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Re: E-M:/ Algae Used to Recover Toxic Heav...

Enviro-Mich message from Rane Curl <ranecurl@engin.umich.edu>

On Thu, 23 May 2002, Maryann Whitman wrote:

> Something has always bothered me about using plants or algae or anything
> along those lines to "sequester" something noxious be it in soil or water.
> Once the noxious item is "sequestered" shouldn't one then have to remove the
> carcasses and do something else with them in order that the noxoius item not
> end up back where it was to begin with?

The "sequestration" captures the pollutant within the body of the plant
material. It only remains sequestered if a) no process reverses and
releases the pollutant and b) the plant material is buried under other
decaying plant (or mineral) material.

In the case of a), decay itself can release the pollutant if the adsorbent
plant material disappears. While this releases the pollutant back into
the environment, it may do so at a much slower rate than it was taken
up, which can reduce it's concentration between toxic levels. It also
may not if (for example) peat that has adsorbed pollutants burns. Finally,
many (especially organic) pollutants are degraded chemically or by
bacterial action while they are sequestered.

> With some noxious organic molecules I understand that the "sequestering"
> process might actually reconstitute them and render them
> 'harmless'....But...nothing (short of alchemy or nuclear tampering) will
> transmogrify lead.  Right?

Right. Sequestered heavy metals are not rendered harmless and can be
released by alterations of the environment. Peat bogs are good at
sequestering heavy metals and can retain them for a very long time - for
all practical purposes if they exist "forever". A lot of peat bogs in
Michigan started forming ca. 10,000 years ago and are still doing their
sequesteration job, as long as they are not disturbed or destroyed.

--Rane Curl

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