Toxification by Transformation in Conventional and Advanced Wastewater Treatment: The Antiviral Drug Acyclovir

Ozonation applied for advanced (waste)water treatment has a great potential to form polar transformation products (TPs) with often unknown toxicity. The antiviral drug acyclovir is transformed during biological wastewater treatment into carboxy-acyclovir. Ozone further transforms carboxy-acyclovir into N-(4-carbamoyl-2-imino-5-oxoimidazolidin)formamido-n-methoxy-acid (COFA). Both TPs have been detected in environmental samples and finished drinking water. Here, carboxy-acyclovir and COFA were produced at bench scale using treated wastewater and sewage sludge and were tested for aquatic toxicity in parallel with acyclovir. Carboxy-acyclovir was found to significantly reduce the level of reproduction of Daphnia magna (by 40% at 102 mg L–1), and COFA inhibited the growth of green algae (ErC10 of 14.1 mg L–1); no toxicity was observed for acyclovir up to 100 mg L–1. The predicted genotoxicity was not increased compared to that of the parent compound. In summary, the results highlight the importance of assessi...