Page 229 - Plant-Based Remediation Processes

11 Flax (Linum usitatissimum L.) and Hemp (Cannabis sativa L.)... 221

similar values for Cd and Pb, while Cu and Zn were more translocated to seeds.
Lo ¨ser et al. (2002) used hemp for model remediation of river sediment highly
polluted with HMs (e.g. Cd 17 mg kg 1 DW, Zn 2120 mg kg 1 DW) versus
reference soil (e.g. Cd <2mgkg 1 DW, Zn 75 mg kg 1 DW)—they studied
phytotoxicity of HMs on hemp growth and also accumulation of selected metals
in plant organs and hemp raw materials (fibre, shives) as related to further industrial
processing. There were practically no differences in Cd accumulation in plant
organs on reference soil, while Cd accumulation (mg kg 1 DW) from river sedi-
ment increased in the following order: seeds (1.4) < shives (1.6) < young leaves
(2.0) < roots (2.4) < old leaves (4.2) < fibres (5.2). Hemp grown on (watered)
sediment contained about 40 times more Cd, Zn and Ni than hemp cultivated on
reference soil. The inhibition of hemp plants growth accompanied by some mor-
phological/physiological abnormalities was considered to be a result of synergistic
action of a low pH and several mobile toxic metals (especially Cd, Zn and Ni; Zn
content of old leaves was even higher than in the settled sediment; Table 11.4). The
high HMs (Cd) contamination of hemp fibre for further industrial processing is
discussed below (Chap. 6). Linger et al. (2002) compared HMs accumulation and
fibre quality of hemp (cv. JUSO 31) grown on HMs-polluted soil (application of
sewage sludge with 102 mg Cd kg 1 DW, 419 mg Ni kg 1 DW and 454 mg Pb kg 1
DW). Leaves contained more HMs than seeds; nevertheless, fibres accumulated
less Cd than reported by Lo ¨ser et al. (2002)—the reason may be the lower Cd
uptake from soil (limited bioavailability) in the field experiment versus hydroponics
(easy uptake of mobile toxic metals). Linger et al. (2005) studied hemp growth, Cd
uptake and photosynthesis parameters by hemp in pot experiment with two levels of
artificial Cd contamination (CdSO 4 ): 17 and 72 mg Cd kg 1 soil. Cd concentrations
up to 72 mg kg 1 soil had no negative effect on hemp seeds germination. Fresh
mass and Cd content in plant organs was measured weekly for 7 weeks and then at
the end of vegetation (133 days after sowing). The roots (plants grown on 17 mg Cd
kg 1 DW) always accumulated the highest Cd concentrations with a maximum of
830 mg Cd kg 1 DW after 24 days, and then began to decline with plant growth.
Stems and leaves accumulated Cd to a much lesser extent; the highest determined
values were 87 and 68 mg Cd kg 1 DW in stem and leaves, respectively. At the end
of vegetation period (133 days), the means were 42 mg Cd kg 1 DW for roots,
20 mg Cd kg 1 DW for stems and 15 mg Cd kg 1 DW for leaves. Plants grown on
72 mg Cd kg 1 DW displayed a very strong growth inhibition, and most plants died
4–5 weeks after sowing (only one plant survived this Cd treatment until 80 days
within negligible biomass). In this study, hemp roots demonstrated a strong resis-
tance to HMs (Cd) and have shown a somewhat “hyperaccumulator-like” potential
(¼ more than 100 mg Cd kg 1 DW); however, this seemed to depend on the
plant development stage (the ability of juvenile roots to produce phytochelatins
and detoxify Cd; the loss of this ability in older roots). According to authors, the
growth inhibition by high Cd concentrations may be connected with a strong
difference between the stem/leaf and root meristems in Cd sensitivity/tolerance
as well as with inhibition of photosynthesis. Angelova et al. (2004) recorded
decreasing trend in Pb, Cu, Zn and Cd accumulation in hemp organs: flowers