Trihalomethanes (THMs) in drinking water are formed as a result of:

• A Reaction of chlorine with naturally occurring organic matter (humic/fulvic acids) ✓
• B Microbial contamination by Cryptosporidium resisting standard chlorination
• C Leaching of lead from old galvanized pipes under acidic pH conditions
• D Aeration removing dissolved oxygen and creating reducing conditions

Explanation

Trihalomethanes (THMs — chloroform, bromoform, bromodichloromethane, dibromochloromethane) are disinfection by-products formed when chlorine reacts with naturally occurring organic matter (primarily humic and fulvic acids from decomposing vegetation). They are potential carcinogens, particularly chloroform (IARC Group 2B). The WHO guideline for total THMs in drinking water is 0.3 mg/L. They are more of a concern in surface water with high natural organic matter than in groundwater.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.