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Environmental fate & pathways

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Under the test conditions of OECD 111 bis(3,3,5-trimethylhexanoyl) peroxide is hydrolytically unstable, with a half-life of probably less than one hour at 5 °C. At environmentally relevant temperatures, the substance will undergo hydrolytical degradation significantly faster.

Seven degradation products were present in GC chromatograms but only 3,5,5-trimethylhexanoic acid (CAS no. 3302-10-1) and 2,4,4-trimethyl-1-pentanol (CAS 16325-63-6) could be identified with sufficient certainty, and only 2,4,4-trimethyl-1-pentanol was quantified against an external standard, for analytical monitoring of the hydrolysis process.

According to the result of a OECD 301B study (modified Sturm test) bis(3,5,5-trimethylhexanoyl)peroxide, including any hydrolysis products, can be considered as readily biodegradable.

Due to the ready biodegradability of the substance including its hydrolytical degradation products additional simulation testing in soil, sediment and surface water as well as an adsorption/desorption screening study are not required.

Measurements of total dissolved organic carbon in ecotoxicity tests show increasing DOC concentrations over time, indicating the formation of degradation products with higher water solubility and lower log Kow. However, as the majority of the degradation products could not be identified, in a worst case approach the assessment of the bioaccumulation potential is based on the environmentally representative breakdown product 3,5,5-trimethylhexanoic acid: The rapid hydrolysis of the peroxide requires using data on the hydrolysis products for the chemical safety assessment. The representative worst case is 3,5,5-trimethylhexanoic acid, with a log Pow of 3.34 (QSAR estimate), whereas the other identifiable degradation product 2,4,4-trimethylpentan-1-ol has a log Pow of only 2.62.

Thus, in view of the rapid hydrolytical degradation, the bioaccumulation potential of any breakdown products is relevant, instead that of bis(3,5,5-trimethylhexanoyl) peroxide itself, since the parent is not expected to be present in the environment. The bioconcentration factor (BCF) of the environmentally representative breakdown product 3,5,5-trimethylhexanoic acid has been estimated at 3.162 L/kg wwt (QSAR), which indicates a negligible bioaccumulation potential of any substance residues ending up in the environment.

The Koc for bis(3,5,5-trimethylhexanoyl) peroxide was estimated by means of QSAR (KOCWIN v2.00). Experimental determination of the Koc is not mandatory under REACH because the substance and its relevant degradation products decompose rapidly (rapid hydrolysis and ready biodegradation).

However, for rapidly hydrolysing substances it is more appropriate to also determine the degree of adsorption of the hydrolysis products (see guidance on information requirements and chemical safety assessment, Chapter R.7a: R.7.1.15.4).

Accordingly, the relevant Koc for the chemical safety assessment is that for 3,5,5-trimethylhexanoic acid, a breakdown product formed during the rapid hydrolysis of bis(3,5,5-trimethylhexanoyl) peroxide. 3,5,5-trimethylhexanoic acid is the environmentally relevant compound, since that with the highest octanol-water partitioning coefficient among the two identifiable breakdown products (log Pow = 3.34; QSAR estimate, see IUCLID section 4.7). Therefore, the properties of 3,5,5-trimethylhexanoic acid govern the environmental fate of any residues of bis(3,5,5-trimethylhexanoyl) peroxide that may end up in the environment.

The Koc for 3,5,5-trimethylhexanoic acid, estimated by QSAR based on MCI, is relatively low (30.38 L/kg), indicating no significant soil adsorption of any environmentally relevant substance residues.