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2 Protocols for Applying Phytotechnologies in Metal-Contaminated Soils 29

likely to predict phytoextraction duration and, more important that thus predicted
durations are 20–50 % longer than when the linear model is used. It should be noted
that slower processes releasing “new” plant-available fractions from the soil matrix
cannot be predicted by this procedure. It may be obvious that phytoextraction
duration is an important indicator and decision instrument for phytoextraction,
but it is just as obvious that costs play an important role as well (Koopmas et al.
2007; Koopmans et al. 2008a).

2.3 How Can We Use Phytostabilization?

2.3.1 Technology Description

Phytostabilization aims at the use of plants to reduce the impact of soil pollutants on
adjacent environmental compartments, including water bodies, agricultural land,
etc. Phytostabilization is most effective on land which is highly contaminated by
heavy metals, other (in)organic pollutants, and also crude oil residues. Such land is
characterized by marginal or nonexistent vegetation and by degenerated soil and
surface ecosystems; such land therefore is highly prone to serve as a secondary
pollution source due to high wind and water erosion rates and high levels of surface
run-off and leaching to the groundwater (Berti and Cunningham 2000; Barbafieri
et al. 2011). Phytostabilization of such land areas can be defined as a set of
measures which permit re-establishment of vegetation and which at least include
the use of chemical/biological soil additives and introduction of productive plants
or natural vegetation. In its simplest form, it consists of the addition of adsorbing
materials and/or other chemicals which reduce the plant-available fraction of heavy
metals and therefore reduce phytotoxicity; the natural vegetation can then return
with or without human assistance. An example is the re-establishment of a natural
perennial vegetation cover on extremely polluted soil in Poland (up to 4 % of heavy
metals) after just adding substantial amounts of rock phosphate and lignite to the
soil (Kucharski et al. 2005); see Fig. 2.4. The benefits of such a vegetation cover are
obvious. Wind erosion rates are decreased and heavy metals are no longer
transported to residential areas and gardens nearby the site.
Leaching is decreased by reducing vertical water transport in the soil as a result
of phytoevaporation in combination with a lower mobility of heavy metals after
addition of adsorbents. The main risk of the re-establishment of such natural
vegetation covers on extremely polluted soil is high uptake of heavy metals by
the (hyperaccumulating) plants which can survive on the site and subsequent food-
chain contamination. At this specific site in Poland, the non-hyperaccumulating
perennial grass gradually won the competition with a hyperaccumulating non-
perennial weed, so that food-chain contamination was not a problem anymore
after some time. The main disadvantage of phytostabilization from a legislator’s
point-of-view is the fact that the pollutant is not removed from the soil, but only