...From the pages of Agricultural Research magazine
| Phytoremediation is an innovative use of green
plants to clean up our environment. The term comes from the Greek word for
plants ("phyto-") that can detoxify, or remediate, soil or water
contaminated with heavy metals or excess minerals.
Think of the industrial wastes, toxins, and byproducts that emerge from our
daily activitieseverything from sewage sludge from cities to toxic heavy
metals from mines or factories to chemicals from agriculture. Produced and used
in moderation and disposed of properly, these compounds aren't a threat to
human health or the environment.
What should we do, however, when these materials accumulate in inappropriate
places to levels that can be harmful? Cleaning them up is a job for
In this issue, you'll read about the work of Agricultural Research Service plant
physiologist Leon V. Kochian and his associates at the ARS Plant, Soil, and
Nutrition Laboratory in Ithaca, New York (p. 4). This laboratory was
established in 1940 with the mission of studying the relationship between the
soil-plant system and the nutritional quality of plant foods.
In keeping with its original mission, the laboratory has also hosted research
that mapped the ability of soils to provide essential nutrients such as
selenium and zinc to our foods. The soil maps are now standard references that
the food industry uses to guide its actions.
Over the last 10 years, though, Kochian has shifted gears a bit. He's been
studying the details of the processes by which plants take up mineral
nutrientszinc, iron, manganesefrom the soil. One plant, alpine
pennycress (Thlaspi caerulescens) was chosen for intensive study because
it accumulates tremendous excesses of some of these elementsas much as
1,000 times more than normal. This behavior has been tracked to an alteration
in nutrient uptake and transport.
Normally, the activity of so-called "transporter" proteins
responsible for micronutrient uptake slows and eventually turns off as the
plant accumulates significant levels. In this plant, however, there is no such
regulation, so it keeps taking in more. Kochian is identifying the genes
involved in the hyperaccumulation and hopes to transfer them to larger, more
ARS agronomist Rufus L. Chaney, a phytoremediation pioneer who published the
first paper on the subject in 1980, is also working with alpine pennycress and
hopes to develop a commercial variety of it. He has found it to be especially
good at removing zinc and cadmium from soil (p. 6). Cadmium is a heavy metal
that is usually released by industries in conjunction with zinc. Chaney has one
pennycress that takes in 10 times more soil cadmium than any other known
Other ARS scientists nationwide are applying the concept of phytoremediation to
many different research problems. Michael P. Russelle in St. Paul, Minnesota,
has developed a novel alfalfa that rapidly absorbs large amounts of
nitrogenin its nitrate formfrom soil and water. He used the plant
to successfully clean up a North Dakota site where derailed tank cars spilled
massive quantities of liquid nitrogen fertilizer.
The plants' ability to tolerate what they've taken in is equally important.
That's the focus of research by David W. Ow at Albany, California. In hunting
for genes that are key to increased tolerance, Ow has worked with Indian brown
mustard (Brassica juncea) plants provided by ARS colleague Gary S.
Bañuelos at Fresno, California.
Ow's team first moved mustard genes into a simple-structured yeast,
Schizosaccharomyces pombe, so they could be more easily copied and
examined for function. Now the scientists are in the process of moving each of
about 50 genes into another model plant, thale cress (Arabidopsis
thaliana), for more detailed studies of their function in plants. They have
found that some genes boost the test plants' ability to withstand high levels
Bañuelos is working with central California farmers whose soils and
recycled irrigation water are overloaded with selenium or borontwo salty
contaminants that are all too common on the west side of the state's famous
central valley. His experiments over the past 12 years have shown that plants
in the Brassica family, like mustard and canola, thrive on the
selenium-laden soils and water.
Bañuelos recently helped coordinate production in California of another
Brassica not usually thought of as a phytoremediatorbroccoli. The
harvested broccoli was shipped to ARS nutritionist John W. Finley at Grand
Forks, North Dakota, for analysis to see whether it can be used in a study of
this veggie's health-imparting benefits (p. 12).
Although the concept of phytoremediation is simplicity itself, this research is
slow, complicated, and painstaking. But compared to the very disruptive and
expensive process of soil removal and physical extraction of contaminants,
phytoremediation may be the best alternative.
If successful, it will provide a low-cost "green" technology for soil
cleanup that can be easily used anywhere without special training or equipment.
An added benefit of phytoremediation is that the plantsafter pulling the
contaminant from the soilalso serve as ready-made storage containers for
the contaminant during shipment and subsequent treatment.
John W. Radin
National Program Leader
Plant Physiology and Cotton
"Forum" was published in the June 2000 issue of Agricultural Research magazine.