Levels of a common chemical linked to cancer are dangerously high in drinking water in all 50 US states, a study suggests.
Chlorine has been added to tap water for more than a century to kill bacteria and make water safe to drink.
However, when chlorine comes into contact with certain ground materials, it produces chemicals which have been associated with a 33 percent higher risk of bladder cancer and a 15 percent higher risk of colorectal cancer.
These chemicals, trihalomethanes (THMs), are produced when chlorine comes in contact with raw organic materials such as decaying plants
Researchers from the Karolinska Institutet in Sweden analyzed more than two dozen studies involving nearly 100,000 people from North America, Taiwan, and Europe that estimated THM levels in drinking water samples and explored links between the chemicals and 14 different types of cancer.
THMs are believed to damage DNA, leading to potentially cancerous mutations and the group of substances has been tied to cancer in rats.
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 determined the true maximum safe level is far lower, at approximately 0.15 ppb.
Chlorine has been used for over a century to disinfect water, but it creates chemicals linked to a 33 percent higher risk of bladder cancer and a 15 percent higher risk of colorectal cancer
According to the EWG’s metrics, 32,136 municipal water systems serving more than 250million people across the US exceed the 0.15 ppb safety standard.
The average total trihalomethanes in New York City’s water is 42 ppb, but it ranges up to 77 ppb.
Los Angeles’ levels are 28.3 ppb. Dallas’ are about 8.85 ppb. Chicago averages about 29.8 ppb, and Boston’s are about 24.2 ppb.
Researchers concluded the risks of bladder and colorectal cancers were highest when THM levels in drinking water reached 41 ppb, well below what officials deem safe.
People within the highest category of exposure across the studies were 33 percent more likely to get bladder cancer compared to people within the category of lowest exposure, and that risk increased by eight percent with every 10 ppb increase in THMs.
The risk of colorectal cancer was 15 percent higher for those in the most exposed versus least exposed groups.
When researchers considered the sexes separately, they found a stronger link between THM exposure and colorectal cancer in men than in women.
THMs didn’t show a clear link to pancreatic, kidney, breast, ovarian, prostate, or blood cancers. However, there was a higher risk of endometrial cancer and melanoma in people with high exposure to THMs.
Dr Emilie Helte, lead author of the study, which was published in the journal Environmental Health Perspectives, said: ‘What we see is alarming and we need some more high-quality studies.’
This graph shows the relationship between THM levels in residential drinking water and the risk of bladder cancer in men and women. A 10-μg/L increase in THMs was linked to a small increase in bladder cancer risk. The lines show both linear and nonlinear risk estimates, with dashed lines representing confidence intervals
The graph shows the linear (light gray dashed lines) and nonlinear (black lines with confidence intervals) dose–response relationship between residential drinking water THM concentrations and colorectal cancer risk in men and women, based on meta-analyses. There were 8,582 total cases, with 2,714 cases in men and 2,589 in women
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THMs can be harmful if either consumed or inhaled.
They easily evaporate from water and breathing them in or absorbing them through the skin while drinking, cooking, washing dishes, or swimming can prove dangerous.
There is still a lot scientists don’t know about THMs. The exact amount of THM exposure considered carcinogenic is not universally agreed upon and can depend on many factors, such as the concentration in drinking water and the duration of time a person is exposed.
Exposure to high concentrations of chemical byproducts, especially over long periods, is believed to pose the greatest health risk.
A 2023 report in the Journal of the National Cancer Institute investigated the link between exposure to THMs in drinking water and colorectal cancer in nearly 59,000 men and women.
After nearly 17 years, there were 1,913 new cases of CRC. For men, higher levels of THMs in drinking water (15 ppb or higher) were linked to an increased risk of colorectal cancer, with a 26 percent higher risk compared to those with no exposure.
The above graph shows the rise of colorectal cancer in Americans under 50 over the last two decades. This is the latest year for which data is available
Scientists warn against relying on bottled water, as it offers no clear health advantage over tap water. A study from the San Francisco Bay Area found potential health risks in all water sources, including bottled
Activated carbon and reverse osmosis can remove THMs and can be found in pitcher, faucet-mounted, and under-the-sink filters.
Scientists also warn not to get lulled into a false sense of security by buying bottled water.
Researchers from the San Francisco Bay Area studied hundreds of water samples, including 603 from the tap, 100 from bottled water, and 111 from household-treated tap water.
They found all ‘three drinking water options had potential health risks’ and further showed bottled water ‘is not a superior alternative to tap water where household treatment is possible.’
The safety of America’s drinking water is top of mind for many given the growing mountain of evidence pointing to the myriad harms of exposure to forever chemicals and microplastics in both tap and bottled water.
Newly-confirmed Health and Human Services Secretary Robert F Kennedy Jr has made bolstering water safety a core aim of his Make America Health Again initiative.
He has set his sights on removing fluoride in the water supply. While it is widely considered one of the highest health achievements of the 20th century, RFK claims it is ‘associated with arthritis, bone fractures, bone cancer, IQ loss, neurodevelopmental disorders, and thyroid disease.’
However, experts say fluoridated water has prevented millions of cavities, saved tens of billions of dollars in dental costs and made children healthier.
