CYA Toxicity

[downwind]

This may not be a totally off the wall question, considering the sad state of affairs around the world:

Should the world go totally awry and the only water you have around is your pool, and the only chemicals you use are liquid chlorine and CYA, what would you have to do to be able to safely drink your pool water? The CYA MSDS only refers to toxicity as:

Toxicity to Animals:
Acute oral toxicity (LD50): 3400 mg/kg [Mouse]. Acute dermal toxicity (LD50): >5000 mg/kg [Rabbit].

These are pretty high levels, but I still would not feel comfortable drinking the pool water as is.

It looks like the CYA may be extracted by distillation, evaporation, etc.

Comments?

 

[frogabog]

CYA can only be extracted by reverse osmosis. Evaporation does not reduce cya in any way, so distillation wouldn't work either.

Dunno about toxicity... but I suppose if all I had to drink was pool water I probably wouldn't worry so much about it (bigger fish to fry so to say). The world would be at it's end around here if there was no water.

Chlorine would disappear completely within a few days of not dosing anyway.

 

[JasonLion]

distillation wouldn't work either

Distillation will work. The CYA stays in the evaporator, so it does not appear when you condense the water vapor. On the other hand CYA is not toxic at the levels used in swimming pools, with a very wide safety margin for humans, so there really isn't an issue here at all.

 

[Isaac-1]

To folllow that up, my rough math shows that a 100 pound person would have to drink over a thousand gallons of pool water to injest an LD50 (mouse) dose of CYA (maybe a bit less if your running an insanely high CYA level in your pool)

 

[chem geek]

See the thread Pool water safe to drink in emergencies?

 

[downwind]

Thanks for the info & the redirection to the other thread.

 

[frogabog]

distillation wouldn't work either

Distillation will work. The CYA stays in the evaporator, so it does not appear when you condense the water vapor. On the other hand CYA is not toxic at the levels used in swimming pools, with a very wide safety margin for humans, so there really isn't an issue here at all.

Now you've piqued my interest. So, if distillation does work... couldn't someone make a buck or two on removing CYA from pools with a big still (and I assume, a vessel truck) rather than reverse osmosis?? lol

At least I'm better educated about distillation now. I just had to read up on it after this. I assumed since evaporation didn't work that distillation wouldn't either thinking the CYA would just rise into the condenser with the water, but apparently it does have a different volatility than water. Evaporation isn't exactly the same as vaporization, duh!

 

[chem geek]

No, it is the same in this case -- evaporation and vaporization are the same thing -- it's what happens afterwards (i.e. which part you end up keeping for the pool water) that is different. With evaporation, water leaves the pool while the CYA stays in it. The fill water brings the water level back up, but doesn't have any CYA in it so there is no net change in CYA concentration.

With distillation, the water vaporizes but the CYA does not, just as with evaporation. The difference here is that you are condensing the vaporized/evaporated water and presumably using that to put back into the pool while leaving the concentrate or solids behind. This is not much different than reverse osmosis in its result. In other words, with distillation, you are using the water that vaporized/evaporated while in the evaporation case, it is lost to the air and you are using what remains behind.

EVAPORATION:
(Water + CYA) ---> (Water + more concentrated CYA) + (Water Vapor lost to the air)
(Water + more concentrated CYA) + (Fill Water) ---> (Water + CYA)

DISTILLATION:
(portion of Water + CYA) ---> (Water + more concentrated CYA) + (Water that is condensed)
(Water + CYA less portion removed) + (Water that is condensed) ---> (Water + less concentrated CYA)

In bold above is the part that you keep, which you can see is different in the two processes. Distillation is far more expensive than reverse osmosis because it takes a lot more energy to heat the water to evaporate it quickly than it does to push it through a membrane.

 

[frogabog]

You're way too darn smart. Slummin here with us is below you, but we're forever grateful :~}