A Tale of Two Wildfires, Mercury Releases in an Alaska Peat Fire, Radionuclides in a Chernobyl Exclusion Zone Fire.

[NNadir]

Last edited Mon Nov 25, 2024, 06:38 AM - Edit history (1)

The papers I'll discuss in this post each discuss a major wildfire, one in Alaska, the other in the famous Chernobyl Exclusion Zone in Ukraine.

They are these:

Effects of Large-Scale Wildfires on the Redistribution of Radionuclides in the Chornobyl River System Yasunori Igarashi, Valentyn Protsak, Gennady Laptev, Igor Maloshtan, Dmitry Samoilov, Serhii Kirieiev, Yuichi Onda, and Alexei Konoplev Environmental Science & Technology 2024 58 (46), 20630-20641

...and...

Substantial Mercury Releases and Local Deposition from Permafrost Peatland Wildfires in Southwestern Alaska Scott Zolkos, Benjamin M. Geyman, Stefano Potter, Michael Moubarak, Brendan M. Rogers, Natalie Baillargeon, Sharmila Dey, Sarah M. Ludwig, Sierra Melton, Edauri Navarro-Pérez, Ann McElvein, Prentiss H. Balcom, Susan M. Natali, Seeta Sistla, and Elsie M. Sunderland Environmental Science & Technology 2024 58 (46), 20654-20664

The first is open to the public to read; the second requires access to a good scientific library, which, happily, I have, at least until the age of fascism begins in the US beginning in January.

Since the planet is on fire generally because, in my view, right wing rhetoric coupled with antinuclear rhetoric (much of which comes from the political left, although I'm on the left and am pronuclear), these two papers are, again in my view, worthy of consideration.

Both are related to energy production; one of the largest source of anthropogenic mercury releases comes from coal combustion where it is released in an aerosol form, ultimately depositing on soils. (I sometimes muse that the reason for the outbreak of political insanity, expressed as fascism, is mercury and lead toxicology, both of which are notable neurological toxins, and both of which are released as aerosols in coal combustion.) Geothermal energy is also a source of mercury pollution, but is a relatively trivial source. (cf. rock A. Edwards, Peter M. Outridge, Feiyue Wang, Mercury from Icelandic geothermal activity: High enrichments in soils, low emissions to the atmosphere, Geochimica et Cosmochimica Acta, Volume 378, 2024, Pages 286-299)


The percentages of anthropogenic mercury emissions are shown in this graphic; it dates from 14 years ago, 2010, but as coal use is increasing worldwide, despite much mythology to the contrary connected with faith based belief that so called "renewable energy" is leading to the decline of coal use, it would be safe to assume that coal generated mercury is as bad or worse in 2024 than it was in 2010. (In Germany, so called "renewable energy" is leading to increases in coal use.)



Source: Mercury Policy at MIT blog. (Accessed 11/23/2024.)

The first paper refers, not to mercury, but to radionuclides released in the much and often discussed explosion of the reactor at Chernobyl, the radioactive residuals of which remain in the environment, although in the case of the discussed radionuclides, ¹³⁷Cs (one of my personal favorite fission products) and ⁹⁰Sr, (which I also find intriguing) they have significantly decayed since 1986. However these nuclides are not associated with use, but rather with contamination. As of this writing, 14,091 days have passed since the Chernobyl reactor failure on April 26, 1986, which can be attributed to poor reactor design (a positive void coefficient) and poor operational practice (conducting an unauthorized experiment with a major reactor without sufficient analysis), with much coal and gas burned to power to computers to carry on endlessly about the reactor failures. In "percent talk" 58.8% of the ¹³⁷Cs has decayed to stable ¹³⁷Ba, and 60.5% of the ⁹⁰Sr has decayed to stable ⁹⁰Zr.

It is notable, in my opinion, that radionuclides are released in bulk from nuclear reactors only in failure modes, whereas mercury, lead, carbon dioxide and particulate matter are released by coal plants continuously in normal operations. This should be an important distinction, but somehow isn't.

From the second paper, related to mercury (Hg) emissions from tundra wild fires:

Mercury (Hg) is a naturally occurring toxic element that accumulates in food webs, posing a health risk to exposed humans. (1) Uptake and oxidation of gaseous elemental Hg (Hg⁰) by vegetation and direct deposition of divalent inorganic Hg (Hg^II) are thought to be the main inputs to terrestrial ecosystems (approx. 2300 Mg y^-1). (2,3) Complexation of Hg^II by organic matter stabilizes it in soils and represents a main global sink of Hg. (4,5) For millennia, a cold climate at northern high latitudes slowed the microbial decomposition of organic matter, promoting the accumulation of large amounts of Hg in upper soil layers (26,000–72,000 Mg). (6,7) Climate-driven warming and intensification of northern wildfire activity (8,9) threaten this reservoir of terrestrial Hg. (10,11) Early estimates suggested that annual Hg emissions from boreal wildfire (23–53 Mg y^-1) were a major component of the northern (greater than 60°N) Hg budget. (11,12) More recent budgets have suggested that Hg emissions from northern wildfire (8.8 Mg y^-1) (13) are minor relative to volatilization from terrestrial ecosystems (24 Mg y^-1), coastal erosion (39 Mg y^-1), (14,15) riverine export (41 Mg y^-1), (16,17) and annual dry and wet deposition to land (118 Mg y^-1). (13) However, wildfire Hg emissions remain among the most uncertain flux terms in northern Hg budgets (e.g., refs (18) and (20)), in part because of limited observational data from northern peatlands, where wildfires are thought to release up to several times more Hg per unit area compared to other ecosystem types. (11)

Assessing peatland wildfire Hg emissions, transport, and deposition is essential for improving the understanding of ecosystem Hg uptake. Hg emissions from a wildfire event are typically estimated by measuring atmospheric composition (12,18,20,21) or by assessing changes in soil Hg stores before and after fire. (11) Laboratory and field experiments can also help to constrain Hg emissions and speciation. (19,22,23) Assessing wildfire Hg emissions at the regional or continental scale requires information on burned area and potential Hg release per unit area. These can be derived from observations or information on fuel load, fractional Hg loss (i.e., the proportion of fuel that experiences Hg release), and biome-specific emissions factors (the unit mass of Hg released per unit mass of fuel). (13,24) Studies on peatland wildfire Hg emissions often assume complete release of Hg. (19,20) Such an assumption is consistent with Hg release from soils within the temperature range of oxidation reactions observed in smoldering combustion that typify peat fire (300–600 °C). (25) Thus, uncertainties associated with Hg emissions at larger scales are primarily from burned area estimates, (26?29) fuel load (i.e., soil Hg stores), and emissions factors.

Smoke plume height and Hg speciation influence the transport and deposition of wildfire Hg emissions. (12,30) Particles and chemical constituents within the planetary boundary layer (PBL) are more likely to deposit at local to regional scales (10s to 100s km), whereas mixing into the free troposphere (FT) promotes hemispheric to global transport. (31,32) Injection of plumes above the PBL requires convective energy, which depends on fire intensity and environmental conditions that influence fire behavior (e.g., moisture content, topography). (31,33,34) The long residence time of Hg⁰ in the atmosphere (approx. 6–12 months) facilitates its long-distance transport, whereas Hg^II species (including Hg^II sorbed to particles) deposit within days to weeks. (35) In peatlands, relatively high soil moisture reduces fuel availability and fire thermal energy, resulting in primarily smoldering combustion. (36) Consequently, peatland wildfires often have a relatively high particulate fraction, low convective energy, and smoke plumes that mostly remain within the PBL (e.g., greater than80% in boreal regions), (31,37) with important implications for deposition to local and regional ecosystems. However, limited research on the release and fate of Hg from northern peatland wildfires (11,23) hinders a more complete understanding of Hg cycling at northern high latitudes and ecosystem implications.
The main objective of this study was to empirically estimate Hg emissions from wildfires during summer 2015 in permafrost-affected tundra peatland in the Yukon–Kuskokwim Delta (YKD), Alaska, using measured Hg, SOC, and soil organic layer burn depth and environmental indices derived from satellite remote sensing data...

Graphics from the paper:



The caption:

Figure 1. Distribution of terrestrial Hg release from wildfires during summer 2015 in the Izaviknek and Kingaglia Uplands (IKU) study area. Hg release was predicted using a machine learning (Random Forest) model, which was developed using measurements of soil and vegetation Hg stores, soil organic carbon stores, burn depth, and environmental indices derived from satellite remote sensing data. Inset maps show locations of wildfire perimeters in the IKU study area (black lines), and the extents for which atmospheric transport and deposition of wildfire Hg were modeled in Alaska (gray box), the Yukon–Kuskokwim Delta (hatched box), and the IKU. Base imagery obtained from Copernicus Sentinel-2a data (European Space Agency, https://sentinel.esa.int/, last access: 01 September 2023).

The caption:

Figure 2. Total mercury (Hg) deposition from background sources (brown) and from the IKU fires (blue) over three domains: Alaska (top), the Yukon–Kuskokwim Delta (YKD; middle), and the Izaviknek and Kingaglia Uplands (IKU; bottom). Fire-attributable deposition is only shown for months where deposition occurred. The shaded blue area represents the range of uncertainty for fire-attributable deposition associated with uncertainties in plume injection altitude, Hg emission speciation, and Hg emission magnitude. The left axis shows areal deposition (?g m^–2 mo^–1), and the right axis shows cumulative deposition over each domain (kg mo^–1). Deposition was simulated using the GEOS-Chem global atmospheric Hg model. (38)




The caption:

Figure 3. Distribution of Hg deposition during the period of active fires in the Izaviknek and Kingaglia Uplands (IKU; June–July, 2015) simulated using the GEOS-Chem global atmospheric Hg model. (a) Monthly mean Hg deposition from background sources and (b) from the IKU fires. (c) the IKU fire-attributable fraction of annual total Hg deposition (background and fire-attributable). YKD = Yukon–Kuskokwim Delta.

The caption:

Figure 4. Annual peatland wildfire Hg emissions in the northern tundra–boreal region (>50°N) (black solid line) and the fraction of total annual wildfire Hg emissions in the northern tundra–boreal region that originate from peatlands (blue dashed line). Shaded regions represent the range of annual total and fractional peatland Hg emissions, estimated from the uncertainty in emissions from this study, as described in Section 2.5.3.

The authors conclude:

In this study, we found that permafrost peatland wildfires in southwest Alaska released a large amount of terrestrial Hg and that rapid deposition contributed significantly to local Hg budgets, adding to scarce research on the magnitude and fate of northern wildfire Hg emissions. (11,12,18,20,23,85) As climate warming increases tundra and boreal wildfire activity, (8,9) we emphasize the need for new measurements of Hg release and improved wildfire monitoring capabilities, especially in peatlands, to refine understanding of wildfire effects on Hg cycling at northern high latitudes. (10)

Now let's turn to the big bogeyman at Chernobyl:

From the introductory text of the first paper, which again, is open for the public to read, cited in this post, that about Chernobyl:

Wildfires in radiologically contaminated areas raise significant societal concerns due to the potential for radionuclide redistribution and increased public exposure. The Chornobyl nuclear disaster in 1986 released 85 PBq of ¹³⁷Cs and 10 PBq of ⁹⁰Sr into the environment. (1) ¹³⁷Cs and ⁹⁰Sr are particularly concerning due to their relatively long half-lives (30.17 and 28.79 years, respectively), continuing to pose environmental radiation concerns. (2) Wildfires in April 2020 within the Chornobyl Exclusion Zone (ChEZ) burned 554 km², (3,4) making them the largest wildfires since the accident (Figure 1). Population living nearby feared that radioactive aerosols would be transported to populated areas. (5) Similarly, when wildfires occurred in the radiologically contaminated area of Fukushima in 2017, concerns were raised about radionuclide redistribution and additional exposure, along with the spread of misinformation. (6) Wildfires in the ChEZ resulted in the release of total 643 GBq of radionuclides (¹³⁷Cs: 630 GBq, ⁹⁰Sr: 13 GBq) into the atmosphere as aerosols. (7) However, dose assessments have shown that additional exposure to external and internal radiation due to wildfires was negligible in resident areas. (8) In addition, aerosols originating from the wildfires in Fukushima did not increase the air dose rate measurements in neighboring areas. (9) Thus, research must focus not only on atmospheric transport but also on additional pathways that may contribute to ¹³⁷Cs and ⁹⁰Sr redistribution due to wildfires...

...Rivers are crucial pathways for ¹³⁷Cs and ⁹⁰Sr redistribution from upstream to downstream regions. Even in the absence of wildfires, 0.015–2% of ¹³⁷Cs (10,11) and 1% of ⁹⁰Sr12 present in the catchment are transported downstream annually by water and sediment movement. Atmospheric redistribution of ¹³⁷Cs and ⁹⁰Sr without wildfires is estimated at 0.0014–0.035%, (13) but it can significantly increase to approximately 4% due to wildfire disturbance. (14) The ¹³⁷Cs and ⁹⁰Sr released into the atmosphere will be widely dispersed not only within Ukraine (8) but also throughout Europe. (15) Further, catchment disturbance by wildfires is expected to affect the redistribution of ¹³⁷Cs and ⁹⁰Sr through the rivers. If the radionuclide concentration in rivers exceeds the permissible limit for drinking water in Ukraine (2 Bq/L for ¹³⁷Cs and ⁹⁰Sr), (16) it raises a significant environmental and public health concern. However, the impact of wildfires on the redistribution of ¹³⁷Cs and ⁹⁰Sr in rivers remains unclear.

Although the fates of ¹³⁷Cs and ⁹⁰Sr in charred residues are currently unknown, the dynamics of ¹³⁷Cs and ⁹⁰Sr in the environment are similar to those of K and Ca. ¹³⁷Cs is sorbed onto specific sites in clay minerals through ion exchange, thereby replacing K or NH4. (24,25) However, ⁹⁰Sr in rivers shows higher mobility than ¹³⁷Cs. (26) This is because Sr²⁺ is not sorbed by soils and sediments selectively and is not being fixed. (27) Additionally, wildfires enhanced soil erosion and ¹³⁷Cs wash-off at plot (28) and catchment (29) scales. Therefore, wildfires in radiologically contaminated areas are thought to affect the concentrations of ¹³⁷Cs and ⁹⁰Sr in rivers by supplying sediment, including charred residues, to rivers.

This study aimed to investigate the effects of large-scale wildfires that occurred in Chornobyl in 2020 on the redistribution of radionuclides in the Chornobyl River system, for further understanding of the environmental and public health concern caused by the wildfires, such as the radionuclide concentration in rivers exceeding the permissible limit for drinking water. To achieve this goal, we (1) quantified the concentrations and inventory of ¹³⁷Cs and ⁹⁰Sr in charred residues and soil after wildfires, (2) identified the speciation of ¹³⁷Cs and ⁹⁰Sr in charred residues and soil affected by wildfires, and (3) analyzed riverine ¹³⁷Cs and ⁹⁰Sr concentrations before and after wildfires using long-term observation data. Our findings will provide fundamental information, based on hydrological insights, for assessing of the impact of wildfires on radiation exposure in various populations...

Some discussion of results:

...Wildfires are natural ecological processes that alter riverine environments by accelerating the biogeochemical processes. (66) When wildfires occur in a catchment, higher suspended solids (SS) concentrations, (19) charred residues, (67) and dissolved elements (68) can be washed off into rivers from the burned areas. The 2020 wildfires in Chornobyl burned 69.2% of the Sakhan River catchment. (3,4) Consequently, ¹³⁷Cs and ⁹⁰Sr in the surface soil and charred residues may also wash off into rivers from these areas. In the Sakhan River, no increase in the concentrations of dissolved ¹³⁷Cs and particulate ¹³⁷Cs was observed before or after the wildfire (Figure 4b,c). Furthermore, both dissolved and particulate ¹³⁷Cs concentrations in the Sakhan River have remained below the Ukrainian permissible level (2 Bq/L) (16) since 2001 (Figure S5b,c). ¹³⁷Cs is known to be strongly adsorbed by clay mineral, (46,47) and dissolved ¹³⁷Cs is thought to quickly adsorb to suspended solid and potentially reach equilibrium (42,69) in the river basin. As a result, there may have been no change in ¹³⁷Cs concentration after the wildfire.

In contrast, wildfires were expected to affect dissolved ⁹⁰Sr concentrations in the river, with the results indicating a postwildfire increase in ⁹⁰Sr. Before the wildfires started, four events exceeded the Ukrainian permissible level for ⁹⁰Sr concentration (2 Bq/L); (16) however, seven such events were observed two years after the wildfire (Figure 4d). Despite a 37% reduction in total ⁹⁰Sr concentrations due to physical decay between 2001 and 2020, the highest ⁹⁰Sr concentration (11.0 Bq/L) since 2001 was observed in May 2021 after the wildfire. Human activity in the Sakhan River, within the ChEZ, remains severely restricted. Consequently, the possibility of direct human exposure to levels of ⁹⁰Sr exceeding 2 Bq/L in drinking water, even after a wildfire, is improbable. Simultaneously, wild animals may directly ingest ⁹⁰Sr from drinking surface water or river water immediately after wildfires. Aquatic biota, such as freshwater fish, also take up ⁹⁰Sr following wildfires. In addition, ¹³⁷Cs and ⁹⁰Sr in charred residues can be transferred to vegetation. This highlights the importance of continuously investigating the dynamics of long-lived radionuclides at sites after wildfires. Even after the wildfire, the concentrations of dissolved ¹³⁷Cs and ⁹⁰Sr in the downstream area of the Pripyat River were several orders of magnitude lower than the Ukrainian permissible levels, and additional human exposure downstream was not expected (SSE Ecocentre, personal communication)...

It is worth noting that the "permissible" level of ⁹⁰Sr of 2 Bq/L is somewhat lower than the radioactivity associated with ⁴⁰K (potassium-40) found naturally in seawater, which is generally on the order of 8-12 Bq/L depending on local salinity. ⁴⁰K has a higher decay energy than ⁹⁰Sr irrespective of its branching to either ⁴⁰Ar or ⁴⁰Ca. (It is thought that the most common isotope of calcium, ⁴⁰Ca is likely to be radioactive, via double beta decay to ultimately ⁴⁰Ar. However if it is, the half-life is so long as to escape detection.) However, ⁹⁰Sr is in secular equilibrium with another radioactive isotope ⁹⁰Y, and ⁹⁰Sr, as a congener of calcium, is preferentially deposited in bones. If one were to drink water above the "permissible level" it remains unlikely that one would face health effects, immediately or otherwise, but the overall risk would be slightly higher for say, bone cancer, still vanishingly small, perhaps so small as to not be measurable. That said, better safe than sorry, I guess.

It doesn't appear to be a big health problem, this mobilization after a fire in the Chernobyl exclusion zone.

I'm going to skip reference to the figures in the paper in the interest of time. Again, the paper is open sourced, and if one is inclined to look at the pictures, one is free to do so by use of the link above.

The death toll in Ukraine from the effects of Chernobyl is dwarfed by the death toll associated with the weapons of mass destruction unleased by the Russians. The war in the Ukraine was largely funded by German antinukes, who, after phasing out their nuclear plants, bought huge amounts of dangerous fossil fuels, including but not limited to, coal from Putin's dictatorship.

I trust you are doing your best to enjoy one of the last weekends before the demise of the 250 year old American Democracy in service to an ignorant, criminal, racist, senile fool and his oligarchical ownership.