Using VIS-NIR Spectroscopy to Quantify Soil Contamination

Researchers at the University of Nebraska-Lincoln have found a new method to assess oil contamination in soil by using VIS-NIR spectroscopy. The technique has significant advantages over previous methods.

Traditional methods of analyzing samples are done in the laboratory and require multiple steps. Samples must be collected from the spill site and then taken off site for analysis. The process is time-consuming, labor-intensive, and costly.

These laboratory-constructed soil samples contain various concentrations of petroleum hydrocarbons. Courtesy of David Weindorf.

“It costs about $50 per sample,” said Nuwan Wijewardane, a post-doctoral research assistant at the University of Nebraska-Lincoln. “And that does not include the cost of labor needed to collect samples from the field. In addition, it can take days or maybe weeks to get results.”

The VIS-NIR spectroscopy method costs only a few dollars per sample, and the results are nearly instantaneous. The tool can also be brought into the field to expedite the process.

The technology works by sending wavelengths of light at a sample and measuring what is absorbed or reflected. Different chemical compounds have specific responses based upon their chemical makeup.

The data is then compared to a model. The researchers found that they could construct accurate model samples mostly in the laboratory, with only a few samples needed from the site, a process called “spiking.” The data from the field samples is added into the original, which helps to customize the model to make it more accurate for the specific location. The reduction of time and labor necessary at the spill site makes the method comparatively quick and inexpensive.

The next step for the researchers is to make the technology more suitable to use directly in the field.

“As long as we extract and use crude oil, there is a risk of environmental contamination that can threaten the ecosystem’s balance,” Wijewardane said. “When it happens, we need immediate actions to detect it, evaluate the situation, and recommend remedial actions. This is where a rapid, cheap, and accurate technique in the field can accelerate the process.”

The research was published in the Journal of Environmental Quality (www.doi.org/10.1002/jeq2.20102).