Organo-tin compounds: Environmental effects
Description
There is no evidence of accumulation of organotin compounds in the environment. However, tributyltin and triphenyltin, both active ingredients of antifouling ship paints, appear to be highly toxic to many species of aquatic organisms at parts per million level or even lower. Non-target aquatic organisms such as crustaceans, molluscs, mussels, clams and oysters may suffer structural changes, growth retardation and death. Tributyltin oxide has been shown to inhibit cell survival of marine unicellular algae. Tributyltin may be an endocrine disruptor (a substance capable of interfering with natural body hormones), with the development of male characteristics in females observed in several snail species and oysters exposed to tributyltin. Generally, larvae of any species are more sensitive to tributyltin exposure than are adult organisms. Tributyltin tends to accumulate in oysters, mussels, crustaceans, molluscs, fish and algae. Freshwater species will bioaccumulate more tributyltin than will marine organisms. In mammals, high levels of tributyltin oxide can affect the endocrine glands, upsetting the hormone levels in the pituitary, gonad, and thyroid glands. Large doses of tributyltin have been shown to damage the reproductive and central nervous systems, bone structure and the liver bile duct of mammals. Tributyltin compounds can also damage the immune system. Tributyltin can be considered moderately toxic to birds. The acute toxicity of organotin compounds to mammals decreases in the order trialkyltins > dialkyltins > monoalkyltins. Ethyl derivatives are the most toxic amongst alkyl groups, with triethyltin acetate being the most toxic of all organotin compounds. Organotins appear to be less toxic with increasing chain length of the organic group, with trioctyltin chloride being virtually non-toxic to animals.
Entering the environment
Organotin compounds can be transported in water. Air contamination by organotins has not been reported so far.
Where it ends up
Organotins have a low water solubility and a strong tendency to adhere to suspended materials and sediments. Organotin particles ultimately settle to the bottom, making widespread surface water contamination unlikely. Organotin compounds appear to be moderately persistent with reported half-lives ranging from several days in freshwater to several weeks in seawater and estuarine locations, depending on the initial concentration. Organotins also adsorb strongly to soil. Although leaching from soil and transport in soil may be possible, it is unlikely to occur. Degradation of organotins to less toxic products (i.e. non-toxic inorganic tin) depends on the organotin compound and is generally accelerated by sunlight and higher temperatures. Microbial degradation is another important transformation mechanism. Biomethylation does not seem to be a significant pathway for the transformation of organotin species. As an example, degradation of tributyltin can take from several months to more than two years depending on the conditions.
Environmental guidelines
Australian Water Quality Guidelines for Fresh and Marine Waters (ANZECC, 1992):
The guideline for tributyltin is 0.008 microgram/L (i.e. 0.000000008 g/L) in fresh waters and 0.002 microgram/L (i.e. 0.000000002 g/L) in marine waters respectively.
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