Predicted toxicity has been used to determine if a treatment process is either beneficial or detrimental to the overall DBP toxicological profile of water samples. Selection of the DBPs to measure is important and may result in biased conclusions.

Free chlorine (HOCl) and monochloramine (NH2Cl) are less-used oxidants than hydrogen peroxide (H2O2) in ultraviolet advanced oxidation processes (UV-AOPs) but have garnered interest from the water reuse industry and scientific community because they can be more cost-effective than H2O2 and provide a protective disinfectant residual. The destruction of organic compounds, creation of UV-AOP byproducts, and change in toxicity during UV-AOP with H2O2, HOCl, NH2Cl, or ambient residual chloramine were evaluated in recycled wastewater by suspect and non-target screening as well as bioanalytical tests (bioassays). Ten compounds were identified in reverse osmosis (RO) permeate via suspect screening with removal near 100% by UV/H2O2 and UV/HOCl, greater than decomposition by UV/NH2Cl and UV/ambient (∼60%), based on suspect screening mass spectrometry peak area. Non-target analysis based on organic features in mixed-mode cation exchange cartridge extracts indicated that UV/H2O2 destroyed a similar or slightly greater fraction of organic compounds, formed fewer transformation products, and reduced the summed peak area of non-target features to the greatest extent. Fewer chlorinated byproducts were produced from the RO permeate treated by UV/H2O2 than exposure to the chlorine-containing oxidants. Addition of NH2Cl to RO permeate resulted in a slight increase in the bioassay oxidative stress response but dropped below the response limit for all samples after UV-AOP for all oxidants.