'Peeing' in pool may create harmful byproducts

Behind the Headlines

Friday March 7 2014

Urine may combine with chlorine to create toxins

Tread water, but don’t pass it

“Peeing in the pool could be bad for your health,” the Mail Online reports. As well as being unpleasant and socially unacceptable, new research suggests that a chemical in wee can react with chlorinated swimming pool water, creating potentially harmful byproducts.

The study in question used lab tests to study the reaction between a chemical found in urine (uric acid) and the chlorine in swimming pools. Researchers found that the combination of these substances can form some potentially harmful chemicals, known as nitrogen-containing disinfection byproducts (N-DBPs).

N-DBPs found at low levels in swimming pools have been linked to eye and throat irritation. At high levels, they can adversely effect the nervous and cardiovascular systems.

These byproducts were already known to be in chlorinated pools and to be formed from the reaction between chlorine and organic chemicals, such as those found in body fluids. This latest study confirms that uric acid is one of the potential sources of these chemicals.

The Mail’s coverage of this study is, primarily, an excuse to run an amusing story about weeing in pools, rather than to report on new research. It shouldn't need a study to tell us that weeing in a pool is not the most hygienic or polite of habits.

Swimming in a pool, with lifeguards to protect you, is a great form of exercise. If you choose to swim in open water, find out how to stay safe when swimming in the great outdoors.


Urine detecting 'shame dye'

You know that special dye that suddenly forms a cloud when somebody pees in the pool, in order to name and shame them? It doesn’t exist. There is no such substance.


It is unclear where this urban myth originated. It was possibly a useful lie, dreamt up by a cunning pool attendant, to discourage children (and adults) from relieving themselves in the water.


Just don’t do it, please.

Where did the story come from?

The study was carried out by researchers from China Agricultural University in Beijing and Purdue University in the USA. It was funded by the Chinese Universities Scientific Fund, the National Natural Science Foundation of China and the National Swimming Pool Foundation in the USA. 

The study was published in the peer-reviewed journal Environmental Science and Technology.

The Mail Online reports the study fairly, quoting a lot of information directly from the scientific paper itself. We suspect that a Chinese study published in a relatively obscure environmental health journal would not have garnered such coverage if it didn’t cover such a topic as public urination.


What kind of research was this?

Chlorine is used to disinfect pools, but it can react with other chemicals in the water  such as human bodily fluids  to produce potentially harmful chemicals. This was a laboratory study looking at the chemical reactions that occur as a result of the mixing of chlorine in pools and a chemical called uric acid, which is found mainly in urine, but also in sweat. 

Previous studies have found that, on average, swimmers release between 0.2 and 1.8 litres of sweat (up to more than 3 pints) and between 25 and 117 millilitres of urine per swim (up to about half a cup of urine).

This study tells us about the chemical reactions that may occur in pools, but didn't look into the health effects of these. The researchers note in their introduction that nitrogen-containing disinfection byproducts (the substance produced by the reaction) “tend to be more genotoxic, cytotoxic and carcinogenic”.


What did the research involve?

In a lab, the researchers mixed chlorinated water with uric acid  or mixtures of chemicals designed to replicate human bodily fluids  under different conditions. They then monitored these to see if certain potentially harmful chemicals, called volatile nitrogen-containing disinfection by-products (N-DBPs), were formed, and how much of them there were. The word “volatile” means these chemicals easily form gases and can therefore be breathed in.

The researchers also collected water from swimming pools in China and analysed them in the lab. In some experiments, extra chlorine or uric acid was added to the pool water to see what chemicals were produced.

The two N-DBPs the researchers looked at (cyanogen chloride and trichloramine) are known to be formed at low levels as a byproduct of chlorination in pools. These chemicals are irritants and potentially harmful to the lungs, heart and the central nervous system above certain levels of exposure. It was already known that these chemicals can form as a result of the reaction between chlorine and amino acids (building blocks of protein that are also found in bodily fluids). However, whether chlorine has a similar effect when mixed with uric acid is unknown.


What were the basic results?

The researchers found that the reaction between the chlorinated water and uric acid in the lab produced both cyanogen chloride and trichloramine.

Swimming pool water analysis showed both cyanogen chloride and trichloramine in all samples. Adding extra uric acid to the swimming pool water led to more cyanogen chloride forming, but the effects on trichloramine levels were less consistent.

Experiments with solutions mimicking body fluids suggested that chlorination of uric acid may account for a considerable proportion of the cyanogen chloride formed in pools, but less of the trichloramine.


How did the researchers interpret the results?

The researchers concluded that as most uric acid is introduced into pools by urination, reducing this habit could lead to benefits in both pool and air chemistry.



This study suggests that certain, potentially harmful, byproducts of pool water chlorination result, in part, from a reaction to the uric acid found in urine.

The media coverage of this study is likely to be more of an excuse to run an amusing story about weeing in pools, rather than the study itself. The byproducts in question were already known to exist in pools, and to be formed from the reaction between chlorine and organic chemicals, such as those found in body fluids. The current study confirms that uric acid is one of the potential sources of these chemicals.

The only swimming pool water tested in this study was from China, and the exact types of disinfectant chemical used, levels of chlorine and extent of weeing in the pool may differ in pools from different countries.

At best, the practice of weeing in a pool is socially unacceptable; at worst, it may be a potential health hazard.

Analysis by Bazian. Edited by NHS Choices.
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Analysis by Bazian

Edited by NHS Choices

Links to the headlines

Peeing in the pool could be bad for your health: Researchers warn unhygenic habit could trigger chemical reactions that cause respiratory problems. Mail Online, March 7 2014

Links to the science

Lian L, E Yue, Li J, Blatchley ER. Volatile disinfection byproducts resulting from chlorination of uric acid: Implications for swimming pools. Environmental Science and Technology. Published online February 25 2014


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