Page 105 - Plant-Based Remediation Processes

94 M. Mleczek et al.

arsenic/gold mines are exposed primarily to toxic concentrations of As, and to a
lesser extent Pb, Al, and Fe. The use of a single extraction procedure demonstrated
variations in the amount of arsenic released from the rhizosphere soil. This likely
resulted from the species-specific root-induced modification of chemical forms of
arsenic and its bioavailability, as a part of a plant strategy to survive in the
contaminated environment. A plant species, Calamagrostis arundinacea (Poaceae),
was identified which, due to its ability to substantially increase the arsenic concen-
tration in the soil solution, likely by efficient uptake, reduced by 40 % the total As
soil concentration in the root zone. The discovered case of natural phytoextraction
points to the usefulness of this species for phytoremediation. Another plant species,
Stachys sylvatica (Lamiaceae Lindl.), as a plant with low As concentrations in
shoots and low concentration of bioavailable As in the rhizosphere (relative to other
plants from the same area), was considered for further detailed study as a plant for
possible use for phytostabilization. There were also species identified with excep-
tional ability to extract elements from the soil and accumulate them at high level in
shoots:
1. Al by Oxalis acetosella (Oxalidaceae) and Geranium robertianum
(Geraniaceae)
2. Mn by Calamagrostis arundinacea (Poaceae)
3. Fe, Sr, and Ba by Fragaria vesca (Rosaceae) (Antosiewicz et al. 2008)
Rubus ulmifolius (Rosaceae Juss.) never accumulated more than 1 g kg 1 of any
of the metals in the aerial plant organs, the criteria indicated for As, Pb, or Ni
hyperaccumulators (Marques et al. 2009). In fact, the metals were mainly
accumulated in the roots of the plant, indicating a low metal translocation into
the aerial section. Translocation rates between roots and stems ranged from 0.02 to
0.16 for As and from 0.08 to 0.13 for Pb. The high metal concentration in roots and
apparent low translocation to the aerial plant organs indicate that the plant is
capable of rather well-balanced accumulation and translocation (Haque et al.
2008). This may suggest a metal exclusion strategy from stems and reproductive
tissue by retaining the metal in the roots (Marques et al. 2009), thus avoiding its
toxicity. Resistance of R. ulmifolius to the metal’s presence can be achieved by an
avoidance mechanism such as precipitation and association with cell walls or
detoxification in vacuoles (Marques et al. 2009). Although each plant species
might have a unique mechanism against heavy metals, other published data also
indicate higher accumulation of As (Madejo ´n et al. 2003, 2007), Pb (Fitzgerald
et al. 2003), and Ni in the roots of plants growing in metal-contaminated soils than
in its aboveground tissues. R. ulmifolius also has shown the same type of accumu-
lation behaviour for Zn; plants accumulated up to 563, 110, and 91 mg Zn kg 1 in
the roots, stems, and leaves, respectively, for a level of Zn in the soil of up
957 mg kg 1 (Marques et al. 2009). This way of accumulation for all the studied
metals truncates the biogeochemical cycles of the metals and limits potential food
chain transfer to a restricted range of root consumer and decomposer organisms of
R. ulmifolius (Marques et al. 2009). Despite the fact that the vegetation remains