Silicic acid, aluminum salt

Toxicity to aquatic algae and cyanobacteria

Description of key information

One study for toxicity to aquatic algae is available on a structurally related compound according to OECD Guideline 201.
In this key study, an eluate of silicic acid, calcium salt (Shieldex AC3) was tested for effects on Scenedesmus subspicatus in a geometric series of 5 concentrations, resulting in an EC50 of 2500 mg/L for growth rate and an EC50 of 410 mg/L for biomass, respectively (Lebertz 1999).
A NOEC value could not be determined, since the lowest concentration of 100 mg/L still showed effects on growth rate and biomass. However, the EC10 values were reported as 41 mg/L (growth rate) and 33 mg/L (biomass), respectively, and could be used for this purpose (as mentioned in OECD 201).

Key value for chemical safety assessment

EC50 for freshwater algae:

2 500 mg/L

EC10 or NOEC for freshwater algae:

41 mg/L

Additional information

The interpretation of the algal toxicity values must be carried out with caution, since it is well known and supported by numerous investigations that the growth-inhibiting effects of complexing agents and ion-exchanging materials, which are often observed in nutrient-poor, but also in standard culture-media of ecotoxicological standard tests, result from the depletion of trace metals essential for algal growth. For such substances, it is recommended to use a nutrient-enriched medium to avoid respective nutrient-depletion effects. Thus, it can be concluded that the inhibitory effect observed in nutrient-poor or standard test media is without any practical relevance and not to be considered as a toxic effect. Hence, EC50 values as well as NOEC values for algae were considerably overestimated by the available study, representing an unrealistic worst-case scenario derived from laboratory experiments without practical relevance for natural environmental conditions.