20
K. KirupaSree et al.
3.2 Lead
Lead can affect the various life forms through contamination from old lead plumbing
pipes, dusts, fuels from various industrial sites and also in the old orchard sites in
production where arsenate and lead is mostly used (Tangahu et al. 2011). Long term
exposure to lead is found to be intensely toxic to both animals as well as plants which
is non-biodegradable and has several harmful effects on organic systems including
soil properties i.e., pH, organic carbon, amorphous iron, aluminium oxides (FEAL),
and cation exchange capacity. (Bradham et al. 2006; Pehlivan et al. 2009). Several
bacteria, such as Arthrobacter spp., Bacillus megaterium, Pseudomonas marginalis,
Citrobacter freundii, Staphylococcus aureus, and E. coli have been found to be
resistant to lead (Das et al. 2016).
3.3 Cadmium
Cadmium is highly soluble in water therefore it is easily up taken by plants which
results in phytotoxicity followed by entry through the pathways into the food chain
causing serious harmful effects to human beings (Buchet et al. 1990). This heavy
metal has been classified into carcinogenic to humans by The International Agency
for Research on Cancer (IARC 1993). Still at low concentrations, cadmium alters
some enzyme activities including those enzymes involved in Calvin cycle, CO 2
fixation, Carbohydrate and Phosphorus metabolisms (Gill and Tuteja 2011). This
may result in the underdeveloped growth, alterations in chloroplast ultrastructure,
Chlorosis, leaf epinasty, inhibition of photosynthesis and pollen germination, alterations in nitrogen (N) and sulphur (S) metabolism and disruption of the antioxidant machinery (Gill and Tuteja 2011). In a report by Roane et al. (2001), Pseudomonas strain H1 and Bacillus strain H9 showed an intracellular mechanism of
cadmium sequestration (36%) for reducing cadmium toxicity. These strains showed
the production of exopolymers (EPS) which accumulated cadmium and reduced
soluble cadmium levels by 22% and 11%, respectively.
3.4 Chromium
Seventh most rich metal on earth is chromium and exists in two stable states in
the environment: they are trivalent Cr
3+ and hexavalent Cr
6+ . Source of Chromium
contamination is due to the use of Cr in many industries such as leather tanning,
metal plating, and other metallurgical procedures. The insufficient disposal of their
wastes may give rise to concentrations above the natural values (Wuana 2011).
Chromium inhibits sulphate membrane transport and causes oxidative damage in
bacteria. Against chromium toxicity, microbes involve in two mechanisms. The first
K. KirupaSree et al.
3.2 Lead
Lead can affect the various life forms through contamination from old lead plumbing
pipes, dusts, fuels from various industrial sites and also in the old orchard sites in
production where arsenate and lead is mostly used (Tangahu et al. 2011). Long term
exposure to lead is found to be intensely toxic to both animals as well as plants which
is non-biodegradable and has several harmful effects on organic systems including
soil properties i.e., pH, organic carbon, amorphous iron, aluminium oxides (FEAL),
and cation exchange capacity. (Bradham et al. 2006; Pehlivan et al. 2009). Several
bacteria, such as Arthrobacter spp., Bacillus megaterium, Pseudomonas marginalis,
Citrobacter freundii, Staphylococcus aureus, and E. coli have been found to be
resistant to lead (Das et al. 2016).
3.3 Cadmium
Cadmium is highly soluble in water therefore it is easily up taken by plants which
results in phytotoxicity followed by entry through the pathways into the food chain
causing serious harmful effects to human beings (Buchet et al. 1990). This heavy
metal has been classified into carcinogenic to humans by The International Agency
for Research on Cancer (IARC 1993). Still at low concentrations, cadmium alters
some enzyme activities including those enzymes involved in Calvin cycle, CO 2
fixation, Carbohydrate and Phosphorus metabolisms (Gill and Tuteja 2011). This
may result in the underdeveloped growth, alterations in chloroplast ultrastructure,
Chlorosis, leaf epinasty, inhibition of photosynthesis and pollen germination, alterations in nitrogen (N) and sulphur (S) metabolism and disruption of the antioxidant machinery (Gill and Tuteja 2011). In a report by Roane et al. (2001), Pseudomonas strain H1 and Bacillus strain H9 showed an intracellular mechanism of
cadmium sequestration (36%) for reducing cadmium toxicity. These strains showed
the production of exopolymers (EPS) which accumulated cadmium and reduced
soluble cadmium levels by 22% and 11%, respectively.
3.4 Chromium
Seventh most rich metal on earth is chromium and exists in two stable states in
the environment: they are trivalent Cr
3+ and hexavalent Cr
6+ . Source of Chromium
contamination is due to the use of Cr in many industries such as leather tanning,
metal plating, and other metallurgical procedures. The insufficient disposal of their
wastes may give rise to concentrations above the natural values (Wuana 2011).
Chromium inhibits sulphate membrane transport and causes oxidative damage in
bacteria. Against chromium toxicity, microbes involve in two mechanisms. The first