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Already well known impact of #wildfire smoke and ash: increased #HeavyMetals "in #particulate matter have been documented during wildfire episodes and may induce cytotoxicity, increase lung #cancer risks, and greatly contribute to #OxidativeStress" [1]
However, "in areas with metal-rich geologies (e.g., serpentinite)" chromium ("naturally abundant in its trivalent form [Cr(III)]" with a "limited hazard to human health") may be transformed "to its carcinogenic form in soil and ash" [1]
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In [1], the authors report: "high #temperatures during California #wildfires catalyzed widespread transformation of chromium to its #carcinogenic form in soil and #ash, as #HexavalentChromium" Cr(VI) - even "in wind-dispersible #particulates"
The geographic distribution of susceptible #soils, and of "fire incidents illustrate the broad global threat of wildfire #smoke- and dust-born metals to populations" [1]
A study in 2019 [2] already suggested this pathway for Cr(VI) formation in soil.
3/
Figure 1 in the suppl. info of [1] shows the global distribution (warning: specific #uncertainty affects geological data maps) of potentially susceptible soils:
As #wildfires may worsen "due to a combination of #ClimateChange and past #FireManagement, post-fire dust emissions are likely to rise"
Knowing more on drivers of fire-catalyzed #HexavalentChromium Cr(VI) may help in supporting how "to mitigate exposure risks to first responders and local communities" [1]
4/
[1] Lopez, A.M., Pacheco, J.L., Fendorf, S., 2023. Metal toxin threat in wildland fires determined by geology and fire severity. Nature Communications 14 (1), 8007+. https://doi.org/10.1038/s41467-023-43101-9
[2] Burton, E.D., Choppala, G., Karimian, N., Johnston, S.G., 2019. A new pathway for hexavalent chromium formation in soil: fire-induced alteration of iron oxides. Environmental Pollution 247, 618–625. https://doi.org/10.1016/j.envpol.2019.01.094
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On #wildfires and their global #emissions, an additional source of #uncertainty on quantification may be "definition-driven":
Analysis on 2023 wildfires in #Canada [3][4]:
"Canadian wildfires in 2023 [...] burned nearly 7.8 million hectares of forest and accounted for more than a quarter of all tree cover loss globally" with "important implications for #GlobalCarbonBudgets because emissions from these wildfires will largely be excluded from official #GreenhouseGasReporting" [3]
6/
A comment [4] by co-authors of [3]:
"forest fires in #Canada and other northern #BorealForests are a common and natural occurrence"
However, "higher temperatures caused by climate change dry out the landscape and make forests more susceptible to fire, driving longer #FireSeasons and larger forest fires. As larger forested areas burn, more #carbon is emitted into the atmosphere, further exacerbating climate change and contributing to even more fires as part of a fires-climate feedback loop"
7/
The comment [4] continues:
Critical appears to be a "large gap between [#wildfire] #emissions reported by countries and what is measured directly in the atmosphere.
And, while this is largely by design to target #anthropogenic sources and many of the differences between #GHG inventories and global atmospheric models have largely been explained and reconciled, the build-up of GHGs in the #atmosphere still does not match the cumulative impact of national reporting."
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On the large gap between #wildfire #emissions reported by countries vs measures in the atmosphere [4]:
"Part of the reason is that the UN only requires countries to document emissions that are #anthropogenic, or #HumanCaused, to track progress against the world’s goal of limiting global temperature rise"
But "the lines between “natural” and “anthropogenic” wildfires are blurring":
"human-driven #ClimateChange is making fire seasons longer, resulting in larger and more frequent wildfires"
[3] MacCarthy, J., Tyukavina, A., Weisse, M.J., et al., 2024. Extreme wildfires in Canada and their contribution to global loss in tree cover and carbon emissions in 2023. Global Change Biology 30 (6), e17392+. https://doi.org/10.1111/gcb.17392
[4] MacCarthy, J., Tyukavina, A., Weisse, M.J., Harris, N., 2024. Canada's record-breaking 2023 wildfires released nearly 4 times more carbon than global aviation. World Resources Institute
https://www.wri.org/insights/canada-wildfire-emissions
(archived:https://purl.org/INRMM-MiD/z-TFN8QJGH)
Daniele de Rigo