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Juvenile Danio rerio were exposed to a single succinic acid concentration of 100 mg/L in a semi-static 96-hour acute toxicity test according to OECD 203. The test design included an untreated control comprising of dilution water only. The concentration of succinic acid was verified analytically and the mean measured concentration was 95.07 mg/L.

The 96-hour LC50 determined was >100 mg succinic acid/L (nominal concentration). The NOEC (no-observed effect concentration) was 100 mg succinic acid/L.

The 48 hour acute toxicity of succinic acid to Daphnia magna was determined in two semi-static tests according to the OECD 202 guideline.

In the first test Daphnia were exposed over a 48 hour period to succinic acid at nominal concentrations of 0 (control), 6.25, 12.5, 25, 50 and 100 mg/L. The pH ranged from 4.7 in the 100 mg/L treatment to 7.4 in the 6.25 mg/L treatment in a dose related response.  Concentrations of succinic acid were verified analytically at test initiation, after 24 hours in both new and old test media and test termination.  Geometric mean measured concentrations was 5.27, 10.62, 25.43, 49.58 and 99.79 mg/L. The 48-hour EC50 was determined to be 63 mg/L with 95 % confidence limits of 55 and 71 mg/L. The corresponding no-observed effect concentration (NOEC) was determined to be 25 mg/L.

In the second test Daphnia were exposed over a 48 hour period to succinic acid at nominal concentrations of 0 (control), 6.25, 12.5, 25, 50 and 100 mg/L. As recommended by the guideline, the pH of the stock solutions used to prepare the test media was adjusted to that of the dilution water before addition of the test substance.  Concentrations of succinic acid were verified analytically at test initiation, after 24 hours in both new and old test media and test termination.  Geometric mean measured concentrations was 5.28, 10.53, 23.47, 49.87 and 102.07 mg/L. Based on the geometric mean concentrations the 48-hour EC50 was determined to be > 102 mg/L. The corresponding no-observed effect concentration (NOEC) was determined to be 23 mg/L.

Based on the fact that the effects seen in the first experiment were influenced by the pH change the most appropriate endpoint to use for the assessment of succinic acid toxicity is the 48 hour EC50value of > 100 mg/L obtained in the study with pH adjustment. 

Two 72 hour algal inhibition experiments were conducted with succinic acid and Pseudokirchneriella subcapitata according to the OECD 203 guideline.

In the first experiment algae were exposed over a 72 hour period to succinic acid at nominal concentrations of 0 (control), 0.39, 0.78, 1.56, 3.13, 6.25, 12.5, 25, 50 and 100 mg/L. The pH ranged from 4.2 in the 100 mg/L treatment to 7.5 in the 0.39 mg/L treatment in a dose response relationship.  Concentrations of succinic acid were verified analytically at test initiation and termination.  The limit of quantification for succinic acid was 3.55 mg/L, therefore the concentrations of the four lowest test media were not quantified. Geometric mean measured concentrations of the remaining test media were 6.02, 13.96, 23.5, 50.41 and 96.37 mg/L. Based on nominal exposure concentrations the 72-hour EyC50 was determined to be 40.7 mg/L with a corresponding NOEC of with 25 mg/L. The 72-hour ErC50 was determined to be 46.8 mg/L with a corresponding NOEC of with 25 mg/L. 

In the second experiment algae were exposed over a 72 hour period to succinic acid at nominal concentrations of 0 (control), 0.39, 0.78, 1.56, 3.13, 6.25, 12.5, 25, 50 and 100 mg/L The pH of the medium ranged between 7.4 and 7.5 at the start of the exposure.

Concentrations of succinic acid were verified analytically at test initiation and termination.  The limit of quantification for succinic acid was 3.55 mg/L, therefore the concentrations of the four lowest test media were not quantified. Geometric mean measured concentrations of the remaining test media were 4.47, 11.9, 24.02, 45.96 and 110.47 mg/L.

Based on the nominal exposure concentration both the 72-hour EyC50 and ErC50 were determined to be > 100 mg/L with corresponding NOECs of 100 mg/L. 

Based on the fact that the effects seen in the first experiment were influenced by the pH change the most appropriate endpoint to use for the assessment of succinic acid toxicity is the 72 hour ErC50 value of > 100 mg/L obtained in the study with pH adjustment. 

Activated sludge obtained from a sewage treatment plant was exposed in a 3-hour respiration inhibition test to nominal concentrations of 0 (control), 7.7, 19.3, 48.2, 120.6 and 301.5 mg succinic acid/L. The test design included duplicate samples and followed OECD guideline 209. The 3-hour EC50 based on respiration inhibition was > 300 mg succinic acid/L.