Chapter 1
Heavy Metals in the Marine
Environment—An Overview
Abstract Heavy metals are the natural constituents of the Earth’s crust, found in very
low concentrations; however, human activities such as industrial waste discharges,
agricultural practices, coastal construction and dredging have inevitably increased the
metal concentrations in the marine environment. Heavy metals are classified as both
essential and non-essential elements. Essential heavy metals have known biological
roles and are only toxic above threshold concentrations whilst non-essential heavy
metals lack any known biological role in marine invertebrates and exhibit high degree
of toxicity if allowed to accumulate at metabolically active sites. Heavy metals are
non-biodegradable, persistent and toxic to the environment, thus causing serious ecotoxicological problems. Heavy metals tend to bioaccumulate and the extent of their
bioaccumulation is dependent on the total amount, the bioavailability of each metal
in the environmental medium and the route of uptake, storage and excretion mechanisms. Metal speciation influences metal bioavailability and toxicity to biota, its
transportation and mobilization, and its interaction with the environment. The actual
metal speciation is influenced by factors such as pH, the types and concentrations of
inorganic ligands and organic ligands and colloidal species present.
Keywords Heavy metals · Metal speciation · Bioaccumulation · Toxicity
1.1 Heavy Metals
Heavy metals are the natural components of the Earth’s crust and regarded as the
members of an ill-defined subset of elements exhibiting metallic properties, including
transition metals, some metalloids, lanthanides and actinides. Lata and Rohindra
(2002) and Shah (2008) reported that heavy metals include metals and metalloids,
having atomic weights between 63.5 and 200.6 g/mol and density greater than
4.5 g/cm
3 . Okoro et al. (2012) highlighted that there are over 50 elements classified
as heavy metals, but only 17 considered both very toxic and relatively accessible.
Heavy metals are the natural constituents of the marine and freshwater environment, commonly found in very low concentrations (Ansari et al. 2004). Natural
processes that bring about the occurrence of heavy metals in the environment include
comets, erosion, volcanic eruptions, and the weathering of minerals; with these heavy
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
S. B. Shah, Heavy Metals in Scleractinian Corals, SpringerBriefs in Earth Sciences,
https://doi.org/10.1007/978-3-030-73613-2_1
1
Heavy Metals in the Marine
Environment—An Overview
Abstract Heavy metals are the natural constituents of the Earth’s crust, found in very
low concentrations; however, human activities such as industrial waste discharges,
agricultural practices, coastal construction and dredging have inevitably increased the
metal concentrations in the marine environment. Heavy metals are classified as both
essential and non-essential elements. Essential heavy metals have known biological
roles and are only toxic above threshold concentrations whilst non-essential heavy
metals lack any known biological role in marine invertebrates and exhibit high degree
of toxicity if allowed to accumulate at metabolically active sites. Heavy metals are
non-biodegradable, persistent and toxic to the environment, thus causing serious ecotoxicological problems. Heavy metals tend to bioaccumulate and the extent of their
bioaccumulation is dependent on the total amount, the bioavailability of each metal
in the environmental medium and the route of uptake, storage and excretion mechanisms. Metal speciation influences metal bioavailability and toxicity to biota, its
transportation and mobilization, and its interaction with the environment. The actual
metal speciation is influenced by factors such as pH, the types and concentrations of
inorganic ligands and organic ligands and colloidal species present.
Keywords Heavy metals · Metal speciation · Bioaccumulation · Toxicity
1.1 Heavy Metals
Heavy metals are the natural components of the Earth’s crust and regarded as the
members of an ill-defined subset of elements exhibiting metallic properties, including
transition metals, some metalloids, lanthanides and actinides. Lata and Rohindra
(2002) and Shah (2008) reported that heavy metals include metals and metalloids,
having atomic weights between 63.5 and 200.6 g/mol and density greater than
4.5 g/cm
3 . Okoro et al. (2012) highlighted that there are over 50 elements classified
as heavy metals, but only 17 considered both very toxic and relatively accessible.
Heavy metals are the natural constituents of the marine and freshwater environment, commonly found in very low concentrations (Ansari et al. 2004). Natural
processes that bring about the occurrence of heavy metals in the environment include
comets, erosion, volcanic eruptions, and the weathering of minerals; with these heavy
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
S. B. Shah, Heavy Metals in Scleractinian Corals, SpringerBriefs in Earth Sciences,
https://doi.org/10.1007/978-3-030-73613-2_1
1