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Subject: Re: Round-Up
From: wtmorgan@pilot.msu.edu (Bill Morgan)
Organization: MSU
Date: Sat, 14 Oct 00 16:06:27
Message-ID: <MOD$001014.13004@rec.gardens.ecosystems>
References: <MOD$001014.7524@rec.gardens.ecosystems>



In article <MOD$001014.7524@rec.gardens.ecosystems>, "Ryan Lenz"
wrote:

> Anyway, my parents claim that Round Up and Crossbow are harmless after a few
> days, that they break down. Is there any merit to this claim? I simply
> can't imagine it.
Round up is Glyphosate, Crossbow is Triclopyr.

Glyphosate has a reported half life in the soil of anywhere 1-174 days, and
the average half-life is thought to be on the order of 47 days. It adsorbs
to the soil particles very rapidly and strongly, meaning that there is
little leaching, and run-off is generally limited to that material which is
bound to soil colloids which are in the runoff. Bacterial action is
responsible for the breakdown, and factors such as volitalization and
exposure to UV play extremely minor roles in the breakdown process. In
water, it also binds quickly to suspended organic and mineral matter, and
the half-life in pond water may range from 12 days to 10 weeks.

Triclopyr has a half-life in the soil of 30-90 days with an average of
about 46 days. Some of the breakdown products are also of concern, and have
half-lives of 8 to 279 days, and in most cases, less than 90 days. The
half-life in aquatic environments is less than a day.

This information comes from EXTOXNET. You can find a lot more there,
including information on acute and chronic toxicity, carcinogenic,
teratogenic, mutagenic and reproductive effects; effects on other
organisms, etc. etc.

The basic URL is:

http://ace.orst.edu/info/extoxnet/

The URL for the Pesticide Information Profiles PIPs) is:

http://ace.ace.orst.edu/info/extoxnet/pips/ghindex.html

The specific PIP for Glyphosate is:

http://ace.ace.orst.edu/info/extoxnet/pips/glyphosa.htm

The PIP for Triclopyr is:

http://ace.orst.edu/cgi-bin/mfs/01/pips/triclopy.htm

A few caveats here:

1) None of this discussion includes the inactive ingredients found in a
commercial pesticide formulation. There's the carrier (usually water in
liquid formulations, but sometimes including organic chemicals),
surfactants, agents to keep the stuff flowing freely, to keep it in
suspension, and to increase its activity.

2) The concept of half-life is precise for radioactive isotopes, but pretty
fuzzy for chemical breakdown. Temperature, humidity, soil type, and all
sorts of other factors can greatly speed or slow the process.

3) No set of information you can get on these topics will ever be complete.
I suppose that's true of most things in life...

4) When it comes to human effects (and really other organisms, too), the
reaction of one individual can be vastly different from that of another.
Averages are averages, after all. A dose that one individual shakes off
easily could be fatal to another. This of course, is how insects have
managed to evolve resistance to many pesticides: selection pressure for
resistance can be very strong. Plants have a tougher time evolving
pesticide resistance, but it can and does happen.

5) No pesticide should be used carelessly. This applies to insecticidal
soap as much as it does to Methyl Parathion, as much to Pyrethrin as to
Sevin. You can hurt yourself with any of these chemicals, though the
potential for that is much greater with some than with others. It's just
good practice to treat any of these things with caution. At the very least,
most are irritants of eyes and respiratory passages. While that might not
be fatal, it can certainly be unpleasant.

6) In many cases, there are alternatives to pesticide use. Often, these
give results equival to or better than those obtained by using pesticides.
The downside is usually that these methods are a lot more work. You imply
that your folks are applying herbicides to bare patches of gravel. Perhaps
if you hand-weeded the area, they wouldn't feel that they need to. Other
alternatives might include burning the weeds out (there are even special
devices for this), or putting a landscape cloth under the gravel (unless
it's a driveway, in which case it probably wouldn't last very long). Some
people spray vinegar (or is it a salt-vinegar mix?) on weeds, and claim
good results. Of course, then we're back to using a pesticide, albeit a
fairly benign one. Still, be careful with that around the eyes...

One final note. You ask if your parents' claim has any Merit. Merit is a
trade name for Bromoxynil, which is an herbicide on the "Restricted Use
Pesticide" (RUP) list. That means only certified applicators can use it. I
certainly hope your folks aren't spraying Merit all over the place....
;_)

Regards,
Bill

--
Bill Morgan
"Those who do not learn the lessons of science fiction are condemned to
live them."

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