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Re: pesticide and herbicide persistence in soils
On Thu, 7 Oct 1999, Steve Pushak wrote:
> I'm curious about the possibility of the persistence of insecticide and
> herbicides in garden soil which we might be collecting and using for
> growing aquatic plants. Some of these toxins are highly poisonous to
> fish. How long can they remain toxic? Do they break down rapidly after a
> few months? I have fruit trees in my back yard and I'm curious if the
> previous owner used insecticides like Malathion. Does anybody know how
> persistent it is?
Modern pesticides and herbicides are made to degrade fairly quickly in the
soil to avoid problems with persistence on or in foods or as contaminants
in soil and ground water. The actual rate of degradation depends on
your soil but I think that usually they'll have a half life of no more
than a few weeks. This time increases under acidic conditions and
decreases under alkaline conditions.
As I recall organic gardener's usually wait three years after chemical
treatments before they consider soil to be flushed of pesticides and
herbicides and started back to natural soil flora and fauna. I think that
to be safe it would be a good idea to wait at least that long before using
a previously treated soil in an aquarium.