Silicic acid, calcium salt

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

no data: aquatic toxicity unlikely

Marine water

Hazard assessment conclusion:

no data: aquatic toxicity unlikely

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

100 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

no hazard identified

Sediment (marine water)

Hazard assessment conclusion:

no hazard identified

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

no data available: testing technically not feasible

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

When dissolved in water Silicic acid, Calcium salt decomposes for a small part in Ca²⁺ and (amorphous silica) SiO₃^2- 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.

Compounds of silicon and oxygen are ubiquitous in the environment; they are present in inorganic matter, like minerals and soils as well as in organic matter, like plants, animals and man. By weathering of soil, rocks and sediments and by atmospheric deposition, silica is released into surface and ground waters from where it may be removed by precipitation and sedimentation or taken up by living organisms, especially diatoms. Silica is found in all surface waters. Median values were reported to be 17 mg SiO₂/L for ground waters and 14 mg SiO₂/L in the US; the worldwide concentration in rivers is 13 mg SiO₂/L and in Europe 7.5 mg/L. SiO₃^{2 -} in water results in SiO₃^{2 -}+ H₂0 --> 2OH^-+ SiO₂ (Solid). All available aquatic toxicity tests with silicates revealed toxicity only at concentrations well above 100 mg/L. This corresponds to well above 50 mg Si/L. The effects observed in the aquatic toxicity studies are stated to be mainly governed by their intrinsic alkalinity. However, most natural aquatic ecosystems are slightly acid or alkaline and due to the high buffer capacity of these ecosystems pH effects of soluble silicates to aquatic organisms are very unlikely. Therefore it is argued that SiO₃^2- will not pose any toxicity among aquatic organisms.

Likewise, Ca²⁺ is an essential element and it is 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 Ca²⁺/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.

It is concluded that the derivation of a PNEC for Silicic acid, Calcium salt or is degradation products is not possible.

Conclusion on classification

A saturated solution of silicic acid, calcium salt is thus not considered to be toxic to aquatic organisms.

Silicic acid, calcium salt is therefore not classified as hazardous to the enviroment according to Regulation 1272/2008/EC