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Objective:To understand the radioactivity levels of water source in five key cities of Chengdu, Yibin, Mianyang, Guangyuan, Leshan in Sichuan province, and evaluate the radiation safety of these water sources.Methods:From 2016 to 2020, the measuring site selection, sampling and analysis were made for measuring the radioactivity levels of total alpha, total beta, 90Sr, 137Cs, 226Ra, U, Th in drinking water sources in these five cities. Reference was made, respectively, to the national standards Determination of total α radioactivity concentration in water thick source method (EJ/T 1075-1998), Determination of total β radioactivity in water evaporation method (EJ/T 900-1994), Radiochemical analysis method of strontium-90 in water and biological samples ash (HJ 815-2016), radiochemical analysis of cesium-137 in the ash of water and biological samples (HJ 816-2016), Analysis and determination of radium-226 in water (GB 11214-1989), Analysis of trace uranium in environmental samples -3 laser fluorescence law (HJ 840-2017), and Food safety in the test of radioactive substances in food determination of natural thorium and uranium (GB 14883.7-2016). Results:The activity concentration ranges from 0.011 to 0.076 Bq/L for total alpha, 0.027 to 0.098 Bq/L for total beta, 0.21 to 0.45 mBq/L for 137Cs, 1.0 to 2.4 mBq/L for 90Sr, 6.1 to 16.0 mBq/L for 226Ra, 0.06 to 0.21 μg/L for Th, and 0.73 to 3.30 μg/L for U. There were no significant differences in the concentrations of total alpha, total beta, 90Sr, 137Cs, 226Ra, U and Th in different water sources and different years ( P>0.05). There were no significant differences in the concentrations of total alpha, total beta, 90Sr, 137Cs and 226Ra during different water periods ( P>0.05). There were statistical differences in U activity concentration in different water periods ( H=16.53, P<0.05), and statistical differences in Th activity concentration in different water periods ( H=15.61, P<0.05). Conclusions:The survey showed that the total alpha, total beta, 90Sr, 137Cs, 226Ra, U and Th radioactivity levels in drinking water sources in Chengdu, Yibin, Mianyang, Guangyuan and Leshan of Sichuan province were at the same level as the relevant data in the Natural environmental radioactivity level in China published by the State Environmental Protection Bureau in 1995. All of there values were within the data range released by the 2013-2021 National Radiation Environment Monitoring Quality Report issued by the Radiation Environment Monitoring Technology Center of the Ministry of Ecology and Environment. The radioactivity level in water sources in the five key cities was at a safe level.
ABSTRACT
ObjectiveTo determine the distribution of various antibiotic resistance genes （ARGs） in raw water from drinking water source， and to explore the correlation between the ARGs and common carbapenem-resistant and multidrug-resistant bacteria isolated from drinking water source， so as to provide scientific evidence for improving the safety of urban drinking water. MethodsA total of 30 raw water samples were collected from a major drinking water source in Shanghai in 2020. Bacterial strains were selectively cultured on Columbia blood agar medium containing 1 μg·μL-1 meropenem， and then identified by MALDI-TOF-MS mass spectrometry system. Minimum inhibitory concentration （MIC） of the strains was detected by broth microdilution method. The water samples were filtered through a 0.45 μm filter membrane and diversity of ARGs was determined by using high-throughput metagenomic sequencing. ResultsA total of 64 strains of carbapenem-resistant bacteria were isolated from the water samples， including Stenotrophomonas maltophilia， Enterococcus faecium， Pseudomonas aeruginosa， Acinetobacter baumannii and Klebsiella pneumoniae， which were resistant to a variety of common antibiotics. Using metagenomic sequencing，1 244 ARGs were identified. The relative average abundance of the top 100 ARGs accounted for 96.1%， and that of the multidrug-resistant ARGs accounted for 63.41%. Furthermore， the multidrug-resistant ARGs were mainly adeJ， mexT， adeC， oprM， mexF， mdfA， mexB， mdtK， adeK， etc. Using Spearman's correlation， five multidrug-resistant bacteria isolated from the drinking water source were significantly associated with the ARGs. ConclusionRelative abundance of multidrug-resistant ARGs is high in raw water from main drinking water source. The five isolated carbapenem-resistant and multidrug-resistant bacteria are significantly correlated with the ARGs. It warrants strengthening the rational and standardized application of antibiotics to protect water resources and ensure the safety of drinking water.