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Well-known member
Jul 17, 2006
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South Georgia
Am taking a refresher course in pesticides this week and with spray season nearly on us I thought I would share some of my notes with you. I hope this information will be some useful to someone.

Synthetic does not mean toxic or poisonous.
Natural does not mean it is safe or low risk.
Chemicals must be evaluated in their biological context of behaviour in organisms. It is the mode of action not the source which is the concern.

Pesticides and other chemicals are ranked by a LD50 which means the amount in milligrams it would take to kill 50% of population.
Category ----------Signal Word -------mg/kg ------------Lethal oral dose
I________________Danger__________ <50____________Taste - tsp
II_______________Warning_________ 50 – 100 ________Tsp - oz
III_______________Caution _________500-5000________Oz - pt
IV______________ Caution__________ >5000__________>pt

Poison – In the USA, any chemical with a LD50 of less than 50 is defined as poison. Label must have the signal word "Danger" and the word "Poison" and must also display the skull and crossbones. Remember – lower the number the greater the danger. So remember, when you are applying herbicides on your weeds you are NOT spraying poison. Be careful with this term and correct anyone who is using it incorrectly so we don't lose these tools due to misinformation and bad PR.

So how dangerous are the things we spray. Here is a little perspective.

Gasoline has an LD50 of 150 mg/kg.
Caffeine has an LD50 of 192 mg/kg
Sevin has an LD50 of 302 mg/kg
Aspirin has an LD50 of 1240 mg/kg
2,4-D has an LD50 of 1250 mg/kg
Garlon 4 has an LD50 of 1419 mg/kg
Baking Soda has an LD50 of 3500 mg/kg
Table Salt has an LD50 of 3000 mg/kg
Tordon has an LD50 of 3000-5000 mg/kg
Roundup has an LD50 of >5000 mg/kg
Sugar has an LD50 of 30,000 mg/kg
Ethanol has an LD50 of 13,700 mg/kg
Water has an LD50 of 80,000 mg/kg

Thinking in ounces, lethal doses of some are:

Caffeine 0.21
Sevin 2.0
Aspirin 3.5
2,4– D 3.7
Garlon 7.0
Tordon 8.0
Table Salt 9.0
Roundup 15.0
Velpar L 20.0

If you dilute a gallon of active chemical in 1 gallon of water you have just reduced the toxicity by 50%.
If you add a gallon of pesticide in 20 gallons of water it is now 95% less toxic.

What I got out of this is that most of the pesticides we use are pretty safe even though they may not be "organic" or "natural". I seriously doubt I'll be drinking a pint of Roundup anytime soon. Of course, I guess, it would take about 2.5 pints since most solutions are only made on a 46% rate. Anyway, these little tidbits tell me we should use the utmost care when mixing and handling the concentrated forms of pesticides cause this is where the true danger lies. So be careful. Use common sense and I hope this was helpful to someone.

And if any of you are now too scared to reach for the salt shaker or brew up some coffee I'll be glad to sell you some a Tyvek Jumpsuit, a respirator and some goggles. ;-) (sorry Macon, just trying to make a buck) :lol2:
My Mrs walked on some grass that had been sprayed a week earlier with roundup.
That night she had an allergic reaction which was bad but not life threatening and was told to stay away from roundup.

Dont know how that fits in with this . Obviously as with all chemicals some people react and some dont.
I dont see any allowance for this just a bunch of absolutes .
That tells me it is likely bunkum
Sorry Joe
How can you be so sure it was the roundup that did this? Never heard of anything like this especially given that roundup was orginally intended for use in the human body. I don't imagine it could have been anything else that caused a reaction.
Thanks for summing that up. What is the Lethal Dose tested on? I took a class this winter to get the RUP lisence, is that the class you are taking?
hayray":2ekztjfq said:
Thanks for summing that up. What is the Lethal Dose tested on? I took a class this winter to get the RUP lisence, is that the class you are taking?

Not sure exactly but it sounded like the internal LD is tested on rats and the external dose is done on rabbits.

I was taking this course to fulfill the requirements for two of my licenses. Didn't really want to go cause some of these things get repetitive but the chance to kill two birds with one stone doesn't happen very often. I enjoyed this course cause we had some really good professors. Unfortunately, they didn't address tytower's concerns about allergies. Never heard of anything like this since roundup breaks down so quickly. But then again, like he said, there are no absolutes. For instance, my wife can't cut okra cause she will break out all over. But that is an allergic reaction and not a poisonous reaction.