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Sun Feb 23, 2020, 04:04 AM

Trends in Nitrate, Arsenic, and Uranium in Groundwater Beneath Irrigated Cropland.

The paper I'll discuss in this post is this one: Using Age Tracers and Decadal Sampling to Discern Trends in Nitrate, Arsenic, and Uranium in Groundwater Beneath Irrigated Cropland (Anthony J. Tesoriero, Karen R. Burow, Lonna M. Frans, Jonathan V. Haynes, Christopher M. Hobza, Bruce D. Lindsey, and John E. Solder, Environmental Science & Technology 2019 53 (24), 14152-14164)

In recent years, I have paid some attention to the destruction of the Ganges River in India - the sacred Ganges among some of the faithful - particularly as it effects the delta nation of Bangladesh. The lower flows have resulted in increased reliance on groundwater for irrigation in Bangladesh, with the concomitant result, since Bangladesh sits on arsenic rich rock formations, with mass poisoning of the population there. One can read about this - among many other places - in another paper in the same journal that features the paper I will discuss: Effectiveness of Different Approaches to Arsenic Mitigation over 18 Years in Araihazar, Bangladesh: Implications for National Policy (Nadia B. Jamil, Huan Feng, Kazi Matin Ahmed, Imtiaz Choudhury, Prabhat Barnwal, and Alexander van Geen, Environmental Science & Technology 2019 53 (10), 5596-5604)

This latter paper contains the following text:

Despite mounting evidence of the negative impacts of drinking well water that is elevated in As, only modest progress has been made in addressing the issue. The first representative survey across Bangladesh concluded that a population of 57 million was exposed in 2000 to As levels above the WHO guideline of 10 μg/L.9 Subsequent drinking-water surveys based on geographically representative sampling indicate that the population exposed relative to this guideline declined to 52 million in 2009 and to 40 million in 2013.10,11

Progress. "Only" 40 million. We need some "renewables will save us" types to come over and make us feel better with percent talk. You know, "Arsenic poisoning in Bangladesh has decreased by 30%!!!!!"

My interest in the Ganges was motivated by that river's role in uranium transport in the Earth's geochemical uranium cycle, when I was doing background research for a post elsewhere on the internet: Is Uranium Exhaustible.

The Ganges transports about 1200 tons of uranium per year to the ocean: Krishnaswami and J. Kirk Cochrane, eds. U-Th Nuclides in Aquatic Systems. Chapter 10, J. Kirk Cochrane and David Kadko, page 293. See also Dunk, R. M., R. A. MiUs, and W. J. Jenkins. Chemical Geology 190, 45-67 (2002)

The transport of naturally occurring elements from the ores in which they are found are obviously affected by environmental chemistry and physical processes. This should be obvious since we use chemistry to isolate elements from their ores. A widely used reagent for the recovery of uranium from its ores - one such ore is used nuclear fuel - is nitric acid, HNO3. Salts of nitric acid, in particular the ammonium salt - an explosive salt that was utilized by the right wing terrorist Timothy McVeigh to blow up a building in Oklahoma City, who may be awarded posthumously the Presidential Medal of Freedom by the anti-Freedom Nazi in the White House (would you really be surprised) - are widely used in agriculture.

It follows that nitrate can mobilize uranium in rocks, and the physical process of pumping water over them, can further exacerbate this extraction process.

From the text of the paper under discussion:

Irrigation has caused large changes in the hydrology and chemistry of agricultural areas.(1,2) Solutes in groundwater may increase when an area is converted to irrigated cropland due to leaching of salts that have accumulated naturally prior to cultivation and the application of fertilizers to the land surface.(1) Nitrate concentrations in groundwater may markedly increase when rangeland is converted to irrigated cropland,(1) with nitrate concentrations in recharging groundwater exceeding the drinking water standard beneath irrigated cropland in some areas.(3)

High concentrations of arsenic and uranium occur in groundwater in irrigated areas due to desorption, redox conditions, and evaporative concentration.(4)Irrigation-induced increases in microbial activity and water–rock interactions or the land application of lime often lead to increases in bicarbonate and calcium in groundwater. These increases in bicarbonate and calcium favor the formation of Ca–U(VI)–CO3 complexes that increase the desorption of U from subsurface sediments(5,6) and/or the dissolution of uranium-bearing minerals,(7) leading to higher uranium mobility. The effect of bicarbonate and calcium on uranium mobility is evidenced by the strong correlation between bicarbonate and uranium concentrations in groundwater in a large regional study in Germany(8) and by concordant changes in bicarbonate and uranium concentrations in a national study in the United States.(9)
Infiltrating irrigation water may also alter redox conditions which may affect the mobility and toxicity of contaminants either by affecting the transformation of contaminants to other species (e.g., creating more oxic conditions which may limit denitrification,(10) arsenic reduction(11)), or by causing the precipitation or dissolution of compounds that contain or sorb contaminants (e.g., sorption of arsenic on iron oxides(12)). Irrigating cropland introduces electron acceptors such as dissolved oxygen and nitrate, which can cause the oxidative dissolution of reduced compounds containing constituents of concern (e.g., arsenic, uranium). The correlation of nitrate concentrations in groundwater with selenium and uranium has been suggested as evidence that nitrate may serve as an electron acceptor in the dissolution of selenium and uranium-bearing minerals.(13,14) In one large regional study, the highest concentrations of uranium were observed in manganese and nitrate-reducing conditions,(8) while laboratory studies have found that nitrate is a stronger oxidant of uranium than dissolved oxygen.(15)Arsenic concentrations in groundwater are also often affected by redox conditions due to the release of sorbed arsenic during the reductive dissolution of iron hydroxides.(12,16) While high arsenic concentrations are often associated with reducing conditions, the oxidative dissolution of arsenic-bearing sulfides may also result in elevated arsenic concentration in certain environments.(17,18)

The authors discuss two areas in which the concentration of these two elements and the nitrate ion have been tracked.

In this study, the sources and trends in nitrate, arsenic, and uranium concentrations in irrigated areas are examined using a novel approach that employs decadal sampling, stable isotopes, and age tracers. Specifically, a study was designed to test the hypothesis that groundwater that recharged after the onset of irrigation has higher concentrations of nitrate, arsenic, and uranium than groundwater that recharged prior to irrigation. Furthermore, we examine how contaminant concentrations within these age cohorts change over time. Age tracers were used to determine the recharge dates of each sample relative to the onset of irrigation.

The authors chose two relatively arid regions where there is intensive irrigated agriculture:

The Columbia Plateau is a largely arid(20) region with intensive agriculture in eastern Washington and Oregon and western Idaho and is underlain by a thick sequence of continental flood basalts that erupted through fissures between 17 and 6 million years ago.(21) The Columbia Plateau is broadly divided into four aquifer units. From youngest to oldest these units are the overburden aquifer (overlying basin-fill sediments), the Saddle Mountains unit, the Wanapum unit, and the Grande Ronde unit (Figure S1).(22) The Saddle Mountains, Wanapum, and Grande Ronde units consist of hundreds of individual basalt flows ranging in thickness from a few meters to more than 100 m(23) along with small amounts of intercalated sediments...

... Groundwater in the basalt units flows preferentially through the tops and bottoms of individual lava flows, rather than through the less permeable interior.(24)

Figure 1 in the paper is a map of this region.

The caption:

Figure 1. Site map of Columbia Plateau wells sampled for this study. Map is from Arnold et al. (2017, https://pubs.er.usgs.gov/publication/ds1063). Identification numbers correspond to ccptsus1b and ccptlusag2b listings in Table 1 of Arnold et al. (2017), where water quality and construction details are provided for each well.

I once encountered a really dumb guy or gal on this website who proudly announced to me that nuclear power is "too dangerous" because a tunnel containing some old chemical reactors at the Hanford Nuclear Weapons plant collapsed. This was in lieu of giving a shit about the 19,000 people who would die each day from the time of his post up to and including today from air pollution. That moron of course, has made it to my wonderful ignore list, but it is notable that the Hanford reservation contains tanks that are rich in nitrate and nitrite and uranium.

You hear these sort of things, but you really don't want to believe that people say these sort of things.

The authors of this paper claim that although the Hanford tanks are well known to contain huge amounts of nitrate and uranium this has had little bearing on their findings:

Historical measurements of the Columbia River indicate that uranium and arsenic are often not detected, with concentrations typically less than 2 μg/L.(27,28) The U.S. Department of Energy’s Hanford site is just west of the study area (Figure 1) and is a potential source of contaminants. However, all of the wells used for this study are across the Columbia River, a regional discharge area,(25) from the Hanford site.

Reference 27 is here: Water Quality of the Lower Columbia River Basin: Analysis of Current and Historical Water-Quality Data through 1994

Reference 28 is here: USGS Water Data for the Nation

Poking around in reference 28, one can learn of the concentrations of uranium in groundwater in Washington State well upstream from the Hanford reservation. Concentrations of Groundwater Uranium Upstream in the Columbia River Watershed, part of this report: Uranium concentrations in groundwater, northeastern Washington Although the authors of this report and the authors of the paper under discussion all work for the USGS, the data does seem to suggest that uranium concentrations in ground water in Washington State are not a function of the existence of the Hanford tanks, although credulous anti-nukes will not believe it.

In any case, the authors second study area is in Nebraska, also in an irrigated region:

The second study area is in the eastern portion of the Northern High Plains aquifer in eastern Nebraska, near the city of York (Figure 2). This area is primarily underlain by sand and gravel with lesser amounts of wind-deposited silt and clay (loess), paleosols, and unsorted and unstratified glacial till.(29)These heterogeneous Quaternary deposits form a layered sequence of coarse- and fine-grained units (Figure S2). The hydrologic conditions of the High Plains aquifer vary from unconfined to confined conditions, with a clayey till often separating the unconfined aquifer from the confined aquifer. (30) The High Plains aquifer is more than 60 m thick in some areas, with the base of the aquifer corresponding to the top of bedrock.(30)

This study area has a humid, continental climate,(20) receiving an average of 68 cm of precipitation each year.(31) Cropland, primarily corn and soybeans, is prevalent in the study area, with most of this cropland receiving irrigation. Rates of recharge from precipitation are estimated to be 14.2 cm/yr, with irrigation recharge estimated to be 6.4 cm/yr.(31) While groundwater has been used for irrigation in the High Plains area since the late 1800s, intensive irrigation did not occur until the mid-1900s. Irrigated cropland began to increase dramatically in the 1950s in the Nebraska portion of the High Plains aquifer; (32) climate change may result in future increases in irrigation demand in this area.(33)

Fertilizer applications have increased markedly since 1950, resulting in dramatic increases in nitrate concentrations in recharging groundwater in recent decades.(3,34) Stanton et al. (2006) sampled shallow groundwater from 30 wells in the High Plains aquifer in 2004 and determined that nitrate concentrations in shallow groundwater ranged from 2.0 to 106 mg/L as N, with a median concentration of 10.6 mg/L.(29) Nitrate-N isotope ratios in agricultural recharge suggest that fertilizer is the primary source of nitrate in groundwater recharge in this area.(3)

The study area:

The caption:

Figure 2. Site map of High Plains aquifer wells sampled for this study. Map is from Arnold et al. (2018, https://pubs.er.usgs.gov/publication/ds1087). Identification numbers correspond to hpgwvfps1 listings in Table 1 of Arnold et al. (2018), where water quality and construction details are provided for each well.

The age of the water tested is determined by the concentrations of the radioactive hydrogen isotope tritium injected into the planetary atmosphere by nuclear weapons testing, particularly by hydrogen bombs:

3.3. Age Dating Techniques
Groundwater samples were analyzed for tritium at all sites and sulfur hexafluoride (SF6) at the High Plains sites. Samples were characterized as premodern, mixed, or modern using the tritium category method.(46) A brief discussion of the tritium category method is provided below, with details provided elsewhere.(46) The tritium category method relies on variations in concentrations of 3H in groundwater given the temporal and spatial variation of 3H in precipitation.(47)3H concentrations in precipitation were at low, naturally occurring levels before 1953 but subsequently increased rapidly due to above-ground nuclear bomb testing (Figure 2b in Lindsey et al., 2019).(46)3H concentrations in precipitation remained high for many years, only returning to near prebomb concentrations in the past decade. However, 3H concentrations in groundwater that recharged prior to 1953 are much lower than recharged in the postpeak era due to the decay of 3H between 1953 and the sample collection date. This decayed concentration of recharge just prior to 1953 represents the upper threshold concentration of what is classified as premodern water. Conversely, a 3H concentration in groundwater that is greater than the lowest decayed concentration expected from precipitation during the postpeak period must have recharged after 1952 and is classified as modern water. Lastly, 3H concentrations that are between the upper and lower threshold are the result of a mixture of modern and premodern water and are termed mixed water. Groundwater ages of modern samples at the High Plains site were further refined by measuring SF6 concentrations in groundwater samples and relating these concentrations to atmospheric inputs.(48)

SF6 is a persistent greenhouse gas, with a global warming potential of 23,900 relative to CO2. It is totally anthropogenic, and has been industrially synthesized to replace PCB's in electrical transformers and to make those wonderful insulated solar windows in modern McMansions. Thus its presence in water is a time marker, given that the gas has only existed in prominent concentrations in recent times; it does not occur naturally.

Here are tables of results from the paper:

Some other graphics:

The caption:

Figure 3. Boxplots of nitrate concentrations as a function of groundwater age class: A) Columbia Plateau, and B) High Plains aquifer near York, Nebraska. Number above plot indicates number of samples used in calculation. Dashed lines show USEPA maximum contaminant level for nitrate. Some outliers are not shown.

The caption:

Figure 4. Boxplots of uranium concentrations as a function of groundwater age class: A) Columbia Plateau, and B) High Plains aquifer near York, Nebraska. Number above each plot indicates number of samples used in calculation. Dashed lines show USEPA maximum contaminant level for uranium. Some outliers are not shown.

The caption:

Figure 5. Boxplots of arsenic concentrations as a function of groundwater age class: A) Columbia Plateau, and B) High Plains aquifer near York, Nebraska. Number above each plot indicates number of samples used in calculation. Dashed lines indicate USEPA maximum contaminant level. Some outliers are not shown.

The caption:

Figure 6. Boxplots of nitrate concentrations in modern groundwater as a function of irrigation water source at the Columbia Plateau site. Samples collected in 2014. Number above each plot indicates number of samples used in calculation. Some outliers are not shown.

The caption:

Figure 7. Stable isotope data for modern groundwater (circles), Columbia River at Vernita Bridge or Richland (squares) and canal water (triangles) at the Columbia Plateau site. GMWL: global meteoric water line; LEL: local evaporation line. Canal water data are from Brown et al., (2011); river data are from NWIS (https://waterdata.usgs.gov/nwis).

The caption:

Figure 8. Stable isotope data for modern groundwater (squares) and the Platte River (fillled circle) at the High Plains site near York, Nebraska. Groundwater (triangles), canals (open circles), and North Platte River (open diamonds) for the Dutch Flats study area (from Böhlke et al., 2007) are also shown. GMWL: global meteoric water line; dashed line indicates a d-excess value of −1.

According to the authors, it does appear that while the concentrations of these analytes has increased since the beginning of irrigation, but the concentrations have stabilized since the early 2000's.

There is some discussion in the paper of the role of phosphate, which along with nitrate, is an element of commercial fertilizers on which the world food supply depends:

Phosphate mobilization of arsenic by outcompeting arsenate for sorption sites(61,62) is indicated by the positive correlation between arsenic concentrations in modern groundwater with phosphorus at the CP site (r = 0.55, p < 0.01; concentrations range from <0.004 to 0.13 mg/L as P). Arsenic was not correlated with nitrate (r = 0.13, p = 0.45) or bicarbonate (r = −0.1, p = 0.71). The reductive dissolution of iron oxides could also lead to the co-occurrence of arsenic and phosphorus. To evaluate this possibility, we examined the relation between arsenic and phosphorus only in oxic samples where reductive dissolution of iron oxides would not be expected. The positive correlation between arsenic and phosphorus (r = 0.60, p < 0.01) is maintained when only oxic modern groundwater samples are considered, indicating that reductive dissolution of iron oxides is not a controlling factor for elevated arsenic in groundwater at this site. Rather, phosphate mobilization of arsenic by outcompeting arsenate for sorption sites(61,62) or a fertilizer source of arsenic(63,64) is suggested. Lead arsenate was used on fruit orchards in Washington State from 1905 to 1947,(65) with soils in these former orchards having significantly higher arsenic concentrations than soils that were not orchards in the past.(66) The linkage between phosphorus and arsenic has also been observed in soils beneath former orchards and cotton cropland.(67,68) The correlation of phosphorus with arsenic suggests that phosphate in fertilizer is either mobilizing an existing source of phosphorus (e.g., lead arsenate, geogenic) or phosphate fertilizers contain a trace amount of arsenic...

Although phosphate here is discussed in connection with its cogener anion arsenate, it is well known that uranium is frequently a constituent of phosphate minerals and historically, before minerals were discovered having a higher concentration, phosphate mines were often considered as uranium ores in addition to phosphate ores. As a result of not removing uranium from phosphates, uranium is widely distributed on agricultural fields as a constituent of fertilizers.

A recent publication, albeit from a few years back, has examined the question of whether uranium should be mined from phosphate: To Extract, or not to Extract Uranium from Phosphate Rock, that is the Question (Haneklaus et al., Environ. Sci. Technol. 2017, 51, 2, 753-754)

It's open sourced; anyone can read it. It contains this text, which is not hostile to the only technology with even a remote chance of addressing climate change, nuclear energy:

Traditional uranium open pit mining for example leaves a significant environmental footprint and requires mine closure and site remediation, whereas ISL uranium mining does not generate any tailings repositories and waste rock dumps. Thus, one of the factors on the environmental impact of nuclear energy is the way uranium is mined. The extraction of uranium from phosphate rock represents a more environmentally and socially responsible form of uranium mining, as phosphate rock is mined anyway for its phosphate component. Thus, it is postulated that extracting uranium from already mined phosphate rock, as schematically described in Figure 1, would lead to cleaner fertilizers with greatly reduced uranium content and to greener nuclear power with its fuel taken from mineral resources that cause a smaller environmental impact.

"ISL" is a technology known as "in situ leaching."

I have argued in many places, here and elsewhere, that uranium mining need not be necessary at all for centuries. If we simply convert the uranium already isolated into plutonium, all of the world's energy needs for all purposes, can be met using uranium (and waste thorium from lanthanide mine tailings) already mined. However it is also possible to recover uranium in remediation schemes for groundwater with mobilized uranium as a result of nitrate leaching, such as that resulting from irrigation or - in the case of abandoned "fracking" fields like those in California and Pennsylvania, from abandoned oil and gas wells. (Coal ash is also a potential source of uranium.) Recovery of this type of uranium as a side product of remediation of natural uranium mobilization as a result of agricultural or industrial processes may well extend the time that the use of uranium can prevent the need for any energy mining, including the disastrous mining of oil, gas and coal, and for that matter, steel, copper, lanthanides and bauxite to support the pixilated so called "renewable energy" industry.

Nuclear technology has the capability of offering sustained high temperatures, and thus has the possibility of running at much higher thermodynamic efficiency than any other technology, meaning that even at current levels of energy production, running about 600 exajoules per year, the benefits of energy might be extended more broadly to those who lack it. (On the other hand, Jevon's paradox does offer a warning counter intuitive caveat on the benefits of efficiency.)

To return to the paper cited at the outset, here is the authors' concluding summary of the paper under discussion:

Evaluating trends in nitrate, arsenic, and uranium concentrations in groundwater beneath irrigated cropland using age dating provides an opportunity to assess trends over a much longer period.(53,54) An analysis of trends using age tracers indicates that large increases in nitrate concentrations in groundwater have occurred since the early 1950s; this increase in nitrate concentrations coincides with a dramatic increase in irrigated cropland.(24,32) Similarly, arsenic and uranium concentrations are higher in groundwater at the CP site that recharged since the onset of irrigation, suggesting that irrigation or associated land use practices are mobilizing and/or contributing these contaminants to groundwater.

These findings suggest several areas that should be prioritized when monitoring groundwater beneath irrigated cropland. First, high nitrate concentrations in shallow modern groundwater have been sustained for decades and pose a future risk to deeper groundwater used for drinking water. Given the oxic conditions of these aquifers, nitrate concentrations may be expected to increase in older modern water as nitrate in the shallow portion of the system continues to migrate into deeper portions of these aquifers. Second, increased monitoring for trace metals in shallow groundwater beneath irrigated areas is warranted, as these contaminants may be mobilized by changes in water chemistry: increases in bicarbonate may mobilize uranium and increases in phosphorus may mobilize arsenic. Third, areas that use groundwater for irrigation may have an elevated risk of high nitrate concentrations due to the repeated dissolution of land applied fertilizers during recirculation.

I trust you are enjoying your weekend.

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Reply Trends in Nitrate, Arsenic, and Uranium in Groundwater Beneath Irrigated Cropland. (Original post)
NNadir Feb 2020 OP
abqtommy Feb 2020 #1
eppur_se_muova Feb 2020 #2
NNadir Feb 2020 #3

Response to NNadir (Original post)

Sun Feb 23, 2020, 08:14 AM

1. Thanks for this, I bookmarked it.

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Response to NNadir (Original post)

Sun Feb 23, 2020, 11:18 PM

2. I was searching for "phosphate" before I got very far in your post.

I recall that commercial phosphate-rock fertilizer is responsible for elevated levels of polonium in tobacco. Of course, that polonium comes from decay of uranium, so why shouldn't we expect to find uranium in phosphate fertilizer as well ? Easier to say "downstream from Hanford, ergo propter Hanford".

And don't forget this recent demonstration that "uranium clings to phosphate":
Then, in 1996, University of Utah radiologist Ramal Jones found the skull using a radiation detector, because the skull itself was radioactive.

This isn’t unusual because fossils are in the ground along with radioactive elements found in soil and rocks, making some dinosaur fossils radioactive enough to be picked up by sensitive instruments, according to researchers at the Houston Museum of Natural Science.


Although something of a contrasting case in terms of cause and effect, it's still interesting to note that acid contamination of groundwater by a phosphate fertilizer plant near Pensacola apparently caused naturally occurring radium already present underground to seep into wells there. Processing and agricultural application of phosphate is done on such a huge scale that even small amounts of contaminants or waste products can have disastrous consequences. And of course where there's phosphate precipitated, there's going to be the congener* arsenate as well.

* noun
noun: congener; plural noun: congeners

a thing or person of the same kind or category as another.
an animal or plant of the same genus as another.
"these birds or their congeners may be found in East Africa"
a minor chemical constituent, especially one that gives a distinctive character to a wine or liquor or is responsible for some of its physiological effects. :/

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Response to eppur_se_muova (Reply #2)

Tue Feb 25, 2020, 11:57 PM

3. Yes, phosphorous has a definite affinity for uranium. A key reagent in the PUREX process is...

...tributyl phosphate.

(I believe that the time for the PUREX process has passed, and I favor some of the newer pyroprocessing/electrorefining processes that have been developed in the last 15 to 20 years. This said there are a number of other phosphate reagents that have been developed for various solvent extraction processes for not just the actinides, but for the lanthanides as well.)

There was another more recent paper published on the subject of isolating uranium from phosphate mined for fertilizer than the one I posted in the OP.

It is not really a research paper, but is an open sourced "viewpoint" article in EST, with a somewhat unfortunate title:

Making Uranium Recovery from Phosphates Great Again?

I recalled reading something along these lines, but simply used the search tool at the EST web page to find the article I posted in the OP.

It's written by two Austrians and a German, scientists from countries that are officially, and ignorantly I might add, anti-nuclear.

Interestingly they propose securing uranium should be reconsidered as a result of "Increased environmental awareness, national energy security..." to use their exact words.

They argue that 15% of the world's uranium supply could be provided by removing it from phosphate, with concomitant reduced risk to the food supply.

Again, I argue that we don't need more uranium than is already in stock if we embrace breed and burn technology, which is increasingly well understood, but it is interesting to note that the idea that nuclear energy is superior to all other forms of energy is a subject of increasing awareness.

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