Plants recruit oil-detoxifying microbes.

The 1991 Gulf War brought oily devastation to much of the Persian Gulf region (SN: 11/16/91, p.316). But testifying to this environment's resiliency, signs of a natural recovery are emerging--even around the perimeter of former oil lakes created by war-ravaged pipelines and wells. From this defiled desert landscape, wildflowers reemerged unexpectedly last year.

Biologists analyzing the spring-blooming plants' tentative comeback now believe they may have unearthed--literally--the roots of a natural, low-tech, and relatively low-cost strategy for cleansing oiled soil: plant cultivation.

"These plants should not have grown at all, because oil contains aromatic compounds, which are toxic," observes Samir Radwan, who led the probe. But when he and his colleagues at the University of Kuwait in Safat dug into the crude-soaked desert, they found the wildflowers' roots not only healthy but free of oil (see photo).

The only logical explanation, Radwan says, was that the roots recruited ubiquitous oil-degrading microbes to clean up. So his team cultured bacteria and fungi residing in the oily sand. And in the July 27 Nature, they report that the root zone was indeed a rich reservoir of well-known oil-eating microbes.

Immediately adjacent to the roots, one family of bacteria (Arthrobacter) accounted for fully 95 percent of the resident microbes. "But go out just 1 centimeter from the root and you find a completely different microflora [community of fungi and bacteria]," Radwan observes. These organisms, too, degraded oil, the microbiologist reports.

The annuals that his team studied in the desert belong to the same family as sunflowers (Compositae). To find out what other plants might survive, the Safat team tainted the sand in greenhouse pots to match the petroleum concentrations in which the wildflowers had been growing--10 percent crude oil by weight. Most of the corn, barley, wheat, termis (a legume), and tomatoes planted in this oiled sand not only germinated but grew into healthy-looking plants, albeit 25 to 40 percent smaller than those raised in clean sand. Naturally occurring microbes also kept roots growing in the tainted sand free of oil.

Oil alone entices many petroleum-noshing bugs to immigrate to polluted areas. However, the rich nutrients exuded by plant roots--such as sugars, amino acids, oxygen, and vitamins--make that environment even more welcoming, Radwan observes. For this reason, his team recommends "densely cultivating suitable plants in polluted Kuwaiti desert areas as a promising approach for their bioremediation."

In fact, this "solar-powered system may find very wide application in many different parts of the world and with many different contaminants," argues toxicologist Barbara T. Walton of Oak Ridge (Tenn.) National Laboratory.

Other groups, her own included, have reported evidence that root-zone microbes have the potential to degrade a number of noxious contaminants, from organic solvents and TNT to persistent pesticides. Critics, however, have questioned the prospects for such "phytoremediation" under the extreme conditions that can plague polluted sites. Now, Walton says, Radwan's team "offers in-your-face evidence that this [phytoremediation] can clean up a contaminant of widespread concern--oil--under extreme conditions."

What's more, phytoremediation could cost far less than conventional cleanup technologies, notes Burt Ensley of Phytotech in Monmouth Junction, N.J.

Because soil-cleaning plants may absorb some of the toxic materials around them, Walton believes that the trick will be to identify plants for cultivation that won't tempt growers or wildlife to dine on them.