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1 Heavy Metals in the Marine Environment—An Overview
1.3.10 Arsenic (As)
As is a naturally occurring metal found in the earth’s crust, occurring either as
elemental (metallic), inorganic, or as organic As (ATSDR 2007). As is a toxic metalloid that exists in two oxidative states: a trivalent form (in the form of arsenous
acid and its salts) and a pentavalent form (in the form of arsenic acid and its salts)
(Chiarelli and Roccheri 2014). The toxicity of As depends upon the nature of the
compound formed and its valency, with the trivalent form being more toxic than the
pentavalent form (Clark 2001).
Kaur et al. (2011) reported that As is one of the most important global environmental pollutant and a persistent bioaccumulative carcinogen. Environmental pollution by As occurs as a result of natural phenomena such as volcanic eruptions and
soil erosion, and through anthropogenic activities (ATSDR 2000). The natural inputs
of As to the sea is chiefly by rivers especially from areas of metalliferrous mining
(Clark 2001; Nair et al. 2003). Anthropogenic sources of As include the smelting
of Cu, Ni, Pb and Zn ores, burning of fossil fuels in households and power plants,
growth stimulants for plants and animals (Chiarelli and Roccheri 2014).
Furthermore, Tchounwou et al. (2012) reported that there are several Ascontaining compounds produced industrially, which have been used to manufacture
products with agricultural applications such as insecticides, herbicides, fungicides,
algicides, sheep dips, wood preservatives, and dye-stuffs. El-Sorogy et al. (2016)
also reported that the largest source of pollution from As result from agricultural
chemicals such as herbicides, fungicides, rodenticides and insecticides.
Marine organisms contain As especially in the form of arsenobutaine (which is
pentavalent) and thus very stable, metabolically inert and non-toxic; whilst marine
algae contain arsenic as carbohydrate compounds (Clark 2001). Even though a variety
of aquatic organisms, including some algae, crustaceans, and fish, bioaccumulate
arsenic, it does not magnify through the food chain (Clark 2001).
1.3.11 Silver (Ag)
Ag is a rare but naturally occurring metal, often found deposited as a mineral ore
in association with other elements (Howe and Dobson 2002). Argentite, nickel ores,
lead-zinc and porphyry copper ores, and platinum and gold deposits are used to extract
Ag, however, other sources of Ag include new scrap generated in the manufacture of
silver-containing products; coin and bullion; and old scrap from electrical products,
old film and photoprocessing wastes, batteries, jewellery, silverware, and bearings
(Howe and Dobson 2002).
Anthropogenic sources of Ag in the environment include emissions from smelting
operations; manufacture and disposal of certain photographic and electrical supplies,
coal combustion, industrial and municipal wastewater outfalls and cloud seeding
1 Heavy Metals in the Marine Environment—An Overview
1.3.10 Arsenic (As)
As is a naturally occurring metal found in the earth’s crust, occurring either as
elemental (metallic), inorganic, or as organic As (ATSDR 2007). As is a toxic metalloid that exists in two oxidative states: a trivalent form (in the form of arsenous
acid and its salts) and a pentavalent form (in the form of arsenic acid and its salts)
(Chiarelli and Roccheri 2014). The toxicity of As depends upon the nature of the
compound formed and its valency, with the trivalent form being more toxic than the
pentavalent form (Clark 2001).
Kaur et al. (2011) reported that As is one of the most important global environmental pollutant and a persistent bioaccumulative carcinogen. Environmental pollution by As occurs as a result of natural phenomena such as volcanic eruptions and
soil erosion, and through anthropogenic activities (ATSDR 2000). The natural inputs
of As to the sea is chiefly by rivers especially from areas of metalliferrous mining
(Clark 2001; Nair et al. 2003). Anthropogenic sources of As include the smelting
of Cu, Ni, Pb and Zn ores, burning of fossil fuels in households and power plants,
growth stimulants for plants and animals (Chiarelli and Roccheri 2014).
Furthermore, Tchounwou et al. (2012) reported that there are several Ascontaining compounds produced industrially, which have been used to manufacture
products with agricultural applications such as insecticides, herbicides, fungicides,
algicides, sheep dips, wood preservatives, and dye-stuffs. El-Sorogy et al. (2016)
also reported that the largest source of pollution from As result from agricultural
chemicals such as herbicides, fungicides, rodenticides and insecticides.
Marine organisms contain As especially in the form of arsenobutaine (which is
pentavalent) and thus very stable, metabolically inert and non-toxic; whilst marine
algae contain arsenic as carbohydrate compounds (Clark 2001). Even though a variety
of aquatic organisms, including some algae, crustaceans, and fish, bioaccumulate
arsenic, it does not magnify through the food chain (Clark 2001).
1.3.11 Silver (Ag)
Ag is a rare but naturally occurring metal, often found deposited as a mineral ore
in association with other elements (Howe and Dobson 2002). Argentite, nickel ores,
lead-zinc and porphyry copper ores, and platinum and gold deposits are used to extract
Ag, however, other sources of Ag include new scrap generated in the manufacture of
silver-containing products; coin and bullion; and old scrap from electrical products,
old film and photoprocessing wastes, batteries, jewellery, silverware, and bearings
(Howe and Dobson 2002).
Anthropogenic sources of Ag in the environment include emissions from smelting
operations; manufacture and disposal of certain photographic and electrical supplies,
coal combustion, industrial and municipal wastewater outfalls and cloud seeding