Ecological risk of substituted p-phenylenediamines and quinones in Chinese freshwaters using QSAR-ICE modeling

The high ecotoxicity of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q) has directed global attention to substituted p-phenylenediamines (PPDs) and their quinone derivatives (PPD-Qs). To date, however, comprehensive evaluations of their toxicity and associated ecological risks in aquatic ecosystems remain scarce. This study utilized an integrated approach combining quantitative structure-activity relationship and interspecies correlation estimation (QSAR-ICE) model predictions, species sensitivity distribution analysis, and ecological risk assessment to evaluate the potential ecological risks of PPDs and PPD-Qs in major river basins of China. Model performance indicated acceptable predictive reliability, with QSAR predictions meeting r² > 0.8 and q² > 0.7 for all compounds and ICE-based predictions yielding R² of 0.66-0.99 and MSE of 0.0070-0.46. The integrated QSAR-ICE framework provided useful screening-level toxicity estimates. Sensitivity distribution analysis based on Chinese native species revealed that 6PPD, 7PPD, and 77PD had the lowest predicted no-effect concentrations. The ecological risk assessment revealed overall low ecological risks in major river basins of China, with risk quotient values mostly below 0.1. However, high exposure levels in the Pearl River and Tarim River basins suggested localized risks. This study provides a comprehensive assessment of the ecological risks of PPDs and PPD-Qs in Chinese freshwater environments, filling gaps in ecotoxicological data related to species sensitivity distribution and chronic toxicity endpoints for Chinese native species, and offering scientific evidence for environmental management.