Re: Interesting Study (Dissertation) on DBP's in indoor pool
Retep said:
If using sodium or calcium hypochlorites it raises the pH , therefore it must be lowered by (for example) Hydrochloric Acid ,and if using chlorine gas (to put it in simple words), we need to add a base ( such as soda ash for example) in order to raise the pH.
What you are saying is that if the TA is low then hypochlorite sources of chlorine got an acidic nature.
Even if your TA is at 20 ppm and you are using a hypochlorite source your pH still will go up and you need to correct it ( less though as if your TA would be high).
There are quite a few pool owners using hypochlorite sources of chlorine who add little or no acid. There are even some spa users using bleach (after initial Dichlor) who likewise have stable pH. Though it is true that there is usually the tendency for the pH to rise when using hypochlorite, if the TA is low enough then the amount of needed acid gets very low and the TA need not get to 20 for that to happen (you can still be over-carbonated and have very little outgassing since the rate is proportional to the square of TA and is not linear). I am not saying that "hypochlorite sources of chlorine got an acidic nature". The usage/consumption of chlorine from ANY source is acidic and it exactly counteracts the pH rise from hypochlorite sources being added except for the "excess lye" in such sources which can be very low (in Clorox bleach at a pH of 11.9 it's 0.063% sodium hydroxide). This effect makes Dichlor net acidic and Trichlor even more acidic than it is upon addition. See
this post for the chemistry.
Retep said:
I know you are an advocate for using CYA in indoor pools and -Yes- it would have been very interesting if one or more of those indoor pools would have been using CYA and the relation to THM's. Also it would have been interesting to see with which levels of FAC would have to be operated by still obtaining microbiological safe water.
As you could see in this study there were no tests made in terms of microbiology ( which was not the purpose of this study to begin with).
If you take a look at those charts which show you the average FAC I am almost certain the microbiology was ok in all those pools. They better be ok considering those high FAC levels.
I don't think there's any problem with bacteriological safety even with relatively low active chlorine levels. The German DIN 19643 at 0.3 without ozone or 0.2 with ozone is still more than enough and remember that its pH is lower as well (around 7.0) so with no CYA present the active chlorine level is about 50% higher than at 7.5. If CYA is present and the FC is at 20% of the CYA level, then this is equivalent to 0.2 ppm FC with no CYA at 7.5. I just think of CYA as a useful chlorine buffer to make the active chlorine level lower while still having plenty in reserve while also protecting it from breakdown in sunlight. It should at least be considered. It won't work with DIN 19643 economically, however, due to the GAC chlorine adsorption/stripping that is part of that system -- that is, chlorine is removed with every turnover and reinjected (at least in some versions -- I've heard inconsistent reports about when GAC has to be used).
The thing you need to keep in mind is that CYA is used in most outdoor pools in the U.S. so the active chlorine level is lower in such pools -- lower than the lowest of German DIN 19643. Most studies have been with indoor pools and the presumption has been that the difference in air circulation explains the differences seen, but sunlight exposure and the use of CYA may also be factors, but aren't generally considered. Even if a pool had 10 ppm FC, that means nothing to me if I don't know the CYA level. If the CYA is 100 ppm, then the hypochlorous acid level is still much lower than the lowest of 19643.
Retep said:
This study clearly proves that the "North American " approach ( = very high chlorine ) to treat pool water is not the proper way to do it.
Proper water treatment starts with proper filtration. Something which got lost in the past 20 years or so. In the "good old days" public pools
used proper filters and proper filtration speeds.
I agree that having a high active chlorine level as with typical North American indoor pools with no CYA is a problem as is the tendency to shock those pools to even higher chlorine levels in an attempt to chase CC to get it lower. Of all the problems, CC is actually the least to worry about if one uses CYA in pools. The reason is that the low active chlorine level should lower the amount of nitrogen trichloride produced by orders of magnitude. However, the CC may measure higher because most of it will be intermediates such as monochloramine and chlororureas that are not a problem even at 1 ppm. Even 19643 focuses on lowering CC, but that's more of a marker for general precursor removal including urea and therefore a proxy for nitrogen trichloride (the reality is that most European pools don't get to 0.2 or 0.3 and operate closer to 0.5 ppm since it's hard to maintain such a low FC level -- yet another reason why CYA could be helpful).
I also agree that very few, if any, pools in North America would pass German DIN 19643. Of course, they aren't using that standard so that's not really a surprise.
I agree that there should be more focus on coagulation/filtration. On the other hand, I'm even more concerned with the suntan lotion effect I saw in my own pool since there are many more users of outdoor pools and nearly everyone uses sunscreen these days. I'm doing more tests hoping that was just an anomaly (even then, what I'm doing is hardly a real scientific controlled experiment).
Retep said:
The last few pages of the previous linked 278 page study (Dissertation) ,shows a few models in term of expected cancer rates when people are exposed to THM's in pool water.
:
I recently downloaded another study, which came out from Canada - just got released about 3 weeks ago and I purchased it online ( too bad not everything is free on the net. . .)
Most studies show that it isn't drinking tap water that is the primary exposure route, but rather dermal and mostly inhalation exposure. That's why showering is also a significant factor though indoor swimming is higher and why competitive swimmers are at greater risk than casual bathers.
Yes, it's good of Canada to take a stab at this, but they will find that maintaining lower FC levels is difficult since even small localized events can wipe out FC. So while 0.5 ppm may be doable with sufficient circulation and monitoring, getting to 0.2 or 0.3 will be more difficult. Again, I think CYA would help here significantly.
Thanks for the additional link. Yes, it's too bad that many of these papers have to be purchased and I've bought many.
I want to put into perspective a few things. First, this dissertation study didn't measure actual air concentrations nor blood levels. Though he wrote that his Henry Law estimates compare well with other studies, there are some where such near-saturation assumptions don't seem to work well and where blood levels aren't as high as would otherwise be expected.
This study is an earlier one showing indoor pools as being more of a problem for the inhalation route of chloroform in terms of blood levels that didn't show up in outdoor pools, but amounts do not follow simplistic Henry's Law calculations and there were no hepatotoxic effects seen. The
Spanish studies I looked at even showed that chloroform was not genotoxic. So I don't believe it's such a slam dunk that chloroform in particular is as serious a health issue at these levels though it is a marker for TTHM which is useful since the brominated THMs have been shown to be far more problematic.
These risks which are projected with linear dose models and have conservative margins of error should be compared against actual lifetime cancer risk from all sources as listed in
this link. The dissertation showed risks 10 to 10,000 times higher than the 1 in a million EPA unacceptability limit making the worst-case 1 in 100. That's pretty bad if it were true, but it's unlikely to be that high since epidemiological studies don't show such high increases (and some such as this
bladder cancer study have
potential flaws). The risk is more likely to be more like 10 times higher so in the 1 in 100,000 range as that is more consistent with other studies that measured more direct physiological effects, though again it's not clear that chloroform is indeed the culprit and the brominated THMs and other factors (nitrosamines) may be more at play.
I'm not saying that this isn't something to improve, but I don't believe it's something to get panicked about either. The risk in outdoor residential pools should be a lot lower, notwithstanding the suntan lotion issue I seem to have stumbled upon.