Reaction mass of disodium metasilicate and sodium hydroxide

Endpoint summary

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records

Reference

Endpoint:

acute toxicity: oral

Type of information:

other: Expert Assessment

Adequacy of study:

key study

Study period:

2015

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Expert assessment as opposed to experimental result

Reason / purpose for cross-reference:

reference to other study

Principles of method if other than guideline:

Assessment

GLP compliance:

no

Test type:

other: Assessment

Remarks on result:

not measured/tested

Remarks:

due to pH>11

Assessment       

Interpretation of results:

Category 4 based on GHS criteria

Remarks:

Migrated information

Executive summary:

This substance is a multi-constituent substance consisting of sodium hydroxide (215-185-5, 1310-73-2) and disodium metasilicate (229-912-9, 6834-92-0). It is the by-product of a reaction between zircon and sodium hydroxide (EC 304-802-4, Frit); after hydrolysis, this substance (EC 910-245-3) is the water-soluble fraction.  

There are two acute oral toxicity studies with a Klimisch rating of 2 reported for disodium metasilicate which gives the LD50 for (male/female) rats of 770-820 mg/kg and 1152 -1349 mg/kg.

There are no reliable LD50 values for sodium hydroxide reported. This could in part be due to the severe localised effects of dosing such a corrosive substance (pH>11), which would also preclude conducting further acute toxicity tests in animals due to animal welfare issues.

There is an acute toxicity study for the precursor to reaction mass of disodium metasilicate and sodium hydroxide (910-245-3), that is Silicic acid (H4SiO4), zirconium(4+) salt (1:1), reaction products with sodium hydroxide (EC 304-802-4, Frit). This study has a Klimisch rating of 2 and reports an LD50 for (male/female) rats of 1,372 mg/kg.

The reaction mass of disodium metasilicate and sodium hydroxide (EC 910-245-3) has a pH of >13 which, if tested for acute toxicity, would give localised effects due to its corrosiveness and preclude conducting further acute toxicity tests in animals due to animal welfare issues. 

As such, the lowest acute toxicity for disodium metasilicate which gave an LD50 for (male/female) rats of 770-820 mg/kg will be used as surrogate for the reaction mass of disodium metasilicate and sodium hydroxide.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LD50

Value:

770 mg/kg bw

Acute toxicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LC50

Value:

2 060 mg/m³ air

Acute toxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Sodium Hydroxide: Source - the sodium hydroxide summary risk assessment report JRC EC 2008

No valid human and animal data are available on the acute systemic inhalation toxicity of NaOH. Limited animal data is available on acute systemic dermal toxicity. The hair of adult mice was clipped and a circular area 2 cm in diameter was painted by applicator with 50% NaOH. Afterwards the area was rinsed with water at various intervals. The mortality of mice was 20, 40, 80 and 71% when they were rinsed 30 minutes, 1 hour, 2 hours or not at all after the application. No mortality was observed when the mice were rinsed immediately after the application.

No acute oral toxicity study with animals has been carried out using (inter)national guidelines. Human case reports involving oral exposure were available in literature. The degree and type of injury after ingestion of NaOH depend on the physical form. Solid NaOH produces injury to the mouth and pharynx and is difficult to swallow. On the other hand liquid NaOH is easily swallowed, being tasteless and odourless, and is more likely to damage the oesophagus and stomach.

As NaOH is a corrosive substance, there is no need for further acute toxicity testing.

Justification for selection of acute toxicity – dermal endpoint
Running an acute dermal study on the reaction mass of disodium metasilicate and sodium hydroxide would add nothing to the hazard assessment for this substance, and risk management measures are driven primarily by its corrosive nature due to the high pH.