Exposure to chemicals found in drinking water after it has been disinfected with chlorine could be responsible for up to 1 in 20 cases of bladder cancer across the European Union. The number rises to as high as 1 in 5 in some countries, asserts an international team of researchers.
Trihalomethanes (THMs) are one of the most common disinfection by-products (DBPs) found in drinking water after chlorination.
They have been associated in particular with an increased risk for bladder cancer; one meta-analysis suggests that exposure to THMs could increase the risk for the disease by more than 50%, the authors state.
Total THM concentrations, defined as the sum of levels of chloroform, bromodichloromethane, dibromochloromethane, and bromoform, are the only DBPs in drinking water that are regulated by the European Union. The maximum is set at 100 µg/L.
Although “major efforts” have been made to reduce THM levels in several countries, “current levels in certain countries could still lead to considerable bladder cancer burden,” said coauthor Manolis Kogevinas, PhD, a senior researcher in cancer and water pollution at the Barcelona Institute for Global Health (ISGlobal), Barcelona, Spain.
This “could be prevented by optimizing water treatment, disinfection, and distribution practices and other measures,” he said in a statement
However, Karis Betts, health information manager at Cancer Research UK, told Medscape Medical News that the study “estimates the proportion of bladder cancers that trace chemicals in drinking water could cause, but it does not show whether or not they can cause cancer in the first place.”
She pointed out that “research on the causes of bladder cancer has shown that the most important cause is smoking, which is linked to about half of all cases.”
Betts said that there “isn’t enough evidence that these chemicals can cause bladder cancer, and the IARC [International Agency for Research on Cancer] only rate it as a possible link.”
For the current analysis, the researchers gathered data on THM levels in drinking water in 26 countries of the European Union. They found that the average exposure was far below the maximum permissible limit, although in nine countries, the maximum limit was exceeded to some degree.
The results, which were published online January 15 in Environmental Health Perspectives, also suggest that just under 5% of bladder cancer cases across the European Union could be attributable to THM exposure.
Of those cases, 44% could be avoided if THM levels were reduced below the average in all thirteen countries that exceeded it, say the authors.
For the study, the team investigated total and individual THM concentrations in drinking water in all 28 countries of the European Union as of 2016.
Lead author Cristina Villanueva, PhD, an environmental epidemiologist at ISGlobal, who coordinated the study, said: “The biggest challenge was collecting representative data on national trihalomethane levels for all EU countries. We hope that these data will become more readily available in the future.”
To get around the problem, they sent a questionnaire to the institutions that maintain water quality data in each country.
They received completed questionnaires for five countries ― Croatia, Finland, Hungary, Lithuania, and Malta. Belgium, Cyprus, the Czech Republic, Estonia, Greece, Italy, Latvia, Poland, Portugal, Slovenia, and the United Kingdom sent raw water monitoring data.
For Germany, Greece, and Luxembourg, online data and reports were used. For Cyprus, Denmark, the Netherlands, Slovakia, and Sweden, data were obtained via direct communication with the authorities or researchers responsible.
In Italy, only partial data were available. Data were not available for Austria, Bulgaria, and Romania, so the team conducted a literature review. For France, Ireland, and Spain, country-level information on THM levels had already been published, and so the authorities in those countries were not contacted.
The researchers were able to determine THM data for the period 2005–2018 in 26 countries, covering 75% of the European Union population aged 20 years or older, although the coverage and accuracy of the data within countries were heterogeneous.
The researchers estimate that the population-weighted mean total THM level in drinking water across the 26 countries was 11.7 µg/L.
The lowest levels were in Denmark (0.02 µg/L), the Netherlands (0.2 µg/L), and Germany (0.5 µg/L); the highest levels were in Cyprus (66.2 µg/L), Malta (49.4 µg/L), and Ireland (47.3 µg/L).
Maximum levels exceeded the 100-µg/L limit in nine countries during the study period: Cyprus, Estonia, Hungary, Ireland, Italy, Poland, Portugal, Spain, and the United Kingdom.
Calculations indicated that THMs accounted for 6561 cases of bladder cancer every year, at an estimated bladder cancer population-attributable fraction of 4.9%.
With respect to each country individually, the researchers found that the lowest population-attributable fraction was in Denmark, at 0.0%, followed by the Netherlands, at 0.1%; the highest fractions were seen in Ireland (17.2%), Malta (17.9%), and Cyprus (23.2%).
They estimate that if total THM concentrations were reduced to the current average in all 26 countries, 2868, or 43.7%, of the annual attributable cases of bladder cancer could be avoided in men and women aged ≥20 years.
The largest relative reduction in attributable cases would be seen in Romania (85.1%), Cyprus (80.3%), Malta (74.5%), and Ireland (73.5%).
The team suggests that “the main efforts in reduction of THM levels should be made in countries with the highest proportion of exceedance and highest average THM levels.”
The study was funded by the EU Seventh Framework Programme EXPOsOMICS Project, the Human Genetics Foundation, and CIBER Epidemiología y Salud Pública (CIBERESP). The authors have disclosed no relevant financial relationships.
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