Swimming Pool Disinfection Revisited: Efficacy of Copper and Silver Ions vs. Chlorine.

Editor's note: This special report consists of an exchange of letters between readers and the authors of an article titled, "Swimming Pool Disinfection: Efficacy of Copper/Silver Ions with Reduced Chlorine Levels," which was published in the May 1999 issue of the Journal of Environmental Health. (Copies of the original article are available, upon request, from a NEHA service specialist at [phone], ext. 0.) We thank everyone who responded in writing after reading the article, and we also thank the authors of the article for taking the time to provide thorough and detailed responses to each question. As the spring and summer seasons are just around the corner, we hope you find the questions asked and answered in this special report to be timely, interesting, and useful.

Dear Editor:

After reading an article on swimming pool disinfection in the May 1999 issue of the Journal, I had several questions and comments:

1. I was most disappointed not to see pH listed in the results, as it is a vital part of the chlorine activity. I wonder if the reduction in sodium hypochlorite resulted in a lower pH and a corresponding rise in activity of the chlorine.

2. Was the pool ever shocked or break-pointed? Was there any staining of the pool walls? What was the pool wall construction?

3. The level of copper was at the upper end of the limit recommended by the National Spa and Pool Institute (NSPI). How were the copper levels controlled to ensure that they did not exceed this level, and, when the study ended, was the same level of surveillance maintained? What would an unannounced visit discover?

4. The range given for chlorine levels in the pool indicates a drop to 0.3 parts per million (ppm). Therefore, it is of little wonder that there were problems with combined chlorine. What were the chlorine levels in the samples taken for bacteriological testing? Were all the water samples taken at the same time of day?

5. The standard chlorine treatment was used to handle the heavy usage during most of the summer, while the testing of copper/silver treatment did not really begin until mid-September. To be fair, I wonder how copper would have performed with more sunshine, higher bather loads, and possibly longer hours of operation?

6. My experience and that of others is that water quality under test conditions always exceeds that of "normal" operations. Just the higher level of surveillance dictated by these protocols increases the attention paid to the pool and results in a better-run facility. What would have happened if the operators had been unaware of the test and had continued to operate as always?

7. I also wonder about the quality of pool operation, given statements referring to combined-chlorine levels of 0.6 ppm and the corrosive effects of chlorine on the pool structures. These chlorine "defects" generally result from defective operation, not from chlorine use.

8. The article states that the copper ions are chemically stable, but that is not always true; they can easily be found deposited on the plaster walls of all too many pools and spas. Copper does stain. It also forms complexes and interferes with chemical testing. The article attacked chlorine and glossed over the problems with copper and silver.

9. Let us not forget that chlorine also performs a vital function not performed by copper -- oxidation.

Sincerely,

Leroy Hitchcock, R.E.H.S., C.S.P.

Placer County Environmental Health Services 

Tahoe City California

Dear Editor:

I read with great interest the article titled "Swimming Pool Disinfection: Efficacy of Copper/Silver Ions with Reduced Chlorine" in the May 1999 issue. The questions addressed and the results presented are, I believe, extremely important, scientifically and socially. Therefore, I would like to raise a few concerns, some regarding information that may be misleading and a couple regarding possible questions for future research.

First, in the discussion of the "disadvantages" of chlorine sanitization, the statement is made that "the lifetime of the free available chlorine (FAC) varies." While this statement is correct, the implication that this is a disadvantage compared with copper/silver treatment is disingenuous. The system described in the article includes a chlorine component--FAC is maintained at 0.4 ppm or greater. The lifetime of FAC would vary with this system, too.

Second, although FAC may be associated with irritation of the eyes, nasal passages, and skin, as well as with objectionable odors in the pool environment, FAC specifically (and chlorine application generally) is not the culprit. Poor water balance, which has many facets, is the real issue. Poorly balanced pools with copper/silver disinfection systems also would exhibit these characteristics.

Third, chlorine, properly applied, usually is not the culprit when corrosion necessitates expensive maintenance work. Again, poorly balanced water (e.g., total dissolved solids exceeding 4,000 ppm) is more commonly responsible.

Assuming that eliminating the remaining "disadvantage" of FAC disinfection--objectionable by-products--is the goal of this alternative sanitization system, the question must be asked: "How much are these by-products reduced by the system?" Again, it should be noted that the sanitization system studied incorporates a chlorine component. What levels of trihalomethanes and chloramines are produced by a system that maintains a 0.4 ppm FAC residual? Is the reduction in FAC significant? What, if any, byproducts are produced by the interaction of copper/silver ions with water contaminants? These questions might provide the basis for future research.

Finally, on a more practical level, I would like to raise three more questions. First, how does the copper/silver-based system work under extraordinary circumstances? For example--in the face of a fecal accident? Second, what are the costs associated with such a system, and how do they compare with those of other sanitization methods/systems? Finally, in practice, how would pool operators and public health officials measure the effectiveness of the system?

Again, thanks to the authors for providing research in this important area. I look forward to feedback about this article as well as to future research.

Sincerely,

John R. Anderson

Manager of Policy and Regulatory Affairs,

Leslie's Poolmart

Chatsworth, California

Dear Editor:

Regarding the article "Swimming Pool Disinfection: Efficacy of Copper/Silver Ions with Reduced Chlorine Levels," I would like to offer the following comments:

* On page nine, column three, the authors state that "FAC levels of 0.6 ppm or greater have been associated with irritation of the eyes, nasal passages, and skin, as well as with objectionable odors in the pool environment." This should read "CAC (combined available chlorine) levels of 0.6 ppm or greater ..." A good discussion of combined chlorine (chloramines) can be found on page 30 in the Pool Spa Operators Handbook, published by the National Swimming Pool Foundation (NSPF). This book serves as the course manual for the Certified Pool Operator (CPO) credential.

* In the next sentence on page 9, the authors state, "Also, chlorine has a corrosive effect on pool structures, necessitating expensive maintenance work." That would be true only if pH and pool water chemistry were not maintained in a "balanced" state.

* On page 10, the authors state, "Chapter V of the Massachusetts Sanitary Code requires swimming pool waters to be disinfected with chlorine at a FAC of 1.0 ppm." Since the efficacy of FAC is pH dependent, the pH of the pool under study should have been noted.

* On page 11, the authors state that "Silver ion levels are not routinely monitored, because their concentration is low." While I agree that levels in the part-per-billion range are low, that is no reason not to monitor them. Many state swimming pool codes, including the code in this state, require the ability to measure any chemical or process that claims to be a disinfectant. While silver test kits are much more expensive than the copper test kit mentioned in the article (and that may be why silver levels are not "routinely monitored"), they are available. One test kit for silver is available through the Hach Company of Loveland, Colorado.

Finally, I object to articles that ostensibly are written as objective studies but that, upon closer examination, appear to push a self-serving agenda or to promote a particular product.

Sincerely,

Dave Johnson 

Bureau Director, Environmental Health Services, Utah County Health Department Provo, Utah

The Authors Respond:

We welcome the opportunity to respond to the letters the Journal has received about our May 1999 article, "Swimming Pool Disinfection: Efficacy of Copper/Silver Ions with Reduced Chlorine Levels," and to clarify several of the points raised.

The principal aim of our study was to prove that combining copper/silver ions with low levels of residual chlorine provides water disinfection in swimming pools that is superior to disinfection provided by chlorine alone. We do not advocate the elimination of chlorine, nor do we overlook the importance of proper water balance. Rather, the study shows that our process enhances proper water balance and retains all the disinfection benefits of chlorine while eliminating virtually all of its drawbacks.

The goal of our field test was to prove the efficacy of laboratory findings by Gerba and others. We took their results out of the laboratory and into the field. The results of the field test demonstrated that our process maximizes the effectiveness of chlorine and improves swimming pool operations, both environmentally and aesthetically. While even a low level of chlorine will vary under changing climatic conditions, the fact that chlorine is not the exclusive disinfectant in our process makes that variation much less critical. The copper/silver process thereby lowers the risk that the inherent instability of chlorine will allow a breakthrough of pathogens.

The rest of our response is divided into the following topics:

1. the role of chlorine in disinfection and its place in our technology;

2. water balance, its importance in corrosion and swimmer discomfort, and its relation to our technology;

3. specific issues of corrosion and swimmer comfort unique to chlorine; and

4. answers to other questions.

The Role of Chlorine in Disinfection

Central to the debate is the crucial role chlorine plays in water disinfection. This does not change with the introduction of our technology. We agree that chlorine is an essential element in effective disinfection. Where we disagree is in our argument that chlorine does not need to be the exclusive agent for disinfection since it generates number of drawbacks ranging from the serious to the aesthetic.

Alternatives to chlorine have been elusive because it is hard to match its quick effectiveness and testable residual. But as more and more organisms have developed resistance to chlorine, residual FAC levels have begun to rise in response. This development is not without its own drawbacks. Higher residual chlorine levels generate significant chlorine usage (chlorine use rises as a square of the free-chlorine level). These higher levels also generate significant levels of chlorine by-products (trihalomethanes and chloramines), which create their own health problems. They also marginalize more and more people out of swimming, especially older adults, because of increased levels of discomfort. Dissatisfaction with chlorine and its by-products continues to increase. Fundamentally, the aim of our research was to show that there are more practical alternatives. Consider other water applications, particularly drinking water, which clearly demonstrates that chlorine can be very effective at very low levels (i.e., 0. 1-0.2 ppm).

Simply, our process maximizes the effectiveness of chlorine so that low levels achieve disinfection equivalent to that normally offered by high levels--while virtually eliminating all the drawbacks. We do not eliminate chlorine; we eliminate the drawbacks.

Water Balance

Water balance is critical in any discussion of water chemistry. Improperly balanced water can significantly affect all aspects of water chemistry. Up to this point, we agree with the correspondents. Where we may disagree is that we may place a greater emphasis on water pH than they do. For legitimate reasons--but for far too long--water pH has taken second place to disinfection. While we do not want too reorder this priority, we do want to focus on those disinfection processes that have less impact on acid/base chemicals. In the following discussion of water balance we address water balance and chlorine, and water balance and copper. The discussion of water balance and copper specifically addresses the potential for staining.

Water Balance and Chlorine

Water balance, especially pH, plays a key role in disinfection. So again, we all agree. We must, however, remember that water balance is significantly affected by disinfection. To appreciate this interdependency we first must recognize that water balance and disinfection are each individual processes with separate objectives and for which there are separate strategies. Let me explain.

Water is a dynamic liquid. Left untreated, it can corrode or scale other materials. Alkalinity (TA), calcium hardness (CH), total dissolved solids (TDS), and pH constitute the four primary factors that affect water balance. All these factors must fall in prescribed ranges to neutralize the natural aggressive and scaling tendencies of water. Up to this point chlorine is not needed. Water, however, also offers a friendly environment for the generation of pathogenic microorganisms that have an adverse impact on public health. Therefore, water needs to be disinfected. That is where chlorine is introduced. While extremely effective as a disinfectant, chlorine also brings with it unique characteristics that are inimical to good water balance.

Chlorine is a part of the halogen disinfectant family. Halogens are potent oxidizing agents that inactivate microorganisms primarily by interacting with the cell membrane and disrupting enzymatic processes. The active species in chlorine are hypochlorous acid (HOCl) and the hypochlorite ion. The hypo acids and their respective ions exist in an equilibrium determined by pH:

HOCl = [H.sup.+] + [OCl.sup.-]

In the pH ranges at which swimming pools are normally maintained, the percentage of free chlorine that exists as HOCl falls off sharply with increasing pH. Since HOCl is a more potent disinfectant than the hypochlorite ion, the pH needs to be kept within a fairly tight range for proper disinfection to be maintained. There is, however, a slight complication to this relationship. Liquid sodium hypochlorite, which is used in intermediatesized pools, and solid calcium hypochlorite, which is used in small residential pools, react with water and increase the pH. So large dosing of hypochlorite into pools will increase pH, which works against proper water balance. Therefore, a process that minimizes chlorine use but delivers the same disinfection contributes to proper water balance. Ionization is that process.

Water Balance and Copper Levels

Although it was not an issue in our study, the potential of copper to stain pool surfaces comes up whenever ionization is discussed. I can state unequivocally that when approved equipment is used and the water-testing regimen is followed, our system will not cause any staining. The heart and soul of this system resides in the precise maintenance of copper at levels below 0.5 ppm. At these levels, there is little or no chance that any copper will fall out of solution and stain pool walls. Ironically, the use of our equipment actually could prevent copper staining of pool surfaces--and here is where that use relates to water balance.

Water balance can affect the level of copper in the water independently of our process. As we know, unbalanced water can become aggressive and attack plumbing elements in the pool--including the heating elements or parts of the filter where copper can be found. This unbalanced condition, if left untreated, could increase copper in the water to excessive levels. At these excessive levels (three to four times higher than levels used by our process) copper has the potential to fall out of solution and stain pool walls. Our process, however, requires daily water testing. This daily testing regimen and the precision involved in keeping the copper level at 0.3 ppm provides an early warning system that other sources of copper may be entering the pool. This early warning gives the pool operator a chance to analyze the cause of rising copper levels, identify where the copper could be coming from, develop a remedy, and make the necessary changes. In most instances, we believe, this early warning would indicate that th e water is unbalanced.

I admit that all ionizers are not alike. There are great disparities among manufacturers and mechanisms. Our process generates copper/silver ions electrolytically. The units are NSF certified and meet all the requirements of NSF Standard 50, which is a rigorous testing mechanism developed to evaluate copper/silver ion generators. Within this standard there is a nonstaining requirement, which, again, our units meet. Only NSF-approved ionizers can achieve this kind of result.

The Role of Chlorine in Corrosion and Swimmer Comfort

Chlorine brings to pool water chemistry its own set of reactions that, when it is used in excess, create unique drawbacks. We accept, in other words, that unbalanced water can cause corrosion or scaling and some swimmer discomfort; however, we believe that chlorine and its by-products create a separate set of problems that contribute to corrosion and swimmer discomfort.

Corrosion

Chlorine hinders good water balance because it can adversely affect pH levels. The active species of chlorine is hypochlorous acid (HOCl), which can corrode the internal apparatus of the pool. Furthermore, chlorine volatilizes into the air, where it can corrode adjacent structures and damage the atmosphere. Therefore, a good deal of corrosion, distinct from that attributable to unbalanced water, is caused by chlorine.

Swimmer Discomfort

Eye irritation and other swimmer discomforts can range from mild to severe. Some discomfort can be ascribed to unbalanced water, but again, chlorine use is a significant contributor. HOCl, the active species of chlorine, reacts when exposed to ammonia and forms chloramines. Bathers add ammonia or ammonia compounds through perspiration and urine, and runoff adds ammonium compounds from fertilizers. Chloramines have been well documented in poor research and have long been identified as the primary cause of eye and skin irritation. They are also the source of the unpleasant odor associated with chlorine. The use of ionization significantly reduces or eliminates these problems because the process allows for a dramatic reduction in chlorine without compromising disinfection.

Answers to Other Questions

Q: How much does the combined disinfection system reduce objectionable chlorine by-products?

A: Significantly Our article actually was the first of a two-part series detailing the results of our test. Our second article specifically addresses the issue of trihalomethane. Without discussing all the details, I can say that our process significantly reduces trihalomethane levels. So our study did foresee the need for future research, and much of that research is done and will be reported on in our second article. Lastly, we do not know of any adverse by-products from copper and silver metal ions. These metals occur naturally and are present in our everyday lives. Additionally, NSF 50 requires that our process meet U.S. Environmental Protection Agency (U.S. EPA) drinking-water standards, which it does.

Q: Was the pH level monitored during the study?

A: Yes. The Commonwealth of Massachusetts, in addition to its requirements for free-chlorine residual levels, also mandates that pH levels be maintained between 7.2 and 7.8. In our study, pH was recorded in the daily log four times a day. The chlorine, copper, and bather loads also were noted. During the baseline period, the average daily pH (ADpH) was 7.44, with a range of 7.3 to 7.6. During the ramp-up period, the ADpH was 7.45, with a range of 7.4 to 7.6. During Pilot Period I, the ADpH was 7.51, with a range of 7.3 to 7.6. During Pilot Period II, the ADpH was 7.59, with a range of 7.5 to 7.7. It was determined that pH did not play a significant role in changing the efficiency or efficacy of the chlorine.

Q: How does the Crystal Water Systems (CWS) copper/silver system perform under extraordinary circumstances-especially in the case of fecal accidents?

A. The fundamental issue associated with fecal accidents is the introduction of pathogenic organisms, including F. coli and Cryptosporidium, into the water. While we do not have any hard-and-fast results for our system in this situation and do not know whether it would be any more effective than the normal high-level chlorine system, we do know that the traditional system has long been recognized as not extremely effective in killing Cry ptosporidium.

Q: How does the cost of your system compare with that of other sanitizing methods?

A. A full-cost analysis found that our system compares quite favorably with other systems when increased pool safety, reduced corrosion, swimmer comfort, and reduced labor costs are factored in. Our system is completely automatic and depends very little on operator administration. It does not require handling or managing of chlo rine or caustic chemicals. We should all place a high premium on the proper application and handling of pool chemicals, particularly chlorine. Improper use can result in potentially catastrophic results- from explosion to fire. Just this safety fac tor alone constitutes a significant cost benefit.

Q: How do pool operators measure the results of the CWS system?

A. Results are measured against the goals set by the pool operator. In some cases, operators want to control algae or decrease odor, or switch to an environmentally friendly system that is healthier for their patrons. From testimonials we have received, we know that users of the CWS system enjoy lower chlorine levels, decreases in costs for other chemical additives such as algaecides, lower levels of maintenance, and increased pool water clarity

Pool operators also work within a regulatory environment. The Commonwealth of Massachusetts has enacted an amendment to its pool code acknowledging copper/silver ions with reduced chlorine levels (0.4 ppm) as an acceptable alternative to the traditional requirement of higher chlorine levels (1.0 ppm to 3.0 ppm). Furthermore, the most recent statewide request for response (RFR) on water chemical treatment required that ionization be offered as an antimicrobial treatment for all state, municipal, and local school district swimming pools, with added bonuses for contracts that provided the most environmentally sound alternative. This is a clear tilt in the direction of lower chlorine emissions.

Q: Does the CWS system stain pool walls?

A. No. The CWS system emits only very discreet levels of copper (0.3 ppm), and at these levels there would be no staining. Also see the discussion on water balance above.

Q: Were there any problems with combinedchlorine levels in excess of 0.6 ppm?

A. No. The 0.6 value referred to in our article relates to free chlorine, not to combined chlorine. Also, the article noted that it is when free-chlorine levels exceed 0.6 ppm that chlorine and its by-products are first detected. These observations are drawn from previously published studies (Clarke and Berman), which are cited in the reference list at the end of our study.

Q: What about testing for silver?

A. The quantity of silver used in our system is minute. To get accurate readings, we strongly recommend laboratory testing with atomic absorption methods. Yes, kits are available for pool-side testing, but the procedures often are quite elaborate. In our estimation, significant training would be required to get consistent readings. Pools experience a high turnover in personnel, so getting consistent readings might prove problematic. For these and other reasons, we would recommend periodic laboratory testing if silver levels would be a major concern for any regulators.

Q. What do you say to critics who think this was a self-serving article camouflaged as a study?

A. This was an objective study We adopted a test protocol generated by academics and practitioners in the water-engineering industry. It was reviewed by the local and state regulatory agencies that control use of our products. We then tested against this protocol. We released all the data obtained and, finally, submitted the results for publication to an independent, juried journal, which subjected them to rigorous peer review. It is the process and the level of independent third-party review that determine whether a study is objective, not the particular bias of the author. We believe our study meets this objective standard.

Having said that, I admit we are not without an agenda. Stated quite simply we believe the extraneous and indiscriminate use of toxic chemicals should stop. Chlorine is extremely effective in very low concentrations. Using significantly higher levels is unnecessary. Therefore, from environmental, human-comfort, and safety perspectives, excess use should be curtailed. We believe that it is unnecessary and ill advised to rely on chlorine alone. From a public health and water sanitation standpoint, we have proved that equivalent protection can be obtained with copper/silver ions and reduced levels of chlorine. Therefore, the use of chlorine in excess of those levels is environmentally unsound.

In conclusion, I wish to thank the Journal and its readers for giving us the opportunity to continue this very important discussion of pool water disinfection. We believe, as, I assume, do all the correspondents, that everyone is well served by continuing research, discussion, and education in the area of pool water disinfection. We would welcome the opportunity to respond to additional questions or comments. Please write to us at Crystal Water Systems, 146 Hammond Street, Newton, MA 02467, call us at [phone], or visit our Web site at [less than]www.crystal-water.com[greater than].

Sincerely yours,

Thomas J. White

President, Crystal Water Systems

Chestnut Hill, Massachusetts