Identification, occurrence, and toxicity prediction of alkylphenolic disinfection by-products in disinfected combined sewer overflows.

Disinfection is essential in managing combined sewer overflows (CSOs) to reduce pathogenic microbial hazards. Disinfection can inevitably generate disinfection by-products (DBPs), which may adversely affect aquatic organisms. However, knowledge of emerging DBPs in disinfected CSOs remains limited because their water components differ from those of regular water sources. In this study, four emerging alkylphenolic DBPs (ap-DBPs) were identified -in 14 real CSOs after chlorination. Among them, 2,4-di-tert-butylphenol (2,4-DTAP) was the most frequently detected species (detection frequency: 100 %) with concentrations ranging from 27.59 ng/L to 325.72 ng/L, followed by chlorinated 2,4-DTAP (Cl-DTAP, 64.3 %, 0.39-33.52 ng/L), p-tert-amylphenol (PTAP, 21.4 %, ND-28.44 ng/L), and 2 chlorinated butylphenols (2Cl-DCBP, 100 %, 0.36-6.21 ng/L). Notably, 2,4-DTBP (33.09-214.15 ng/L) and PTAP (ND-10.91 ng/L) were detected in the CSO samples before chlorination (p > 0.05) respectively. The predicted toxicity thresholds of the ap-DBPs (LC/EC: 0.11-0.47 mg/L; ChV: 0.02-0.21 mg/L) were several orders of magnitudes lower than those of trichloromethane (LC/EC: 89.00-264.07 mg/L; ChV: 12.37-24.50 mg/L), dichloroacetic acid, and phenol. Notably, 2,4-DTAP and PTAP demonstrated potential estrogen interference in aquatic organisms, while Cl-DTAP and 2Cl-DCBP were associated with oxidative stress. Furthermore, toxicity predictions have demonstrated that estrogen receptor β (ERβ, binding sites: serine452) and p53 protein (threonine306) were important binding proteins for these ap-DBPs exerting relevant adverse effects. This study highlights the occurrence of ap-DBPs during the chlorination of CSOs, suggesting potential hormone interference and developmental toxicity of disinfected CSOs in natural water bodies.