Augmented environmental risks from composite photoinitiator contamination and phototransformation in waters adjacent...

The widespread use of photoinitiators (PIs) and their documented toxicity have raised increasing concerns about environmental health impacts. Urgent research is needed to understand their environmental occurrence and phototransformation in aquatic systems, where information remains limited. This study revealed elevated levels of PIs in a Chinese light industrial region, with Σ₂₄PIs concentrations reaching 1.99-3.14 μg/L in surface water and 2.03-4.54 μg/L in groundwater, marking the first report of high groundwater contamination primarily from paper manufacturing, printing, and dyeing activities. Laboratory photolysis experiments showed that ten representative PIs undergo first-order transformation, with rate constants (k) ranging from 2.7 × 10^-2 h^-1 to 4.0 × 10^-1 h^-1. Two transformation mechanism including direct photolysis and photosensitization were identified, which are governed by substituent-specific electronic effects on the benzophenone (BP) core of PIs. Using BP as a model compound for aromatic PI, we identified a novel dual regulatory function: (1) facilitating synergistic transformation of coexisting PIs through triplet-state-mediated photosensitization, while (2) suppressing direct photolysis of certain PIs under hydrogen donor-deficient conditions that limit triplet-state reactivity. Other coexisting dissolved organic matter also had effects on PI phototransformation. Among 132 identified phototransformation products (TPs), predominantly hydroxylated derivatives, seven at confidence levels 1 were quantified in field-collected surface water samples. Risk assessments revealed that 2,4-diethylthioxanthone (DETX) in the field area would pose high ecological risks. Besides, phototransformation does not guarantee detoxification, as multiple TPs showed increased toxicity and environmental persistence. Given the structural similarity among commercial PIs, these findings provide critical insights for enhancing environmental risk assessment and management strategies for PIs and their TPs with high risks.