Conferences

ATTA and the Curious Case of Krypton-81

Matt Herod September 14, 2015

Ok, so I took some license with the title. This isn’t really a curious case and neither Krypton-81 nor ATTA are actually people. In fact, Krypton-81 (81Kr) is a radioisotope of the noble gas krypton and ATTA, which stands for atom trap trace analysis, is the revolutionary technique that has made its analysis possible. I recently heard about developments with ATTA at the IAEA Isotope Hydrology Symposium and have been doing some reading about the method and its revolutionary application to the dating of both young and ancient groundwater.

Figure 1. Dr. Z-T Lu working on the ATTA system at Argonne National Labs. Used with permission.

81Kr has long been a bit of a dangling carrot for groundwater dating people like myself. 81Kr is a long lived radioisotope of Kr (half-life: 229,000 years) that is produced by cosmic ray interaction in the atmosphere with other krypton isotopes. This production results in about 5 atoms of 81Kr for every 10^13 atoms of the other Kr isotopes. This 81Kr then settles to the earth surface and is incorporated into groundwater recharge and can then used to date groundwater from 150 thousand to 1.5 million years old. The way this works is that once water reaches the water table no new krypton is added and the clock starts ticking as the 81Kr decays away. In order to use this method we assume that the initial concentration in the recharge is in equilibrium with the concentration of 81Kr in the atmosphere, which is well mixed. ATTA then measures the amount of 81Kr that is left in the water sample compared to the other Kr isotopes and an age can be calculated from the difference between this ratio and the intial ratio.

ATTA can also be used for the short-lived isotope krypton-85 (half-life: 10.8 years). 85Kr is produced by fission in nuclear reactors and is released during nuclear fuel reprocessing. The short half life of 85Kr makes it useful for dating recently recharged groundwater from 1 to 40 years old.

Figure 2. Dating ranges of 85Kr, 39Ar, 81Kr and other established radioisotope tracers. (Source). Used with permission.

The reason krypton is such a useful tracer for groundwater dating is that as a noble gas the interaction of Kr with soils, rocks and the biosphere is minimal whereas other tracers such as 36Cl, 14C or 3H are often subject to retardation during transport or inputs from multiple sources which makes extensive corrections necessary or renders them completely unusable for dating. Furthermore, very few reliable tracers exist in the range that Kr isotopes cover making them extremely useful. One isotope that I haven’t mentioned as much is argon-39, which can be used to date water from 50-1000 years old, is also a noble gas, and can also be measured with ATTA.

Measurements of krypton can also be used for dating of ancient ice cores as well. Atmospheric gases including Kr are trapped in air bubbles in the ice and therefore, using the same method as groundwater dating, an absolute age for an ice core can be obtained. There are several other applications for Kr dating as well such as dating of deep crustal fluids and brines.

Figure 3. Sampling ice cores for Kr analysis by ATTA. Photo: V. Petrenko. Used with permission.

The development of atom trap trace analysis was first reported in Science in 1999 and since then has undergone several substantial improvements primarily aimed at reducing the required sample size required for an analysis of Kr. ATTA (Figure 4) works by trapping Kr atoms with a laser which causes a slight and temporary change in their atomic structure which lasts for about 40 seconds. During this period the Kr atoms in the laser beam are focussed and slowed and then trapped in an MOT (magneto optical trap) where they are held in place for an average of 1.8 seconds. Once the Kr atom is in the MOT it fluoresces as it returns to its original state. This fluorescence is detected by a camera which is sensitive enough to detect the emission from a single atom (Figure 5)!

Figure 4. Schematic layout of the ATTA-3 apparatus. (Source). Used with permission.

One of the key features of ATTA is that this laser induced fluorescence within the MOT occurs uniquely for every isotope as the laser frequency is tuned specifically! This means that only atoms of of the desired Kr isotope are trapped. Furthermore, this means that ATTA is completely immune to interference from other elements, isotopes, isobars, or molecules. In essence nothing can confuse the detection of the 81Kr atom once it fluoresces and therefore there is no background of spurious detections that need to be corrected for. Among low-level analytical techniques this is unique and a really big deal! As a user of AMS, which is another low level analytical method that does suffer from these issues, this is statement is an eye-catcher.

Figure 5. A CCD image showing the response of an atom in the MOT. Used with permission.

Since its invention ATTA has evolved considerably. We are now on the 3rd iteration of ATTA and significant improvements have been made that make ATTA much more practical for routine use. Specifically, the amount of sample required for an analysis has been reduced drastically. The first version of ATTA could only be used for atmospheric measurements as the quantity of Kr needed was too large to be extracted from water. ATTA-2 required ~1000 kg of water to extract 50uL of Kr gas. Now, ATTA-3 only requires 5-10uL of Kr which can be obtained from only 100-200 kg of water or 40-80 kg of ice. This advancement means that ATTA is now usable for groundwater dating applications never before possible. This has been demonstrated by the use of ATTA to date groundwater in Egypt to around 500,000 years old and even older water in Brazil up to 800,000 years. Other dating methods have confirmed that ATTA measurements are accurate.

Now that the sample sizes required for an 81Kr or 85Kr analysis have been lowered so dramatically the method is even more useful to the geoscience community. One of the messages from Dr. Lu’s talk at the IAEA meeting was that this technique is open for business and the geoscience community is strongly encouraged to reach out for collaboration and discussion. Furthermore, it may also be possible to use ATTA to measure argon-39, calcium-41 and potentially lead-205, strontium-90 and cesium-137,135 at extremely low levels.

Note: During the writing of this blog I corresponded with Dr. Z-T Lu, one of the creators of ATTA. I would like to thank him for allowing me to use his personal photos in this post. Dr. Lu is now establishing a radiokrypton dating centre at the University of Science and Technology of China.

References

Lu Z-T, Schlosser P, Smethie WM, Sturchio NC, Fischer TP, Kennedy BM, et al. Tracer applications of noble gas radionuclides in the geosciences. Earth-Science Rev. 2014;138:196–214.

Chen CY. Ultrasensitive Isotope Trace Analyses with a Magneto-Optical Trap. Science (80-). 1999;286(5442):1139–41.

Du X, Purtschert R, Bailey K, Lehmann BE, Lorenzo R, Lu Z-T, et al. A New Method of Measuring 81Kr and 85Kr Abundances in Environmental Samples. Geophys Res Lett. 2003;30(20):2068. Available from: http://arxiv.org/abs/physics/0311118

Aggarwal PK, Matsumoto T, Sturchio NC, Chang HK, Gastmans D, Araguas-Araguas LJ, et al. Continental degassing of 4He by surficial discharge of deep groundwater. Nat Geosci. 2014;8.

Lu Z-T. Atom Trap, Krypton-81, and Saharan Water. Nucl Phys News. 2008;18(2):24–7.

Shades of L’Aquila: Italian Geochemists avoid Huge Miscarriage of Justice

Matt Herod December 3, 2014

On rare occasions I hear about a story that must be told. This story is one of those and I feel that it deserves attention from the broader geoscience community.

We have all heard of the L’Aquila verdict against the Italian seismologists concerning the devastating earthquake in 2009. If you haven’t, read these articles by Chris Rowan. At the time the guilty verdict was handed down the entire geoscience community felt stunned that such a thing could have happened. The prevailing attitude was that it should not be possible to accuse and convict scientists for practicing responsible science. However, the old adage goes: those who don’t learn from history are doomed to repeat it. This brings me to the topic of this post, which was a very near miss by the Italian justice system against four geochemists from the University of Siena.

I originally heard of the story at Goldschmidt 2013 in Florence during a presentation by Dr. Luigi Marini and I wrote a short note about it in my daily summary of the conference on this blog. After the conference I asked Dr. Marini for more information as I felt the details of this case needed to be heard. I recently heard back from Dr. Marini that the case has now been resolved in favour of the geochemists and I am now free to write about their story on this blog.

The story begins, in December 2002, with several geochemists from the University of Siena being asked by the Italian Ministry of Defense to perform a geochemical-environmental study in the Sardinian Poligono Interforze Salto di Quirra (PISQ), comprising the two firing ranges of Perdasdefogu and Capo San Lorenzo.

Numerous different military activities were carried out at the PISQ since July 1st, 1956, including: (i) launch of rockets (ii) release of bombs from airplanes and helicopters (iii) use of artillery, from land and ships (iv) tests of pressurized pipes.

According to media and some local associations, Depleted-Uranium (DU) ammunitions were used in the PISQ and caused the so-called “Quirra Syndrome”. The “Quirra Syndrome” refers to an apparently greater-than-normal incidence of illnesses in the local population and military personnel that served at the Quirra base. It occurs mainly as cancers and natal genetic malformations. However, the “Quirra Syndrome” has not been confirmed by the Italian national health authority, the Istituto Superiore di Sanità (ISS).

So one of the goals of the Siena geochemists was to determine if DU had been used in tests.

Google screen capture of Sardinia. Quirra, which is the subject of the study, is the red pointed location.

On the face of it the task seems simple enough: analyze soil, plants and water for U and its isotopic ratio and other potential contaminants from the munitions range (of which are there many). However, the complicating factor in all of this is that fact that adjacent to the firing range is an abandoned mine site called Baccu Locci. The Baccu Locci mine contains significant quantities of arsenopyrite and galena, which are arsenic and lead bearing minerals. Both arsenic and lead are known to have detrimental effects on the environment and humans. So the real question then becomes which is it? Mine waste or DU or other military contaminants? Furthermore, historical records from PISQ say no DU was used in the region, however, lots of other munitions with their own suite of toxic components may have been. Therefore, isolating a single cause of the possible impacts on the environment and humans becomes very complex indeed.

Taking a quick step back let’s review some of the basic science in question here.

What is DU?

DU stands for depleted uranium and it was the central contaminant discussed in the case. Uranium comes in many isotopes but the two most common are 238U and 235U. Most uranium found in nature is ~99.2% 238U and ~0.7% 235U. However, most nuclear reactors use fuel that is enriched in the isotope 235U to around 20% as it is more easily fissionable than natural uranium. A by-product of the enrichment process is uranium that is missing its 235U and has a larger proportion of 238U than is normally found in nature. This uranium is said to be depleted as it has had the 235U removed. This DU can then be used for other applications outside of the nuclear industry as it has the rare property of being one of the most dense metals known. This property makes it used in a wide variety of industries but particularly in military applications as a tip for missiles, armour penetrating bullets and other types of scary munitions. DU munitions have been used in Desert Storm, Bosnia, Kosovo and recently in Iraq and Afghanistan and at numerous munitions test sites around the world.

Gunner's mates inspect linked belts of Mark 149 Mod 2 20mm ammunition before loading it into the magazine of a Mark 16 Phalanx close-in weapons system aboard the battleship USS MISSOURI

US Navy personnel inspect linked belts of DU tipped ammunition (Wikimedia Commons)

The problem is that when DU munitions are used the uranium is blown into millions of tiny particulates that can spread on the wind and introduce widespread contamination to the environment. DU contamination is a serious issue. The radiological risks of DU are low in comparison to many other radionuclides due the long half life of 238U and the low energy alpha particles that it emits although they cannot be ignored altogether if the concentration of DU is high. The far greater risk from DU, however, is the high toxicity of the uranium metal itself as it attacks the kidneys in people similar to metals such as lead and cadmium. DU exposure has been linked to cancer, birth defects and other diseases for people living in contaminated areas and diseases afflicting veterans of the Gulf War as it acts in concert with other contaminants from these former war zones.

Acid Mine Drainage

Acid mine drainage is a phenomenon that many geochemists work with every day. In brief it occurs when sulphide minerals like galena (PbS), pyrite (FeS2) or arsenopyrite (FeAsS) are left exposed to open atmosphere and precipitation. What happens is a chemical oxidation reaction in which the sulphide minerals such as galena (PbS), pyrite (FeS) or arsenopyrite (FeAsS) react with air and water to release sulphuric acid and free metal ions. In the case of galena you get lead or arsenic from arsenopyrite.

Rio_tinto_river_CarolStoker_NASA_Ames_Research_Center

An extreme example of acid mine drainage from a mine in Spain. (Wikimedia Commons)

Indeed, Frau et. al. (2009), found significant evidence of contamination from Baccu Locci Mine wastes in streams leading from the region, which is a tributary of the larger Quirra River that flows through the village into the Tyrrhenian Sea. The paper found elevated concentrations of lead, cadmium, zinc and arsenic near mine wastes, however, concentrations decreased downstream due to dilution and precipitation of insoluble lead-arsenic minerals. These heavy metals could have detrimental effect on the health of local residents.

OK, so back to the case.

The researchers from the University of Siena did what was asked of them and analyzed over 1500 samples for a variety of contaminants, including the 235U/238U ratio (on selected samples), totalling 25,000 results. Their findings were that there was no contamination from DU in the region and that the 235U/238U was on par with the natural 235U/238U ratio. However, they did find elevated levels of arsenic and lead around the former mine site and in catchments draining it.

Distribution map of uranium concentrations in top-soils of the two firing ranges of Perdasdefogu and Capo San Lorenzo and nearby areas (from the Siena University report, 2004).

Histogram (left) and statistical parameters of uranium concentrations in the top-soils of the two firing ranges of Perdasdefogu and Capo San Lorenzo and nearby areas (from the Siena University report, 2004).

Furthermore, one of the supporters of the Quirra syndrome conducted health related modelling using a code called HOTSPOT and found that in order to cause the anomalous number of cancers observed in Quirra between 80-140 tons of DU had to have been used, which is an absolutely huge amount (Zucchetti 2005).

These results met with extreme opposition from the local prosecutor who acted on the advice of a nuclear physicist from the University of Brescia who felt that geochemistry was not the proper way to investigate this problem and that the University of Siena scientists were hiding something. Indeed, the physicist felt that thorium was the true culprit and that geochemists were not qualified to analyze for radioactive contamination. (I obviously take great exception to this notion as a radioisotope geochemist and user of an accelerator mass spectrometer). Anyway, the geochemists were charged with two crimes in connection with their results:

Not stating the danger of anomalous concentrations of thorium present at the firing ranges.
Using knowledge the geochemists had gained from their previous work on DU in Kosovo to select methods that prevented them from detecting depleted uranium at PISQ.

In answer to the first charge the geochemists provided results of Th analyses for soils in the Quirra region. These show that there are no Th anomalies present in the soil. Therefore, the notion that Th is somehow the hidden, skulking culprit in all of this is simply not the case.

In answer to the second charge that the geochemists knowingly sampled in such a way as to conceal the detection of DU one simply has to look at the aims of the two investigations. In Kosovo the Siena scientists were sampling a small area with known DU contamination and a documented history of DU use. This makes it much simpler to find DU and sample for it. On the other hand, in Quirra, the use of DU has not been confirmed and the study area was far larger. This means that instead of a small scale, targeted sampling campaign the appropriate investigation tactic was a broad, large scale sampling effort that attempted to give an overview of contamination in the region. If DU was found a more detailed look could then be performed in that specific site. However, since no DU was found no more sampling was necessary.

Ultimately, the court appointed an independent expert to examine the results of the University of Siena geochemists in the light of these two charges before proceeding to trial. The expert found that the methods used by the University of Siena researchers were completely reasonable and that there was no evidence of a Th or DU anomaly. Thus on July 11, 2014 the case against the geochemists was dismissed and they were completely exonerated as the victims of unjustified persecution.

This entire episode was certainly very hard for the scientists from the University of Siena. In addition, it should also serve as a cautionary tale for the larger scientific community. This story can only breed hesitation and reticence on the part of scientists to participate in such efforts to help the public. Such aggression on the part of the local prosecutor is a warning to other scientists to stay away from the Quirra region and avoid the potential liability that comes with it. On a larger scale, this trial warns scientists outside of Italy that participating in issues involving human health, or ones that are emotionally charged, can be a bad thing. This lesson is not one that helps people. By telling scientists that if we don’t like your results we’ll attack you personally only turns us away and ultimately enhances ignorance and short sighted decision making. It will be a sad day indeed when I or others turn down a project because of the liability risk involved when we could actually be helping the public interest by practicing responsible science. I hope that this is not what Italy or other nations are coming to.

Thanks for reading! I would also like to acknowledge Dr. Luigi Marini for keeping me updated over the past several months as the trial progressed and his permission to blog about such an important issue.

References

Cristaldi M, Foschi C, Szpunar G, Brini C, Marinelli F, Triolo L. Toxic emissions from a military test site in the territory of Sardinia, Italy. Int J Environ Res Public Health. 2013;10(4):1631–46.

Frau F, Ardau C, Fanfani L. Environmental geochemistry and mineralogy of lead at the old mine area of Baccu Locci (south-east Sardinia, Italy). J Geochemical Explor. 2009;100(2-3):105–15.

Marini L. – Goldschmidt Abstracts 2013. Mineral Mag. 2013;77(5):1661–817. Available from: http://goldschmidt.info/2013/abstracts/finalPDFs/1685.pdf

Zucchetti M. Environmental Pollution and Health Effects in the Quirra Area, Sardinia Island (Italy) and the Depleted Uranium Case. J Environ Prot Ecol. 2006; 7(1): 82-92

#AESRC2014 Highlights

Matt Herod April 8, 2014

Well, AESRC is done for another year and with it my role as co-chair of the organizing committee! Thank goodness for that! Hopefully, I can finally get some actual thesis related work done in the coming months…and maybe get back to blogging a bit as well. However, as grateful as I am that AESRC is done, I have to say that it was a fantastic conference this year with a host of terrific talks from keynotes and grad students alike.

As I mentioned in my conference opening post AESRC is the only conference in Ontario, maybe Canada for all I know, that is organized by and for graduate students. The entire organizing committee is composed of graduate students and all of the talks, with the exception of keynotes, are given by graduate students. AESRC is meant to be a place where new and experienced grads alike can talk about their work in a less nerve-racking environment. We encourage in progress research or research that does not even have results yet. The idea is that every graduate student can feel comfortable, practice presenting to an educated audience and hopefully enjoy themselves and meet their colleagues from across the province.

This AESRC was by far the most well attended in the past 10 years, with over 100 delegates attending from 8 different universities. The conference kicked off with the Icebreaker at a campus pub, where we all got meet each other or reconnect in many cases, while watching hockey and drinking beer. A nice relaxing end to the week and prelude to the science of the weekend. On a personal note, it is always worth attending the Icebreaker at every conference I have been to. More often than not there is free food and drink, but it is a great opportunity to meet new people, spot that keynote you want to talk with and introduce yourself. I try to make of point of meeting at least one new person at every Icebreaker I go to.

Saturday started with some great talk on Environmental Geoscience (my session) and Sedimentology and Petroleum Geology. We had two keynote speakers on Saturday: Paul Mackay from the Canadian Society of Petroleum Geologists and Dr. Jack Cornett from uOttawa. The video of Jack’s talk is below.

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To summarize, in case you didn’t watch the entire video, Jack discusses the incredible range of radionuclides that are found naturally occurring on Earth and the vast range of geologic problems these nuclides can be applied to. He also talks about how we can use accelerator mass spectrometry to measure these radionuclides at incredibly low levels, which is how we are able to apply them to geologic questions. To illustrate this point Jack discussed the case study of chlorine-36 in the Cigar Lake uranium mine in Saskatchewan, Canada.

Saturday concluded with a fantastic dinner at the nearby National Arts Centre and another terrific keynote by Dr. Becky Rogala on the challenges of extracting bitumen from the oil sands and the importance of having an accurate understanding of the sedimentology to ensure maximum efficiency of SAGD recovery. There was also quite a bit of beer.

Sunday started nice and early with the Geophysics session as well as the Paleontology and Tectonics sessions as well. Our keynote for the geophysics session was Dr. Glenn Milne from uOttawa, who was an author on the most recent IPCC report and is an expert on sea level change.

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We also had another great keynote from uOttawa in the tectonics session in Dr. Jon O’Neil. The video of his talk on the oldest rocks on Earth (4.4 billion years old) is coming soon! That pretty much wraps up AESRC2014! It was a great weekend, there was lots of great science and I am really glad its over. I likely won’t be around for next year’s AESRC at Queens University (fingers crossed), however, I am sure it will be great.

Yours truly giving his talk on iodine-129 fallout from Fukushima. (Photo: Viktor Terlaky)

Opening of #AESRC2014

Matt Herod March 28, 2014

Today marks the opening of the 13th annual AESRC conference at uOttawa. The AESRC (Advances in Earth Science Research) is the geology conference in Canada that is organized by and for graduate students only. This year uOttawa is the host and March has been a ridiculously busy month preparing to host AESRC for over 120 delegates including faculty from uOttawa and other Canadian geology departments as well as industry representatives.

This year’s AESRC marks a number of significant milestones for the conference and we hope it will be the best ever. This will be the biggest AESRC ever with close to 50 oral presentations and 30 posters by graduate students from all over Ontario and Quebec. This is also the first time AESRC has had to run concurrent session rooms as well. One of the best things about AESRC is that it allows grad students a somewhat lower stress place to present research in progress to their peers without fear of being embarrassed at a large international conference where most talks are nearly ready for or already have been published. AESRC is considered and excellent place to present work that is in varying stages of completion from early conception and looking for suggestions and constructive feedback to practicing a talk for an upcoming Goldschmidt or AGU. This philosophy makes AESRC unique as far as I know and it is a truly valuable and rewarding experience to be a part of (plus there is a lot of prize money up for grabs)!

We are also fortunate enough to have several excellent keynotes whose talks will be videotaped and posted here and on the AESRC website for all to enjoy. I will also be live tweeting AESRC under the hashtag #AESRC2014 and posting a few blog posts here as well briefly summarizing some of the terrific science that Canadian geology grad students are working on.

One thing I should also mention is that AESRC would not be possible without the generosity of the Canadian geology community, the department hosting and the host university. Numerous times all I had to do was say the words “grad student run conference” to get university departments to lower fees and help facilitate this weekend. There are also perennial AESRC sponsors that year after year contribute money to help the local organizing committee put on a fantastic conference and allow us to charge only a nominal registration fee.

Stay tuned for lots more to come!

Matt