Wang Yaodong, Greger Maria
Department of Botany, Stockholm University, SE-106 91 Stockholm, Sweden.
Sci Total Environ. 2006 Sep 1;368(1):30-9. doi: 10.1016/j.scitotenv.2005.09.034. Epub 2005 Oct 19.
Low bioavailability of mercury (Hg) in soil is a restricting factor in phytoextraction of Hg-contaminated soil. Iodide is known to mobilize Hg in soil and, therefore, the aim of this study was to investigate the possibility to use iodide to increase phytoextraction of Hg. The sensitivity of willow to iodide was investigated in both hydroponics with 0-10 mM KI and in soil with 0.2 and 1 mM KI addition. The capacity to accumulate HgI(2) was compared with that of Hg(NO(3))(2) in hydroponics. Soil extractions with 0-2 mM KI were used to study mobilization of Hg in aged Hg-spiked soil. Additions of KI (0.2-1 mM) were used in pot tests with aged Hg-spiked soil as well as in field trials in an industrial Hg-contaminated soil to study whether iodide addition increased the accumulation of Hg from contaminated soil and the translocation of Hg to the shoots. The total Hg contents in plants, soils and extracts were analyzed by CVAAS. The results showed that too high KI concentration was toxic to plants. Moreover, KI was toxic to plants at lower concentrations in hydroponics than in soil additions. KI (85 microM) in hydroponics gave 50% growth decrease in terms of dry weight of shoot biomass, whereas 0.2 mM KI in soil addition could be tolerated by the plant without growth disturbance. Willow accumulated Hg from HgI(2) solution slower than that from Hg(NO(3))(2) solution. KI mobilized Hg in contaminated soil and thereby increased the bioavailability of Hg in soil. Up to 1 mM KI addition increased the Hg concentrations to about 5, 3 and 8 times, respectively, in the leaves, branches and roots. However, the Hg translocation to the shoots did not show an increase with KI addition. Only less than 1% of the total Hg accumulated in the plant was distributed in the shoots. We may conclude that iodide addition enhances the phytoextraction of Hg, however, the translocation of Hg to the shoots is still too low and therefore it will not be realistic to use this method for phytoextraction of Hg-contaminated soil in practice.
土壤中汞（Hg）的生物有效性低是汞污染土壤植物提取的限制因素。已知碘化物能使土壤中的汞活化，因此，本研究的目的是探讨使用碘化物提高汞植物提取率的可能性。在添加0 - 10 mM KI的水培试验以及添加0.2和1 mM KI的土壤试验中，研究了柳树对碘化物的敏感性。在水培试验中，比较了柳树积累HgI₂和Hg(NO₃)₂的能力。用0 - 2 mM KI进行土壤提取试验，研究老化汞污染土壤中汞的活化情况。在老化汞污染土壤的盆栽试验以及工业汞污染土壤的田间试验中，添加KI（0.2 - 1 mM），以研究添加碘化物是否能增加污染土壤中汞的积累以及汞向地上部的转运。采用冷原子吸收光谱法（CVAAS）分析植物、土壤和提取物中的总汞含量。结果表明，过高的KI浓度对植物有毒。此外，在水培试验中，KI在较低浓度时对植物的毒性就比对土壤添加物中的毒性大。水培试验中85 μM的KI使地上部生物量干重下降50%，而土壤添加0.2 mM KI时植物能够耐受，生长未受干扰。柳树从HgI₂溶液中积累汞的速度比从Hg(NO₃)₂溶液中慢。KI能使污染土壤中的汞活化，从而提高土壤中汞的生物有效性。添加高达1 mM KI时，叶片、枝条和根系中的汞浓度分别增加到约5倍、3倍和8倍。然而，添加KI后汞向地上部的转运并未增加。植物积累的总汞中只有不到1%分布在地上部。我们可以得出结论，添加碘化物可提高汞的植物提取率，然而，汞向地上部的转运仍然过低，因此在实际中使用这种方法进行汞污染土壤的植物提取并不现实。
