Best way to clean up toxic plumes? Give ’em a pill

A staple of chemistry classroom demonstrations may offer a solution for cleaning up decades’ worth of toxic solvents polluting the environment, new research suggests.

Potassium permanganate is a disinfectant used by water treatment plants, and is sometimes also used to treat pollution stemming from industrial-grade solvents that were buried 30 to 40 years ago.

“But most people who use potassium permanganate to treat pollution pump it into a well in liquid form every day for a couple of months,” said Frank Schwartz, a study co-author and a professor of geological sciences at Ohio State University. Like salt, potassium permanganate is granular and dissolves when it comes into contact with water.

“There’s often no control over where the potassium permanganate goes once it’s pumped into an injection well,” Schwartz said. “The system is usually just as bad after the treatment as it was before.”

So he and his colleagues created solid forms, or chunks, of organic material that contain potassium permanganate. When buried in wet soil, these chunks slowly dissolve over a matter of weeks and months. These chunks allow researchers to better control the distribution of potassium permanganate at a pollution site.

These toxic plumes can extend for miles. Health effects can be severe, with clusters of leukemia cases occasionally developing as people drink contaminated water, Schwartz said.

“We’re going after legacy contaminants – degreasers and solvents left over from nearly every manufacturer in the 1960s and ’70s who made something from metal” he said.

Schwartz conducted the study with David Li, a postdoctoral researcher in geology at Ohio State. Li presented the findings Wednesday in Anaheim at the meeting of the American Chemical Society.

So far, the researchers have only tested the time-released potassium permanganate chunks in laboratory experiments. But the results are promising. They added the chunks, which are about the size of a tapered candle, to experimental tanks of wet soil tainted with the solvents trichloroethene (TCE) and perchloroethene (PCE) – two compounds used in commercial dry-cleaning as well as to clean grease off of metal. The tanks ranged in size from a 10-gallon fish aquarium to a refrigerator turned on its side.

In these controlled experiments, the chemicals are converted into non-toxic components in a matter of weeks. In the field, however, Schwartz said it could take many years to rid an area of solvents at a given site.

“Some sites have a higher volume of solvents than other sites,” he said. “But most sites have two things in common – a pure source of the solvent, usually found near the dump site, and plumes, where flowing water has dissolved some of the original chemical and carried it through underground aquifers.”

These toxic plumes can extend for miles. Health effects can be severe, with clusters of leukemia cases occasionally developing as people drink contaminated water, Schwartz said.

The researchers believe that chunks containing potassium permanganate could stop plumes in their tracks and, as the potassium permanganate slowly dissolves, mixes with the solvents and eventually obliterates the plumes. The scientists’ next step is to test time-released potassium permanganate chunks in the field.

“Theoretically, these chunks could be made in whatever size is appropriate for the site that needs cleaned,” Schwartz said. “We could put the chunks into pre-existing wells, or drill holes into the ground below the water table, insert the chunks and then cover them up. Ideally, we could leave the site alone for a year or two and eventually replace the chunks if necessary.”

Potassium permanganate essentially eats away at TCE and PCE, turning these solvents into harmless minerals, water and carbon dioxide.

It’s also cheap and plentiful.

“Potassium permanganate is a much cheaper and much more cost effective way of managing and getting rid of solvents,” Li said. “Time-released potassium permanganate could literally save hundreds of thousands, if not millions, of dollars in waste clean-up and management fees.”

Current waste treatment methods include pumping tainted water out of the ground and treating it at the surface.

“This requires a constant source of electricity and continuous monitoring, and there’s always the chance that the system could break down,” Schwartz said.

With potassium permanganate, there’s little chance that any would be left in the water supply once these reactions happen, Schwartz said.

“Potassium permanganate isn’t as serious a contaminant as a solvent, but you wouldn’t want to drink it,” he said. “It also gets oxidized when it reacts with the solvents, and breaks down into harmless by-products.”

Support for this research came from the U.S. Department of Energy and the Department of Interior.

Contact: Frank Schwartz, (614) 292 6196; frank@geology.ohio-state.edu. David Li, (614) 292-6193; li@geology.ohio-state.edu.

Written by Holly Wagner, (614) 292-8310; Wagner.235@osu.edu