1,3-dichlorobenzene

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

(Q)SAR

Adequacy of study:

weight of evidence

Study period:

2022

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)
Individual model BIOWIN (v4.10) included in the Estimation Programs Interface (EPI) Suite.


3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
Smiles: CLc1cccc(CL)c1
Molecular Formula: C6 H4 Cl2
Molecular Weight: 147.00


4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
- Defined endpoint: Probability of rapid biodegradation

- Unambiguous algorithm:
BIOWIN 1 and 2:  
A total dataset of 295 chemicals was used to derive the fragment coefficients that are used in Biowin 1 and 2.  The dataset consists of 186 compounds that were critically evaluated as "biodegrades fast" and 109 chemicals that were critically evaluated as "does not biodegrade fast". The evaluated dataset was used to select 36 chemical fragments that have a potential effect on biodegradability.  There is also one continuous variable, molecular weight.  A matrix of dimensions 295 compounds by 37 variables (36 fragments+MW) was formulated.  The number of instances of each fragment occurring in each compound was entered into the matrix along with the compound's molecular weight.  A biodegradation matrix of dimensions 295 compounds by one evaluation was also formulated.  The evaluation was either 1 (the compound biodegrades fast; probability of 1.0) or 0 (the compound does not biodegrade fast; probability of 0.0).  The matrices were then subjected to multiple linear and non-linear regression analyses to determine the coefficient for each fragment.  The coefficients were then used to determine the biodegradation probability for each compound.  A biodegradation probability greater than 0.5 is considered as "biodegrades fast".  A biodegradation probability less than 0.5 is considered as " does not biodegrades fast". The molecular weight parameter was not included in the original version of  the Biodegradation Probability Program©.  When a structure contained none of the fragments for which coefficients were developed, the program could not estimate the probability.  With the inclusion of the molecular weight parameter, estimates are possible for all structures.
Calculation of probability of fast biodegradation
Linear model (Biowin1)
The fast biodegradation probability for any  compound is calculated by summing, for all the fragments present in that compound, the fragment coefficient multiplied by the number of instances of the fragment in the compound (for MW, the value of that parameter is multiplied by its coefficient), and then adding this summation to the equation constant which is 0.7475.  The summed values for each fragment coefficient multiplied by the number of instances appear in the "VALUE" column of the linear results screen.
Non-linear model (Biowin2)
Calculation of the fast biodegradation probability for any compound begins by summing, for all the fragments present in that compound, the fragment coefficient multiplied by the number of instances of the fragment in the compound (for MW, the value of that parameter is multiplied by its coefficient), then adding this summation to the equation constant which is 3.0087.  The summed values for each fragment coefficient multiplied by the number of instances appear in the "VALUE" column of the non-linear results screen.  The non-linear fast biodegradation probability is then calculated from the logistic equation as follows, where total = 3.0087 + the summation as described above:
Non-linear probability  =  exp(total) / (1 + exp(total) )

BIOWIN 3 and 4
These two models estimate the time required for "complete" ultimate and primary biodegradation.  Primary biodegradation is the transformation of a parent compound to an initial metabolite.  Ultimate biodegradation is the transformation of a parent compound to carbon dioxide and water, mineral oxides of any other elements present in the test compound, and new cell material.  It is normally determined experimentally by measuring carbon dioxide production, oxygen uptake or disappearance of dissolved organic carbon attributable to test substance.  The models are based upon a survey of 17 biodegradation experts conducted by EPA, in which the experts were asked to evaluate 200 compounds in terms of the time required to achieve ultimate and primary biodegradation in a typical or "evaluative" aquatic environment (Boethling et al. 1994).  This survey followed a similar survey for 50 compounds, described by Boethling and Sabljic (1989).  In the second survey, each expert rated the ultimate and primary biodegradation of each compound on a scale of 1 to 5.  The ratings correspond to the following time units:   5 - hours;  4 - days;  3 - weeks;  2 - months;  1 - longer.   It should be noted that the ratings are only semi-quantitative and are not half-lives.  Thus for example if the averaged expert rating for ultimate degradation of a compound is 2.5, it means the experts considered that the compound would biodegrade completely in a time frame somewhere between "a matter of weeks" and "a matter of months", with no exact time or half-life being applied.
 The ratings for each compound were averaged to obtain a single value for modeling.  Matrices were then formulated for both ultimate and primary biodegradation using the same 36 fragments and molecular weight parameter as used in the Linear/Non-Linear Models (Biowin1 and 2).  Finally, linear regressions were performed on the matrices using the averaged expert ratings as the solution matrices.
Calculation of Ultimate/Primary Rating
 The ultimate or primary rating of a compound is calculated by summing, for all the fragments present in that compound, the fragment coefficient multiplied by the number of instances of the fragment in the compound (for MW, the value of that parameter is multiplied by its coefficient), and then adding this summation to the equation constant which is 3.1992 for Biowin3 and 3.8477 for Biowin4 .  The summed values for each fragment coefficient multiplied by the number of instances appear in the "VALUE" column of the results screen.
Ultimate/Primary Rating in Time Units
The following explains how the numerical ratings calculated by the models for a given compound are used to assign the words that are given in parentheses in the results.

Calculated rating                         Words assigned, representing expected total
(numerical value from model)                degradation time
>4.75 - 5                                hours
>4.25 - 4.75                                hours to days
>3.75 - 4.25                                 days
>3.25 - 3.75                                 days to weeks
>2.75 - 3.25                                 weeks
>2.25 - 2.75                                 weeks to months        
>1.75 - 2.25                               months
<1.75                                         recalcitrant
 
BIOWIN 5 and 6
Under its Chemical Substances Control Law (CSCL), the Japanese have tested approximately 900 discrete substances in the Ministry of International Trade and Industry (MITI)-1 test.  This protocol for determining ready biodegradability is among six officially approved as ready biodegradability test guidelines of the OECD (Organization for Economic Cooperation and Development).  A total dataset of 884 chemicals was compiled to derive the fragment probability values that are applied in this MITI Biodegradability method.  The dataset consists of 385 chemical that were critically evaluated as "readily degradable" and 499 chemicals that were critically evaluated as "not readily biodegradable". Appendix G lists all 884 compounds, critical evaluations, and BIOWIN predictions.
Derivation of Fragment Values
The 884 compound dataset was divided into a training dataset (589 compounds) and a validation dataset (295 compounds).  The critical biodegradation evaluations (results of the MITI tests) were either "readily degradable" or "not readily degradable"; "readily degradable" was assigned a numeric value of 1 and "not readily degradable" was assigned a numeric value of 0 (0 to 1 is the full probability range).  The basic approach for deriving the fragment values is very similar to the approach used for the original linear/non-linear model described above (see section 6.1).
Although the majority of fragments in the new MITI models are identical to fragments in the models described above (sections 6.1 and 6.2), the new MITI models incorporate various changes.  For example, to provide fuller characterization of alkyl chain length and branching, the original C4 terminal alkyl group fragment was replaced with a fragment set consisting of -CH3, -CH2 (both linear and ring types), -CH (both linear and ring types), and -C=CH (alkenyl hydrogen). The final MITI models contain 42 fragments and molecular weight as independent variables.

- Defined domain of applicability:
BIOWIN 1 and 2
Currently there is no universally accepted definition of model domain.  However, biodegradability estimates are generally considered less accurate for compounds outside the MW range of the training set compounds (Linear / non-Linear Biodegradability: 31.06 - 697.7 g/mol; Ultimate-Primary Biodegradability: 30.02 - 959.2 g/mol), and/or that have more instances of a given fragment than the maximum for all training set compounds.  It is also possible that a compound may have a functional group(s) or other structural features not represented in the training set, and for which no fragment coefficient was developed; and that a compound has none of the 36 fragments in the model’s fragment library.  In the latter case, predictions are based on molecular weight alone.  These points should be taken into consideration when interpreting model results.

- Appropriate measures of goodness-of-fit and robustness and predictivity:
BIOWIN 1 and 2
BIOWIN 1: Total Correct = 264/295; % Correct Total = 89.5; % Correct "fast" = 97.3; % Correct "slow" = 76.1
BIOWIN 2: Total Correct = 275/295; % Correct Total = 93.2; % Correct "fast" = 97.3; % Correct "slow" = 86.2

BIOWIN 3 and 4
Regression Performance of BIOWIN 3 and BIOWIN 4 for the Training Set Compounds
BIOWIN 3: R2 = 0.72; Mean Residual (abs. value): 0.206
BIOWIN 4: R2 = 0.71; Mean Residual (abs. value) = 0.173
Classification Performance of BIOWIN 3 and 4 for the Training Set Compounds
BIOWIN 3: Total Correct = 167/200; % Correct Total = 83.5; % Correct "fast" = 93.5; % Correct "slow" = 71.7
BIOWIN 4: Total Correct = 165/200; % Correct Total = 82.5; % Correct "fast" = 84.9; % Correct "slow" = 79.0

BIOWIN 5 and 6
BIOWIN produces two separate MITI probability estimates for each chemical.  The first estimate is based upon the fragments derived through linear regression.  The second estimate is based upon the fragments derived through non-linear regression.  Prediction accuracy of the training and validation sets are as shown below.  The numbers correspond to correct predictions (either "readily degradable" or "not readily degradable"):
Training Set: Critically Evaluated as "Readily Degradable"
 Linear Model:                201/254  (79.1%)
 Non-Linear Model:        204/254  (80.3%)
Training Set: Critically Evaluated as "Not Readily Degradable"
 Linear Model:                284/335  (84.8%)
 Non-Linear Model:        284/335  (84.8%)
Training Set:  TOTAL
 Linear Model:                485/589  (82.3%)
 Non-Linear Model:        488/589  (82.9%)


5. APPLICABILITY DOMAIN
- Descriptor domain: The molecular weight of the substance falls within the general applicability domain defined for each BIOWIN model
- Structural domain: There are no fragments in the substance that were not present in the training set


6. ADEQUACY OF THE RESULT
The prediction satisfied the criteria defined by ECHA under Regulation (EC) No 1907/2006 for use in a weight-of-evidence argument in support of a conclusion concerning the ready biodegradability of the substance.

This endpoint study record is part of a Weight of Evidence approach comprising a
QSAR (this study) and an experimental value. Both data sources agree on the ready biodegradability of the substance and are sufficient to fulfil the information requirements as further
explained in the provided endpoint summary.

Principles of method if other than guideline:

- Software tool(s) used including version: EPISUITE v4.10
- Model(s) used: BIOWIN v4.10
- Model description: see field 'Justification for non-standard information'
- Justification of QSAR prediction: see field 'Justification for type of information'

GLP compliance:

no

Inoculum or test system:

other: Not applicable for (Q)SAR study

Key result

Parameter:

probability of ready biodegradability (QSAR/QSPR)

Remarks on result:

not readily biodegradable based on QSAR/QSPR prediction

Conclusions:

Based on the results of the BIOWIN models (1, 2, 3, 5, and 6) the substance is not considered to be readily biodegradable.

Executive summary:

The ready biodegradability of the substance was estimated using BIOWIN v4.10.  This is a valid model for this substance which falls into its applicability domain as presented in this study summary.  The substance is concluded to be not readily biodegradable.

Reference 2

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1981-10-05 till 1982-01-23

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Study conducted in accordance with OOECD 301C Guideline, but with limited documentation. Used in a weight-of-evidence approach with a valid (Q)SAR prediction (BIOWIN).

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 C (Ready Biodegradability: Modified MITI Test (I))

Deviations:

no

GLP compliance:

not specified

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge (adaptation not specified)

Details on inoculum:

- Source of inoculum/activated sludge: Sludge samplings were made at 10 places in Japan. They included three city sewage plants, one industry sewage plant, three riverine areas, one lake area and two bay areas.
- Laboratory culture: About 30 minutes after ceasing the aeration to the sludge mixture, supernatant corresponding to about 1/3 of the whole volume was removed. Then the equal volume of dechlorination water was added to the remaining portion and aerated again, followed by addition of synthetic sewage, concentration of that portion was to be 0.1 (W/V) %. This procedure was repeated once every day. The incubation temperature was 25 °C ± 2 °C
- Synthetic sewage: 1 g each of glucose, peptone, and potassium dihydrogenphosphate disolved in 1 L of water and pH adjusted to 7.0 ± 1.0 with NaOH
- Method of cultivation: 5 liters of the filtrate of the supernatant of the currently-tested sample was mixed and incubated with an equal amount of a filtrate of the supernatant of a new sample
- Storage conditions: Prefiltered open air was used for aeration; the mixture was cultured at pH 7.0 ± 1.0 and 25 °C ± 2 °C.
- Concentration of sludge: 30 mg/L
- Water: purified water was used

Duration of test (contact time):

28 d

Initial conc.:

100 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS
- Composition of medium: 3 mL each of liquids A, B, C and D having compositions prescribed in JIS K0102-1998-21 were mixed and purified water was added up to 1 L
- Test temperature: 25 °C ± 1 °C
- pH: 7.0 ± 1.0
- pH adjusted: yes
- Aeration of dilution water: yes

TEST SYSTEM
- Measuring equipment: closed system oxygen consumption measuring apparatus (Coulometer: Ohkura Electric Co., Ltd.)

Reference substance:

aniline

Parameter:

% degradation (O2 consumption)

Value:

0

Sampling time:

28 d

Results with reference substance:

The biodegradation of aniline was 73 % after 28 days.

Validity criteria fulfilled:

not specified

Interpretation of results:

under test conditions no biodegradation observed

Conclusions:

Activate sludge (adaptation not specified) was used as inoculum at a concentration of 30 mg/L; the concentration of 1,3-dichlorobenzene was of 100 mg/L. Ready biodegradability was measured in terms of BOD; no biodegradation was observed after four weeks (28 days) of incubation.

Executive summary:

The test was conducted according to the OECD Guideline 301 C (Ready Biodegradability: Modified MITI Test (I)); no deviations from the guideline were observed. Activate sludge (adaptation not specified) was used as inoculum at a concentration of 30 mg/L; the concentration of 1,3-dichlorobenzene was of 100 mg/L. Ready biodegradability was measured in terms of BOD; no biodegradation was observed after four weeks (28 days) of incubation.

Description of key information

28d % Biodegradation = 0%; OECD 301C; MITI (1992)

Readily Biodegradable: "No"; BIOWIN v4.10 (2022)

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Additional information

This endpoint is covered in a weight-of-evidence approach, in accordance with ECHA Guidance on Information Requirements and Chemical Safety Assessment.

The substance was tested for rapid degradation using OECD 301C (modified MITI test) method (MITI, 1992).  Although limited documentation of this study was available, no significant biodegradation was observed during this study (0% after 28-days), and this the study, which used a method suitable for the substance, concluded that it was not readily biodegradable.  Due to the limited documentation of this study, further data are presented in a weight-of-evidence from the model BIOWIN v4.10 (2022).  The results of the BIOWIN model were as follows:

Biowin1 (Linear Model Prediction) : Does Not Biodegrade Fast
Biowin2 (Non-Linear Model Prediction): Does Not Biodegrade Fast
Biowin3 (Ultimate Biodegradation Timeframe): Weeks-Months
Biowin5 (MITI Linear Model Prediction) : Not Readily Degradable
Biowin6 (MITI Non-Linear Model Prediction): Not Readily Degradable
Ready Biodegradability Prediction: No

In accordance with ECHA Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.7b (2017), BIOWIN models 1, 2, 3, 5 and 6 may be used when predicting the ready biodegradability of substances. It is noted that according to various validation studies performance of the models seem to differ, but in general predictions about no ready biodegradability seem to be more certain than predictions about ready biodegradability (GHS 2004 and OECD 2004: (ENV/JM/TG/2004)26Rev1 and references therein).  Similarly, in accordance with ECHA Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.11 (2017), the combined results of BIOWIN 2, 6 and 3 may be used as follows:

- Non-linear model prediction (BIOWIN 2): does not biodegrade fast (probability < 0.5) and ultimate biodegradation timeframe prediction (BIOWIN 3): ≥ months (value < 2.25), or
- MITI non-linear model prediction (BIOWIN 6): does not biodegrade fast (probability < 0.5) and ultimate biodegradation timeframe prediction (BIOWIN 3): ≥ months (value < 2.25)

For the prediction presented for the registered substance, the BIOWIN 2 and 6 predictions meet the criteria for the substance to be considered as potentially persistence in accordance with PBT criteria.  Although the ultimate biodegradation timeframe from BIOWIN 3 (≥ months, value < 2.25) is not met, the prediction still indicates that the ultimate degradation of this compound is in the weeks-months window.

Given the available data, considered collectively, the evidence indicates that the substance is not expected to be readily biodegradable, when considering the OECD 301C study, and suite of predictions from the BIOWIN v4.10 model, for which the registered substance falls within the applicability domain.