Pool Water Chlorination: a Disinfection Method that Targets Bacteria and Human DNA?

It’s hard to imagine swimming in an unchlorinated pool. The components of chlorine basically perform two functions to safeguard the health of the bathing public. One deactivates bacteria and another conducts residual cleaning to take care of contaminants which swimmers bring to the pool batch after batch.

While chlorination appears to be the standard protocol for killing micro-organisms, the disinfection method itself is associated with a number of side effects. The usual complaints cover sore eyes and skin irritation. In addition, recent studies hint that short-term exposure to chlorinated water may also destroy the swimmers’ DNA.

By-Product Formation

In principle, chlorine ought to destroy pathogenic bacteria in water. In reality, the disinfectant reacts with other pollutants which the swimmers themselves may unknowingly introduce to the water: sweat, tanning lotions, sun block formula and a variety of cosmetics.

The reaction of chlorine against these foreign compounds would lead to the creation of other chemicals and new problems. One of the latest fears expressed by the research community is that the disinfection by-products could be mutagenic. Mutagens collectively refer to any agent capable of inducing genetic mutation in cells.

DNA Damage

A research conducted on the DNA mutation of 49 swimmers confirmed that pool water chlorination does generate mutagenic by-products and that pool water is in fact twice more toxic than tap water.

During the study, the respondents were asked to swim in an indoor pool in Barcelona, Spain for 40 minutes. They underwent a series of tests prior to and after the swimming session.

In the laboratory, the cells extracted from the swimmers were purposely stained in order to make out the genetic material. The appearance of dots suggested that a mutagen has broken a chromosome.

The dots that surface are actually the micronuclei and they are indicative of DNA damage, explained researcher David DeMarini from the Environmental Protection Agency in North Carolina.

Here are some of the observations recorded in the laboratory:

• There was an increase of micronuclei in the white blood cells of the respondents after the swim.

• The rise of micronuclei co-related with the concentration of trihalomethanes detected in pool water. (Trihalomethane is one of the widely documented by-products of pool water disinfection.)

• Two particular brominated (not chlorinated) trihalomethanes – the bromodichloromethane and the exhaled bromoform – accounted for 25 percent of the observed increase of micronuclei in the respondents’ blood.

The findings were published in 3 separate papers, all of which Cristina Villanueva has co-authored. According to the Barcelona-based environmental epidemiologist from the Municipal Institute of Medical Research, the documented genetic mutations were “low,” “repairable” and “temporary” in nature.

Frequent and extended exposure to the same waterborne mutagens though could trigger cancers, she warned.

Missing Pieces

Critics say DeMarini’s and Villanueva’s papers drew significant attention on the backlash of pool water chlorination. A major letdown however is that the study could be difficult to replicate.

Other researchers reportedly wanted to know pieces of information that were either missing or hardly discussed in the papers such as:

• How was pool disinfection controlled?
• Were automatic controllers employed?
• What were the targeted chlorine levels?
• What levels needed to be maintained?
• Where did ventilation fit in and at what rates?

Longer List of By-Products

Before, the identified by-products of pool water chlorination only amounted to a handful. This year, the number has soared to hundreds. The rise is attributed to improved laboratory facilities and continuous research efforts.

In particular, the team of Susan Richardson from the Environmental Protection Agency in Georgia is one of those credited for identifying, naming and analyzing more than 300 water disinfection by-products out of an estimated 600. Their investigation encompasses both drinking water and pool water.

The scientific community and the pool operators alike do not find it surprising that new “bad guys” are emerging from the pool water scene. They include nitrogen which reacts with urine and perspiration to cause irritation, and mutagenic bromoform which has dethroned chloroform.

Note: Contents of this article are based on a report sourced to Janet Raloff of Science News and published in the September 2010 issue of the US News website.



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