From: Oz <Oz@upthorpe.demon.co.uk>
Newsgroups: misc.rural,rec.gardens.edible,rec.gardens,sci.agriculture
Subject: Re: Septic Gardening
Date: Wed, 9 Sep 1998 20:54:57 +0100

In article <35F6CD78.1CCE9138@postoffice.swbell.net>, Tyler Hopper
<thopper@postoffice.swbell.net> writes
>Oz wrote:
>>
>> In article <35EFF497.6912@prodigy.net>, Prof. Zooks <PZOOKS@prodigy.net>
>> writes
>>
>> >Zooks must respectfully disagree... Plant roots can go very deep.
>> >Lettuce roots may go down as much as 3 feet, and plants WILL pull up
>> >anything they find.
>>
>> No they won't. Roots normally live in soil which is known to carry
>> pathogens and they don't take any of them up. Smaller molecules can be
>> taken up but probably the only ones that would give even minscule
>
>Really? Then am I to assume that the talk recently of using sunflowers,
>poplars, etc. to clean up toxic waste dumps is myth? One plant was used
>to help to cleanup at Chernobyl though that isn't an issue here.

They will NOT pull up anything they can find, quite the contrary in
fact. With the exception of some small or specially designed molecules
they screen off everything else. So you will get elements (as simple
salts) absorbed and these may comprise some heavy metals (although these
are typically strongly bound to soil organic matter) but with the
exception of a few elements (and their close relations) that are
actively transported most of these have some trouble entering plants,
after all plants don't want to be poisoned either.

So plants can be used to remove some trace heavy metal contaminants from
soil (too much and the plants get killed) because the heavy metals
typically don't move in the soil and so about the only way to reduce the
level is to grow plants and remove them and their traces of heavy
metals. Don't think huge amounts are removed this way, because they
aren't. It takes very many years to reduce the level even by small
amounts, but the area sure looks better.

Now, as you presumably already know, the typical worrysome radioactive
problems at Cherobyl were caesium, radium, iodine (mostly decayed by
now), plutonium and a few others that I forget just now. Caesium is
preferentially taken up and used in lieu potassium by plants so it's a
perfect element for bioremoval. Radium is a group two and I would expect
it to be preferentially taken up in an acid soil (I think the area round
Cherobyl is mostly acid peat) with any calcium. No idea how well
plutonium is taken up, it's one of the rare earth's group and they are a
bunch of wierdoes.

Note here we are talking elements and not dirty great bacteria. No self
respecting (or even one who wishes to live long) plant is going to let
bacteria inside, indeed plants are so good at dealing with bacteria
there are only a tiny handful of bacterial plant diseases (like pea wilt
:-((( ). It is fortunate that plant diseases are typically fungi which
in general don't attack animals, and animal diseases typically bacteria
that don't attack plants. So animal excreta full of bacteria is good
food for plants because they never let the bugs inside and plant foods
are good for animals because the fungi cannot attack them. Nature is
neat, n'est-pas?

If in doubt about heavy metals it's not that expensive to take advice
and have produce tested, and you should only need to do it once. It's
either OK or not and that shouldn't change unless you apply heavy metals
to the soil yourself.

--
Oz