number of adverse effects like skin disease in the form of dermatitis, kidney
problems, various heart diseases, respiratory tract cancer and lung fibrosis [58, 92].
Lead (Pb) is a normal component of the earth’s crust and occurs naturally in very
low concentration in soil and water [74]. It exists in two oxidation states of 0 and 2
and the dominant species found in normal water pH are Pb
+2 , PbOH
+ and
PbHCO 3
+
. Of these Pb
+2 is more common and reactive form. Lead is less mobile in
soil and therefore usually found in minute quantities in deep aquifers in comparison
to other heavy metals like Hg, As and Cd. Various sources contribute to the lead
contamination in drinking water such as industrial wastes, vehicle exhausts and
household paint. The WHO admissible limit for Pb concentration in drinking water
is 0.01 mg/L. Lead usefulness in human physiology is unknown [74], but on
contrary, its overdose exposure for longer times could affect major body organs and
systems like neurological, gastric, haematopoietic, heart, reproductive system and
immune system and also affects skeleton and kidneys [80, 111]. Lead has hazardous
effects on pregnant women which can cause delay in development, under weight of
fetus and cases of miscarriages are also recorded [8].
The naturally occurring compound Mercury (Hg) is considered as “persistent bio
accumulative toxin” [114]. The WHO permissible limit for mercury in drinking
water is 0.001 mg/L. Inorganic form of Mercury is less toxic than its organic forms
owing to the differences in bioavailability [11]. In aquatic environments bacteria
can transform mercury to methyl mercury which is highly toxic in nature [32] and
can easily accumulated by fish and biomagnification takes place in the food chain.
Coal fired power plants, smelting, alkali processing, apart from other industrial
activities contribute to the mercury in environment. Historically, mercury was used
in number of ways until its adverse effects became known. In the environment, the
mercury cycles between air, water, soil, sediment, and biota. This causes difficulties
in determination of its proper source. Occurrence of mercury in nature is also
recorded in the sediments after the volcanic eruption which causes its mixing in
atmosphere. Besides, the fly ash of power plants also contains mercury which
directly mixes with atmosphere [91]. Only mercury has the property of biomagnification in the food chain and has serious detrimental effect on human health as
well as the environment. Being a potential cellular toxin it has various harmful
effects on our nerve cells, production of neurotransmitter even on the rate of production of thyroid and testosterone hormones [32].
Cadmium (Cd) exists in 0 and 2 oxidation states and is found in relatively low
concentration in aquatic environment [61]. Its concentration could increase due to
different activities like mining, seepage from hazardous waste site, wastewater
disposal from industries or continuous use of Cd containing phosphate fertilizers.
Cd is widely used in industrial applications including manufacture of batteries
(NiCd), pigments, plastics etc. Its dominant form in pure water is Cd
2+ (in fresh
water the aquo-complexes are sticked to humic matters) and at high salinity, it
forms a mixture of chloro-complexes, with CdCl 3
− overriding in seawater [91].
Therefore the toxicity of same metal varies in different aquatic systems with
diverse conditions. There are some metals and metalloids of polyatomic anions like
Types of Water Pollutants: Conventional and Emerging
27
problems, various heart diseases, respiratory tract cancer and lung fibrosis [58, 92].
Lead (Pb) is a normal component of the earth’s crust and occurs naturally in very
low concentration in soil and water [74]. It exists in two oxidation states of 0 and 2
and the dominant species found in normal water pH are Pb
+2 , PbOH
+ and
PbHCO 3
+
. Of these Pb
+2 is more common and reactive form. Lead is less mobile in
soil and therefore usually found in minute quantities in deep aquifers in comparison
to other heavy metals like Hg, As and Cd. Various sources contribute to the lead
contamination in drinking water such as industrial wastes, vehicle exhausts and
household paint. The WHO admissible limit for Pb concentration in drinking water
is 0.01 mg/L. Lead usefulness in human physiology is unknown [74], but on
contrary, its overdose exposure for longer times could affect major body organs and
systems like neurological, gastric, haematopoietic, heart, reproductive system and
immune system and also affects skeleton and kidneys [80, 111]. Lead has hazardous
effects on pregnant women which can cause delay in development, under weight of
fetus and cases of miscarriages are also recorded [8].
The naturally occurring compound Mercury (Hg) is considered as “persistent bio
accumulative toxin” [114]. The WHO permissible limit for mercury in drinking
water is 0.001 mg/L. Inorganic form of Mercury is less toxic than its organic forms
owing to the differences in bioavailability [11]. In aquatic environments bacteria
can transform mercury to methyl mercury which is highly toxic in nature [32] and
can easily accumulated by fish and biomagnification takes place in the food chain.
Coal fired power plants, smelting, alkali processing, apart from other industrial
activities contribute to the mercury in environment. Historically, mercury was used
in number of ways until its adverse effects became known. In the environment, the
mercury cycles between air, water, soil, sediment, and biota. This causes difficulties
in determination of its proper source. Occurrence of mercury in nature is also
recorded in the sediments after the volcanic eruption which causes its mixing in
atmosphere. Besides, the fly ash of power plants also contains mercury which
directly mixes with atmosphere [91]. Only mercury has the property of biomagnification in the food chain and has serious detrimental effect on human health as
well as the environment. Being a potential cellular toxin it has various harmful
effects on our nerve cells, production of neurotransmitter even on the rate of production of thyroid and testosterone hormones [32].
Cadmium (Cd) exists in 0 and 2 oxidation states and is found in relatively low
concentration in aquatic environment [61]. Its concentration could increase due to
different activities like mining, seepage from hazardous waste site, wastewater
disposal from industries or continuous use of Cd containing phosphate fertilizers.
Cd is widely used in industrial applications including manufacture of batteries
(NiCd), pigments, plastics etc. Its dominant form in pure water is Cd
2+ (in fresh
water the aquo-complexes are sticked to humic matters) and at high salinity, it
forms a mixture of chloro-complexes, with CdCl 3
− overriding in seawater [91].
Therefore the toxicity of same metal varies in different aquatic systems with
diverse conditions. There are some metals and metalloids of polyatomic anions like
Types of Water Pollutants: Conventional and Emerging
27