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Ecotoxicological information

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The activated sludge respiration test showed that the 3h-EC50 and 3h-NOEC of Crystalline calcium silicate hydrates on the inhibition of the respiration of activated sludge were > 1000mg/L and ≥ 1000 mg/L.

All other aquatic toxicity tests are waived based on the very low concentrations of non-toxic ions and on based on exposure considerations:

The water solubility study with silicic acid, calcium salt showed that the test substance decomposes for a small part in Ca2+and SiO32-ions. The solubility was shown to be 8.9 mg/L Si-ion and 17.5 mg/L Ca-ion. It is argued that these concentrations do not pose any harm to aquatic organisms.

 Ca2+is an essential element and one of the elements in standard water (ISO 6341& 7346, OECD 202 & 203) used in aquatic toxicity tests. The required Ca content in ISO 6341 standard water is 80 mg Ca2+/L. Thus, the 17.5 mg/L is below the advised level of Ca2+content in water used for toxicity testing. Moreover, an overview of toxicity data in the database Aquire (US EPA) shows that 17.5 mg/L Ca2+does not result in any toxicity among aquatic organisms.

Concerning SiO32-, this ion in water results in SiO32-+ H20 --> 2OH-+SiO2(Solid). The solubility of SiO32-is at the background level, whereas the toxicity data in the literature are far above this level. Therefore it is concluded that SiO32-solved from Silicic acid, calcium salt will not pose any toxicity among aquatic organisms.

 

The toxicity of these ions and their concentration in a 100 mg/L solution is presented in the table below.

Element

100 mg/L solution in medium

Toxicity

(mg/L, screening in EPA-ECOTOX)

Ca

17

EC50 > 100

Si

8

EC50 > 100

Ecotox data for the elements were collected from the EPA-ECOTOX database. The limit listed in the last column of the table is a conservative level covering many tests and species.

 

It is concluded that the concentration of the elements (ions) that are released on dissolution of silicic acid, calcium salt in the test do not reach the EC50 values for any of the elements. Thus silicic acid, calcium salt will not be toxic at loading rates of 100 mg/L.

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