Trihalomethanes and the chlorination of water


A study of the Medical Research Institute(IMIM) and the Chemical and Environmental Research Institute (CSIC) of Barcelona, have identified trihalomethanes in the faucet water of four Spanish areas at concentrations 'very high' to the European average . The study, co-directed by the epidemiologist Manolis Kogevinas and the chemist Joan Grimalt, attributed 'a risk of 20% of average' of bladder cancer associated with these compounds in areas with high concentrations and long periods of exhibition.


Thestudy, by C.M. Villanueva a,b / M. Kogevinas a / J.O. Grimalt b, was published in January of 2001 in the Spanish magazine Gaceta Sanitaria.

a. Institut Municipal d’Investigació Mèdica (IMIM). Unitat de Recerca Respiratòria i Ambiental.
b. Consejo Superior de Investigaciones Científicas (CSIC). Instituto de Investigaciones Químicas y Ambientales de Barcelona. Departamento de Química Ambiental

Correspondence: M. Cristina Villanueva. C/ Dr. Aiguader, 80. 08003 Barcelona.

  • Some conclusions of the study

The water quality in origin is the main determinant of the amount of chlorination by-products generated and explains the differences between the studied areas of Spain.

The calculation of attributable risk for bladder cancer is based on certain assumptions and for this reason must be considered with caution. Secondly, cancer is a disease with a long latency period, reason by the real exhibition is not associated with the current effect, is the exhibition during several decades before clinical manifestation.

Assuming an intermediate exposure in the Spanish scope, the attributable risk would be higher than 20% of annual deaths in Spain by bladder cancer attributable to this environmental exposure would be around 600 deaths.

It´s necessary to indicate that the chemical and bacteriological prevention of the water isn´t antagonistic, specially for a country of the socioeconomic level like Spain.The risk of the water chlorination on the human health is avoidable, as there arealternative methods of water disinfection and purification, with the same disinfectant capacity and with a minor formation of chlorinated substances.


In these last times, new controversies with respect to chlorination in the potable water, and the formation of Trihalomethanes have arisen (THM). The Trihalomethanes are organic compounds that appear in the potable water after being put under chlorination in the presence of humic substances, potentially cancerigenic.

The chloroform or trichloromethane is one of the trihalometanes formed during the water chlorination to disinfect it. It is a colorless, volatile liquid, of characteristic odor.During long time the choroform was used like anesthetic, but it was discontinued because of it´s toxicity. At the moment, the chloroform is used like dissolvent in the chemical industry but, as it happens with all the halogenated organic compounds (mainly fluorine and chlorine) the character of polluting substance, causes the restriction of its consumption .Small amounts of chloroform are formed when the chlorine that it´s used for the water disinfection makes in contact with the organic substances presents in it.


Sources of information used:

Universidad de Puerto Rico. Recinto de Río Piedras. Facultad de Ciencias Naturales. Departamento de Matemáticas. El Uso del Cloro en la Desinfección del Agua.

The chlorine is discovered in 1774 by the Swedish Chemistry Karl Wilhelm Scheele.

Chlorine andchlorinecompoundsarea powerfuloxidizersand candissipate itin reactions witha variety oforganic and inorganic materialsinthe water before a sufficient disinfection will be obtained.

The waters that arrive at treatment plant contain reducing agents (organic and inorganic compounds like nitrites, iron ions, lead and sulfides), as well as microorganisms and bacteria.

Chlorineis applied inexcess (approx. 2 mg /L)so that it cansatisfy the demand tooxidizethese compounds and eliminate thebacteria,and thus, reduces anamount of residual chlorinein thewater conduits. This chlorine is free in the water after being disinfected in the plant. It´s utility is to continue disinfecting the water since it leaves the treatment plant until it arrives at the consumer.

This residual chlorine is important that it is at safe levels for the human consumption. If the chlorine is in excess, this substance can be toxic for the consumption. An excess of chlorine can react with various compounds, increasing the risk of occurrence of trihalomethanes, that are carcinogen compounds for the humans.

The trihalometanes are in the potable water like a result of the interaction of chlorine with natural organic matter that is in the water.

On the other hand, if the residual chlorine is less than the necessary, the water can retain pathogenic bacteria, protozoos and virus that threaten the health of the consumer.

Other sources of information:

- Asociación Nacional de Productores de Cloro Dirección C/ Raimundo Fernández Villaverde, 65 Madrid 28003 España
Teléfono 34 91 555 12 17.

- Asociación Sudamericana del la Industria del Cloro-Soda y sus Derivados, Clorosur




Councils of Health of the Autonomous Communities



Authors: de Ciurana Gay, C.;Om Tubau, J.
Title: Dióxido de cloro y su efecto en la formación de trihalometanos. Aplicación práctica en la ETAP de Montfullá.
Title in English: The effect of chlorine dioxide on the formation of trihalomethanes.
Workplace: Lab. Aigües Girona "Salt i Sarriá de Ter" S.A., Bescanó (Girona), España
ISSN: 0211-8173
Journal: Tecnología del agua
Year, data, source: 2000, 20 (201): 75-81, 8 Ref
Summary: El dióxido de cloro presenta una alta reactividad con determinados compuestos orgánicos e inorgánicos. En la potabilización, una de las características más valoradas del dióxido de cloro, es la oxidación de precursores de trihalometanos, que permite su disminución en las aguas de consumo. La generación del dióxido de cloro debe realizarse en el punto de dosificación. Tanto la generación como su control puede realizarse de forma sencilla. Desde hace ya algunos años en la ETAP de Montfullá se están realizando estudios con el fin de disminuir la concentración de trihalometanos. En este trabajo se expone la generación, el control de dosificación, y la reducción de trihalometanos obtenidos con la dosificación de dióxido de cloro a diferentes dosis (A).

Authors: Valero Cervera, F.
Title: Trihalometanos (THMs) en una red de distribución de agua potable en alta. Evolución de su concentración.
Title in English: Increasing concentrations of trihalomethanes (THMs) in a drinking water distribution network.
Workplace: Aguas Ter Llobregat (ATLL), Barcelona, España
ISSN: 0211-8173
Journal: Tecnología del agua
Year, data, source: 1999, 19 (194): 18-23, 12 Ref
Summary: Los THMs son subproductos formados durante la cloración de aguas. Su concentración depende del nivel de precursores y del tipo de tratamiento. Este trabajo estudia la evolución del nivel y de la especiación de THMs a lo largo de toda la red de abastecimiento regional de ATLL (450 km de tuberías), que parte de sus dos ETAPs (Llobregat y Ter). El estudio permite determinar distintos origenes o aportaciones externas al sistema, además de mostrar que no se observan diferencias de nivel a lo largo de la red (A).

Authors: Aguirre Pascual, G.;Monforte de Monleón, L.;Tós Boix, S.
Title: El permanganato potásico y sus aplicaciones en el tratamiento de aguas. (2). Efecto sobre la formación de trihalometanos.
Workplace: Gamaser, Valencia, España;Aguas de Valencia S.A., Valencia, España
ISSN: 1134-4520
Journal: IN. Innovación química
Year, data, source: 1997, 4 (25): 62-65, 21 Ref

Authors: Freiria Gándara, M.J.;Alvarez Devesa, A.;Lorenzo Ferreira, R.A.;Racamondo Hiebra, F.;Rodríguez Rojo, A.
Title: Compuestos orgánicos halogenados en aguas tratadas con cloro.
Workplace: Fac. Cienc. Orense Univ. Vigo Dep. Quim. Pura Apl., Orense, España;Fac. Quim. Univ. Santiago de Compostela Dep. Quim. Anal. Nutr. Bromatol., Santiago de Compostela (La Coruña), Spain

* Everything that appearsin this section has informative character onlyand is subordinateto that reportedin the correspondingofficialbulletins, official publications and original documents.