Calcium hexaboride

Endpoint summary

Description of key information

An acute dermal lethality study was conducted on Calcium Hexaboride and an acute inhalation lethality study was conducted on a structural analog, Titanium Diboride. The results of the studies are:

 

Acute dermal LD50 is greater than 2,000 mg/kg body weight in rats when tested according to OECD 402 (2017).

 

Acute inhalation toxicity is greater than 5.05 mg/L, dust, in rats when tested according to OECD 403.

Additional information

The acute dermal lethality and skin irritation potential of the test article was evaluated in three female Wistar rats. The test was performed according to OECD 402 (2017) and the study was conducted in compliance with OECD GLP (1997) regulations. The test article was suspended in 1% aqueous carboxymethyl cellulose. One day before dosing, an area of approximately 5x7 cm on the back of the animals was clipped. 2,000 mg/kg body weight of the test item was applied to each rat in an area of approximately 10% of the total body surface, i.e. approximately 18 cm² for females. The test item was held in contact with the skin with a dressing, consisting of a surgical gauze patch (Surgy 1D), successively covered with Coban elastic bandage. A piece of Micropore tape was additionally used for fixation of the bandages in females only. The application period was 24 hours, after which the dressing was removed and the skin cleaned of residual test item using water. The dose volume for each animal was based on the body weight measurement prior to dosing. A dose volume of 10 mL/kg body weight will be used for each dose. Post-dose observations were performed at periodic intervals on the day of dosing (at least three times) and once daily thereafter. The observation period was 14 days. All the animals were examined for reaction to dosing. The onset, intensity and duration of these signs was recorded (if appropriate), particular attention being paid to the animals during and for the first hour after dosing. Animals were weighed individually on Day 1 (pre-dose), 8 and 15. Skin reactions were assessed approximately 24, 48, and 72 hours after removal of the test article and scored using the standard Draize scoring method. No mortality occurred during the study. No signs of systemic toxicity were noted. No skin irritation was noted for any animals at any time point. Black staining of the treated skin was noted for the animals on Days 2 and/or 3. Additionally, blue discoloration of the skin was noted for one animal on Day 3. This was considered to be due to the staining properties of the test item. The body weight gain shown by the surviving animals during the observation period was within the range expected for rats used in this type of study. No abnormalities were found at macroscopic post mortem examination of the animals. Based on the results of the study, the dermal LD50 of the test article is greater than 2,000 mg/kg body weight and no skin irritation was noted in any animal at any time point.

 

The acute inhalation lethality results for titanium diboride (CASRN 12045 -63 -5) (source) are reported for read-across to calcium hexaboride (CASRN 12007 -99 -7) (target). An acute inhalation toxicity test was conducted with rats to determine the potential for Titanium Diboride to produce toxicity from a 4-hour exposure via the inhalation (nose-only exposure) route. Under the conditions of this study, the single exposure acute inhalation LC50of the test substance is greater than 5.05mg/L in male and female rats. Based on the results of this study, Titanium Diboride has no labeling requirements for acute inhalation toxicity and is not classified.

After establishing the desired generation procedures during pre-test trials, ten healthy rats (5/sex) were exposed to the test atmosphere for 4 hours. Chamber concentration and particle size distributions of the test substance were determined periodically during the exposure period. The animals were observed for mortality, signs of gross toxicity, and behavioral changes at least once daily for 14 days following exposure. Body weights were recorded prior to exposure and again on Days 1, 3, 7 and 14 (termination). Necropsies were performed on all animals at terminal sacrifice.

The gravimetric chamber concentration was 5.05mg/L. Based on graphic analysis of the particle size distribution as measured with an ACFM Andersen Ambient Particle Sizing Sampler, the mass median aerodynamic diameter was estimated to be 3.5.

All animals survived exposure to the test atmosphere. Following exposure, all animals exhibited abnormal respiration. However, the animals recovered from this symptom by Day 6 and appeared active and healthy for the remainder of the 14-day observation period. Although all animals lost body weight by Day 1 and/or Day 3, all animals showed a continued weight gain thereafter through Day 14. No gross abnormalities were noted for any of the animals when necropsied at the conclusion of the 14-day observation period.

Justification for classification or non-classification

Based on the results of the studies, the test article is not classified for acute dermal or inhalation lethality according to CLP in Europe.