Higher risk of bladder and colorectal cancer in the US due to chemicals in drinking water

A study by Sweden’s Karolinska Institutet found dangerously high levels of carcinogenic chemicals in drinking water in all 50 US states. The chemicals are tied to chlorine, which is usually applied to tap water to kill bacteria. When it comes into contact with certain organic materials like decaying plants, however, it produces substances that are harmful to human health. These substances, known as trihalomethanes (THMs), have been linked to several types of cancer, especially bladder and colorectal cancer. The maximum level of THMs deemed safe in drinking water, according to state governments, is 80 parts per billion (ppb), but a peer-reviewed study by the Environmental Working Group (EWG) poses it far lower, at approximately 0.15 ppb. According to EWG’s metrics, thousands of municipal water systems in the US far exceed this safety level, with an average of 42 ppb recorded in New York City, 29.8 ppb in Chicago, 28.3 ppb in Los Angeles, and 24.2 ppb in Boston.
Analyzing more than two dozen studies conducted in North America, Taiwan, and Europe, researchers at Karolinska estimated THM levels in drinking water and discussed their links with cancer. They concluded that the risks of bladder and colorectal cancers were highest when THMs levels reached 41 ppb, well below official state limits. The risk of bladder cancer was 33% higher in the people most exposed to the chemicals, and it increased by 8% with every 10 ppb increase. The risk of colorectal cancer was instead 15% higher. Researchers also found stronger links between THM exposure and colorectal cancer in men than in women. Dr Emilie Helte, the leading author of the study, said that the findings were alarming and underlined the need for further high-quality research to better assess the situation. THMs can also easily evaporate from water and be absorbed by breathing. And even bottled water is not safe: research conducted in the San Francisco Bay Area over hundreds of water samples, including 100 from bottled water, found that all drinking water options had “potential health risks” and that “bottled water is not a superior alternative to tap water where household treatment is possible.”