Formation of iodinated disinfection by-products from high-dose disinfection with two types of iodine disinfectant in aquaculture

Iodinated disinfection by-products (I-DBPs) have raised concerns due to their potential cytotoxicity and genotoxicity compared to chlorine and bromine-based by-products. In aquaculture, high-dose iodine-based disinfectants can react with natural organic matter (NOM) in water, generating significant amounts of I-DBPs that might pose environmental risks. This research explored the reaction characteristics of I-DBPs by using two commonly used iodine-based disinfectants (iodine tincture and Polyvinylpyrrolidone-iodine (PVP–I)) in aquaculture. The results indicated that controlling pH at around 8.0 effectively reduced I-DBP formation. A higher concentration of PVP-I (10 μM) was required to produce triiodomethane (TIM) compared to iodine tincture (2.5 μM), likely due to the slower release of iodine from PVP-I. The concentrations of I-DBPs showed a multiplicative growth trend as the concentrations of the iodine-based disinfectants increased. Humic acid (HA) demonstrated a stronger potential for I-DBP formation than algal-derived organic matter (AOM), including extracellular organic matter (EOM) and intracellular organic matter (IOM), due to its strong electron-withdrawing aromatic structure. While EOM led to a greater variety of I-DBPs, IOM contributed more significantly to TIM formation at higher disinfectant concentrations, probably due to its large molecular size and abundance of reactive carbon atoms. The I-DBP formation patterns in the aquaculture water are similar to those of HA, possibly due to the presence of similar compositional components, such as lignin and proteins. The study provides important insights for optimizing iodine disinfectant use in aquaculture and managing I-DBP risks.