Preliminary toxicity assessment of water after treatment with uv-irradiation and UVC/H2O2

Photooxidation (UV radiation) and enhanced photooxidation (UVC/H₂O₂) are water treatment technologies which remove aquatic natural organic matter (NOM) by photodegradation, producing lower molecular weight components and CO₂. Since these technologies are being investigated for the treatment of drinking water, knowledge of the potential toxicity of the photooxidation by-products is vital. The potential toxicity of UVA-, UVB-, UVC-irradiated, and UVC/H₂O₂-treated aquatic NOM in two spot samples from two Australian reservoirs was analysed in two spot samples using Vibrio fischeri in the Microtox^TM test, African green monkey kidney cells (AS/NZS 4020:1999), and Daphnia carinata in an acute immobilisation test. Toxicity was not apparent for both the Microtox^TM procedure and cytotoxicity analyses for the UVC-irradiated and UVC/H₂O₂-treated NOM samples, while UVA- and UVB-irradiated water samples were non-toxic to D. carinata. In contrast, acute toxicity was observed for UVC- and UVC/H₂O₂-treated water samples. The observed toxicity was attributed to photooxidative degradation of NOM-metal binding sites, which resulted in the release of bioavailable copper ions, as evidenced by higher concentrations of free copper ions in photooxidised water. As the total copper concentrations of the two raw water samples were well below the Australian Water Quality Guidelines for metals in domestic supplies, the release of copper from photooxidised NOM is unlikely to cause health concerns in these samples.