LD50 is one measure. For the consumer, half life and non-acute toxicity is probably a better measure to use.

The organophosphate (e.g., methyl chlorpyrifos, dimethoate, methidathion and methyl parathion) pesticides used in conventional agriculture have half lives of a little less than a week to two weeks on the surface (and a half life of years in water and soil), while pyrethrins have a half life of hours in sunlight and 2 weeks in soil.

Both organophosphates and pyrethrins have toxic effects on mammals, but one is less likely to be present on purchased produce since, at least, four half lives (97% degraded) will have passed for pyrethrins, in a single day.

In the extreme, organochlorines (e.g., aldrin, chlordane, dieldrin and dicofol [OK, DDT and such are in this class too]) were spayed on conventional crops. These have half lives measured in years (on the surface), and their residues are found, in the environment, decades after specific compound bans.

Finally, US grown rice/citrus contains arsenic (there is no safe limit established for inorganic arsenic) because of conventional pesticides containing arsenic being sprayed on cotton fields (California rice/citrus is generally safer than that grown in Southern states).

All this said, I believe (opinion) that USDA organic allowing the use of so many pesticides was a give away to big ag, so they could participate in the "organic craze" without substantially changing their production practices. Personally, I buy pesticide free vs. organic when available.

LD50 (acute toxicity) does not necessarily correlate with harmful health effects from chronic exposure. Can you cite studies that demonstrate harms from exposure at the levels used in organic farming?

We are talking about risks to people working in the fields. Every time a farmer applies anything to a field, he will have to put on safety gear, measure out an amount, mix it with water, load it into the sprayer, drive the tractor around, and then clean up afterwards. When you are working with enough of a chemical to kill a hundred people, every single one of these steps carries the risk of an acute exposure. Dead is dead, regardless of how it happens. Don't dismiss it.

edit: From source [1]:

> Chronic toxicity: Vineyard sprayers experienced liver disease after 3 to 15 years of exposure to copper sulfate solution in Bordeaux mixture [8]. Long term effects are more likely in individuals with Wilson's disease, a condition which causes excessive absorption and storage of copper [25]. Chronic exposure to low levels of copper can lead to anemia [8]

So yeah, its still bad for you.

Perhaps I generalized a bit too much (I suppose I should not have commented when I was dead tired...) However, the USDA does in fact allow non-prohibited chemicals to be used on USDA certified organic produce.

USDA National Organic Program: http://goo.gl/OUCAXM USDA National List of Allowed and Prohibited Substances: http://goo.gl/YXLUJ5