17, Dr. Jang-Eok Kim, who participated as a visiting professor in the Penn State project, described the coupling of the herbicide, Bentazon, with humic constituents. Kim is a member of the Department of Agricultural Chemistry, Kyungpook National University Taegu, Korea.
Kim says that, usually, only molecules that have particular chemical groupings on their molecules, either an oxygen/hydrogen grouping, called a hydroxyl, or nitrogen/hydrogen grouping, called an amino group, react and bind to humus. Bentazon has neither. Yet, in the presence of catechol, a humic derivative, and the enzyme laccase, Bentazon binds and was completely transformed within 30 minutes. The transformation products, a dimer comprised of one catechol and one Bentazon molecule, and a trimer, consisting of one catechol molecule and two Bentazon molecules, were identified with C-13 NMR spectroscopy.
In his presentation at the ACS meeting, Bollag described two transformations undergone by the fungicide, Cyprodinil, in the presence of humus constituents. The Cyprodinil molecule is first split and then the two parts each bind to humic acid. Once again, the reaction products were identified with C-13 NMR spectroscopy.
Bollag notes "Until now, most of the research on the determination of bound residues was carried out using C-14-labeled chemicals. Our recent studies have demonstrated that significant progress in the evaluation of pesticide binding to soil can be achieved with C-13-labeled compounds and C-13 NMR spectroscopy."
He adds, "Our group has carried out numerous studies to try to determine whether the detoxification effect of humus can be enhanced through stimulation of the binding process. We have found that certain enzymes and nonbiological catalysts do enhance the process. Of course, some contaminants are not good candidates for treatment with enzymes but we have found that they still can be detoxified indirectly by increasing the content of reactive chemicals in the soil.
"Fortunately, amending soil with additional organic matter to enhance detoxification is becoming more common as companies offer humus preparations possessing detoxifying capabilities."
Other members of the research team include Dr. Jerzy Dec, Penn State research associate; and Dr. A. Schaffer, Ciba-Geigy Limited, Basil, Switzerland.
The research has been supported in part by Ciba-Geigy, manufacturer of Cyprodinil.