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Toxicity to soil microorganisms

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Reference
Endpoint:
toxicity to soil microorganisms
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:
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 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) 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 substances are within the scope of the TLM and EqP frameworks. The model used for the calculations was the PETROTOX v4.0 model. PETROTOX is a well-documented and peer reviewed model that is widely used across the chemicals industry.
Qualifier:
no guideline required
Guideline:
other: R.6 guideline on QSAR modelling
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'
Test organisms (inoculum):
other: Nitrobacter
Total exposure duration:
24 h
Key result
Duration:
24 h
Dose descriptor:
other: EL50
Effect conc.:
218 938 mg/kg soil dw
Nominal / measured:
estimated
Conc. based on:
other: QSAR prediction
Basis for effect:
other: nitrite utilization
Remarks on result:
other: QSAR predicted value
Duration:
24 h
Dose descriptor:
other: EL10
Effect conc.:
41 942 mg/kg soil dw
Nominal / measured:
estimated
Conc. based on:
other: QSAR prediction
Basis for effect:
other: nitrite utilization
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).
Conclusions:
The toxicity of this substance to soil microorganisms has been predicted using the target lipid model (TLM) and HC5, and using the equilibrium partitioning (EqP) model. The predicted 24-h EL50 (nitrite utilization) of this substance to Nitrobacter is 218938 mg/kg soil dw and the predicted 24-h EL10 (nitrite utilization) is 41942 mg/kg soil dw.
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. The model used for the calculations was the PETROTOX v4.0 model. PETROTOX is a well-documented and peer reviewed model that is widely used across the chemicals industry. As such, modelled data are considered fit for purpose.

 

The predicted 24-h EL50 (nitrite utilization) of this substance to Nitrobacter is 218938 mg/kg soil dw and the predicted 24-h EL10 (nitrite utilization) is 41942 mg/kg soil dw.

Description of key information

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. The model used for the calculations was the PETROTOX v4.0 model. PETROTOX is a well-documented and peer reviewed model that is widely used across the chemicals industry.

Key value for chemical safety assessment

Additional information