Heptane

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

(Q)SAR

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: This summary has a reliability of 2 because the results are estimated using a computer model that is appropriate for use with this petroleum substance.

Justification for type of information:

The registered substance is a complex mixture whose constituents within the mixture have variable physicochemical properties. Therefore, a modeling framework is needed to account for the bioavailability of the constituents in the mixture, which was then used to predict the toxicity of the substance as a whole. A computer-based program, PETROTOX (v4.0), was used to calculate aquatic toxicity. The program is an extension of the three-phase partitioning (to calculate the partitioning of constituents in air, water, and non-aqueous phase liquid phases) and toxicity models used to predict the toxicity of complex substances, and incorporates the Target Lipid Model (TLM), which has been validated for applications to individual narcotic chemicals and mixtures. Composition information is entered as separate hydrocarbon blocks according to carbon number range and chemical classes, which comprise the substance.Representative constituents input to model located in the attachment "PETRORISK and PETROTOX block allocation" in Section 13.2 of IUCLID.

The TLM is a framework that relates toxicity to the physicochemical properties of a nonpolar organic constituent. The TLM is used to calculate the toxicity of the dissolved constituents to aquatic organisms. Toxicity of complex mixtures with common toxic modes of action is determined using toxic units (TU) that normalizes aqueous concentrations by their inherent toxicity. To compute a TU for each component, the estimated concentration, Cw, from the partitioning model is divided by the aqueous effect concentration (e.g., LC50 or NOEC). The individual toxic units are then summed to compute the toxicity of the mixture. The lethal or chronic loading is determined by iterating until a loading is determined that yields one TU.

The model contains a database of TLM parameters for more than 70 individual organisms including several fish, daphnid, and algal endpoints. The model contains a database of TLM parameters for more than 70 individual organisms including several fish, daphnid, and algal endpoints. The TLM framework was validated previously for acute and chronic aquatic toxicity endpoints. As such, modeled data are considered fit for purpose for classification and labelling and risk assessment.

Principles of method if other than guideline:

The aquatic toxicity was estimated by a QSAR, the PETROTOX computer model (v 4.0). 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. For model description and justification of QSAR prediction: see field 'Justification for type of information'.

Analytical monitoring:

not required

Test organisms (species):

activated sludge

Test type:

other: QSAR modelled data

Water media type:

freshwater

Limit test:

no

Total exposure duration:

15 h

Key result

Duration:

15 h

Dose descriptor:

other: EL50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

estimated

Conc. based on:

other: QSAR prediction

Basis for effect:

inhibition of total respiration

Remarks on result:

other: QSAR predicted value

Key result

Duration:

15 h

Dose descriptor:

other: EL10

Effect conc.:

4.16 mg/L

Nominal / measured:

estimated

Conc. based on:

other: QSAR prediction

Basis for effect:

inhibition of total respiration

Remarks on result:

other: ACR 5.22 (McGrath et al., 2018)

Remarks:

QSAR predicted value

Details on results:

Chronic endpoints were estimated using typical acute-to-chronic ratio of 5.22 (McGrath et al., 2018).

Validity criteria fulfilled:

yes

Conclusions:

The PETROTOX-estimated freshwater 15-h EL50 (Effect Loading Rate 50%) value for activated sludge is > 1000 mg/L based on inhibition of total respiration, and the PETROTOX-estimated freshwater 15-h EL10 (Effect Loading Rate 10%) value for activated sludge is 4.16 mg/L based on inhibition of total respiration.

Executive summary:

The aquatic toxicity was estimated using the PETROTOX computer model (v4.0), 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 nonpolar 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 partitioning coefficients (KMW) that describe the partitioning of the hydrocarbons between the water and organism.

The PETROTOX-estimated freshwater 15-h EL50 (Effect Loading Rate 50%) value for activated sludge is > 1000 mg/L based on inhibition of total respiration, and the PETROTOX-estimated freshwater 15-h EL10 (Effect Loading Rate 10%) value for activated sludge is 4.16 mg/L based on inhibition of total respiration.

Description of key information

The aquatic toxicity was estimated using the PETROTOX computer model (v4.0), 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 nonpolar 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 partitioning coefficients (KMW) that describe the partitioning of the hydrocarbons between the water and organism.

Other disregarded data is also available for the structural analogue Octane. In this study the test procedure was flawed and the reported data do not reliably characterize the aquatic toxicity of the test substance. The data for this substance is presented in this dossier for completeness. The data is read across to these substances based on analogue read across and a discussion and report on the read across strategy is provided as an attachment in IUCLID Section 13.