| The distribution characteristic of selenium(Se) in the environment is closely related to human health. In order to characteristic the distribution and the relation to human health of Se, researches of Se in rocks, soil, plants, food and human body in all over China were reviewed. Plant, water and human hair samples from Ping’an adequate Se region in Qinghai and Ziyang seleniferous region were collected in this study. Concentrations of total Se were determined in all the samples. Se distribution, soil Se bioavailability, daily dietary Se intake and Se in human hair in the local environment of these two areas were investigated. A five-step sequential extraction procedure was used for Se fractionation in soil from Ziyang seleniferous. The results were shown as below:1. Se varied significantly in different environment mediums in China. Highest Se concentrations were observed in rocks with a range of 2.11~1251.1 mg/kg; followed by soil with Se concentration of 0.095~27.81 mg/kg; relatively low Se were observed in plants(0.00005~5.64 mg/kg) and drinking water(0.017~46.0 μg/L). Se concentration samples varied significantly in different kind of food, following a descending order of animal-based food > vegetable > grain > fruit. Se concentration in grains had an order of rice > corn > wheat. Se concentration in drinking water in China was all lower than the maximum limation(10 μg/L) recommended by WHO except Enshi and Ziyang. Dietary Se intake of residents in China ranged from 15.8 to 2144 μg/d. Human Se intake in more than 40% areas of China were lower than the physiological requirement level of human body(40 μg/d). Human Se intakes only in Enshi of Hubei province, Ziyang and Xi’anof Shaanxi province, Guangzhou of Guangdong province, Biejing and Ji’nan of Shandong province met the recommend level by WHO(55 μg/d). Se in human hair of residents in China were 0.144~21.5 mg/kg, the geographical distribution of which were significantly similar with human Se intake and Se in soil. In conclusion, low Se distributes in most areas of China and mainly range from the northeast to the southwest of China with negative effects on human health in these areas, including Inner Mongolia, Zhangjiakou of Hebei province, north Shaanxi of Loess Plateau, Sichuan basin, Qinghai-Tibet Plateau and Yunnan province. On the contrary, high Se concentrations were observed in Guizhou, Zhejiang, Hu’nan, Xinjiang and Fujian province as belt or point; while Se-toxic areas were found particularly in Enshi of Hubei province, Ziyang of Shaanxi province, Wanshan, Qingzhen and Kaiyang of Guizhou province and Xuzhou of Jiangsu province in China, where soil Se concentrations can be > 2 mg/kg.2. Se concentrations in 573 soil samples in Ping’an of Qinghai province ranged from 0.076 mg/kg to 1.882 mg/kg with an average of 0.369±0.236 mg/kg. More than 86.8% soil samples in Ping’an were Se-rich. High Se soil mainly distributes in the north of Hongshuiquan town in the study region, which indicated that Ping’an is a Se-rich ares. On the contrary, Se concentration in 43 plant samples varied significantly from 0.01 to 904 μg/kg, following a descending order of pasture > grain > vegetable > fruit, which was much lower than other regions in China. The predicted daily dietary Se intake(48±20 μg) in Ping’an met the demand of WHO recommend Se amount of 55 μg per person; and the Se concentration in human hair was adequate with an average of 0.299±0.104 mg/kg. These were due to available Se in the soil accounted for only 3% of the total soil Se, which was much lower than other regions in China(10%).3. Se concentration in soil in Shuang’an of Ziyang County ranged from 0.21 to 36.07 mg/kg, averaged at 4.10±5.17 mg/kg. All the soil samples contained more than 0.175 mg/kg Se which could be considered as Se-rich, more than 47% soil samples were Se-toxic with more than 3 mg/kg Se. Extremely high Se concentration was also observed in plants with an average of 3.79±5.69 mg/kg; Se in surface water and drinking water were 17.2±9.19 μg/L and 11.8±6.36 μg/L, respectively, it was higher than the national upper-limitation of drinking water(10 μg/L). The predicted daily dietary Se intake(1769.7 μg per person) in the study region far exceed the recommend toxic dose of Se(400 μg) in human diet. The result of Se concentration in human hair also showed a poisonous indication(over 68.9% samples were Se-toxic), it indicated that there was health threaten by high Se in Shuang’an of Ziyang County. To better evaluate the potential risk of Se in Ziyang high Se area, the speciation of Se in the environment should be considered.4. Organic matter-bound Se, iron and manganese oxides-bound Se and residual Se were the dominant Se fractions with the proportion of 95% in Shuang’an of Ziyang County. Soluble and exchangeable Se p H were significant correlated with p H(P < 0.05), while organic matter-bound Se were negatively correlated with p H(P < 0.01). Organic matter-bound Se and iron-manganese oxides-bound Se had significant correlation with organic matter(P < 0.05). It indicated that Se bioavailability in soil was mainly influenced by p H, organic matter and carbonate in the procedure of Se distribution in liquid-solid phase in soil.In conclusion, a large variation in daily Se intake was observed in different geographical areas in China. Most areas of the Country were under the level of Se-deficiency or potential Se-deficiency in China. Even Se in soil was high in Ping’an of Qinghai province; however, the higher Se content in soils didn’t grantee a high Se human daily Se intake because of the low bioavailability. On the other hand, Ziyang of Shaanxi province is one of the Se-toxic region in China, Se-toxic risk was observed due to extremely high human Se intake and Se in hair were found in Ziyang. Therefore, the rearserch of the distribution and bioavailibity of Se in the environment was much more necessary to reasonably utilize the Se resource and ensure human health. |
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