[permaculture] Heavy metal issues

Mark mpludwig at facstaff.wisc.edu
Thu Sep 19 11:04:14 EDT 2002


At 09:33 AM 9/19/02 -0400, you wrote:
>Good day:)
>
>In a message dated 9/18/02 4:35:09 AM, georg at websuxxess.com writes:
>
><< mushrooms are known to store heavy metals, so if these
>
>are present in the water hyazint growing medium, they will end up on the
>
>consumers plate? >>
>
>Glad you brought this up Georg. I've always wondered about how utilization of
>plants that are known to store heavy metals affects compost, food grown from
>that compose etc.
>
>Persons who advocate such use often offer little scientific proof. The best
>hope is that in the process of breaking these things down somehow the heavy
>metals are either converted to a harmless form or are somehow used up.
>
>As you can see I don't have a clue about the actual process:)  Frank

This is certainly an interesting topic, I'll try to dredge up my soil 
pollution class from 10 years ago...

On the topic of plants accumulating heavy metals, they are definitely still 
present in the plant, the key questions become what form they are in (how 
bio available they are) and what to do to dispose of the metals.  I would 
guess that in most cases the bio availability is going to be quite high in 
plants, thats certainly the case with other minerals.  As to what to do 
with them, as un-PC as it sounds the landfill may be the best bet for Pb, 
Hg, Cd and other metals which have no value for man, beast or plant.  Zn, 
Cu, Cr and other metals that are of value as trace mineral could be safely 
spread around from areas of over concentration to areas where they could 
have value.
Another interesting fact is that many of these minerals bind fairly tightly 
to soils or may be microbially converted to less available forms over 
time.  It may make sense in some situations to simply cover polluted soils 
with a membrane for a few months/years in order to limit leaching and allow 
these conversions to take place rather than extracting the metals and 
moving the problem elsewhere.


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Mark P. Ludwig
Poultry Research Lab
University of Wisconsin -Madison
608-262-1730 WK
608-846-7125 HM




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