Diantimony trioxide

PBT assessment

PBT assessment: overall result

PBT status:

the substance is not PBT / vPvB

Justification:

The REACH Regulation (EC) 1907/2006) states that a PBT and vPvB (very persistent very bioaccumulative) assessment shall be conducted as foreseen in Article 14 (3) (d) in conjunction with Annex I Section 4 according to the criteria as laid down in Annex XIII (as updated in Commission Regulation (EU) No 253/2011 of 15 March 2011). The PBT and vPvB criteria of Annex XIII however only apply to organic substances, including organometals.

The draft Guidance to Regulation (EC) No 1272/2008 on Classification, Labelling and Packaging of substances and mixtures for metals and metal compounds qualitatively distinguishes metals from organometals based on their dissociation behaviour upon dissolution in water:“Organometals do not dissociate or dissolve in water as the metal ion, as metals and inorganic metal compounds do. … Metal compounds that contain an organic component but that dissociate easily in water or dissolve as the metal ion should be treated in the same way as (inorganic) metal compounds".

The following Sb compounds from the i2a substance list beyond doubt represent inorganic substances: Sb metal, Sb₂O₃, Sb₂S₃, SbCl₃, Sb₂O₅, NaSbO₃, SbCl₅and NaSb(OH)₆. Whereas antimony triacetate (Sb(CH₃COO)₃) and diantimony tris ethylene glycolate (Sb₂(C₂H₄O₂)₃) contain organic moieties, they also clearly constitute inorganic substances, since they lack a covalent bond between the metal and any carbon atom of the anionic organic moiety. Thus, they do not comply with the IUPAC definition of organometallic compounds, despite that results from the transformation/dissolution tests conducted for both compounds indicated that both ligands appeared to stabilise Sb(III) in solution compared to other Sb(III) substances, which showed a more pronounced oxidation of Sb(III) to Sb(V) upon dissolution (CanMET, 2010). This is, however, no direct proof for the occurrence of Sb-complexes in solution and up to 31% of the dissolved Sb is still oxidised to Sb(V) within 28 days at pH 8.5.As argued in sections 4 and 7, inorganic Sb substances will dissolve and generate antimony ions in the environment (Vangheluwe et al., 2001) and it is the fate and ecotoxicity of the antimony ion that is of most relevance in assessing potential persistence, bioaccumulation and toxicity

Therefore, strictly spoken, there is no legal obligation for a PBT and vPvB assessment for these inorganic Sb substances.However, the available data has nevertheless been compared to the criteria and is discussed below.All inorganic Sb substances are covered by the PBT assessment of the Sb-ion released upon dissolution.

Persistence: whereas antimony formally meets the criterion for persistence based on the absence of any degradation, this criterion is considered not to be applicable to inorganic elements. In addition, under conditions of a standard EUSES lake and the median partition coefficient for suspended matter, Sb meets the criteria for rapid removal from the water column.

Bioaccumulation:Antimony does not meet the criteria for bioaccumulation because the BCF values reported for aquatic organisms are all much lower than the threshold of 2,000 l/kg, and there is evidence to support that antimony does not biomagnify in the food chain.Therefore, antimony is not considered bioaccumulative (B) or very bioaccumulative (vB) based on the definitive criteria.

Toxicity:Chronic NOEC values are available for fish, invertebrates and algae. The lowest NOEC is 1.13 mg Sb/l for fish (Kimball, 1978b). Antimony and antimony compounds do not meet any of the PBT criteria based on carcinogenicity, mutagenicity or reprotoxicity and there is no evidence of other chronic concerns. Therefore, antimony is not considered toxic (T) based on the definitive criteria.

It is therefore concluded that antimony and inorganic antimony compounds are neither a PBT substance, nor a vPvB substance.