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Chlorination by-products

Disinfection by chlorine is still the most popular, although more effective and ecological methods are gaining popularity. Chlorine has been used as one of the water treatment technologies since the beginning of the 20th century. It is obtained by electrolysis of aqueous solution of sodium chloride. The popularity of chlorine did not come from nowhere – since the mass use of this disinfectant, the incidence of various infectious diseases has decreased significantly – this is due to chlorine’s high bactericidal potential. Unfortunately, the use of chlorine has not only positive effects. According to our knowledge – during the chlorination process, compounds are formed that have a strong toxic effect and are therefore not inert to health. The reaction of chlorine with water (and organic compounds in it) may pose a serious health risk, especially if it comes to drinking water. As such water is used very often, the application of small doses of chlorine with it (almost continuous) may contribute to the activation of various pathogenic processes, including cancer. Chlorine may also have adverse dermatological effects. It also affects metabolic abnormalities.

Side products of chlorine use. There are many of them and they have stronger or weaker, but usually negative, effects on our health, so the use of chlorine and its combination with other substances is strictly regulated.


These are organic by-products of chlorine use. They belong to the carbonyl compounds. Formaldehyde, acetaldehyde, glyoxal and methylglyoxal are formed in reaction with chlorine in water. In the context of health hazard, formaldehyde is most often mentioned as a carcinogen. Other compounds mentioned above may also cause cancer – in the gastrointestinal tract and in the respiratory tract. The intensity of aldehyde formation in chlorinated water is mainly affected by the amount of organic substances contained in it.


These are derivatives of chlorine dioxide decomposition, they can also be isolated in water as a result of hypochlorite use. Some of them (potassium, calcium and sodium chlorates) are classified as pesticides. They can cause tissue hypoxia. The maximum allowable concentration of chlorates in water must not exceed 0.7 [mg/l].


They are classified as pesticides. Formed in drinking water, as a result of chlorination of water containing phenols. Their effect is toxic, definitely negatively influencing the cardiovascular, nervous and respiratory systems. Moreover, they are also known as carcinogens. Water containing these substances has a characteristic, very unpleasant taste and smell.


It is formed by the reaction between chlorine and organic substances contained in the treated water. Chloroform (included in haloforms) is a substance with a strong toxic effect. It has a negative impact on the central nervous system – can cause eye disorders, dizziness, various types of neuralgia, agitation, and even dazedness. This substance has a narcotic effect. Harmful to many internal organs, especially liver and kidneys. It causes skin problems. May contribute to the formation of cancer.


Substances which are chlorinated derivatives of aliphatic hydrocarbons. These include, among others, trichloro methane (THM). They are formed as a result of chlorination, from organic and humic compounds. They are particularly dangerous due to their high activity. Reaction with organic substances in drinking water takes place until one of the reaction-forming components (either the organic substance or the chlorine) is run out. Another danger is that dangerous THM formation reactions occur not only directly at the water treatment site, but also in the network through which the water is then distributed. Haloforms are characterized by extremely negative effects on human health, destabilizing the functioning of many organs. They are highly toxic and carcinogenic compounds.


One of the haloforms – forms in drinking water, after chlorination. It shows carcinogenic, narcotic and toxic effects. It is particularly dangerous to the central nervous system. May cause eye problems. If we have prolonged contact with it, we endanger the condition of our heart, liver and kidneys.