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 PM 1 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. EDITORTiina Reponen

Cytotoxic and genotoxic responses of human lung cells to combustion smoke particles of Miscanthus straw, softwood and beech wood chips

“…Our results are not consistent with those of Kasurinen et al (2015b), who reported that none of the particle-bound PAHs concentrations were significantly lower in the PM 1 emissions from Miscanthus sp. pellets (97 mg/kg) than in the PM 1 emissions from softwood (401 mg/kg), poplar (37 mg/kg) or wheat-straw pellets (128 mg/kg).…”

“…While the MSPM 0.4–1 contained relatively high levels of Zn (>2 g/kg), it did not induce toxicological responses in the human lung cells used in this study. This is not in agreement with the results of Kasurinen et al (2015b), who found that the Zn-rich and PAH-poor PM 1 emissions from combustion of Miscanthus (pellets) induced a strong cytotoxic response. Moreover, Kasurinen et al (2015b).…”

“…This is not in agreement with the results of Kasurinen et al (2015b), who found that the Zn-rich and PAH-poor PM 1 emissions from combustion of Miscanthus (pellets) induced a strong cytotoxic response. Moreover, Kasurinen et al (2015b). observed strong genotoxic responses in RAW264.7 cells exposed to PM 1 emissions from Miscanthus pellets, and these responses were significantly more pronounced than those induced by PM emissions from combustion of standard softwood pellets.…”

“…In contrast, the (non-pelletized) MS straw used in our study had low density and high porosity, thus providing optimal oxygen supply during combustion, which in turn further promotes more complete combustion (Daragon et al, 2014). Consequently, the combustion conditions in the study of Kasurinen et al (2015b) were very different to those used in our experiments; the resulting emissions and their observed toxicity also differed in the two studies. Another study on combustion of Miscanthus focused on the physicochemical properties of the emissions from a small-scale multi-fuel boiler (Forbes et al, 2014).…”

“…pellets (97 mg/kg) than in the PM 1 emissions from softwood (401 mg/kg), poplar (37 mg/kg) or wheat-straw pellets (128 mg/kg). However, should be noted that Kasurinen et al (2015b) studied the effects of emissions from wood and Miscanthus pellets rather than wood chips and Miscanthus straw, i.e. the fuel/air interface was distinct.…”