Jan. 15 (UPI) -- Drinking water may elevate bladder cancer risk, at least based on the findings of a study done by European researchers and published Wednesday in the journal Environmental Health Perspectives.

The authors of the paper found that more than 6,500 cases of bladder cancer diagnosed each year in Europe -- nearly 5 percent of the total -- can be attributed to trihalomethane, or THM, exposure through drinking water.


Researchers based at the Barcelona Institute for Global Health found the connection after analyzing tap water from 26 European Union countries

"Over the past 20 years, major efforts have been made to reduce trihalomethane levels in several countries of the European Union, including Spain," ISGlobal researcher Manolis Kogevinas said in a statement. "However, the current levels in certain countries could still lead to considerable bladder cancer burden, which could be prevented by optimizing water treatment, disinfection and distribution practices and other measures."

According to the U.S.-based Water Quality and Health Council, THMs are actually a group of chemical compounds -- including chloroform, bromodichloromethane, dibromochloromethane and bromoform -- first identified in drinking water in the 1970s. These compounds are formed as an unintended consequence of drinking water treatment or decontamination, when organic matter in natural water reacts chemically with chlorine disinfectants, and are just one type of a larger family of chemicals known as "Disinfection Byproducts."

In the United States, THMs have been linked with the so-called "Flint Water Crisis." The Environmental Protection Agency has published a rule limiting total THM to a maximum allowable annual average level of 80 parts per billion.

An analysis by the non-profit Environmental Working Group has identified communities in 32 states in which the drinking water has total THM levels above this legal limit. These water supplies serve more than 850,000 people.

For the Environmental Health Perspective study, the authors sent questionnaires to governing bodies within the EU that are responsible for municipal water quality, requesting information on the concentration of total and individual THMs at the tap, in the distribution network and at water treatment plants. They obtained additional open data online, and from reports and scientific literature, among other sources.

THMs data for 2005 to 2018 were obtained for all EU countries -- except Bulgaria and Romania, where less information was available -- covering 75 percent of the continent's population.

Overall, the average level of THMs in drinking water in all countries was well below the maximum permissible limit in the EU --11.7 μg/L versus 100 μg/L -- but the maximum reported concentrations did exceed the limit in nine countries: Cyprus, Estonia, Hungary, Ireland, Italy, Poland, Portugal, Spain and Britain.

"The biggest challenge was collecting representative data on national trihalomethanes levels for all EU countries," said Cristina Villanueva, the ISGlobal researcher who coordinated the study. "We hope that these data will become more readily available in the future."

The authors then estimated the number of attributable bladder cancer cases using a statistical calculation linking average levels of THMs with the international information available of bladder cancer incidence rates for each country. Spain and Britain had the largest number of attributable cases of bladder cancer -- 1,482 and 1,356, respectively -- due in part to the high incidence of bladder cancer and their large population.

The countries with the highest percentage of bladder cancer cases attributable to THM exposure were Cyprus, at 23 percent; Malta and Ireland, at 17 percent; Spain, at 11 percent; and Greece, at 10 percent. The authors noted that if the 13 countries with the highest average THM levels were to reduce them to the EU average, an estimated 2,868 annual bladder cancer cases -- 44 percent of the total -- could potentially be avoided.