Page 213 - Plant-Based Remediation Processes

11 Flax (Linum usitatissimum L.) and Hemp (Cannabis sativa L.)... 205

The leading idea and common objective of early reports on linseed and heavy
metals was to eliminate or minimise the heavy metal (mainly Cd) accumulation in
the seeds and subsequent food-chain transfer to human body. Because Cd has a
half-life of ca. 20 years in the human body, the consumption of Cd-contaminated
foods may lead to chronic toxicity. According to WHO (1972), the maximum
tolerable intake limit for an adult is 60–70 μg Cd per day. Thus, the accepted
dietary critical value is 0.3 mg Cd kg 1 DW of the flax seed according to German
Richtwer (Klein and Weigert 1987; Anonymous 1988; Marquard et al. 1990),
maximum permitted concentration of Cd proposed for confectionery linseed traded
on the international market is even lower—0.25 mg Cd kg 1 DW (Codex
Alimentarius Commission 1993; Hocking and McLaughlin 2000). Lukipudis
(2001) studied the contamination of flax fibre by Cu, Cd and Pb in polluted areas
in Bulgaria and found the exceeding of HAC (highly admissible concentration) of
complex contamination of fibre by heavy metals according to DIN/ISO standards as
related to clothing production for adults and children. The solution of the problem
may be reached by selection of genotypes with naturally low uptake and transloca-
tion of heavy metals, by avoiding the growing areas heavily polluted by heavy
metals or by managing agricultural systems preventing the heavy metal ions
bioavailability to flax plants (Grant et al. 1998).
Wide possibilities of utilisation of flax (and other fibre crops) for industrial (non-
food) products resulted in the half of nineties of the last century in speculations and
first experiments directed on phytoremediation potential of flax for heavy metals
(Bo ¨hm et al. 1992; Kozlowski et al. 1993, 1993/1994; Mankowski et al. 1994;
Baraniecki et al. 1995). Thus, the demands for uptake and accumulation of heavy
metals by flax plants changed into quite contrast to hygienic aspects. It was known
from previous studies that flax accumulates in seeds relatively high heavy metal
concentrations as compared to other grain crops and even evidently elevated Cd
content as compared to soil Cd concentration (Gaudchau and Marquard 1990;
Schubert 1992;Bo ¨hm et al. 1992;Bo ¨hm and Marquard 1993a, b; Moraghan
1993; Schneider and Marquard 1996). The aim of studies was to prove if flax
may uptake and accumulate in aboveground parts elevated amounts of heavy metals
and—at the same time—not to decrease the yield and quality of harvested raw
material for subsequent industrial processing. It was necessary to find if there is a
genotype variation in uptake, translocation and accumulation of heavy metals and
by which agrotechnological treatments is possible to increase the bioavailability
and uptake of heavy metals by flax roots. Research activities in that way were
substantial in Poland, where besides of pot experiments (Kozlowski et al. 1993a, b;
Mankowski et al. 1994), the first on site studies started—e.g. experiments on
polluted soils near Copper Smelting Factory in Glogo ´w (Baraniecki et al. 1995,
2001; Grzebisz et al. 1997a, b; Grabowska and Baraniecki 1997). An overview of
Cd (as the most frequently studied toxic metal element) research in flax is provided
in Table 11.3.
There was an absence of knowledge on hemp as related to heavy metals up to the
beginning of the 1990s of the last century (similar situation as in flax). The hemp
research was mainly concentrated on drugs and oil content/composition (seed