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Toxicity to microorganisms

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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
(Q)SAR
Adequacy of study:
key study
Study period:
2020
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:
Detailed information covering the calculation model, compositional data used as input, validity, applicability and adequacy of the result are in the attached document.

The registered substance is a complex hydrocarbon UVCB whose constituents have variable physicochemical properties. Therefore, a modelling 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.

The target lipid model (TLM) is a framework that relates toxicity to the physicochemical properties of a nonpolar organic constituent. The TLM, and HC5, have been applied to soils and sediment using equilibrium partitioning (EqP) model. This framework utilizes organic carbon partition coefficients (KOC) to convert aquatic based effect levels (CW) to bulk soil- and sediment-based effect levels. The combined TLM-EqP framework was validated previously for soil and sediment acute and chronic toxicity endpoints. The constituents in this substance are within the scope of the TLM and EqP frameworks.:
Qualifier:
no guideline required
Principles of method if other than guideline:
The target lipid model (2015) and equilibrium partitioning model as described in the cited references were used to determine soil or sediment effect levels following an estimation of initial loading of the registered substance and its constituents in the substrate. A full explanation of the calculation method is provided in the 'attached justification'.
For model description and justification of QSAR prediction: see fields 'justification for type of information' and 'attached justification'
GLP compliance:
no
Remarks:
The data were calculated by a computer model
Analytical monitoring:
not required
Vehicle:
no
Test organisms (species):
Tetrahymena sp.
Test type:
other: QSAR modeled data
Total exposure duration:
48 h
Duration:
48 h
Dose descriptor:
other: EL50
Effect conc.:
> 1.31 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth inhibition
Validity criteria fulfilled:
yes
Conclusions:
The hydrocarbons, C9-C11, n-alkanes, isoalkanes, <2% aromatics, estimated protozoan, Tetrahymena elliotti, 48-hr EL50 value for this substance is 1.31 mg/L based on growth inhibition.
Executive summary:

The registered substance is a complex petroleum UVCB whose constituents 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. The target lipid model (TLM) and HC5, have been applied to soils and sediment using equilibrium partitioning (EqP) model. As such, modeled data are considered fit for purpose.

Description of key information

The aquatic toxicity was estimated by a QSAR, the Petrotox computer model. 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.

Key value for chemical safety assessment

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