2,3-dimethylbutane

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

17th March 1993 to 22nd January 1994

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Guideline study.

Justification for type of information:

A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across: supporting information

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

SBP 60/95 LNH is a C6 -C7 hydrocarbon solvent with a n-hexane content of less than 3%. Being made from hydrogenated feedstock, its aromatics and olefins content is very low.

Analytical monitoring:

no

Details on test solutions:

This test medium is mixed with test substance for 23 h, then allowed to settle for 1 h. Aqeous phase was then used in the experiment.

Test organisms (species):

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

Details on test organisms:

TEST ORGANISM
- Source (laboratory, culture collection): American Type Culture Collection
- Method of cultivation: 1.5% m/v of agar is added to liquid medium, then autoclaved. Once cooled, the medium is placed in sterile petri dishes. Once set, the algal cultures are streaked on, and maintained under continuous illumination at 18-22 ºC for up to 14 days. Cultures are transferred to liquid medium using a sterile loop. 100 mL batch cultures are grown in 250 mL Erlenmeyer flasks for up to 4 days at 22-26 ºC under constant illumination of 3000 lux.

Test type:

static

Limit test:

no

Total exposure duration:

72 h

Test temperature:

24-25 ºC

pH:

7.3-8.9

Nominal and measured concentrations:

Nominal: 0, 1.0, 3.0, 10, 30, 100, 300, 1000 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Material, size, headspace, fill volume: 300 mL Erlenmeyer flasks completely filled
- Initial cells density: 5000 cells/mL
- No. of vessels per concentration (replicates): 4, 3 replicates and 1 flask was not inoculated to determine particle counts
- No. of vessels per control (replicates): 7, 1 flask was not inoculated to determine particle counts

GROWTH MEDIUM
- Standard medium used: yes, Miller, WE, Greene, JC, and Shiroyama, T. (1978). The Selenastrum capricornutum (Prinz) algal assay bottle test. EPA-660/9-78-018. Exceptions: boric acid was added 105 μg/L and sodium bicarbonate at 50 mg/L.

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Reconstituted water autoclaved at 1.0 kg/cm2 for 15 min. After cooling 20 mL/L of 0.45 μm millipore sterilized solution of sodium bicarbonate was added.

OTHER TEST CONDITIONS
- Photoperiod: constant illumination
- Light intensity and quality: ~3000 lux

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: Coulter Multisizer

Key result

Duration:

72 h

Dose descriptor:

other: EbL50

Effect conc.:

26 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Remarks on result:

other: 21-33 mg/L

Key result

Duration:

72 h

Dose descriptor:

other: ErL50

Effect conc.:

55 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 28-110 mg/L

Duration:

72 h

Dose descriptor:

other: NOEL

Effect conc.:

30 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

There was less growth in cultures exposed to 1 and 3 mg/L of test substance than in control cultures and the cultures exposed to 10 and 30 mg/L.

Growth of Raphidocelis subcapitata 0-72 h

Concentration (mg/l)	Mean cell Concentration (million cells/mL)	Calculated mean area (A/ 1 million)	Mean reduction in A relative to controls (%)	Mean calculated µ	Mean reduction in µ relative to controls (%)
Control	0.23	3.6	-	0.049	-
1	0.19	3.1	15	0.049	-0.6
3	0.16	2.5	31	0.047	2.6
10	0.23	3.7	-2.1	0.053	-9.9
30	0.22	3.4	5.5	0.052	-7.5
100	0.0054	-0.1	100	0.0002	100
300	0.0046	-0.13	100	-0.011	120
1000	0.0026	-0.12	100	-0.020	140

Validity criteria fulfilled:

yes

Conclusions:

The 72- ErL50 was 55 mg/L, and the 72-h EbL50 was 26 mg/L (WAF).

Executive summary:

This study examined the short-term toxicity of the test substance SBP 60/95 LNH to Raphidocelis subcapitata. Cultures of R. subcapitata were exposed to concentrations of 0, 1.0, 3.0, 10, 30, 100, 300, and 1000 mg/L of test substance. The growth of the algae was then measured at 0, 24, 48, and 72 h and compared to controls.

The E_rL₅₀ at 72 h was 55 mg/L, the E_bL₅₀ at 72-h was 26 mg/L and the NOEL was calculated to be 30 mg/L based on growth rate.

Description of key information

There is no data available for this substance. However, key and supporting data is available for the structural analoguesHydrocarbons, C6-C7, isoalkanes, cyclics, <5% n-hexane and Hexane. The data is read across to this substance based on analogue read across and a discussion and report on the read across strategy is provided as an attachment in IUCLID Section 13.

Hydrocarbons, C6-C7, isoalkanes, cyclics, <5% n-hexane presented a 72-h ErL50 of 55 mg/L, a 72-h EbL50 of 26 mg/L and a 72-h NOEL of 30 mg/L for Raphidocelis subcapitata based on growth rate.

Hexane presented a 10-d EC50 (growth rate) for Chlorella pyrenoidosa of 2.66% v/v of test substance.

Additional information

Two study reports were available and input as endpoint records. The studies were scientifically reliable according to Klimish (Klimish et al., 1997) scoring (Klimish 1 and 2).

The study from Shell (1994) examined the short-term toxicity of the test substance SBP 60/95 LNH (Hydrocarbons, C6-C7, isoalkanes, cyclics, <5% n-hexane) to Raphidocelis subcapitata. Cultures of R. subcapitata were exposed to concentrations of 0, 1.0, 3.0, 10, 30, 100, 300, and 1000 mg/L of test substance. The growth of the algae was then measured at 0, 24, 48, and 72 h and compared to controls. The ErL50 at 72 h was 55 mg/L, the EbL50 at 72-h was 26 mg/L and the NOEL was calculated to be 30 mg/L based on growth rate.

The study from Stratton and Smith (1988) examined the toxicity of n-hexane to green algae. The green algae C. pyreniodosa was exposed to concentrations of test substance varying between 1.0 - 14 % v/v. The exposure lasted for 10 -14 days. The growth rate and cell count was monitored. Results showed an EC50 of 2.66% v/v of test substance.