How and why do borates suppress algae?

[chem geek]

The 0.16mg/kg is accurate and works out to about 10.88 mg per day for a 150 lb. adult.
Source: http://www.food.gov.uk/multimedia/pdfs/evm_boron.pdf

The 1.6 mg/kg was my estimate of a conservative "safe" dose for a dog to drink every day (note: I did put “per day” in my post).
___________________________________________________________________________________________
According to http://www.ehponline.org/docs/1994/Supp ... livan.html

I think that there is a lot of room to debate what a "safe" dose would be for a dog to drink on a regular basis. I think that there is a lot of room between what is a "safe" dose and what is an "adverse" dose. I agree that it would be best to have the dog avoid drinking any pool water at all. However, it is always good to know, or at least have an educated opinion, about exactly what we are doing. There will always be dogs that drink the water. We should know how much is OK for them to drink on a regular basis. What is everyone's opinion about what is the highest safe dose for a dog to drink everyday? I think that 3 liters is a bit high, even for an 85 lb. dog. Possibly closer to 1 liter per day, every day; although 3 liters periodically would probably be fine.

Note to Richard: Re your quote: "Since you are a long-time service tech, your most valuable contribution would probably be the experience you have in what you have seen over the years and figured out from cause and effect."

Perhaps you did not mean it in any derogatory way, but to be clear, I do not need anyone trying to figure out some sort of niche that they can assign me to fit into. You do not know me. You do not know what I know and don't know. I will post whatever I feel can be helpful. If you disagree with something I say and want to challenge it, then do so. We don't always have to agree.

You are right, I didn't mean to be derogatory and I'm sorry it sounded like that. I've had interactions on forums with people who just search and post whatever they find on the Internet without considering sources, but now that you've provided links I see that you are looking at scientific studies (mostly the same studies referred to in multiple sources) so that's good. That's valuable information. We shouldn't fool ourselves, however. I'm not a doctor nor epidemiologist and if we had one on this forum then that would be very helpful in this discussion so we have to be careful about the conclusions we draw here.

Thank you again for the links. Now I see where the 0.16 came from. It started with rat studies and used a factor of 10 for inter-species and a factor of 6 for inter-individual variation. I prefer looking at direct studies on the species of interest. I knew that Anna was concerned about her dogs and that she probably wasn't drinking the pool water herself.

The larger 2-year study of dogs would indicate a NOAEL of 8.8 mg/kg/day which is what I've used. The 90-day smaller study even showed some weight loss and spleen-to-body weight reduction at 0.44 though if one ignores that then one would use the 4.4 mg/kg/day level which is what another link you had showed.

As for what to conclude from this, I would say that for dogs, a reasonable number to use is in the ballpark of the 4.4 to 8.8 indicated above. Since the 2-year study was longer and larger, I used the 8.8 number. I ignored the relatively small dietary intake amount (which was for humans and would be even lower for dogs unless they eat lots of vegetables :-D ). So the simplified formula would be:

(1.057 quarts/liter) * (8.8 mg/kg/day) * (pounds weight) * (0.454 kg/pound) / ppm Borates (measured as ppm Boron or mg/liter) =

maximum quarts per day = 4.2 * (pounds weight of dog) / (ppm Borates)

or a rough rule that is even simpler to compute:

maximum gallons per day = (pounds weight of dog) / (ppm Borates)

To be safe, one should aim lower than the above and in general should train their dogs not to use the swimming pool as a water bowl. Swimming in the water and lapping some up should not be a problem, but regular drinking in quantity should be avoided. I'm not sure if we can come to anything more definitive than that.

Richard

 

[Guest]

Actually, the ppm Borates for pools is measured as ppm Boron, not boric acid. It's true that the primary chemical species in pool water is boric acid with a small amount of borate ion, but the measurement is in ppm Boron. This is why Michael Beach's calculator was incorrect because he used the molecular weight of boric acid instead of boron. It's also why something seemingly as low as 50 ppm has a rather large effect on pool water buffering. 50 ppm Boron is equivalent to 286 ppm boric acid. You and I figured this out a long time ago and there are posts somewhere about it.

Richard, you are correct (it WAS a while back!) but I seem to remember that we discussed this in PMs and not in a forum. The very long thread on borates at PF that we collaborated on did not really discuss this but you did state in that thread that the measurement was in ppm boron (which is where the error in Bleachcalc comes from since it was based on boric acid) yet the main species that exists at normal pool pH is boric acid. Hence the source of my confusion. I should have referred back to PF instead of relying on memory. The memory is not what it once was!
What was I saying???

 

[AnnaK]

Wowser!

So Pax can drink 67 quarts per day. He'll explode long before his testicles shrink from boron toxicity.

Now, how about the algaecidal effects of borates on pool water?

 

[chem geek]

Gee Anna, doesn't your curiosity every stop? Just kidding.

67 quarts would imply pounds per ppm of 16 so even at 30 ppm Borates that's 480 pounds. Did I miss something here? [EDIT] A 50 pound dog in a pool with 50 ppm Borates should not drink more than 4.2 quarts (about a gallon) a day. To be on the safe side, they should drink considerably less. [END-EDIT]

The original link I posted has tables showing toxicity to various forms of algae from boron levels though it's rather inconsistent and species-dependent. Table 18, for example, shows growth inhibition of around 50% (i.e. half the growth rate or alternatively half the population affected) at around 34 to 52 ppm. At 100 ppm, the growth rate gets close to stopping completely. At the other end, no effect levels for freshwater green algae are between 10 and 24 ppm.

Interestingly, I just communicated with someone on another forum who regularly added borates to their pool (the actual level is unknown) and had no algae growth even with no chlorine in the pool for several days. waterbear has also reported significant inhibition of algae growth even at the 50 ppm level we recommend and his pool has very high phosphate levels. So I would say there is no question that at 50 ppm, borates inhibit algae enough to provide some insurance against runaway growth if the chlorine gets too low. It may not stop growth completely in every situation, but I would say that it's only somewhat less effective than a weekly PolyQuat dose though not as effective as proper chlorine levels or copper ions (the latter we do not recommend due to its side effects).

We have generally recommended the 30-50 ppm Borates range since that is what is recommended by the industry and it appears to provide sufficient pH buffering and algae growth inhibition though for the latter, 50 ppm would be better. Though a 100 ppm Borates dose might be even more effective at preventing algae growth, it's better to have chlorine as the first line of defense. It's still something to think about, though the higher level is (as pointed out in earlier posts) more toxic if you drink it.

Richard

 

[Guest]

I was on vacation for 12 days and just shut off the pump and SWG. I expected to return to a green pool but it was clear! I shocked it before I left and shocked it again when I returned and it was fine.

As far as dosing, 30-50 ppm is recommended for chlorine/bromine and 50-80 ppm for biguanide. Makes sense since the halogen sanitizers will kill algae and bigaunide won't!

 

[AnnaK]

Gee Anna, doesn't your curiosity every stop? Just kidding.

67 quarts would imply pounds per ppm of 16 so even at 30 ppm Borates that's 480 pounds. Did I miss something here? [EDIT] A 50 pound dog in a pool with 50 ppm Borates should not drink more than 4.2 quarts (about a gallon) a day. To be on the safe side, they should drink considerably less. [END-EDIT]

I had used your formula: maximum quarts per day = 4.2 * (pounds weight of dog) / (ppm Borates)
Plugging in the appropriate values it becomes x = 4.2 * 80/5 = 67 quarts.

But let's move away from the dog and get back to the initial intent of this thread. I fear I somehow hijacked it with my question about how to relate mg/kg body weight to ppm borax, and I am sorry about that.

How and why borates suppress algae would be of great interest to me. And no, my curiosity rarely stops

 

[chem geek]

Oh, I see that you don't really have lots of borates in your pool -- just a small amount probably leftover from using Borax for pH, I suppose.

As for mechanisms in killing algae, I don't know. That same document refers to general chemical mechanisms that probably apply to most organisms in addition to specific ones affecting algae (in section 9.1.1.1). It's just that algae being small single-celled are more affected more readily than larger animals (though some fish seem particularly sensitive). Borates even show some ability to inhibit bacterial growth, but not nearly as much. I suspect the difference has a lot to do with the fact that bacteria reproduce much more quickly at 15-60 minutes per doubling in population (in ideal conditions) compared to 3-8 hours for algae and some of the key disruptive effects of boron seem to be associated with chlorophyll. Quoting from the inchem document:

Martinez et al. (1986) observed that boric acid caused a decrease in growth rates, protein content, and chlorophyll content in the blue-green alga Anacystis nidulans, following exposure to 75 and 100 mg boron/litre as boric acid. The photosynthetic pigments completely disappeared after 72 h of exposure. Nitrate uptake was also lowered. An accumulation of carbohydrates was observed, probably because the loss of the photosynthetic pigments inhibited their degradation.

Richard

 

[AnnaK]

Oh, I see that you don't really have lots of borates in your pool -- just a small amount probably leftover from using Borax for pH, I suppose.

That's correct. pH management is all I've ever used borax for, and then switched to sodium hydroxide because I was concerned about the effect of borates on the dogs.

But now I'm beginning to read more and more about the sanitizing effects of borates, especially Evan's experience after a 12 day absence, which has revived my interest and especially my curiosity about toxicity levels for dogs. Thanks much for hanging in there with me.