Malic acid

Toxicity to aquatic algae and cyanobacteria

Description of key information

Algal growth inhibition: EC50 = > 100 mg/L; NOEC = 100 mg/L

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:

100 mg/L

Additional information

Two 72 hour algal inhibition experiments have been conducted with fumaric acid. In the first experiment algae were exposed over a 72 hour period to fumaric acid at nominal concentrations of 0, 0.39, 0.78, 1.56, 3.13, 6.25, 12.5, 25, 50 and 100 mg/L. pH ranged from 3.4 in the 100 mg/L treatment to 7.5 in the 0.39 mg/L treatment in a concentration related manner. The 72 -hour E_yC₅₀was determined to be 37.2 mg/L with a corresponding NOEC of with 25 mg/L. The 72-hour E_rC₅₀was determined to be 38.9 mg/L with a corresponding NOEC of with 25 mg/L. In the second experiment algae were exposed over a 72 hour period to fumaric acid at a nominal concentration of 0 and 100 mg/L. The pH of the 100 mg/L medium was adjusted to 7.4 at the start of the exposure period.   The 72-hour E_yC₅₀and E_rC₅₀were 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 fumaric toxicity is the 72 hour E_rC₅₀value of >100 mg/L obtained in the study with pH adjustment. 

Read across from fumaric acid to malic acid is considered valid and malic acid is concluded to have low toxicity to aquatic organisms. The rational for read across is that fumaric acid will metabolise in biological systems to malic acid. Fumaric acid is also slightly more fat soluble and is considered more likely to absorb to membranes and increase exposure to aquatic organisms.