Investigation of Chlorinated Disinfection By-Products in Treated Municipal Drinking Water Across Four Geopolitical Zones in Nigeria

Chlorination of drinking water generates disinfection by-products including trihalomethanes and haloacetic acids whose concentrations and speciation depend on source water chemistry, chlorine dose, and temperature. This study investigates trihalomethane and haloacetic acid concentrations and formation potential in treated municipal drinking water from eight water treatment facilities serving major cities across four Nigerian geopolitical zones, including Kaduna and Kano in the North West, Lagos and Ibadan in the South West, Enugu and Onitsha in the South East, and Port Harcourt and Warri in the South South. Water samples were collected at the point of treatment and at distribution system endpoints and analysed by purge-and-trap gas chromatography with electron capture detection for trihalomethanes and liquid-liquid extraction GC-ECD for haloacetic acids. Formation potential tests were conducted on raw and treated water. Precursor characterisation by dissolved organic carbon fractionation was performed. Results show that total trihalomethane concentrations at distribution endpoints ranged from 12 to 118 micrograms per litre, with three facilities exceeding the WHO guideline of 300 micrograms per litre for chloroform equivalents at peak periods. Haloacetic acid concentrations were below WHO tentative guidelines at all sites. Trihalomethane formation was strongly correlated with raw water dissolved organic carbon and chlorine dose. Humic fraction organic matter was the dominant precursor. Cancer risk assessment for lifetime exposure via ingestion and inhalation during showering was quantified. Recommendations focus on dissolved organic carbon removal prior to chlorination as the most effective control strategy. Keywords: disinfection by-products, trihalomethanes, chlorination, drinking water, Nigeria