Indirect photochemical transformations of acyclovir and penciclovir in aquatic environments increase ecological risk

Abstract

Acyclovir and penciclovir, 2 antiviral drugs, are increasingly detected in aquatic environments. The present study explores the natural photochemical transformation mechanisms and fate of these drugs, examining direct and indirect photochemical transformation under simulated sunlight irradiation. The 2 antiviral drugs are photostable under certain conditions but significantly degrade in the presence of chromophoric dissolved organic matter (DOM). The degradation rate associated with the drugs' indirect photochemical transformation scaled with chromophoric DOM concentration. Quenchers and sensitizers were used to identify indirect photochemical transformation mechanism. Results suggested that both pharmaceuticals could be transformed by reacting with 1 O 2 , • OH, and excited chromophoric DOM. The 1 O 2 played an important role in indirect photochemical transformation. Furthermore, the reaction kinetics between their substructural molecules, guanine, isocytosine, and imidazole, with different reactive oxygen species were evaluated to determine which substrate functionalities were most susceptible to singlet oxygenation. Imidazole was identified as the reaction site for 1 O 2 , and preliminary 1 O 2 oxidation mechanisms were further evaluated based on liquid chromatographic-tandem mass spectrometric results. Finally, aquatic ecotoxicity assessment of phototransformed solutions revealed that the degradation of acyclovir and penciclovir may not ultimately diminish environmental risk because of either formation of more toxic intermediates than parent pharmaceuticals or some synergistic effects existing between the intermediates. Environ Toxicol Chem 2016;35:584-592. # 2015 SETAC

Prediction of Photochemically Produced Reactive Intermediates in Surface Waters via Satellite Remote Sensing

“…Surface waters are impacted by a myriad of organic pollutants, including pharmaceuticals and pesticides . After their use in agriculture, stockbreeding, medicine, and industry, the chemicals enter surface waters through wastewater discharges or stormwater runoff. − Studies have reported that photochemical reactions, including indirect photolysis pathways, where a photosensitizer absorbs light and generates reactive species, are important in the degradation of many organic pollutants. − For example, photolysis of various pesticide classes has been investigated in prairie wetland surface waters, and Remucal found that indirect photolysis drives the aquatic fate of various pesticide classes . Understanding the photolysis of pollutants in surface waters is essential for assessing potential exposures and risks to aquatic organisms as well as to humans via drinking water supplies.…”

Essential role of sunlight irradiation in aqueous micropollutant transformations: influence of the water matrix and changes in toxicities

“…72,109 For Environmental Science: Water Research & Technology Critical review instance, acyclovir, penciclovir and their substructural unit imidazole which are rich in electrons are identified as the reaction units for 1 O 2 through Diels-Alder reactions. 118 The diphenhydramine molecule is not rich in electrons, and quenching 1 O 2 enhanced its photodegradation rate, proving the insignificant roles of 1 O 2 . 32 3 DOM* is able to quench ˙OH, and MPs whose photolysis can be enhanced by ˙OH can therefore be inhibited by 3 DOM*.…”

“…72,109 For instance, acyclovir, penciclovir and their substructural unit imidazole which are rich in electrons are identified as the reaction units for 1 O 2 through Diels–Alder reactions. 118 The diphenhydramine molecule is not rich in electrons, and quenching 1 O 2 enhanced its photodegradation rate, proving the insignificant roles of 1 O 2 . 32…”

“…[˙OH] ss in surface waters under sunlight generally ranges from 10 −18 M to 10 −16 M, which is sufficient to facilitate the phototransformation of some MPs. 7,79,118 For instance, the influence of natural ˙OH scavengers such as HCO 3 − and Cl − in water matrices is expected to be minimal in natural water environments. However, PO 4 3− ions in surface water can inhibit N 4acetylsulfamethazine (Ac-SMT) degradation at environmental concentrations, which is also shown in Fig.…”