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Long-term toxicity to aquatic invertebrates

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Endpoint:
long-term toxicity to aquatic invertebrates
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
other: Read-across from an analogue substance for which there is available information (Klimish =4).
Justification for type of information:
REPORTING FORMAT FOR THE ANALOGUE APPROACH
See cross-reference to justification of read-across.
Reason / purpose:
read-across source
Reason / purpose:
read-across: supporting information
Key result
Duration:
21 d
Dose descriptor:
EC50
Effect conc.:
0.49 mg/L
Nominal / measured:
not specified
Conc. based on:
not specified
Basis for effect:
not specified
Remarks on result:
other: Based on the read-across from an analogue substance.
Key result
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
0.27 mg/L
Nominal / measured:
not specified
Conc. based on:
not specified
Basis for effect:
not specified
Remarks on result:
other: Based on the read-across from an analogue substance.
Conclusions:
Based on the read-across from an analogue substance the 21-d NOEC is estimated to be 0.27 mg/L.
Executive summary:

Based on the read-across from an analogue substance  the 21-d NOEC is estimated to be 0.27 mg/L.

Endpoint:
long-term toxicity to aquatic invertebrates
Type of information:
(Q)SAR
Adequacy of study:
weight of evidence
Study period:
Not applicable (calculated data)
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Calculation with a valid QSAR (ECOSAR), l-limonene falls within the applicability domain of the (Q)SAR model, the prediction fits for the regulatory purpose, and the information is enough documented.
Justification for type of information:
1. Relevance of the model

ECOSAR v1.00 is reported as a usable valid model by ECHA (R6: QSARs and grouping of chemicals, May 2008).
ECOSAR contains a library of class-based QSARs for predicting aquatic toxicity, overlaid with an expert decision tree for selecting the appropriate chemical class. ECOSAR Version 1.00 is programmed to identify over 120 chemical classes and allows access to over 600 QSARs for numerous endpoints and organisms.
The structure-activity relationships (SARs) presented in ECOSAR v1.00 are used to predict the aquatic toxicity of chemicals based on their similarity of structure to chemicals for which the aquatic toxicity has been previously measured. SARs are developed for chemical classes based on measured test data that have been submitted by industry to the US-Environmental Protection Agency or collected from publicly available sources. To date, over 440 SARs have been developed for more than 120 chemical classes. The supporting data sets (training sets) used to derive SARs within a chemical class range from the very large, e.g., neutral organics, to the very small, e.g., aromatic diazoniums. The class with the greatest number of SARs based on measured data is the neutral organics class, which has SARs ranging from acute and chronic toxicity to fish to a 14-day LC50 SAR for earthworms in artificial soil.
The ECOSAR Class Program is a computerized version of the ecotoxicity analysis procedures as currently practiced by the Office of Pollution Prevention and Toxics (OPPT) when data are lacking for regulatory endpoints. It has been developed within the regulatory constraints of the Toxic Substances Control Act (TSCA). It is a pragmatic approach to SAR as opposed to a theoretical approach.

2. Validation of the model

- Endpoint (OECD Principle 1)
Acute toxicity to invertebrates (lethality). For freshwater invertebrates, species frequently include Daphnia magna or Daphnia pulex. The studies collected for the training set chemicals in ECOSAR undergo an extensive data validation step to ensure appropriateness for inclusion in the model. ECOSAR study criteria articulate that the toxicity should be measured at pH 7 (replicating environmental conditions), the total organic carbon content should not exceed 2 mg/L, the water hardness should be approximately 150 mg/L CaCO3, results should be adjusted to, or measured at, 100% active ingredient, and flow-through measured is preferred over static nominal, etc. Data received or identified in the open literature which is not accompanied with full study details to confirm conditions are often not considered appropriate for model development.

- Algorithm (OECD Principle 2)
The daphnid ChV values used to develop this SAR were measured and the octanol water partition coefficients (Kow) were calculated using the computer program, KOWWIN (Version 1.67). The SAR equation used to estimate toxicity is:
 
Log 16-d ChV (mmol/L) = - 0.7469 log Kow + 0.1961
 
The ChV is in millimoles per liter (mM/L); To convert the ChV from mM/L to mg/L, multiply by the molecular weight of the compound.

-Applicability domain (OECD Principle 3)
Neutral organic chemicals are non ionizable and nonreactive and act via simple nonpolar narcosis generally thought of as a reversible, drug-induced loss of conscience (general anesthesia). This general narcosis is often referred to as baseline toxicity (Franks and Lieb 1990, Veith and Broderius 1990).

Application:
Solvents, non-reactive, non-ionizable neutral organic compounds
1. Alcohols
2. Acetals
3. Ketones
4. Ethers
5. Alkyl halides
6. Aryl halides
7. Aromatic hydrocarbons
8. Halogenated aromatic hydrocarbons
9. Halogenated aliphatic hydrocarbons
10. Sulfides and di-sulfides

Limitations:
Maximum Kow: 8.0
Maximum MW: 1000
If the log Kow value is greater than 8.0, or if the compound is solid and the LC50 exceeds the water solubility by 10X, no effects at saturation are predicted.


- Uncertainty of the prediction (OECD Principle 4)
N = 29 + 1; and the Coefficient of Determination (R2) = 0.8593.


4. Mechanistic interpretation: The QSAR for neutral organics is based on the assumption that all chemicals have a minimal toxicity based on the interference of the chemical with biological membranes, which can be modelled by the octanol-water partition coefficient (Kow).

5. Adequacy of result for classification & labelling an/or risk assessment
According to the main criteria used by Hulzebos and Posthumus, ECOSAR is a reliable QSAR to predict 16d-ChV for invertebrates. The ECOSAR prediction of toxicity of l-limonene on invertebrates is adequate for the purpose of risk assessment and classification and labelling.
Qualifier:
no guideline followed
Principles of method if other than guideline:
The QSARs in ECOSAR for neutral organics are based on a linear mathematical relationship between the predicted log Kow values and the corresponding log of the measured toxicity values (mmol/L) for a suite of training set chemicals within each class of interest. The studies collected for the training set chemicals in ECOSAR undergo an extensive data validation step to ensure appropriateness for inclusion in the model. ECOSAR study criteria articulate that the toxicity should be measured at pH 7 (replicating environmental conditions), the total organic carbon content should not exceed 2 mg/L, the water hardness should be approximately 150 mg/L CaCO3, results should be adjusted to, or measured at, 100% active ingredient, and flow-through measured is preferred over static nominal, etc. Data received or identified in the open literature which is not accompanied with full study details to confirm conditions are often not considered appropriate for model development. Therefore, many measured ecotoxicity data points can be found in the open literature which are not considered suitable for inclusion in the ECOSAR model.

In the latest version of ECOSAR, the log Kow values for each training set chemical is predicted using the KOWWIN program from U.S. EPA’s EPISuite model (Meylan and Howard 1995).

Toxicity values (mmol/L) for untested chemicals may be calculated in a three-step process: (1) select the appropriate class using the ECOSAR class definitions, (2) input the measured or estimated log Kow value of the molecule into the mathematical regression equation to estimate the toxic effect concentration (mmol/L), (3) use molecular weight of the subject chemical to convert the estimated effect concentration from mmol/L to mg/L for use in aquatic toxicity hazard profiles. The computerized ECOSAR program is designed to automatically complete all three steps when providing estimates based on the users chemical input.
GLP compliance:
no
Remarks:
the data was calculated by a computer model
Analytical monitoring:
no
Details on sampling:
Not applicable (calculated data)
Vehicle:
no
Details on test solutions:
Not applicable (calculated data)
Test organisms (species):
other: For freshwater invertebrates, species frequently include Daphnia magna or Daphnia pulex.
Details on test organisms:
Not applicable (calculated data)
Test type:
other: QSAR modeled data
Water media type:
freshwater
Limit test:
no
Total exposure duration:
16 d
Post exposure observation period:
Not applicable (calculated data)
Hardness:
ECOSAR study criteria articulate that the water hardness should be approximately 150 mg/L CaCO3
Test temperature:
Not applicable (calculated data)
pH:
ECOSAR study criteria articulate that the toxicity should be measured at pH 7 (replicating environmental conditions)
Dissolved oxygen:
Not applicable (calculated data)
Salinity:
Not applicable
Nominal and measured concentrations:
Not applicable (calculated data)
Details on test conditions:
Not applicable (calculated data)
Reference substance (positive control):
not required
Key result
Duration:
16 d
Dose descriptor:
other: ChV=geometric mean of NOEC and LOEC
Effect conc.:
0.115 mg/L
Nominal / measured:
estimated
Conc. based on:
test mat.
Basis for effect:
immobilisation
Details on results:
1. Relevance of the model

ECOSAR v1.00 is reported as a usable valid model by ECHA (R6: QSARs and grouping of chemicals, May 2008).
ECOSAR contains a library of class-based QSARs for predicting aquatic toxicity, overlaid with an expert decision tree for selecting the appropriate chemical class. ECOSAR Version 1.00 is programmed to identify over 120 chemical classes and allows access to over 600 QSARs for numerous endpoints and organisms.
The structure-activity relationships (SARs) presented in ECOSAR v1.00 are used to predict the aquatic toxicity of chemicals based on their similarity of structure to chemicals for which the aquatic toxicity has been previously measured. SARs are developed for chemical classes based on measured test data that have been submitted by industry to the US-Environmental Protection Agency or collected from publicly available sources. To date, over 440 SARs have been developed for more than 120 chemical classes. The supporting data sets (training sets) used to derive SARs within a chemical class range from the very large, e.g., neutral organics, to the very small, e.g., aromatic diazoniums. The class with the greatest number of SARs based on measured data is the neutral organics class, which has SARs ranging from acute and chronic toxicity to fish to a 14-day LC50 SAR for earthworms in artificial soil.
The ECOSAR Class Program is a computerized version of the ecotoxicity analysis procedures as currently practiced by the Office of Pollution Prevention and Toxics (OPPT) when data are lacking for regulatory endpoints. It has been developed within the regulatory constraints of the Toxic Substances Control Act (TSCA). It is a pragmatic approach to SAR as opposed to a theoretical approach.

2. Validation of the model

- Endpoint (OECD Principle 1)
Acute toxicity to invertebrates (lethality). For freshwater invertebrates, species frequently include Daphnia magna or Daphnia pulex. The studies collected for the training set chemicals in ECOSAR undergo an extensive data validation step to ensure appropriateness for inclusion in the model. ECOSAR study criteria articulate that the toxicity should be measured at pH 7 (replicating environmental conditions), the total organic carbon content should not exceed 2 mg/L, the water hardness should be approximately 150 mg/L CaCO3, results should be adjusted to, or measured at, 100% active ingredient, and flow-through measured is preferred over static nominal, etc. Data received or identified in the open literature which is not accompanied with full study details to confirm conditions are often not considered appropriate for model development.

- Algorithm (OECD Principle 2)
The daphnid ChV values used to develop this SAR were measured and the octanol water partition coefficients (Kow) were calculated using the computer program, KOWWIN (Version 1.67). The SAR equation used to estimate toxicity is:
 
Log 16-d ChV (mmol/L) = - 0.7469 log Kow + 0.1961
 
The ChV is in millimoles per liter (mM/L); To convert the ChV from mM/L to mg/L, multiply by the molecular weight of the compound.

-Applicability domain (OECD Principle 3)
Neutral organic chemicals are non ionizable and nonreactive and act via simple nonpolar narcosis generally thought of as a reversible, drug-induced loss of conscience (general anesthesia). This general narcosis is often referred to as baseline toxicity (Franks and Lieb 1990, Veith and Broderius 1990).

Application:
Solvents, non-reactive, non-ionizable neutral organic compounds
1. Alcohols
2. Acetals
3. Ketones
4. Ethers
5. Alkyl halides
6. Aryl halides
7. Aromatic hydrocarbons
8. Halogenated aromatic hydrocarbons
9. Halogenated aliphatic hydrocarbons
10. Sulfides and di-sulfides

Limitations:
Maximum Kow: 8.0
Maximum MW: 1000
If the log Kow value is greater than 8.0, or if the compound is solid and the LC50 exceeds the water solubility by 10X, no effects at saturation are predicted.


- Uncertainty of the prediction (OECD Principle 4)
N = 29 + 1; and the Coefficient of Determination (R2) = 0.8593.


4. Mechanistic interpretation: The QSAR for neutral organics is based on the assumption that all chemicals have a minimal toxicity based on the interference of the chemical with biological membranes, which can be modelled by the octanol-water partition coefficient (Kow).

5. Adequacy of result for classification & labelling an/or risk assessment
According to the main criteria used by Hulzebos and Posthumus, ECOSAR is a reliable QSAR to predict 16d-ChV for invertebrates. The ECOSAR prediction of toxicity of l-limonene on invertebrates is adequate for the purpose of risk assessment and classification and labelling.
Results with reference substance (positive control):
Not applicable (calculated data)
Reported statistics and error estimates:
Not applicable (calculated data)

No data

Validity criteria fulfilled:
yes
Remarks:
Log Kow < 8; MW = 136 g/mol
Conclusions:
Based on a measured log Kow, results of computer modelling to estimate chronic toxicity in a 16-day freshwater aquatic invertebrates study show that the ChV (geometric mean of NOEC and LOEC) was 0.115 mg/L.
Executive summary:

The acute toxicity of l-limonene to aquatic invertebrates was estimated using the ECOSAR model from EPISUITE 4.1 reported as a valid model by ECHA (R6: QSAR and grouping of chemicals, May 2008). ECOSAR computes toxicity based on a linear mathematical relationship between the predicted log Kow values and the corresponding log of the measured toxicity values (mmol/L). l-limonene feld in the applicability domain of this QSAR model. The calculation was ran using the experimental log Kow value of 4.38 and water solubility of 12.3 mg/L for d-limonene as these values are expected to be similar for both enantiomers.

The result of the computer modelling to estimate the chronic toxicity of l-limonene on daphnid after 16 days exposure is ChV (geometric mean of NOEC and LOEC)= 0.115 mg/L.

This ECOSAR prediction of chronic toxicity of l-limonene on daphnids is adequate for the purpose of risk assessment and classification and labelling.

Description of key information

Weight of evidence: Experimental data are available on dipentene from the Japan Ministry (formerly MITI) which measured chronic toxicity values on daphnia of 21d-EC50= 0.49 mg/L and 21d-NOEC=0.27 mg/L. These values are in line with the acute toxicity values measured on the same organism and with an adequate QSAR prediction (ECOSAR) calculating a 16d-ChV of 0.115 mg/L (corresponding to the geometric mean of NOEC and LOEC). Therefore the experimental NOEC value on dipentene is estimated to be the relevant value to be considered for risk assessment and Classification & Labelling purposes.

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater invertebrates:
0.27 mg/L

Additional information

For this endpoint, an experimental value is derived from the Japan Ministry (formerly MITI) study on the dipentene racemic form. The values of 21d-EC50= 0.49 mg/L and 21d-NOEC = 0.27 mg/L are reported but there is no detail on test material and conditions.

 

The software ECOSAR was used to assess the toxicity of l-limonene based on his smiles characterisation and the experimental values of Log Kow and water solubility of d-limonene which are expected to be similar for both enantiomers. Considering its neutral organic status, the resulting value for chronic aquatic toxicity was 16d-ChV= 0.115 mg/L corresponding to the geometric mean of the NOEC and the LOEC.

Therefore, the available chronic toxicity data on daphnia form MITI (experimental) and ECOSAR (calculated) belong to the same range and are similar with the validated study results.

From theses observations, it can be concluded:

- that both enantiomers, l and d limonene, have the same chronic toxicity level against daphnids.

- that the MITI studies on which we have little information, were conducted in conditions that were accurate enough to measure effects at the very low concentration levels corresponding to the one measured in the validated study. It reveals that the properties of the substance as regard to degradation or volatilisation were taken into account and/or the real concentrations measured. Indeed other available data, resulting of studies which didn’t consider these testing difficulties, belong to the range of 10-100 mg/L.

Therefore it is estimated that the experimental value of 21d-NOEC= 0.27 mg/L is adequate for risk assessment and Classification & Labelling purposes.