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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Administrative data

Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2010
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Report Date:
2010

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
impurity

Test organisms

Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
Strain No.: CCAP 278/4.

Reason for this choice: species commonly used in Europe for aquatic toxicity testing and recommended in OECD and EEC guidelines.

Origin: Culture Collection of Algae and Protozoa (CCAP), SAMS Research Services Ltd, Dunstaffnage Marine Laboratory, Dunbeg, OBAN, Argyll PA37 1QA, Scotland.

Cultured at: CIT.

Culture method: the algae are cultured under sterile conditions and maintained at exponential growth rate.

Study design

Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
72 h

Test conditions

Hardness:
Any requirement but water hardness will be measured once in test water before the start of the test.
Test temperature:
Should be set between 21°C and 24°C and not varying by more than ± 2°C throughout the test.
pH:
between 7.0 and 7.2 at the beginning of the test and should not deviated by more than 1.5 units in the control throughout the test
Nominal and measured concentrations:
0.01, 0.1, 1 and 6 mg/L
Details on test conditions:
Test vessels were sealed and headspace was kept at minimum with full conical flasks. In addition, an addition of 0.3 g/L of NaHCO3 then a pH adjustment to pH 7.1 +/-0.1 of OECD medium was performed (to prevent limitation of growth coming from CO2 depletion and important increasing pH).
A preliminary test, including a combined range-finding and limit test, preceded the definitive test.
Reference substance (positive control):
no

Results and discussion

Effect concentrationsopen allclose all
Duration:
24 h
Dose descriptor:
EC50
Effect conc.:
5.35 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
3.26 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
3.22 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
1.54 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
1.57 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
cell number
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.76 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
cell number
Details on results:
The results showed a clear dose-response relationship which is why the ErC(x)s and EyC(x)s values were calculated from the nominal concentrations by statistical analysis. (The 24, 48 and 72-hours ErC(x)s and 72-hours EyC(x)s calculations are reported in Appendix 5 for information).

However all measured concentrations without were below the limit of quantification (0.8 mg/L) at the test concentration of 3.75 mg/L or less.

Therefore according to these analytical results it was assumed that the nominal concentrations were higher and not representative of the concentrations actually tested.

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Conclusions:
In a 72-hour algal growth inhibition test with Pseudokirchneriella subcapitata, the EC50 of 2 Ethylhexyl nitrate was < 0.8 mg/L (nominal) based on average specific growth rate (ErC50) and < 0.8 mg/L based on yield (EyC50).

However, there is sufficient uncertainty in what was the actual concentration that caused the algal growth inhibition that we should not use the value of <0.8 mg/l as the EC50 value for 2-ethylhexyl nitrate.

We therefore propose that you use the nominal concentration to calculate the EC50:

72 hour EC50 (Growth Rate) = 3.22 mg/l
72 hour EC50 (Yield) = 1.57 mg/l

The use of nominal concentrations can be justified on the basis of the difficulties incurred in measuring dissolved concentrations.