Effect of different iron species on disinfection byproducts formation in drinking water distribution systems

• Fe(II) promotes the formation of HAAs and HANs but inhibits the THM S . • The precursors of HANs and THMs are high MW organic matter, but HAAs are low. • ·Cl and ·OH compete for organic matter with organic matter with high MW . • The water containing FeOOH with higher turbidity-inducing ability and health risk. Iron particles are frequently found in drinking water distribution systems (DWDS) and can affect the formation of disinfection by-products (DBPs). Here, the effect of four iron species (Fe(II), FeOOH, Fe 2 O 3 , Fe 3 O 4 ) on the formation of DBPs were investigated. Experimental results revealed that Fe(II) promoted the formation of haloacetonitriles (HANs) and haloacetic acids (HAAs), while inhibited the formation of trihalomethanes (THMs). The precursors of trichloromethane (TCM) in THMs and dichloroacetonitrile (DCAN) in HANs were mainly identified to be high molecular weight (MW) organic matter, while low MW organic matter predominantly contributed to HAA formation. Competitive mechanisms were identified between·OH and·Cl for high-MW organic substrates, coupled with precursor competition between TCM and DCAN during chlorination, collectively explaining the THM suppression by Fe(II). In addition, FeOOH significantly amplified water turbidity during chlorination, with post-chlorination turbidity nearly doubling (92% increase). Cytotoxicity assessment revealed that FeOOH-mediated DBPs exhibited 2.3-fold higher toxicity compared to control groups. These findings will provide mechanistic insights for optimizing iron corrosion control strategies and developing targeted approaches to mitigate DBP-related health risks and discoloration issues in DWDS.