The dark side of chlorine

Disinfection using chlorine has played an important role in the supply of drinking water, but its use also involves some risk. In the latest issue of the magazine Science, Professor Urs von Gunten of EPFL and EAWAG and David L. Sedlak of the University of California put the dangers and consequences of using chlorine into perspective.

When used in very large quantities in drinking water, chlorine presents significant risks to public health. As well as neutralizing the pathogens found in water, chlorine reacts with the natural organic matter and produces a variety of disinfection by-products (DBPs).

The discovery of a potential link between DBPs and an increased rate of miscarriages and bladder cancers has led to the implementation of stricter regulations, as well as changes in the design of water-treatment systems during the last decade.

These concerns, added to the risks involved in the storage of chlorine in gaseous form, have recently persuaded many sewage or water-treatment stations to partially stop using chlorine for the disinfection of water. Many systems are now using chloramine instead.

However, as described by Urs von Gunten (School of Architecture, Civil and Environmental Engineering at EPFL and EAWAG) and David L. Sedlak (University of California) , a series of recent studies suggests that this change from chlorine to chloramine has led to unexpected consequences that present risks to public health and the environment. It was discovered that monochloramine can form NDMA, a substance that has proved to be much more toxic than the “traditional elements” formed by chlorine.

The risks of chlorine

“This problem affects mainly the U.S.”, explains Urs von Gunten “as the use of monochloramine is illegal in Switzerland. What’s more, in Switzerland the water is often pumped directly from the water-table, and is distributed without chlorine."

In particular, they apply to the protection of drinking-water sources, the appropriate treatment of water, and the maintenance of distribution networks . These measures enable the authorities to minimize the presence of chlorine, or to avoid its presence altogether.

Urs von Gunten also raises the issue of the different levels of acceptance in the population. In Switzerland, the taste of chlorine causes suspicion and complaints from the public. “In the U.S. it’s the opposite,” he explains. “If drinking water doesn’t taste of chlorine, people are concerned!”

This specialist of drinking-water treatment notes a rather diversified situation in Europe: “The application of standards differs from one country to another. In Switzerland, Germany and Austria the use of chlorine as a disinfectant for water is avoided as far as possible. In Spain, however, it is used a lot, and France is somewhere in between.

Considering the risks that the use of chlorine presents to public health, Urs von Gunten offers this conclusion: “The solution can be found in a rigorous regulation that protects drinking water resources, that guarantee clean disinfection, and that maintain distribution systems - these measures would avoid using large quantities of chlorine as a disinfectant and avoid the unpleasant odors, tastes, and health risks that accompany it.”

Author: Didier Bonvin

Source: EPFL