Page 233 - Plant-Based Remediation Processes

11 Flax (Linum usitatissimum L.) and Hemp (Cannabis sativa L.)... 225

In general, lower values of soil pH stimulate higher heavy metal uptake;
nevertheless, published results in flax are not always unequivocal, sometimes
even contradicting. Gaudchau and Marquard (1990) found small increase of Cd
accumulation in the stem and seeds of linseed after CaO application. Bo ¨hm and
Marquard (1993a, b) reported that liming of soils with natural Cd content did not
result in evident decrease of Cd uptake. In contrast, liming of soils with artificially
elevated Cd content explicitly decreased Cd uptake and Cd content in roots, stems
and capsules; only seeds behaved indifferently. Heyn and Janssen (1991) proved an
effect of liming (neutral soil pH recommended) on decreased Cd uptake by linseed
plants—more markedly in seeds than in the stem. Schubert (1992) found higher Cd
uptake in seeds in alluvial soil with pH ¼ 7.2, high clay fraction (63 %) and higher
organic matter content (3.3 %) as compared to brown soil with pH ¼ 6.7, 12 % of
clay and 0.4 % organic matter. Cd uptake by flax roots in hydroponics increased in
pH range 4.0–6.0 (pH ¼ 6.0 being optimum), pH ¼ 7.0 induced drop in Cd uptake.
Increasing CaSO 4 concentration in hydroponics resulted in decreased Cd uptake by
flax roots (Schubert 1992). Lukipudis (2001) tested three cvs of fibre flax in the
region of heavy polluted soils (Zlatica-Pirdop valley, Bulgaria)—decreasing soil
pH (pH 6.1, 6.0, 5.9, 5.5, 5.0 and 4.8) led to increasing uptake of Cu, Cd and Pb and
their increased accumulation in the fibre and seed. Application of CaCO 3 (change
of soil pH from 4.6 to 6.6) decreased the bioavailability of Cd, Cu, Ni, Pb and Zn in
hemp (Gorlach 1994). The year-to-year effect is represented mainly by the level of
precipitation. Higher soil water content may increase the mobility of Cd in the soil
and the transport flux of Cd through the plant; thus, enhanced moisture may
increase ability of flax to accumulate Cd and translocate it from the tissue to the
seed (Grant et al. 2000; Bjelkova ´ et al. 2011a, b). Based on above-mentioned data it
is evident that heavy metal distribution is considerably affected by experimental
conditions, namely soil properties, as well as genotypes used. Thus, properly
designed agrotechnology may either stimulate or inhibit uptake of HMs by flax
and hemp.

11.5.4 On Site Studies

Despite the minimum scientific knowledge on heavy metals behaviour in flax and
hemp crops in the early nineties of the last century, on site pilot studies started in
Europe, particularly in Poland—the reason was the long-lasting tradition in the
breeding and growing of flax and hemp in this country and also the search for new
roles of these crops both in agriculture and in industry in the end of the century.
In addition, phytoremediation technology emerged at this time as new approach to
clean environment. Later, on-site studies were extended to Bulgaria (Lukipudis
2001), Slovenia (Kos and Les ˇtan 2004), Germany and the Czech Republic (Tlustos ˇ
et al. 2006) also thanks to locations historically contaminated by heavy industry.