Phytostabilization of arsenic - In-Situ Remediation of Arsenic-Contaminated Sites - page 63

increase As mobility (Clemente et al ., 2010; Pond et al ., 2005; Stolz and Greger, 2002). The
costs of combining amendments or of achieving optimal physicochemical conditions to phy-
tostabilize all pollutants in an area might be un-realistic. Phytostabilization in combination with
phytofiltration could prove a cost-effective and realistic alternative. Several plant species, for
example, duckweed ( Lemna sp., Spirodela sp., and Wolffia sp.), watercress ( Nasturtium officinale
and Nasturtium microphyllum ), water hyacinth ( Eichornia crassipes ), water fern ( Azolla sp.),
and Hydrilla ( Hydrilla verticillata ), have produced promising results in the phytofiltration of As
(Azizur Rahman and Hasegawa, 2011b). In addition, Canadian waterweed ( Elodea Canadensis )
could remove up to 75% of the As from polluted water (Greger et al ., 2010).

3.8 CONCLUDING REMARKS

Phytostabilization of As has not always produced satisfactory results when strategies for phy-
tostabilizing heavy metals have been employed, such as adding organic matter amendments and
introducing plants (Renella et al ., 2008; Stolz and Greger, 2002). Instead, management plans that
combine As phytostabilization parameters could be used as tool to obtain successful results. For
example, specific attention must be paid to As soil chemistry, including maintenance of a high
redox potential (p E > 10) and a pH of approximately 7. The use of organic matter to improve
poor-quality soil should be used in combination with other amendments, for example, iron-based
ones, to reduce the risk of increased As mobility. Specific consideration should be given to the
recycling of nutrients in the phytostabilized area to promote self-sustaining, long-term pollutant
control. Adding nutrients to the phytostabilized area, in the form of either compost or inorganic
nutrients, may lead to increased As mobility due to anionic competition (Clemente et al ., 2010;
De La Fuente et al ., 2010). If multiple contaminants need to be dealt with, which is often the
case, plants successfully tested for As phytostabilization might fail to control As in the long term
by reducing its mobility. In sites with multiple contaminants, capping along with the planting
of shallow-rooted plants may be preferable to prevent leaching of both metals and As. Another
option is to establish deep-rooted plants that do not increase As mobility upon mineralization
(Moreno-Jiménez et al ., 2009).
If the above parameters for successful As phytostabilization cannot be met, and As
remains mobile, phytofiltration could be used to supplement phytostabilization. Organic matter
amendments can be used for the phytostabilization of heavy metals. Thereafter, the problem of
increased As mobility due to the additional organic matter can be addressed by employing
phytofiltration.

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