Accumulation rates of natural radionuclides (40K, 210Pb, 226Ra, 238U, and 232Th) in topsoils due to long-term cultivations of water spinach (Ipomoea Aquatica Forssk.) and rice (Oryza Sativa L.) based on model assessments: A case study in Dong Nai province, Vietnam.

In topsoils, the activity concentrations of natural radionuclides (hereafter NRs) increase due to the addition of NRs from fertilizers, irrigation water, and air dust pollution. On the other hand, various physical-chemical and environmental processes such as radioactive decay, volatilization, leaching, erosion, and plant uptake were responsible for the decrease of the activity concentrations of NRs in the topsoils. In this study, behaviours of 40K, 210Pb, 226Ra, 238U, and 232Th in topsoils were modelled by the CEMC soil model and the HYDRUS-1D model. An exponential equation was proposed for estimating the accumulation rates of these radionuclides in the topsoils. Long-term accumulation of radionuclides was assessed for water spinach (Ipomoea Aquatica Forssk.) soil (hereafter VES) and rice (Oryza sativa L.) soil (hereafter RIS). We found that the current agricultural practices caused the increase of 40K activity concentration in the water spinach soil, and 40K, 210Pb, 226Ra, and 232Th activity concentrations in the rice soil. The accumulation rates of radionuclides were in the order 238U < 232Th < 226Ra < 210Pb < 40K. 25 years of cultivation with water spinach can increase/decrease + (165 ± 6) Bq of 40K, - (8.2 ± 0.7) Bq of 210Pb, - (4.3 ± 0.2) Bq of 226Ra, - (7 0.3 ± 0.3) Bq of 238U, and - (1.8 ± 0.1) Bq of 232Th in 1 kg soil. For rice cultivation, these values are + (1004 ± 39), + (3.3 ± 0.2), + (3.0 ± 0.2), - (5.1 ± 0.3), (2.2 ± 0.1) Bq kg-1 for 40K, 210Pb, 226Ra, 238U, and 232Th, respectively.

Modelling the mitigation speeds of 137Cs, 90Sr and 131I in the topsoils and assessment of the radiological hazards.

Fate modelling of artificial radionuclides (ARs) in top soils are necessary to assess the radiological effects to population. Among ARs, 137Cs, 90Sr and 131I are very important since the large abundances in the environment. In this study, the fates of 137Cs, 90Sr and 131I in the surface soil layers were simulated by the soil model which was developed by the Canadian Centre for Environmental Modelling and Chemistry (CEMC). The scenario that 137Cs, 90Sr and 131I contaminated in topsoil in the exclusion of Fukushima Daiichi nuclear power plant (NPP) accident was evaluated. The results show the expected time for the minimum hazardous level of exposure. It is 115.5 days after the exposure, when the total effective dose is 1 mSv y-1 in which 0.46 mSv y-1 from ingestion and 0.54 mSv y-1 from gamma exposure. Hazard levels due to exposure progresses are varied in order gamma exposure (82.14%) > ingestion (17.47%) > inhalation (0.39%). The hazard levels from radionuclides are varied in order 137Cs (63.34%) > 131I (33.48%) > 90Sr (3.18%).

Treatment for removing radium in soil and groundwater.

The results of 226Ra activity concentration measurements in 50 soil and groundwater samples in Ninh Son region, Vietnam were evaluated in the present study. Average activity concentration in the soils was significantly higher than the worldwide average concentration in soils published by UNSCEAR, 2008. 90% of groundwater samples had concentrations of 226Ra that were higher than the USEPA drinking water standard. The results showed that there was a linear correlation between the 226Ra radioactivity in the soils and the concentration of 226Ra in the groundwater samples. The procedure for removal of 226Ra from soil and groundwater samples was built upon the chemistry behavior of radium. 226Ra in contaminated groundwater samples was removed by using MnO2 fiber. The removal efficiency of 226Ra reached ∼ 91% for the groundwater samples and ∼ 70% for the soil samples. Chemical removal of 226Ra from soils was investigated using a three-step extraction procedure (Easily leachable and exchangeable, Acid-reducible, and Oxidisable-organic). A moderate mobility of 226Ra (22-52%) was noted and mainly found in acid-reducible fractions, which suggests that 226Ra is mainly bound to Fe/Mn oxides and hydroxides. A multiple regression indicates that the 226Ra removal efficiency appears to be significantly dependent on Fe/Mn and organic matter content.

Levels of 226Ra in groundwater samples collected in Phu Yen province, Vietnam associated with health risks to local population and impacts on the maize (Zea mays L.) soil.

Groundwater is a major source of drinking water and agricultural water in some regions of the world. However, it contains a high level of 226Ra that is potentially hazardous to human health and the environment. Normally, the activity concentration of 226Ra in groundwater is determined to assess the quality of groundwater that can be used as drinking water. There are few studies on the accumulation of 226Ra in the agricultural soil due to irrigation with groundwater. In this study, levels of 226Ra were determined on over 60 groundwater samples collected from the public water supply wells in Phu Yen province, Vietnam. Besides assessment of the health risks to population due to drinking groundwater samples, the impact of groundwater irrigation to the maize field in the study area was studied. For this purpose, two chemical fate models were applied and the comparison of their results was performed. Based on the model assessments, we predicted that the present agricultural practices increased the 226Ra activity concentration in the maize soil, and the level of 226Ra activity concentration in the topsoil can exceed the recommended level at 11.4 years of the present agricultural practices on the maize soil.

Soil radon gas in some soil types in the rainy season in Ho Chi Minh City, Vietnam.

Field experiments on soil radon and radium concentrations were carried out in eighteen locations in Ho Chi Minh City, Vietnam. Soil radon depth profiles (10-100 cm) of loam, sand and clay soil samples in the rainy season were measured using RAD7 radon detector. Mean concentrations of 222Rn and 226Ra were found to be 28.6 ±â€¯2.0 Bq.kg-1 and (1.56 ±â€¯0.06) × 104 Bq.m-3 in clay soil while they are 31.2 ±â€¯2.5 Bq.kg-1 and (1.15 ±â€¯0.05) × 104 Bq.m-3 in loam soil. They are 30.7 ±â€¯2.0 Bq.kg-1 and (9.37 ±â€¯0.52) × 103 Bq.m-3 in sandy soil, respectively. Values of radon diffusion length and diffusion coefficient for different soils were obtained using semi-empirical fit method linked to the poor diffusion of gas in clay soil (0.2 × 10-6 m2 s-1), the moderate diffusion coefficient (0.9 × 10-6 m2 s-1) in loam and good diffusion of radon gas in sandy soil (1.4 × 10-6 m2 s-1). An unexpectedly unclear linear relation was found between soil radon concentration and radium content. The grain size smaller than 0.1 mm was dominant reason for the lowest (0.15 ±â€¯0.01) and highest (0.40 ±â€¯0.03) values emanation coefficient for sand and clay soil, respectively. A strong positive correlation was found between radon concentration and soil pH level leads to soil pH is an indirect dynamic parameter affecting the migration of radon in soil.

Radon and radium concentrations in drinkable water supplies of the Thu Duc region in Ho Chi Minh City, Vietnam.

The results of (222)Rn and (226)Ra activity measurements in drinkable water supplies of the Thu Duc region in Ho Chi Minh City, Vietnam, are presented in this paper. The measurements were performed using a RAD 7 radon detector manufactured by Durridge Company, Inc. Mean concentrations of (222)Rn and (226)Ra were found to be 0.11±0.01Bql(-1) and 0.11±0.02Bql(-1) in 14 drinking water samples. They are 0.12±0.01Bql(-1) and 0.10±0.02Bql(-1) in 15 tap water samples, respectively. The mean (222)Rn concentration of 1.40±0.03Bql(-1) in the 20 groundwater samples of this study is also lower than the WHO advised level of 100Bql(-1). Fifty percent of groundwater samples analysed have (226)Ra levels in excess of the USEPA recommended maximum contaminant level of 0.185Bql(-1). The occurrence of elevated concentrations of (226)Ra in groundwater samples was explained by pH and alkaline conditions.