Two Grants Support Old Dominion University Chemist's Studies of Soils

Ordinary dirt would not seem to be a difficult target for modern analytical chemistry, but for decades now scientists with high-powered instruments have squared off against the stuff without being able to claim a clean victory.

Now, an Old Dominion University researcher, Jingdong Mao, is gaining notice for innovative strategies that could provide a much better understanding of sediments and soils, and the National Science Foundation (NSF) is supporting the work with more than $300,000 in grants.

The research is important for many reasons, but perhaps the most pressing involve pollutants and how they react when they enter the soil.

Mao's expertise is with nuclear magnetic resonance (NMR) analysis, which is done with instruments very similar to the magnetic resonance imaging (MRI) devices that physicians use to see inside the human body.

The focus of his latest NSF grant is soil/sediment organic matter (SOM), which comes mostly from the decomposition of plants. SOM is a challenge for scientists to study because the basic building blocks are large and complex carbon-based molecules. SOM also is more likely than the soil's nonorganic sand and minerals to bind with organic pollutants, including petroleum products and many pesticides.

Mao, an assistant professor of chemistry and biochemistry, joined ODU not long after the launch of the College of Sciences Major Instrumentation Cluster (COSMIC) Laboratory in 2006. One of the first instruments installed was a 400MHz solid-state NMR spectrometer that cost $500,000.

Patrick Hatcher, who holds the university's Batten Endowed Chair in Physical Sciences and who is the director of the COSMIC lab, said Mao is doing things with NMR that nobody else is. "Jingdong's development of new approaches to tease out additional information about natural organic matter with nuclear magnetic resonance is beginning to make an impact on the field of environmental chemistry," Hatcher explained.

The NSF invested $225,000 in Mao's study, "Collaborative Research: Advanced Solid-State NMR Characterization of Non-Covalent Interactions of Organic Compounds in Soil and Sediment Organic Matter." The grant runs from July of this year through June 2012 and the collaborating researcher is Joseph Pignatello, who works at the Connecticut Agricultural Experiment Station and is an adjunct professor of chemical engineering and environmental engineering at Yale University.

Mao is also working on another NSF-funded project, "Unraveling Structural Conundrum of Organic Nitrogen in Soil and Sediment Organic Matter Using Advanced Solid-State NMR: Insights into Formation Mechanisms of Stabilized Nitrogen." That grant is for $80,000 and the researcher said the work will result in an improved advanced solid-state protocol for investigating organic nitrogen forms in natural organic matter.

The larger grant has a broader aim, he added, and that is to influence the way research is designed and the way major concepts are taught in environmental engineering and science. The work could advance techniques to clean up contaminated soils, a job that is often tedious because of insufficient know-how about pollutant sorption, or bonding, with SOM.

"Society will benefit broadly by changes in approaches to risk assessment and remediation design that will result from an improved conceptual model of the sorption process," Mao said. "The collaboration will significantly build research infrastructure because it will open additional avenues that can be explored in environmental engineering and science with NMR."

With NMR analysis, a sample is placed in a large, external magnetic field and also irradiated with radio waves. This excites different atomic nuclei in different ways and when the nuclei re-emit the radiation, an antenna and a powerful computer can receive and turn those signals into a virtual image of molecules in the sample. This is like the MRI "picture" of an internal organ.

While NMR spectroscopy is potentially a powerful molecular-scale tool, it has so far provided limited insight into the mechanisms of sorption by solid-state SOM due to poor resolution. But Mao has been able to get valuable new information about the structure of SOM solids via his pioneering work with spectral editing techniques in solid-state NMR analysis.

According to the grant proposal, the materials of focus for the researchers will be humic acid particles, whole soils and isolated SOM, black carbon standards, coal reference standards and polymer standards. The objectives are to probe structural changes of SOM taking place during sorption, to probe preferential sites of sorption and to quantify fused-ring content and size and their influence on sorption affinity.