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Environmental fate & pathways

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The key and supporting studies by Hydrotox (2004) and Wildlife International (2006) are GLP compliant and follow standard guidelines. They both support the characterisation of 2,4,4 -trimethylpentene as not readily biodegradable. In the EU RAR (2008), it is concluded that, based on the available information a sound assessment of biodegradation is not possible, so as a worst-case 2,4,4-trimethylpentene has to be assessed as not biodegradable. The data are supported by the results from the QSAR estimations using the BIOWINand BioHC models.

One of the screening criteria for persistence in the PBT assessment is that if a substance is considered to be readily biodegradable the substance is screened as not P and not vP. The study conducted by Hydrotox (2004) following OECD test guideline 301B indicated that 2,4,4-trimethylpentene is degraded by 1.6% in 28 days and is therefore not readily biodegradable. Since this substance is not considered to be readily biodegradable it does qualify for a screening assignment of P or vP. The EU RAR (2008) for 2,4,4-trimethylpentene reports a result of 0% biodegradation (BOD) in a MITI-List, Closed Bottle Test (Japan Chemical Industry Ecology-Toxicology & Information Center, 1992). This study was given a reliability of 1 in the EU RAR. On the basis of this information, it is concluded that 2,4,4-trimethylpentene has to be assessed as not biodegradable.

Based on the Biowin predictions, 2,4,4-trimethylpentene meets the screening criteria for P. BioHCwin v1.01 predicts that the half life of 2,4,4-trimethylpentene will be 6.759 days, based on four fragments. These fragments are as follows: a carbon with four single bonds and no hydrogens, a methyl group [-CH3], -CH2- [linear] and a –C=CH [alkenyl hydrogen]. According to a study by Atkinson (1984) the photodegradation half-life for 2,4,4-trimethylpentene was determined to be <1day in the atmosphere and the calculated half-life used in the EU RAR (2008) for 2,4,4-trimethylpentene is 7.24 hours. Due to the weight of evidence, 2,4,4-trimethylpentene is considered to meet the screening criteria for P/vP.