Some Plants Really Dig Poisoned Soil

After blasting away continuously for decades, the huge coke manufacturing ovens at Ford Motor Co.'s (F ) River Rouge site in Dearborn, Mich., left behind a chemical time bomb. Thirty acres of land are tainted with polyaromatic hydrocarbons, or PAHs--carcinogens that persist in the soil indefinitely.

Now Ford wants to revamp the River Rouge site as a showcase for green manufacturing techniques, and the poisoned soil has to go. But rather than strip off the contaminated earth and ship it away--the standard, costly way to clean up brownfields--Ford contacted the Phyto-remediation Research Lab at Michigan State University. And what will the muckbusters do? Grow plants.

The list of plant species that are known to sequester or metabolize toxic compounds is now hundreds long. For the MSU scientists, the challenge was to find some that would not just survive in the poisoned soil, but would break PAHs down into harmless compounds. So they carted off buckets of the offending dirt, and after testing dozens of different plants, found a number of promising matches. Beginning this spring, River Rouge's blasted earth will be sown with the seeds of 20 or so species of woody, herbaceous, and shrub-like plants native to Michigan. "After a couple years, we think we'll be at a very safe level," says Clayton L. Rugh, an MSU soil mineralogy professor working with Ford.

LONG WAIT. The scientists could use a big win. Right now, state and federal environmental agencies don't recognize phytoremediation as a viable solution. One concern: Plants can take several seasons to reduce toxin concentrations to safe levels, while heavy equipment can remove the soil in days. And it's not clear whether plants, which excel in treating surface contamination, can cope with deep spills.

Nonetheless, interest in this approach is growing. State and federal authorities approved the River Rouge experiment. And companies saddled with polluted sites like the idea of cleanup costs just one-third those of traditional "dig 'n' dump" methods. Plus, "phytoremediation is very appealing to the public," says Lena Q. Ma, a professor of soil and environmental chemistry at the University of Florida. It's natural--and the plants look great on the sites.

By Jeff Green in Detroit and Petti Fong in Vancouver, B.C.

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