In the cemetery of San Amaro, in A Coruna, there is a chapel under which is a common grave in which, at the end of the 19th century, the remains of those killed by the cholera epidemic of 1854 were deposited. In only 20 days caused the death of 2,026 of the 10,000 inhabitants of the city.
At that time the city did not have a home supply of drinking water or, of course, a health guarantee for it. This, initially without treatment, began in A Coruña in 1908 as a result of the cholera episode described. In 1915 a sand bed filtration system was installed to which, already in 1925, the purification was added by hypochlorite (the active component of the bleach).
Since then there have been no problems in the city related to the lack of water purification.
The presence of pathogenic organisms in drinking water produced in our cities, until recently, catastrophic epidemics of fatal diseases such as cholera, typhus, dysentery and gastroenteritis. The first water chlorination plant was launched in Middelkerke (Belgium) in 1902, and from there, its use spread throughout the world.
Since then, water chlorination has been one of the sanitary procedures that have most contributed to our health and well-being; A process that is also economical. Life magazine declared in 1997: “The filtration of drinking water along with the use of chlorine is probably the most important public health advance of the millennium.”
In Spain, between 1910 (decade in which chlorination became widespread) and 2010, life expectancy doubled from 40 to 80 years. Unfortunately, it is estimated that in 2010 there were still 13% of the world’s population without access to potable water.
A study published last week has generated alarm by suggesting the possible relationship between bladder cancer and water consumption with the presence of trihalomethanes (THM).
These types of data associations, generally biased, poorly explained by the media and poorly understood by the population, generate chemophobia and contribute nothing to the implementation of evidence-based decision-making systems.
What are trihalomethanes?
Trihalomethanes are small molecules, consisting of a carbon atom, three halogen atoms and a hydrogen atom. They are formed during the processes of chlorination of water by the reaction between chlorine and small molecules (amino acids, aldehydes and ketones), which in turn are generated during the decomposition by hydrolysis (reaction with water) of organic matter (such as leaves and branches ).
That there is organic matter in the water of rivers, lakes and underground springs is normal and inevitable. It is not an indication of contamination, and its quantity is not constant, but varies according to the time of the year, the rainfall regime and the runoff.
The precursor molecules of trihalomethanes are dissolved even in the most pristine springs, and it is not feasible to remove them from the water before chlorination. It is not because of its low and variable concentration, and because of the cost that this process would entail for a volume of water such as that used in a water treatment plant, even in a small one.
Chlorination is a method of purification and disinfection, not removal of contaminants. When chlorine gas (Cl₂) is added to the water, two new chemical species are formed: hypochlorous acid and hypochlorite. The relationship between the quantities of these two species depends on the pH of the water.
Hypochlorous acid is more reactive and also more disinfectant, and predominates in slightly acidic pH. It is able to penetrate the cell membrane and access the inside of the cells of pathogenic microorganisms, which causes irreversible damage by oxidizing their DNA.
Today we have other methods of purification, such as the use of ozone and ultraviolet radiation. Its cost could compete with that of chlorination, but there is an important problem. From the exit of the water treatment plant, the water circulates through many kilometers of pipes, and it must remain portable and free of pathogens when it reaches our faucets. Therefore, although initially another method is used, a post- chlorination is applied in which a residual amount of chlorine is added to ensure that the water we drink is potable.
The higher the organic load of the water and the more chlorine added, the more likely it is that trihalomethanes are formed. These substances tend to pass into the gas phase, so as the water moves through the pipes and out of the ducts their concentration decreases.
Even so, we will always have a small number of trihalomethanes present. To minimize our exposure, the ideal would be to reach a balance between the amount of organic matter, the added chlorine and the aeration time of the water before drinking it.
The solubility of the gases increases as the temperature decreases so that at room temperature, there will be fewer trihalomethanes than in very cold water. In any case, the quantities that remain in the water are tiny, of the order of parts per billion (ppb). In the amounts, a healthy person drinks should not represent a health problem.
For an intake of 2.5 liters of water per day, with the average value reported for Spain in the above-mentioned study of 28.8 ppb (well below the maximum allowed of 100 ppb), the intake would be 72 µg (0.000072 g). This, assuming that the water was at the maximum solubility temperature of the trihalomethanes (that is, very cold)
The actual data would be significantly lower since hot water has a much lower solubility. Most of the population carry out, every day, consciously or unconsciously, practices that are much more risky for their health.
Most cases, in two countries
The aforementioned study is based on routine monitoring, through questionnaires and access to open data, of four trihalomethanes (chloroform, bromodichloromethane, dibromochlormethane and bromoform) in distribution water.
The projections made do not reflect past or future exposures by the population. In addition, the factors considered (age, sex, educational level, tobacco use, high irrigation occupation, daily consumption and coffee intake) do not reflect other extraordinarily relevant ones, related to the intake of other substances that affect bladder cancer.
Among these substances could be some substances of habitual consumption (food, diet supplements, infusions), legal abuse (alcohol, tobacco), illegal abuse (drugs), drugs, exposure to urban or industrial pollution and the way water intake majority.
In 2016, 135 011 cases of bladder cancer were reported in the European Union, of which almost all were older than 20 years. The mentioned study makes a projection that 6 561 cases could be attributable to exposure to trihalomethanes. Even accepting the projection that, as has been shown, is questionable, it would be 4.8% of cases. In addition, the data provided shows that almost half of the cases of bladder cancer reported occurring in 2 countries out of 26, despite which the analysis is extended to the whole as a whole.
What is the margin of error of these projections? Can there be any conflict of interest? Is it worth the media to focus on a potential risk of such a low and objectionable level?
The fact is that a water treatment technique has been called into question that has made a fundamental contribution to human health and has generated distrust in the population. Chlorination is the best alternative we have today; It is necessary, safe and essential.
Chlorination has given us many years of life and has reduced the incidence of many diseases, some eradicated in our society. It cannot and should not be demonized. Our waters are safe for drinking. The potable water that we receive in our faucets is, without a doubt, the safest and most economical beverage alternative.
Let’s continue drinking tap water, and an economical alternative with an environmental impact much less than others. If you detect any smell or taste in the water, fill a jar and let it air for a while, the vapor pressure will do its job. Unless you drink abnormally high amounts of water, you will have no problem. Pay more attention to other risk factors that, surely and as we all do, will be exposed voluntarily, even frequently and with pleasure.