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Toxicity to microorganisms

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Description of key information

The effect concentrations to microorganisms for the three main constituents of potassic extracts are the following: 
Potassium sulfate (K2SO4): NOEC >= 100 mg/L (estimated)
Calcium sulfate (CaSO4): 3h NOEC (activated sludge) = 1000 mg/L (by analogy with the hydrated form)
Sodium sulfate (Na2SO4): 37d NOEC (bacteria in activated sludge) = 26 g/L ; 37d NOEC (Stalked ciliates in activated sludge) = 8 g/L.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
100 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 aquatic organisms at concentration higher than 100 mg/L, showing absence of harmful effect to the tested organisms, as it is also showed for the other main 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.


Reliable data are available for one main constituent of the substance (i.e. Sodium sulfate). Additionally, a reliable data is available for the hydrated form of a second main constituent (i.e. Calcium sulfate, dihydrate). No data is available for the main constituent having the highest concentration in the substance, i.e. potassium Sulfate. However, in view of the use of the substance (fertilizer) and the available data on the other trophic levels (fish, invertebrates and algae) with the different inorganic salts, no toxicity is expected from potassium sulphate. By default, and as a worst case, the NOEC value is considered to be 100 mg/L for potassium sulfate.


The reliable study available for Sodium sulfate (Tokuz, 1986) is a 37-d toxicity study, where activated sludge were exposed to Sodium sulfate at nominal concentrations of 0, 8,10, 12, 14, 15, 17, 20, 23, 26, 30 and 35 g/L under flow-through conditions. The NOEC for Stalked ciliates in activated sludge was 8 g/L but the NOEC for bacteria in activated sludge was 26 g/L. It was observed by microscope that the high salinity caused filamentous microorganisms to appear. Such organisms did not cause any decrease in settling rates and the sludge flocculated and settle well. Salinity increase also caused the population of the protozoa to decrease. In the sodium sulfate system stalked ciliates disappeared early but even at 26 g/L salinity motile protozoa were observed.


The reliable study available on Calcium sulfate, dihydrate (Youngs N., 2010) has been performed in accordance with the OECD testing guideline 209 and the GLP. The respiration rates of activated sludge fed with synthetic sewage were measured in after a contact time of 3 hours at test item concentrations ranging from 10 to 1 000 mg/L. No inhibition of the respiration of the activated sludge has been observed at all tested concentrations. Therefore, the 3h NOEC has been determined to be 1 000 mg/L.


Based on these data, potassic extracts is considered as not hazardous to microorganisms. As a worst case approach, a NOEC value of 100 mg/L is considered for the assessment of the 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)