The Connection Between THMs in Drinking Water and Cancer Risk
- Published:
- Updated: December 16, 2024
Summary
Uncover the connection between THMs in drinking water and cancer risk:
- Chlorination process: Chlorine disinfection of water can lead to the formation of THMs, volatile organic compounds associated with health risks.
- Health effects: Long-term exposure to THMs may result in liver, kidney, and central nervous system problems, as well as potential reproductive effects.
- Cancer risk: Studies suggest that THMs, particularly chloroform, may increase the risk of bladder and colorectal cancer by damaging cellular DNA.
Trihalomethanes (THMs) are a class of volatile organic compounds that can occur naturally in water supply. These are four chemical species: chloroform, bromodichloromethane, dibromochloromethane and bromoform. They are white, water insoluble, and smell sweet like ether.
THMs generally are the byproducts of the reaction of chlorine (a popular disinfectant in water treatment) with naturally occurring organic compounds in water. Chlorination is a step toward ensuring safe water, but THMs as byproducts can present health hazards, and there should be a conversation about how they’re managed.
THMs and the Chlorination Process
Chlorination is at the heart of THMs. Chlorine is the most common water disinfectant since it kills pathogenic microorganisms to keep the water in our bodies safe. But when chlorine reacts with natural organic compounds in water, disinfection products such as THMs can also result.
What causes THMs to form during the chlorination process is dependent on organic matter and chlorine concentration, water pH, temperature, and contact time. These are the factors that need to be known to avoid and control THM production during water treatment.
What are the health effects of long-term exposure to THMs?
Chronic consumption of THMs is linked to a series of health side-effects. Beyond being carcinogenic, as we’ll look at more fully below, if you expose yourself to high concentrations of THMs, you might develop liver, kidney or central nervous system dysfunction.
There are also some studies showing reproductive consequences, with high THM levels potentially associated with low birth weights, miscarriages and some birth defects. It’s not yet clear whether these non-cancerous effects are a cancer but they do highlight the need to keep THM concentrations in our drinking water under control.
Understanding the Connection Between THMs and Cancer
THMs’ link to cancer has been a scientific curiosity for decades. There are several researches suggesting that chronic THM exposure increases the risk of some types of cancer, particularly bladder and colorectal cancer. The International Agency for Research on Cancer (IARC) considers chloroform, one of the THMs, possibly human carcinogenic.
We don’t know precisely how THMs could lead to cancer. But they are suspected of damaging cellular DNA and, in the long run, turning cancerous. Even if there isn’t yet conclusive research on the connection between THMs and cancer, the current evidence shows that avoiding exposure to these chemicals should be minimised.
Regulations and Guidelines for THMs in Drinking Water
With THMs being a health hazard, many countries have regulations and standards to regulate their concentrations in water supply. The U.S. Environmental Protection Agency (EPA), for instance, limits total THMs to 80 parts per billion.
Ingestion of the most common THM, chloroform, also contains a tentative guideline value from the World Health Organization (WHO) in drinking water. These rules and regulations are meant to balance risks and benefits associated with water chlorination, in order to supply clean, safe drinking water.
Testing and Monitoring for THMs in Drinking Water
THMs are managed by regular testing and monitoring of drinking water for the presence of these chemicals. The different methods to detect and quantify THMs are gas chromatography, mass spectrometry, and others.
This kind of testing can also be very useful to have THM data to make informed water treatment and THM reduction decisions. Water providers should conduct these tests on a regular basis so they are compliant with regulation and not compromising public health.
What are some effective ways to reduce the levels of THMs in drinking water?
THM reduction in water is a municipal and household level solution. At the municipal level, chlorination in the water treatment plants can be improved to remove as much THM as possible. This may include changing when and where chlorine is added, or with other disinfection methods, like ozonation or ultraviolet light.
There are a number of things you can do at home to mitigate THM exposure:
Activated carbon filters: These filters are used to get rid of THMs from tap water.
Fertilising tap water: THMs are volatile — they will evaporate from the water after a while if left unattended.
Removing THMs from air through a warm water source Water is released more easily in air when the water is cold, so water should be cold used to wash dishes.
Looking Forward: Future Research on THMs and Cancer Risk
And more needs to be done, to really know what exactly THMs do to your risk of cancer. We will learn more in the future, about how THMs might cause cancer, and what might happen if exposed to various types and concentrations of THMs.
That kind of research could also influence regulations or water treatment practices. For example, now that we know more about the harms of THMs, health officials could choose to reduce the permitted concentration of these chemicals in water supplies.
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