Reaction mass of disodium metasilicate and sodium hydroxide

Short-term toxicity to fish

Description of key information

The toxicity of sodium hydroxide is approximately 10-fold greater than for the disodium metasilicate. After correcting for composition of approximately 50%, the LC50 values for sodium hydroxide have been selected

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

20 mg/L

Marine water fish

Marine water fish

Effect concentration:

20 mg/L

Additional information

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

The results of single-species acute toxicity tests with NaOH include tests with fish and invertebrates; all but one test were performed with freshwater species. The tests with fish resulted in acute LC50 values and toxic / lethal concentrations ranging from 35 to 189 mg/l. The results for invertebrates are very similar, with a range of 33 to 450 mg/l. There are no data for algae and higher aquatic plant species. For chronic toxicity of NaOH only one limited study is available, with fish (guppy) Lebistes reticulatus.This study clearly showed effects on survival, growth and reproduction of fish at long-term exposure to NaOH concentrations of 25 mg/l and higher. The available data indicate that NaOH concentrations of 20 to 40 mg/l may be acutely toxic to fish and invertebrates. Data on pH-increases due to the addition of these amounts of NaOH in the used test waters are lacking. In waters with a relatively low buffering capacity, NaOH concentrations of 20-40 mg/l may result in a pH increase with one to several pH units.

The data on the pH tolerance of fish show that an increase in pH value from around 8.5 to 9.5-10.5. i.e. an increase with 1 to 2 pH units results in acute lethality in fish that were not acclimatized to intermediate values. The data further show that pH values of 9-10 may be toxic or lethal to some fish species and above a pH value of 10 mortalities may be expected for many species exposed for a prolonged period.

Disodium Metasilicate:

A semi-static study with Brachydanio rerio by Adema (1988), following OECD guideline 203, was performed under GLP for a sodium silicate solution (MR 3.46, 34.8 wt %). The 96 h LC50 was determined to be 1108 mg active matter/L. The NOEC values for mortality and swimming behaviour were 348 and 1114 mg active matter/L, respectively. The pH varied depending on the test substance concentration from 7.9 to 10.3.

In another non-GLP study, Maruyama et al. (1989) examined the toxicity of a neutralised sodium silicate solution (MR 3.1, concentration not indicated) to rainbow trout (Oncorhynchus mykiss). In four replicates the 96 h LC50 varied from 260 mg/L (pH 6.8 - 7.5,) to 310 mg/L (pH 7.2 - 8.0). Necrosis of gill filaments as a result of the formation of colloidal silica was observed. However, this is considered a physical rather than toxic effect