2,2-dimethylbutane

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

(Q)SAR

Adequacy of study:

key study

Study period:

Not applicable, calculated value

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification

Justification for type of information:

A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13. Petrotox is a well documented and peer reviewed model that is widely used across the petrochemicals industry. This substance fits within the criteria of the model and there are no reservations about the validity of the model runs. It is expected that this data is reliable with restrictions.

Qualifier:

no guideline followed

Principles of method if other than guideline:

The aquatic toxicity was estimated by a QSAR, the Petrotox computer model (v. 3.06). This model combines a partitioning model used to calculate the aqueous concentration of hydrocarbon components with the Target Lipid Model used to calculate acute and chronic toxicity of non-polar narcotic chemicals. Petrotox computes toxicity based on the summation of the aqueous-phase concentrations of hydrocarbon block(s) that represent a hydrocarbon substance and membrane-water partition coefficients (KMW) that describe the partitioning of the hydrocarbons between the water and organism

GLP compliance:

no

Remarks:

The data were calculated by a computer model.

Specific details on test material used for the study:

All data on input parameters are presented in Section 13 of IUCLID

Analytical monitoring:

not required

Details on sampling:

No data

Vehicle:

no

Details on test solutions:

No data

Test organisms (species):

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

Details on test organisms:

No data

Test type:

other: QSAR modelled data

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Post exposure observation period:

No data

Hardness:

No data

Test temperature:

No data

pH:

No data

Dissolved oxygen:

No data

Salinity:

No data

Nominal and measured concentrations:

No data

Details on test conditions:

No data

Reference substance (positive control):

not required

Key result

Duration:

72 h

Dose descriptor:

other: LL50

Effect conc.:

1.56 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: QSAR

Remarks:

Based on QSAR data

Details on results:

No data

Results with reference substance (positive control):

No data

Reported statistics and error estimates:

No data

Validity criteria fulfilled:

yes

Conclusions:

The estimated algal, 48-hr LL50 value for this substance is 1.56 mg/L based on growth inhibition.

Executive summary:

The aquatic toxicity was estimated using the Petrotox computer model, which combines a partitioning model used to calculate the aqueous concentration of hydrocarbon components as a function of substance loading with the Target Lipid Model used to calculate acute and chronic toxicity of non-polar narcotic chemicals. Petrotox computes toxicity based on the summation of the aqueous-phase concentrations of hydrocarbon block(s) that represent a hydrocarbon substance and membrane-water partition coefficients (K_MW) that describe the partitioning of the hydrocarbons between the water and organism.

The estimated algal, 48-hr LL50 value for this substance is 1.56 mg/L based on growth inhibition.

Description of key information

A QSAR prediction using Petrotox v3.06 predicted an acute LL50 for algae of 1.56 mg/l, which is considered the key value for algae toxicity.

 

This is supported by two experimental studies on the read-across substance n-hexane which reported an E_rL₅₀ of 55 mg/L, E_bL₅₀ of 26 mg/L and a NOEL of 30 mg/L based on growth rate in one study and an EC₅₀of 2.66% v/v of test substance.

Additional information

Key data available for 2,2 -Dimethylbutane. Additionally, data is also available for Hydrocarbons, C6, isoalkanes, <5% n-hexane; Hexane; Hydrocarbons, C5 -C7, n-alkanes, isoalkanes, n-hexane rich; and Isohexane. This data is used for read across to 2,2 -Dimethylbutane.

The aquatic toxicity was estimated using the PETROTOX computer model, which combines a partitioning model (used to calculate the aqueous

concentration of hydrocarbon components as a function of substance loading) with the Target Lipid Model (used to calculate acute and chronic toxicity of non-polar narcotic chemicals). PETROTOX computes toxicity based on the summation of the aqueous-phase concentrations of hydrocarbon block(s) that represent a petroleum substance and membrane-water partition coefficients (K_MW) that describe the partitioning of the hydrocarbons between the water and organism.

The estimated algal 48-hr EL₅₀ value for Hydrocarbons, C6, isoalkanes,  <5% n-hexane is 13.56 mg/L and the estimated 48-hr NOEL is 3.034 mg/L (CONCAWE, 2009 p,q).

The calculated green algae 96-hour EC₅₀ for Methylcyclopentane is 5.048 mg/L.

In addition, an experimental study measured a 72 -hour E_rL₅₀ of 55 mg/L and a 72 -hour E_bL₅₀ of 26 mg/L for iso-hexane, both measured as a water accommodated fraction (Shell, 1994a).