Cytotoxicity of Water Samples Condensed from Indoor Air: An Indicator of Poor Indoor Air Quality

Introduction: The impurities of the air inside the buildings and the resulting adverse health effects have become an increasing problem. Typically indoor air impurities are mixtures of many chemical substances at relative low concentrations. The toxicity of individual substances may be negligible, the mixture effect being the primary cause for toxicity and the potential adverse health effects. Standardized screening methods for identifying the health hazard are lacking. The aim of this study was, by using conventional cytotoxicity/cell viability assays, to investigate whether indoor air cytotoxicity can be detected from water samples condensed from indoor air. Materials and Methods: The cytotoxicity of 712 water samples condensed from indoor air was investigated. First, 24 samples were tested in four different cell types (human bronchial epithelial cells, BJ fibroblasts, Tohoku Hospital Pediatric-1 [THP-1] monocytes, and THP-1 macrophages) using neutral red uptake and water-soluble tetrazolium salt 1 (WST-1) assays. Thereafter, 688 samples were tested using THP-1 macrophage/WST-1 assay. All samples were tested at 10% sample concentration, 56 samples were also tested at 25% concentration to see dose-response effects. Results: THP-1 macrophage/WST-1 assay was the most reproducible method for assessing indoor air cytotoxicity. The adverse effects of indoor air samples on THP-1 cells ranged from ca. 33% loss in cell viability to ca. 17% increase in mitochondrial activity ("cell stress"). Indoor air samples from 75% sampling sites where people reported health symptoms caused adverse effects in THP-1 macrophage/WST-1 assay. Conclusions: The assessment of indoor air cytotoxicity using water samples condensed from the indoor air and THP-1 macrophage/WST-1 assay provides a novel and practical biological approach for investigating indoor air quality. This method does not replace existing methods, but supplements them and provides a fast and cheap alternative for the first-stage screening for recognizing poor indoor air regardless of its source.