HealthMap

Chlorine Gas and Organic Matter: Trihalomethanes (THMs)

Chemical Reaction

• Direct Interaction: When chlorine (whether as chlorine gas, sodium hypochlorite, or calcium hypochlorite) is introduced into water containing natural organic matter (such as humic and fulvic acids from decayed vegetation), a chemical reaction occurs.
• Disinfection By-Products: Chlorine acts as a strong oxidizing agent and halogenating agent. It reacts with these dissolved organic compounds, particularly in the presence of bromide and iodide.

Formation of THMs

• Halogenation Process: During this oxidation and substitution process, chlorine atoms substitute into the chemical structures of the organic molecules.
• Resulting Compounds: This reaction produces a group of chemical compounds known as Trihalomethanes (THMs), most notably chloroform, bromodichloromethane, dibromochloromethane, and bromoform.

Health and Environmental Significance

• Water Treatment Concern: This is a primary concern in municipal water treatment, where chlorination is used for disinfection, but the presence of organic precursors leads to the unwanted creation of THMs, which are regulated due to potential health risks.