Mineral Ionizers: Don’t Forget the Chlorine

Mineral ionizers treat swimming pool water by releasing metals such as copper and silver into the water. These metals are known to have germ-destroying properties, but do they do the job adequately? While some marketers claim that their technology results in a chlorine-free pool, research suggests that mineral ionizers should, in fact, be used in conjunction with low levels of chlorine.

According to the US Environmental Protection Agency (EPA), mineral–or metal–ionizers are regulated “to kill algae and as an adjunct to the chlorination process.”i In other words, EPA recognizes that metal ionizers are effective against algae, but that they are to be used in conjunction with the chlorination process to destroy pathogens in pool water such as E. coli, which can cause swimmer’s diarrhea, and P. aeruginosa, which can cause swimmer’s ear.

Yu et al. (2002)ii tested the germicidal properties of copper, low levels of chlorine, and a combination of copper and low levelsiii of chlorine. The researchers found copper alone destroyed E. coli at an average rate of about 62 percent.  Very low chlorine levels destroyed E. coli at an average rate of more than 93 percent.  However, when copper and low levels of chlorine were combined, the average killing rate of E. coli approached 100%, indicating a significant synergistic effect between copper and chlorine.  The results are presented in the table below. Several other scientific studies also found evidence for a synergistic effect between copper and chlorine.iv,v,vi  How are pool owners to make sense of marketing information and make healthy choices?

Germicidal Test Results of Yu et al. (2002)

4 Hour Exposure of E. coli to Copper Ions Alone (1 mg/L) in Aqueous Solution 4 Hour Exposure of E. coli to Free Available Chlorine Alone (0.1 mg/L) in Aqueous Solution 4 Hour Exposure of E. coli to a Combination of 1.0 mg/L Copper Ions and 0.1 mg/L Free Available Chlorine in Aqueous Solution
Average Killing Rate of E. coli bacteria




Choosing a Pool Sanitizer

Swimming Pool Sanitizers and EPA

The word “pesticide” may seem out of place when discussing swimming pools, but EPA categorizes disinfectants used for drinking water and swimming pools as “antimicrobial pesticides” under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA).

Antimicrobial pesticides help to control microorganisms that can cause human disease; these substances are regulated by EPA under the statutory authority of FIFRA. Individual states are authorized to regulate pesticides under FIFRA and under state pesticide laws, which may be more restrictive than FIFRA.

According to the EPA Pesticides website, all pesticides must be registered both by EPA and the state before distribution. Furthermore, all pesticides must be distributed bearing their EPA-approved pesticide label.  Additionally, it is unlawful to distribute an unregistered pesticide or a registered pesticide with claims that differ from those approved by EPA.

When it comes to choosing a pool sanitizer, pool owners have many options. Here are some tips for making an informed selection:

  • All companies that distribute pool sanitizers are required to register their product with EPA, but not all products advertised online, for example, are in fact registered.  Check the product label for its EPA registration under the Federal Insecticide, Fungicide and Rodenticide Act (see sidebar).  You can also search the Purdue University National Pesticide Information Retrieval System, which is a database of federally-registered pesticide products.
  • EPA registration is important because the registration process requires EPA to ensure that the pesticide, when used according to label directions, can be used with a reasonable certainty of no harm to human health and without posing unreasonable risks to the environment.
  • Always follow manufacturer’s directions carefully; we recommend this Pool Chemical Safety video for tips on the safe storage and handling of pool chemicals.

Fred Reiff, P.E., is a retired official from both the U.S. Public Health Service and the Pan American Health Organization, and lives in the Reno, Nevada area.

i September 21, 2007 Federal Register Notice
iiYu, P., An, Z., Ren, Z., Liang, X. (2002). Experimental observation on synergetic efficacy of available chlorine and copper ion in killing Escherichia coli. Chinese Journal of Disinfection, 19, 185-186.
iii0.1 mg/L of chlorine was used; typical recommended levels of chlorine for swimming pool sanitation are 1-3 mg/L.
ivZheng, Y., Lin, Q., Xie, L. (2004). Observation on synergetic efficacy of chlorine and metal ion in killing microorganisms in water.  Zhongguo Xiaduxue Zazhi, 21, 204-207.
vBeer, C., Guilmartin, L., McLoughlin, T., White, T. (1999). Swimming pool disinfection efficacy of copper/silver ions with reduced chlorine levels. Journal of Environmental Health, 61, 9-12.
viYayha, M., Landeen, L., Kutz, S., Gerba, C. (1989). Swimming pool disinfection: An evaluation of the efficacy of copper/silver ions. Journal of Environmental Health, 51, 282-285.