Hi Steve,
First, you've been worried about Headline, but I hear talk of other
products available to fight the rust, Quadris and Bravo, in
particular. I haven't checked the labels on them. Do you share the
same concerns regarding these products?
I am not worried about Headline (pyraclostrobin) or the other
fungicides. I jumped into the discussion because I felt that
misleading statements were being made about the toxicity of these
fungicides.
Second, I've been told by an individual in a large agrichemical
company who deals with EPA registrations that exposure rates to
such products are based on the rate at which there is a first
observed effect.
Fungicide registration has always been difficult due to the extremely
*LOW* acute mammalian toxicity of most fungicides. Traditionally,
chronic feeding studies are performed at the "No Observed Effect Level"
(NOEL). This is the highest dose at which no acute effects are
observed. With many fungicides the NOEL is
astronomically high (the acute toxicity is low). So they sometimes jam
multigram quantities down the rat's throat with a tube. At these
levels, all sort of frightening teratogenic and carcinogenic effects
sometimes occur, that may not be relevant. Perversely, some dreadfully
toxic insecticides used to have no problem getting registered because
the NOEL is very low. Such insecticides are generally not carcinogenic
or teratogenic. The rats can't get cancer or birth defects if they die
in a few minutes.
The EPA has gotten smarter than they used to be, and now chemicals that
are obviously safer alternative are moved through the system
expeditiously (it still takes years of work and millions of dollars).
There are a great deal of toxicological data on the registered
strobilurins (as there are on all registered pesticides). If people
are interested in how the EPA deals with these things they should
examine the summaries of pyraclostrobin toxicity as an example.
http://frwebgate.access.gpo.gov/cgi-bin/getdoc.cgi?dbname=2004_register&docid=fr29oc04-22
The only reason I am singling out pyraclostrobin is that Joe brought it
up.
Then, automatically EPA reduces the allowed rate by a factor of ten.
If the product will end up on food, it is reduced by another factor
of ten, and if the product is applied to food that would potentially
be eaten by children, it is reduced again by a factor of ten.
Therefore, if the product is used on food that children will be
exposed to, the allowable rate is one-thousandth of that at which
any adverse effect is observed. Is that accurate? Does it agree
with your knowledge of the process?
I think that is basically right, but I am not up-to-date on the
details. Maybe we can find an authoritative description of the
registration process to post here.
If so, what is the real relevance of statements suggesting that a
product is "linked to cancer"?
As far as I can tell from reading data on the web, the strobilurins are
actually NOT "linked to cancer" (some competing fungicides are) even in
the very conservative testing regime required by the EPA.
Dale
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