Impact of Natural Organic Matter on Plutonium Vadose Zone Migration
Last edited Sat Mar 14, 2020, 06:44 PM - Edit history (1)
The paper I'll discuss in this post is this one: Impact of Natural Organic Matter on Plutonium Vadose Zone Migration from an NH4Pu(V)O2CO3(s) Source (Melody Maloubier, Hilary Emerson, Kathryn Peruski, Annie B. Kersting, Mavrik Zavarin, Philip M. Almond, Daniel I. Kaplan, and Brian A. Powell* Environmental Science & Technology 2020 54 (5), 2688-2697)
The current rate of air pollution deaths is roughly 6.5 million people per year, somewhat lower than it was a few years ago, but still rather impressive, and now, in cultures around the world featuring the political celebration of ignorance, likely to rise again with the indiscriminate relaxation of anti-pollution laws.
Global, regional, and national comparative risk assessment of 79 behavioural, environmental and occupational, and metabolic risks or clusters of risks, 1990–2015: a systematic analysis for the Global Burden of Disease Study 2015 (Lancet 2016; 388: 1659–724)
This means that since the year 2000, at least 130,000,000 million human beings had their life span shortened by exposure to volatile air pollutants. We. Couldn't. Care. Less.
As this website is a political website with a science section, I mention the year 2000 as it is useful to note that in the year 2000 there was a political candidate working actively to elect George W. Bush, an ignoramus, on the grounds that "Bush was the same as Gore." That candidate was a scientifically illiterate emotionally paranoid attorney named Ralph Nader who, when he wasn't scamming college kids with their limited resources to fund his PIRG ignorance squads by working to put PIRG charges on their tuition bills, was popularizing very stupid urban myths, only one of which was that "Plutonium is the most toxic substance ever known."
It is interesting to note that some of the same people who were helping Ralph Nader to elect criminal Republicans to the White House because he hated Democrats are still around today doing the same thing. For example the smug, stupid movie maker Michael Moore, who has worked to induce snickering about events like the murder of children in their high school by gun wielding disturbed children is now attacking the likely Democratic nominee on the grounds that he is the same as Moore's fellow moron, the racist pig in the White House who is putting children in cages. (Maybe someday that can sell movie tickets, who knows.)
Eating plutonium is not good for you, anymore than drinking gasoline is good for you, or for that matter, having coal ash run off in your drinking water is good for you.
I think most rational people understand that.
But of course, although clearly it was ill advised, there was a period between 1945 and roughly the mid 1960's wherein several major countries around the world actively vaporized plutonium in the open atmosphere on a ton scale in nuclear weapons tests.
According to a Wikipedia page, there have been 2121 tests of nuclear weapons, most of which were conducted by the United States (1032 such tests). The second most prolific nation to test nuclear weapons was of course, the former Soviet Union, which conducted 727 tests, followed by France, which conducted 217 tests. Worldwide of all nuclear weapons test 520 nuclear weapons by all countries, the US, the USSR, France, Britain and China and others, 512 were conducted in the open atmosphere and 8 were under water.
I am currently reading an interesting book Big Science, Ernest Lawrence and the Invention That Launched the Military–Industrial Complex which is about the cyclotron, the instrument utilized to produce the first sample of plutonium. That sample is on display in the Smithsonian's Museum of History; I've seen it. For a long time it was kept in a cigar box. The book contains an interesting account of how Ernest Lawrence and Edwin Teller agitated strongly against stopping open air nuclear weapons testing, participating actively in arguments that nuclear weapons testing was if not good for you, was at least not all that bad for you but in any case was good, overall, for America.
That of course, was a dubious idea, even though it was advanced by people who were very, very, very, good at science, but probably less impressive, overall, as human beings.
It is interesting that both Lawrence and Teller, in league with a right wing non-scientist asshole named Lewis Strauss - he of the famous claim that nuclear energy would be "too cheap to meter" - were instrumental in the vilification of the scientist who actively oversaw the creation of nuclear weapons, Robert Oppenheimer, on the grounds that they claimed, or at least supported the idea, that Oppenheimer was a "fellow traveler" with communists.
It is also notable that many people who claim to be political liberals, despite apparent indifference to hundreds of millions of air pollution deaths all over the planet since 1965, like to quote this right wing asshole, Lewis Strauss, on the "too cheap to meter" claim, although their favorite form of energy, so called "renewable energy" is not to cheap to meter either. In fact, the countries most invested in so called "renewable energy" - which is irreversibly destroying huge tracts of wilderness - Germany and Denmark have the highest electricity rates in the world. These same people, who also love to carry on about so called "nuclear waste" are completely uninterested in the fact that so called "renewable energy" has been spectacularly useless at addressing the accumulation of the dangerous fossil fuel waste carbon dioxide in the atmosphere. For the entire period during which trillions of dollars have been invested in solar and wind energy, the rate of said accumulation is accelerating, not slowing. The annual mean concentration of the dangerous fossil fuel waste carbon dioxide in 1965 was 320.04 ppm. The concentration of the same dangerous fossil fuel waste which is actively destroying ecosystems around the world was, as of yesterday,
There is nothing about selective attention that even crudely approximates critical thinking. Selective attention in fact, involves bad thinking and overt dishonesty.
Anyway.
Anyway.
The plutonium was vaporized in nuclear weapons tests in any case, and in many cases was formed in situ in nuclear weapons tests, particularly in tests of so called "hydrogen bombs" which used lithium diverted to nuclear weapons tests to form in situ tritium, which fused with deuterium to release neutrons to cause depleted uranium to be partially fissioned and partially converted to plutonium. These types of weapons, which were very popular in the Soviet Union, released large amounts of energy and fairly large amounts of plutonium vapor; it turns out that even though the Soviet Union conducted fewer tests than the United States, the tests they did conduct were more energetic and probably released more plutonium.
Almost all of that plutonium is still here. The half life of plutonium-239, the most common isotope involved in nuclear weapons tests, is 24,110 years. One can calculate easily therefore that since 1965, 99.84% of the plutonium present in the environment in that year is still here. Anti-nukes - particularly those dumb enough to wallow insipidly in the remarks made by the right wing syndic Lewis Strauss because nuclear energy is decidedly not "too cheap to meter" as if there were any forms of electricity that are "too cheap to meter" - also like to throw around the claim that what they call "nuclear waste" must be stored for "millions of years," or something terrible will happen. What exactly that terrible thing is never defined. It is easy to calculate, assuming one has opened a math book in one's life time and is thus ineligible to join Greenpeace, that in one million years the amount of plutonium that was present in the environment in 1965 will have decayed to 0.32 trillionths of what was present in 1965. With a totally due lack of respect for Ralph Nader, there is no evidence that the distribution of this plutonium in the atmosphere and ultimately on land and in the seas has led to any loss of life that even remotely approaches the loss of life associated with dangerous fossil fuel waste, at least 130,000,000 people since 1965. It is very unlikely that 0.32 trillionths as much in one million years will be more dangerous than what is here now.
The detection of molecules and elements depends on the release of energy - energy that is either absorbed or released by the analyte in question. The sensitivity of an analytical method depends on the detection of this energy. Because nuclear reactions release, on an atomic scale large amounts of energy which can be picked up by very sensitive devices called scintillators - often containing crystals of salts like strontium or cesium iodide - it is possible to see nuclear reactions take place on an atom by atom basis. (It is this high energy density with respect to mass which makes nuclear fission - and were it to prove to be technologically viable, nuclear fusion - environmentally superior to all other forms of energy.)
The paper cited at the outset will give the accepted standard for permissible concentrations of plutonium in drinking water, which is "15 pCi." The unit "pCi" is a picocurie. A curie, which was originally based on the average number of decays that were thought to take place in a gram of radium per second is 37 billion decays per second. It follows that a picocurie, a trillionth of a curie, represents 0.037 decays every second, or one nuclear decay every 27 seconds. It is simply not true that any nuclear decay in one's flesh will kill them, since there are zero people on this planet who would survive for a New York microsecond without potassium in their flesh. Potassium is naturally radioactive owing to the presence of the primordial isotope potassium-40. A 70 kg human being will contain about 140 grams of potassium, which corresponds, from the decay constant and isotopic composition of potassium to 4250 decays per second. Anyone not having roughly this many nuclear decays in their bodies would die.
Of course, in order for one to absorb plutonium one needs to ingest it in some fashion, eat or drink or breathe it or some such thing. People who spout stupid platitudes about the "millions of years" that so called "nuclear waste" must be contained although they are spectacularly uninterested in whether broadly toxic dangerous fossil fuel wastes can be contained for a microsecond, like to pretend for reasons designed to incite hysteria and not for any reason designed to demonstrate a whit of rational thought, that if a canister of plutonium anywhere on the earth were to leak, it would magically find its way directly into someone's brain tissue. This is simply not true. A canister of plutonium buried 500 meters under ground would need to migrate though 500 meters of rock, mobilized by water, being diluted intrinsically in the process, and how much would do this, and how long it would take before becoming bioavailable is dependent on the chemical nature of plutonium. The solubility product of plutonium oxide, PuO2, is 10^(-54.85). (This equivalent to saying pKsp = 54.85.) If one has passed an introductory college level chemistry class - or such a class in a good high school - one can calculate that to dissolve one atom of plutonium in water at neutral pH, pH=7, would require 4,920,000 liters of water. However, doing this calculation is somewhat misleading, because plutonium has a very, very, very rich chemistry, and exhibits multiple oxidation states having differing solubilities. Although industrially it is difficult to dissolve plutonium dioxide in at least one of its structural forms, a polymeric form, even with acid, it can take place with the use of oxidants and/or reducing agents. It is therefore possible if not probable for plutonium to migrate in geological formations, although it is not clear that it can do so at such a rate as to represent the same kind of health or environmental risk as dangerous fossil fuel waste; you cannot take a breath anywhere on this planet with being exposed to dangerous fossil fuel waste. Scientists have been studying this question for more than half a century: How can plutonium migrate in geological situations. This is because the general public has been trained to have a waste mentality rather than a use mentality.
I make this point all the time: It is extremely ignorant to advocate for the dumping of used nuclear fuel; since there are zero constituents therein that cannot be utilized to do important things; some of those things cannot be done as well by anything other than certain constituents of used nuclear fuel. It the current context, it is useful to note that radiation is an excellent tool for sterilizing materials; radiation is used for this purpose industrially. Dumping plutonium is just, in my opinion, stupid. I favor a plutonium based industrial energy economy. This makes me eccentric, of course, but the fact that I am eccentric does not mean that the focus of my eccentricity, advocacy of a plutonium fuel cycle, has any bearing on whether my claim that a plutonium economy would be the most environmentally sustainable approach to world survival is true or not. What is popular is often based on untruths.
In any case, the paper referenced at the outset of this post is about plutonium migration, not in theory but as an experimental result. There are ways that plutonium can migrate in the environment that do not depend on dissolution, in particular, it can travel attached to flowing particles, something to which the authors refer.
From the paper's introduction:
Evaluation of Pu migration in the environment is particularly complex due to the fact that Pu may be simultaneously present in multiple oxidation states (from +III to +VI).(3−6) Previous studies have shown that subsurface migration of actinides is influenced by many factors including redox behavior, sorption, and complexation.(7−10) The speciation and mobility of Pu are highly dependent on the initial depositional environment and form of plutonium.(11) For example, Batuk et al. examined the speciation of Pu in soil from different contaminated field sites (Hanford Site, Rocky Flats, and Los Alamos) through a combination of X-ray absorption spectroscopy (XAS) and X-ray fluorescence element maps.(11) They identified different forms such as mononuclear Pu and PuO2+x precipitates that can incorporate other elements (Fe and P) and particles. Various mechanisms leading to the observed species were proposed based on a priori knowledge from the site (e.g., the initial form and disposal conditions), especially to explain incorporation with other elements. To understand the fate of Pu previously discharged to the seepage basins and to mitigate potential future releases, it is important to investigate the behavior of Pu under field conditions. An improved understanding of Pu behavior in the field will help to develop more robust geochemical models for predicting the long-term fate of Pu at the SRS and others. The knowledge of the behavior of Pu according to its initial source material and the site conditions will allow us to determine the transport mechanisms and predict a future behavior in other sites.
Previous field lysimeter studies at the SRS have demonstrated reduction of PuVIO2(NO3)2(s) and oxidation of PuIIICl3(s) sources to unspecified Pu(IV) solid phases.(12,13) These studies have also shown that Pu originating from a PuVI(NO3)2(s) source was transported significantly further than PuIV(NO3)4(s) and Pu(III) sources.(1,12,13) Based on these data and speciation modeling, Pu(V) is expected to be the most mobile oxidation state in natural waters.(10,14,15) However, the behavior of Pu(V) sources and the impact of organic matter were not previously studied. The current work seeks to monitor the chemical and physical changes of well-characterized NH4PuVO2CO3(s) sources to compare with these earlier results. In contrast to measurements of Pu bearing samples recovered from legacy management sites, the initial source material and experimental conditions of the current study are well-known, allowing for a direct evaluation of the transformation of Pu solid phases under environmental conditions.
Following the release from the initial Pu source, migration of Pu can be influenced by colloids, organic matter, and redox reactions. Formation of pseudocolloids (e.g., Pu bound to mineral colloids or organic colloids) can have a strong impact on Pu migration in the subsurface. Several studies have shown that the fate of Pu in the environment may be controlled by transport on colloidal iron oxide and clay mineral particles.(16−18) Additional studies have demonstrated that association of Pu with organic colloids can enhance pore water concentrations.(19−27) Moreover, the presence of organic matter can affect the oxidation state as it is known that Pu is rapidly reduced from Pu(VI)/Pu(V) to Pu(IV)/Pu(III).(3,4,28,29) The overall influence of organic matter on Pu migration appears to be dependent on the nature of the organic matter(17,30,31) and the Pu–organic matter interactions, and further studies are warranted. Most previous research that has been conducted via laboratory experiments is not representative of natural conditions (wet/dry cycles, preferential flow, rainfall, etc.). However, there is a need to supplement these data with field scale experiments under more representative environmental conditions.
So the authors set up a device known as a lysimeter. Some experimental details about how this worked:
Clemson University and the Savannah River National Laboratory (SRNL) have installed and are currently operating a radionuclide lysimeter facility at the SRS in South Carolina. Out of 48 total lysimeters at RadFLEx, 22 lysimeters were installed to evaluate the long-term migration of Pu and Np through vadose zone soils. Six lysimeters contained NH4PuVO2CO3(s) sources. Each lysimeter consists of a 60 cm × 10 cm poly(vinyl chloride) pipe with a representative sandy clay loam soil from the SRS. Three of the six lysimeters contained soil amended with 10% by weight NOM prepared by mixing a dried sample of organic matter collected from a wetland area upgradient of the field lysimeter facility. The NOM was isolated from a 20 kg leaf litter sample collected by hand from a forested wetland floor along the edge of Tims Branch in Aiken South Carolina (33° 19′ 58″ N, 81° 43′ 09″ W). The forest contained black gum (Nyssa sylvatica), black willow (Salix nigra), red maple (Acer rubrum), and water tupelo (Nyssa aquatica). The litter was dried at 60 °C in a forced air oven for 1 week. The dried leaf litter was ground to a fine powder in Thomas Wiley Mill Model 4, equipped with a 40 mesh sieve. The ground leaf litter was then mixed using a shovel with lysimeter sediments at a leaf litter/sediment weight ratio of 1:10. For radiation protection when transferring the Pu source into the field, the source (held between filter papers as described below) was packed into the center in a 5 cm diameter × 8 cm tall cylinder which was extruded into the field lysimeter and then surrounded with an additional 10% by weight NOM-amended soil.
The main properties of the soil are detailed in Table1...
Table 1:
A description of the preparation of the plutonium source with brief reference to how it behaved when exposed to weather:
ICP-MS is a very sensitive analytical tool, not quite as sensitive as radiochemical determinations, but still capable of easily, quickly and cheaply measuring quantities in trillionths of a gram.
Some pictures from the text:
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A summary of the results of the paper:
1. The Pu concentration profiles are different (Figure 1). The downward migration of Pu was hindered by the presence of NOM.
2. Pu migration after three years is very limited, with more than 95% of the Pu remaining within 2 cm of the source material. More specifically, the highest soil Pu concentration was found within 1 cm of the source and corresponding to 2–5% of the initial Pu mass. Pu concentrations in the soil decreased by approximately an order of magnitude per cm in the first 2 cm and decreased more gradually with depth, approaching a concentration of 1 Bq/g 239Pu below 12 cm.
3. Plutonium migration was similar to a previously published two-year Pu(VI) lysimeter experiment. Both the Pu(V) and Pu(VI) sources traveled farther than previous 11-year Pu(IV, III) lysimeter experiments (though NOM was absent in all of the previous lysimeter experiments).(12)
4. Pu migration in this NOM-amended lysimeter experiment was similar to the previously published Pu(IV) and Pu(III) lysimeter experiments with an order of magnitude decrease in Pu concentration per cm for the first 3 cm below the source.(12)
Some commentary in the paper's conclusion:
This study demonstrates that the presence of NOM can have a significant impact on the mobility of Pu in the subsurface through formation of ternary surface–NOM–Pu complexes and/or stabilization of Pu(IV) by NOM that prevents further downward migration of reoxidized Pu(V) formed from incoming rainwater. Overall, the downward migration in these Pu lysimeters was influenced by the initial source oxidation state, where the Pu(V) lysimeters in the current work exhibited greater migration than previous studies using Pu(IV) or Pu(III) sources.(16) The mobilized Pu(V) appears to be reduced to Pu(IV) in the order of hours, indicating that downward migration of Pu may be due to cycling between Pu(V) and Pu(IV) as previously observed.(1,55) The form of reduced Pu within the soil may differ depending on the initial oxidation state of the source. Moreover, the presence of NOM in the soil accelerates the reduction of Pu(V) to Pu(IV) and enhances immobilization because of the strong sorption of Pu(IV) onto mineral surfaces leading to a behavior similar to Pu(IV)- and Pu(III)-amended lysimeters. EXAFS analyses of the sources showed that Pu(V) was reduced to Pu(IV) after 3 years of exposure including in the archived source stored in an inert nitrogen atmosphere likely as colloids or other PuO2+x–y(OH)2y·zH2O-type compounds with high disorder. Therefore, the mobility of Pu in similar soils at the SRS will be controlled by (1) transformation of the initial source to a PuO2+x–y(OH)2y·zH2O-type phase on the time scale of months to years and (2) reduction of soluble Pu(V) to Pu(IV). Additionally, the presence of NOM appears to enhance both reduction of the Pu(V) source as well as Pu sorption to soils. Therefore, Pu is expected to be less mobile in the presence of NOM under the SRS vadose zone geochemical conditions. Interestingly, this observation contrasts with previous studies that have shown organic matter to enhance Pu migration in the surface and groundwater.(17,30) This difference may be attributable to the relative immobility and nature of the organic matter to which Pu is associated (i.e., soluble vs mineral-bound organic matter). The findings from this study can be used to evaluate the potential for Pu mobility in other subsurface environments with organic matter.
I recognize that many of the results of this experiment kind of fly in the face of the claim that we have to worry more about plutonium than we do about the 130,000,000 (at a minimum) air pollution deaths since 1965. Again, this flies in the face of the popular imagination, which cares a great deal about plutonium and far less about the total and complete destruction of the planetary atmosphere.
In my tenure here, it has been my misfortune to engage many people making such an argument as to fit precisely into the popular imagination. My favorite one was some ass who pulled up one of my old posts to tell me all about a collapsed tunnel at the Hanford nuclear weapons plant and to announce that this "proved" nuclear energy was dangerous. (It appears, on further investigation, that the tunnel contained an old rail car on which a plutonium processing chemical reactor had been discarded. I would imagine, although I do not know, that the plutonium contamination of the reactor, to the extent it was real, was represented in the chemical form the aforementioned PuO2, which is difficult to dissolve, which like I described above and the authors of the paper described above, is difficult to put into a mobile form.
We live in times of the rising celebration of ignorance, led by the avatars of my generation, the baby boomers.
History will not forgive us, nor should it.
Despite all the isolation taking place around the world, I trust you will nonetheless find a way to enjoy this weekend. Spring is likely to arrive early this year - it has done so here in New Jersey - but this is not necessarily a good thing.
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