Baranovskaya, Nataliya Vladimirovna

Matveenko, Irina Alekseevna

Nanping Wang

Rikhvanov, Leonid Petrovich

Zlobina, A. N.

Electronic archive of Tomsk Polytechnic University

771Радиоактивность и радиоактивные элементы в среде обитания человекаTHE CAUSES OF HIGH NATURAL RADIOACTIVITY IN THE SOILS AND RADIOECOLOGICALPROBLEMS IN AREAS WITH HIGHLY RADIOACTIVE SOILSL.P. Rikhvanov1, A.N. Zlobina1, Nanping Wang2, N.V. Baranovskaya1, I.A. Matveenko11Tomsk Polytechnic University, anastasiyazl@mai.ru, rikhvanov@tpu.ru2China University of Geosciences, Beijing, China, 1996010992@cugb.edu.cnThere are several provinces on the globe that have a highcontent of natural radioactive elements in soil. Examples arethe soils of MinasGerais State in Brazil, soils of Kerala Statein India, soils of Nuie Island and soil in the SouthChineseProvince Guangdong  [1].The character of soil radioactivity varies from pureuranium radioactive (U >Th, which is typical for soil of NiueIsland) to mixed uraniumthorium (Th/U >2.5–5) and thorium(Th/U >5, as it is in the soil of Guangdong Province). For theTable 1. The chemical composition of soil Guangdong Province by the instrumental neuron activation analysisElements Ca, % Na, % Fe, % Th U Ta La Ce Sm Nd ZnContent, g/t 0.22 0.04 1.6 43.6 9.2 8.4 17.6 89 3.5 14.5 68.6Elements Eu Tb Lu Yb Cr Au Hf Ba As Br CsContent, g/t 0.2 1.2 1.1 7.4 18 0.0003 9.6 51 2.1 4.9 9.5Table 2. The chemical composition of soil of Auvergne region by the instrumental neuron activation analysisElements Sm Ce Ca, % Lu U Th Cr Yb Au Hf Ba Sr Nd As AgContent, g/t 2.14 29.3 2.53 0.103 6.44 4.6 11.7 0.8 0.002 2.26 482 30 20.8 24.3 0.5Elements Br Cs Tb Sc Rb Fe, % Zn Ta Co Na, % Eu La SbContent, g/t 5.8 96.51 0.33 3.2 443.8 1.19 108.9 7.01 2.19 0.48 0.65 11.3 1.28Fig. 1. The data of measurement by method gammaray spectrometryFig. 2. The elemental composition of soil Guangdong province by the instrumental neuron activation analysis772Материалы V Международной конференции, г. Томск, 13–16 сентября 2016 г.latter, it is suggested that its radioactivity is explained by thepresence of monocyte [3].As a reason for the formation of high natural radioactiveconcentrations in soil, elevated concentrations of theseelements in primary parent rocks and various geologicprocesses leading to accumulation of radioactive elements,for example, insolation processes of uranium accumulationFig. 3. The elemental composition of soil of Auvergne region by the instrumental neuron activation analysisas well as anthropogenic contamination with radioactivecomponents in vicinity of mining factories can serve.The purpose of the given work is to study the causes ofhigh soil radioactivity in the SouthChinese Guangdongprovince and in the Auvergne region.The preliminary gammaspectrometric soil analysisshows that they are characterized by thorium radioactiveFig. 4. The phosphates of heavy and light rare earths in clay fraction (б), energy dispersivespectrum (в) and composition (а) in soil of Guangdong province773Радиоактивность и радиоактивные элементы в среде обитания человекаnature (Th190 Bq/kg; U (in terms of Ra)120 Bq/kg; K150Bq/ kg) in soil of Guandong province.In soil, there are also some traces of technogenic isotopeCs137 that points to presence of the abundant isotopefallouts after nuclear weapon tests in the atmosphere.The Guandong province soil research by theinstrumental neuron activation analysis in the NuclearGeochemical Laboratory of the Geoecology andGeochemistry Department (made by А.F. Sudyko, ananalyst) revealed that the content of Th in soil amounts 43.6g/t, but U9.2 g/t ). Particular attention is drawn by the highconcentration of Th in the rare earth soil (Σ  TR = 134.5 g/t),particularly Ce and Nd (see Table 1). Low contents of Ca,Fe, Na and high content of U, Th as well as rare earthelements suggest that the original substrate for soilformation was potassium granite due to the presence ofsilica relics and Kfeldspar in soil.As for Auvergne region soil, the operational soil researchby the instrumental neuron activation analysis has revealedthat the content of U in soil amounts 6,44 g/t, but Th – 4,6g/t ) (Table 2). Low content of Ca, Fe, Na and high contentof U, Th as well as rare earth elements suggests that theoriginal substrate for soil formation was twomica granites.For further research, siltloam fraction of the given soilwas separated. Its portion amounted 37.4 % of the totalsample weight. Sand soil fraction (of >0.01 mm in size) wassubjected to the classic sieve analysis.Granulometric analysis shows that the C horizon ischaracterized by increased content of fine fraction (0.04mm). While increasing horizons (from C to A), the percentage(%) of the fine dust fraction decreases.According to data of measurement by of methodgammaray spectrometry (Fig. 1) potassium is an activemigrant. Intense leaching of K occurs in the B1 horizon. Thedistribution of thorium in the soil profile differentiated weakerthan the other elements.However, the existing variations in the distribution of Thallow us to trace the trend of its accumulation in the horizonsB2, BC, C closer to the soilforming rocks.  The redistributionof uranium in the soil profile indicates a high mobility of theelement in the illuvialeluvial process. Significant removal ofU is observed in the AB horizon and an intense accumulationof U from soil solutions is found in the humus horizon A.The data analysis of instrumental neuron activationshowed that maximum accumulation of radioactive elementswas found in fraction – 0.04 and clay fraction of soil fromGuangdong province. In addition, maximum accumulationof U was revealed in the fine sand fraction (22.7 g/t), but Th– in the clay fraction (110.4 g/t). Thoriumuraniumrelationship in them varies from 4.3 to 9, respectively. In finesand (<0.04) and clay (<0.01) fractions, there was maximumaccumulation of rareearth, Ta, and a number of otherelements (Fig. 2).Fig. 5. The mineral of monacyte in clay fraction (б), energy dispersive spectrum (в) and composition (а) in soil ofGuangdong province774Материалы V Международной конференции, г. Томск, 13–16 сентября 2016 г.Fig. 6. The mineral zircon with impurities of thorium and uranium in clay fraction (б), energy dispersive spectrum(в) and composition (а) in soil of Guangdong provinceThe data same analysis showed that maximumaccumulation of radioactive elements was found in fraction– 0.04 and clay fraction of Auvergne region soil (Fig. 3). Inaddition, maximum accumulation of U was revealed in thefine sand fraction, but Th – in the clay fraction. Thoriumuranium relationship in them is 0.7.An important evaluation indicator of soil condition isthoriumuranium ratio. High (>5) thoriumuranium ratio inthe soils is characteristic for areas with thoriumbearinggeological formations. This is the area found in soils ofGuangdong province (the ratio of thorium to uranium in thefractions varies from 4.3 to 9). The given soil can be classifiedas a ferrallitic soil group of humid tropical and subtropicalregions in terms of the set of chemical indicators. The regionis characterized by high degree of soilforming materialweathering.Reduced thoriumuranium ratio has observed inuraniumbearing soils areas. The soils of the region ofAuvergne have low thoriumuranium ratio in the range 1–2.4. The region is located within the French Massif Central.There are uranium ore deposits (Limousin, Foretz, Morvan).The deposits are confined to the twomica granite massifs(San Silvestre et al.) with a high content of uranium, whichare located along the fault Argens. The soils of this regionare autochthonous.In view of the results of the optical and electronmicroscopic analysis (electron microscope Hitachi S3400N) of heavy fraction (soil of Guangdong province), itwas stated that clay particles crooked with fine mixture ofhydrargillite with adhesions of hematite predominating in it.In these aggregates, the unclear mineral phase is visible. Interms of its composition, it represents neodymium and ironoxides (Fe – 47.9%, Nd – 13.6%, O – 35.3%). In some cases,the grains of thoriumcontaining zircon (Тh up to 2.2%) andcassiterite were noticeable. In the clay fraction phosphateswith heavy and light rare earths (Fig. 4), monacyte (Fig. 5),zircon (Fig. 6), xenotime (Fig. 7), thorite, and rare earthcerium phase with thorium were identified. The mostcommon minerals are iron and titanium oxides, copper andzinc compounds (such as brass), and barite. Besides, silvergray trace minerals in the form of sulfide silver (it is notpossible to state accurately), micromineral formation ofbismuth and sulfur dioxide, zirconium (baddeleyite), coppernickel compound are likely to be present.Further mineralogical analysis of fine fractions of soilfrom Auvergne region was made with the electronmicroscopic (electron microscope Hitachi S3400N)research methods. Barium phosphate, mineral galena weredetected, the most common mineral formations weretitanium oxides and iron oxides. Uraniumbearing andthoriumbearing minerals were not detected.According to research by N. Wang Also, there is high775Радиоактивность и радиоактивные элементы в среде обитания человекаradon hazard in Guangdong province. The distribution ofsoilgas 220Rn obviously has geological features. Most siteswith high 220Rn concentrations in soilgas are mainly relatedto the outcrops belonging to the Jurassic and Cretaceousgranite. The average value is 100.41 kBq/m3 (excludingtheabnormal point), and the maximum reaches 1199 kBq/m3[4]. Zhuhai is one of the highest radioactivity backgroundareas in China. The measured highest terrain airabsorbeddose rate at the height of 1m above ground is 266.54nGy·h–1 in Zhuhai, and the average value is 66.28±11.78nGy·h–1 in sediment, 145.90±32.19 nGy·h–1 in weatheredgranite and 145.16±26.33 nGy·h–1 in Zhuhai, respectively.It is the reason for the fact that broken fresh granite detritusand weathered granite sands are used as road constructionmaterials and building ground foundation materials [5].Scientists Gal Frederick, Gadalia Alain noted highconcentrations of radon in soil air near city Vichy (Lake Pavin)in Auvergne region. Study in the field of radioecology showsthat on the territory of the French Massif Central activity ofradionuclides has increased (>150 Bq/m3) in the houses ofthe Auvergne region [2].ConclusionIn the course of the work it was stated that highlyradioactive soil of Guangdong province has been formed dueFig. 7. The mineral xenotime with impurities of thorium and heavy rare earths in clay fraction (б), energy dispersivespectrum (в) and composition (а) in soil of Guangdong provinceto deep chemical weathering of highly radioactive potassiumgranites. High uranium and thorium contents in them arecaused by specific conditions of weathering crust formationand subsequent pedogenesis. The concentration ofradionuclides in soils depends on their content in theunderlying rocks.The soils of the region of Auvergne have high content ofuranium and low thoriumuranium ratio in the range 1–2.4.Uranium ore deposits (Limousin, Foretz, Morvan) are locatedin Auvergne region. The deposits are confined to the twomica granite massifs (San Silvestre et al.) With a high contentof uranium, which are located along the fault Argens. Thesoils of this region are autochthonous. As a currenthypothesis, it can be suggested that in our case the sorptionconcentration mechanism of U, Th, and rareearth elementshas revealed in kaolinitegibbsite soil aggregate. The highnatural radioactivity of soils in China’s Guangdong Provinceis associated with the high content of radioactive elementsin the predominantly fine clay fraction.According to electron microscopic analysis of the soilsof Guangdong province, mineral  concentrators of rareearth and radioactive elements are monazite, phosphatesof heavy rare earths, xenotime, and zircon.The elevated concentrations of natural radionuclides inthe soils lead to high concentrations of radon, which, in turn776Материалы V Международной конференции, г. Томск, 13–16 сентября 2016 г.causes ecological problems. Scientists have provennegative effects on human health associated with highaverage doses of radiation.  In the areas with increasedcontent of radionuclides chromosomal and genetic changes,leukemia, lung cancer, sarcoma, nasopharyngeal carcinomaetc. can be observed.References1. Eizenbud M., Geselit. Enviromental radioactivity fromnatural – industrials and military sources. – Academic Press,1997.2. Gal F., Gadalina A. Soil gas measurements around the mostrecent volcanic system of metropolitan France (lake Pavin,Massif Central) // Comptes Rendus Geosciences. – 2011. –Vol. 343, Issue 1. – P. 43–54.3. Rikhvanov L.P. Radioactive elements in the environmentand the radioecological problems: Manual. – Tomsk : TPUUniversity Press, 2009.4. Wang N., Peng A., L. Xiao. The level and distribution of 220Rnconcentration in soilgas in Guangdong province, China //Radiation Protection Dosimetry. – 2012. – Vol. 152, No.1–3. – P. 204–209.5. Wang N., Shengqing Xiong, Zhengguo Fan et al. Mappingthe terrestrial airabsorbed gamma dose rate based on thedata of airborne gammaray spectrometry in southern citiesof China //  Journal of Nuclear Science and Technology. –2012. – Vol. 49, No. 1. – P. 61–70.

The causes of high natural radioactivity in the soils and radioecological problems in areas with highly radioactive soils

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