The original post may be related to the "eat the weeds" movement, one I have
long considered a good idea while suffering no illusions that it will have
any real impact upon the weed "problem."
I eat weeds because I prefer them to most of their highly developed or CMO'd
relatives. The weeds often, in addition to being more tasty, contain more
nutrition than their cultivated cousins. Chenopodium album, for example, a
common roadside weed, is one of my favorites. It is an "accumulator" (what
plant isn't), containing a lot of iron (iron is a vital nutrient; it also is
a poison--dosage is important). I do, however, pay attention to the
substrate upon which they are growing. I prefer hillsides to stream bottoms
unless I know the watershed is pretty free of contamination. Stream bottoms,
especially those into which contaminants, often in the form of raw sewage
drain, often contain the "best" crops of the lushest weeds. In my ignorance
of the specifics, I rely upon the precautionary principle, "the solution to
pollution is dilution," and a smidgen of knowledge (which we all know can
often get one into more trouble than ignorance), and perhaps some myths I
have unwittingly adsorbed (or worse, absorbed) along the way. I avoid
roadsides and vacant lots of unknown history too. I trust my own ignorance
more than that of agribusiness, but that's far from perfect.
WT
----- Original Message -----
From: "malcolm McCallum" <[email protected]>
To: <[email protected]>
Sent: Saturday, April 16, 2011 7:10 AM
Subject: Re: [ECOLOG-L] where do edible plants retain lead and other
contaminants?
Wayne brings up a good point.
The bioavailability of toxic compounds, including metals is affected
by many things among which pH can be one.
In fact, the issue of TMDLs in the clean water act is based on problem
that each stream has its own water chemistry and organic load. This
causes us to require specific total maximum daily loads (TMDLs) of
each compound for each stream (or portions thereof). TMDLs were
supposed to be completed for surface waters in most states a long time
ago, unfortunately the process is not done everywhere!
Malcolm
On Fri, Apr 15, 2011 at 9:03 PM, Wayne Tyson <[email protected]> wrote:
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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