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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The effect concentrations to algae obtained on the three main constituents of potassic extracts are the following: 
Potassium sulfate (K2SO4): 72hEC50 = 1430 mg/L;
Calcium sulfate (CaSO4): 120h EC50 (Nitscheria linearis) = 3200 mg/L;
Sodium sulfate (Na2SO4): 120h EC50 (Nitscheria linearis) = 1900 mg/L.

Key value for chemical safety assessment

EC50 for freshwater algae:
1 430 mg/L

Additional information

Potassic extracts is a multiconstituent substance. As its main constituents are simple inorganic salts (i.e. potassium sulfate, sodium sulfate and calcium sulfate), in aquatic environment, the soluble portion of each constituent completely dissociates into the sulfate ion (SO42-) and the corresponding cations: potassium (K+), sodium (Na+) and calcium (Ca2+) at neutral pH.


Although calcium sulfate is less soluble than the other main constituents of the potassic extracts, its water solubility is sufficiently high to determine the absence of toxicity to algae at concentration higher than 100 mg/L, showing absence of harmful effect to the tested organisms, as it is also showed for the other constituents. The other physico-chemical properties of the main constituents are similar: high melting point (> 880°C), high boiling point or decomposition before boiling, vapour pressure expected to be extremely low.


Based on the above information, the results obtained on the individual salts present in the potassic extracts are used in a read-across approach to assess the fish toxicity of the multiconstituent substance.


One key study (Patrick et al., 1968) is available which reports toxicity results to diatoms for two main constituents individually (i.e. calcium sulfate and sodium sulfate). As no reliable algae study with potassium sulphate is available, a weight of evidence approach is applied to assess the toxicity of this constituent to algae.


The results reported in the key study were obtained in a 120-h toxicity study. The cultures of Nitscheria linearis were exposed to Sodium sulfate and Calcium sulfate (test concentrations not indicated) under static conditions. The EC50values were based on reduction of cell number and were reported as follows:

- Calcium sulfate (CaSO4): 120h EC50 = 3200 mg/L

- Sodium sulfate (Na2SO4): 120h EC50 = 1900 mg/L


Based on these results, Calcium sulfate and Sodium sulfate are considered not hazardous to the organisms tested in accordance with EC regulation n°1272/2008.

A study performed according to the OECD Testing guidelline 201 and the GLP is available for the hydrated form of the calcium sulfate (i.e. calcium sulfate, dihydrate). In this limit test performed on Pseudokirchnerella subcapitata, there was no significant difference in the growth curves between the test group at 100 mg/L of CaSO4.2H2O and the control group. When corrected to calcium sulfate anhydrous, this result corresponds to a 72hEC50 > 79 mg/L. This study is used as a supporting study to conclude on the low toxicity profile of calcium sulfate to algae.

No reliable algae study with potassium sulphate is available. However, one secondary source is available (IUCLID of the European Commission (2000)) reporting a 72h EC50 (Scenedesmus subspicatus) of 1430 - 2900 mg/L obtained according to the method DIN 38412 Part 33. Additionally, a reliable study with ammonium sulphate is available (Tam N.F.Y. and Wong Y.S., 1996). This static 18 -day test with Chlorella vulgaris showed an 18d EC50 of 2700 mg/L based on cell number. Applying a weight of evidence approach on these two studies, Potassium sulfate is considered not hazardous to the organisms tested in accordance with EC regulation n°1272/2008.


Even if the validity of the study on potassium sulfate is not assignable due to secondary litterature source, as it presents the lowest EC50 to algae and as this constituent has the highest concentration in the multiconstituent substance, as a worst case approach, this EC50 is selected as the key value for the chemical assessment of the multiconstituent substance.

Moreover, the possibility to apply the results obtained on the mono-constituents to the multiconstituent substance, is supported in the ECHA Guidance on QSAR and grouping of chemicals (2008)