mercury (Chen et al. 1998; Travieso et al. 1999) present in effluents. Chlorella is
found to grow in a mixotrophic environment (Karlander and Krauss 1996). Sheng
et al. (2007) used two locally harvested brown marine algae Sargassum sp. and
Padina sp. for the removal of cations (Cd
2+ and Cr
3+ ) and an anion (Cr 2 O 7
2- ) from
dilute aqueous solutions. Pithophora sp. showed bioaccumulation potential for Cr,
Cd, and Pb removal at various concentrations (2, 5, 10, 20, and 30 ppm). The metal
uptake was increased with increase in the incubation period. Marine algae such as
Ascophyllum and Sargassum are effectively used in the biosorption of pollutants
(Yu et al. 1999) and reduced the concentrations of heavy metals in the polluted
environment to a very low level. In recent years, several species of the green algae
Enteromorpha and Cladophora have been utilized to measure heavy metal levels in
many parts of the world. Macroalgae have been extensively used to measure heavy
metal pollution in marine environments throughout the world.
Cyanobacteria (blue-green algae) are the most primitive photosynthetic prokaryotes and appeared on the planet during the Precambrian period. Cyanobacteria
occupy a vast array of habitats and are susceptible to various physical and chemical
changes (e.g., light, salinity, temperature, and nutrient composition) (Boomiathan
2005; Semyalo 2009). Cyanobacteria have great potential to be used in wastewater
and industrial effluent treatment, bioremediation of aquatic and terrestrial habitats,
chemical industries, food and feed, and fuel, as biofertilizers, etc. (Cairns and
Dickson 1971). Chojnacka et al. (2005) reported the biosorption performance of
Cr
+3 , Cu
+2 , and Cd
+2 ions by blue-green algae Spirulina.
The use of immobilized algae in the removal of heavy metal is an efficient method
and offers significant advantages in bioreactors (Hameed and Ebrahim 2007). Huge
loads of wastes from industries, domestic sewage, and agriculture practices find their
way into rivers and ponds resulting in large-scale deterioration of water quality
leading to the availability of potable water. There is an urgent need to screen and
develop efficient alga for the bioremediation of wastewater.
5.1.3.1 Heavy Metal Accumulation and Tolerance Mechanisms in Algae
Synthesis of metallothioneins (MTs) or phytochelatins (PCs), complex formation,
compartmentalization, exclusion, and translocation into vacuoles are various defense
mechanisms that respond against heavy metals stress (Mejáre and Bülow 2001).
Thalassiosira pseudonana and Thalassiosira weissflogii are marine algae that produce phytochelatins in large quantities due to the higher activity of phytochelatin
synthase, which has greater affinity for the glutathione substrate or metal ions (Ahner
et al. 2002). Ligands like histidine (His), citrate, oxalate, malate, nicotianamine, and
phosphate derivatives (phytate) play an important role in detoxification and tolerance. Algae have high negatively charged surface (cell wall components) which
leads to increased adsorption, phytosorption, and affinity of heavy metal cations in
wastewater treatment (Sekabira et al. 2011). Micrasterias denticulata (Volland et al.
2012) and Spirogyra hyaline (Kumar and Oommen 2012) showed promising results
for sequestration of cadmium ions from contaminated sites. The principal
15 Cadmium as an Environmental Pollutant: Ecotoxicological Effects, Health. . .
373
found to grow in a mixotrophic environment (Karlander and Krauss 1996). Sheng
et al. (2007) used two locally harvested brown marine algae Sargassum sp. and
Padina sp. for the removal of cations (Cd
2+ and Cr
3+ ) and an anion (Cr 2 O 7
2- ) from
dilute aqueous solutions. Pithophora sp. showed bioaccumulation potential for Cr,
Cd, and Pb removal at various concentrations (2, 5, 10, 20, and 30 ppm). The metal
uptake was increased with increase in the incubation period. Marine algae such as
Ascophyllum and Sargassum are effectively used in the biosorption of pollutants
(Yu et al. 1999) and reduced the concentrations of heavy metals in the polluted
environment to a very low level. In recent years, several species of the green algae
Enteromorpha and Cladophora have been utilized to measure heavy metal levels in
many parts of the world. Macroalgae have been extensively used to measure heavy
metal pollution in marine environments throughout the world.
Cyanobacteria (blue-green algae) are the most primitive photosynthetic prokaryotes and appeared on the planet during the Precambrian period. Cyanobacteria
occupy a vast array of habitats and are susceptible to various physical and chemical
changes (e.g., light, salinity, temperature, and nutrient composition) (Boomiathan
2005; Semyalo 2009). Cyanobacteria have great potential to be used in wastewater
and industrial effluent treatment, bioremediation of aquatic and terrestrial habitats,
chemical industries, food and feed, and fuel, as biofertilizers, etc. (Cairns and
Dickson 1971). Chojnacka et al. (2005) reported the biosorption performance of
Cr
+3 , Cu
+2 , and Cd
+2 ions by blue-green algae Spirulina.
The use of immobilized algae in the removal of heavy metal is an efficient method
and offers significant advantages in bioreactors (Hameed and Ebrahim 2007). Huge
loads of wastes from industries, domestic sewage, and agriculture practices find their
way into rivers and ponds resulting in large-scale deterioration of water quality
leading to the availability of potable water. There is an urgent need to screen and
develop efficient alga for the bioremediation of wastewater.
5.1.3.1 Heavy Metal Accumulation and Tolerance Mechanisms in Algae
Synthesis of metallothioneins (MTs) or phytochelatins (PCs), complex formation,
compartmentalization, exclusion, and translocation into vacuoles are various defense
mechanisms that respond against heavy metals stress (Mejáre and Bülow 2001).
Thalassiosira pseudonana and Thalassiosira weissflogii are marine algae that produce phytochelatins in large quantities due to the higher activity of phytochelatin
synthase, which has greater affinity for the glutathione substrate or metal ions (Ahner
et al. 2002). Ligands like histidine (His), citrate, oxalate, malate, nicotianamine, and
phosphate derivatives (phytate) play an important role in detoxification and tolerance. Algae have high negatively charged surface (cell wall components) which
leads to increased adsorption, phytosorption, and affinity of heavy metal cations in
wastewater treatment (Sekabira et al. 2011). Micrasterias denticulata (Volland et al.
2012) and Spirogyra hyaline (Kumar and Oommen 2012) showed promising results
for sequestration of cadmium ions from contaminated sites. The principal
15 Cadmium as an Environmental Pollutant: Ecotoxicological Effects, Health. . .
373