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Name: Neil O.
Status: other
Age: 30s
Location: N/A
Country: N/A
Date: 1999-2001 

I see from an article on the Argonne home page today (2001 Feb 26) that the lab has received a Facility Progress Award from USEPA for its innovative work in removing contamination from soil and groundwater. The article mentions the technique of "phytoremediation -- using plants to break down and remove contaminants" and shows a photograph of some of the 800 poplar and willow trees that were planted to implement this technique.

However, another Argonne web article states: Similar plantings of hybrid poplars in Washington state indicate that of the organic contaminants taken up by the trees, about 70 percent are converted to non-volatile compounds and held in the plant. The other 30 percent is vaporized from the leaves along with the transpired water.

I'd like to know more about the consequences of using phytoremediation. In particular, why is it better to transport contaminants from a relatively controlled, low-mobility environment (e.g., soil, groundwater) into a relatively uncontrolled, high-mobility environment (e.g., atmosphere, surface water)? Do the plants involved in phytoremediation become contaminated and hazardous as they absorb contaminants from the soil? What happens to wildlife that may feed on the plants? What environmental risks arise when the plant sheds leaves, blossoms, seeds, twigs, or other material that may be carried by wind or surface water far from the original contaminated location? Similarly, what environmental risks arise when the plant transpires to the atmosphere 30 percent of the absorbed contaminants in unconverted form?

Possibly useful:

Anthony R. Brach

Junqiang :

I agree that the sun looks like a disk when viewed from earth, but I would think that it could be treated as a point source in terms of light reaching the earth's surface. By "brightness on the disk for a given wavelength", I assume you mean intensity as a function of wavelength. My understanding is that the distribution of energy as a function of wavelength (or frequency) is that of a black-body radiator with a temperature of 6000 degrees Kelvin. Some further discussion on this can be found in a book called "The Refrigerator and the Universe: Understanding the Laws of Energy" by Martin Goldstein.

Good luck,

Jim Rubin

Hi Neil,

The use of phytoremediation is a classic case of being stuck between a rock and a hard place. The better option is not to have put the contaminants there in the first place, but it looks like we are only slowly learning the lesson that blithely assuming most new compounds we introduce are harmless only means that later we spend a lot of time and money cleaning up the mess.

Groundwater is actually not that controlled or contained an environment, some of it often ends up seeping into lakes and rivers, but of course the primary concern in keeping groundwater clean is human health- we are perhaps the only animal species where a significant portion of our water supply comes from ground rather than surface water.

The plants absorbing the contaminants often do in fact become hazardous, with concentrations reaching levels requiring disposal in hazardous waste facilities in some cases. However, in cases where the contaminant is widely dispersed, particularly at lower concentrations, it is somewhat preferable and less labor intensive than other cleanup methods (e.g. pump out and treat all the water in the aquifer, removal of millions of cubic yards of soil). That the vegetative material from the phytoremediative plant becomes the primary transport mechanism of these contaminants into the biosphere is true, supplanting the somewhat slower dispersal through groundwater into surface waters, or the less well-characterized "phytoremediation" that would occur anyway as the result of native vegetation taking up some of the groundwater. It's a matter of picking your poison. The primary advantage that I see in purposeful phytoremediation is that there is some anticipation and monitoring of where the contaminants go, and thus the more hazardous uses of contaminated plant material (e.g. as food material, whether for humans or wildlife) are generally better avoided.

Don Yee

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