From: klier@iscsvax.uni.edu
Newsgroups: rec.gardens
Subject: Re: glyphosate and composting
Date: 7 Apr 92 18:16:02 -0500
Organization: University of Northern Iowa

In Ecology Center Fund <ecologycntr@igc.org> writes:
> 
> The guy didn't know what he was talking about, but it's not his fault, really.
> Though its true that many garden chemicals will break down in a hot compost
> pile, the question is, what do they break down INTO?  In general, only the
> chemicals' manufacturers know even the littlest bit about potential breakdown 
> products of most commercial pesticides, and they aren't telling.
> 
> Much as I admire Kay Klier's wealth of knowledge, for instance, I don't
> share her acceptance of glyphosate (Roundup) primarily for this reason.  Its
> sold as a product that "breaks down on contact with soil", but i have never,
> in a decade of trying, found any info on its breakdown products in soil and
> their potential effects.  (Hint: breakdown don't mean the stuff gets less toxic.If table salt broke down, you'd get a toxic metal which burst into flames on
> contact with air, and a poison gas once used in chemical warfare . ;))

Hi, Chris.  No, it's not a great wealth of knowledge, just an idea of how
to dig for it...     And I'm certainly not a great proponent of pesticides;
but I think that they have their place when _thoughtfully_ and _carefully_
used in selected situations.

Rhizobium (yes, the nitrogen fixing bacterial genus) cleaves glyphosate
into methylglycine and inorganic phosphate.  Methylglycine can be easily
metabolized to carbon dioxide and glycine, the amino acid.  See Liu, CM, et
al.  1991.  Degradation of the herbicide glyphosate by members of the family
Rhizobiaceae.  Appl. & Environmental Microbiol. 57(6): 1799-1804.

The findings in this study correspond with my recollections of earlier
studies with mixed soil bacterial populations and with Pseudomonas, a
genus of bacteria common in soils.    

Glyphosate seems to block the enzyme 5-enolpyruvateshikimate-3-phosphate
synthase.  My general biochem is kind of rusty, but I think this enzyme is
confined to photosynthetic organisms.

OK, that's _pure_ glyphosate, not the commercial preparations.  And that's
where we run into trouble.  Manufacturers add all sorts of stuff to herbicide
preparations, including spreaders, stickers and surfactants (usually 
detergents), various "safeners", buffering agents, and just about everything
including the kitchen sink.  These are considered "inert ingredients" and
do not appear on the labels.  Trying to get information about these
inert ingredients from the manufacturers is just about impossible.
IMHO, ***EVERY*** ingredient in an herbicide should appear on the label.
Manufacturers don't agree with me, and it will take an act of Congress
to put that complete labeling into law.

A couple of other articles of potential interest:
Stenstrom, J. et al.  1991?  Kinetics and effects of moisture content and 
pre-incubation on the decomposition of 14-C labeled herbicides in soil.
Toxicity Assessment  5:15-29

Feng, et al., 1990.  Fate of glyphosate in a Canadian forest watershed...
J Ag. & Food Chemisty 38:1118-1125.

Kay Klier   Biology Dept  UNI

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