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Experimental testing of the toxicity of bis(3,5,5-trimethylhexanoyl) peroxide is not considered to be required for the following reasons:

According to column 2 of Annex IX, section 9.4, testing on short term toxicity on terrestrial organisms does not need to be conducted if direct and indirect exposure of the soil compartment is unlikely. Any uses of the substance involving direct emissions to soil are not foreseen. bis(3,5,5-trimethylhexanoyl) peroxide undergoes extremely rapid hydrolytical degradation (see IUCLID section 5.1.2), hence the substance in itself can be expected not to be present in the environment. In view of the established rapid hydrolysis also indirect exposure of the soil compartment can be ruled out.

Indirect exposure of soil to substance residues, consisting of largely unknown hydrolysis products (except the two identified breakdown products 3,5,5-trimethylhexanoic acid and 2,4,4-trimethylpentan-1-ol) cannot be definitely excluded, although their ready biodegradability has been demonstrated by the OECD 301B test employing the parent substance (which automatically covers any hydrolysis products). Testing is nevertheless considered to be unnecessary for lack of significant exposure: According to Annex XI, section 3.2(a)(ii) and (iii) information requirements may be adapted if "a DNEL or a PNEC can be derived from results of available test data for the substance concerned taking full account of the increased uncertainty resulting from the omission of the information requirement, and that DNEL or PNEC is relevant and appropriate both to the information requirement to be omitted and for risk assessment purposes" and "the comparison of the derived DNEL or PNEC with the results of the exposure assessment shows that exposures are always well below the derived DNEL or PNEC". The risk assessment for substance residues of bis(3,5,5-trimethylhexanoyl) peroxide, using distribution/partitioning data on the representative worst case degradation product 3,5,5-trimethylhexanoic acid , and a PNEC derived from aquatic ecotoxicity data through the equilibrium partitioning method, again using partitioning data for this breakdown product, has resulted in RCRs for soil being consistently lower by a factor of at least 2 than the RCRs for the aquatic compartment. This is the case with all exposure scenarios.

Therefore, it can be concluded that the risk for the terrestrial compartment is invariably significantly lower than for the aquatic compartment, based on an established extrapolation method. Furthermore, since both 3,5,5-trimethylhexanoic acid and 2,4,4-trimethylpentan-1-ol have a low potential for adsorption to soil (Koc = 30.38 L/kg for 3,5,5-trimethylhexanoic acid, with 2,4,4-trimethylpentan-1-ol being even less adsorptive), use of the equilibrium partitioning method instead of toxicity testing is justified, in full accordance with Annex IX, section 9.4.