Tin sulphate

Additional ecotoxological information

Administrative data

Endpoint:

additional ecotoxicological information

Type of information:

other: Literature review

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: review of different literature, without guideline, in part from US EPA

Data source

Reference

Reference Type:

other: Literautre review

Title:

Unnamed

Year:

2012

Materials and methods

Test guideline

Qualifier:

no guideline required

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

Sn2+

IUPAC Name:

Sn2+

Test material form:

other: not relevant

Results and discussion

Any other information on results incl. tables

Malinovskiy et al. (2009) studied the methylation and demethylation of Sn in aqueous solution by isotopic fractionation. It was shown, that mechanism of biomethylation includes equilibrium fractionation between Sn(II) and Sn(IV) Species in solution, followed by addition of a methyl group to Sn(II) atoms directly or via an CH3Sn(III)* intermediate. In the presence of oxygen the monomethyltin(II) or CH3Sn(III) intermediate are quickly oxidized to monomethyltin (IV), further the mechanism is depending on the pH.

Tressier et al. (2003) showed that the biomethylation does not stop with the monomethylation, there was found natural di- and trimethylated species, too.

On the other side studies of alkylated Sn compounds have similarly shown their degradation in the sediment and it is likely that anaerobic microbes can demethylate most of the commonly found methylated metal(loid)s in the environment (Manson et al., 2013). The data form Kubilay et al. (1996) shows the following distribution of Methyltin compounds in the North-Eastern Mediterranean:

Table 1– Methyltin concentrations in seawater samples (ng/l as chlorides), adopted from Kubilay (1996)

Sample station	Sampling date	Methyltin concentrations
		MeSnCl3	Me2SnCl2	Me3SnCl
Iskendreum Habour	May 1988	< 0.30	< 0.15	7.40
	Oct. 1988	< 0.30	< 0.15	13.70
	Feb. 1989	< 0.30	< 0.15	< 0.25
Botas	May 1988	< 0.30	< 0.15	5.30
	Oct. 1988	< 0.30	< 0.15	17.10
Isdemir	Nov. 1988	< 0.30	1.00	2.80
	Mar. 1989	< 0.30	< 0.15	< 0.25
Mersin Harbour	Oct. 1988	< 0.30	< 0.15	39.70
Antalya Marina	Oct. 1988	< 0.30	4.40	44.2
	Mar. 1989	< 0.30	< 0.15	< 0.25
Göksu River Delta	Oct. 1988	< 0.30	< 0.15	27.50
	Feb. 1989	< 0.30	< 0.15	< 0.25

Table 2– Methyltins concentrations (as chlorides) in sediment samples (ng/g dry wt), adopted from Kubilay (1996)

Sample station	MeSnCl3	Me2SnCl2	Me3SnCl
Manavgat	15	36	143
Esen	38	58	107
Seyhan	65	81	159
Göksu	375	477	1696
Marmaris	22	36	87
Iskenderum	26	56	81

In the sediments were find higher concentrations than in the seawater. This is allegeable amongst other things with the models discussed before.

 

In order there is not to see a local concentration maximum for the monomethyltin, it can be concluded, that the demethylation is faster than the methylation. This evidence is supported (Manson et al., 2013) by studies in freshwater and marine sediments, which confirm that the rate of demethylation is rapid, and that the rate constant for this process is higher than that of methylation, and that demethylation occurs across the redox gradient. The complex kinetic is discussed by Pasquale et al. (2000), Hollweg et al. (2010), Heyes et al. (2006), Oremland et al. (1991), Kim et al. (2006) using mercury, arsenic and selenic.

Kim et al. found, that the demethylation rate constants were 2–3 orders of magnitude higher than methylation rate constants. According to Hintelman et al. (2000) methylation and demethylation can be described as pseudo first order reactions.

So in a first order approximation a steady state with insignificant concentrations will be reached in a short period.

 

In conclusion the data show, that the biomethylation is a part of the oxidation process of Sn(II) to Sn(IV), after the oxidizing process the demethylation is part of the formation of a more thermodynamic stable Sn(VI) species.

Applicant's summary and conclusion

Conclusions:

Biomethylation of Sn2+ is part in the oxidation process of Sn2+ to Sn4+. The Methyltin species is only an instable intermediate with very short life time. So the biomethylation of Sn2+ is not relevant for human and environment