Page 45 - Plant-Based Remediation Processes

32 M. Barbafieri et al.

Fig. 2.6 Barley root elongation test. Phytotoxicity increases from left to right dependent on the
used additive mixture

Fig. 2.6) (Kapustka 1997). The root development of barley seeds is highly sensitive
to stress caused by pollution and the root length is a good indicator of such stress.
The picture shows such a standard test. Using this cheap, fast, and technically easy
test many soil/additive combinations can be assessed in a relatively short time and
the most suitable combinations can be selected, also taking into account the other
success factors, especially the price and local commercial availability of the
additives. After this, the best performing additives with the optimum application
rates can be tested in pot experiments or small lysimeter studies using the proposed
vegetation types (natural species or production crops) to assess crop performance.
Accumulation of heavy metals in the crops (issue v) can then be assessed easily as
well. When performing these preliminary tests, a check of site heterogeneity has
to be carried out as well. If the site is very heterogeneous regarding soil biogeo-
chemical characteristics and pollution levels, it can be decided whether it is
(economically) most viable to investigate and apply different phytostabilization
schemes to account for the spatial differences in site characteristics or to physically
homogenize the upper soil layer, possibly in combination with additive application.

2.4 Conclusions and Recommendations

• In most cases, phytoextraction still requires a long time to attain target pollutant
levels in the soil which satisfy the legislators. Therefore commercial
applications are being hindered not only by a lack of legal acceptance of the
technology as a soil remediation option but also because of the often unpredict-
able financial burden over a long period of time. These constraints can only be
overcome if it can be shown to policy makers that the risk to the environment at