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Selenium Busters
Dr. Norman Terry's U.C. Berkeley lab is well known for research into plants that can tackle selenium, that bane of agricultural drainage, by absorbing and volatilizing it-transforming and releasing it as a harmless gas. Over the past several years, Terry has been experimenting with everything from broccoli to cattails, with the goal of finding the ultimate selenium buster. Last summer, pickleweed, that tiny, salt marsh plant beloved by rails and mice, astonished lab researchers by taking up and volatilizing selenium faster than any other plant studied before. As part of a BurRec-sponsored demonstration project for on-farm drainage management at Red Rock Ranch in Fresno County, one of Terry's post-docs, Dr. Zhiqing Lin, filtered selenium-laden ag drainage through a one-hectare plot of pickleweed and compared the rates at which the pickleweed volatilized selenium to those of 11 different species of plants. Pickleweed, says Lin, volatilized over 500 micrograms of selenium per square meter per day. "That's 10 to 160 times greater than any other species tested," says Lin. The secret lies in pickleweed's unique physiology, explains Terry. Unlike other plants, pickleweed can take up selenate and easily convert it to the forms of selenium that can be volatilized rapidly. When Terry and Lin compared the pickleweed field to several other plant species growing at Corcoran and Chevron marshes in Richmond, nothing else came close.
An alternative approach is to use plants to suck the selenium from the soil into their aboveground parts, which can then be harvested and removed. "You need to have really good site management," says Lin, referring to the necessity of preventing mice or other animals from consuming or making their homes in the treatment pickleweed. "It's not something you can just create and walk away from."
Terry is also looking for ways to enhance selenium uptake in a variety of plants, including pickleweed, through genetic manipulation. Though he's succeeded in increasing rates of selenium uptake in Indian mustard by three-fold, for example, he's still not satisfied. "In phytoremediation, we're striving for 10-fold or 100-fold increases," he explains, placing plants firmly on the front lines of humanity's battle with contaminants.
Contact: nterry@nature.berkeley.edu; zlin@nature.berkeley.edu. LOV
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