Lead bis(tetrafluoroborate)

Endpoint summary

Description of key information

Acute toxicity, oral: LD50 2000 mg/kg bw
Acute toxicity, inhalation: data waiving
Acute toxicity, dermal: data waiving

Additional information

Acute toxicity, oral:

Read across concept:

No studies on acute oral toxicity with lead bis(tetrafluoroborate) are available. Instead, read across from lead compounds (in particular from water soluble substances) and tetrafluoroborate salts is considered to be justified. The toxicity of lead bis(tetrafluoroborate) may reasonably be considered to be determined by the bioavailability of lead²⁺and tetrafluoroborate^-. As a first surrogate for bioavailability, the water solubility may be used. Lead chloride is water-soluble up to 10 g/L at 20°C, tetrafluoroborate salts (e.g potassium tetrafluoroborate, sodium tetrafluoroborate and triethylmethylammonium tetrafluoroborate) from 1.3 g/L at 20°C (KBF₄) up to 2000 g/L at 20°C (TEMABF₄). The water solubility of lead bis(tetrafluoroborate) is > 500 g/L at 20°C. Thus, read-across without restriction is fully justified.

Lead compounds

The available studies made available in this technical dossier indicate a very low acute oral toxicity of seven inorganic lead compounds similar in physical and chemical properties to lead dichloride. Lead dichloride is water soluble >500 g/L at 20°C, somewhat higher than the lead compounds tested (0.3 – 530 mg/L). However, water solubility does not equate with gastrointestinal bioavailability as evidenced by the fact that lead carbonate has limited water solubility and yet has oral bioavialability equal to that of soluble lead compounds. There was also no evidence of any local or systemic toxicity associated with the oral administration of any of these compounds. Whether or not the compound contained the anion of an inorganic acid or an organic acid had no effect upon toxicity, and literature searches found no indications that anions present in high production volume compounds not tested would impart properties of toxicity different from those that have been tested. Based upon these overall observations, read across from these lead compounds permits the conclusion to be drawn, that other similar inorganic lead compounds will not be acutely toxic via oral exposure routes. Support for this is derived from oral LD₅₀values for lead dichloride cited in the secondary literature that indicate that the oral LD₅₀in rats is > 1947 mg/kg/bw. This finding is not unexpected given the pharmacokinetics of lead uptake into the body. Lead uptake is generally quite low and heavily reliant upon easily saturable active transport mechanisms. Once saturation of these uptake mechanisms has occurred, uptake proceeds by inefficient passive diffusion. The uptake of lead is thus highly non-linear as a function of dose with uptake efficiency declining with the amount of lead administered to a test animal or an exposed human. Although toxic under chronic exposure situations, the acute toxicity of inorganic lead metal compounds appears to be quite low via all exposure routes.

Tetrafluoroboric acid and tetrafluoroborate salt

Studies performed with different tetrafluoroboric salts are available which indicate that the toxicity is driven by the metal cation, and not the tetrafluoroborate moiety. While supportive data on sodium tetrafluoroborate indicate an LD₅₀(oral) of > 2000 mg/kg bw (see robust study summary 7.2.1), the LD₅₀of potassium tetrafluoroborate is 5854 mg/kg bw according to the MSDS of Sigma Aldrich. The study performed with triethylmethylammonium tetrafluoroborate reported an LD₅₀between 300-2000 mg/kg bw.

However, since the solution (50:50) of lead bis(tetrafluoroborate) as marked has a pH value of < 2, further animal studies are not justified. The substance will be classified as corrosive by worst case.

Acute toxicity, inhalation:

The existing group entry according to annex I of directive 67/548/EEC for the classification of lead compounds for acute inhalation toxicity is not considered to be applicable in view of the physical nature of the substance, which is only stable, produced and marketed in aqueous solution, thus rendering any inhalation exposure negligible.

Acute toxicity, dermal:

No study is available for lead bis(tetrafluoroborate) solution. However, according to regulation (EC) 1907/2006 column 2 Annex VIII point 8.5.3, testing is not considered to be required since the substance is corrosive via skin and eyes, but also because the dermal absorption of lead cations has been shown to be negligible.

Justification for classification or non-classification

The current classification of lead compounds not otherwise described in Annex I is:

Xn; R20/22 (harmful by inhalation and if swallowed)

and under CLP:

Acute Tox. 4 *                       (H332)

Acute Tox. 4 *                       (H302)

Acute toxicity, oral:

Existing classifications for acute toxicity for lead compounds is not supported by the existing experimental and read across data. Acute toxicity is not observed in animals after oral exposures up to the limit values of acute toxicity testing for seven different similar inorganic lead compounds and is reported to be > 1947 mg/kg for lead chloride. Further, it could be stated that the toxicity of tetrafluoroborate salts are based on the respective cation and not on the tetrafluoroborate. Therefore, the classification of harmful if swallowed in accordance with annex I is considered not to be justified. Nevertheless, since lead bis(tetrafluoroborate) aqueous solution (50:50) has a pH of <2 and must be classified as corrosive by worst case.

Acute toxicity, inhalation:

The existing group entry according to annex I of directive 67/548/EEC for the classification of lead compounds for acute inhalation toxicity is not considered to be applicable in view of the physical nature of the substance, which is only stable, produced and marketed in aqueous solution, thus rendering any inhalation exposure negligible.

Acute toxicity, dermal:

No study is available for lead bis(tetrafluoroborate) solution. However, according to regulation (EC) 1907/2006 column 2 Annex VIII point 8.5.3, testing is not considered to be required since the substance is corrosive via skin and eyes, but also because the dermal absorption of lead cations has been shown to be negligible.