Distinct baseline toxicity of volatile organic compounds (VOCs) in gaseous and liquid phases: mixture effects and potential molecular mechanisms

Volatile organic compounds (VOCs) are significant pollutants found in various environments, posing health risks. Traditionally, the gaseous VOCs are adsorbed and eluted in liquid phases, and then subjected to toxicity testing, which deviates from the actual exposure scenarios of gaseous VOCs. How the physical states of VOCs (gaseous or liquid) affect their toxicity has not been well understood. This study examined the baseline toxicity of VOCs in both gaseous and liquid phases using a self-assembled passive colonization hydrogel (SAPCH) with luminous bacteria (Vibrio fischeri). The findings revealed that gaseous VOCs exhibited higher baseline toxicity than their liquid counterparts, attributed to the higher free energy and electronic activity of gaseous VOC molecules. Furthermore, the study elucidated that the differences in electronic transitions and energy gaps significantly impact the combined toxicity of VOC mixtures in different phases. Understanding these differences is crucial for assessing the real-world impact of VOCs on health and the environment.