Tin bis(tetrafluoroborate)

Toxicity to microorganisms

Description of key information

The substance is inhibitory to microbial systems based on OECD 209 at 99 mg/l

Additional information

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 (Sn_⁴⁺) 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)₃⁻at low concentrations, and this behaviour 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.

 

 

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).