Distribution of natural and artificial radioactivity in soils, water and tuber crops

Soil-to-plant transfer factors of uranium and thorium in mining and non-mining districts of Ghana

The activity concentrations of natural radionuclides in water, soil, cassava, cocoyam and yam grown in two mining districts and a non-mining district in Ghana were determined using a high-resolution gamma spectroscopy system with high-purity germanium detector. The estimated absorbed dose for soil from Amansie, Konongo, and Mampong were 206 nGy/h, 224 nGy/h and 198 nGy/h, respectively, which were all above 60 nGy/h set by the United Nations Scientific Committee on the Effects of Atomic Radiation. The soil-to-plant transfer factors (TF) for 2³⁸U, 2³2Th, and ⁴⁰K ranged from 0.11 to 1.11, 0.03 to 2.39, and 0.03 to 22.07, respectively. The results showed that the highest TF for 238U and 232Th were 1.11 and 2.39, respectively in cassava. There was no significant variation in the TF of 238U and 232Th among the soils in the different communities. The estimated transfer factors for 238U and 232Th for cassava, cocoyam and yam were higher than that reported by the International Atomic Energy Agency.

Study of activity concentrations of 40K, 238U and 232Th for assessment of radiation dose in agricultural soils of southwestern Nigeria

Gamma spectrometric measurement of natural radionuclides activity concentrations by HPGe detectors was conducted in 150 agricultural soil samples collected from six states of southwestern Nigeria. The overall activity concentrations of radionuclides ranged from 15.27 to 972.00 Bqkg-1 for 40K, 0.66 to 336.19 Bqkg-1 for 232Th and 1.32 to 123.01 Bqkg-1 for 238U, with mean values of 143.95, 17.02 and 22.92 Bqkg-1, respectively. The overall averages results from this study were generally lower than worldwide average value of 420, 33 and 45 Bqkg-1 for 40K, 238U and 232Th, respectively, thus minimal transfer to plant may be expected. The estimated radiation dose levels of the soil indicated acceptable limits for general public exposure. The radioactivity levels of 40K, 232Th and 238U in the investigated agricultural soil of southwestern Nigeria are within acceptable limits. Therefore, stochastic radiological health effects of radiation exposure by farmers may not be feasible at the current moment.

Ingestion exposure of public to natural radionuclides and committed effective dose and cancer risk through tuber crops cultivated in Ebonyi State, Nigeria

Internal exposure of public to radiation arising from ingestion of natural radionuclides in tuber crops of Ebonyi State origin was investigated in this study. Committed effective doses and lifetime cancer risk of 40K, 226Ra, and 232Th in cassava, cocoyam, water yam, and white yam were calculated. The average activity concentrations of 40K, 226Ra, and 232Th determined by gamma spectrometric Na (TI) detector were, respectively, 199.15 ± 23.51, 77.57 ± 7.98, and 118.20 ± 10.72 Bq/kg in cassava; 146.62 ± 40.69, 43.42 ± 7.63, and 75.61 ± 2.89 Bq/kg in cocoyam; 162.81 ± 20.43, 63.17 ± 11.36, and 81.50 ± 10.27 Bq/kg in water yam; and 184.50 ± 20.22, 80.23 ± 10.93, and 116.29 ± 5.93 Bq/kg in white yam. The total committed effective dose via ingestion aligned in this order of cassava (7.05 mSv/year) > white yam (4.38 mSv/year) > water yam (0.42 mSv/year) > cocoyam (0.21 mSv/year) with overall average dose of 3.12 mSv/year. The values of dose were higher than world average of 0.29 mSv/year given by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). The lifetime cancer risk values were above tolerance level of >10-4 prescribed by United States Environmental Protection Agency (USEPA), suggesting probable evolvement of radiogenic cancer morbidity. The data presented in this study contributes to baseline information on radiological characteristics of tuber crops in Ebonyi, which would be valuable to WHO/FAO food safety policy in Nigeria and rest of the world.

Gamma spectroscopy study of soil-plant transfer factor characteristics of 40K, 232Th and 226Ra in some crops cultivated in southwestern region of Nigeria

Soil-plant transfer factor (TF) is one of the vital variables employed in assessing plants uptake of radionuclides and their transfer to food chain for predictive ingestion dose and risk evaluation. To further this goal, the TF characteristics of natural 40K, 232Th and 226Ra were thus investigated in some crops (yam, cassava, rice, maize, groundnut, cowpea, okra, pumpkin leaf, banana and pawpaw) cultivated in southwestern part of Nigeria using HPGe gamma spectroscopy. The obtained results of activity concentration (AC) of the radionuclides across all the cultivated soil samples indicated average values that are less than the global average, whereas in the crops, average values of 226Ra and 232Th, were higher than reference values for different crops group. The overall range of the calculated TF of 40K, 232Th and 226Ra across all the crops was 0.05 (in maize and cowpea) to 15.01 (in banana), 0.01 (in pumpkin leaf and groundnut) to 19.80 (in pawpaw), and 0.04 (in cassava) to 21.30 (in cowpea), respectively. Overall arithmetic mean and geometric mean were estimated as 2.66 and 1.60, 1.11 and 0.43, and 1.10 and 0.54 for 40K, 232Th and 226Ra, respectively. TFs mostly correlated negatively with soil radionuclides, while positive correlation was mostly noticeable in the case of crop. Log normal transform of the TFs data indicated a near normal distribution as against the calculated data. The derived results of this study is here presented as a baseline data suggested for possible radiological risk assessment of food chain of the local population.

Activity concentrations and radiological hazard assessments of 226Ra, 232Th, and 40K in soil samples of oil-producing areas of South Africa

The specific activity of natural radionuclide in soil samples of the oil-producing areas of South Africa was measured using a High Purity Germanium detector. The activity of226Ra, 232Th, and 40K in the soil range from 16.5 ± 1.3 to 64.9 ± 3.1, 16.8 ± 1.5 to 88.6 ± 1.2, 135.2 ± 17.5 to 604.8 ± 13.4 Bqkg-1 for Mossel Bay; 14.3 ± 1.2 to 48.9 ± 8.2, 22.3 ± 1.4 to 45.1 ± 3.2, 237.7 ± 10.9 to 486.5 ± 40.1 Bqkg-1 for Cape Town; 10.5 ± 1.1 to 25.8 ± 3.2, 13.1 ± 1.9 to 44.3 ± 5.2, 140.2 ± 10.9 to 229.8 ± 12.8 Bqkg-1 for Nelson Mandela Bay and 5.6 ± 2.2 to 13.1 ± 2.9, 4.5 ± 2.5 to 14.1 ± 2.7, 62.7 ± 22.6 to 126.5 ± 21.2 Bqkg-1 for Msunduzi. Most soil samples' radiological hazards were within the world average.

Soil-to-plant transfer factors of 238U and 232Th in rice from Ezillo paddy fields, Ebonyi State, Nigeria

The uptake of radionuclides by plants and their subsequent relocation to the human body through ingestion is one major pathway of human internal exposure. Thus, the present study was conducted to examine the levels of natural radionuclides, ²³⁸U and ²³²Th, in soil of Ezillo paddy fields (field 1 and field 2) at depths 0-4 cm and 4-8 cm, their transfer and accumulation in rice grains. The mean concentrations of both radionuclides in the soil were clearly greater than the UNSCEAR estimated worldwide average while that of the rice with values of 11.7 ± 4.3 and 3.0 ± 1.3 Bq/kg in field 1 and 8.5 ± 4.2 and 4.3 ± 1.6 Bq/kg in field 2 for ²³⁸U and ²³²Th respectively, were well below the worldwide average. The radionuclide transfer factors (TFs) across both depths ranged from 0.03 to 0.67 and 0.01 to 1.20 for ²³⁸U and ²³²Th respectively. The overall geometric means and geometric standard deviations of the TF estimated in field 1 were respectively 0.22 and 1.52 for ²³⁸U and 0.18 and 4.21 for ²³²Th (soil_,0-4cm); 0.43 and 1.80 for ²³⁸U and 0.18 and 3.79 for ²³²Th (soil_,4-8cm) whereas in field 2 the values were respectively 0.12 and 2.62 for ²³⁸U and 0.06 and 4.15 for ²³²Th (soil_,0-4cm); 0.11 and 1.85 for ²³⁸U and 0.12 and 4.15 for ²³²Th (soil_,4-8cm). The nuclide concentrations in the rice and the present TFs are within the ranges of values in the literature.

Soil-to-crop transfer of natural radionuclides in farm soil of South Africa

The activity concentration of natural radionuclides in farm soil and most common indigenous food crops (maize, potato, cowpea) in oil-producing (Philippi, Uitenhage, and Hertenbos farms) and non-oil-producing (Ukulinga farm) areas of South Africa was measured using a Hyper Pure Germanium detector. Consequently, the transfer of these radionuclides from soil-to-crops was estimated. The mean activity concentration of ²²⁶Ra, ²³²Th, and ⁴⁰K for farm soil samples are 30.71 ± 11.77, 31.97 ± 8.90, 345.97 ± 98.62 Bq.kg^-1 for Philippi; 18.67 ± 6.70, 31.55 ± 11.48, 191.93 ± 33.39 Bq.kg^-1 for Uitenhage; 38.03 ± 17.44, 41.18 ± 31.54, 381.89 ± 163.40 Bq.kg^-1 for Hartenbos; and 8.47 ± 2.87, 8.65 ± 3.52, 94.22 ± 25.97 ± 25.97 Bq.kg^-1 for Ukulinga. The mean activity concentration of ²²⁶Ra, ²³²Th, and ⁴⁰K for crop samples are 4.54 ± 1.47, 4.87 ± 1.69, 140.18 ± 35.38 Bq.kg^-1 for Philippi; 9.17 ± 4.79, 3.85 ± 1.87, 136.75 ± 22.04 Bq.kg^-1 for Uitenhage; 7.97 ± 2.91, 4.62 ± 2.40, 105.97 ± 48.65 Bq.kg^-1 for Hartenbos; and 4.23 ± 1.63, 2.72 ± 1.19, 48.36 ± 15.55 Bq.kg^-1 for Ukulinga. The activity concentration and soil-to-crop transfer factors for ⁴⁰K were found to be much higher, possibly because this element is critical in crop growth. The results showed that the crop samples' transfer factor is in the order cowpea>potato>maize. This study showed that activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K in crops and the corresponding transfer factors depend on activity concentrations of the same radionuclides in soil.

The assessment of the annual effective dose due to ingestion of radionuclides from drinking water consumption: calculation methods

In the present paper the different ways of assessing the annual effective dose due to ingestion of radionuclides by drinking water consumption were examined and exemplified. On a set of 10 samples the gross alpha activity, the gross beta activity, the concentration of 210Po, 210Pb, 238U, 232Th and, 226Ra were measured. The highest annual effective dose values assessed by relying on the investigated sample set were found by using the rationale according to which all the gross alpha and beta activity is due to the alpha and beta radionuclide, with the highest effective dose coefficient, namely 210Po and 210Pb/228Ra, respectively.

A national survey of natural radionuclides in soils and terrestrial radiation exposure in Iran

In the past, some efforts have been made for measuring natural radioactivity and evaluating public exposure to natural radiation in certain areas of Iran especially in well-known High Level Natural Radiation Areas (HLNRA) in Ramsar and Mahallat. However, the information on radionuclide concentrations, and, consequently, terrestrial radiation exposure for many other areas are not available. There was therefore a need for a systematic and nation-wide survey. For this purpose, 979 soil samples from 31 provinces were collected. The activity concentrations of ⁴⁰K, ²²⁶Ra and ²³²Th were measured by HPGe detector. The average activity concentrations for Iran were found to be 457.7 Bq/kg for ⁴⁰K, 24.3 Bq/kg for ²²⁶Ra and 25.8 Bq/kg for ²³²Th. Results were compared with previous regional or provincial surveys. The population-weighted average outdoor and indoor annual effective dose due to external exposure to terrestrial sources of radiation are 0.06 mSv and 0.33 mSv, respectively. It was shown that there is a significant correlation between the activity concentrations of ²³²Th and ⁴⁰K in soil. In addition, the results of chi square tests show normal and lognormal distributions cannot be considered for the frequency distributions of activity concentration of ²³²Th and ²²⁶ Ra while ⁴⁰K has a normal distribution.

Environmental-Impact Assessment of Natural Radioactivity Around a Traditional Mining Area in Al-Ibedia, Sudan

Recently, in the Sudan, traditional gold mining has been growing rapidly and has become a very attractive and popular economic activity. Mining activity is recognized as one of the sources of radioactivity contamination. Hence, the radioactivity concentration and radiological hazard due to exposure of radionuclides (226)Ra, (232)Th, and (40)K were evaluated. The measurements were performed using gamma-ray spectrometry with an NaI (Tl) detector. The results show that (226)Ra, (232)Th, and (40)K activity concentration ranged from 2.66 to 18.47, 9.20 to 51.87, and 0.17 to 419.77 Bq/kg with average values of 7.54 ± 4.91, 20.74 ± 11.29, and 111.87 ± 136.84 Bq/kg, respectively. In contrast, (222)Rn in soil, (222)Rn in air, and (226)Ra in vegetables along with radiation dose were computed and compared with the international recommended levels. Potential radiological effects to miners and the public due to (226)Ra, (232)Th, (40)K, and (222)Rn are insignificant. (226)Ra transferred to vegetables appears to be negligible compared with the allowable limit 1.0 mSv/year set by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). The average value of the annual gonadal dose equivalent (AGDE) is lower than the global average of 300 µSv/year (UNSCEAR 2000). However, some locations exhibit values >300 µSv/year. To the best of our knowledge, so far there seems to be no data regarding radioactivity monitoring in traditional mining areas in the Sudan.