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Toxicity to microorganisms

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Reference
Endpoint:
toxicity to microorganisms
Type of information:
(Q)SAR
Adequacy of study:
key study
Study period:
April 24th, 2017
Reliability:
1 (reliable without restriction)
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:
See enclosed study report, QRPF and QMRF documents
Principles of method if other than guideline:
The purpose of this QSAR model is to accurately predict the toxicity to microorganisms as would be expected in a laboratory experiment following OECD Guideline 209) and EC method C.11 for specific, named modes of action to provide a value that can effectively replace a 30 to 180 minutes EC50 value from an experimental study. The regression based method used to achieve this has been fully validated following the OECD (2004) recommendations.
Analytical monitoring:
not required
Vehicle:
no
Test organisms (species):
activated sludge
Details on inoculum:
This study is not performed on a single or known species as such. Results were acquired from studies where the following test system was used: Activated sludge collected and treated according to the method outlined in OECD 209
Test type:
static
Water media type:
not specified
Limit test:
no
Total exposure duration:
180 min
Remarks on exposure duration:
Results from a test duration of 30 to 180 minutes only were used for this algorithm: both data were compiled.
Hardness:
not specified
Test temperature:
The temperatures varied from approximately 20 to 25 °C depending on the studies used to construct the algorithm. This small difference is not expected to contribute to the variability of the EC50 values found in experimental data.
pH:
Test results were taken from studies with measured pHs between 6 - 9.
Dissolved oxygen:
not specified
Salinity:
not specified
Conductivity:
not specified
Nominal and measured concentrations:
This study is typically performed using nominal concentrations.
Details on test conditions:
The studies used to construct the algorithm were verified for the following validity criteria:
- Controls: controls used accoding to the guideline.
- Test duration: The study duration was between 30 and 180 minutes.
- Klimisch verification: The studies used in the dataset were considered valid under the REACH regulation (REACH, 2006) (i.e. Klimisch score 1 or 2) by registrants of the substances included in the training and test sets were revalidated by KREATiS and the critical parameters of the study were considered to be within acceptable limits.
- Test concentrations There was sufficient evidence presented to determine that the stubstance was stable under test conditions or, if not, the value was based on measured concentrations.
Reference substance (positive control):
not required
Key result
Duration:
180 min
Dose descriptor:
EC50
Nominal / measured:
nominal
Conc. based on:
not specified
Basis for effect:
not specified
Remarks on result:
not determinable because of methodological limitations
Remarks:
EC50 > water solubility limit
Details on results:
Adequacy of prediction:

The water solubility value given as input to the iSafeRat® ASRIT HA-QSAR model falls within the descriptor domain of the model between log water solubility (in log (mol/L)) of -2.72 to 1.01. Below this value the algorithm is no longer applicable but the toxicity of the substance can be considered as greater than the subccoled solubility limit. Moreover, the prediction is supported by the fact that the test item can be considered as insoluble in water.
Validity criteria fulfilled:
yes
Conclusions:
The result below is the toxicity value anticipated further to a 30-180 minute study on activated sludge based on measured concentrations:
Parameter: 30-180min EC50
Toxicity value (mg test item.L-1): > water solubility limit
Executive summary:

Introduction.

A QSAR model was used to calculate the inhibition of respiration to activated sludge of the test item 2,6,10,15,19,23-hexamethyltetracosane. This QSAR model has been validated to be compliant with the OECD recommendations for QSAR modeling (OECD, 2004) and predicts the endpoint value which would be expected when testing the substance under experimental conditions in a laboratory following Guideline for Testing of Chemicals No. 209, "Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation)", referenced as Method C.11 of Commission Regulation No. 440/2008 (2). The criterion predicted was the 30 to 180 minutes EC50 (Median Effective Concentration for specific respiration rate), a statistically derived concentration which is expected to cause 50% inhibition of intrinsic rate of respiration of the test system within a period of 30 to 180 minutes as an effect on the organic carbon oxidation process. The results from this study do not include the supplementary test results that may be required to determine the effect on nitrification. It should be noted that a specific test duration time could not be determined for this model as 30 and 180 minute data were available but not in sufficient quantity to separate them into two separate models.

Methods.

The respiration inhibition of activated sludge was determined using a validated QSAR model for the Mode of Action in question (MOA 1, non-polar narcosis). The QSAR model is based on validated data for a training set of 12 chemicals derived from 30-180 minute EC50 for which the concentrations of the test item had been determined by chemical analyses over the test period. Further valid data were available but the values were all above the water solubility of the substance and were therefore not included as part of the regression. On the other hand, these data could be used to determine the point at which the regression no longer holds true and results from experimental studies on this MOA are expected to be greater than the solubility limit (i.e. test substance concentrations up to 100 mg/L will result in no effect on activated sludge respiration).

Results.

The result below is the toxicity value anticipated further to a 30-180 minute study on activated sludge based on measured concentrations:

 Parameter  Toxicity value (mg test item.L-1)
 30-180min EC50  > water solubility limit

Description of key information

The respiration inhibition of activated sludge was determined using a validated QSAR model for the Mode of Action in question (MOA 1, non-polar narcosis). The result below is the toxicity value anticipated further to a 30-180 minute study on activated sludge based on measured concentrations:

 Parameter  Toxicity value (mgtest item.L-1)
 30-180min EC50  > water solubility limit

Key value for chemical safety assessment

Additional information