Ecolog:
This rings a vague bell for me too. There was some work done in the British
Isles (Scotland) on very crisp ecotones across pH differences using one
grass species. Also, I seem to recall that the Dutch were using willows that
were supposed to be hyperaccumulators and they were burning them for fuel,
then disposing of (or "mining") the heavy-metal "laden" ash. There is, of
course, considerable literature on "phytoprospecting." I, too, would like to
be brought up to date in this area, and educated on the particulars. For
example, I would like to know just how accumulation or "rejection"
functions, and what processes are involved. For example, how does pH affect
the rate and amount of absorption? What other chemical and physiological
processes are involved? Why are some heavy metals (chromium, selenium,
arsenic, etc.) apparently readily absorbed (by the Chenopodiaceae, for
example--and the mustard family), and lead apparently not? Is it as simple
as semipermeable membranes, whether or not they are soluble and under what
conditions? Is something going on in the rhizosphere that evades some
analytical procedures?
WT
----- Original Message -----
From: "Martin Meiss" <[email protected]>
To: <[email protected]>
Sent: Friday, April 15, 2011 9:04 AM
Subject: Re: [ECOLOG-L] where do edible plants retain lead and other
contaminants?
A long time ago, when I was learning about plant ecotypes, I heard of
research on the adaptation of plants to high lead levels found in piles of
mine tailings. If I remember correctly, local races of plants were forming
that were able to adapt to toxic soils. This raises these questions: if
plants ARE NOT taking up the heavy metals, what is the mode of toxicity?
(Are ions in the soil blocking the uptake of needed substances?) What is
the mechanism of resistance that was evolving? If it involved the blocking
of uptake of lead and other metals, that implies that other, non-adapted
plants DO take them up.
Can any one comment on this aspect of the issue?
Martin M. Meiss
2011/4/15 Judy Che-Castaldo <[email protected]>
Hi Ben,
In general you are unlikely to find lead in the shoots of plants, because
it
is not very soluble and most plants exclude heavy metals. The edible
plants
that may have Pb would likely be leafy vegetables (grown close to the
ground) and root vegetables (as mentioned earlier) because of the
associated
soil particles containing Pb.
There are some plants that uptake heavy metals into their shoots but few
for
Pb, and even those may only do so under rare circumstances (such as
phosphorous deficiency - Chaney 2007 J. Environ. Qual. 36:1429–1443). If
you are interested in other contaminants you can look into the metal
hyperaccumulation literature. Many of these plants are in the mustard
family but probably are not normally eaten.
best,
Judy
Judy Che-Castaldo
BEES program, Biology Dept.
University of Maryland
(301)351-8290
http://www.life.umd.edu/grad/BEES/students/che.html
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