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

Toxicity to microorganisms

Description of key information

Zirconium acetate did not show any adverse effect on aquatic micro-organisms in the key study (Bayliss, 2013). When the test substance (Frit) 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 silicates also had high thresholds of toxicity and the toxicity of sodium hydroxide was due to the high pH. For sodium hydroxide In a test system with the freshwater ciliated protozoan Tetrahymena thermophila, NaOH is used as a positive control. At the NOEC (EC10) of 167 mg/l the calculated pH value was 11.6, assuming that the dilution medium has no buffer capacity.
The inhibition of the bioluminescence of the marine bacterium Photobacterium phosphoreum by NaOH has been measured with the Microtox test system, resulting in a 15-minutes EC50 of 22mg/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 NOEC (EC10) of 167 mg/l equates to 334 mg/L for the substance and 15-minutes EC50 of 22 mg/l equates to 44 mg/L.

Key value for chemical safety assessment

EC50 for microorganisms:

44 mg/L

EC10 or NOEC for microorganisms:

334 mg/L

Additional information

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

In a test system with the freshwater ciliated protozoan Tetrahymena thermophila, NaOH is used as a positive control. At the NOEC (EC10) of 167 mg/l the calculated pH value was 11.6, assuming that the dilution medium has no buffer capacity.

The inhibition of the bioluminescence of the marine bacterium Photobacterium phosphoreum by NaOH has been measured with the Microtox test system, resulting in a 15-minutes EC50 of 22mg/l.

There are two studies available for zirconium:

The study from Borne and Humphrey (1977) has a Klimisch score of 3 and is not considered reliable. However the study is used as supporting information giving an indication of the toxicity. The 4-h EC75 values reported are 400 mg Zr/L for carbonaceous oxidation and 150 mg Zr/L for nitrification. The 4-h NOECs were 150 and 50 mg Zr/L, respectively. The results of the respirometer tests cannot be used because of confounding effects from precipitation of zirconium and/or phosphate depletion. Therefore the data are only indicative.

A new study was executed (Bayliss, 2013). A relatively large increase in respiration rate was observed in the test vessels at 1000 mg a.i./L (anhydrous zirconium acetate), which was considered to be due to metabolism of the acetate component of the test item. No statistically significant toxic effects were shown at all of the test concentrations. The 3-h EC50 for zirconium acetate was set at > 1000 mg/L, or, when based on nominal zirconium, > 742 mg/L.

For silicates:

The toxicity of a sodium silicate solution (MR 3.46, 34.8 wt%) has been determined with a growth inhibition test in compliance with German standards and GLP using the bacterium Pseudomonas putida (Hanstveit 1989). The 18 h toxicity threshold (EC10, 10 % inhibition) of a neutralised silicate solution of pH 7.6 - 7.8 was > 3480 mg active matter/L, the highest concentration tested, while for the unneutralised solution (pH 7.9 - 10.4) effects were found at concentrations above 348 mg active matter/L. In a further GLP guideline study complying with German standards corresponding to OECD 209, the toxicity to Pseudomonas putida was tested in an oxygen consumption inhibition test. Concentrations of a sodium silicate solution (MR 3.0, 34.54 wt%) of up to 3454 mg active matter/L at pH 8.0 - 11.1 did not cause toxic effects (Kirch 1993).

EC0 (18h, growth inhibition) > 10000 mg/L for neutralized concentrations (pH 7.6-7.8). Equivalent to > 3480 mg active matter/L (Pseudomonas putida)

EC0 (18h, growth inhibition) > 1000 mg/L for unneutralised concentrations (pH > 9). Equivalent to > 348 mg active matter/L (Pseudomonas putida)

EC0 (30min, oxygen consumption inhibition) 3454 mg/L