Ethylene

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

(Q)SAR

Adequacy of study:

weight of evidence

Study period:

Up to 2021

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:

Episuite and the Biowin/BioHCWin models are well documented and commonly used QSARs for predicting the biodegradation potential of chemicals. Substances within LOA fall within the applicability domain of these models and they have been recommended by ECHA in the Information Requirement Guidelines.

Principles of method if other than guideline:

Biowin v4.1 in EPISuite 4.1 (2013). The Biodegradation Probability Program (Biowin) estimates the probability for the rapid aerobic biodegradation of an organic chemical in the presence of mixed populations of environmental microorganisms. Estimates are based upon fragment constants that were developed using multiple linear and non-linear regression analyses.
BioHCwin v1.01 in EPISuite 4.1 (2013). The BioHCwin program was developed specifically for the biodegradation half-life prediction of petroleum hydrocarbons. Primary biodegradation half-lives for individual petroleum hydrocarbons are estimated using multiple linear regression against distinct molecular fragments, using a similar approach to several other biodegradation models such as those within the Biodegradation Probability Program (Biowin).

GLP compliance:

no

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
Not applicable

Oxygen conditions:

aerobic

Inoculum or test system:

not specified

Details on inoculum:

Not applicable

Based on:

other: QSAR calculation

Parameter followed for biodegradation estimation:

other: QSAR calculation

Details on study design:

Not applicable

Preliminary study:

Not applicable

Parameter:

half-life in days (QSAR/QSPR)

Remarks:

BioHCWin

Value:

2.905

Remarks on result:

readily biodegradable based on QSAR/QSPR prediction

Parameter:

probability of ready biodegradability (QSAR/QSPR)

Remarks:

BIOWIN 2

Value:

0.931

Remarks on result:

readily biodegradable based on QSAR/QSPR prediction

Parameter:

calculated rating of total degradation time (QSAR/QSPR)

Remarks:

BIOWIN 3

Value:

3.137

Remarks on result:

readily biodegradable based on QSAR/QSPR prediction

Parameter:

probability of ready biodegradability (QSAR/QSPR)

Remarks:

BIOWIN 5

Value:

0.487

Remarks on result:

readily biodegradable based on QSAR/QSPR prediction

Parameter:

probability of ready biodegradability (QSAR/QSPR)

Remarks:

BIOWIN 6

Value:

0.692

Remarks on result:

readily biodegradable based on QSAR/QSPR prediction

Details on results:

Biowin2 (Non-Linear Model Prediction): Biodegrades Fast (0.9315)
Biowin3 (Ultimate Biodegradation Timeframe): Weeks (3.1372)
Biowin5 (MITI Linear Model Prediction): Biodegrades Fast (0.4868)
Biowin6 (MITI Non-Linear Model Prediction): Biodegrades Fast (0.6918)
BioHCwin BioHC Half-Life (days): 2.9054

Biowin 2, 5 and 6 Result Classification: A probability greater than or equal to 0.5 indicates “Biodegrades Fast” and a probability less than 0.5 indicates “Does NOT Biodegrade Fast”
Biowin 3 and 4 Result Classification (primary and ultimate): 5.00 – hours, 4.00 – days, 3.00 - weeks, 2.00 - months, 1.00 - longer

Results with reference substance:

Not applicable

For the purpose of the PBT assessment, the screening assessment was conducted using predicted biodegradability obtained by using EPI Suite v4.1. A substance is considered to be P if they fulfil the screening criteria listed below. Based on the Biowin predictions, xylene isomers do not meet the screening criteria for P.

Screening criteria for Persistence

Biowin 2 - does not biodegrade fast (probability <0.5) and Biowin 3 – ultimate biodegradation timeframe prediction: ≥months (value <2.2)

Biowin 5 – does not biodegraded fast (probability <0.5) Biowin 6 – does not biodegraded fast (probability <0.5) and Biowin 3 – ultimate biodegradation timeframe prediction: ≥months (value <2.2)

Validity criteria fulfilled:

not applicable

Conclusions:

The results of the Biowin and BioHCwin for ethylene indicate that they are expected to biodegrade rapidly, with a half-life of 2.9054 days.

Executive summary:

The use of a QSAR to predict the biodegradability of the substance is an appropriate technique as these substances clearly fall within the applicability domain of the model, with all substructures included in the model. The results indicate that the substance is expected to biodegrade rapidly, with a half-life of 2.9054 days.

The use of QSAR estimates to predict the biodegradability of hydrocarbons because they are included in the training sets of the BIOWIN and BioHC models. The databases were created using experimental biodegradation data for compounds found in crude oil and its products, with biodegradation references obtained for each of these compounds, mainly from the BIOLOG and DATALOG files of EFDB, TOXLINE and American Chemical Society Chemical Abstracts as well as literature searches. For the BioHC model, a single recommended biodegradation half-life was chosen for use in the regression analysis from the primary biodegradation data that were compiled for each hydrocarbon structure.

Description of key information

Biowin prediction indicates ethylene is expected to be readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

As ethylene is a gas at standard temperature and pressure conducting a standard ready biodegradability test is technically difficult and based on exposure estimates the test may not be relevant. Therefore, the use of a QSAR to predict the biodegradability of ethylene is an appropriate technique to use as part of a weight of evidence approach. The use of Biowin (Howard et al. 1992) is appropriate for ethylene as this compound falls within the applicability domain of the model. The Biowin prediction indicates that ethylene is expected to be readily biodegradable.