| On March 11, 2011, the Fukushima Nuclear Power Plant accident occurred as a consequence of a big earthquake and the subsequent tsunami. The accident released large amounts of radionuclides into the land and ocean environment. As a result, radioactive contamination of food aroused great concern. In this paper, we summarized and analyzed the detection methods and control measures of radioactive contamination in food at home and abroad, studied the applicaition of sourceless efficiency calibration gamma spectrometry method in radioactive contamination of food, investigated the radioactivity concentration in seafood around the Qingdao coast, and systematically evaluated the effects of topsoil removal practice and fertilization on radioactive cesium concentration of rice. The main contents and results are as follows:(1) The detection method of sourceless efficiency calibration gamma spectrometry for the determination of radionuclide activity concentration in food was established. The relative standard deviations(RSD) of measurement results were less than 10%. According to the analysis results of the influencing factors of sourceless efficiency calibration method, the detection efficiency of different energies decreased with the the geometric parameters(height, diameter and volume) and chemical composition of the samples. In addition, the geometric parameters and chemical composition of the samples markedly influenced the measurement of radionuclides emitting low-energy photons(< 200 keV) but has minimal impact on the measurement of radionuclides emitting high-energy photons(> 200 keV). In addition, when the ratio of diameter and height for different volume of cylindrical samples was 3–4, better detector efficiency was obtained.(2) In this study, the activity concentrations of radionuclides were estimated in 11 different marine species(Chub mackerel, Sardina, Largehead hairtail, Sea catfish, European perch, Redwing searobin, Yellow croaker, Crawfish, Short necked clam, Sea snail and Kelp) collected around the Qingdao coast in China, and we calculated the internal radiation doses to both the marine biota and human beings. The results showed that the mean 226 Ra activity concentration was 0.39±0.45 Bq kg-1 w.w. for all the collected seafood samples and ranged from 0.08±0.03 Bq kg-1 w.w. to 1.65±0.60 Bq kg-1 w.w. 232 Th activity concentrations ranged from 0.09±0.02 Bq kg-1 w.w. to 1.44±0.10 Bq kg-1 w.w., with a mean value of 0.44±0.50 Bq kg-1 w.w. for the eleven samples. The concentration of 40 K ranged from 26.89±1.25 Bq kg-1 w.w. to 219.25±5.61 Bq kg-1 w.w., and the mean value is 99.08±47.99 Bq kg-1 w.w. for the collected samples. And the 137 Cs activity concentrations were below the minimum detectable activity of 0.06 Bq kg-1 w.w. In all of analyzed samples, the activity concentrations of radionuclides in seafood obtained in the study were within the background level of China. The calculated internal radiation dose rate to marine biota was estimated to be in the range of 16.55 to 62.41 nGy h-1, and the internal dose rates obtained were significantly lower than the baseline safety level of 400 μGy h-1 that is widely accepted for aquatic organism. The committed effective dose via the intake of radionuclide through seafood consumption for different age and gender population groups was estimated to be ranged from 10.55 to 36.17 μSv y-1 for all age groups. And the total committed effective dose was also lower than the reference value of 100 μSv y-1. Therefore, we can suggest that there was no risk to public health from direct ingestion of the seafood in China at the time of this study.(3) In this study, we evaluated the remediation effect of topsoil removal practice on contaminated paddy field with radiocesium in Japan from the three aspects of soil, irrigation water, and rice plant. Our results showed that most of the radiocesium deposited from the Fukushima nuclear accident was concentrated on the topsoil of the paddy field. And removal of topsoil(5-10 cm) could remove more than 95% radiocesium from the paddy field. Meanwhile, we found that radiocesium activity concentrations gradually decreased with the depth of soil. The inflow of radiocsium from irrigation water was mainly through suspended sediments containing radiocesium in paddy fields, and the radiocesium activity concentration in suspended sediment in irrigation water exponentially decreased with time. During the study period from 2011 to 2014, the activity concentrations of radiocesium were all below the standard of 100 Bq/kg in rice. In addition, we found that the absorption of radiocesium by rice plant was not significantly reduced in the decontaminated paddy field with topsoil removal compared with control paddy field(p>0.05), and on the contrary, the concentration ratio of radiocesium for rice plant increased in the decontaminated paddy. The reason is probably associated with the irrigation water containing radiocesium. Therefore, it is very important that the radiocesium activity concentrations in irrigation water should be determined during the cultivation especially for the decontaminated and non-polluted paddy fields.(4) The effect of potassium and nitrogen in soil on radiocesium accumulation in rice plants was investigated under different fertilizer conditions in the contaminated paddy field. Our study demonstrated that high nitrogen and low potassium conditions increased radiocesium concentrations and concentration ratios both in brown rice and straw. Thus, it is significant to apply rational fertilizer condition to avoid high concentration of radiocesium in rice grain. |
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