Study of the Photoinduced Fate of Selected Contaminants in Surface Waters by HPLC-HRMS

Photoinduced transformation of contaminants of emerging concern (CECs) can occur in aquatic environment and could lead to the formation of transformation products (TPs) of greater concern than the parent compounds. For such, the fate of epoxiconazole, hymecromone, and coumarin in water was investigated by simulating photoinduced abiotic transformations to assess the toxicity of their TPs and which CEC may be of greatest concern.

Heterogeneous photocatalysis with TiO₂ and direct photolysis of selected CECs were exploited to simulate their TPs. The TPs were assessed by means of HPLC coupled with an Orbitrap MS analyser in ESI positive mode, while their toxicity was evaluated through a Vibrio fischeri bioluminescence assay, and ECOSAR tool.

The formation of numerous TPs via different photoinduced pathways was noticed (27 for epoxiconazole, 6 for coumarin, and 8 for hymecromone, some of which are in the form of structural isomers). Toxicity assessment via V. fischeri assay showed that, unlike coumarin species, epoxiconazole transformation proceeds through the formation of toxic compounds. By means of ECOSAR software, the formation of predominant more noxious TPs of epoxiconazole was proved than the parent compound for both acute and chronic toxicities. Instead, most TPs of coumarin and hymecromone generally exhibited "harmful" and "toxic" levels of acute and chronic toxicities.

A probable structural identification was assigned to the monitored TPs via HPLC-HRMS to recognize the several transformation pathways, of which the hydroxylation reaction was predominant, and which compound may be more hazardous in the aquatic system due to its TPs. Epoxiconazole transformation brought to potentially toxic TPs, whereas photoinduced degradation of coumarin and hymecromone resulted in less hazardous TPs. The most significant aspect of this work is the ability of this overall approach to identify the formation of photoinduced TPs that are potentially more toxic than the original CEC.