Abstract Volatile organic compounds (VOCs) are widely present in the environment, and their mixture toxicity, including synergistic and antagonistic effects, is of increasing concern. However, the complex interactions and inconsistent understanding of mixture toxicity and hormesis require further study, specifically for predicting low-dose effects. This study aimed to assess how mixing VOCs affects their toxicity and analyse relationships with physicochemical parameters. Formaldehyde (FA), acetaldehyde (AA), toluene (TL), and ethylbenzene (EB) were selected as model compounds, and their mixtures were tested using the marine luminescent bacterium Allivibrio fischeri to measure bioluminescence inhibition. The physicochemical parameters assessed included the volatility index (VI), which measures the escaping ability of VOCs from a solvent, and Gibbs free energy of mixing (ΔGmix), which evaluates mixing stability. The results demonstrated the half-maximal effective concentration (EC50) of single VOCs decreased with increasing hydrophobicity, and hormetic responses were observed for hydrophilic VOCs. Low-dose stimulation was observed in any combination of FA and AA with TL and EB. The hormetic response was also observed in the TL-EB combination, likely because of antagonistic effects. We found the mixing effects can be attributed to the escaping ability of VOCs from the solvent. Additionally, the EC50 values of the two components exhibited a significant correlation with ΔGmix when one component was hydrophobic. These findings demonstrate that the physicochemical parameters act as predictive tools for assessing mixture toxicity, offering a novel framework for assessing environmental risks caused by VOCs in mixed forms.
Sekine et al. (Thu,) studied this question.