| 天津污灌区内气态汞的污染特征及在叶菜类蔬菜中的富集 |
| 摘要点击 2741 全文点击 1180 投稿时间：2014-04-14 修订日期：2014-06-18 |
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| 中文关键词 污灌区 汞 土壤 气态汞 叶菜 |
| 英文关键词 wastewater-irrigated area mercury soil gaseous mercury leafy vegetable |
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| 中文摘要 |
| 污灌区土壤相当于一个巨大的汞（Hg）源向水体和大气释放汞，挥发的气态汞可以通过植物叶片的气孔进入植物体内，严重威胁着当地农产品安全及人类健康. 天津污灌区是汞污染的重灾区之一，本研究选取天津污灌区内某稻田（污灌约30 a）、菜田（污灌约15 a）和污灌区边缘某草地（无污灌史，对照）作为监测地点，以5种常见叶菜（菠菜、苋菜、油菜、生菜、韭菜）作为生物监测实验对象，考察污灌区内产地土壤、大气汞的浓度及其在叶菜中的富集特征. 结果表明：①经过长期污灌，稻田和菜田土壤汞含量已显著高于区域土壤汞背景含量和土壤环境质量标准一级标准，但未超过二级. 对照草地土壤汞含量在背景含量与一级标准之间. 稻田和菜地大气环境已受到较为严重的汞污染，气态总汞均值分别为71.3 ng·m-3和39.2 ng·m-3，远高于北半球大气总汞含量的背景水平（1.5~2.0 ng·m-3），对照草地总汞含量平均为9.4 ng·m-3. ②叶菜汞含量与污灌区气态汞含量对数之间呈现极显著的线性关系，5种叶菜对污灌区气态汞的敏感程度依次为菠菜>苋菜>韭菜>油菜>生菜. 菠菜和苋菜Hg含量的中位值及平均值均超出食品卫生限量标准，其中菠菜的中位值及均值在20 μg·kg-1以上，其余3种叶菜中位值及均值在限量值标准以下. ③污灌区内叶菜Hg来源主要通过叶片吸收气态汞进入植株体内，而非颗粒态汞. 研究表明在污灌地区种植叶菜，不仅需要考虑土壤污染的因素，也需要考虑气态汞暴露的风险. |
| 英文摘要 |
| Gaseous Hg can evaporate and enter the plants through the stomata of plat leaves, which will cause a serious threat to local food safety and human health. For the risk assessment, this study aimed to characterize atmospheric mercury (Hg) as well as its accumulation in 5 leafy vegetables (spinach, edible amaranth, rape, lettuce, allium tuberosum) from sewage-irrigated area of Tianjin City. Bio-monitoring sites were located in paddy (wastewater irrigation for 30 a), vegetables (wastewater irrigation for 15 a) and grass (control) fields. Results showed that after long-term wastewater irrigation, the mean values of mercury content in paddy and vegetation fields were significantly higher than the local background value and the national soil environment quality standard value for mercury in grade Ⅰ, but were still lower than grade Ⅱ. Soil mercury contents in the studied control grass field were between the local background value and the national soil environment quality standard grade Ⅰ. Besides, the atmospheric environment of paddy and vegetation fields was subjected to serious mercury pollution. The mean values of mercury content in the atmosphere of paddy and vegetation fields were 71.3 ng·m-3 and 39.2 ng·m-3, respectively, which were markedly higher than the reference gaseous mercury value on the north sphere of the earth (1.5-2.0 ng·m-3). The mean value of ambient mercury in the control grass fields was 9.4 ng·m-3. In addition, it was found that the mercury content in leafy vegetables had a good linear correlation with the ambient total gaseous mercury (the data was transformed into logarithms as the dataset did not show a normal distribution). The comparison among 5 vegetables showed that the accumulations of mercury in vegetables followed this order: spinach>edible amaranth>allium tuberosum>rape>lettuce. Median and mean values of mercury contents in spinach and edible amaranth were greater than the hygienic standard for the allowable limit of mercury in food. Spinach appeared to accumulate more mercury than the other four vegetables, in which the median and mean mercury content were both higher than 20 μg·kg-1. The mercury concentrations in rape, lettuce and allium tuberosum were lower than the standard. Moreover, test results indicated that the Hg content in leafy vegetables was mainly the gaseous mercury through leaf adsorption but not the Hg particulates. This study clearly manifested that there should be a great concern on the pollution risk of both air-and soil borne mercury when cultivating leafy vegetables in long-term wastewater-irrigated area. |
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