Page 212 - Plant-Based Remediation Processes

204 M. Griga and M. Bjelkova ´

anemophilous (wind pollinated). Cannabis exhibits a dual response to day length.
During the first 2 or 3 months of growth it responds to increasing daylength with
more vigorous vegetative growth, but later it requires shorter days (or more
accurately long nights) to flower and complete its life cycle (Clarke 1999).
Similarly as flax, hemp represents a multipurpose crop. The strong fibres, edible
fruits/seeds and psychoactive drugs produced by Cannabis have attracted humans
since Neolithic times (Clarke 1999; Ranalli and Venturi 2004). Hemp fibre is
traditionally used as a raw material for paper and textile production. The last
decades showed a renewed interest in natural fibres and their novel use in automo-
tive industry, furniture and building industry, mainly in the form of composite
materials (Brouwer 2000; Karus and Vogt 2004). The oil content of hemp seed is
high (35 %) and comparable in yields per hectare with rape and sunflower oil; in
addition, it has important pharmaceutical properties. High above-ground biomass of
hemp may be also used advantageously as a combustible raw material for energy
production (Scholz and Ellebrock 2002; Ranalli and Venturi 2004). Thus, due to the
agricultural benefits (weed control, pest and disease resistance, pesticide elimina-
tion, soil improvement by means of crop rotation, high biomass production with
low inputs), the plethora of industrial uses (Karus and Vogt 2004) and a limited
environmental impact, hemp is potentially profitable crop, having the right profile
to fit into sustainable (both conventional and organic) farming systems, promoting
long-term land management strategy (Ranalli 1999; Ranalli and Venturi 2004).

11.4 Flax, Hemp and Heavy Metals Studies: Hygienic Versus
Bioremediation Aspect

Prevalence of industrial use and relatively high uptake of heavy metals from the soil
(flax often accumulates in its tissues higher concentrations of e.g. Cd as compared
to soil Cd content—Gaudchau and Marquard 1990; Schubert 1992;Bo ¨hm et al.
1992;Bo ¨hm and Marquard 1993a, b; Moraghan 1993; Schneider and Marquard
1996) predeterminates this crop to be a potential candidate for phytoremediation of
soils polluted by heavy metals. The beginning of systematic research of flax in
relation to heavy metals was dated 25 years ago (Klein and Weigert 1987) and it
may be characterised particularly by two points of view (1) hygienic aspect
connected with the effort to minimise heavy metal accumulation in seeds and
(2) Cd was the most frequently studied element (less information available on
other heavy metals). Nevertheless, first reports on possibilities of utilisation of flax
(and fibre crops generally) for phytoremediation appeared very soon after these
“hygienically oriented studies” (Bo ¨hm et al. 1992; Kozlowski et al. 1993, 1993/
1994; Mankowski et al. 1994; Baraniecki et al. 1995). In fact, the monograph on
linseed (Gill 1987) as well as the comprehensive review on mineral nutrition of flax
and linseed (Hocking et al. 1988) did not contain any data about heavy metal effects
on flax/linseed growth or on their content in plant organs.