2
1 Heavy Metals in the Marine Environment—An Overview
metals characteristically present in insoluble forms such as in mineral structures,
precipitated or complex forms (Ayangbenro and Babalola 2017).
Anthropogenic activities such as mine drainage, offshore oil and gas exploration, industrial (pesticides, paints, leather, textile, fertilizers, pharmaceuticals) and
domestic effluents, wastewaters, agricultural runoff, acid rain waste discharges, and
coastal construction and dredging have inevitably increased the metal concentrations in the marine environment (Ansari et al. 2004; Fu and Wang 2011). Heavy
metals from anthropogenic sources typically have a high bioavailability due to their
soluble and mobile reactive forms (Ayangbenro and Babalola 2017). Metal inputs
are permanent additions to the marine environment and do not get broken-down by
bacterial action and are rendered inert (Hudspith et al. 2017). However, they can only
be converted into less toxic species (Ayangbenro and Babalola 2017).
The term ‘heavy metal’ is used synonymously with ‘trace metal’ (Rainbow 1995)
and are considered as trace elements because of their presence in trace concentrations
(ppb range to less than 10 ppm) in various environmental matrices (Kabata-Pendia
2001). Hooda (2010) also mentioned that ‘heavy metal’ is the most popularly used
and widely recognized term. Hence, this monograph adopted the use of heavy metals
in accordance with the definitions and descriptions provided by Rainbow (1995),
Kabata-Pendia (2001) and Hooda (2010).
Heavy metal comprises of both essential and non-essential trace metals (Rainbow
1995; Richir and Gobert 2016). Essential elements recognized by WHO (1996)
include copper [Cu], selenium [Se], chromium [Cr], molybdenum [Mo], zinc [Zn]
and iron [Fe]. Essential elements are vital components of enzymes, respiratory
proteins and certain structural elements of organisms (Brown and Depledge 1985),
but above certain threshold concentrations, they are potentially toxic to both humans
and aquatic biota. Being essential micronutrients, trace metals are also important in
controlling marine productivity (Chen et al. 2015).
Non-essential elements consist of cadmium [Cd], lead [Pb], or mercury [Hg];
and play no physiological role and are often toxic even in small quantity (Nordberg
et al. 2007). Since non-essential elements lack any known biological role in marine
invertebrates, they would exhibit high degree of toxicity if allowed to accumulate at
metabolically active sites. These heavy metals may imitate essential metals and thus
gain access to important molecular targets (Chiarelli and Roccheri 2014).
Heavy metals are serious pollutants because of toxicity, persistence, ubiquitous
nature and non-biodegradability in the environment (Pekey 2006; DeForest et al.
2007; Naser 2013; Wu et al. 2016) and have a series of deleterious sub-lethal and
lethal effects on marine biota (Peters et al. 1997). Heavy metals tend to bioaccumulate
(DeForest et al. 2007; Naser 2013), meaning that their concentration increases in a
biological organism over time. The extent of bioaccumulation of metals is dependent
on the total amount, the bioavailability of each metal in the environmental medium
and the route of uptake, storage and excretion mechanisms (Chiarelli and Roccheri
2014).
The transportation of heavy metals to long distances is via atmospheric and hydrological processes (Guzmán and Jiménez 1992; Marx and McGowan 2010). McLusky
et al. (1986); Rainbow (1997) and Marsden and Rainbow (2004) reported that heavy
1 Heavy Metals in the Marine Environment—An Overview
metals characteristically present in insoluble forms such as in mineral structures,
precipitated or complex forms (Ayangbenro and Babalola 2017).
Anthropogenic activities such as mine drainage, offshore oil and gas exploration, industrial (pesticides, paints, leather, textile, fertilizers, pharmaceuticals) and
domestic effluents, wastewaters, agricultural runoff, acid rain waste discharges, and
coastal construction and dredging have inevitably increased the metal concentrations in the marine environment (Ansari et al. 2004; Fu and Wang 2011). Heavy
metals from anthropogenic sources typically have a high bioavailability due to their
soluble and mobile reactive forms (Ayangbenro and Babalola 2017). Metal inputs
are permanent additions to the marine environment and do not get broken-down by
bacterial action and are rendered inert (Hudspith et al. 2017). However, they can only
be converted into less toxic species (Ayangbenro and Babalola 2017).
The term ‘heavy metal’ is used synonymously with ‘trace metal’ (Rainbow 1995)
and are considered as trace elements because of their presence in trace concentrations
(ppb range to less than 10 ppm) in various environmental matrices (Kabata-Pendia
2001). Hooda (2010) also mentioned that ‘heavy metal’ is the most popularly used
and widely recognized term. Hence, this monograph adopted the use of heavy metals
in accordance with the definitions and descriptions provided by Rainbow (1995),
Kabata-Pendia (2001) and Hooda (2010).
Heavy metal comprises of both essential and non-essential trace metals (Rainbow
1995; Richir and Gobert 2016). Essential elements recognized by WHO (1996)
include copper [Cu], selenium [Se], chromium [Cr], molybdenum [Mo], zinc [Zn]
and iron [Fe]. Essential elements are vital components of enzymes, respiratory
proteins and certain structural elements of organisms (Brown and Depledge 1985),
but above certain threshold concentrations, they are potentially toxic to both humans
and aquatic biota. Being essential micronutrients, trace metals are also important in
controlling marine productivity (Chen et al. 2015).
Non-essential elements consist of cadmium [Cd], lead [Pb], or mercury [Hg];
and play no physiological role and are often toxic even in small quantity (Nordberg
et al. 2007). Since non-essential elements lack any known biological role in marine
invertebrates, they would exhibit high degree of toxicity if allowed to accumulate at
metabolically active sites. These heavy metals may imitate essential metals and thus
gain access to important molecular targets (Chiarelli and Roccheri 2014).
Heavy metals are serious pollutants because of toxicity, persistence, ubiquitous
nature and non-biodegradability in the environment (Pekey 2006; DeForest et al.
2007; Naser 2013; Wu et al. 2016) and have a series of deleterious sub-lethal and
lethal effects on marine biota (Peters et al. 1997). Heavy metals tend to bioaccumulate
(DeForest et al. 2007; Naser 2013), meaning that their concentration increases in a
biological organism over time. The extent of bioaccumulation of metals is dependent
on the total amount, the bioavailability of each metal in the environmental medium
and the route of uptake, storage and excretion mechanisms (Chiarelli and Roccheri
2014).
The transportation of heavy metals to long distances is via atmospheric and hydrological processes (Guzmán and Jiménez 1992; Marx and McGowan 2010). McLusky
et al. (1986); Rainbow (1997) and Marsden and Rainbow (2004) reported that heavy