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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Reference
Endpoint:
toxicity to aquatic algae and cyanobacteria
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:
1. SOFTWARE
EPISuite v4.11

2. MODEL (incl. version number)
ECOSAR v1.11

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
SMILES : O(CCCCCC)CCCCCC
CHEM : Hexane, 1,1 -oxybis-
CAS Num: 000112-58-3
MOL FOR: C12 H26 O1
MOL WT : 186.34
Wat Sol: 2.874 (mg/L, EPISuite WSKowwin v1.43 Estimate)

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
ECOSAR had been utilized by the scientific community for prediction of aquatic toxicity since the 1990’s. While developed by the US EPA, the program underwent an independent peer review as a part of the development of the Organization for Economic Cooperation and Development (OECD) principles established for quantitative structure-activity relationship ((Q)SAR) validation. As of 2011, ECOSAR was the subject of 20 peer reviewed publications regarding its validation and performance.

Also ECOSAR has been incorporated into the OECD Toolbox and was considered a top performer for use in profiling chemicals. Inclusion in the OECD toolbox requires specific documentation, validation and acceptability criteria and subjects ECOSAR to international use, review, providing a means for receiving additional and on-going input for improvements.

ECOSAR is listed as one of the QSARs tools for use in predicting aquatic toxicity values in the Guidance on information requirements and chemical safety assessment Chapter R.10: Characterisation of dose [concentration]-response for the environment and Chapter R.6: QSARs and grouping of chemicals.

In summary, ECOSAR has had its scientific validity established repeatedly.


5. APPLICABILITY DOMAIN
ECOSAR’s training set generally includes chemicals that had log Kow’s between -3 and 8 with molecular weights less than 1000. While the applicability domain of ECOSAR is considered to be larger than just the training set, the log Kow (4.978) and molecular weight (186.34) fall within the range of the training set values and is thus considered within the applicability domain. The log Kow (4.978) is also lower than the maximum log Kow for the neutral organics equation (6.4).

6. ADEQUACY OF THE RESULT

ECOSAR’s Neutral Organic’s (Baseline Toxicity) model uses the following equation for calculation of acute aquatic toxicity to algae:

Organism Endpoint Equation
Green Algae 96 hr EC50 Log EC50 (mmol/L) = -0.6922 log Kow + 0.9253

The equation has the following statistics:
Number of substances = 41
Correlation coef (r2) = 0.678

ECOSAR’s Neutral Organic’s (Baseline Toxicity) model uses the following equation for calculation of chronic aquatic toxicity to algae:

Organism Endpoint Equation
Green Algae 96 hr ChV Log ChV (mmol/L) = -0.6029 log Kow + 0.1648

The equation has the following statistics:
Number of substances = 34
Correlation coef (r2) = 0.697

These correlation coefficients indicate the ECOSAR models calculate results that are equivalent to those generated experimentally and are, hence, adequate for the purpose of classification and labelling and/or risk assessment.

Furthermore, documentation and validity of the ECOSAR QSAR models are provided in the following references:

Clements, RG, Nabholz, JV and Zeeman, R. 1996. Estimating Toxicity of Industrial Chemicals to Aquatic Organisms Using Structure-activity Relationships.
ECHA (2008) “Guidance on information requirements and chemical safety assessment Chapter R.6: QSARs and grouping of chemicals”.
ECHA (2008) “Guidance on information requirements and chemical safety assessment Chapter R.10: Characterisation of dose [concentration]-response for the environment”.
Mayo-Bean, K, Nabholz, JV, Clements, R, Zeeman, M, Henry, T, Rodier, D, Moran, K, Meylan, WM and Ranslow, P. 2011a. Methodology Document for the Ecological Structure-Activity Relationship Model (ECOSAR) Class Program.
Mayo-Bean, K, Nabholz, JV, Meylan, WM, Howard, PH and Moran-Bruce, K. 2011b. Operation Manual for the Ecological Structure-Activity Relationship Model (ECOSAR) Class Program.



Principles of method if other than guideline:
- Software tool(s) used including version: EPISuite v4.11
- Model(s) used: ECOSAR v1.11
- Model description: see field 'Justification for type of information'
- Justification of QSAR prediction: see field 'Justification for type of information'
Specific details on test material used for the study:
OTHER SPECIFICS:
SMILES : O(CCCCCC)CCCCCC
CHEM : Hexane, 1,1 -oxybis-
CAS Num: 000112-58-3
MOL FOR: C12 H26 O1
MOL WT : 186.34
Log Kow: 4.978 (EPISuite Kowwin v1.68 Estimate)
Wat Sol: 2.874 (mg/L, EPISuite WSKowwin v1.43 Estimate)
Key result
Duration:
96 h
Dose descriptor:
EC50
Effect conc.:
0.562 mg/L
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: QSAR
Duration:
96 h
Dose descriptor:
other: ChV
Effect conc.:
0.272 mg/L
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: QSAR
Key result
Duration:
96 h
Dose descriptor:
NOEC
Remarks:
Based on ChV (Division by square-root over 2)
Effect conc.:
0.192 mg/L
Conc. based on:
test mat.
Basis for effect:
growth rate
Validity criteria fulfilled:
yes
Conclusions:
The ECOSAR predicted toxicity values are considered valid and fit for purpose.
Executive summary:

A reliable QSAR model (Ecological Structure-Activity Relationship (ECOSAR) version 1.11) was used to predict the toxicity of dihexyl ether to algae. The 96 hour EC50 was 0.562 mg/L for the neutral organic class. In addition, the algae 96 hour ChV was 0.272 mg/L for the neutral organic class.

The ChV was divided by2to estimate a NOEC equivalent value of 0.192 mg/l.

Description of key information

A reliable QSAR model (Ecological Structure-Activity Relationship (ECOSAR) version 1.11) was used to predict the toxicity of dihexyl ether to algae. The 96 hour EC50 was 0.562 mg/L for the neutral organic class. In addition, the algae 96 hour ChV was 0.272 mg/L for the neutral organic class. The ChV was divided by2to estimate a NOEC equivalent value of 0.192 mg/l.

The experimental acute invertebrate toxicity value (EC50 -48h) was used as basis for the chronic environmental classification in the absence of chronic experimental data.

Key value for chemical safety assessment

EC50 for freshwater algae:
0.562 mg/L
EC10 or NOEC for freshwater algae:
0.192 mg/L

Additional information