Silicic acid (H4SiO4), zirconium(4+) salt (1:1), reaction products with sodium hydroxide

Short-term toxicity to fish

Description of key information

The substance reacts with water. The water soluble reaction product is a multi-constituent substance: Reaction mass of disodium metasilicate and sodium hydroxide(EC 910-245-3).
Disodium Metasilicate: An LC50 of 210 mg/L for freshwater Brachydanio rerio (new name: Danio rerio) and an LC50 of 2320 mg/L for freshwater for Gambusia affinis.
Sodium Hydroxide: The available data indicate that NaOH concentrations of 20 to 40 mg/l may be acutely toxic to fish and invertebrates. 
The residual insoluble Zirconium salts: LC50 >100 mg/L
Therefore, it is the sodium hydroxide formed when the substance that reacts with water that is the most toxic. Therefore, these data are used for the chemical safety assessment after correction for composition of a maximum of 50% sodium hydroxide equivalence (after reaction with water). Therefore a sodium hydroxide LC50 of 20 mg/L equates to 40 mg/L for the substance.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

40 mg/L

Marine water fish

Marine water fish

Effect concentration:

40 mg/L

Additional information

The substance reacts with water. The water soluble reaction product is a multi-constituent substance:

Reaction mass of disodium metasilicate and sodium hydroxide(EC 910-245-3)

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.

Residual insoluble material: Zirconium salts

Two studies were identified as containing relevant and reliable information.

In the first study (Harris, 2013), preliminary stirring experiments were executed with test concentrations of 100 mg/L (referring to anhydrous zirconium acetate) to determine the dissolved zirconium in solution. After prolonged stirring of the test item, a measurable amount of zirconium could not be obtained in solution. Therefore, no ecotoxicity testing was performed and the 96-h LC50 was set at > 100 mg/L.

When zirconium acetate is added to the test medium, a pH drop occurs. When adjusting pH back to environmentally relevant levels, precipitation occurs. The zirconium acetate quickly hydrolyses and zirconium precipitates out of solution forming insoluble zirconium hydroxides or zirconium oxide, rendering the substance unavailable to the test organisms. Therefore, read across can be done from tests with similar 'soluble' zirconium substances, as well as from tests with insoluble zirconium substances such as zirconium dioxide.

In the study from Bazzon (2000), the toxicity of zirconium dioxide to zebra fish (Brachydanio rerio) was studied under static conditions, according to OECD Guideline 203. No mortality was observed during the test, neither in the control nor in the group exposed to the test item. The 96 hour LC50 was > 100 mg/L (ZrO2). This study result can be used for read across purposes to indicate that zirconium acetate is not toxic to fish either at equivalent doses.

The third study from Abram et al. (1978) yielded a 7-d LC50 to rainbow trout of 58.7 mg Zr/L. However, precipitation was observed after introduction of the test substance. Since no analytical monitoring results of the test substance in dissolution have been presented in the study report, the study cannot be considered reliable (Klimisch 3) but is used as supporting study.