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1 Heavy Metals in the Marine Environment—An Overview
1.4 Metal Speciation
Metal speciation refers to the various physical and chemical forms in which an
element may exist in the marine environment; and hence this determines the
behaviour of metals (Ansari et al. 2004). Speciation influences metal bioavailability and toxicity to biota, its transportation and mobilization, and its interaction
with the environment. An understanding of chemical speciation and bioavailability
becomes paramount in the study of fate and effects of trace metals in the environment (VanBriesen et al. 2010). Upon dissolution and reaction with anions available
in seawater, heavy metals give a number of chemical species at different pH’s (Ansari
et al. 2004), thus influencing metal bioavailability and toxicity. Factors such as pH, the
types and concentrations of inorganic and organic ligands, and the colloidal species
present influence the actual metal speciation (Violante et al. 2010). The formation of
metal-organic complexes influences the speciation of many heavy metal ions, which
have the tendency to bind with natural organic compounds such as fulvic acids or
with colloidal matter.
Elder (1988) reported that the toxicity of a given trace metal is intimately linked to
chemical speciation, which is governed by the physico-chemical nature of seawater
and can be variable in dynamic coastal waters. Metal loads tend to be higher in
coastal marine waters due to surrounding landmasses and associated human activities
(Furness and Rainbow, 1990).
Libes (1992) mentioned that one of the keys to considering metal toxicity is
understanding the effects of the physico-chemical characteristics of water on metal
speciation and bioavailability, as not all forms of metals are equally toxic. Heavy
metal toxicity is dependent upon chemical speciation (Ansari et al. 2004). The toxicity
data obtained contribute to the development of risk assessment tools such as water
quality guidelines and bioavailability-based models (Gissi et al. 2017). Governments
and relevant stakeholders use the water quality guidelines to set thresholds indicating
potential risks to aquatic environments from exposure to contaminants such as metals
(Wang et al. 2014b) and is in fact a good initiative as specific water quality guidelines
would be set for all heavy metal pollutants.
Some analytical techniques used in heavy metal speciation in fresh, estuarine
and marine environments include anodic stripping voltammetry, ultrafiltration, ion
exchange or chelating resins, dialysis and UV irradiation.
1.5 Summary
Being natural constituents of the earth’s crust, heavy metals generally are in very
low concentrations; however, human activities have unavoidably increased the metal
concentrations in the marine environment. When present in low concentrations, heavy
1 Heavy Metals in the Marine Environment—An Overview
1.4 Metal Speciation
Metal speciation refers to the various physical and chemical forms in which an
element may exist in the marine environment; and hence this determines the
behaviour of metals (Ansari et al. 2004). Speciation influences metal bioavailability and toxicity to biota, its transportation and mobilization, and its interaction
with the environment. An understanding of chemical speciation and bioavailability
becomes paramount in the study of fate and effects of trace metals in the environment (VanBriesen et al. 2010). Upon dissolution and reaction with anions available
in seawater, heavy metals give a number of chemical species at different pH’s (Ansari
et al. 2004), thus influencing metal bioavailability and toxicity. Factors such as pH, the
types and concentrations of inorganic and organic ligands, and the colloidal species
present influence the actual metal speciation (Violante et al. 2010). The formation of
metal-organic complexes influences the speciation of many heavy metal ions, which
have the tendency to bind with natural organic compounds such as fulvic acids or
with colloidal matter.
Elder (1988) reported that the toxicity of a given trace metal is intimately linked to
chemical speciation, which is governed by the physico-chemical nature of seawater
and can be variable in dynamic coastal waters. Metal loads tend to be higher in
coastal marine waters due to surrounding landmasses and associated human activities
(Furness and Rainbow, 1990).
Libes (1992) mentioned that one of the keys to considering metal toxicity is
understanding the effects of the physico-chemical characteristics of water on metal
speciation and bioavailability, as not all forms of metals are equally toxic. Heavy
metal toxicity is dependent upon chemical speciation (Ansari et al. 2004). The toxicity
data obtained contribute to the development of risk assessment tools such as water
quality guidelines and bioavailability-based models (Gissi et al. 2017). Governments
and relevant stakeholders use the water quality guidelines to set thresholds indicating
potential risks to aquatic environments from exposure to contaminants such as metals
(Wang et al. 2014b) and is in fact a good initiative as specific water quality guidelines
would be set for all heavy metal pollutants.
Some analytical techniques used in heavy metal speciation in fresh, estuarine
and marine environments include anodic stripping voltammetry, ultrafiltration, ion
exchange or chelating resins, dialysis and UV irradiation.
1.5 Summary
Being natural constituents of the earth’s crust, heavy metals generally are in very
low concentrations; however, human activities have unavoidably increased the metal
concentrations in the marine environment. When present in low concentrations, heavy