Page 238 - Plant-Based Remediation Processes

230 M. Griga and M. Bjelkova ´

¨
• Fibre contains HMs over accepted limits for garment textiles (Oko Tex Standard
2005; Table 11.7): composite materials, paper industry, geotextile and other
industrial applications.
¨
• Fibre contains acceptable amounts of HMs (Oko Tex Standard 2005; Table 11.7)
or HMs are mainly concentrated in tissues out of fibre: garment textile industry,
shives either burnt or used for other industrial applications.

This strategy may be changed as new scientific knowledge emerges or new plant
materials will be produced (e.g. transgenic fibre crops with novel traits as related to
HMs—Vrbova ´ et al. 2012).

11.7 Conclusion: Concept of the Use of Flax and Hemp for
Phytoextraction of Heavy Metals from Polluted
Agricultural Soils

Nearly 25 years of research of two important fibre crops—flax and hemp—enable
to make some conclusions and to formulate a strategy for future research and
exploitation of HMs phytoextraction technology. The critical assessment of litera-
ture sources and our own long-term experience with both crops helped to make a
more or less realistic view on the problem.
Unfortunately, the expectations were not fulfilled that hyperaccumulators will be
found within commercial cvs and germplasm resources of the both crops—in flax/
linseed, several hundreds of genotypes were tested for a trait “HMs tolerance and
accumulation”, nevertheless, the genotypes with desirable level of accumulation of
Cd, Pb and other toxic elements in above-ground biomass have not been recorded.
The limited number of up-to-date studied genotypes in hemp still offers a chance to
find the hemp genotypes of interest. First successful results of genetic engineering
of flax for HMs tolerance and accumulation (Vrbova ´ et al. 2012) represent a
promising approach how to improve phytoremediation potential of fibre crops.
On the other hand, the positive point of reported results is that medium or even
high soil concentrations of metal elements do not have negative effect on the growth,
yield of biomass and technological quality of raw material of both crops (here
mainly fibre), and thus the production of flax and hemp from HMs polluted areas
may be sold and industrially processed. The medium values of phytoextraction
1
potential, i.e. tens or hundreds g. HMs ha per vegetation period result in time
needed for complete decontamination ca. in tens or hundreds years (Bo ¨hm et al.
1992; Linger et al. 2002). Based on these facts it is evident that flax and hemp cannot
clean up the heavily metal-polluted sites in a short time, but they may have a specific
role in successive decontamination of agricultural soils by their incorporation to
specifically designed crop rotation systems on soils polluted by heavy metals
(Grzebisz et al. 1997b). The idea is a gradual decreasing of heavy metal content to
natural levels in the reasonable period of time in order to make possible the use of
these soils for food production purposes again. The possibility of further industrial