Environmental Engineering Reference
In-Depth Information
6.2.4
Application Potential
of Chelating Agent EDTA
for Amelioration
division and elongation (Hatwar et al.
2003
).
Adverse effect of Cr was found to be nullified
by the supply of suitable amount of Fe and Zn
in moong, gram, and pea plants, possibly due to
the importance of these two essential nutrients
in growth and metabolism of plants (Vazquez
et al.
1987
). Among the factors which may limit
NO
3
−
assimilation, Fe plays a crucial role, being
a metal cofactor of enzymes of the reductive as-
similatory pathway (NR, nitrite reductase (NiR),
and GOGAT, all requiring Fe as Fe-heme group
or Fe-S cluster (Borlotti et al.
2012
). Fe is also
suggested to induce NR activity and/or prevent
degradation of the enzyme. It might induce NR
synthesis by mobilization of intracellular NO
3
−
and provide protection to in vivo NR degradation
in absence of NO
3
−
(Singh et al.
1997
). Yadav
et al. (
2007
) observed that the fresh weight, shoot
length, and chlorophyll in leaves of 2 mM Cr +
0.2 mM Fe-treated maize plants was higher than
that in 2 mM Cr-treated plants, both after 45 and
90 days. To overcome the toxic effects of Cr in
R. sativus
, Nath et al
.
(
2009
) used Fe in the re-
covery treatments and reported a significant re-
covery in most of the studied plant growth pa-
rameters. Hasegawa et al
.
(
2012
) also observed
that foliar spray of Fe or increased Fe supply to
roots also ameliorated the chlorosis in rice plants
under exposure to high Ni concentrations. Sinha
et al. (
2005
) conducted an experiment to deter-
mine whether the ill effects of excess Cr can be
ameliorated by Fe application in spinach by with-
drawal of Cr by iron application through different
modes. After 14 days of metal supply, the pots
of spinach with excess Cr were divided into five
lots and different recovery treatments were given
with a separate lot of control pots without Cr.
With all these various treatments, recovery from
ill effects of Cr was observed, and most con-
spicuously when Fe was supplied through roots
(250 μM) and through spray (250 μM) together.
This resulted in changes in the Biomass, concen-
tration of chlorophylls, ferrous content, Hill reac-
tion activity, relative water content; and recovery
in activity of CAT, peroxidase, ribonuclease, and
starch phosphorylase; along with lowered Cr
concentration.
Chelation is simply defined as a process by which
a molecule encircles and binds to the metal. Che-
lating agents such as low molecular weight or-
ganic acids (LMWOAs), e.g., citric acid, oxalic
acid, tartaric acid, etc., and synthetic chelators
(ethylenediaminetetraacetic acid, EDTA and di-
ethylene triamine pentaacetic acid, DTPA) are
the amendments most commonly applied for
chemically assisted phytoextraction of metals
from soils (Nascimento et al.
2006
). Such sub-
stances are capable of forming complexes with
metal ions, thereby increasing the bioavailability
of heavy metals in soils. Synthetic chelators like
EDTA form chemically and microbiologically
stable complexes with heavy metals, which oth-
erwise contaminate groundwater (Satroutdinov
et al.
2000
). LMWOAs provide alternative che-
lators by being easily biodegradable and more
environmentally compatible (Meers et al.
2005
;
Nowack et al.
2006
; Bala and Thukral
2011
).
Synthetic chelating agents have considerable ef-
fects on the fraction and solubility of heavy met-
als in soils. EDTA is a synthetic chelating agent
commonly used in various fields (pulp and paper
industry, detergents industry, food industry, med-
icine, biomedical labs) in order to remove harm-
ful metal ions from many processes and products
(Iranshahi et al.
2011
). It also reflects a promising
alternative in plant protection under heavy metal
toxicity. In a supporting evidence, Mohanty and
Patra (
2011
) observed that total chlorophyll
content in the rice (
Oryza sativa
L.) seedlings
treated with Cr(VI)-EDTA (10 μM) solution was
more as compared to the untreated. The alfalfa
(
Medicago sativa
cv.
Trifolium alexandrinum
) is
a sensitive plant to heavy metal (e.g., Co and Cr)
stress. Zeid et al. (
2013
) investigated the effect of
different concentrations of Co and Cr on alfalfa
growth, photosynthesis, antioxidant enzymes,
carbohydrate, protein, and mineral ion content
with an aim to overcome the toxic effects of these
heavy metals. There was a gradual reduction in
growth, metabolic activities, and the antioxidant
enzyme activity with increasing concentrations
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