Methyltin compounds

In the EU, a total of 12 779 tonnes of inorganic tin in 2001 was used in the production of the various organotin compounds, as well as in the production of inorganic tin compounds. It should be further noted that the above tonnage applies only to butyltin and octyltin compounds methyltin compounds, while used in the EU, are produced only outside the EU and are imported. 

Methyltin compounds, in addition to being used as stabilizers in PVC products, can also be produced via natural processes in the environment. Thus, as with butyltin compounds, it is not possible to exactly attribute the source of methyltin compounds in the environment. 

Summer et al. (2003) also reviewed the concentrations of methyltin compounds in the environment (Table 13). No higher values were found in later literature. As indicated above, methyltin compounds can be produced naturally in the environment by microorganisms (Maguire, 1991). 

There is some evidence to suggest that methyltin compounds bind to sewage sludge. Concentrations... 

The generation and recovery of stannane, methyl-, dimethyl-, and trimethyl-stannane were studied in seawater. Average tin recoveries for the six samples analysed, to which were added 0.4-1.6 ig methyltin compounds and 3ng inorganic tin, ranged from 96 to 109%. Reanalysis of analysed samples shows that all methyltin and inorganic tin is removed in one analysis procedure. 

The methyl-[14C]-dimethyltin chloride was used to compare the performance of packed and megabore capillary columns in a gas chromatographic analysis for separating mixtures of a carbon-14 labelled trimethyllead chloride, tetramethyltin, dimethyltin dichloride and methyltin trichloride. The megabore column was able to separate all four methyltin compounds quickly, i.e., before the tetramethyltin decomposed into trimethyltin chloride and dimethyltin dichloride (equation 47), a reaction which did occur on the packed columns. Thus, the megabore column enabled the determination of the precise distribution of the various methyltin compounds in an environmental sample. The packed columns, on the other hand, could not separate dimethyltin dichloride and the methyltin trichloride and allowed significant decomposition of the tetramethyltin during the 15 minutes the analysis required. 

The formation of methyltin derivatives in the environment has been of concern because methyltin compounds are quite toxic. As a result, several workers have attempted to determine how the methyltin compounds are generated in the environment. In one study,... 

Disproportionation reactions are well known in tin chemistry and can account for the occurrence of several methyltin compounds, assuming a methyltin species was present in the first place. Similarly, transmethylation can occur between inorganic tin species and methylated forms of other elements. Examples of this nature, some of which may take place in water, are given in Section V, Reference 2. Their environmental significance is unknown. Disproportionation reactions are also covered in Section V, Reference 1. A general theory of methylation by MeCoBn was proposed, based on redox potentials51. 

A considerable number of organometallic species of germanium, tin and lead have been detected in the natural environment. A number of these are nonmethyl compounds which have entered the environment after manufacture and use (e.g. butyltin and phenyltin compounds by diffusion from antifouling paints on boats, and ethylleads from leaded gasoline). Only a few methyl compounds are now manufactured and used (e.g. some methyltin compounds are used as oxide film precursors on glass)1. 

Braman and Tompkins first reported methylated tin compounds in environmental materials43. Saline water, estuary water, fresh water, rain water and tap water were analyzed for methyltin compounds tin levels were at ng 1 1. Average total tin concentration of human urine (11 samples) was 1 i-gSn 1 1, and those of methyltin, dimethyltin and trimethyltin were 90, 73 and 42 ngSnl-1, respectively. Methyltin compounds were also observed in shell samples at the 0.1 ng g 1 level. About 17-60% of the total tin was present in monomethyltin form43. 

TABLE 11. Experimental design and yields of methyltin compounds 2 (modified from Reference 74)... 

Donard, O.F.X., F.T. Short, and J.H. Weber. 1987. Regulation of tin and methyltin compounds by the green alga Enteromorpha under simulated estuarine conditions. Canad Jour. Fish. Aquat. Sci. 44-140-145. 

Sinex et al. [71] have described a method for the determination of methyltin compounds based on reaction with sodium borohydride to form tin hydrides then purge and trap analysis followed by gas chromatography with mass spectrometric detection. Down to 3-5pg absolute (as tin) of methyltin compounds equivalent to the sub pg kg 1 range can be determined by this procedure. 

Arakawa et al. [96] have pointed out that methyltin compounds may be extracted from complex matrices and analysed by conventional gas chromatography. However, the procedure is lengthy, involving multiple steps where speciation may be altered and vessel adsorption effects may be large. Detection limits achievable with a flame ionization detector are 10-100pg [97],... 

Gilmour et al. [89] converted methyltin compounds in sediments to tin hydrides with sodium borohydride prior to ion monitoring by mass spectrometry. 

Methyltin compounds were determined in complex samples by a sensitive purge and trap method at detection limits of 3-5pg with 6-18% precision. The method is selective and specific and free from most interferences. 

Andreae and Byrd [101] have pointed out that methylstannanes produced by hydridization of methyltin compounds is both stable and volatile with... 

Several years ago Brinckman, Iverson, and co-workers reported that a species of Pseudomonas found in the sediments of Chesapeake Bay would form methyltin compounds in the presence of both mercury and tin, methylmercuric and methyltin compounds formed (5, 113. 114). Based on their laboratory and field observations, these authors proposed a crossover mechanism (Fig. 5) wherein an appropriate methyltin species generated by Pseudomonas reacted with environmentally formed Hg(II) to form methylmercuric ion 114). 

In recent years organotin compounds have been increasingly used in various technological applications that would facilitate their entry into the environment 115, 116). Methyltin compounds have been found in natural waters at very low concentrations, as have butyltin compounds 117-119). The latter probably come from widespread commercial use of butyltin compounds in antifouling paints or agricultural biocades 113, 114, 118). 

It has been reported (72) that three unassociated methyltin compounds with highly shielded tin nuclei show linear increases in chemical shift with temperature Me2Sn(OlBu)2 + 0-06 ppm K-1 MeSn(OlBu)3 + 0-11 ppm K-1 MeSnI3 + 0-26 ppm K-1. 

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