Registration Dossier

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 waiving:
other justification
Justification for data waiving:
other:

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

Reference
Name:
Unnamed
Type:
Constituent
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 wasshowed, 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)* indermediate. In the presence of oxygen the monomethyltin(II) or CH3Sn(III) intermediate are quickly oxidized to monomethyltin (IV), further the the mechanism is depending on th 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:


Table1– 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


Table2– 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 methyllation. 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 ofmagnitude higher than methylation rate constants. According to Hintelman et al. (2000) methylation and demethylation can be descriped 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 iinstable ntermediate with very short life time. So the biomehtylation of Sn2+ is not relevant for human and environment