Mixed LOF

Toxicity to microorganisms

Administrative data

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:

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:

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 (v3.06), 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 "PetroTox (v3.06plus_EqP).xlsx" 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 toxic unit.

The model contains a database of TLM parameters for more than 70 individual organisms including several fish, daphnid, and algal endpoints; these characterize the expected range of species sensitivities for acute and chronic toxicity of nonpolar organic chemicals.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.

Data source

Reference

Reference 1

Reference Type:

publication

Title:

Re-evaluation of Target Lipid Model–Derived HC5 Predictions for Hydrocarbons

Author:

McGrath, J.A., C.J. Fanelli, D.M. Di Toro, T.F. Parkerton, A.D. Redman, M. Leon Paumen, M. Comber, C.V. Eadsforth, K.den Haan

Year:

2018

Bibliographic source:

Environmental Toxicology and Chemistry

Reference 2

Reference Type:

publication

Title:

Application of the Target Lipid Model for Deriving Predicted No-Effect Concentrations for Wastewater Organisms

Author:

Redman, A., J. McGrath, E. Febbo, T. Parkerton, D. Letinski, M. Connelly, D. Winkelmann, D. Di Toro

Year:

2007

Bibliographic source:

Environmental Toxicology and Chemistry, 26(11): 2317–2331

Reference 3

Reference Type:

publication

Title:

Refinement and validation of TLM-derived HC5 values. Independent review.

Author:

McGrath JA, Di Toro DM, Fanelli CJ

Year:

2015

Bibliographic source:

HDR, Mahwah, NJ

Reference 4

Reference Type:

publication

Title:

PETROTOX: An aquatic toxicity model for petroleum substances.

Author:

Redman, AD, Parkerton, TF, McGrath, JA, Di Toro, DM

Year:

2012

Bibliographic source:

Environmental Toxicology and Chemistry 31: 2498-2506

Reference 5

Reference Type:

other: Company report

Title:

Unnamed

Year:

2010

Materials and methods

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. For model description and justification of QSAR prediction: see field 'justification for type of information'

Test material

Test material information

Constituent 1

Reference substance name:

Mixed LOF

IUPAC Name:

Mixed LOF

Test material form:

other: liquid

Test organisms

Test organisms (species):

Tetrahymena pyriformis

Results and discussion

Effect concentrations

Effect concentrations 1

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

11.6 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth inhibition

Effect concentrations 2

Key result

Duration:

48 h

Dose descriptor:

other: NOELR

Effect conc.:

1.37 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth inhibition

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Conclusions:

The estimated protozoan, Tetrahymena pyriformis, 48-hr NOELR value for this substance is1.4 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 partitioning coefficients (KMW) that describe the partitioning of the hydrocarbons between the water and organism.