116
researchers (Alberic et al. 2006). Heavy metals like lead, cadmium, chromium and
mercury are highly toxic pollutants which could be significantly associated with
bioaccumulation within a myriad of ecological systems because they cannot be
biologically degraded and instead get concentrated within sediments (Agoramoorthy
et al. 2008). Globally, there has been a unanimous agreement that the reported
levels of heavy metals within mangrove sediments are increasing every year as a
result of pollution and activities caused by developmental growth and urbanization
(Agoramoorthy et al. 2008; Basamba et al. 2010).
Out of one of the fifty nine different types of mangrove species present within the
world, Avicennia marina is a cosmopolitan species which can grow within several
coastal habitats like Indonesia, Arab Gulf and Eastern Africa (Shriadah 1999;
Burchett et al. 2003; Rajkumar et al. 2009), India (Mitra 2013; Mitra and Zaman
2016).
Although there are variations in the levels of heavy metal tolerance exhibited by
different types of mangroves, the grey mangrove Avicennia marina has a relatively
higher tolerance level when compared with other mangrove species (Burchett et al.
2003; Agoramoorthy et al. 2008). This quality qualifies grey mangrove to be a good
bio- indicator and enables researchers to obtain quantitative information about the
environmental/ecological quality of its habitat through monitoring and experimental testing. It is speculated that Avicennia marina could be more tolerant to heavy
metal by developing several adaption mechanisms including avoiding the uptake of
metals actively and exclusion of ions (Burchett et al. 2003). Numerous studies have
utilized mangrove species and their sediments as reliable bio-indicators for heavy
metal pollution and contamination (Burchett et al. 2003; Defew et al. 2005).
Interestingly, the bio-concentration of various metals in this plant differs according
to the type of tissue. For instance mangrove leaves tend to accumulate lower levels
of metals as compared with mangrove roots and sediments (Defew et al. 2005). It
has been reported that very low heavy metal concentrations are found in the mangrove leaf tissues because most of the absorbed heavy metals get accumulated in
stem and root tissues. Nevertheless, root tissue is the most commonly used bioindicator for heavy metal pollution with high reliability and accuracy as compared
to leaves (Defew et al. 2005).
A study conducted by the Shankhadeep Chakraborty in 12 stations in Indian
Sundarbans revealed that Avicennia marina, Avicennia alba, Avicennia officinalis
and Excoecaria agallocha can be a potential indicator of heavy metal pollution in
this mangrove dominated deltaic complex.
The Indian Sundarbans, at the apex of Bay of Bengal (between 21°30′ N to
22°30′ N latitude and 87°25′ E to 89°10′ E longitude) offers a unique test bed for
studying the bioaccumulation pattern of heavy metals by mangrove floral species.
As species like Avicennia alba, Avicennia officinalis, Avicennia marina and
Excoecaria agallocha are endemic and dominant species of Indian Sundarbans
region, they are regularly exposed to heavy metal pollution, as most of the region is
contaminated with conservative pollutants (Mitra 1998; Mitra et al. 2011; Banerjee
et al. 2012; Mitra and Ghosh 2014).
5 Mangroves: A Sink of Heavy Metals
researchers (Alberic et al. 2006). Heavy metals like lead, cadmium, chromium and
mercury are highly toxic pollutants which could be significantly associated with
bioaccumulation within a myriad of ecological systems because they cannot be
biologically degraded and instead get concentrated within sediments (Agoramoorthy
et al. 2008). Globally, there has been a unanimous agreement that the reported
levels of heavy metals within mangrove sediments are increasing every year as a
result of pollution and activities caused by developmental growth and urbanization
(Agoramoorthy et al. 2008; Basamba et al. 2010).
Out of one of the fifty nine different types of mangrove species present within the
world, Avicennia marina is a cosmopolitan species which can grow within several
coastal habitats like Indonesia, Arab Gulf and Eastern Africa (Shriadah 1999;
Burchett et al. 2003; Rajkumar et al. 2009), India (Mitra 2013; Mitra and Zaman
2016).
Although there are variations in the levels of heavy metal tolerance exhibited by
different types of mangroves, the grey mangrove Avicennia marina has a relatively
higher tolerance level when compared with other mangrove species (Burchett et al.
2003; Agoramoorthy et al. 2008). This quality qualifies grey mangrove to be a good
bio- indicator and enables researchers to obtain quantitative information about the
environmental/ecological quality of its habitat through monitoring and experimental testing. It is speculated that Avicennia marina could be more tolerant to heavy
metal by developing several adaption mechanisms including avoiding the uptake of
metals actively and exclusion of ions (Burchett et al. 2003). Numerous studies have
utilized mangrove species and their sediments as reliable bio-indicators for heavy
metal pollution and contamination (Burchett et al. 2003; Defew et al. 2005).
Interestingly, the bio-concentration of various metals in this plant differs according
to the type of tissue. For instance mangrove leaves tend to accumulate lower levels
of metals as compared with mangrove roots and sediments (Defew et al. 2005). It
has been reported that very low heavy metal concentrations are found in the mangrove leaf tissues because most of the absorbed heavy metals get accumulated in
stem and root tissues. Nevertheless, root tissue is the most commonly used bioindicator for heavy metal pollution with high reliability and accuracy as compared
to leaves (Defew et al. 2005).
A study conducted by the Shankhadeep Chakraborty in 12 stations in Indian
Sundarbans revealed that Avicennia marina, Avicennia alba, Avicennia officinalis
and Excoecaria agallocha can be a potential indicator of heavy metal pollution in
this mangrove dominated deltaic complex.
The Indian Sundarbans, at the apex of Bay of Bengal (between 21°30′ N to
22°30′ N latitude and 87°25′ E to 89°10′ E longitude) offers a unique test bed for
studying the bioaccumulation pattern of heavy metals by mangrove floral species.
As species like Avicennia alba, Avicennia officinalis, Avicennia marina and
Excoecaria agallocha are endemic and dominant species of Indian Sundarbans
region, they are regularly exposed to heavy metal pollution, as most of the region is
contaminated with conservative pollutants (Mitra 1998; Mitra et al. 2011; Banerjee
et al. 2012; Mitra and Ghosh 2014).
5 Mangroves: A Sink of Heavy Metals