Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

As acetylene 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. An OECD 301D closed bottle test has been identified (MITI 2001) which reports 0 % biodegradation over 28 days. We have been unable to obtain a copy of the original report in order to assess its reliability.

The use of the QSARs, BioHCwin v 1.01 in EPI Suite 4 2009 (Howard et al 2005) and Biowin v 4.1 in EPI Suite v 4 2009 (Howard et al 1992), to predict the biodegradability of acetylene has also been conducted as part of a weight of evidence approach to fulfil this endpoint requirement. The use of BioHCwin must be treated with caution as this compound falls outside the applicability domain. However, the predictions from both model suggest that acetylene does have the potential to biodegrade.

Furthermore, acetylene is expected to primarily partition to air, thus its fate in the atmosphere is an important consideration, although it is not a REACH requirement. Acetylene is expected to rapidly degrade by indirect photolysis in air. The dominant process is by reaction with hydroxyl radicals, although it can also react with ozone. Atkinson (1985) recommended a rate constant of 0.8150 E-12 cm3 /molecule/sec for the reaction rate with hydroxyl radicals and a recommended rate constant of 0.003 E-17 cm3/mol/sec for the reaction rate with ozone. These rate constants equate to half lives of 13.1 and 382 days respectively.

Acetylene has the potential to rapidly volatilise from surface waters, based on a calculated Henry's Law constant of 2.20E +003 Pa m³/mol at 25°C. It is not expected to partition to suspended matter or sediments based on its log Kow of 0.37. In summary, although unlikely to persist in the aquatic environment, data are not available to demonstrate that acetylene is readily biodegradable and, for the purposes of a risk assessment, ready biodegradability will not be assumed.