A pioneer in particle physics and the study of cosmic rays, W. F. G. Swann was the first Director of the Bartol Research Foundation of the Franklin Institute. From its inception in 1927, Swann guided the Foundation for over thirty years, developing it into a major center for research in the physical sciences.

Born at Ironbridge, England on August 29, 1884, Swann demonstrated an early aptitude for music, but little in the sciences. While his love for music continued to grow, however, Swann nevertheless elected to pursue what seemed to be a more practical course in medicine when he entered Brighton Technical College as a scholarship student in 1900. At Brighton, Swann was introduced to James Clerk Maxwell's treatise on electricity and magnetism, and swayed by its elegance and precision, he switched from medicine to physics, transferring to the Royal College of Science, from which he received his BSc in 1905.

As a Junior Demonstrator at the Royal College, Swann gained valuable teaching experience while strengthening his background in the "practical things of science" by studying electrical engineering. His combination of experimental and teaching prowess earned him an appointment as Assistant Lecturer and demonstrator at the University of Sheffield in 1907, where he worked while completing his doctoral studies at the University College London. He received his DSc in 1910. It was the first stop in an upward climb into increasingly prestigious academic appointments.

Despite low pay and less than ideal working conditions, Swann displayed sufficient promise in mathematical physics, electrodynamics, and in the new quantum theory that he garnered the attention of the Carnegie Institution of Washington. Lured away from Sheffield in 1913, Swann was appointed Chief of the Physical Division at the Department of Terrestrial Magnetism, spending much of the next four years in the design and production of an apparatus to assist in magnetic and atmospheric-electric observations aboard the ship Carnegie, but with his reputation rising, other offers were not long in coming.

After war-time service working on submarine detection with the National Bureau of Standards and with the army to determine why their balloons were prone to explosion, Swann accepted a standing offer to join the faculty at the University of Minnesota. An administrative prodigy, Swann developed the graduate program with such remarkable success, reaping the rewards along the way, that by the time he left in 1923, he had become the highest paid professor at the University. Two of his own students won National Research Council Fellowships, but in his own opinion, his greatest success was in mentoring a young Edwin O. Lawrence.

The next stop in Swann's academic climb was the University of Chicago, who in 1923 offered Swann a substantial increase in pay to replace Robert Millikan. Even before he accepted, however, Yale approached him with even more lucrative honor: full professorship, Director of the supremely well-equipped Sloane Laboratory, and responsibilities for only one postgraduate course. As Yale was courting, other offers poured in, including the Franklin Institute in Philadelphia, who struck up what Swann called a "fliratation" in connection with a proposed research institute for "practical Electrical Engineering." Funded by a bequest from Henry W. Bartol (d. 1918), a prominent industrialist and member of the Franklin Institute, the institute got off the ground in 1925, when Arthur Bramley became the first Bartol fellow even before a facility or staff were available.

Faced with a Hobson's choice of Chicago, Yale, or the prospective Bartol, Swann chose Yale. The Ryerson Lab at Chicago, he reasoned, was crowded and antiquated, and the research opportunities at Yale offered by Pres. James B. Angell were simply too attractive to turn down. After only one year at Chicago, and despite his department's pleas, Swann therefore moved to New Haven, bringing Lawrence in tow. As the Bartol got off the ground, however, Swann soon reconsidered, and when the number of fellows rose to five, he was tapped as the first Director of the Bartol Research Foundation.

One of Swann's first acts as Director was to secure an agreement with Swarthmore College to relocate the institute from its temporary quarters in Philadelphia to facilities on the college campus. Always meticulous and detail-oriented, his administrative oversight extended even to minor custodial expenditures, yet he was well regarded by the fellows and staff he oversaw, however his attentions appear to have been well appreciated by Bartol fellows. Swann was concerned that "the great industrial rese'rch laboratories" instilled a culture that led physicists away from "using their own hands," and he therefore insisted on manufacturing his own apparatus, including blowing his own glass, and he was adamant that his fellows follow suit. On a personal level, several fellows considered Swann to be something of a "father confessor" as well as scientist.

An immensely productive researcher, who wrote over 250 publications during his career, Swann continued to blend theoretical and empirical approaches, evolving as rapidly as his discipline to touch on relativity theory, condensed matter physics, atomic structure, matter, antimatter, and gravitation. He was best known, however, for his pioneering work on cosmic rays and high energy physics. In the late 1920s and early 1930s, he developed a mechanism for accelerating charged particles to cosmic ray energies by means of changing magnetic fields, a device he named the cygnatron ("swan tube" ). More in the public eye, he took part in organizing a number of high profile projects to investigate cosmic ray intensities at high altitudes, including a series of manned balloon flights funded by the National Geographic Society and the U.S. Army. Swann subsequently took these studies to airplanes, ships, underwater, and on mountain tops. Late in his career, Swann developed a keep interest in the relationship between religion and science and in psychic research.

As charismatic in presentation as he was dramatic, Swann was a natural teacher and effective public spokesman for science at various levels. Throughout his tenure at the Bartol, he conducted seminars for high school students at the Franklin Institute, he lectured on electrodynamics at the Moore School of Electrical Engineering at the University of Pennsylvania, and later in life, was Professor of Physics at Temple University. His 1934 book The Architecture of the Universe, its interpretation of the new, and often abstruse developments in modern physics, was a major success with the broader public, and as a result, Swann was regularly called upon to appear on the radio and interviewed in the newspaper. With a slightly eccentric image and trademark shock of long white hair, he was a natural as well for television, hosting a weekly program in Philadelphia popularizing science during the 1950s.

Despite the demands of a rigorous schedule of research, administration, and public appearances, Swann managed to preserve time and energy for his great passion, music. An accomplished cellist who had studied under Diran Alexanian, Swann maintained an active social and musical correspondence with musicians and kept an active hand in the music scene in Philadelphia. In addition to his performing as a soloist and with various orchestras, he helped found the Swarthmore Symphony Orchestra, worked as assistant conductor of the Main Line Orchestra and as director of the Philadelphia Academy of Music, and was a supporter and honorary fellow of Trinity College of Music, London. Music entered deeply into his private life as well: After his first wife, Frances Mabel Thompson died in 1954, he married Helene Diedrichs, a former child prodigy, pianist and Chair of the Piano Department at the Philadelphia Musical Academy. Mrs. Swann (who played professionally under her maiden name) had studied under Carl Wendling at the Leipzig Conservatory of Music and received degrees from the Royal Academy of Music and the Tobais Matthay Pianoforte School.

Swann was elected a member of the American Philosophical Society in 1926, and served as vice president of the American Association for the Advancement of Science (1923-1924) and president of the American Physical Society (1931-1933). He received honorary degrees from Yale (1924), Swarthmore (1929), Temple (1954), and was made a fellow of the Imperial College of Science in Technology (1956) and was awarded the Elliot Cresson Medal of the Franklin Institute (1960) for his research on cosmic rays. The final honor awarded Swann vaulted him literally to the heavens: In 1967, the International Astronomical Union named a lunar crater in Swann's honor.

In August 1959, already 75 years old, Swann retired to emeritus status at the Bartol Institute and was succeeded by Martin Pomerantz. Unburdened by administrative duties, he continued to conduct research almost until the day he died, January 29, 1962. He was survived by Helene Diedrichs, two sons, William F. Swann and Charles P. Swann, and a daughter Sylvia Swann Briggs. Both sons became prominent physical scientists, Charles at the Bartol.

...For the next 50 years, Bartol scientists employed Swarthmore students in various capacities, taught classes at the college, and collaborated with faculty members. The foundation also produced a host of scientists who made major contributions to their fields, a feat made even more impressive given its small size.

Known for its pioneering studies of cosmic rays and work in nuclear physics, Bartol hosted an international contingent of scientists and researchers. During World War II, Bartol's principal work involved the development of magnetron cathodes. William Elmore, a member of Swarthmore's physics department, conducted research at Bartol at that time. After the war, basic research in solid state and surface physics continued, along with the resumption of cosmic ray investigations led by Bartol director W.F.G. Swann...

...Yet Bartol never became an integral part of the College and, even among the College's science faculty, was known well by only a few. When Bartol's lease came up for review in the 1970s, the College ended its relationship with the foundation and took possession of its building. The inability of both institutions to develop closer collaborations is now viewed by many on both sides as a lost opportunity.

Renamed the Bartol Research Institute, it moved to its present location at the University of Delaware in 1977. The building it once occupied on campus was renamed Papazian Hall and for 40 years housed the College's philosophy and psychology departments. It was demolished in 2017 and is the future site of the Biology, Engineering, and Psychology building.

The Bartol Research Institute
A Brief History
Mr. Henry W. Bartol, a member of The Franklin Institute, died on the 19th of December, 1918, leaving behind a will and codicil that provided for the establishment of the Bartol Research Institute. In that will Mr. Bartol designated as residuary legatee the Franklin Institute of the State of Pennsylvania. He stipulated: "All the rest, residue and remainder of my estate, except such as is situated in France, I give, devise, and bequeath to the Franklin Institute... to be applied to the establishment and maintenance of a department of practical Electrical Engineering..." The codicil subsequently changed this to "...the founding and maintenance of an institute... the preference however, being given to workers or those making researches into electrical science."
Mr. Bartol was a prominent Philadelphia industrialist. Although his gift in 1918 was sufficient to fund an institute of scientific study, the birth of the Bartol Research Institute (then called the Bartol Research Foundation) was slow and difficult. It was not until the end of 1925 that the first Bartol Fellow, Dr. Arthur Bramley, was appointed. The first publication of research supported by the Bartol Research Foundation, and performed by Dr. Bramley, appeared in the January, 1926 issue of the Journal of the Franklin Institute. This report discussed the multiplet structure in the Zeeman effect. The number of Bartol Fellows rose to five and on February 3, 1927, Dr. W. F. G. Swann was elected by the Board of Managers to be the first director of the Bartol Research Foundation.

W. F. G. Swann was appointed the Director of the Bartol Research Foundation at the age of 43. Born in England, he was educated at Brighton Technical College, the Royal College of Science, University College, Kings College and the City Guilds of London Institute. Dr. Swann came to this country in 1913 as head of the Physical Division of the Department of Terrestrial Magnetism at the Carnegie Institute in Washington. Later he was Professor of Physics at the University of Minnesota, the University of Chicago and Yale, where he became Director of the Sloane Laboratory. A man of many talents, Dr. Swann was an accomplished cellist, founder of the Swarthmore Symphony Orchestra, a former assistant conductor of the Main Line Orchestra and former director of the Philadelphia Academy of Music.

By the time of his appointment, Professor Swann had already distinguished himself as an excellent teacher, an outstanding researcher, and an emerging leader of the scientific community. Although Dr. Swann is perhaps best known for his experimental and theoretical efforts in the area of cosmic ray physics, his research interests touched on many other disciplines such as condensed matter physics, relativity, and charged particle acceleration. In the last seven years of his life he had 22 publications on such diverse subjects as atmospheric electricity, thermal conductivity of solids, the restricted theory of relativity, matter, antimatter and gravitation, and charged particle acceleration to cosmic ray energies. His grasp of electromagnetism was far reaching and entered into most of his research. In his capacity as a professor he is perhaps best known as the advisor of Dr. E. O. Lawrence who subsequently was awarded the Nobel Prize for developing the cyclotron. Lawrence followed Dr. Swann from Minnesota, to Chicago, and then to Yale where he received his Ph.D. Altogether Dr. Swann had over 250 publications including a well known book "The Architecture of the Universe". In 1967 the International Astronomical Union honored Professor Swann when it gave his name to a crater on the lunar surface at 52 º north latitude and 112 º east longitude.

Shortly after his appointment as Director of the Bartol Research Foundation, Dr. Swann secured an agreement with Swarthmore College to move the Foundation from its temporary lodgings in Philadelphia to the home campus of the college where it was able to enjoy the benefits of a college atmosphere. During the early 30's Dr. K. T. Bainbridge, then a Bartol scientist, developed a magnetic spectrograph with which he was able to make accurate mass determinations of low Z elements including 6Li using their accelerator. At about the same time Cockroft and Walton performed measurements on the 7Li + p = 2 reaction using their accelerator. Bainbridge was then able to verify Einstein's famous principle of mass- energy equivalence using the established masses for the proton and 7Li.

Several "high" altitude manned balloon flights were made in 1934 and '35 for the purpose of studying cosmic rays. Two of these, one of which crashed on descent, were sponsored by the National Geographic Society and the Army Air Corps and were flown by Air Corps personnel; fortunately the men on the crashed flight were able to eject and come down on parachute. Three other flights were flown by Dr. Jean Piccard and his wife. All of these flights contained a significant amount of Bartol equipment for the study of cosmic rays. Related investigations of cosmic rays were pursued from mountain tops, airplanes and ships, underwater, and in unmanned balloons.

Bartol became further involved in nuclear physics research with the construction of a 2.5 MV Van de Graaff accelerator under the guidance of Dr. W. E. Danforth. Bartol personnel also constructed a cyclotron in the late 1930's, the first cyclotron outside of Berkeley. This machine was actually built for The Franklin Institute's Biochemical Foundation, which was housed in the present Penny Hall of the University of Delaware. An extensive nuclear physics program did not develop until after World War II, with the completion of the 2.5 MV Van de Graaff and the construction of a second Van de Graaff with a potential of 5 MV. The principal research interests during the war, conducted in close collaboration with the Radiation Laboratory at the Massachusetts Institute of Technology, involved the development of magnetron cathodes. Basic research in solid state and surface physics continued after the war, in parallel with the resumption of cosmic ray investigations. Bartol's scope was further expanded in the 1960's with the initiation of research programs in astronomy and astrophysics...

The annual mean rate of growth of CO2 in a given year is the difference in concentration between the end of December and the start of January of that year. If used as an average for the globe, it would represent the sum of all CO2 added to, and removed from, the atmosphere during the year by human activities and by natural processes. There is a small amount of month-to-month variability in the CO2 concentration that may be caused by anomalies of the winds or weather systems arriving at Mauna Loa. This variability would not be representative of the underlying trend for the northern hemisphere which Mauna Loa is intended to represent. Therefore, we finalize our estimate for the annual mean growth rate of the previous year in March, by using the average of the most recent November-February months, corrected for the average seasonal cycle, as the trend value for January 1. Our estimate for the annual mean growth rate (based on the Mauna Loa data) is obtained by subtracting the same four-month average centered on the previous January 1. Preliminary values for the previous year are calculated in January and in February.

The estimated uncertainty in the Mauna Loa annual mean growth rate is 0.11 ppm/yr. This estimate is based on the standard deviation of the differences between monthly mean values measured independently by the Scripps Institution of Oceanography and by NOAA/ESRL. The annual growth rate measured at Mauna is not the same as the global growth rate, but it is quite similar. One standard deviation of the annual differences MLO minus global is 0.26 ppm/year.

hahn: At any rate, Heisenberg, you’re just second raters and you might as well pack up.

heisenberg: I quite agree.

hahn: They are 50 years further advanced than we.

heisenberg: I don’t believe a word of the whole thing They must have spent the whole of their £500,000,000 in separating isotopes; and then it is possible.11

...On Bethe's desk at Cornell University, where he lived and taught for almost 70 years, there was always a pad of paper that he used for calculations. His door was usually open; students and colleagues came in constantly to discuss a wide variety of problems. Bethe would instantly switch his attention from his own problem to theirs. As soon as they left the room, he would instantly switch his attention back and continue his calculation where he had left off.

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He continued to pour out a stream of research papers while carrying a full load of teaching and administrative duties and supervising an army of graduate students. When I was one of his graduate students, he came every day to eat lunch with us at the student cafeteria, sharing our problems and telling stories of his adventures in Germany and in Los Alamos. We learned even more at the lunches than we did at his lectures. Everyone called him Hans. He told us that one of the best things about moving from Germany to America was that nobody in America called him “Herr Professor.”

Bethe remained active as a physicist, doing calculations and publishing papers, well into his nineties. From the age of 70 to the age of 95, he enjoyed a fruitful collaboration with Gerald Brown, working out theories of supernova explosions and gamma-ray bursts. Brown has published a delightful account of the collaboration, with the title “Fly with Eagles” (2). Brown says, “I had to wait until he was more than 70 years old in order to have any chance of keeping up with him. He worked like a bull-dozer, heading directly for the light at the end of the tunnel.” The last time I talked with Bethe, he said, “It is a shame. Now I am 98 and I cannot be as active as I was when I was 90.”

Bethe carried in his head all the numbers that play an important role in physics or in engineering. Given any question, he could estimate a numerical answer with lightning speed. His estimates were amazingly accurate. He put this skill to good use when he helped Robert Wilson to design a succession of particle accelerators at Cornell. The same skill made him an ideal leader for the theoretical division at Los Alamos, designing the first atomic bomb during World War II and helping to design the first hydrogen bomb in 1952.

For the 60 years that he lived after 1945, he worked hard to educate the public about the facts of nuclear weaponry and the impossibility of winning a nuclear war. He was actively engaged in fighting for arms-control treaties and against escalations of the arms race. At the age of 90, he wrote in a letter to President Clinton: “The time has come for our nation to declare that it is not working, in any way, to develop further weapons of mass destruction of any kind. …You might consider making a suitable pronouncement along these lines, to discipline the bureaucracy, and to reassure the world that America is vigilant in its desire to ensure that new kinds of nuclear weapons are not created.” Now that he is dead, it is up to us to continue the good fight that he fought for nuclear sanity, moderation, and common sense.

At the same time as I am arguing for saving lives, I am arguing that the population must be reduced for decent human life to remain – or in too many cases to become – sustainable. It would seem that these ethical arguments are at cross purposes. However, with some exceptions, it is now understood by observation that those places where the fertility rate is at or below replacement level are most often the same places where people are secure in their homes, the places where they are well provided for, where they are educated and safe. Maybe, just maybe, the key to yet saving what might be saved of the planetary environment would be involved with honoring in practice, rather than broach, the 25th article of the Universal Declaration of Human Rights of 1948.[36]

Modern lifestyles depend on petroleum-derived products such as plastics and synthetic rubbers for containers, clothes, and appliances, mainly because of advantages in terms of their lightweight and highly moldable nature. Global plastic production currently accounts for more than 320 million tons (Mt), resulting in global waste issues for the marine environment in addition to human exposure.(1?3) Another environmental concern is that global greenhouse gas emissions (GHG) related to plastic production will almost quadruple by 2050 compared with 2015 levels unless mitigation strategies including renewable energy, recycling, and demand-management are implemented.(4) On the other hand, from a carbon metabolism point of view, these petroleum-derived products that are in use or remain fixed in a landfill can be seen as a form of carbon reservoir, alongside forests, wood products, and carbon dioxide (CO2) capture and storage (CCS). Therefore, although mechanical and chemical recycling approaches for material recovery could reduce the dependency of production on raw material extraction, most current waste treatment approaches lead to the release of embedded CO2 to the atmosphere during incineration, regardless of the energy recovery process employed.(5) Reducing CO2 in line with national targets is another crucial issue in order to prevent serious climate change.(6?9)

The carbon physically contained in products at the global and local scale has been analyzed in previous studies.(10?14) Lauk et al.(11) found wood products and plastic, respectively, accounted for 61% and 17% of total carbon stored in socioeconomic stocks around the globe in 2008, highlighting that per-capita plastic usage has shown high growth since 1900. Further, Ohno et al.(5) first addressed the linkage between the amount of carbon contained in products and final consumption. This research elucidated the structure of physical carbon retention for both wooden and petroleum-derived products, namely, materially retained carbon (MRC) induced by Japanese final consumption in 2011, finding that 14.2 Mt of carbon was newly added in Japan, corresponding to 4.1% of total annual CO2 emissions in the same year if it were all incinerated. Passenger motor cars are the largest contributor, followed by plastic products, cosmetic products, and apparel goods...

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 ?g/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

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)

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 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. 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.

Historical measurements of the Columbia River indicate that uranium and arsenic are often not detected, with concentrations typically less than 2 ?g/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.

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)

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.

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)

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.

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.

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.

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).

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.

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...

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.

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.

The Japan Atomic Energy Agency has been pursuing research and development regarding the partitioning and transmutation of long-lived minor actinides (MAs). Partitioning and transmutation technology will help to reduce the potential toxicity and volume of high-level radioactive waste [1]. One approach is the double-strata fuel cycle, which comprises a commercial reactor fuel cycle and a dedicated fuel cycle for transmutingMAs using an accelerator-driven system (ADS). MAs partitioned from high-level liquid waste generated in the commercial reactor fuel cycle would be fed into the transmutation fuel cycle. The mass flow of actinides in the transmutation fuel cycle would be approximately two orders of magnitude smaller than in the commercial reactor fuel cycle [2]. It has been demonstrated that a mononitride solid solution of MAs and Pu diluted with ZrN is a prime candidate for MA transmutation fuel because of the superior thermal and neutronic properties of this compound [3]. The role of Pu in this fuel is to mitigate the burn-up reactivity swing. Mutual solubility among actinide mononitrides ensures flexibility in the fuel composition. Nitrogen enriched in 15N is planned to be used in the nitride fuel to prevent the formation of long-lived 14C.

Outdoor air pollution adversely affects human health and is estimated to be responsible for five to ten per cent of the total annual premature mortality in the contiguous United States1,2,3. Combustion emissions from a variety of sources, such as power generation or road traffic, make a large contribution to harmful air pollutants such as ozone and fine particulate matter (PM2.5)4. Efforts to mitigate air pollution have focused mainly on the relationship between local emission sources and local air quality2. Air quality can also be affected by distant emission sources, however, including emissions from neighbouring federal states5,6. This cross-state exchange of pollution poses additional regulatory challenges. Here we quantify the exchange of air pollution among the contiguous United States, and assess its impact on premature mortality that is linked to increased human exposure to PM2.5 and ozone from seven emission sectors for 2005 to 2018. On average, we find that 41 to 53 per cent of air-quality-related premature mortality resulting from a state’s emissions occurs outside that state. We also find variations in the cross-state contributions of different emission sectors and chemical species to premature mortality, and changes in these variations over time. Emissions from electric power generation have the greatest cross-state impacts as a fraction of their total impacts, whereas commercial/residential emissions have the smallest...

Long-term exposure to fine particulate matter (PM2.5) and ozone leads to an increased risk of premature death7,8,9,10,11,12. Indeed, PM2.5 and ozone are the most prominent known causes of early deaths associated with outdoor air pollution, resulting in more than 90% of total air-pollution-related mortalities8,11. For this reason, PM2.5 and ozone have become the predominant pollutants for quantifying air quality2. These pollutants form mainly through atmospheric chemical reactions following the release of precursor emissions. PM2.5, which consists of particles and liquid droplets, forms from gaseous precursor emissions of nitrogen oxides (NOx), sulfur oxides (SOx), ammonia (NH3), and others. PM2.5 can also be emitted directly, as in the case of black carbon. Ozone forms from gaseous precursor emissions of NOx and volatile organic compounds (VOCs). The adverse health impacts due to exposure to PM2.5 and ozone can therefore be attributed to the precursor emissions that lead to their formation. Such attribution is useful, as it is these emissions that can be directly controlled, rather than the exposure that results from them.

Combustion emissions constitute the largest source of anthropogenic emissions in the USA, and therefore contribute to the formation of PM2.5 and ozone2. The health impacts attributable to these emissions have been estimated in various studies6,13,14, with estimates varying between 90,000 and 360,000 early deaths per year. In the context of the Environmental Protection Agency (EPA) Cross-State Air Pollution Rule (CSAPR) and individual state regulation, measures to further reduce the health impacts of pollution would benefit from a greater understanding of which sectors and which states are responsible for the health impacts in every other state.

In this work, we estimate the pollution exchange between the 48 contiguous US states, and form source–receptor relationships between them for combustion emissions from seven sectors: electric power generation; industry; commercial/residential; road transportation; marine; rail; and aviation. The commercial/residential sector includes residential combustion (for example, of biomass), nonindustrial commercial and institutional processes, and waste treatment, among other sources. This analysis yields estimates for the number of early deaths due to PM2.5 (primary and secondary, excluding secondary organic aerosols) and ozone exposure in every state, with attribution of impacts to each sector and each emitted chemical species from every state. We estimate combustion emissions for the seven sectors for 2005 (based on the 2005 National Emissions Inventory (NEI)), 2011 (based on NEI2011) and 2018 (based on the NEI2011 forecast), and present these findings in Extended Data Table 1. Lists of the specific sources that are grouped in each sector are included in the associated data repository (see Methods).

a, Source–receptor matrix showing total early deaths per year for 48 × 48 states (right), and its breakdown into PM2.5- and ozone-attributable impacts (left). b, Source–receptor early-death attribution to emission sectors (top) and emission species (bottom) that lead to the formation of PM2.5 and/or ozone. States are grouped into US Bureau of Economic Analysis regions24 and ordered west (left) to east (right) (ordering presented in Extended Data Fig. 1). Boxed percentages represent the fraction of impacts that occur out of the state that caused the corresponding emissions. Obtaining the summarized matrices shown using conventional approaches (‘forward difference’) would require 433-year-long simulations. Extended Data Fig. 2 presents corresponding matrices for 2005 and 2018.

The left plots (a) show the total aggregate early deaths caused by emissions in each state, divided by the population of the emitting state. The middle plots (b) show the total early deaths caused in each state, divided by the population of the state. The right plots (c) show the total early deaths exported by each state, divided by the population of the state (that is, the difference between plots a and b). These impacts are based on summed contributions from each emitted species (see Fig. 3).

a, Total annual early deaths attributable to each emission sector. b, Total annual early deaths attributable to each emission species that leads to the formation of PM2.5 and/or ozone. c, Total annual early deaths. Data are shown for 2005, 2011 and 2018, and for PM2.5 and ozone. In c, three totals are presented: the sum of all sectors/species (‘Summed’), which does not account for nonlinear interactions between species; the sum of all sectors/species with varying emissions, but constant (2005) atmosphere (‘Constant atmospheric response’); and the total impacts after accounting for nonlinear interactions between species. Tabulated results are presented in Extended Data Table 3.

In terms of speciated impacts—that is, emissions species that contribute to the formation of, and exposure to, PM2.5 and/or ozone—primary PM2.5 emissions had the greatest impact in all three model years. They also stayed relatively consistent, with a 13% reduction in health impacts from 2005 to 2018. SO2—which was the third-greatest contributor to impacts in 2005, making up 19% of the summed impacts—was contributing less than 6% by 2018. This was due to an approximately 80% reduction in SO2 emissions.

Ammonia-attributable impacts increased by around 21% between 2005 and 2018. This difference was driven by an increase in the sensitivity of PM2.5 exposure with respect to a unit of ammonia emissions between 2005 and 2011. Owing to the decline in the importance of SO2, ammonia impacts went from being the fourth-greatest to the third-greatest contributor to total impacts over this period, increasingly close to the contribution of NOx species. NOx remained the second-greatest contributor to impacts from 2005 to 2018. Despite the roughly 50% reduction in total NOx emissions between 2005 and 2018, impacts attributable to NOx reduced by only around 35% between the two years. This is largely due to the increased sensitivity of PM2.5 formation to NOx emissions between 2005 and 2011, as noted previously23