Page 43 - Plant-Based Remediation Processes

30 M. Barbafieri et al.

Fig. 2.4 Heavily polluted site in Poland (4 % heavy metals) before (left) and 1 year after (right)
application of lignite and phosphate rock. Perennial grass and flowering hyperaccumulating
species start growing spontaneously
turned less harmful. The main problem legislators have with this is the fact that in
the future, heavy metals may become mobile again and once again can cause
environmental problems. Another disadvantage is the fact that the land will remain
unproductive on the longer term which gives a longer term management burden to
authorities or problem-owners. The reason why phytostabilization remains a good
polluted land management option despite the above-mentioned disadvantages is the
fact that other options are absolutely not possible due to high costs.
A method to reduce or to completely mitigate the longer term polluted land
management costs is to grow non-food crops on the polluted land; this includes
energy crops and especially energy crops which provide a perennial vegetation
cover (grasses, woody species) and do not cause food-chain contamination
problems. Recent research in China and Vietnam has shown that growing energy
crops on polluted land can be made profitable (considering the low economic
value of the land) even if crop yields are lower than on good agricultural soil.
Figure 2.5 shows an energy crop test site in China, nearby a copper/zinc smelter. An
interesting example of the interrelation of productive crops and natural vegetation is
the effort by Chinese researchers to grow energy crops on extremely polluted
(copper, arsenic) mine tailings in Tongling (Anhui, China). After adding rock
phosphate and liming the tailings, different tested potential energy crops grew but
provided only very low yields which made the whole process economically nonvi-
able. However, after dismantling the energy crop test area, abundant natural
vegetation recovered on the site, which has been bare during decades. So no
economic profits could be obtained, but the natural vegetation cover which started
to reappear did not require high management costs and at the same time reduced the
transport of pollutants to neighboring paddy field by decreasing erosion rates and
controlling leaching.

2.3.2 Protocols for Phytostabilization

The principal critical success factors for the phytostabilization process are:
1. The effectiveness of the soil additives regarding their effect on reducing the
mobility/bioavailability of heavy metals in the soil at the polluted site.