1.3 Common Heavy Metals in the Marine Environment
13
1.3.9 Tin (Sn)
Sn occurs naturally in the earth’s crust and is found in various environmental media
in both inorganic and organic forms. Sn metal is used to line cans for food, beverages, and aerosols (ATSDR 2005). Inorganic Sn compounds (e.g. stannous chloride,
stannous sulphide, and stannic oxide) are used in toothpaste, perfumes, soaps, food
additives and dyes; whilst organic tin compounds (e.g. dibutyltin, tributyltin, triphenyltin) are used to make plastics, food packages, plastic pipes, pesticides, paints
and insect repellents (ATSDR 2005).
Sn enters the environment by both natural processes as well as through anthropogenic activities such as mining, coal and oil combustion, and the production and
use of tin compounds (ATSDR 2005). Soil dust and forest fires are the natural sources
of atmospheric Sn emissions (Byrd and Andreae 1982). Sn enters the aquatic environment through atmospheric deposition, riverine input, and sediment resuspension
(Duan et al. 2012). Once in the environment, metallic Sn quickly converts to inorganic
tin compounds whilst inorganic Sn only changes its forms and organic tin compounds
are degraded into inorganic Sn compounds by sunlight and bacteria (ATSDR 2005).
Organotin compounds have been extensively used in boat paint since 1960 because
of their excellent and long lasting antifouling properties (Okoro et al. 2011). Tributyltin (TBT) and tributyltin fluoride (TBTF) are used in antifouling paints as a
finish coat to the immersed sections of boats and floating structures. Hence, there is
a possibility of global dispersion of TBT throughout the marine environment, from
the coastal zone to the open ocean (de Mora 1999).
TBT is extremely surface active and therefore readily adsorbed onto suspended
particulate material (de Mora 1999). TBT degrades; either through photochemical
reactions or microbial mediated pathways; in a process referred to as debutylation in
seawater to give nontoxic compounds dibutyltin and monobutyltin (de Mora 1999;
Maata and Koshy 2001). Despite being the most widely used active component in
antifouling paints, a global ban was ratified in 2008 on the application of TBT paints
(Tornero and Hanke 2016).
TBT is extremely toxic and lethal to a variety of planktonic organisms (Clark
2001); and thus results in a wide range of deleterious biological effects on non-target
organisms (de Mora 1999). It has an endocrine disrupting effect, particularly on
shellfish (Dafforn et al. 2011). de Mora (1999) reported that concentrations as low
as 0.02 µg TBT-Sn L
−1 is lethal to some shellfish; and lower concentrations result in
sub-lethal effects such as poor growth rates and reduced recruitment leading to the
decline of shellfisheries.
Sn is an essential element for organisms yet is a toxic cumulative element and
moderate level of Sn may impede the growth of organism and lead to harmful environmental effects (Duan et al. 2012). Sn toxicity grows with the augmenting of both
pH values and duration in aquatic systems (Duan et al. 2012), thus the bioavailability
of Sn is highest at neutral and slightly alkaline pH and reduced in the presence of
humic acid (Pawlik-Skowro´ nska et al. 1997).
13
1.3.9 Tin (Sn)
Sn occurs naturally in the earth’s crust and is found in various environmental media
in both inorganic and organic forms. Sn metal is used to line cans for food, beverages, and aerosols (ATSDR 2005). Inorganic Sn compounds (e.g. stannous chloride,
stannous sulphide, and stannic oxide) are used in toothpaste, perfumes, soaps, food
additives and dyes; whilst organic tin compounds (e.g. dibutyltin, tributyltin, triphenyltin) are used to make plastics, food packages, plastic pipes, pesticides, paints
and insect repellents (ATSDR 2005).
Sn enters the environment by both natural processes as well as through anthropogenic activities such as mining, coal and oil combustion, and the production and
use of tin compounds (ATSDR 2005). Soil dust and forest fires are the natural sources
of atmospheric Sn emissions (Byrd and Andreae 1982). Sn enters the aquatic environment through atmospheric deposition, riverine input, and sediment resuspension
(Duan et al. 2012). Once in the environment, metallic Sn quickly converts to inorganic
tin compounds whilst inorganic Sn only changes its forms and organic tin compounds
are degraded into inorganic Sn compounds by sunlight and bacteria (ATSDR 2005).
Organotin compounds have been extensively used in boat paint since 1960 because
of their excellent and long lasting antifouling properties (Okoro et al. 2011). Tributyltin (TBT) and tributyltin fluoride (TBTF) are used in antifouling paints as a
finish coat to the immersed sections of boats and floating structures. Hence, there is
a possibility of global dispersion of TBT throughout the marine environment, from
the coastal zone to the open ocean (de Mora 1999).
TBT is extremely surface active and therefore readily adsorbed onto suspended
particulate material (de Mora 1999). TBT degrades; either through photochemical
reactions or microbial mediated pathways; in a process referred to as debutylation in
seawater to give nontoxic compounds dibutyltin and monobutyltin (de Mora 1999;
Maata and Koshy 2001). Despite being the most widely used active component in
antifouling paints, a global ban was ratified in 2008 on the application of TBT paints
(Tornero and Hanke 2016).
TBT is extremely toxic and lethal to a variety of planktonic organisms (Clark
2001); and thus results in a wide range of deleterious biological effects on non-target
organisms (de Mora 1999). It has an endocrine disrupting effect, particularly on
shellfish (Dafforn et al. 2011). de Mora (1999) reported that concentrations as low
as 0.02 µg TBT-Sn L
−1 is lethal to some shellfish; and lower concentrations result in
sub-lethal effects such as poor growth rates and reduced recruitment leading to the
decline of shellfisheries.
Sn is an essential element for organisms yet is a toxic cumulative element and
moderate level of Sn may impede the growth of organism and lead to harmful environmental effects (Duan et al. 2012). Sn toxicity grows with the augmenting of both
pH values and duration in aquatic systems (Duan et al. 2012), thus the bioavailability
of Sn is highest at neutral and slightly alkaline pH and reduced in the presence of
humic acid (Pawlik-Skowro´ nska et al. 1997).