RESUMO

The term "commercial ornamental stones" comprises different natural stones with different mineralogical components and the distribution and amount of natural radionuclides depended on the mineralogy. Few studies on natural radioactivity in ornamental stones carried out in Rio de Janeiro (Brazil) and the present work were carried out in order to analyze the distribution of activity concentration in these materials. The activity concentration of 238U, 235U, 226Ra, 232Th and 40K in Ornamental Stones measured using γ-ray spectrometry to estimate the radiation hazard as well as establishing a database for radioactivity levels. Samples were collected in stores in Rio de Janeiro, carefully transported, weighed, packed with PVC film and left to rest for at least 45 days to reach secular equilibrium. Samples analyzed by gamma spectrometry using a hyper pure germanium detector (HPGE). Detection efficiency for each sample was obtained using LabSOCS software. The activity concentrations for samples were within the ranges (0.83 ± 0.15 to 39.96 ± 1.19, 8.04 ± 2.54 to 111.36 ± 13.33, 0.43 ± 0.03 to 264.58 ± 0.98, BDL to 8.17± 0.65 and 1.30 ± 0.57 to 1567.01 ± 65.08) Bq⋅kg-1 for 238U, 226Ra, 232Th, 235U and 40K, respectively. The world average for building materials is 50 Bq⋅kg-1 for 238U, 50 Bq.kg-1 for 232Th and 500 Bq⋅kg-1 for 40K. In the present work, the average for granite was 19.43 ± 0.39 Bq⋅kg-1 for 238U, 56.70 ± 1.13 Bq⋅kg-1 for 232Th and 1113.28 ± 20.27 Bq⋅kg-1 for 40K, thus the values for 232Th and 238U are above the world average. Analyzing for the granite that showed the highest concentrations of activity the average values of Transport Rate was 3.12 ± 0.04 Bq⋅m-2⋅s-1, Emanation Rate was 0.16 ± 0.00 Bq⋅kg-1⋅s-1, Exhalation Flow was 530.26 ± 6.05 Bq⋅m-3, Effective Equivalent Dose Due to Radon Exposure was 0.78 ± 0.01 WLM⋅year-1 and Annual Effective Dose Due to Radon and Thoron was 7.02 ± 0.10 mSv⋅year-1. Annual Effective Dose Due to Radon and Thoron it is above the annual limit for public individuals which is 1 mSv⋅year-1 and below the occupationally exposed individual, which is 20 mSv⋅year-1 in an average of 5 years, it does not exceed the maximum level recommended by ICRP-60.

RESUMO

Climate, soil type and geology that can influence the activity concentrations of natural radionuclides in soils. For this, 41 samples were collected in the first 25 cm of soil from the state of Alagoas, Northeast Brazil. This sample collection represents the mains soils classifications, parental rocks, and rainfall variability in this locality. The samples of soils were processed and analyzed by means of gamma-ray spectrometry for the 40K, 226Ra and 228Ra. The non-parametric Mann-Whitney U test was applied to perform the statistical inference on the differences in activity concentration for each soil class studied. There was a significant difference in the 40K activity distributions between the combination for most soil types. The results for 226Ra show no significant difference. However, Planosols differ significantly from Yellow Acrisols and Regosols for 228Ra. The strong relationship of the 40K concentration with the rock classes was shown. On the other hand, an association of the activity concentration of 226Ra and 228Ra with the rock type was not evidenced. There was a negative correlation between the 40K activity concentration and the rainfall index. 226/228Ra concentrations showed no correlation with the rainfall index.

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The activity concentrations of 40K, 210Pb, 210Po, 226Ra, 228Ra, 228Th, 230Th, 232Th, 234U, and 238U were determined in 82 food samples, grouped into 20 food groups according to the Brazilian Total Diet, which reflects the dietary habits of a population, for the rural and urban areas of Poços de Caldas city, a High Background Radiation Area. The highest activity concentration found in the food samples was due to 40K being present in all types of food. Among the other radionuclides, high activity concentrations were found for 210Pb in beans and salt, 210Po in fish, 226Ra and 228Ra in nuts and seeds. The main food groups that contributed most to the effective dose, in urban and rural regions, were beans and beverages. The effective doses, due to the ingestion of the analysed food groups, were of 0.44 and 0.60 mSv y-1 and the lifetime cancer risks were 1.6 × 10-3 and 2.3 × 10-3 for the urban and rural Poços de Caldas population, respectively.

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To investigate whether and in which extension the levels of natural radionuclides in soils vary with parent rock, soil type, and climatic condition factors, a large-scale survey was carried out to cover the semiarid and tropical wet climate regions of the territory of Pernambuco state (Brazil). The radionuclide concentrations were analyzed by gamma spectrometry. The median values of the activity concentrations of 226Ra (20), 228Ra (38) and 40K (458) (Bq kg-1) in the soils agreed with the values reported worldwide. The concentrations of 40K in the soils from the semiarid region were higher than those in the soils from the tropical region, whereas the radium isotope levels were higher in soils from the tropical region. The less-developed soils from the semiarid region, such as Leptosols and Neosols, had the highest 40K levels, unlike the more developed soils (Acrisols and Ferrosols) from the tropical wet area, which showed the lowest contents of 40K and the highest content of radium isotopes. The low 40K contents in well-developed soils may be attributed to the leaching of 40K by the high rainfall rates of the tropical area. In contrast, the rainfall scarcity and high potential evaporation rates of the semiarid environment may be responsible for 40K accumulation in soils. The highest Ra isotope concentrations in the well-drained soils from the tropical climate may be ascribed to the presence of heavy minerals and adsorption on Fe oxyhydroxides, which are very common in those soils. The more developed the soil the lower the K concentration, regardless of the climate. For Ra, the differences are more significant for well-drained soils, and in this case, the tropical climate, with its high rainfall rate, makes the difference. As a conclusion, climate and soil formation time showed high and contrasting influence on the 40K and radium isotope contents in soils. Less developed soils from semiarid had the highest content of 40K, whereas the more developed soils from tropical areas had the highest content of radium.

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Located in the south-western part of Brazil, the state of Rio de Janeiro is geotectonically contained within a complex structural province that resulted in the amalgamation of the Western Gondwana Paleocontinent. To undertake an extensive radiological characterization of this complex geological province and investigate the influence of bedrock, soil type and soil chemical-physical characteristics on natural radionuclide levels in soils, 259 surface soil samples were collected that encompassed the main soil types and geological formations throughout the state. Gamma spectrometry analysis of the samples resulted in median values of 114 Bq.kg-1for 40K, 32 Bq.kg-1 for 226Ra and 74 Bq.kg-1 for 228Ra. The median value for 226Ra was similar to the world median value for soils, the 40K value was well below the worldwide value, and that for 228Ra exceeded the world median value. The intense weathering caused by the high rainfall rates and high temperatures may be responsible for the low levels of 40K in the soils, of which the strongly acidic and clayey soils are markedly K-depleted. A soil from a high-grade metamorphic rock (granulite) presented the lowest 226Ra (18 Bq.kg-1) content, whereas the highest levels for 226Ra (92 Bq.kg-1) and 228Ra (139 Bq.kg-1) were observed in a young soil enriched in primary minerals (Leptsol). A lowland soil (Gleysol) showed the highest median of 40K (301 Bq.kg-1). Strongly acidic soils tended to present high amounts of 226Ra, and sandy soils tended to contain low levels of 228Ra. The external radiation dose indicates that the state has a background radiation level within the natural range.

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The main phosphate industries in Brazil are responsible for the annual production of 5.5 million tons of a residue (phosphogypsum), which is stored in stacks. The presence of radionuclides and metals puts restrictions on the use of phosphogypsum in agriculture. To assure a safe utilization, it is important to estimate the lixiviation of the radionuclides ((238)U, (226)Ra, (210)Pb, (210)Po, (232)Th and (228)Ra) and metals (As, Cd, Cr, Ni, Se, Hg and Pb) present in phosphogypsum. For this purpose, an experiment was carried out, in which columns filled with sandy and clay Brazilian typical soils mixed with phosphogypsum were percolated with water, to achieve a mild extraction of these elements. The results obtained for the concentration of the radionuclides and metals in the leachate were low; giving evidence that, even when these elements are present in the phosphogypsum, they do not contribute to an enhancement of their content in water.

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The accumulation, enrichment and provenance of selected trace metals (Ag, As, Cd, Cr, Cu, Hg, Ni, Pb, V and Zn) were studied in sediment cores collected from three lakes located in the Central Mexican Plateau, selected on the basis of their contrasting degree of urbanization: Santa Elena Lake, in a rural and remote area; El Tule Lake, in a rural and slightly urbanized area; and Chapala Lake, in a highly urbanized area. Grain size, magnetic susceptibility and sedimentary constituents such as organic carbon, calcium carbonate, as well as major (Al, Fe, Mn) and minor (Ca, Li, Rb, Sr, Th) elements were analyzed to explain the concentration trends of trace metals. Factor analysis (FA) was used to assess the provenance of the trace elements. The highest metal enrichment factor (EF) above natural concentration levels was found at Chapala Lake for Ag (EF = 3.9), although other trace element EF in all lakes was <2.0, indicating slight contamination. However, the concentration levels of Cr and Ni in all lakes, Hg and Zn in Chapala Lake, Cu in El Tule Lake and As in Santa Elena Lake were above international benchmarks for which adverse effects are expected to occur frequently, even for those metals only slightly enriched (e.g. As, Cr). Through FA, the terrigenous contribution was identified as the most important source of trace metals to the three lakes, most likely related to deforestation and erosion of the surrounding areas, followed by atmospheric transport of volcanic ashes, rather than to direct sources.

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