Dichloroacetic acid

Toxicity to aquatic algae and cyanobacteria

Key value for chemical safety assessment

EC50 for marine water algae:

148.2 mg/L

EC10 or NOEC for freshwater algae:

1 485 mg/L

EC10 or NOEC for marine water algae:

39.9 mg/L

Additional information

In the publication from Fisher et al (2014) the toxicity of DCA on the unicellular algae Isochysis galbana (clone T. iso) was investigated in brackish water. The test was performed according to ASTM E1218-04. The pH was not adjusted. In total 5 concentrations were tested. Nominal: Control, 26.2, 52.3, 104.5, 209 and 418 mg/L (the lowest concentration was calculated from the information that the four highest concentrations were 52.3, 104.5, 209 and 418 mg/L and 5 concentrations were set up). The test was performed for 72 hours. Chemical stability tests indicate that dichloroacetic acid is stable. The 72-h acute I. galbana growth data generated in this test indicates a relatively strong relationship between the low pH of the highest dichloroacetic acid treatments and reduced population growth. There was complete lack of population growth at the highest test concentration of 418 mg/L (pH = 2.86)and very reduced growth at a dichloroacetic acid concentration of 209 mg/L (pH = 5.37). The statistical analysis also indicates reduced algal growth at 104.5 mg/L dichloroacetic acid with a test solution pH of 6.55 (LOEC). The NOEC was 52.3 mg/L. The 72-h EC50 for I. galbana exposed to dichloroacetic acid was 148.2 mg/L and the EC10 was calculated to be 39.9 mg/L.The data were based on cell number. Typically, this endpoint is more sensitive than the evaluation based on growth rate. Furthermore, the pH was not adjusted and it could be speculated that the decreased pH might have affected the algae growth. Therefore, these values are considered worst case data.

The EC50 and EC10 are considered relevant and reliable for the risk assessment.

 

 In the non-GLP study from the Umweltbundesamt (1982), the growth inhibition of DCA on Desmodesmus subspicatus (reported as Scenedesmus subspicatus) was determined according to Bringmann and Kühn, 1980. In total 11 concentrations (spacing factor 2) were set up in 300 mL Erlenmeyer flasks filled with 50 mL test solution. The test flasks were set up in triplicate. The test was performed with continuous illumination at 27°C. The algae were re-suspended once a day by gentle shaking. Seven days after start of the exposure the optical density of the cultures was determined at 578 nm. The EC3 was determined to be 1485 mg/L. This EC3 result will be used as EC10 for the risk assessment for freshwater algae.

For the risk assessment the EC10 of 39.9 mg/L and the EC50 of 148.2 mg/L will be used.