Borates Experience

[chem geek]

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).

[BigDave]

I guess I misunderstand - highly likely.

As I understand, the last paragraph on page 9 of the EPA report describes product labeling that recommends "4.5 lb ai per 1,000 gallons (540 mg/L pool water concentration), 4 lb ai per 1,000 gallons (480 mg/L pool water concentration)" which I took to mean 540ppm and 480ppm or about 500ppm Boron. I assumed that this value was Boron as it is used to calculate Margin of Exposure and is compared to other sources of boron in the environment.

The report goes on to say (page 14) that the "Sodium borate applications to swimming pools and spas resulted in unacceptable risks for some of the higher boron concentrations in pool water (e.g., concentration in water of 480 mg/L and 540 mg/L); however, the lower concentration of 240 mg/L did not result in risks of concern. Therefore, the end-use product labels for swimming pool products must be revised to delete application rates above 240 mg/L. Registrants have agreed to amend their labels by removing the higher application rates to Agency acceptable levels."

It wasn't clear to me why the label dosage would be so high when algae would be effectively clobbered at a much lower level.

I apologize for my bad chemistry, I thought I understood the reports - Doh!

[chem geek]

Don't worry about making the mistake. It took waterbear and I a while to figure out that the units were ppm Boron. It took me a year before I figured out that chlorine was measured in ppm Cl2 units. These things aren't obvious until you see them defined somewhere.

4.5 pounds is 2.041 kilograms and 1000 gallons is 3785 liters so that's about 540 mg/L of sodium tetraborate pentahydrate which is 291.29 g/mole. There are four boron that result from this compound with each at 10.812 g/mole so this amount of product produces 80 mg/L Boron or what we call Borates.

I think the EPA report was saying that some products recommended dosages that were too high, but that's not the example given above. As for why some products used such high dosages, one reason is that not all algae are killed at 50 or even 80 ppm borates though most algae are inhibited at that level. Another reason is that higher borates levels provide greater pH buffering.

Current products such as ProTeam Supreme use 2 pounds per 1000 gallons for around 35 ppm Borates which is in their 30-50 recommended range.

[BigDave]

So...
If I'm not still dopey; (I probably am)
Tetra(4)borate(Borax) contributes 4 boron with each sodium tetraborate pentahydrate molecule. Borax "weighs" 291.29 compared to 10.812 for each of the four boron in each of the Borax molecules added to solution. Therefore: every 291.26 mass units of borax adds 43.248 mass units of boron to the mix.
So...
540 mg/l of borax contributes (540/291.29*4*10.812)=80.174122mg/l boron to the solution you throw it in?
So...
240 mg/l of borax contributes (240/291.29*4*10.812)=35.6329431/l boron to the solution you throw it in?
and...
mg/l is ppm
So...
50 ppm boron is somewhere between the FDA's "unacceptable" level of 80ppm and thier "acceptable" level of 35ppm?

I'm guessing that I'm still miserably (and pointlessly) confused.
But...In my own defense...I do have a desire to understand at least the basics of the water I soak my family in. (in wich I soak my family?)

[chem geek]

You got the calculations right until you got to the EPA (not FDA) interpretation of acceptable vs. unacceptable levels and then it looks like you found a flaw in my assumptions. I assumed that the pool doses that exceeded the margin of exposure limits for small children were 360 ppm from Table 5 in the EPA report and note that 540*65/100 = 351, 480*74/100 = 355, 240*150/100 = 360, 5.4*5600/100 = 302 so I just used 360 ppm as the approximate limit and again this is with a margin-of-exposure of 100. Or put another way, it is at around 360 ppm Boron where the margin-of-exposure is 100 which is what EPA defines as the limit of what is acceptable vs. unacceptable.

I think I misunderstood what was meant in the table by "chemical concentration in water (mg/L)". I assumed this did not mean product concentration, but rather boron concentration. This is certainly confusing because in the text when referring to dosages of product they refer to "pool water concentration" in terms of mg/L of product (i.e. sodium tetraborate pentahydrate). The only significant hint that Table 5 may use a different measurement is the sentence before the table: "Exposure to adult and older child swimmers did not result in risks which exceed the LOC; however the higher boron concentrations in pool and spa water resulted in risks for children 7 to 10 years of age which do exceed the LOC", but that was an incorrect assumption on my part.

The "Adjusted ADD" in mg/kg/day is the effective exposure to boron and the calculation of Margin of Exposure (MOE) in that table uses 8.8 mg/kg/day Boron as the No Observed Adverse Effect (NOAE) limit as you can see from 0.134*65 = 8.71, 0.119*74 = 8.81, 0.059*150 = 8.85, 0.0016*5600 = 8.96. The 8.8 mg/kg/day is the NOAEL from the 2-year dog study and confirmed by other studies as described on page 4 of the report.

The interpretation of the "acceptable" vs. "unacceptable" amounts all depends on their assumption for how much someone drinks and the weight of the child. Let's look at 540/0.134 = 4030, 480/0.119 = 4034, 240/0.059 = 4068, 5.4/0.0016 = 3375 and let's use the inverse of 4030 or 0.000248 L/kg/day or 0.25 ml/kg/day is the implied amount drank per weight per day assuming the first column was mg/L Boron and not product. Note how the last ratio is different than the others because it is boric acid and not sodium tetraborate pentahydrate -- I should have seen that as a clue, but didn't, and I ignored the fact that the amounts listed in the first column matched what they were describing in the text -- I think I tried doing the calculations that follow below, but didn't do them correctly the first time so didn't change my assumption about what the first column meant.

If the first column was product, then converting to boron would give (540/291.29)*4*10.812 = 80.17, (480/291.29)*4*10.812 = 71.27, (240/291.29)*4*10.812 = 35.63 and (5.4/61.83)*1*10.812 = 0.9443. Using these numbers for the ratio of boron to adjusted ADD we get 80.17/0.134 = 598, 71.27/0.119 = 599, 35.63/0.059 = 604, 0.9443/0.0016 = 590. So this certainly is closer to being similar and implies that you are right about the table and I was wrong. It implies 1000/600 = 1.67 ml/kg/day.

Instead of focusing on the table, just focus on the known core facts: the 8.8 mg/kg/day NOEL and the 100 MOE. The net of these two then imply how much someone can drink. At 50 ppm Boron, I calculated 14 ml for very young children assuming a weight of 8 kilograms (17.6 pounds) which is way lower than the average 7 year old at 50 pounds. That is, (50 mg/L)*((14 ml/day)/(1000 ml/L))/((8.8 mg/kg/day)/(100 MOE)) = 7.95 kg. I think I was calculating for babies/infants where 8 kilograms would be the average 6-month old boy or 8-month old girl. And again don't forget that these amounts are for drinking every day, not one-time dosages. These calculations of drinking limits in my post are still valid since they are about the amount one can drink to get up to the NOEL limit with an MOE of 100 and aren't about the borate level that the EPA deems "acceptable".

So I think you are right that the first column in the table is product concentration and the assumption is that children are gulping larger amounts of water, namely 1.67 ml/kg/day which for a 23 kg (about 50 pounds) 7-year old would be around 1.67*23 = 38 ml or 2-1/2 tablespoons, again with a margin-of-exposure safety factor of 100.

Thanks for catching that error. I don't believe it changes the conclusions since the EPA analysis is very conservative, but might explain current dosing limits on borate products for pools of around 50 ppm Borates (ppm Boron) since (23 kg)*((8.8 mg/kg/day)/(100 MOE))/((38 ml/day)/(1000 ml/L)) = 53 mg/L.

[BigDave]

Thanks for the personalized schooling. Sorry about the FDA slip, I'm in New Jersey and Pharma is everywhere. Thanks for demonstrating how the EPA came to thier acceptable / unacceptable levels, good to know it was based on the published research. It's too bad you had to run it all backwards to find the basis for thier conclusions. It would have helped me understand had the report described the units and assumptions that went into the ADD. Perhaps that's all stuff that 'everybody knows' in the report's audience.

Thanks also for describing / providing the scientific basis for the poolcare method followed here; the work you all (Ben, Mods, regular contributors) do here is invaluable.

[Climb on soapbox]
We all lead our daily lives according to our belief systems. As it comes to poolcare I believe that the methods and advice I find here are safe, accurate, and based on empirical science (Chem Geek spoon fed me the science behind Borate safety). Too many people have poolcare belief systems built on less sturdy foudations: "I believe the poolstore will tell me what to do to take care of my pool -> The poolstore believes that selling me phosphate remover will fill the cash drawer.

Thanks again for the work done here. It's good to know that greed and superstition and the subsequent opinions and consensus don't rule everything.

[HofstraJet]

I am planning to add ProTeam Supreme Plus to my 20,000 gal pool (I just don't have the time or the patience to collect 20 Mule Team boxes and get the acid, etc.). My question is dosage: the threads I read all approximate 2#/1000 gal and that's what the package recommends, but then this chart (http://www.proteampoolcare.com/image...oseChart_1.pdf) says to get to 50 ppm, I need 67#. It looks like the 2#/1000 gal just gets me to 30 ppm. Is that accurate? Want to make sure I order the right amount.

Oh, and the LaMotte test strips are $11 on amazon delivered. Cheaper than the lumber store I saw linked in other threads.

Thanks!