Radon isotopes in Northeastern Vietnam’s karst environment

At the entrance of Rồng Cave during field work for the first project about methane in Sảng Tủng commune, Đồng Văn, Hà Giang  in 2015. High radon-222 concentrations was first discovered inside the cave’s passages.

Funded by Nafosted (2016-2019)

A chance discovery during field work for the first project about methane in the Đồng Văn district, Hà Giang province in 2015, yielded intriguingly high radon-222 concentrations in Rồng Cave near the Sảng Tủng commune.

Even higher levels of environmental radioactivity were measured in March 2016 when our group was relaxing in an ancient mud-built house in Đồng Văn town that serves as a restaurant. The latter geohazard for human health was discovered in the form of high thoron (radon-220) concentrations in room air near mud walls and the mud floor. Our discoveries led us to our second project entitled “radon isotopes in Northeastern Vietnam’s karst environment” (recently funded by Vietnam’s NAFOSTED science grant agency).

Duong, Arndt and Thomas (SARAD GmbH – a German company) checking radon and thoron in a karst sinkhole at Dong Van, Ha Giang (March 2016).

Our study uses modern, portable radiation-spectroscopic analytical instrumentation to isotope-specifically assess the radon-induced health hazards in houses, in the open air in villages and towns, on fields, and in caves and karst sinkholes in northeastern Vietnam during climatically different seasons.

Professors and students are relaxing in front of an ancient mud-built house that serves as a restaurant. The group first discovered high thoron (220 Rn) concentrations in this house behind plastic wall covering (Đồng Văn town, Hà Giang, March 2016).

Low-cost housing construction in developing countries often relies on the use of local soil or clay that is compacted and dried to form the walls of dwellings. Depending on the local geological context, the soil and clay building materials may contain enough thorium and uranium to produce significant exhalation of radon isotopes. Unlike their metallic precursor elements, monoatomic noble gas radon can diffuse into the room air where it can be inhaled by humans, dissolve in lymph fluid, and pose a radiation health hazard not only due to radon’s own radioactive decay, but also due to the subsequent radioactive decay chains of their unstable metallic daughter nuclides in the human body.

In an ancient coffee house in Đồng Văn, we discovered extremely high thoron concentrations in the air space between a mud wall and its dilapidated plastic wall covering.

Among all radon isotopes, traditionally only 222Rn and its progeny have been considered a health risk in indoor environments due to (i) their contribution to the overall radiation dose and their potential for inducing lung cancer, (ii) widespread occurrence in buildings in developed countries, and (iii) because 222Rn is relatively easy to quantify in room air. In contrast, the contribution of 220Rn (called thoron) to the radiation dose in room air has not received sufficient international attention, in spite of pioneering research in China, Germany, Hungary, India and Japan.

EOS group checks radon and thoron in an agriculturally used sinkhole next to Rồng Cave, Sảng Tủng commune and interviews a group of curious local students to inquire about the general health of local inhabitants of mud houses (December 2016).
Closeup view of the porous exterior wall of a ‘mud house’ constructed with compacted soil
Jan digs a hole in a plowed field in Hà Giang in March 2016 in preparation for the collection of radon-containing soil gas.
Collection of soil gas in a buried, perforated beer can that is connected via tubing to a radon detector
Dương stands in front of a mud house in Bạch Đích commune, Yên Minh, Hà Giang – near border between Vietnam and China. The interior is always dark and the air quality is sometimes quite poor, especially during the preparation of meals over open wood fires. A high concentration of particulates and smoke in room air serves as an exacerbating co-factor towards ill health effects from thoron-related radioactivity in room air.

Thoron concentrations in excess of 1000 Bq m-3 were frequently encountered in room air close to mud walls of northern Vietnamese mud houses. Inhabitants often place their beds next to walls where thoron concentrations are much higher than in the center of the room. In contrast to thoron with its short half-life of ~55 seconds, the longer-lived 222Rn with a half-life of ~3.8 days is rarely of concern in mud houses because their typically drafty construction allows for fast ventilation of room air. An inhaled atom of 222Rn will likely be exhaled over the next day before it decays in a human body, whereas an inhaled atom of thoron that readily dissolved in the lung’s fluid will almost certainly decay in the human body and contribute to radiation damage in tissue.

EOS member Nguyet reads radon-222 and thoron data from SARAD RTM2200 instrument near a mud wall and try to explain to the mud-house owner Mr. Minh about displayed number and thoron health hazard (Bạch Đích commune, Yên Minh district, Hà Giang province, December 2016).
An open plastic box is overturned to mud floor to trap a constant volume of air that was in contact with a defined area of mud floor. The exhalation of radon and thoron was measured in closed-circuit mode with SARAD RTM2200 at an air flow rate of 1 liter per minute (Bạch Đích commune, Yên Minh district, Hà Giang province – near the Vietnam – China border, December 2016).

Neither the population nor governmental and public health authorities in Vietnam have been aware of the wide-spread thoron geohazard. Enhanced ventilation of rooms is unable to significantly decrease the concentration of thoron near mud walls. The literature provides no example of a feasible remediation strategy that fits the needs of developing countries. Barring expensive filtering approaches, the only promising strategy is to apply a diffusion barrier on inside walls and to delay the escape of 220Rn until the short half-life of ~55 seconds has caused safe decay within the porous mud wall.

Open plastic box was fitted with foam insulating strips and were pressed against treated sections of mud walls to trap a constant volume of air that was in contact with a defined area of mud wall. The exhalation of radon and thoron was measured in closed-circuit mode with SARAD RTM2200 or RAD7 instruments (Bạch Đích commune, Yên Minh district, Hà Giang province – near the Vietnam – China border, December 2016).
Mr. Minh helps EOS group collecting soil sample for brick experiment in Hanoi (near a border guard station in Yên Minh district, Hà Giang – December 2016)

Our group performed numerous assessments of surface sealing techniques both in an authentic mud house in northern Vietnam and using standard-sized artificial mud bricks in the laboratory in Hanoi using RAD7 and SARAD® RTM2200 instruments.

We were able to develop methodologies and test the results from specific methods of surface sealants to prevent thoron from entering room air. We met our goal to develop methods that are effective, affordable, non-toxic, environmentally sustainable, and socially acceptable. The required materials are readily available in developing countries.

In our upcoming communication with the IAEA, we would contribute towards our outreach and training efforts in developing countries. There may be a possibility that the IAEA will be willing to financially support training activities in Vietnam (and other developing countries), and in such a case we would want to apply for travel money to enable experts to participate in person.

Before making mud bricks EOS member and students pour water to add more moisture for soil sample collected (Hanoi, January 2017).
Compaction of wet soil with structural reinforcements to generate artificial soil bricks for radon/thoron measurements.
After drying and receiving various types of surface treatments, soil bricks are ready for
measurements of their radon/thoron emission.
Relative dry mud bricks are numbered before checking radon and thoron emission in Hanoi
Brick is placed in plastic box for checking radon and thoron emission (Hanoi, January 2017)
  • Nguyễn-Văn H., Nguyễn-Thuỳ, D., Nguyễn, N.T.A., Streil, T., Schimmelmann, J., , Doiron, K., Nguyễn-Đình, T., Nguyễn-Thị H, Schimmelmann, A., 2020. Excessive radon-based radiation in indoor air caused by soil building materials in traditional homes on Đồng Văn karst plateau, northern Vietnam. Chemosphere. Vol. 257, Oct. 2020, 127119. https://doi.org/10.1016/j.chemosphere.2020.127119. [VSI: Air pollution in developing countries].
  • Dương Nguyễn-Thuỳ, Hướng Nguyễn-Văn, Jan P. Schimmelmann, Nguyệt Thị Ánh Nguyễn, Kelsey Doiron and Arndt Schimmelmann (2019) 220Rn (thoron) geohazard in room air of earthen dwellings in Vietnam.  Geofluids, Vol. 2019, Article ID 7202616, 11 pages; DOI: 10.1155/2019/7202616
  • Nguyễn Thị Ánh Nguyệt, Nguyễn Thùy Dương, Arndt Schimmelmann & Nguyễn Văn Hướng, 2018. Human exposure to radon radiation geohazard in Rong Cave, Dong Van Karst Plateau Geopark, Vietnam. Vietnam Journal of Earth Sciences, Vol 40. No. 2, p117-126, 2018. DOI: 10.15625/0866-7187/40/2/11092
  • Nguyễn-Thùy D, Nguyễn-Văn H, Schimmelmann A, Nguyễn-Ánh N, Đặng PT, 2016. Radon concentrations in karst caves in Dong Van karst plateau. VNU Journal of Science – Earth and Environmental Sciences Vol. 32, No. 2S, 2016 [Full PDF].
  • Đặng PT, Nguyễn-Thùy D, Nguyễn-Ánh N, Nguyễn-Văn H, Schimmelmann A, 2016. Preliminary investigation into radiological environment in Dong Van district, Ha Giang province. VNU Journal of Science – Earth and Environmental Sciences Vol. 32, No. 2S, 2016 [Full PDF].
  • Nguyễn-Ánh N, Nguyễn-Thùy D, Schimmelmann A, Nguyễn-Văn H, Tạ HP, Đặng PT, Ma NG, 2016. Radon concentration in Rong cave  in Dong Van Karst Plateau Geopark. Full paper in Proceeding of International Symposium Hanoi Geoengineering 2016 [Full PDF] [Poster PDF].
  • Nguyen-Thuy, Duong, A. Schimmelmann, Phuong Ta Hoa, Agnieszka Drobniak, and Minh Schimmelmann (2016) Radon and carbon dioxide in northern Vietnamese limestone caves. 5th International Conference on Earth Science & Climate Change, July 25-27, 2016, Bangkok, Thailand. http://earthscience.conferenceseries.com/abstract/2016/radon-and-carbon-dioxide-in-northern-vietnamese-limestone-caves
Duong presented her research at the 5th International Conference on Earth Science & Climate Change, July 25-27, 2016, in Bangkok, Thailand.
Duong presented her research at the Biennial Conference at Faculty of Geology, VNU University of Science, November 24, 2016, in Hanoi, Vietnam.
Duong presented her research at the Biennial Conference at VNU University of Science, November 24, 2016, in Hanoi, Vietnam.

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