Subject: Re: toxicity of pesticdes
From: moholt@gardens.com (Carol Moholt)
Organization: The Bay Area Gardener
Date: Wed, 10 Sep 1997 08:12:44 -0700
Message-ID: <MOD$970910.27073@rec.gardens.ecosystems>
References: <MOD$970902.18871@rec.gardens.ecosystems>


Bill and Troy were talking about the various LD (lethal dose) ratings
which measure immediate toxicity levels in test populations. While they
are one method to use in determining whether to use a particular product
or not, a more complete method is doing a Risk Assessment. In Risk
Assessment, one considers four factors, only one of which refers to the
immediate toxicity measured by the LD tests:

In making a risk assessment to determine whether or not to use a
pesticide, take the following factors into account:

1. Human safety. Toxicity categories measure immediate dangers to the
person applying the pesticide and others at the site. They do not,
however, measure long-term effects of repeated application.
2. Off-site movement. Pesticides may be carried beyond their initial site
of application, through air or water, and affect other populations. For
example, it may kill fish if finds its way into streams, rivers, lakes, or
ponds.
3. Soil contamination. Some pesticides have little effect on the soil at
the time of application, others may persist for long periods.
4. Phytoxicity. Referring to the poisoning of a plant, this assessment
considers the tradeoff between eliminating a pest and harming a plant.
5. Effectiveness. Some pesticides solve a problem with one application.
They may rank higher in toxicity or other factors than other pesticide
choices; yet since they only are applied one time, rather than several,
they may be the most effective choice for the situation.

While most of us on this group don't use any to few pesticides, I think
it's important for us to understand as much as possible about them. For
example, I get concerned about the widespread use of Pyrethrins, whose
toxicity levels are so low that many consider them a "safe" pesticide.
Yet, I see how consumers use this product almost as if it were water and
are very cavalier in washing it into drains (where it can get to fish) or
even around water sources where a lizard or snake may drink and be
poisoned). Weighing the five risk assessment factors against a
Pryethrin-based product-- rather than just the toxicity levels -- helps
one realize that the use of any pesticide is complex in terms of overall
effect.

Carol Moholt