Bis(3,5,5-trimethylhexanoyl) peroxide

Bioaccumulation: aquatic / sediment

Description of key information

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.

Key value for chemical safety assessment

BCF (aquatic species):

3.162 L/kg ww

Additional information

Bis(3,5,5-trimethylhexanoyl) peroxide is susceptible to hydrolysis when mixed with water. The hydrolytical half-life is extremely short, i.e. < 1 h at 5 °C (see IULCID section 5.1.2). Accordingly, any environmental exposure to the parent substance can be excluded. Since it can be legitimately expected that bis(3,5,5-trimethylhexanoyl) peroxide will not be present in the environment, the bioconcentration factor of the parent is an irrelevant parameter in the risk assessment. Instead, the bioaccumulation potential of any substance residues reaching the environment shall be assessed on the basis of any relevant and identifiable degradation products formed during hydrolysis.

Two hydrolysis products were identifiable:

• 3,5,5-trimethylhexanoic acid (CAS no. 3302-10-1)
• 2,4,4-trimethylpentan-1-ol (CAS no. 16325-63-6)

An additional five degradation products were detected in the hydrolysis study, but proved to be non-identifiable. Nevertheless, considering the molecular structure of the parent substance it may be assumed that also the unidentified breakdown products are smaller molecules than the parent, and more hydrophilic. Therefore, the log P_ow of 3,5,5-trimethylhexanoic acid of 3.34 may be taken as a representative worst case figure for the entire spectrum of degradation products. This worst-case assumption can be directly adopted for the bioaccumulation potential and for allocating the bioconcentration factor: Among the spectrum of the largely unknown hydrolysis products 3,5,5-trimethylhexanoic acid can be considered as the representative compound governing processes of uptake into organisms and bioconcentration of any residues of bis(3,5,5-trimethylhexanoyl) peroxide. In particular, 2,4,4-trimethylpentan-1-ol exhibits a lower bioaccumulation potential than 3,5,5-trimethylhexanoic acid according to its log P_ow and is therefore covered by the BCF estimate for the latter. Any other breakdown products are also covered, particularly since they have been shown to be readily biodegradable by the OECD 301 test on the parent substance.

The bioconcentration factor for the representative worst-case breakdown product 3,5,5-trimethylhexanoic acid is BCF = 3.162 L/kg wwt (QSAR estimate, BCFBAF v3.01), which is adopted as the key value for CSA.

Experimental testing of the BCF in fish is not considered to be necessary, in view of the rapid hydrolytical degradation of the parent, the negligible bioaccumulation potential of the environmentally representative breakdown product, and for animal welfare reasons.