Quote Originally Posted by BigDave View Post
Why, I wonder, would the borate pool product providers label thier product dosage (from the EPA report) at ten times that rate? Is the idea to use boron as the primary sanitizer?
I don't know where you are getting the "ten times that rate" -- are you implying that the product dosages are 500 ppm which is 10x 50 ppm? That isn't true. Remember that the borates measurement is in ppm Boron with a molecular weight of 10.812 g/mole and not in ppm Boric Acid at 61.83 g/mole or sodium tetraborate pentahydrate at 291.29 g/mole.

As for the tablespoon limit, that includes a safety factor of 100 since no studies were done on humans, only on other animals (rats, dots, etc.) and as you point out it's a chronic limit for regular drinking since the body does process boron and in fact it's an essential nutrient. You just don't want to overwhelm your body with it. In practice, I think the borates at 50 ppm are safe for humans in pools and even for children who may occasionally gulp some water. It would be more of a concern for dogs drinking lots of water every day from the pool -- mostly getting close to the edge of first symptoms (shrunken testicles in male dogs).