Using Borax to kill fleas?

[chem geek]

Borax in water becomes Boric Acid plus Sodium Hydroxide and raises the pH. So ingesting Borax would be somewhat similar to ingesting Boric Acid as far as the toxicity related to Boric Acid is concerned, though the pH would be alkaline instead of acidic.

This link is to an EPA report on the toxicity of Boron compounds. The dog study had some disputes in that even some dogs in the control group had some effects, but generally the No Observed Adverse Effect Level (NOAEL) was on the order of 9 mg B/kg-day and the Lowest Observed Adverse Effect Level (LOAEL) was 13.3 in the newer study. A 9 kg dog (around 20 pounds) could consume 81 mg Boron per day with no observed effect and that is equivalent to 463 mg Boric Acid per day and is roughly 0.32 milliliters in volume of solid substance (powder might be about double this volume) and is about 1/15th of a teaspoon.

If you disperse the Boric Acid as a powder on a rug, then the dog would have to be licking it up a lot to get even a small amount. I suspect it doesn't taste good (think the tart taste from the acidity of lemon juice). Even if the dog were to consume this Boric Acid, the main effect is testicular atrophy and this was only after daily consumption over many months. So the risk is quite low, in my opinion, especially for a one-week exposure. This is a little different than dogs drinking pool water at 50 mg/liter (and that's mg/l Boron or about 285 mg/l Boric Acid) every day. There was another reference that I can't find right now that said there was a lower spleen to body weight ratio in dogs at a 0.44 mg/kg/day so that's why I had previously cautioned (i.e. in this post) having dogs drink from a pool with borates every day.

Richard