Page 232 - Plant-Based Remediation Processes

224 M. Griga and M. Bjelkova ´

within a soil type (Grant and Bailey 1997). In contrast, accumulation of Zn was
unrelated to seed yield. Several papers described competition between Cd and Zn
uptake by flax plants (Moraghan 1993; Grant and Bailey 1997; Chakravarty and
Srivastava 1997a). Zn and Cd are chemically similar and may compete for binding
sites in the soil system and for uptake sites in the plant. At equimolar concentrations
of Cd and Zn, Zn outcompetes Cd due to interactive ion uptake, resulting in
reduction of Cd toxicity. Thus, based on this Cd–Zn antagonism or competitive
effect, the Cd uptake may be manipulated through Zn soil bioavailability (soil-
applied Zn may reduce Cd concentration in flax seed—hygienic aspect; decreased
Zn soil availability may increase Cd uptake and translocation—phytoremediation
aspect).
Nitrogen fertilisation elevated Cd concentration in flax seed and tissue in sites
with naturally higher Cd soil content, but not in soils with low Cd backgrounds
(Grant et al. 2000). As N fertiliser did not contain Cd, the increase in Cd concen-
tration may be explained by the effect of fertiliser on soil chemistry and/or impacts
on plant growth—N fertilisation may increase the bioavailability of Cd by increas-
ing ionic strength of the soil solution or decreasing soil pH. N application may also
increase root growth and plant vigour, which could increase the ability of the crop
to access and accumulate Cd. Zn concentration in the seed and tissue decreased
with N application (Grant et al. 2000). Phosphorus fertilisation (monoammonium
phosphate containing Cd contamination) seems to increase Cd concentration and
accumulation and to decrease Zn concentration in flax seed (Grant and Bailey
1997). Nevertheless, the results with P fertilisers later presented by the same
group (Grant et al. 2000) were a little bit contradicting, namely that effects of
N and P fertilisation on Cd concentration in flax seed were minor. Also Moraghan
(1993) reported minimum effect of P fertilisation on Cd uptake by linseed. N, P and
Cu (CuSO 4 ) fertilisation affected the bioavailability of several HM elements
(Fe, Mn, Zn, Cu and Mo) also in hemp (Jurkowska et al. 1990, 1992; Jasiewicz
1991; Gorlach and Gambus ´ 1992).
A specific type of fertilisation is using sewage sludge, which not only is rich in
organic as well as inorganic compounds, but which also brings to the soil toxic
heavy metals. If well applied, sewage sludge may increase not only the biomass
yield on the one side but also HMs accumulation on the other side as demonstrated
both in flax and hemp (Piotrowska-Cyplik and Czarnecki 2003a, b, 2005; Bjelkova ´
et al. 2011b; Bjelkova ´ 2011). However, heavily polluted sediments, e.g. river
sediments may results in severe HMs plant contamination (Lo ¨ser et al. 2002).
The important component of HMs bioavailability in soil are chelating
compounds (EDTA, DTPA, HEDTA, CDTA, NTA and citric acid), which increase
the mobility or solubility of metal element binded on organic matter and thus its
better phytoextraction. Kos et al. (2003) studied the effect of industrial soil (5.5 mg
1
Cd kg ) on HMs uptake by hemp plants in above-ground biomass. The application
of 5 mmol kg 1 EDDS (EDTA) resulted in significant increase of Cd (5.8 %) and
Zn (16 %), in case of Pb the concentration was increased 22-fold as compared to
control without EDTA.