Page 160 - Enzymes in Tropical Soils

148 Enzymes In Tropical Soils

corn. It was also reported that a metalophyte plant from Belgium Thlaspi
caerulescens was a heavy metal hyperaccumulator, that can grow well in a medium
-1
-1
with concentrations of up to 25,000 mg Zn kg and 1,000 mg Cd kg . This plant
was tolerant to heavy metals and may absorb extremely high Cd without yield
decrease and could be used in phytoextraction of soils contaminated by Zn and Cd
(Brown et al., 1995). Several varieties of Indica were also potential as contaminant
Cd phytoextractors in paddy fields because this paddy variety may have
accumulated Cu in its tissue and possesed high biomass. In their research, it was
indicated that after planting this variety for two years, the concentration of Cd in
contaminated paddy soils decreased by 18%, therefore, the soil was then safer for
planting non-phytoextractor paddy. Guo et al. (2013) reported that the
bioavailability of heavy metals could still be high after washing the heavy metal
contaminated soil. Liming the washed soil may release the adsorbed metal-
chelates. The phytoextraction by Sedum alfredii after soil washing was an effective
to deplete the mobile Cd activated by soil washing.
Laidlaw et al. (2012) used several Salix (willows) species/cultivars to extract
heavy metals from contaminated soils. Except S. chilensis, all other cultivars
-1
produced 10 ro 20 ton ha biomass, while most cultivars growing in biosolids
-1 −1
produced less biomass (< 6 ton ha ). Salix matsudana (20 t ha ) and S. reichardtii
−1
A. Kerner (18 t ha ) produced similar aboveground biomass production in both soil
and biosolids. These cultivar, driven by the superior biomass production, were the
most effective cultivars in extracting metals from biosolids. The willows were
effective in extracting the most soluble/exchangeable metals (Cd, 0.18; Ni, 0.40;
−1
and Zn, 11.66 kg ha ).
Analysis of contaminated Aspen garden soils by Boon and Soltanpour (1992)
showed that in general leafy portions of plants contained the highest
concentrations of Pb and Cd followed by roots and fruits. Cabbage and brocolli
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leaves contained Pb of less than 5 mg kg while lettuce and spinach contained 41
-1
to 45 mg kg of Pb. The Plant (lettuce or spinach) Pb showed a linear relationship
with AB-DTPA soil extracts Pb conncentration (Y = 2.36 + 0.05x, r = 0.95) and so did
Cd concentration (y = 2.07 + 0.95x, r = 0.86). These findings demonstrate that
lettuce and spinach may accumulate Pb much better and may be used to
accumulate the Pb in contaminated soils. Cabbage and brocolli are, therefore,
recommended for vegetable consumption from contaminated soils. Lead uptake
-1
into vegetable grown on a high-level Pb-contaminated soil (461 mg kg ) is shown in
Fig 9.13. However, Gothberg et al. (2004) reported that water spinach exposed to
metals retained most of the metals in the roots, that have a higher tolerance than
shoots with respect to high internal metal concentrations. Buss et al. (2012) also

Abdul Kadir Salam - 2014