Phytostabilization of arsenic - In-Situ Remediation of Arsenic-Contaminated Sites - page 62

Table 3.3. Soil and plant species parameters for successful As phytostabilization.

Soil/plant
parameters Setting Reference

Amendments Fe-based, MnO x , AlO x alkaline, clay Kumpiene et al . (2008)

Organic matter Below 10% (possibly associated with Mench et al . (2003); Neuschütz

a sealing layer) and Greger (2010)

pH 7 Renella et al . (2008)

Phosphate < 1 mM Wovkulich et al . (2010)

Plant species Root mineralization supports As immobilization Moreno-Jiménez et al . (2009)

Redox potential p E > 10 Zhao et al . (2010)

3.7.2 Amendments that encourage plant vegetation and As immobility
Amendments, such as iron compounds, manganese and aluminum oxides, alkaline materials,
and clay minerals, could be added to reduce the mobility of As in soils (Kumpiene et al ., 2008)
(see Section 3.6.1). By-products from industrial manufacturing can be ideal materials for As soil
remediation. For example, iron-rich industrial by-products have proven to successfully reduce the
availability of As and metals from a contaminated gold mine area (Lee et al ., 2011).
In soils that are poor in quality in terms of nutrients and phytotoxic levels of trace metals and
other contaminants, such as mine wastes, organic matter may have to be added to allow plant
growth for phytostabilization (Moreno-Jiménez et al ., 2010). Amendments added to soil have
to be adjusted to maintain low As availability and to improve soil quality and stability. Organic
matter amendments may increase As mobility (see Section 3.6.2), but a combination of organic
matter and iron-based amendments could provide a good alternative for achieving this purpose
(Moreno-Jiménez et al ., 2010). An alternative for reducing the addition of organic matter, while
still promoting a habitable soil for plants, is the vertical separation of the soil into different strata.
The addition of a sealing layer between the As-contaminated soil and a vegetative cover could
reduce the need to add organic matter to the soil. For example, pyrite mine tailings were covered
with a sealing layer composed of fly ash from wood combustion, followed by a layer of sewage
sludge; this vertical separation reduced the mobility of both nutrients and metals (Neuschütz and
Greger, 2010).

3.7.3 Selecting plant species for arsenic phytostabilization
The selection of plant species for As phytostabilization should ensure that the plant species
does not increase the As mobility from the area and that it is suitable for As phytostabilization
in terms of As accumulation (see Section 3.5.2). For example, Moreno-Jiménez et al . (2009)
demonstrated that root mineralization in five species of shrubs, i.e., Arbutus unedo , Myrtus
comunnis , Pistacia lentiscus , Retama sphaerocarpa , and Rosmarinus officinalis , did not increase
As mobility, supporting the idea of successful As phytostabilization. However, one plant species,
Tamarix gallica , promoted higher release of As from the soil after mineralization, compared with
the control soil, highlighting the importance of plant-specific characteristics and of selecting
proper plant species for phytostabilization (Moreno-Jiménez et al ., 2009). Table 3.3 summarizes
some of the soil and plant parameters that can be used when developing management plans for
successful As phytostabilization.

3.7.4 Methods suitable for combining with arsenic phytostabilization
Phytofiltration could be employed as an additional strategy in combination with phytostabilization
in situations in which phytostabilization is insufficient to reduce As mobility. This could occur
in areas with multiple contaminants, a situation common in polluted areas. Treatments that
reduce heavy metal mobility, for example, organic matter amendments, might at the same time