Disinfection By-Products in Drinking Water

Water utilities currently face an ongoing challenge due to increasing concentrations of natural organic matter in source water. Natural organic compounds is a broad term that is used to describe a complex mixture of compounds derived from decaying plant and animal matter that occur naturally in water.

Changes in the complexity of natural organic matter in catchments has impacted the performance of direct filtration plants, resulting in reduced treatment capacity, increased chemical consumption and waste sludge production. Failure to successfully control the natural organic matter issue could result in hundreds of millions of dollars of upgrades to the treatment processes at some Utilities.

When high levels of organic matter, such as algae for example, are present, utilities are spurred to heavily disinfect with chlorine to kill any pathogenic microbes that may potentially pose a public health threat. But the conundrum is that the chemicals used to disinfect water can react with natural organic matter to form disinfection by-products, known as trihalomethanes (THMs), many of which are carcinogenic and therefore pose significant health risks of their own.

What are Trihalomethanes (THMs)

THMs are a group of four chemicals — bromodichloromethane, dibromochloromethane, tribromomethane (bromoform) and trichloromethane (chloroform) — that form when chlorine reacts with natural organic matter present in water. As THMs are considered a drinking water contaminant, their levels are regulated. In Europe and the USA, the maximum allowable levels for THMs in drinking water (i.e. for all four THMs combined) is 80 parts per billion (80 μg/L).

In Australia, however, the allowable limit is much higher at 250 parts per billion (250 μg/L).

What are the Health Risks Associated with THMs?

THMs are known carcinogens that have been linked to an increased risk of cancer. particularly bladder cancer. A study led by scientists at the Barcelona Institute for Global Health (ISGlobal), which was published in the scientific journal Environmental Health Perspectives in 2020, estimates that more than 6,500 European residents get bladder cancer every year as a result of exposure to THMs in drinking water, contributing to 5% of bladder cancer cases in Europe annually.

Other health risks associated with exposure to THMs include damage to the kidneys, liver and central nervous system, as well as reproductive system disorders, infertility, and an increased risk of miscarriage, stillbirths and birth defects.

What is even more concerning, is that the risk of exposure to THMs is not limited to drinking water. Another study published in Environmental Health Perspectives in 2005 confirms that exposure to THMs through the skin  while bathing, showering or even washing dishes can be significant, as can inhaling steam while someone else is taking a shower.

Are there Other Disinfection By-products of Concern?

In a 2021 research study, which was published in Environmental Science: Processes & Impacts, Carsten Prasse, assistant professor in the Department of Environmental Health and Engineering at John Hopkins University, voices his concerns with regard to the health risks posed by disinfection by-products in drinking water. He also proposes a new approach for assessing the quality of drinking water, which could vastly improve its safety. Dr Prasse is concerned about the fact that only eleven compounds out of more than 700 disinfection by-products that have been identified in chlorinated water to date, are currently regulated. It is also concerning that very little is known about the health impact of these unregulated chemicals, which by extension are not even monitored.

"We are exposing people to these chemical compounds without knowing what they even do," says Prasse. "I'm not saying that chlorination is not important in keeping our drinking water safe. But there are unintended consequences that we have to address and that the public needs to know about. We could do more than what we're doing."

According to Dr Prasse, while water utilities have been monitoring eleven disinfection by-product compounds since the 1990's, no additional compounds have been added to the list of regulated disinfection compounds despite strong evidence suggesting there are other harmful disinfection by-products in drinking water. Prasse suggests that it would not be feasible to apply methods currently used to assess the health risks associated with chemical compounds in water on the growing list of disinfection by-products as they typically involve laboratory studies conducted on animals and are outdated, costly and time consuming to conduct. Prasse believes that at the very least, new methods are needed to identify which disinfection by-products pose the greatest health threat.

Prasse proposes a novel "reactivity-directed analysis" approach for identifying a wider range of toxic chemicals in water samples by targeting the largest group of toxic chemicals known as "organic electrophiles". "This method can help us prioritize which chemicals we need to be paying closer attention to with possible new regulations and new limits while saving time and resources," says Prasse. Prasse's approach uses a combination of advanced molecular toxicology methodology and analytical chemistry to identify toxic chemicals according to how they react with molecular tissue of living organisms that are essential for healthy bodily functioning. "We know that the toxicity of many chemicals is caused by their reaction with proteins or DNA which alter their function and can result, for example, in cancer," Prasse explains.

How to Reduce THMs in Water

According to the Water Research Center, concentrations of disinfection by-products tend to increase with temperature, pH, and time. They are also influenced by the level of natural organic matter that serves as a precursor for the chemical reaction with chlorine to form the disinfection by-products. Therefore, in order for water utilities to reduce these unwanted disinfection by-product chemicals, they shouldn't chlorinate the water before it has passed through filters that are capable of filtering out the organic matter precursors responsible for triggering the chemical reaction with chlorine that causes THMs and potentially other disinfection products to form. Chlorine should only be added once the organic matter has been removed.

Infinite Water has demonstrated exceptional reductions in natural organic matter concentrations while improving the overall quality of the water (for example, reducing  disinfection by-products and heavy metals, and improving water colour, taste and clarity).

Journal References

Iro Evlampidou, et al. Trihalomethanes in Drinking Water and Bladder Cancer Burden in the European Union. Environmental Health Perspectives, January 2020. https://doi.org/10.1289/EHP4495.

Nuckols, John R et al. Influence of tap water quality and household water use activities on indoor air and internal dose levels of trihalomethanes. Environmental Health Perspectives, vol. 113,7 (2005): 863-70. doi:10.1289/ehp.7141

Carsten Prasse. Reactivity-directed analysis – a novel approach for the identification of toxic organic electrophiles in drinking water. Environ. Sci.: Processes Impacts, 23 (2021), 48-65. doi:10.1039/D0EM00471E