U.S. Water News Online
LINCOLN, Neb. -- A relatively simple method of mixing iron into soil contaminated with pesticides could save millions of dollars for those faced with cleaning up environmental spills.
"There are always going to be spills that go unreported in large part because of the high costs associated with treating them. If a low-cost, low-tech way of cleaning up pesticide spills can be used as an alternative, more of them may be reported and dealt with and that's good for the environment," said Steve Comfort, a University of Nebraska soil environmental chemist.
As part of ongoing research on ways to clean up soil and groundwater contaminated with potentially toxic pesticides and ordnance compounds, Comfort and NU residue chemist Pat Shea recently struck upon a method of mixing pesticide-contaminated soil with fine-grained metallic iron and water. This approach can successfully eliminate up to 99 percent of the contamination, allowing the soil to be returned to its original site.
The NU Institute of Agriculture and Natural Resources (IANR) researchers were able to test their treatment method on a large scale last summer in southwest Nebraska.
The site was a farm cooperative where nearly five years ago an accidental spill dumped more than 750 gallons of metolachlor into a clay-lined waste lagoon at the co-op.
Metolachlor is one of the most commonly used farm herbicides in Nebraska, most often encountered under the "Dual" trade name.
"The water table is shallow at the site and analysis of groundwater and soil from locations near the lagoon indicated high potential for groundwater contamination," Comfort said.
After the accidental spill, about 1,000 cubic yards of contaminated soil were excavated from the lagoon and held at the site, awaiting either removal or remedial treatment.
"The pesticide concentrations were high enough that they posed a risk of sustaining groundwater contamination, as well as being potentially toxic to surrounding plant and animal life," Shea said.
As part of their demonstration project, the IANR research chemists placed the stockpiled, contaminated soil into long windrows using common earthmoving equipment and then mixed three times with a high-speed implement that its manufacturer has trademarked under the name "microenfractionator." The device combines the actions of homogenizing the soil, reducing the size of its particles and aeration. A tractor is used to pull the implement through the windrows of soil. as part of the treatment process, fine-grained iron particles are added to the mixing operation, along with water.
"The microenfractionator provided uniform distribution of the iron within the windrowed soil and helped make the initial pesticide concentration more uniform," Shea said. The mixed and treated windrows were then covered with sheets of clear plastic and kept moist for the next three months.
Following the addition of the iron particles, along with some other amendments, such as acetic acid and aluminum sulfate, the metolachlor concentrations in the contaminated soil rapidly decreased, with chemical destruction rates between 72 and 99 percent within the first 90 days, said Comfort. Even one day after treatment, the soil began showing measurable decreases in metolachlor contamination.
Not only did the environment benefit from this process, the potential cost savings are huge.
Using the current, accepted practice of transporting and incinerating the 2.5 million pounds of contaminated soil would have cost more than $3.1 million. Using Comfort and Shea's approach was estimated at less than $65,000, including the labor.
"The iron is the key. It shows the potential to very quickly and effectively promote the decomposition of a wide variety of pesticides," said Shea. An added bonus of this method is that people can be quickly and inexpensively trained to do it, using relatively inexpensive and readily available machinery and supplies, soil additives, and techniques.
The IANR Agricultural Research Division research is ongoing and is being funded and sponsored in part by NU's School of Natural Resource Sciences and Water Center/Environmental Programs and a grant from the U.S. Geological Survey.
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