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Absence of Hg transpiration by shoot after Hg uptake by roots of six terrestrial plant species
Stockholm University, Faculty of Science, Department of Botany.
Stockholm University, Faculty of Science, Department of Botany.
2005 (English)In: Environmental Pollution, ISSN 0269-7491, E-ISSN 1873-6424, Vol. 134, no 2, 201-208 p.Article in journal (Refereed) Published
Abstract [en]

In this paper we investigated if, and to what extent, six different plant species accumulate, translocate and emit mercury (Hg) into the air. The Hg uptake by roots, distribution of Hg to the shoot and release of Hg via shoots of garden pea, spring wheat, sugar beet, oil-seed rape, white clover and willow were investigated in a transpiration chamber. The airborne Hg was trapped in a Hopcalite trap or a gold trap. Traps and plant materials were analysed for content of Hg by CVAAS. The results show that all plant species were able to take up Hg to a large extent from a nutrient solution containing 200 μg L−1 Hg. However, the Hg translocation to the shoot was low (0.17–2.5%) and the Hg that reached the leaves was trapped and no release of the absorbed Hg to the air was detected.

Mercury translocation to shoots was low.

Place, publisher, year, edition, pages
2005. Vol. 134, no 2, 201-208 p.
Keyword [en]
Mercury, Accumulation, Translocation, Hg release
National Category
Biological Sciences
URN: urn:nbn:se:su:diva-23475DOI: 10.1016/j.envpol.2004.08.007OAI: diva2:192259
Available from: 2004-11-30 Created: 2004-11-30 Last updated: 2010-10-28Bibliographically approved
In thesis
1. Phytoremediation of mercury by terrestrial plants
Open this publication in new window or tab >>Phytoremediation of mercury by terrestrial plants
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mercury (Hg) pollution is a global environmental problem. Numerous Hg-contaminated sites exist in the world and new techniques for remediation are urgently needed. Phytoremediation, use of plants to remove pollutants from the environment or to render them harmless, is considered as an environment-friendly method to remediate contaminated soil in-situ and has been applied for some other heavy metals. Whether this approach is suitable for remediation of Hg-contaminated soil is, however, an open question. The aim of this thesis was to study the fate of Hg in terrestrial plants (particularly the high biomass producing willow, Salix spp.) and thus to clarify the potential use of plants to remediate Hg-contaminated soils.

Plants used for phytoremediation of Hg must tolerate Hg. A large variation (up to 30-fold difference) was detected among the six investigated clones of willow in their sensitivity to Hg as reflected in their empirical toxicity threshold (TT95b), the maximum unit toxicity (UTmax) and EC50 levels. This gives us a possibility to select Hg-tolerant willow clones to successfully grow in Hgcontaminated soils for phytoremediation.

Release of Hg into air by plants is a concern when using phytoremediation in practice. No evidence was found in this study that Hg was released to the air via shoots of willow, garden pea (Pisum sativum L. cv Faenomen), spring wheat (Triticum aestivum L. cv Dragon), sugar beet (Beta vulgaris L. cv Monohill), oil-seed rape (Brassica napus L. cv Paroll) and white clover (Trifolium repens L.). Thus, we conclude that the Hg burden to the atmosphere via phytoremediation is not increased.

Phytoremediation processes are based on the ability of plant roots to accumulate Hg and to translocate it to the shoots. Willow roots were shown to be able to efficiently accumulate Hg in hydroponics, however, no variation in the ability to accumulate was found among the eight willow clones using CVAAS to analyze Hg content in plants. The majority of the Hg accumulated remained in the roots and only 0.5-0.6% of the Hg accumulation was translocated to the shoots. Similar results were found for the five common cultivated plant species mentioned above. Moreover, the accumulation of Hg in willow was higher when being cultivated in methyl-Hg solution than in inorganic Hg solution, whereas the translocation of Hg to the shoots did not differ.

The low bioavailability of Hg in contaminated soil is a restricting factor for the phytoextraction of Hg. A selected tolerant willow clone was used to study whether iodide addition could increase the plant-accumulation of Hg from contaminated soil. Both pot tests and field trials were carried out. Potassium iodide (KI) addition was found to mobilize Hg in contaminated soil and thus increase the bioavailability of Hg in soils. Addition of KI (0.2–1 mM) increased the Hg concentrations up to about 5, 3 and 8 times in the leaves, branches and roots, respectively. However, too high concentrations of KI were toxic to plants. As the majority of the Hg accumulated in the roots, it might be unrealistic to use willow for phytoextraction of Hg in practice, even though iodide could enhance the phytoextraction efficiency.

In order to study the effect of willow on various soil fractions of Hg-contaminated soil, a 5-step sequential soil extraction method was used. Both the largest Hg-contaminated fractions, i.e. the Hg bound to residual organic matter (53%) and sulphides (43%), and the residual fraction (2.5%), were found to remain stable during cultivations of willow. The exchangeable Hg (0.1%) and the Hg bound to humic and fulvic acids (1.1%) decreased in the rhizospheric soil, whereas the plant accumulation of Hg increased with the cultivation time. The sum of the decrease of the two Hg fractions in soils was approximately equal to the amount of the Hg accumulated in plants. Consequently, plants may be suitable for phytostabilization of aged Hg-contaminated soil, in which root systems trap the bioavailable Hg and reduce the leakage of Hg from contaminated soils.

Place, publisher, year, edition, pages
Stockholm: Botaniska institutionen, 2004. 41 p.
phytoremediation, phytoextraction, phytostabilization, bioavailability, willow, Hg
National Category
urn:nbn:se:su:diva-307 (URN)91-7265-975-0 (ISBN)
Public defence
2004-12-21, föreläsningssalen, Botanicum, Lilla Frescativägen 5, Stockholm, 10:00
Available from: 2004-11-30 Created: 2004-11-30Bibliographically approved

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