Toxicity of airborne dust as an indicator of moisture problems in school buildings.

Moisture-damaged indoor environments are thought to increase the toxicity of indoor air particulate matter (PM), indicating that a toxicological assay could be used as a method for recognizing buildings with indoor air problems. We aimed to test if our approach of analyzing the toxicity of actively collected indoor air PM in vitro differentiates moisture-damaged from non-damaged school buildings. We collected active air samples with NIOSH Bioaerosol Cyclone Samplers from moisture-damaged (index) and non-damaged (reference) school buildings (4 + 4). The teachers and pupils of the schools were administered a symptom questionnaire. Five samples of two size fractions [Stage 1 (>1.9 µm) and Stage 2 (1-1.9 µm)] were collected from each school. Mouse RAW264.7 macrophages were exposed to the collected PM for 24 h and subsequently analyzed for changes in cell metabolic activity, production of nitric oxide (NO), tumor necrosis factor (TNF)-α and interleukin (IL)-6. The teachers working in the moisture-damaged schools reported respiratory symptoms such as cough (p = 0.01) and shortness of breath (p = 0.01) more often than teachers from reference schools. Toxicity of the PM sample as such did not differentiate index from reference building,s but the toxicity adjusted for the amount of the particles tended to be higher in moisture-damaged schools. Further development of the method will require identification of other confounding factors in addition to the necessity to adjust for differences in particle counts between samples.

Evaluation of sampling methods for toxicological testing of indoor air particulate matter.

There is a need for toxicity tests capable of recognizing indoor environments with compromised air quality, especially in the context of moisture damage. One of the key issues is sampling, which should both provide meaningful material for analyses and fulfill requirements imposed by practitioners using toxicity tests for health risk assessment. We aimed to evaluate different existing methods of sampling indoor particulate matter (PM) to develop a suitable sampling strategy for a toxicological assay. During three sampling campaigns in moisture-damaged and non-damaged school buildings, we evaluated one passive and three active sampling methods: the Settled Dust Box (SDB), the Button Aerosol Sampler, the Harvard Impactor and the National Institute for Occupational Safety and Health (NIOSH) Bioaerosol Cyclone Sampler. Mouse RAW264.7 macrophages were exposed to particle suspensions and cell metabolic activity (CMA), production of nitric oxide (NO) and tumor necrosis factor (TNFα) were determined after 24 h of exposure. The repeatability of the toxicological analyses was very good for all tested sampler types. Variability within the schools was found to be high especially between different classrooms in the moisture-damaged school. Passively collected settled dust and PM collected actively with the NIOSH Sampler (Stage 1) caused a clear response in exposed cells. The results suggested the higher relative immunotoxicological activity of dust from the moisture-damaged school. The NIOSH Sampler is a promising candidate for the collection of size-fractionated PM to be used in toxicity testing. The applicability of such sampling strategy in grading moisture damage severity in buildings needs to be developed further in a larger cohort of buildings.