Toxicological characterisation of particulate matter from moisture-damaged schools

Public examination of a doctoral dissertation in the field of Environmental Health
Doctoral candidate: MSc Jenni Tirkkonen
Date and venue: 19.12.2018 at 12 noon, SN200, Snellmania, Kuopio Campus
Language of the dissertation: English
Language of the public examination: Finnish


Poor indoor air quality (IAQ) is a significant problem worldwide and many people suffer its consequences, including both acute symptoms and chronic diseases such as cough, fatigue, headache and asthma. The main reasons for poor IAQ are emissions from outdoor and indoor sources, e.g., traffic near buildings or moisture damage in building structures, and the situation is often exacerbated by inadequate ventilation rates and resuspension due to occupant activity. Physical factors such as humidity, temperature, light and noise also affect the wellbeing of the occupants. This thesis aims to characterize the toxicity of particulate matter (PM) in school buildings and assess if a toxicity assay could differentiate moisture-damaged from non-damaged buildings.

In the first phase of this thesis, the main focus was comparing the toxicity of settled dust from moisture-damaged (index) and non-damaged (reference) schools in Finland, Spain and the Netherlands with analysis of the microbial characteristics of the collected samples. PM samples were collected with the passive settled dust box (SDB) method, standardised for the sampling time and area. Murine macrophages (RAW264.7) were exposed to the PM samples to assess the toxicity of the material. In addition the effect of the PM samples on oxidative damage to bacterial plasmids and haemolysis of human red blood cells were analysed to further characterize the possible mechanisms of action. It was found that the PM from all the studied countries caused inflammation, toxicity and oxidative stress in vitro, and that the immunotoxicological potency varied significantly between the countries. In Spain and the Netherlands, the samples from index schools induced higher inflammatory responses and toxicity compared to reference schools, but in Finland, the overall level were much lower and there was no differences, between the categories of schools. The oxidative capacity of the Dutch samples, was higher compared to the other countries, but again, levels were similar in index and reference schools. Haemolytic activity was increased in a few of the Spanish index schools. The concentration of microbial markers was slightly higher in index schools compared to reference schools, but the difference was not statistically significant. The moisture score of the buildings was associated with grouped bacterial and fungal components, which in turn correlated with immunotoxicity and oxidative potential.

In the second phase of this thesis the compatibility of four sample collection methods for the purposes of toxicity testing were assessed.  The assessed methods were a passive SDB method, and three active methods including Harvard Impactor, Button sampler and NIOSH bioaerosol cyclone sampler. First, the methods were compared by collecting PM from two Finnish schools (one index and one reference building) and exposing murine macrophages (RAW264.7) to the collected material. On the basis of the toxicological analyses the best method was the NIOSH sampler, because it collected a sufficient amount of sample material directly into a sampling vial, and the results from toxicity testing showed some promise of an ability to differentiate the index school from reference school. The NIOSH sampler was then further tested in four index and four reference schools in Finland. In the exposure experiments the PM collected from all of the schools increased the indicators of toxicity and inflammation dose-dependently, but there were no differences between the school types. However, adjusting  the toxicological parameters with the PM mass somewhat improved the differentiation of index schools from reference schools.

In summary, the immunotoxicological characteristics and microbial compositions of indoor particulate matter are linked with moisture conditions in the schools, but the tested toxicity assay needs more development to reliably differentiate moisture-damaged buildings from non-damaged ones. Geographical area of the school as well as the number of particles in the sample affect the result of the toxicity testing. In addition to the microbial components studied here,  other factors such as chemicals or combustion particles may also induce toxicity of PM in moisture-damaged school buildings, thus more research is needed for development of a reliable toxicity test for buildings suffering from poor IAQ.

The doctoral dissertation of MSc Jenni Tirkkonen, entitled Toxicological Characterisation of Particulate Matter from Moisture-damaged Schools will be examined at the Faculty of Science and Forestry. The opponent in the public examination will be Professor Heidi Salonen, Aalto University and the custos will be Maija-Riitta Hirvonen, University of Eastern Finland.

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