Managing Water Budgets with the Help of the Tritium/Helium-3 Technique
Scientists use isotopic techniques to study the age and origin of water from springs in northern Morocco. (Photo: CNESTEN)
Managing water is like managing money in your bank account: you need to know exactly how much will be coming in, how much you can take out, and what could cause that to change. A miscalculation could have serious, potentially long-lasting consequences. In the world of water, this could mean water shortages or contaminated, unusable water resources.
To set up a reliable water budget, one of the key factors is knowing the exact age of water. For young water, which is more likely to be affected by current climate conditions and contamination, scientists use the tritium/helium-3 technique. With this and other techniques, scientists from 23 countries are working with the IAEA to collect data about water resources.
“The age of water tells you where it most likely came from, how quickly it is replenished, and how likely it is to be contaminated,” said Hamid Marah, Scientific Director at Morocco’s National Centre for Nuclear Energy, Sciences and Technology (CNESTEN). “With the tritium/helium-3 technique, we can say if water is 1, 5 or 25 years old instead of just saying it’s young, old or both.”
The age of water can range from a few months to millions of years. If water is one year old, for example, this means it will take one year for it to be replenished and is much more likely to be affected by current climate conditions and contaminants. If water is 50 000 years old, it will take 50 000 years to be replenished and is less likely to be contaminated or affected by changes in the current climate.
Nearly all of the world’s available fresh water supplies are found in aquifers, which are the porous layers of permeable rock under the earth’s surface. The water they contain is called groundwater. As groundwater is recharged, or replenished, it eventually flows into the sea or out onto the earth’s surface naturally as rivers, springs and lakes.
“The growing demand for groundwater, combined with the impact of agriculture, climate change and human activity makes sustainability even more important,” Marah said. “By extracting too much water from an aquifer, the level of water goes down and this can be catastrophic. We are not talking about 10 to 20 years from now: its impact lasts for generations.”
The tritium/helium-3 technique is one of the most commonly used techniques for studying young water, which is water under 60 years old (see The Science box). The data collected from these studies can help decision makers develop more targeted and sustainable water resource management strategies and policies.
“Using nuclear techniques for water resource studies is breaking paradigms and changing our classical understanding of the key drivers controlling hydrological processes,” said Ricardo Sánchez-Murillo, Isotope Hydrologist and Associate Professor at the National University of Costa Rica. “In Costa Rica, for example, results from using isotopic techniques are making their way into water management plans and decision making, helping the country achieve United Nations Sustainable Development Goal 6 on water by 2030.”
A more exact budget
The tritium/helium-3 technique has become an increasingly important technique over the last decade because previous methods using just tritium are becoming less useful.
“Tritium can tell us the age of groundwater and whether it’s being recharged, which is very important information, but tritium alone cannot give us the level of detail we need. Decision makers need to know more: what does it mean that the water is young? How young is young?” Marah said.
Due to atmospheric tests of thermonuclear devices in the 1950s, levels of tritium in the atmosphere sharply increased in the 1960s and have since gradually declined.
Naturally occurring radioactive isotopes present in water, such as tritium (3H) and carbon-14 (14C), and noble gas isotopes dissolved in the water, such as krypton-81 (81Kr), can be used to estimate groundwater age. (Image: IAEA)
Helium is a noble gas, which means it is stable and does not have chemical reactions with other elements found in rocks or water. This makes it a consistent and reliable reference point. By knowing the concentration of helium that comes from tritium — helium-3 — compared to the total helium in the water, as well as the concentration of other noble gases, scientists can determine the exact age of young water.
“The use of noble gases for water studies is growing because now analytical devices have improved enough to detect the very small amounts these gases come in,” said Takuya Matsumoto, an isotope analyst at the IAEA. “For many countries, though, it is not economical or feasible to set up their own labs to do these analyses. The IAEA Isotope Hydrology Laboratory makes this service available to countries so they can benefit from this sophisticated technique.”
The IAEA Isotope Hydrology Laboratory is one of just a handful of laboratories in the world capable of performing these analyses. Beginning in 2010, a team of IAEA and external experts from ten countries spent six years setting up, calibrating and testing the IAEA’s mass spectrometer machine, as well as the mathematical model for analysing results. They also developed guidelines for using the tritium/helium-3 technique. The lab has since been working around the clock processing between 300 to 400 samples each year from countries worldwide.
Tritium is one of the three isotopes of hydrogen. As a radioactive isotope, tritium decays over a certain period of time and turns into helium-3, a stable isotope, which does not decay. Scientists know that it takes about 12 years for half of tritium atoms in water to decay into helium-3.
Scientists use a specialized machine called a mass spectrometer to sort the isotopes by weight and identify their concentrations. By knowing these concentrations and how long it takes for tritium to become helium-3, scientists can track and determine how old the water is and how often it is replenished.
This article was featured in the April 2019 Bulletin edition on Water.
A doctor reviewing CT scan images at Vienna General Hospital in Austria. (Photo: L. Dojcanova/IAEA)Experts at a recent IAEA meeting proposed measures to ensure medical benefits always exceed risks for patients who need frequent radiological imaging exams for diagnosing and monitoring their diseases. New data presented at the meeting based on 2.5 million patients in 15 countries showed that more than 1% of patients receive cumulative doses above 100 mSv from multiple exams in their lifetime. This is significantly higher than previously thought. Receiving radiation in significant doses increases the risk of cancer later in life.Around 50 experts from 26 countries and nine international organisations and professional and industrial bodies met at the IAEA in Vienna from 4 to 6 March to explore the issue. New data on exposure has surfaced thanks to the introduction of automatic exposure tracking systems in many hospitals in recent years.“The medical community should find a way to improve safety of patients who need recurrent imaging exams, while not limiting their medical benefits,” said Madan M. Rehani, Director of Global Outreach for Radiation Protection at the Massachusetts General Hospital in the United States, who presented some of the new data.Medical imaging like computed tomography (CT), X-rays and interventional procedures have provided immense medical benefits in diagnosis and follow-up of diseases to better manage health conditions of millions of patients worldwide. A patient can get exposed to 100 mSv from 10-12 CT exams, which is required in different chronic conditions or malignant diseases or when treatment requires frequent follow-up examinations.Participants at the meeting agreed that several steps could be taken to improve protection of patients who need frequent imaging exams:CT scanners capable of achieving adequate image quality at sub-mSv radiation dose.Physicians need to ensure the appropriate use of imaging exams when dealing with diseases that require frequent tests.Strengthen guidelines by professional medical bodies for those treating patients who require frequent imaging studies.Integrated technological solutions for monitoring patient exposure data within the electronic healthcare records.Concrete radiation protection recommendations on how to avoid high level of exposures without curtailing medical benefits.“The new data show that all stakeholders must come together to find suitable strategies and solutions with focus on radiation protection of this specific group of patients,” Jenia Vassileva, IAEA Radiation Protection Specialist. “The IAEA will continue coordinating international efforts by engaging with the medical industry, by organizing multi-stakeholder’s meetings and by taking action to raise awareness of and educate healthcare providers and patients.”
Food irradiation, using X-rays or gamma rays, helps countries prevent fruit and vegetables from going to waste. With the support of the IAEA, a food irradiation facility in Havana, Cuba has reopened after 20 years. Click link to watch video:https://www.iaea.org/newscenter/multimedia/videos/making-fruit-and-vegetables-last-longer-with-food-irradiation19 March 2019Story and Editing: Alejandra Silva Camera: Martin Klingenboeck
The Aedes albopictus is the world’s most invasive mosquito species. A successful pilot trial for controlling this insect pest recently concluded and the results were published in Nature on 17 July 2019. (Photo: N. Culbert/IAEA)For the first time, a combination of the nuclear sterile insect technique (SIT) with the incompatible insect technique (IIT) has led to the successful suppression of mosquito populations, a promising step in the control of mosquitoes that carry dengue, the Zika virus and many other devastating diseases. The results of the recent pilot trial in Guangzhou, China, carried out with the support of the IAEA in cooperation with the Food and Agriculture Organization of the United Nations (FAO), were published in Nature on 17 July 2019.SIT is an environmentally-friendly insect pest control method involving the mass-rearing and sterilization of a target pest using radiation, followed by the systematic area-wide release of sterile males by air over defined areas. The sterile males mate with wild females, resulting in no offspring and a declining pest population over time. IIT involves exposing the mosquitoes to the Wolbachia bacteria. The bacteria partially sterilizes the mosquitoes, which means less radiation is needed for complete sterilization. This in turn better preserves the sterilized males’ competitiveness for mating.While SIT, as part of area-wide insect management strategies, has been successfully used to control a variety of plant and livestock pests such as fruit flies and moths, the control of mosquitoes still had to be demonstrated.The main obstacle in scaling up the use of SIT against various species of mosquitoes has been overcoming several technical challenges with producing and releasing enough sterile males to overwhelm the wild population. Researchers at Sun Yat-sen University, and its partners, in China, have now successfully addressed these challenges, with the support of the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, which is leading and coordinating global research in SIT.For example, the researchers used racks to rear over 500 000 mosquitoes per week that were constructed based on models developed at the Joint FAO/IAEA Division’s laboratories near Vienna, Austria. A specialized irradiator for treating batches of 150 000 mosquito pupae was also developed and validated with close collaboration between the Joint FAO/IAEA Division and the researchers.Mosquito larval rearing racks at a mosquito mass-rearing facility at the Wolbaki Biotech Company in Guangzhou, China, in May 2019. The company is using the most advanced mass-rearing technology for mosquitoes. These racks are based on models developed by the Joint FAO/IAEA Insect Pest Control Laboratory. Each has the capacity of producing about 500 000 males per week. (Photo: J. Bouyer/IAEA)The results of this pilot trial, using SIT in combination with the IIT, demonstrate the successful near-elimination of field populations of the world’s most invasive mosquito species, Aedes albopictus (Asian tiger mosquito). The two-year trial (2016-2017) covered a 32.5-hectare area on two relatively isolated islands in the Pearl River in Guangzhou. It involved the release of about 200 million irradiated mass-reared adult male mosquitoes exposed to Wolbachia bacteria.The study has also shown the importance of socioeconomic aspects for the successful use of the IIT/SIT approach. Social acceptance, for example, increased during the study as support of the local community went up following mosquito releases and the resulting decrease in nuisance biting; for the IIT/SIT approach to be successful, the local community needs to be on board and work together to ensure consistent and integrated use of the approach over the entire area in order to effectively counteract and control the movement of the insects. Another aspect is the cost-effectiveness; overall future costs of a fully-operational intervention are estimated at US$ 108-163 per hectare per year, which is considered cost-effective in comparison with other control strategies.Experts in China plan to test the technology in larger urban areas in the near future using sterile male mosquitoes from a mass-rearing facility in Guangzhou, said Zhiyong Xi, Director of Sun Yat-sen University-Michigan State University’s Joint Center of Vector Control for Tropical Diseases and Professor at Michigan State University in the United States. The company operating the facility uses advanced mosquito mass-rearing and irradiation equipment that have been developed in collaboration with the Joint FAO/IAEA Division.Global cooperation on the development of SIT to control mosquitoes intensified following the Zika epidemic in 2015 to 2016. The incidence of dengue is on the rise, with the number of cases reported to the World Health Organization (WHO) increasing from 2.2 million in 2010 to over 3.3 million in 2016. The actual incidence is much higher, and one estimate, according to the WHO, indicates 390 million new infections each year.https://www.iaea.org/newscenter/news/mosquito-population-successfully-suppressed-through-pilot-study-using-nuclear-technique-in-china
Food products undergo irradiation processes at VINAGAMMA using an electron beam irradiator, pictured here, and a gamma irradiator. (Photo: E. Marais/IAEA)Ho Chi Minh City, Viet Nam – Each morning hundreds of boxes filled with frozen seafood, dried fruits and vegetables, oriental medicines and health foods are queued up in a store room in Ho Chi Minh City, Viet Nam. They will undergo a process similar to security screening at airports, but with higher intensity beams of photons or electrons – in a food irradiation programme installed with IAEA support in the last two decades.Depending on the dose, food irradiation will ensure that the root vegetables and fruits do not sprout or ripen prematurely; that parasites are killed and spices are decontaminated; that salmonella are destroyed and that fungi that could spoil meat, poultry and seafood is eliminated.The process was first introduced in Viet Nam in 1999 with the help of the IAEA and the Food and Agriculture Organization of the United Nations (FAO), and a large market for irradiated products has since opened up, significantly increasing the ability of companies to export their food products. Food irradiation has matured into a mainstay of the country’s food industry and is an important contributor to the country’s agricultural competitiveness.“In 1999 we were irradiating 259 tonnes of food per year, and this has grown to 14,000 tonnes by 2017,” said Cao Van Chung, Head of the Electron Beam Department of the Viet Nam Atomic Energy Institute’s Research and Development Center for Radiation Technology, VINAGAMMA. “This shows a real boom in demand for our work. Today we are one of the leading facilities in the country in the field of radiation technology – pioneering in food irradiation.”Introduction of gamma and electron beam irradiationThis growth has been possible thanks to the introduction of two irradiation methods. A gamma irradiator introduced in 1999, which uses ionizing energy from a radiation source shielded in a concrete room, and an electron beam (EB) irradiator has been in use since 2013. EB irradiators do not rely on a radioactive source, using instead streams of highly charged electrons produced from specialized equipment such as a linear electron accelerator. The food never comes into contact with radioactive material, and the irradiation both maintains the quality and increases the safety of the food while leaving no residual radioactivity.While the process of irradiation for the two methods is the same, each brings distinct and complementary advantages, Chung said. The gamma irradiator uses tall aluminum boxes, which can accommodate a broad range of product sizes, and the boxes are moved through the irradiation chamber around the radioactive source suspended on an overhead monorail system. Products require two rounds of irradiation to ensure all sides of the packaged product have been treated. Tall aluminum boxes filled with food products await irradiation using the gamma irradiator. (Photo: E. Marais/IAEA)The EB irradiator, on the other hand, contains double sided beams, which makes the irradiation process three times quicker than the use of the gamma irradiator, because all areas of the product can be irradiated in a single round. However, the EB irradiator has a limited dimension, with a maximum box size of 60x30x50 cm and weight of 15 kg, so for larger and heavier products gamma irradiation must be used. The machines work side by side, running 24 hours a day seven days a week, only stopping over the Vietnamese New Year period.Before the introduction of the gamma irradiator and EB accelerator, spoilage prevention of food products such as seafood, fruits and vegetables was carried out using traditional methods including canning, refrigeration and freezing and chemical preservatives, which due to lower effectiveness, hindered the manufacturers’ ability to export their products.The irradiation machines were acquired with support from the IAEA’s technical cooperation programme, which also supplied training for staff and expert advice. Viet Nam is one of 40 countries that the IAEA is supporting in this area.Growth in the use of radiation technologyVINAGAMMA has grown from 20 employees when the Center was set up in 1999 to 79 today. Besides food irradiation services, it provides radiation sterilization of medical products and pasteurized foodstuffs, and commercializes its research and development products, such as plant protectors used in agriculture and gold and silver nanogels used in medicine.The Center also carries out research and development and provides training in the field of radiation technology. It also works with international partners to research ways of improving irradiation technology further.THE SCIENCEIrradiationIrradiation is the exposure of a substance to beams of electromagnetic radiation. For example, microwaving food involves exposing it to beams that have just enough energy to cause water molecules in the food to rub against each other and generate heat by friction. But food irradiation involves higher frequency beams that have enough energy to give atoms positive and negative electrical charges (ionization) for an instant. It is used to improve food safety and to maintain its quality. During irradiation, energy is transferred into the treated product just like when food is heated, but it doesn’t involve a significant increase in temperature.The most important irradiation process parameter is the amount of energy absorbed per unit mass of food, which is termed ‘absorbed dose’ or simply ‘dose’. The technology can be used to destroy microbes that cause food poisoning; it can help keep food fresher for longer because it reduces the numbers of spoilage organisms; it also slows down ripening and prevents sprouting in foods like onions, garlic and potatoes. Therefore, it improves food safety and reduces waste.In gamma irradiators the source of radiation is a radionuclide, usually cobalt-60 (60Co). Gamma rays are electromagnetic waves and hence they can pass through dense materials. Products can be irradiated in large sacks or shipping cartons, carried through the irradiator in boxes or stacked on a pallet that will be transported to and from the irradiator in hanging carriers or on roller bed conveyors. It may take an hour or so to irradiate a large pallet of products.In electron beam irradiators the beams are produced by electricity in a machine. Electrons have a negative charge and a small but appreciable mass and so readily interact with atoms in food, transferring all their energy over a relatively short distance. Therefore, electron beams can only be used to irradiate smaller food packets that they can easily penetrate. However, the energy can be delivered quickly, and the process takes a fraction of a second as the beam is scanned over the food.
CNNC (China National Nuclear Corporation has developed advantageous positions in the fields of isotope products, radiation processing products and service, and ray application instrumentation. It has cultivated a number of major high-tech enterprises and created remarkable benefits.CNNC’s isotope products have a lion’s share of the domestic market, supplying 70 percent of radiopharmaceuticals and radioactive sources.The explosive detection system developed by CNNC goes a long way to solving the global problem of explosive security inspection. It is one of the most advanced and practical explosive detection techniques in the world. It has been successfully applied to large public activities including the Beijing Olympic Games, Shanghai World Expo, and the 60th Chinese National Day. The self-shielded mail irradiation sterilization device can kill hazardous bacteria like bacillus anthraces, and has been applied to key national departments.Co-60 production with HWR and large power irradiation accelerators has been industrialized. Key projects including nuclear power seawater desalination have made important progress.The China Isotope Radiation Co Ltd (CIC) is the biggest nuclear technological enterprise inChinaintegrating R&D, production, sales and service. It is involved with preparation of isotopes, production of radiopharmaceuticals, preparation of radioactive sources, irradiation project and processing. The corporation owns about 50 various production lines and provides 70-plus nuclides and 300-plus products for a variety of clients.CIC keeps in long-term close cooperation with worldwide nuclear medical research and development institutions and companies, actively introduces and communicates the latest radiopharmaceutical technology and products, and meets the demand of nuclear medical development.Nuclear pharmaceutical centers have been built in about 20 cities, and the network of radiopharmaceutical sales and technical services covers the country.