Toxicity Screening of Wood Combustion Fine Dust Using a Microbial Test Battery

Abstract

Claimed as renewable energy source, wood is increasingly used in stoves and boilers for heating purposes in western countries due to economic reasons and environmental consciousness. Consequently, domestic wood combustion contributes significantly to atmospheric loads of particulate matter (PM) nowadays. Epidemiological and controlled human, animal, and in vitro studies have proven that wood smoke exposure is injurious to human health. In this context, three standardized microbial assays, the bacterial contact assay BCT (Arthrobacter globiformis), the Umu-Test (Salmonella typhimurium TA1535/pSK1002) and the Yes-Test (Saccharomyces cerevisiae BJ3505) were adapted in this thesis in order to achieve a toxicological characterization of PM bound compounds in direct contact with the test organisms. Modifications included the assessment of bacterial and yeast viability via resazurin reduction, thereby replacing the conventional optical density measurement (OD600). This new endpoint indicated a highersensitivity to compounds that affect organism’s activity. Seven bulk fine dust samples and 13 filters loaded with PM with varying soot fractions, i.e. representative for complete andincomplete combustion, were tested as aqueous suspension or small filter cutouts. Regardless of the combustion type, all assumed types of toxicity were detected among the samples. Comparedto other mode-of-action bioassays with nematodes and human cell lines in the overall project, the BCT turned out to be most sensitive for detection of baseline toxicity. Water content and type ofwood of used pellets most likelinfluenced the baseline toxicity. The assumption that aqueous and thus bioavailable Zn may dominate PM baseline toxicity was not proven by X-ray diffraction or mixture experiments with Zn and PM samples. Expected over-additive toxicity of Zn when exposed simultaneously with the PAH fluoranthene was not observed.Furthermore, emitted fine dust that was subsequently oxidized in an atmospheric transport simulation chamber wasassessed. Oxidized samples were only genotoxic when tested on the nitroarene sensitive NM3009 Salmonella strain not on the conventional Salmonella strain of the Umu-Test. Non-oxidized PM was not genotoxic, proving the formation of nitro-PAHs during atmospheric oxidation. Themicrobial test battery presented provides a screening technique for unknown fine particles that is rapid, sensitive, easy to handle and low-priced, while offering high-throughput testing. Therefore, it constitutes an excellent tool for evaluation of different stoves and boilers and can contribute to possible mitigation actions. For a cost-benefit-analysis of small-scale wood combustion devices, obtained toxicity results should be related to their total emission loads and heating values.