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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Environmental fate & pathways

Biodegradation in water: screening tests

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biodegradation in water: ready biodegradability
Data waiving:
study technically not feasible
Justification for data waiving:
the study does not need to be conducted because the substance is inorganic
biodegradation in water: ready biodegradability
Data waiving:
study technically not feasible
Justification for data waiving:
the study does not need to be conducted because the substance is inorganic
biodegradation in water: ready biodegradability
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
As calcium carbide instantly hydrolyses to Ca(OH)2 and C2H2 upon contact with water/moisture the assessment is based on the degradation products. For details please refer to the read across report in section 13.
Reason / purpose for cross-reference:
read-across source
Key result
Remarks on result:
readily biodegradable based on QSAR/QSPR prediction
Details on results:
Acetylene is considered readily biodegradable.

Predicting Ready Biodegradability

The following line appears at the end of the Biowin prediction results:

Ready Biodegradability Prediction: (YES or NO)

The criteria for the YES or NO prediction are as follows:

If the Biowin3 (ultimate survey model) result is "weeks" or faster (i.e. days, days to weeks, or weeks) AND the Biowin5 (MITI linear model) probability is >= 0.5, then the prediction is YES (readily biodegradable). If this condition is not satisfied, the prediction is NO (not readily biodegradable). This method is based on the application of Bayesian analysis to ready biodegradation data for US Premanufacture Notification (PMN) chemicals, derived collectively from all six OECD301 test methods plus OECD310. The approach is fully described in Boethling et al. (2004).

The linear and nonlinear MITI models (Biowin5 and 6) also predict ready biodegradability, but for degradation in the OECD301C test only, and based exclusively on data from the Chemicals Evaluation and Research Institute Japan (CERIJ) database (

Validity criteria fulfilled:
not applicable
Interpretation of results:
readily biodegradable
Acetylene is readily biodegradable.
Executive summary:

As no experimental data on the water soluble gas acetylene are available, ready biodegradability of the substance has been estimated by means of BIOWIN v4.10.

The ECHA Guidance R.7b cites the BIOWIN software program for prediction of ready biodegradability. The ECHA Guidance states that “various QSAR models for biodegradation estimation with the exception of BIOWIN 1, 2, 3 & 4 have been developed based on training set data consisting of results from ready biodegradability tests, in particular MITI I data, which uses a uniquely derived inoculum. The training set for BIOWIN 1, 2, 3 (ultimate degradation time frame) and 4 (primary degradation timeframe) on the contrary, was based on the overall conclusions of a panel of USEPA experts for rapid or slow environmental degradation and based on various types of degradation information on the training set substances. Nevertheless also the BIOWIN 1, 2 and 3 model has been tested (validated) in literature for its predictability concerning not ready and ready biodegradability.”

The BIOWIN v4.10 estimation results in "ready biodegradability: yes".

Regulatory purpose: The prediction is used to cover the information requirements for the chemical’s registration under REACH Annex VII-IX.

Approach for regulatory interpretation of the model result: Acetylene is a gaseous substance which has a high water solubility (1200 mg/L). Based on the BIOWIN V4.10 acetylene is considered to be readily biodegradable. This result is used in the REACH endpoint valuation Ready biodegradability (IUCLID section 5.2.1 Biodegradation in water: screening test).

Outcome: Based on the very short chain chemical structure of the substance, the ready biodegradability prediction: "yes" of BIOWIN v4.10 is accepted.

Conclusion: The final result is considered adequate for a regulatory conclusion, no additional information is required.

This information is used in a read-across approach in the assessment of the target substance. For justification of read-across please refer to the read-across report attached to IUCLID section 13.

Description of key information

Calcium carbide is inorganic hence the biodegradability concept is not applicable to the substance itself.

However, in contact with water acetylene is instantaneously released, a short-chained gaseous hydrocarbon. Acetelyene is considered to be readily biodegradable, based on reliable QSAR predictions.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information