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Toxicity to aquatic algae and cyanobacteria

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Description of key information

Algal growth inhibition test_Pseudokirchneriella subcapitata_OECD 201/EU Method C.3: ErC10(72h), ErC20(72h) and ErC50(72h) > 120 mg/L / EbC10(72h): 7.7 mg/L, EbC20(72h): 120 mg/L (extrapolated) and EbC50(72h) > 120 mg/L (extrapolated). NOEC(72h): 21 mg/L. NOEC(72h): 69 mg/L 
Calculation with ECOSAR v0.99g and v1.00 (EPIWIN software by US-EPA):
Main component with chlorine: EC50(96h): 14324 mg/L; ChV(4d): 11676.9 mg/L
Main component without chlorine: EC50(96h): 33823 mg/L; ChV(4d): 12795.8 mg/L

Key value for chemical safety assessment

EC50 for freshwater algae:
120 mg/L
EC10 or NOEC for freshwater algae:
21 mg/L

Additional information

The effects of 1,2,3-Propanetriol, glycidyl ethers on the growth of the freshwater green algal species Pseudokirchneriella subcapitata was investigated according to OECD Guideline 201 / EU Method C.3 (Liedtke, 2013). The study was conducted under certificated GLP compliance. Exponentially growing cultures of the test organisms were exposed to the different concentrations of the test substance over a period of 72 hours and the inhibition of algal growth in relation to control cultures was assessed over several generations. The selection of the test concentrations was based on the results of a range-finding test and on results of a pre-experiment to determine the solubility of the test substance. The following nominal concentrations were chosen: 0.32, 1.0, 3.2, 10, 32 and 100 mg/L (three replicates per concentration). Additionally, a control was tested in parallel (six replicates). The initial cell density was 5000 cells/mL (nominal). A static test design was applied. A small volume of the algal suspension was withdrawn daily from each test flask for the measurement of the biomass, and was not replaced. The concentrations of the test substance were determined in one of the duplicate test medium samples from the nominal test concentrations of 32 and 100 mg/L. The samples from the nominal test concentrations of 0.32 to 10 mg/L were not analyzed, since these concentrations were below the NOEC determined in this test. From the control samples, one of the duplicate samples was analyzed per sampling time. The measured concentrations in the test media of the nominal test concentrations of 32 and 100 mg/L were 77 and 79 % of the nominal values at the start of the test, respectively. During the test period of 72 hours, a decrease of test item concentration in the test media occurred. At the end of the test, 58 and 61 % of the nominal values were found, respectively. The microscopic examination of the algal cells at the end of the test showed no difference between the algae growing at the nominal test concentration of 100 mg/L and the algal cells in the control. The shape and size of the algal cells were obviously not affected by the test item up to at least this concentration. No remarkable observations were made concerning the appearance of the test media. All test media were clear solutions throughout the test period. The biological results based on growth rate can be summarized as follows: ErC10(72h), ErC20(72h) as well as ErC50(72h) were found to be > 120 mg/L. Based on yield, the results were reported as: EbC10(72h): 7.7 mg/L, EbC20(72h): 120 mg/L (extrapolated) and EbC50(72h) > 120 mg/L (extrapolated). The NOEC was found as 21 mg/L and the NOEC as 69 mg/L after 72 hours exposure duration, respectively. Defined values for EC10 (growth rate), EC20 and EC50 (growth rate and yield) could not be calculated due to the low toxicity of the test item for the algae. Confidence intervals could not be calculated.

As supporting information, the acute and chronic toxicity to green algae (species not further specified) of the test substance was predicted by the computer program ECOSAR v0.99g and v1.00 (EPIWIN software) by US-EPA (Chemservice S.A., 2012; Chemservice S.A., 2015c). An extensive set of structure – activity relationships (SARs) is utilized by the computer program, to predict the acute and chronic toxicity for three trophic levels for aquatic species, based on the ECOSAR-classes of “Diepoxides” (v0.99g) and “Epoxides, Poly” (v1.00). For the main component with chlorine, an EC50 of 14324 mg/L is predicted after a test substance exposure of 96 h to green algae. Concerning the main component without chlorine, the EC50 is predicted as 33823 mg/L. Regarding long-term toxicity, the so-called Chronic Value (ChV) is predicted, which is defined as the geometric mean of the Lowest Observed Effect Concentration (LOEC) and the No Observed Effect Concentration (NOEC). It can just classify a substance according to a low, moderate or high toxicity concern. For the test substance concerning long-term toxicity to green algae a ChV(4d) of 11676.9 mg/L is predicted for the main component with chlorine and a value of 12795.8 mg/L for the main component without chlorine. Both values indicate that there is no toxicity concern.