Inorganic residual from kraft or soda pulping separated from green liquor in the chemical recovery cycle.

Short-term toxicity to aquatic invertebrates

Description of key information

Short term Daphnia tests showed acute effects at the tested concentration range 40-10 600 mg/l (wet wt.). Since the insoluble part of the test substance was filtered out from the test solutions, the wording Effective Loading (EL) is used instead of Effective Concentration (EC). Observed effective loading rate EL50 based on the nominal (WAF) test substance loading rate was 10600 mg/l (wet wt.). The effective loading level causing 50% immobility was the highest nominal tested concentration. The no effect level NOEL for immobility was 77 mg/l (wet wt.). The test results were given in wet weight basis of the test substance. Moisture content in the test substance was 53.3 %. 

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

4 950 mg/L

Additional information

UVCB substances which are not completely homogenic and not completely soluble in test media and may affect the pH of test water may be problematic in laboratory testing and may not give very clear or repeatable dose-response relationships. There are many factors affecting the test conditions, actual test concentration and bioavailability of soluble constituents. The acute Daphnia test resulted in a diffuse dose response relationships that reflect these testing difficulties. The method of preparing test solutions has also influence on responses seen in the tests. This study used WAF method, separate samples for each concentration, 72 hour dissolution time and filtered final samples.

The test results showed immobility of 40% at 148 mg/l (wet wt.) of test substance. The next higher concentration 304 mg/l had no effect. The statistical power of a test is low due to the high variability in the measured response. The immobilisation of the Daphnia in the group containing the highest loading rate could be caused or influenced by the alkaline pH. However, the pH in the respective test group decreased after 48 hours of incubation from 9.7 to 7.6. The reason of this decrease in pH has not been explained. Additionally, as the study conductor also emphasised, it should be noticed that also in a test substance group containing much lower loading rates and showing a pH value of 8.0 to 7.5 an immobilisation rate of 40 % was observed. It can also be argued that high pH is even protective against toxic effects of heavy metals and free sulfides. Metals are often more soluble and in a more toxic (cationic) form at low pH conditions. It is also a very well known phenomenon for sulfides that the toxicity increases and follows the increase of H₂S concentration as the pH decreases.