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Read-across concept (environment) for tin bis(tetrafluoroborate):

Tin bis(tetrafluoroborate) is an inorganic substance which will dissociate into tin and tetrafluoroborate ions upon dissolution in the environment (water solubility >50 % w/w).

 

In the environment, tin is likely to partition to soils and sediments. In water, inorganic tin may exist as either divalent (Sn2+) or tetravalent (Sn4+) cations under environmental conditions. Whereas tin(II) dominates in reduced (oxygen-poor) water and will readily precipitate as tin(II) sulfide or as tin(II) hydroxide in alkaline water, tin(IV) readily hydrolyses and can precipitate as tin(IV) hydroxide. In general, tin(IV) would be expected to be the only stable ionic species in the weathering cycle. Tin(II) can be hydrolysed into SnOH+, Sn(OH)2, and Sn(OH)3at low concentrations, and thisbehaviour can be described by the following equation:

 

SnX2+ H2O <--> "SnXOH"(s) + HX

 

This Sn2+specific behaviour may be a hindrance when conducting tests at low or very low tin concentrations.Since the Sn2(OH)22+and Sn(OH)42+polynuclear species predominate at higher concentrations, highly concentrated and acidified Sn2+solutions are stable and only tend to precipitate at a very low rate.

 

On release to estuaries, inorganic tin is principally converted to the insoluble hydroxide and is rapidly scavenged by particles, which are the largest sinkfor the metal. Subsequent release of inorganic tin from benthic sediments is unlikely, except at highly anoxic sites. Since the mobility of Sn is highly pH dependent, Sn2+is only present in acid and reducing environments. Weathering of most natural and anthropogenic Sn carriers is intensified under acid, reducing conditions, although SnS2is insoluble under reducing conditions. In stream sediment, most detrital Sn is held in resistant oxide phases, such as cassiterite, which release Sn very slowly during weathering. Any Sn2+ released oxidises rapidly and is subsequently bound to secondary oxides of Fe or Al as Sn(OH)4or SnO(OH)3-. Tin forms soluble and insoluble complexes with organic substances. Tin is generally regarded as being relatively immobile in the environment. Ambient levels of tin in the environment are generally quite low. Tin occurs in trace amounts in natural waters, i.e. average concentrations in stream water are assumed to be less than 0.01μg/L (summarised in WHO, 2005 and athttp://www.gtk.fi/publ/foregsatlas, accessed on 12.03.2013).

 

The environmental behaviour of the tetrafluoroborate anion is expected to be different, and in a conservative approach it is assumed that the tetrafluoroborate anion remains stable and mobile under environmental conditions.

 

Upon release to the environment and dissolution in aqueous media, tin bis(tetrafluoroborate) will dissociate and only be present in its dissociated form, i.e. as tin cation and tetrafluoroborate anion, andtoxicity (if any) will be driven by tin and the tetrafluoroborate anion. Therefore,data are read-across for the tin cation and for the tetrafluoroborate anionto assess theecotoxicity of tin bis(tetrafluoroborate).Read-across to other soluble tetrafluoroborates, i.e. potassium tetrafluoroborate (CAS# 14075-53-7) and sodium tetrafluoroborate (CAS# 13755-29-8), and soluble tin substances, including tin bis(methanesulfonate) (CAS# 53408-94-9) and tin dichloride (CAS# 7772-99-8) is fully justified. The lowest effective concentrations of short- and long-term toxicity available for algae, daphnia and fish, respectively, are summarized in the Table below.

 

Short-term aquatic toxicity:

Substance specific guideline data of tin bis(tetrafluoroborate) are available for the acute toxicity to invertebrates (D. magna) and fish (Oncorhynchus mykiss) (Palmieri and Buccafusco, 1983) and EC50/LC50s of 87 mg/L and 78 mg/L, respectively, are well above classification criteria for acute aquatic hazard according to CLP-Regulation (EC) No 1272/2008.

 

Tin:

Wong et al (1982) tested the toxicity of SnCl2to different algal species (Anabaena flosaquae, Ankistrodesmus falcatus, and Scenedesmusquadricauda), and EC50 values when recalculated for tin bis(tetrafluoroborate) indicate a similar lack of acute toxicity to algae; the lowest EC50 for 8-d growth ofA. falcatusis 12 mg/L Sn2+(corresponding to ≥ 30 mg/LSn(BF4)2).

 

Tetrafluoroborate:

A guideline study is available for toxicity of potassium tetrafluoroborate in alga (Pseudokirchnerella subcapitata); the 72-h EC50 for growth rate inhibition is >100 mg/L (corresponding to > 116 mg/LSn(BF4)2).

A guideline study for short-term toxicity is available for aquatic invertebrates; the 48-h EC50 forDaphnia magnais >100 mg/L (corresponding to > 116 mg/LSn(BF4)2).

A guideline study for short-term toxicity is available for freshwater fish; the 96-h LC50 amounts to 760 mg/L for golden orfe (Leuciscus idus) (corresponding to 882 mg/LSn(BF4)2).

 

Long-term aquatic toxicity:

Long-term toxicity data of tin bis(tetrafluoroborate) are not available.

 

Tin:

Wong et al (1982) tested the toxicity of SnCl2to different algal species (Anabaena flosaquae, Ankistrodesmus falcatus, and Scenedesmusquadricauda), the lowest NOEC for 8-d growth ofA. falcatusamounts to ≥ 10 mg/L Sn2+(≥ 25 mgSn(BF4)2/L).

The 21-d NOEC for the toxicity of tin bis(methanesulfonate) to reproduction of D. magna as determined in a guideline study is 12.5 mg/L (corresponding to a NOEC of 11.8 mg/L Sn(BF4)2).

The 28-d NOEC for specific growth rate inhibition of O. mykiss by tin bis(methanesulfonate) was determined in a guideline study with 0.78 mg/L (corresponding to a NOEC of 0.74 mg/L Sn(BF4)2). However, an EC10 was not determined in this study. Furthermore, parts of the observed effects with tin bis(methanesulfonate) may be due to the effect of the anion whereas no such contribution is expected for the tetrafluoroborate anion. Thus, the NOEC derived for long-term toxicity of tin bis(methanesulfonate) to fish is not taken forward for the chemical safety assessment. Indeed, Kapur and Yadav (1982) derived a NOEC of 7.8 mg/L Sn for reproduction ofCyprinus carpio, corresponding to a NOEC of 19 mg/L Sn(BF4)2).

 

Tetrafluoroborate:

A guideline study is available for the toxicity of potassium tetrafluoroborate to algal growth (Pseudokirchnerella subcapitata); the NOEC is 100 mg/L (corresponding to 116 mgSn(BF4)2).

Data on the long-term toxicity of sodium tetrafluoroborate to aquatic invertebrates are available, the 21-d NOEC for reproduction ofD. magnais 188 mg/L (corresponding to 250 mgSn(BF4)2).

Data are not available to assess the long-term toxicity of the tetrafluoroborate anion to fish. However, considering that fish are the least sensitive to the acute toxicity of tetrafluoroborate, it is assumed that fish are also not more sensitive than algae and daphnia long-term.

 

Table: Aquatic toxicity of tin and tetrafluoroborate substances

 

Tested substance

Effective concentration

(mg/L)

Short-term aquatic toxicity

 

 

Algae - EC50

tin dichloride: SnCl2

potassium tetrafluoroborate: KBF4

> 30*

> 116**

Daphnia – 48-h EC50

tin bis(tetrafluoroborate): Sn(BF4)2

potassium tetrafluoroborate: KBF4

87

> 116**

Fish – 96-h LC50

tin bis(tetrafluoroborate): Sn(BF4)2

potassium tetrafluoroborate: KBF4

78

882**

Long-term aquatic toxicity

 

 

Algae – NOEC

tin dichloride: SnCl2

potassium tetrafluoroborate: KBF4

> 25*

116**

Daphnia - NOEC

tin(II) bis(methanesulfonate): Sn(CH3SO3)2

sodium tetrafluoroborate: NaBF4

11.8*

250**

Fish - NOEC

tin dichloride: SnCl2

19*

Toxicity to microorganisms

 

 

Respiration inhibition – EC10

tin(II) bis(methanesulfonate): Sn(CH3SO3)2

99*

Respiration inhibition – EC50

Pseudomonas putida

tin(II) bis(methanesulfonate): Sn(CH3SO3)2

potassium tetrafluoroborate: KBF4

283*

638**

*Effective concentrations were recalculated for tin bis(tetrafluoroborate) based on an average tin content of 40.6%.

**Effective concentrations were recalculated for tin bis(tetrafluoroborate) based on an average tetrafluoroborate content of 59.4%.

 

Discussion

Substance-specific data indicate a lack of toxicity of tin bis(tetrafluoroborate) to daphnia and fish below acute classification criteria of CLP-Regulation (EC) No 1272/2008 (Table 4.1.0 (a)). Based on read-across of acute algae toxicity data available for tin and tetrafluoroborate, tin bis(tetrafluoroborate) also does not meet the hazard criteria for acute (short-term) aquatic hazard. The lowest available NOEC, i.e. the NOEC of 25 mg/L tin bis(tetrafluoroborate) for growth inhibition of algae is taken forward for the chemical safety assessment.

 

Substance-specific long-term toxicity data are not available for tin bis(tetrafluoroborate). Based on read-across of long-term data available for the toxicity of tin to algae, daphnia and fish, the lowest 21-d NOEC available for toxicity to reproduction ofD. magnarecalculated fortin bis(tetrafluoroborate) amounts to 11.8 mg/L, and this value is taken forward for the chemical safety assessment.

 

Long-term data available to assess the toxicity of tetrafluoroborate to algae and daphnia also indicate a lack of toxicity potential below classification criteria of CLP-Regulation (EC) No 1272/2008 (Table 4.1.0 (b)(i)) for non-rapidly degradable substances. Based on acute toxicity data available for all three trophic levels and the fact that fish are the least sensitive species, it is assumed that effective concentrations for the toxicity of tetrafluoroborate to fish are not below classification criteria for long-term aquatic hazard. Further, according to long-term classification criteria of CLP-Regulation (EC) No 1272/2008, Table 4.1.0 (b)(iii) for substances for which adequate chronic toxicity data are not available, the 96-hLC50 available for toxicity of tetrafluoroborate to fish or any other EC/LC50 available for algae and daphnia would not result in a classification of long-term hazard.

 

Based on read-across of chronic toxicity data available for tin and tetrafluoroborate, tin bis(tetrafluoroborate) also does not meet the hazard criteria for long-term aquatic hazard.

 

According to classification criteria of CLP-Regulation (EC) No 1272/2008 (Table 4.1.0), tin bis(tetrafluoroborate) does not meet the criteria for aquatic hazard and does not require classification and labelling.

 

Toxicity to microbes

Microbial toxicity data of tin bis(tetrafluoroborate) are not available. Based on read-across of microbial toxicity data available for tin and tetrafluoroborate, the lowest resulting EC10/50 are based on tin and amount to 99 and 283 mg/L tin bis(tetrafluoroborate) (see below).

 

Tin: The recalculated EC10/50 determined in a guideline conform respiration inhibition study with tin(II) bis(methanesulfonate) amount to 99 and 283 mg/L tin bis(tetrafluoroborate), respectively.

 

Tetrafluoroborate: The 18-h EC50 for growth inhibition of potassium tetrafluoroborate toPseudomonas putidais 550 mg/L (corresponding to 638 mg Sn(BF4)2).