2-ethylhexyl nitrate

Toxicity to aquatic algae and cyanobacteria

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 concentrations

Effect concentrations 1

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

Effect concentrations 2

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

Effect concentrations 3

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

Effect concentrations 4

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

Effect concentrations 5

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

Effect concentrations 6

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.