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Disinfection by-Products (DBPs): What’s in Your Drinking Water?

In 1902, the first continuous use of chlorine to disinfect drinking water occurred in Belgium. From then on, this chlorination method became popular around the world to treat drinking water because it can kill the harmful microorganisms in the water and maintain an environment in the water-distributing pipes where these microorganisms cannot live due to the remaining chlorine. Unfortunately, some scientists found that even though the chlorine kills these microorganisms, it reacts with other dissolved carbon-based compounds (organic compounds), and forms a group of compounds: disinfection by-products (DBPs), which are dangerous because they are carcinogenic.

Figure 1. Formation Process of DBPs

So how do these DBPs form in the drinking water? Believe it or not, there are many more elements to drinking water than just water. One of those is organic compounds, which are invisible to the human eye. As is shown in figure 1, carbon atoms (solid black balls) in these compounds will act like magnets that attract hydrogen atoms (solid white balls) and oxygen atoms (solid green balls), and that is how organic compounds form. But when chlorine is added, chlorine atoms (solid red balls) will replace several hydrogen position (marked as 1, 2 and 3 in the figure) in these organic compounds, simply because chlorine atoms (solid red balls) are larger than hydrogen atoms (solid white balls) and can be attracted to carbon atoms (solid black balls) more strongly. This varied mixture of chlorine, carbon, hydrogen, oxygen atoms will lead to more than 250 different types of DBPs, where the most common groups are haloacetic acids (HAAs) and trihalomethanes (THMs).

If even only few atoms are replaced in organic compounds, the toxicity of newly-formed DBPs is very high compared to the original organic compounds. According to the World Health Organization, DBPs can cause detrimental effects on the human’s liver, kidney and reproductive system as well as induce certain cancers. Thus, the US Environmental Protection Agency has established maximum allowable contaminants levels for the different group of DBPs where THMs and HAA5 are 0.08 mg/L (6.67×10-7 pounds/US gallon) and 0.06 mg/L (5.00×10-7 pounds/US gallon), respectively.

Overall, there is always a trade-off between how many microorganisms are killed and how much DBPs are formed when using chlorine to disinfect drinking water, and we all should be aware of what is in our drinking water.

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