Silicic acid, lithium salt

Endpoint summary

Description of key information

Oral (OECD 423), rat: LD50 cut-off: 2500 mg/kg bw  (limit test)
Inhalation: due to physicochemical properties inhalation is unlikely to occur
Dermal: negligible dermal absorption through the skin

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion

Dose descriptor:

LD50

Value:

2 500 mg/kg bw

Additional information

Oral

The acute oral toxicity of silicic acid, lithium salt (Molar Ratio SiO2/Li2O: 4.8) was determined in a GLP-Guideline study according to OECD 423 (Colas, 2010). The test substance was administered to 6 female rats at a dose of 2000 mg/kg bw. The death of two animals was noted on day 1 and day 2 post-dose, respectively. The mortalities were preceded by a decrease in spontaneous activity (2/2), and in body temperature (2/2), increased lachrymation (1/2), bradypnea (2/2), tremors (1/2), piloerection (1/2) and absence of righting reflex (1/2). Macroscopical examinations revealed a thinning of the corpus associated with red spots in both animals and a thinning of the forestomach in one of the two dead animals. The observed effects may be a consequence to the alkalinity of the test substance. This assumption is confirmed by acute oral toxicity studies with silicic acid, sodium salt or sodium metasilicate, in which the toxicity the observed toxicological symptoms are indicative effects due to alkalinity (CEES, 2008).

In the survival animals, similar observations including a decrease in spontaneous activity (4/4), and in body temperature (1/4), increased lachrymation (1/4), bradypnea (2/4), piloerection (2/4) and absence of righting reflex (2/4) were made on the first day of the study. All animals recovered to a normal behaviour at 24 hours post-dose. No treatment-related changes were noted in the four surviving rats at necropsy at the end of the study.

In conclusion, the oral LD50 cut-off value for silicic acid, lithium salt is 2500 mg/kg bw in the rat according to the acute toxic class method described in the OECD guideline 423 since one animal each died in two separate steps.

 

Inhalation

An acute inhalation limit test with the technical product AgSil™ 25 Potassium Silicate Solution (active ingredient: 30%) no deaths occurred after inhalation of 2 mg/L (MMAD 2.7µm) for 4 hours (Durando, 2004). Hunched posture and hypoactivity were noted during in-chamber animal observations. These clinical signs were reversible, after removal from the exposure chambers all rats appeared active and healthy over the 14-day observation period. Thus, the LC50 of the test substance is considered to be greater than 2.06 mg/L in rats.

 

However, silicic acid, lithium salt contains ca. 85.5% particles with a particle size larger than 149 μm, and ca. 14.7% particles with a particle size between 18 μm and 149 µm. Very few particles are smaller than 18 μm (IUCLID section 4.5: Paulus, 2010). Therefore, the test substance is rarely inhalable (particles < 100 µm) and even less respirable (particles < 4 µm). If particles are inhaled they will remain in the upper airways and/or will be either be coughed out or swallowed, with few or no particles reaching the pulmonary alveoli. Toxic effects after swallowing is sufficiently covered by the available acute oral toxicity study.

For an inhalation assay grinding to a fine and respirable powder would be required, representing a test substance, which is not existing under real life conditions.

The vapour pressure of silicic acid, lithium salt will be immeasurably small, which also indicates a low potential for exposure via inhalation. The vapour pressures for solid e.g. sodium silicates were extremely low (0.016 hPa at 1172 °C (MR 3.0); 0.0031 hPa at 1165 °C (MR 2.0)) and it is not expected that these for silicic acid, lithium salt vary significantly from those determined.

In addition for workers, the implemented risk management measures ensure that the potential for acute toxicity via the inhalation route is estimated to be minimal.

Therefore, during normal handling and use of silicic acid, lithium salt, it can be assumed that no acute toxic effects due to inhalation of the test substance are likely to occur.

 

Dermal

No reliable QSAR estimations for the dermal absorption rate can be provided for silicic acid, lithium salt due to the inorganic character of the test substance. However, Dermwin v2.01 predicts a permeability constant of 5.78E-07 cm/h based on an estimated Log Pow of -4.46. Although this value is outside the estimation domain of the QSAR tool, the dermal absorption rate for silicic acid, lithium salt can be regarded as very low.

The assumption, that after contact with silicic acid, lithium salt, the bioavailability of the test substance is very low, was confirmed in an acute dermal limit test with AgSil™ 25 Potassium Silicate Solution (active ingredient: 30%). There was a complete absence of mortalities after application of 5000 mg potassium silicate solution/kg bw to the skin of ten rats for 24 hours (Durando, 2004). In five animals erythema and alopecia was noted between day 1 and 8. No other effects were noted. Under the conditions of the test, the dermal LD50 for potassium silicate solution is greater than 5000 mg/kg bw.

In conclusion, the acute oral toxicity study, which resulted in an LD50 > 2000 mg/kg bw, is considered as worst case scenario in regard to systemic effects after short-term exposure to silicic acid, lithium salt.

 

References

CEES, Centre Européen d’Etudes des Silicates: Soluble Silicates, Chemical, toxicological, ecological and legal aspects of production, transport, handling and application, last update: June 2008, http://www.cees-silicates.org/recentpublicationscees.html

 

 

Justification for classification or non-classification

The available data on acute toxicity of the test substance do not meet the criteria for classification according to Regulation (EC) 1272/2008 or Directive 67/548/EEC, and are therefore conclusive but not sufficient for classification.