higher levels since more and more of nitrogen is consistently used to the land
surface on yearly basis. It has been observed that the water with greater than 50 mg/
l of nitrate concentration could create health problems in humans and animals [36,
115]. If the nitrate polluted groundwater is discharged to the low nitrate concentration water bodies, it may result in eutrophication [98]. Various researches have
observed that the increased nitrate concentration in groundwater can serve as an
indirect indicator of the existence of other pollutants that are derived from human
activities [28, 77]. The NO 3
− , component of nitrogen cycle in nature, signifies the
most oxidized chemical form of nitrogen found in the natural systems and forms an
important part of building blocks of living organism, i.e. DNA, RNA, hormones
protein, vitamins, and enzymes [75]. Therefore human health consequences for
humans because of high nitrate level exposure remain a great concern. The NO 3
−
binds itself to the hemoglobin and therefore its increased concentration levels
decreases the oxygen-carrying capacity in the blood which causes methemoglobinemia or “blue baby syndrome”, a condition that may result in the mortality
due to asphyxiation especially in the new born babies [2]. The infants (of <6
months of age) remain at highest risk because their digestive systems have bacteria
which speedup the binding process. It is reported that nitrate can be endogenously
reduced to nitrate, undergo nitrosation reactions in stomach with amines and then
amines to form a variety of N-nitroso compounds (NOC) and are mostly carcinogens [106, 100, 113].
2.3 Trace Metals and Metalloids
Natural water dissolves the impurities of trace elements/heavy metals which are
already present in water while seeping downward as a part of hydrological cycle
[48]. Additionally, several human activities including large scale use of agricultural
pesticides, fertilizers, dyes and improper disposal of industrial and municipal wastes
introduce these metals to both the surface as well as groundwater [56]. Though for
human health many of these metals are considered essential [44], however, their
increased concentrations result in water pollution and lead to acute health issues in
humans and other organisms. The speciation or the form in which they exist in a
given water system determines the fate and toxicity of these metals even as it is a
metal’s freely dissolved form which is normally the most toxic. The EPA has
included metalloids, metals & organics under priority water pollutants [64]. The
metals and metalloids include Sb, As, Be, Cd, Cr, Cu, Pb, Hg, Ni, Se, Ag, Zn and
Th. Most of them are transition elements, like Cd and Cu, or heavy metals like Pb
and Ag and have tendency to form complexes with organic or inorganic ligands. In
a solution ligands easily supply a pair of electrons to positively charged metal ions
in solution and hence form complex ions with one to six ligands bound to the
central metal atom. In fact, metal cations in water are hardly ever present as just the
freely dissolved ions. If nothing else, water molecules can serve as ligands and tie to
metal ions forming aquo-complexes. The ability of formation of various complex
Types of Water Pollutants: Conventional and Emerging
25
surface on yearly basis. It has been observed that the water with greater than 50 mg/
l of nitrate concentration could create health problems in humans and animals [36,
115]. If the nitrate polluted groundwater is discharged to the low nitrate concentration water bodies, it may result in eutrophication [98]. Various researches have
observed that the increased nitrate concentration in groundwater can serve as an
indirect indicator of the existence of other pollutants that are derived from human
activities [28, 77]. The NO 3
− , component of nitrogen cycle in nature, signifies the
most oxidized chemical form of nitrogen found in the natural systems and forms an
important part of building blocks of living organism, i.e. DNA, RNA, hormones
protein, vitamins, and enzymes [75]. Therefore human health consequences for
humans because of high nitrate level exposure remain a great concern. The NO 3
−
binds itself to the hemoglobin and therefore its increased concentration levels
decreases the oxygen-carrying capacity in the blood which causes methemoglobinemia or “blue baby syndrome”, a condition that may result in the mortality
due to asphyxiation especially in the new born babies [2]. The infants (of <6
months of age) remain at highest risk because their digestive systems have bacteria
which speedup the binding process. It is reported that nitrate can be endogenously
reduced to nitrate, undergo nitrosation reactions in stomach with amines and then
amines to form a variety of N-nitroso compounds (NOC) and are mostly carcinogens [106, 100, 113].
2.3 Trace Metals and Metalloids
Natural water dissolves the impurities of trace elements/heavy metals which are
already present in water while seeping downward as a part of hydrological cycle
[48]. Additionally, several human activities including large scale use of agricultural
pesticides, fertilizers, dyes and improper disposal of industrial and municipal wastes
introduce these metals to both the surface as well as groundwater [56]. Though for
human health many of these metals are considered essential [44], however, their
increased concentrations result in water pollution and lead to acute health issues in
humans and other organisms. The speciation or the form in which they exist in a
given water system determines the fate and toxicity of these metals even as it is a
metal’s freely dissolved form which is normally the most toxic. The EPA has
included metalloids, metals & organics under priority water pollutants [64]. The
metals and metalloids include Sb, As, Be, Cd, Cr, Cu, Pb, Hg, Ni, Se, Ag, Zn and
Th. Most of them are transition elements, like Cd and Cu, or heavy metals like Pb
and Ag and have tendency to form complexes with organic or inorganic ligands. In
a solution ligands easily supply a pair of electrons to positively charged metal ions
in solution and hence form complex ions with one to six ligands bound to the
central metal atom. In fact, metal cations in water are hardly ever present as just the
freely dissolved ions. If nothing else, water molecules can serve as ligands and tie to
metal ions forming aquo-complexes. The ability of formation of various complex
Types of Water Pollutants: Conventional and Emerging
25