Environmental Engineering Reference
In-Depth Information
important role in P storage, as an energy store, as
a source of cations and as a source of
myo
-inosi-
tol and also helps in initiating dormancy (Singh
et al.
2011
). In cereals and legumes, phytic acid
accumulates in the aleurone particles and globoid
crystals, respectively (Reddy et al.
1982
; Tyagi
and Verma
1998
). Graf et al. (
1987
) suggested
that phytic acid in seeds acts as a natural anti-
oxidant during dormancy. The unique phytate ion
structure, with 12 replaceable protons and high
density of negatively charged phosphate groups
(responsible for its characteristic properties), al-
lows it to form very stable complexes with mul-
tivalent cations (Dost and Tokul
2006
). A consid-
erable number of researchers have reported the
chelating ability of the phytate ion with several
mineral elements including, Cu
2+
, Zn
2+
, Co
2+
,
Cd
2+
, Mg
2+
, Mn
2+
, Fe
2+
, Fe
2+
, Ni
2+
and Ca
2+
to
form phytate-mineral and/or other protein-min-
eral-phytate complexes (Sapna et al.
2013
). In-
testinal absorption is a key and complex stage
for maintaining normal mineral homeostasis and
requires that minerals remain in the ionic state
for absorption (Lopez et al.
2002
). Due to the in-
ability of monogastric animals to hydrolyse the
phytate-mineral complex, minerals are not ab-
sorbed in the intestine and are excreted out. Also,
binding or interaction of phytic acid with dietary
proteins reduces their digestibility due to steric
hindrance to proteases through changes in pro-
tein solubility or by altering the protein structure
(Cowieson et al.
2006
). According to Liu et al.
(
2010
), phytate can also interfere with lipid me-
tabolism and consequently energy regulation in
chickens. The inhibition of activity of important
digestive enzymes such as α-amylase, trypsin,
lipase, acid phosphatase and pepsin was also re-
ported to be affected by phytic acid (Harland and
Morris
1995
; El-Batal et al.
2001
).
Apart from some antinutritional effects given
above, phytic acid has been shown to exert an
antineoplastic effect in animal models of both
colon and breast carcinomas (Iqbal et al.
1994
).
The inositol phosphate intermediates synthesised
from phytic acid hydrolysis play a role in the cel-
lular transport, whereas inositol triphosphates
play a role in signal transduction and regulation
of cell functions in plant and animal cells (Vohra
and Satyanarayana
2003
; Greiner and Konietzny
2006
; Rao et al.
2009
; Singh and Satyanarayana
2011
; Sapna et al.
2013
).
7.3
Consequences of Phosphorus
Pollution
7.3.1
Phosphorus Loss, Buildup
and Environmental Impacts
Phosphorus remains in short supply over large
parts of the globe, still some developed coun-
tries with a long history of P fertiliser applica-
tion and intensive animal farming despite having
small lands are facing problems of P pollution.
There are two major aspects related to P depo-
sition and pollution. First, elaborated systems
of fertility management and prolonged use of P
fertiliser in some developed countries have built
up an extensive level of soil P up to the extent
that further limited or no addition of P is required
for crop production. However, continued use of
P fertilisers and use of P-supplemented animal
feed is leading to the deposition/production of
P waste resulting in P pollution (Howarth et al.
2000
; Bomans et al.
2005
). The problem is fur-
ther perplexed by variation in plant capability
for P uptake with crop type, crop yield and soil
type. The low uptake of P by crops can allow P to
accumulate in soils, which can eventually create
P runoff and contaminate nearby surface water
(Garikipati
2004
).
Second, intensive animal production on farms
with little land produces manure in excess of
the nutrient requirements of crops and pasture
lands. Generally, the application this manure to
field is determined by measuring N content of
the manure and the N requirement of the crop.
Because animal manures are typically rich in P
(P concentrations range from 4 to 7 mg/g dry
weight of dairy manure, compared to 0.08-
1.56 mg/g dry weight of benchmark soils and
0.486-2.439 mg/g dry weight of surface soils),
its use leads to accumulation of excess P to the
soil (Garikipati
2004
). According to NRC (
2001
),
among all dietary mineral elements for dairy ani-
mals, P represents the greatest potential risk if
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