Cellular respiration toxicity: A novel comprehensive water quality index based on universal biological processes

Assessing water quality comprehensively is crucial for predicting environmental risks. However, existing toxicity assessments are limited to specific physiological processes or reference organisms, failing to capture holistic hazards. Here we define a toxicity index-Cellular Respiration Toxicity (CRT)-based on the universal process of cellular respiration. By quantifying changes in intracellular reduced coenzyme levels using a dual-compartment electrochemical cell and K₃[Fe(CN)₆], CRT measures inhibition of energy metabolism across life forms. We systematically applied CRT to 76 common pollutants spanning 18 classes (including antibiotics, non-steroidal anti-inflammatory drugs, steroid estrogens, pesticides, heavy metals, and disinfection byproducts) as well as complex mixtures. The results demonstrate narrow intra-class EC₅₀ distributions for most pollutant categories, indicating conserved respiratory toxicity mechanisms, in contrast to literature data showing two orders of magnitude variability. Mixture toxicity analysis revealed previously undetected synergistic and antagonism effects in various molecules. Environmental risk assessment using a stringent risk quotient threshold identified heavy metals and disinfection byproducts as priority hazards, while uncovering unexpected risks from ethanol accumulation. Compared to conventional chemical parameters and single-endpoint bioassays, CRT offers standardization, universality, avoidance of false positives/negatives, and ease of implementation. This study provides a robust methodological tool and a comprehensive toxicity dataset that enables structure-activity prediction for congeners and informs mixture-based regulatory frameworks. CRT advances water quality assessment by directly linking toxicity to a core cellular process, offering both immediate practical utility for environmental monitoring and a foundation for future research into chronic exposure and combined pollution effects.