Nature Tackles a Cleanup

Terry Team Finds Plants Like Broccoli, Cabbage and Rice Can Capture, Disarm Selenium

by Robert Sanders

A Berkeley biologist is assembling a team of scientists to show that plants can help clean up selenium, one of the major contaminants of agricultural runoff and industrial waste in the Western U.S.

Selenium is a toxic chemical element dumped into bays and streams all along the West Coast. San Francisco Bay alone is the sink for selenium-contaminated waste water from six major oil refineries, amounting to thousands of pounds of selenium each year.

For economic reasons alone, these industries are searching desperately for a solution to the problem. Earlier this year Shell Oil Co. was fined $12.5 million for excessive dumping of selenium into San Francisco Bay.

Perhaps the most well-known selenium contamination problem, however, involves irrigation runoff from agricultural land throughout the West, where much of the soil has a high selenium concentration. The problem hit the front pages in 1983 with the discovery that farm runoff into Kesterson Reservoir in California's Central Valley had so contaminated the water with selenium that fish and wildfowl were being poisoned and their offspring deformed.

"Agricultural drainage water is collecting in evaporation ponds all over the West, effectively creating a large number of toxic dumps," says Norman Terry, professor of plant biology. "A solution is desperately needed, because this has the potential for being an ecological disaster."

Since 1990 Terry has been looking at the potential of plants to remove selenium from waste water and runoff. Several years ago he showed that some plants--including crop plants like broccoli, cabbage and rice--not only accumulate selenium in their tissues but also have the ability to convert selenium into a non-toxic gas that is easily dispersed. Marsh plants, in particular, seem to be very effective at this.

Moreover, his team showed last year that selenium is converted to a gas primarily in the roots. This means that selenium can be removed without the danger of it entering the food chain, which can happen when selenium is taken up into seeds and leaves.

Terry predicts that some crops or wetland plants could be genetically engineered to greatly increase the amount of selenium they take up from the soil and send into the atmosphere, providing a much needed solution for industry and agriculture.

"Using plants to clean up large volumes of waste water with low levels of contamination really is the only method we've got," Terry says. "If you've got thousands of acres contaminated with selenium what else can you do? You can't cover it up with other soil like at Kesterson.

"We're in an area where there are very few options. The only thing we can do is grow crops or plants that accumulate selenium," he said.

Terry and his Berkeley colleagues, including physiologist Adel Zayed, reviewed their recent work and assessed prospects for using plants to clean up selenium in a talk April 22 at a scientific conference in Columbia, Mo.

Entitled "Will Plants Have a Role in Bioremediation?" the April 19 to 22 meeting at the University of Missouri was the first ever on the use of plants to clean up toxic waste--a hot new field dubbed phytoremediation.

What makes plants attractive in bioremediation--cleaning up pollution using living organisms like bacteria and algae--is that their roots have an amazing ability to penetrate every nook and cranny in the soil and pull out chemicals like salt and toxic trace elements like selenium, cadmium and lead, Terry says.

One plan is to harvest the selenium-containing plants as cattle feed for ranchers in areas of the world where lack of selenium is a problem. In minute amounts selenium is an essential nutrient in the diet.

An alternative Terry prefers, however, is to genetically engineer plants to do an even better job of accumulating selenium and sending it into the air. Molecular biologist Elizabeth Pilon-Smits recently joined his team to work on that problem.

Another tack is to manipulate the interaction between the plant's roots and soil microbes to enhance selenium uptake and volatilization, converting soil selenium into a gas. Microbiologist Hassan Azaizeh on his team is investigating this.

Terry's work is funded by the state Water Resources Board, Chevron Corp., the University of California Salinity/Drainage Taskforce and the Electric Power Research Institute.


Copyright 1995, The Regents of the University of California.
Produced and maintained by the Office of Public Affairs at UC Berkeley.
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