Determining the impact of Deepwater Horizon’s spill on soil

Immediately after the Deepwater Horizon oil spill some immediate questions posed were:

• how bad is the spill in terms of coastal pollution; and,
• what new technologies could be brought to bear for environmental quality assessment?

To evaluate these questions engineers and spill responders were brought in. Their job was to evaluate new and innovative technologies that could prove useful in addressing the spill. The current methods involved taking soil samples, bringing them back to labs, and processing them. While the testing was accurate, it was slow, time-consuming and costly.

Luckily, right before the spill, a Louisiana State University doctoral student, Somsubhra Chakraborty, was working on oil detection. He found a way to replace previous testing methods with a rapid, on-site analysis.

Scientists inspecting soil after the Deepwater Horizon residue reached shore. Credit: D Weindorf

Chakraborty used a portable sensor called visible near infrared diffuse reflectance spectroscopy. Though it sounds complicated, the premise is very simple. A light source in a probe emits visible and near-infrared light. When the light hits the soil, some of it is reflected back to the probe. This reflected light is a signal is carried via fiber optic cable to a battery-operated spectrometer mounted in a backpack. The spectrometer precisely measures the wavelengths of reflected light. The reflection patterns are associated with the amount of pollutant oil in the soil. Essentially, the more oil in the soil, the less light is reflected.

The hope was that this probe-spectrometer combination could deliver the accurate and quick results needed.

Chakraborty’s research was evaluated on Grand Isle, Louisiana and Pensacola, Florida. In many ways, the application of this type of spectroscopy to this spill was the best combination of circumstances for testing the technology. The instrument was sensing black oil on a light-colored beach. There was also a relatively uniform soil texture and very low organic matter. This took away many variables that might reduce the viability of the tools to analyze oil content.

The contrast of colors between the white sand of Florida’s beaches and the dark, oily residue that washed ashore, helped the tools developed by the LSU team to accurately detect oil contamination in the field. Credit: D Weindorf

As such, the predictions of oil pollution provided by this spectroscopy on-site produced strong, stable results. Furthermore, the approach showed wide “dynamic range.” It measured low to high levels of oil pollution directly with no reduction in accuracy. This added to value of this type of spectroscopy to hydrocarbon pollution detection.

Several other lessons were also learned throughout the study. Older techniques of measuring oil in soil involve drying the soil samples. Oil is a hydrocarbon. As such, it has a “volatile” portion – the reason you can smell oil is that some of it turns to vapor. Drying samples vaporized a certain part of the sample. The visible near-infrared diffuse reflectance spectroscopy measured both volatile and non-volatile portions of the oil. This is valuable added information.

Studies of our results showed that they were extremely accurate, and sensitive to oil quantification across the beaches we studied. Thus, we were able to report how much oil was present on the beaches and wetlands and help inform recovery methods.

A few years after Deepwater Horizon, we researched making detection even better. Our research group combined spectroscopy with another technique call fluoroscopy, also in a portable device that could be brought to the study sites. Fluoroscopy is a type of x-ray.

The team from LSU using their portable technology to evaluate beaches for oil contamination. Credit: D Weindorf

Both types of tools were used separately with good results. But we found that by combining the information from two types of detection devices, we could provide even better analysis. Both the portable spectrometer and fluoroscopy measurement tools were complete systems. They didn’t require consumables like chemical reagents. They each provided results within seconds. The combination provided several advantages in detecting and quantifying soil contaminants.

In the wake of this national environmental tragedy, science rose to the challenge. Tools were found for quick detection and research has provided us with new tools for environmental quality analysis that will be used for years to come around the world.

Answered by David Weindorf, Texas Tech University

Read our other blogs about Deepwater Horizon here:

How did Deepwater Horizon’s spill affect the coastal soils and wetlands in the Gulf of Mexico?

What will the future bring? 

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