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Short-term toxicity to aquatic invertebrates

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Description of key information

The effect concentrations to aquatic invertebrates (Daphnia magna) obtained on each of the three main constituents of potassic extracts are the following: 
Potassium sulfate (K2SO4): 48h LC50 = 720 mg/L
Calcium sulfate (CaSO4): 48h LC50 > 1970 mg/L
Sodium sulfate (Na2SO4): 48h LC50 = 4580 mg/L

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Effect concentration:
720 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 invertebrates 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 in the same study. The other physico-chemical properties of the 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 aquatic invertebrates toxicity of the multiconstituent substance.

 

One key study (Mount et al., 1997) is available which reports toxicity results to Daphnia magna for each main constituent individually. Additionally, this study reports results for combined salts which can be used to support the read-across approach.

 

The results reported in the key study were obtained in 48-h acute toxicity tests performed according to the standardized EPA guideline for acute effluent toxicity testing but not in accordance with GLP. In these tests, Daphnia magna were exposed to different inorganic salts under static conditions. Stock solutions were prepared by dissolving 10 000 mg/L of each salt in moderately hard reconstituted water. Test solutions were then prepared by serially diluting of the stock solution. Ion concentrations measured in the stock solutions were compared to nominal values. If the measured concentrations differed from the nominal value by more than 20%, the actual measured concentrations were substituted for the nominal concentrations.

As CaSO4 was not fully soluble at 10000 mg/L, stock solutions of CaSO4 were filtered through a 1µm glass fiber filter prior to testing and ion concentrations were measured in filtered solutions.

 

It should be noted that daphnids were fed during the test, what constitutes a deviation compared to the guideline. Tests have included feeding because analysis of initial experiments performed on Ceriodaphnia dubia with and without feeding to assess the potential effect of feeding on major ion toxicity, showed that the addition of food represented only a small influence on Ceriodaphnia dubia survival. Therefore, this deviation is not considered to have affected the result of the tests.

 

Additionally to this deviation, it was not possible to check all of the OECD validity criteria due to lack of data as listed below:  

- Control mortality below 10%: no data

- Constant conditions maintained throughout the test: this criteria has been fulfilled as pH ranged from 7.5 to 9.0 and organisms were tested at 20°C

- Dissolved oxygen concentration at least 60 % of the air saturation value throughout the test: this criteria has not been fulfilled as the dissolved oxygen concentrations were only above 40% of saturation

- Test substance concentration maintained during the test: no data as only initial ions concentrations have been measured.

 

To incorporate inter-test variability into the data set, test substances were tested on different occasions over several months, resulting in several test results for each substance. The results obtained showed low variability and are listed below:

 

-      Potassium sulfate (K2SO4): 48h LC50 = 720 mg/L (this result is an arithmetic mean of values obtained in 4 studies performed at different times, providing 48hLC50 values between 580 and 880 mg/L.)

-      Calcium sulfate (CaSO4): 48h LC50 > 1970 mg/L (this result has been obtained in two separate studies)

-      Sodium sulfate (Na2SO4): 48h LC50 = 4580 mg/L (this result is an arithmetic mean of values obtained in 4 studies performed at different times, providing 48hLC50 values between 4 060 and 5 360 mg/L.)

 

Based on the results of this study, Potassium sulfate, Calcium sulfate and sodium sulfate are considered not hazardous to the organisms tested in accordance with EC regulation n°1272/2008.

 

Considering the deviations discussed above but also the low variability of the results obtained, along with the LC50 values well above the threshold value of 100 mg/L for classification as hazardous, this key study is considered as reliable with restrictions.

 

Additionally, this study reports results for combined salts, obtained in the same test conditions as described above. Test solutions were prepared by combining equal volumes of the two stock solutions, then diluting as necessary. Results obtained with the constituents under consideration were as follows:

 

-      Potassium sulfate (K2SO4) and Calcium sulfate (CaSO4): 48h LC50 = 1 200 mg/L

-      Sodium sulfate (Na2SO4) and Potassium sulfate (K2SO4): 48h LC50 = 4 610 mg/L

 

Based on these results, it is possible to conclude that when combined, the toxicity of the three main constituents is not expected to be increased. Therefore, these results support the read-across approach.

A study performed according to the OECD Testing guidelline 202 and the GLP is available on the hydrated form of the calcium sulfate (i.e. calcium sulfate, dihydrate). In this limit test, no immobility of Daphnia magna has been observed at a concentration of 100 mg/L of CaSO4.2H2O. When corrected to calcium sulfate anhydrous, this result correspond to a 48hEC50 > 79 mg/L. This study is used as a supporting study to conclude on the low toxicity profile of calcium sulfate to Daphnia magna.

Considering that potassium sulfate is the main constituent presenting the lowest 48hLC50 to aquatic organisms and having the highest concentration in the multiconstituent substance, as a worst case approach, its 48h LC50 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)