QUESTION:

What happens when a person comes in contact with a pesticide after it has dried?

ANSWER:

This speaks to a couple of issues Dominick, and these include the affinity pesticide molecules have for a surface and the relative toxicity of that dried residue. As we know, nearly all pesticide Labels for products that are mixed with water and applied wet as a spray or fog will recommend keeping people and pets off of the treated surface "until the spray has dried". This is an important consideration for treatments such as fleas or bed bugs where large areas of carpets or other interior surfaces may be treated. It often is a standard recommendation from PMP's that the occupants stay out for 2 hours, or 4 hours, but the proper protocol would be to stay out until the floor or walls or beds are DRY, and this could very well be much longer than 4 hours depending on the weather and time of year.

From what I have learned over many years, pesticide molecules (the actual active ingredient) tends to cling or bind to the surface it is applied to. This may not be quite the case with particles like microencapsulated insecticides, but for other kinds fo sprays once the water has evaporated and the surface is dry it is very difficult to remove any significant amount of the active ingredient by casually contacting that surface. If someone were to lick the surface then sure, he could be re-dissolving it and removing it, but let's hope that is not a common practice to lick carpets. Still, whenever we are able to apply an insecticide directly into cracks, crevices, and voids for the ideal control of the pest (bed bugs, roaches, etc.) that not only enhances the control effort but also hides the active ingredient from any human or animal contact.

My comparison, which hopefully is relatively accurate, would be like using a can of spray paint. While you are spraying the paint it is airborne and can be inhaled, and immediately after spraying it on a surface it is wet and could be touched and easily taken onto the skin. Once the paint dries you cannot remove it by touching the surface. This could be similar to spraying a pesticide - airborne mists could be inhaled and while still wet it easily gets onto the skin, but once dried it adheres to the surface quite tightly.

The second consideration is that of LD-50 and how much of that diluted spray material would have to be ingested or absorbed to realistically cause a health concern, and this would be a very high amount. I did the math once and hope it was accurate, but based on an LD-50 of 4000 mg/kg for permethrin insecticide, and this should be the LD-50 for the pure active ingredient, the amount of diluted permethrin at a 1% concentration (termite control) that would have to be swallowed by a 175 pound human to (presumably) cause his death would be a whopping 10 gallons. Even if he drank the concentrate liquid of 37% active ingredient it would take a full quart of that concentrate to reach the presumed LD-50 for that 175 lb human. Clearly this would be a deliberate effort on the part of that idiot to poison himself.

I believe that the vast majority of the pesticide products in use by our industry today have a tremendous safety factor once they are applied in diluted form and then dry. This is even a misconception that the internet spreads wildly with respect to "nontoxic" (their words, not mine) substances like boric acid. Boric acid dust is often a 98% concentrate, and even though the LD-50 of the pure boric acid is about equal to that of the pyrethroids the dust is not diluted for use, making the end use material far more hazardous than the end use water diluted insecticides like permethrin.

Bottom line - be sure to use the product as the Label requires, keep people and pets off the treated surface until it is dry, and there should be no health concerns or risk to the people.

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