Bromate... drain and refill

[Ohm_Boy]

So evidently, the preferred solution to high bromate levels is a drain and refill cycle. Story here
(No offense to affected Californians)

Couple of questions...
1) How does chlorine + UV = bromates?
2) How much bromate is dangerous, in CA as well as the rest of the world?

 

[chem geek]

First of all, you have to have bromide or bromine in the water to get bromates. In a normal pool you won't have that. If you have a bromine pool (rare) or spa (more common), then shocking with chlorine or non-chlorine shock (MPS) will convert bromide to bromine and usually it will stop there, but if you shock with a very high level of chlorine, then some of the bromine can get converted to bromate (but generally only a small amount in the area of high pH near the hypochlorite solution). Remember that in water treatment, rather high levels of chlorine are used for disinfection (they don't use CYA, for example) so bromate is more common as a disinfection by-product (but not as common as other DPBs that are worse, such as higher-order chloramines -- dichloramine, nitrogen trichloride -- and trihalomethanes). The use of ozone in a bromine spa is more likely to produce bromate since ozone is a more powerful oxidizer than chlorine and its intensity is high in the ozonator.

UV will not produce bromates. In fact, this is one of the advantage of disinfecting with UV -- it doesn't produce disinfection by-products. I'm not sure where you got chlorine + UV = bromates.

Bromates are not dangerous to swim in at the concentrations we are talking about above. As noted in the article, you'd have to drink a lot of water with bromates in them before there is a possible cancer concern. You generally don't drink your pool or spa water so I wouldn't worry about it. If you are concerned about bromates, just don't use bromine for disinfection -- use chlorine instead. For a pool, that's probably what you are already doing (i.e. using chlorine and not bromine).

You can read more about health studies with bromate here, but again this shouldn't be a concern in a pool at all and is only of minor consequence in a spa unless you drink lots of spa water.

Richard

 

[Ohm_Boy]

I really never expected this particular situation to be a big concern with a pool, I was merely intrigued by the happenstance of it happening in Calafornia.
I mentioned UV because the article cited:

Silver Lake and Elysian reservoirs registered elevated levels of the suspected carcinogen bromate between June and October, the result of an unusual combination of intense sunlight, bromide naturally present in groundwater and chlorine...

Granted, I assumed that the area of interest for the sunlight component was UV - perhaps not. Maybe it is heat. I was just asking.

 

[Guest]

Bromates are formed by the oxidation of bromides. In this case the bromides were present in the water (they are naturally occuring in water in many parts of the country) and the oxidation came from the chlorine used to sanitize the water. The only effect I can see the sunlight having was actually concentrating the level of bromates through evaporation of the water in the resevoirs, causing the bromate level to skyrocket.