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Date: | Sun, 22 Apr 2012 07:31:55 -0600 |
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> If a pesticide has a long half life in the soil, then that means that it
> can't be leaching into the water. Conversely, if it is leaching into the
> water, then that means that it is not leaving residue in the soil. Peter,
> you can't have it both ways.
I don't see how that follows.
The half life in soil is the half life in soil and has to do with
breakdown and has nothing AFAIK to do with leaching. If a chemical
leaches out, it has left the soil in question, but is still intact.
That queers that particular measurement.
The half life in soil reflects (or should) only the breakdown of the
chemical in some imaginary "typical" soil when it actually stays there.
Often these measurements conveniently omit mention of the metabolites
which sometimes (not always by any means) be more destructive than the
original chemical.
Half life is a concept which is applied to many different processes
somewhat indiscriminately. Some decay rates are dependent on
concentrations or the development of biological populations that feed on
the chemical. The Deepwater Horizon incident demonstrated that nature
is complex and has a unpredictable response curve that even the experts
cannot explain -- or predict.
Moreover, these sorts of numbers that are bandied around without
qualifying statements are usually averages made up from composites and
listeners (and often those quoting them) have no idea what the scatter
is in the underlying data -- or how outliers were treated.
As always, these dumbed-down numbers do more to obfuscate the real
concerns than illuminate the landscape. As beekeepers, we are very
interested in the exceptions. By virtue? of the process, exceptions or
anomalies are ignored or discounted.
Leaching is a special case. If leaching takes place, then that process
will remove the chemical from the soil, but not affect the half-life,
just as washing a nuclear waste from a Japanese power plant into the sea
and the soil does not affect the half life of those byproducts, merely
to location.
Stan has dealt with question of the the real-world hall life in water.
but again, I would question the presentation of any one number as being
particularly meaningful.
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