Toxicological characterization of particulate emissions from straw, Miscanthus, and poplar pellet combustion in residential boilers

ABSTRACT

Wood pellets have been used in domestic heating appliances for three decades. However, because the share of renewable energy for heating will likely rise over the next several years, alternative biomass fuels, such as short-rotation coppice or energy crops, will be utilized. We tested particulate emissions from the combustion of standard softwood pellets and three alternative pellets (poplar, Miscanthus sp., and wheat straw) for their ability to induce inflammatory, cytotoxic, and genotoxic responses in a mouse macrophage cell line. Our results showed clear differences in the chemical composition of the emissions, which was reflected in the toxicological effects. Standard softwood and straw pellet combustion resulted in the lowest PM₁ mass emissions. Miscanthus sp. and poplar combustion emissions were approximately three times higher. Emissions from the herbaceous biomass pellets contained higher amounts of chloride and organic carbon than the emissions from standard softwood pellet combustion. Additionally, the emissions of the poplar pellet combustion contained the highest concentration of metals. The emissions from the biomass alternatives caused significantly higher genotoxicity than the emissions from the standard softwood pellets. Moreover, straw pellet emissions caused higher inflammation than the other samples. Regarding cytotoxicity, the differences between the samples were smaller. Relative toxicity was generally highest for the poplar and Miscanthus sp. samples, as their emission factors were much higher. Thus, in addition to possible technical problems, alternative pellet materials may cause higher emissions and toxicity. The long-term use of alternative fuels in residential-scale appliances will require technological developments in both burners and filtration.

Copyright © 2016 American Association for Aerosol Research

EDITOR:

• Tiina Reponen

Acknowledgments

The authors wish to thank Mrs. Miia Koistinen of the University of Eastern Finland for her excellent technical assistance in the toxicological studies. The PAH analysis of particulate samples by MSc Annika Virén of the University of Eastern Finland is also much appreciated.

Funding

This study was funded by the Finnish Funding Agency for Innovation (Tekes) as part of the ERA-NET program of the EU, the Austrian Research Promotion Agency (FFG) and the Research Program on Sustainable Energy of the Academy of Finland. This project belongs to the strategic funding of the University of Eastern Finland (Sustainable Bioenergy, Climate Change and Health).