Insights into the implication of halogen ions on the photoactivity of dissolved black carbon for the degradation of pharmaceutically active compounds

•Ionic strength of halogen ions had no effect on Ф1O2 from DBC.•The increase in [T]ss with halogen ions was because of the inhibition of IS effect to ks’ at the same time FT remained constant.•Halogen ions were the dominant competitor to carbamazepine for 3DBC*, resulting in the indirect photolysis retardation.•Halogen ions affected 3DBC* and 1O2 along with slowing down CT, resulting in the reduction of 17β-estradiol photolysis.