Radionuclides In Surface Soil Research Articles

Change of the Asian dust source region deduced from the composition of anthropogenic radionuclides in surface soil in Mongolia

Abstract. Recent climate change, especially during the 2000s, may be the primary reason for the expansion of the Asian dust source region. The change in the dust source region was investigated by examining anthropogenic radionuclides contained in surface soil samples from Mongolia. Surface soil was globally labeled by radioactive fallout from nuclear testing during the late 1950s and early 1960s, but there are no current direct sources for anthropogenic radionuclides in the air (before the Fukushima nuclear power plant accident in 2011). Radionuclides in the atmosphere are therefore carried mainly by wind-blown dust from surface soil, that is, aeolian dust. Asian dust carries traces of 90Sr, 137Cs, and other anthropogenic radionuclides; the heaviest deposition occurs in spring and has been recorded in Japan since the early 1990s. The composition of anthropogenic radionuclides in atmospheric depositions would be affected by a change in the dust source. Previous studies of atmospheric deposition at long-term monitoring sites (e.g. in Tsukuba, Japan) have detected changes in the 137Cs/90Sr ratio and in the specific activity of the radionuclides. These changes in the composition of observed atmospheric depositions are supposed to reflect changes in the climatic conditions of the dust source region. To investigate this dust source change, we conducted a field survey of radionuclides (90Sr and 137Cs) in surface soil samples in September 2007 in the eastern and southern regions of Mongolia, where dust storms have occurred more frequently since 2000. The specific activities of both radionuclides as well as the 137Cs/90Sr ratio in the surface soil were well correlated with annual average precipitation in the Mongolian desert-steppe zone. Higher specific activities and a higher 137Cs/90Sr ratio were found in grassland regions that experienced greater precipitation. These findings suggest that the increased specific activities and the activity ratio detected in atmospheric depositions in Japan during years with frequent Asian dust transport events in the 2000s are a sign of grassland degradation.

Natural radionuclide emission from coal-fired power plants in the southwestern of Turkey and the population exposure to external radiation in their vicinity

To evaluate the effect of radionuclide emission on the environment from Yataǧan, Yeniköy and Kemerköy coal-fired power plants which are located in southwestern Anatolia of Turkey, the concentrations of natural radionuclides such as 226Ra, 232Th and 40K in coal, bottom ash and fly ash samples, have been measured, as well as the concentration of the same radionuclides in surface soils. The dose rate arises from the total radioactivity content of soil that the people living by the power plants are exposed to be assessed additionally. The average activity concentrations of 226Ra for Yataǧan CPP is 80 ± 22 Bq kg–1 ranging from 56 to 131 Bq kg–1, for Yeniköy CPP is 138 ± 20 Bq kg–1 ranging from 115 to 189 Bq kg–1, for Kemerköy CPP is 238 ± 80 Bq kg–1 ranging from 134 to 356 Bq kg–1 in coal; average activity concentrations of 226Ra in fly ash and in bottom ash for above-mentioned power plants are 334 ± 60 Bq kg–1 ranging from 291 to 481 Bq kg–1, 461 ± 33 Bq kg–1 ranging from 398 to 511 Bq kg–1, 815 ± 254 Bq kg–1 ranging from 316 to 1260 Bq kg–1, 276 ± 51 Bq kg–1 ranging from 222 to 349 Bq kg–1, 285 ± 69 Bq kg–1 ranging from 213 to 409 Bq kg–1, 743 ± 234 Bq kg–1 ranging from 366 to 1098 Bq kg–1, respectively. The radionuclides activity concentrations of surface soil in the vicinity of coal-fired power plants are 32 ± 9 Bq kg–1 (18–53 Bq kg–1) for 226Ra, 37 ± 16 Bq kg–1 (17–89 Bq kg–1) for 232Th, 455 ± 165 Bq kg–1 (203–794 Bq kg–1) for 40K relevant to Yataǧan CPP; 42 ± 30 Bq kg–1 (9–168 Bq kg–1) for 226Ra, 32 ± 14 Bq kg–1 (6–74 Bq kg–1) for 232Th, 365 ± 151 Bq kg–1 (117–937 Bq kg–1) for 40K relevant to Yeniköy and Kemerköy CPP. As a result, average dose rates in the vicinity of coal-fired power plants have been calculated to be 56 ± 16 nGy h–1 ranging from 30 to 100 nGy h–1 for Yataǧan CPP, 54 ± 22 nGy h–1 ranging from 15 to 126 nGy h–1 for Yeniköy and Kemerköy CPP. To sum up, the natural radionuclide activity concentrations of burnt coal and ashes thrown out from these three power plants are quite high relative to the world average UNSCEAR[ 1 ] data. In addition, the average 226Ra, 232Th and 40K activity concentration values of surface soil samples and the calculated gamma dose rates in the vicinity of power plants were located within the worldwide intervals reported by UNSCEAR,[ 30 ] with some local differences.

First measurements of anthropogenic and natural radionuclides in surface soils (10cm) of Côte d'Ivoire

Abstract 239–240Pu and 137Cs activities in soil samples were measured in two sites of the littoral part of Cote d'Ivoire: Abidjan and the classified forest of “la Comoe”. Two areas were chosen: a forest and a clearing. The aim of this work is to establish a starting point for nuclear contamination data of a non-nuclear country. Measured soil cores were of 10 cm depth. 137Cs and 239–240Pu activities, mainly due to weapon nuclear tests in the 1960s, were in the range 0.37–2.3 and 0.023–0.125 Bq kg−1 respectively. 239–240Pu/137Cs values were found to be about 0.024–0.19 in agreement with the expected value for nuclear tests.

Modeling the inhalation enhancement factor in prospective radiological risk assessment

Inhalation of suspended particulates originating from contaminated soil is an important exposure pathway that may result from disposal of long-lived solid radioactive waste. A hypothetical scenario was evaluated involving long-term irrigation of agricultural land with contaminated water and ensuing accumulation of radionuclides in surface soil. One of the factors affecting the dose from inhalation of suspended soil particulates is the radionuclide enhancement (enrichment) in airborne soil particles relative to that of the underlying soil. The enhancement factor (enrichment factor) is defined as a ratio of airborne particle activity concentration (Bq kg-1 ) to surface soil activity concentration (Bq kg-1 ). The values of this parameter and its effect on inhalation dose were evaluated for different soil types and inhalation exposure conditions.

Radioactivity concentrations and dose assessment for soil samples around Adana, Turkey

The concentrations of natural radionuclides in surface soils around Adana, Turkey were determined using gamma ray spectrometry with an HPGe detector. The natural gamma ray radioactivity of the terrestrial radionuclides in air was calculated throughout different areas of Adana. The average activity concentrations of 238U, 232Th and 40K were found to be 17.6, 21.1 and 297.5 Bq kg −1, respectively. Outdoor gamma dose measurements in air 1 m above ground level were determined by using a portable gamma scintillation detector. The gamma dose measurements in air were taken from the same places where soil samples were taken. Average outdoor gamma dose rates in sample stations were determined as 67 nGy h −1. The annual effective dose to the public was found to be 82 μSv.

URANIUM PARTITION COEFFICIENTS (K d) IN FOREST SURFACE SOIL REVEAL LONG EQUILIBRIUM TIMES AND VARY BY SITE AND SOIL SIZE FRACTION

The environmental mobility of newly deposited radionuclides in surface soil is driven by complex biogeochemical relationships, which have significant impacts on transport pathways. The partition coefficient (Kd) is useful for characterizing the soil-solution exchange kinetics and is an important factor for predicting relative amounts of a radionuclide transported to groundwater compared to that remaining on soil surfaces and thus available for transport through erosion processes. Measurements of Kd for 238U are particularly useful because of the extensive use of 238U in military applications and associated testing, such as done at Los Alamos National Laboratory (LANL). Site-specific measurements of Kd for 238U are needed because Kd is highly dependent on local soil conditions and also on the fine soil fraction because 238U concentrates onto smaller soil particles, such as clays and soil organic material, which are most susceptible to wind erosion and contribute to inhalation exposure in off-site populations. We measured Kd for uranium in soils from two neighboring semiarid forest sites at LANL using a U.S. Environmental Protection Agency (EPA)-based protocol for both whole soil and the fine soil fraction (diameters<45 microm). The 7-d Kd values, which are those specified in the EPA protocol, ranged from 276-508 mL g-1 for whole soil and from 615-2249 mL g-1 for the fine soil fraction. Unexpectedly, the 30-d Kd values, measured to test for soil-solution exchange equilibrium, were more than two times the 7-d values. Rates of adsorption of 238U to soil from solution were derived using a 2-component (FAST and SLOW) exponential model. We found significant differences in Kd values among LANL sampling sites, between whole and fine soils, and between 7-d and 30-d Kd measurements. The significant variation in soil-solution exchange kinetics among the soils and soil sizes promotes the use of site-specific data for estimates of environmental transport rates and suggests possible differences in desorption rates from soil to solution (e.g., into groundwater or lung fluid). We also explore potential relationships between wind erosion, soil characteristics, and Kd values. Combined, our results highlight the need for a better mechanistic understanding of soil-solution partitioning kinetics for accurate risk assessment.

Distribution of primordial radionuclides in surface soils from Serbia and Montenegro

The specific activities of primordial radionuclides in soil samples from 21 different locations in Serbia and Montenegro were determined by gamma-ray spectrometry. The results obtained were compared with those from other studies conducted worldwide. Concentrations of radionuclides in soils analyzed in this study ranged from 1.28 to 4.80 ppm for uranium, from 5.26 to 19.0 ppm for thorium, and from 0.97% to 2.87% for potassium. The mean concentrations of U (2.76 ppm) and Th (10.4 ppm) are similar to the world average (2.64 and 11.1 ppm for U and Th, respectively), whereas the mean concentration of K (1.98%) is about 1.4 times higher than world average value (1.37%).

Dose assessment due to terrestrial gamma radiation in Ibadan, South Western Nigeria

The activities of primordial radionuclides in surface soil at Ibadan, South-Western Nigeria have been measured with a 7.6cm x 7.6cm NaI(TL) detector. The mean absorbed dose rate, annual effective dose and the collective effective dose at Ibadan were evaluated from measurement of 40K; 238U; 232Th activities and their mean values found to be 0.070 ± 0.008 mGy.h-1, 86.1 mSv.y-1 and 344.2 man Sv.y-1, respectively. Keywords: soil; dose; effective; collective; 40K; 238U; 232Th; exposure [Global Jnl Pure & Appl. Sci. Vol.9(3) 2003: 393-396]

Characterization of hot particles in surface soil around the Chernobyl NPP

Surface soil samples (0–1 cm) were collected to understand the role of hot particle (HP) in migration of radionuclide approximately 11 years after the Chernobyl accident. Three types of HPs were found by the analyses using alpha-track technique and scanning electron microscopy/energy dispersive X-ray spectrometer (SEM/EDX). The dissolution of HPs has been affected by the existing type of HPs. Six-stage sequential selective extraction procedure was carried out to define the chemical forms of uranium, 241Am and 137Cs. The chemical form of radionuclides in surface soil is significantly different between the west and the north traces of radioactive plumes approximately 11 years after the accident.

Environmental radionuclides in surface soils of Vietnam.

A database on U, Th, K, and Cs in surface soils was established to provide inputs for the assessment of the collective dose to the population of Vietnam and to support soil erosion studies using Cs as a tracer. A total of 292 soil samples was taken from undisturbed sites across the territory and the concentrations of radionuclides were determined by gamma spectrometry method. The multiple regression of Cs inventories against characteristics of sampling locations allowed us to establish the distribution of Cs deposition density and its relationship with latitude and annual rainfall. The Cs deposition density increases northward and varies from 178 Bq m to 1,920 Bq m. High rainfall areas in the northern and central parts of the country have received considerable Cs inputs exceeding 600 Bq m, which is the maximum value that can be expected for Vietnam from the UNSCEAR global pattern. The mean activity concentrations of naturally occurring radionuclides U, Th, and K are 45, 59, and 401 Bq kg, respectively, which entail an average absorbed dose rate in air of 62 nGy h, which is about 7% higher than the world average.

Measurement of natural radioactivity levels in soil in Tripoli

The activity concentration of radionuclides in surface soil around Tripoli metropolitan area have been measured using gamma-ray spectrometry. The average radioactivity concentrations of 238U, 232Th and 40K are 10.5, 9.5 and 270 Bq kg −1 respectively. The average outdoor terrestrial absorbed dose rate in air from gamma-radiation 1 m above the ground surface 23 nGy h −1.

Measurement of Radioactivity Levels in Soil in the Nile Delta and Middle Egypt

Concentrations of radionuclides in surface soil across the Nile Delta, the north coast of Egypt, and Middle Egypt have been measured using a hyperpure germanium spectrometer. The concentrations obtained for 40K, the 232Th series, and the 226Ra series are expressed in Bq kg-1 of dry weight, and the exposure rates are expressed in nGy h-1 of wet weight. The activity concentrations of 137Cs in soil are expressed in Bq m-2.

Determination of concentrations of selected radionuclides in surface soil in the U.S.

Background radionuclide concentrations in surface soil across the U.S. have been measured by the Remedial Action Survey and Certification Activities Group of the Health and Safety Research Division at Oak Ridge National Laboratory (ORNL). These measurements have been made as part of the ORNL program of radiological surveillance at inactive uranium mills and sites formerly utilized during Manhattan Engineer District and early Atomic Energy Commission projects. The background soil sampling program involved determination of 226Ra, 232Th and 238U concentrations in surface soil samples for comparative purposes to determine the extent of contamination present at the survey sites and surrounding off-site areas. The sampling program to date has provided background information at 356 locations in 33 states. The nationwide average concentrations of 226Ra, 232Th and 238U in surface soil were determined to be 1.1, 0.98 and 1.0 pCi/g, respectively. This paper summarizes the results of these background measurements and provides a brief analysis of regional differences and similarities in data values.

Characterization of Radionuclide Behavior in Low-Level Waste Sites

Our laboratory is investigating the subsurface migration of radionuclides in groundwater at the Maxey Flats, Kentucky, shallow land burial site and at a low-level aqueous waste disposal facility. At Maxey Flats, radionuclide and tracer data indicate groundwater communication between a waste trench and an adjacent experimental study area. Areal distributions of radionuclides in surface soil confirm that contamination at Maxey Flats has been largely contained on site. Of the radionuclides detected in the surface soil, only 3H and 60Co concentrations appear to be derived from waste. Plutonium exists in the anoxic subsurface waters at Maxey Flats as a reduced, anionic complex; some of the plutonium appears to be complexed with EDTA, whereas organic acids seem to be associated with 137Cs and 90Sr. At the aqueous waste disposal site, 3H and mainly anionic species of certain radionuclides, including 60Co, 106Ru, 99Tc, 131I, and traces of 238,239,240Pu, appear to migrate from a trench through soil adjacent to the trench. Radionuclides in the particulate and cationic forms appear to be efficiently retained by the soil. In general, observations indicate that the physicochemical form of the radionuclides mediates their subsurface migration in groundwater at both waste disposal sites.

Distribution of Radionuclides in Surface Soil and Bottom Sediment in the District of Jessore, Bangladesh and Evaluation of Radiation Hazard

This paper presents the first reports on the natural and anthropogenic radionuclides in soil and sediment of Jessore, a south-western district of Bangladesh. Surface soil and freshwater sediment were collected from in and around some major water-bodies of this district. To assess the radiological hazard of the natural radioactivity, the radium equivalent activity, the absorbed dose rate, and the external and internal hazard indices were calculated. In the soil and sediment in general, the activity concentration of 232Th was found to be higher than that of 226Ra, while that of 40K markedly exceeds the values of both 226Ra and 232Th. The average activities of 226Ra and 232Th in this area were found to be higher than the world average. There was no activity due to fallout (137Cs) in this area. The radium equivalent activity and the absorbed dose rate due to the natural radionuclides were found to be respectively lower and higher than the world average. The external and internal hazard indices were found to be well below the hazard limit of unity. Our results compare fairly well with other published results. Key words: Soil, Sediment, Natural lake, Radioactivity, Dose rate DOI: 10.3329/jbas.v33i1.2956 Journal of Bangladesh Academy of Sciences, Vol. 33, No. 1, 117-130, 2009