Hydrocarbons, C9-C10, n-alkanes, isoalkanes, cyclics, <2% aromatics

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

August to December 1996

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: This robust summary has a reliability rating of 1 because the study followed a standard guideline, followed GLP guidelines, and was conducted without deviations that would invalidate the study.

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Deviations:

no

GLP compliance:

yes

Analytical monitoring:

yes

Details on sampling:

Samples for analysis of new and old test solutions were taken new at 0 hours (test initiation) and old at 72 hours (test termination).

Vehicle:

no

Details on test solutions:

The water accommodated fractions of the test material were prepared by stirring the test material at each loading level in the exposure solution that also contained a biocarbonate solution for 46 hours with a 1 to 1.5 hour settling period, after which each aqueous phase was removed and added to a test system. An equilibration study was conducted over a period of 72 hours prior to the definitive study to determine the approximate length of time needed to stir the test substance in the test media to achieve a saturated solution. Results suggested that a stirring period of 20 to 28 hours would be sufficient to reach equilibrium.

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Details on test organisms:

Organisms used in the test were from a laboratory culture, originally derived from a strain (CCAP 278/4) obtained from the Institute of Freshwater Ecology, Windermere, Cumbria, UK.

Test type:

static

Limit test:

no

Total exposure duration:

72 h

Post exposure observation period:

None

Test temperature:

23 to 23.5 degrees C

pH:

6.5 to 9.3

Nominal and measured concentrations:

The nominal loading rates were 1, 3, 10, 30, 100, 300, and 1000 mg/L. A control was also tested. Based on analyses of new and old test solution samples taken new at 0 hours (test initiation) and old at 72 hours (test termination), the nominal/measured (mean) concentration values were: control/<0.02 mg/L; 1.0/0.13 mg/L; 3/0.11 mg/L; 10/0.31 mg/L; 30/0.33 mg/L; 100/0.36 mg/L; 300/0.37 mg/L; and 1000/0.40 mg/L.

Details on test conditions:

The study was conducted in sealed test systems with no headspace that were not renewed during the study. The test systems used were glass Erlenmeyer flasks that contained 287 ml when full. Each treatment level was evaluated in triplicate test systems and the control in 6 replicate test systems. Control and treatment systems were innoculated with a concentration of 5000 cells/ml. Test systems were incubated under constant illumination (approximately 4250 lux) on an orbital incubator.

Reference substance (positive control):

no

Duration:

24 h

Dose descriptor:

EL50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

cell number

Duration:

24 h

Dose descriptor:

EL50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

48 h

Dose descriptor:

EL50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

cell number

Duration:

48 h

Dose descriptor:

EL50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EL50

Effect conc.:

1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

cell number

Key result

Duration:

72 h

Dose descriptor:

EL50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

NOELR

Effect conc.:

1 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

cell number

Key result

Duration:

72 h

Dose descriptor:

NOELR

Effect conc.:

< 1 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Reported statistics and error estimates:

The percentage of inhibition at each loading rate was calculated as the difference between the mean of areas under the control curves and the mean of areas under the loading rates growth curves. The percentage reduction in average specific growth rate was determined for each loading rate of the test substance in comparison to the control. A William's test (William, 1971, 1972) was used to calculate the significance of difference in area under the growth curve and average specific growth rate data from the control and treatment systems to determine the NOELR values (calculated at a 5% probability level).

Validity criteria fulfilled:

yes

Conclusions:

Growth of alga cultures, as measured by biomass, exposed to water accommodated fractions (WAFs) of the test substance prepared at 1000 mg/L was inhibited by 50% after 72 hours. Therefore, the 72-hr ELb50 value is reported as 1000 mg/L. In comparison, growth of alga cultures, as measured by growth rate, were not inhibited by more than 50% by the 1000 mg/L WAF after 72 hours. Therefore, the 72-hr ELr50 value is reported as >1000 mg/L. The 72-hr NOELR values for biomass and growth rate are 1 and <1 mg/L, respectively.

Executive summary:

Growth of alga cultures, as measured by biomass, exposed to water accommodated fractions (WAFs) of the test substance prepared at 1000 mg/L was inhibited by 50% after 72 hours. Therefore, the 72-hr ELb50 value is reported as 1000 mg/L. In comparison, growth of alga cultures, as measured by growth rate, was not inhibited by more than 50% by the 1000 mg/L WAF after 72 hours. Therefore, the 72-hr ELr50 value is reported as >1000 mg/L. The 72-hr NOELR values for biomass and growth rate are 1 and <1 mg/L, respectively.

Description of key information

Growth of alga cultures, as measured by biomass, exposed to water accommodated fractions (WAFs) of hydrocarbons, C9-C10, n-alkanes, isoalkanes, cyclics, <2% aromatics, prepared at 1000 mg/L was inhibited by 50% after 72 hours. Therefore, the 72-hr ELb₅₀ value is reported as 1000 mg/L. In comparison, growth of alga cultures, as measured by growth rate, were not inhibited by more than 50% by the 1000 mg/L WAF after 72 hours. Therefore, the 72-hr ELr₅₀ value is reported as >1000 mg/L. The 72-hr NOELR values for biomass and growth rate are 1 and <1 mg/L, respectively.

Additional information

Growth of alga cultures, as measured by biomass, exposed to water accommodated fractions (WAFs) of hydrocarbons, C9 -C10, n-alkanes, isoalkanes, cyclics, <2% aromatics, prepared at 1000 mg/L was inhibited by 50% after 72 hours. Therefore, the 72-hr ELb₅₀ value is reported as 1000 mg/L. In comparison, growth of alga cultures, as measured by growth rate, were not inhibited by more than 50% by the 1000 mg/L WAF after 72 hours. Therefore, the 72-hr ELr₅₀ value is reported as >1000 mg/L. The 72-hr NOELR values for biomass and growth rate are 1 and <1mg/L, respectively.