Bis(3,5,5-trimethylhexanoyl) peroxide

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.073 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

0.073 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

7.3 µg/L

Assessment factor:

1 000

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

75 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

0.48 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.048 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

0.054 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Conclusion on classification

Bis(3,5,5-trimethylhexanoyl) peroxide is readily biodegradable (75 % within 28 days, however failing the 10-day-window criterion).

Furthermore, 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. 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.

Measurements of total dissolved organic carbon in ecotoxicity tests show increasing DOC concentrations over time, supporting the hypothesised formation of degradation products with higher water solubility and lower log P_ow. In a worst case approach the assessment of environmental hazards 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 P_ow of 3.34 (QSAR estimate), whereas the other identifiable degradation product 2,4,4-trimethylpentan-1-ol has a log P_ow of only 2.62.

Thus, in view of the rapid hydrolytical degradation, the partitioning and distribution properties of any breakdown products are relevant, instead those of bis(3,5,5-trimethylhexanoyl) peroxide itself, since the parent is not expected to be present in the environment.

The hydrolysis behaviour of bis(3,5,5-trimethylhexanoyl) peroxide implicates that aquatic toxicity tests are inevitably performed on environmentally relevant degradation products of the parent. Thus, it is justified to use distribution parameters, e.g. log P_ow or Koc, for modelling the environmental fate, combined with ecotoxicity endpoints obtained from studies where bis(3,5,5-trimethylhexanoyl) peroxide itself was employed, since toxic effects are in fact exerted by the mixture of breakdown products formed hydrolytically during preparation of test solutions.

Acute toxicity values are available for all three trophic levels. The lowest aquatic acute toxicity value is reported for fish (Danio rerio (96 -h LC₅₀ = 7.3 mg/L; geometric mean measured concentration). Chronic toxicity data are not available for the substance. Therefore, the assessment is performed on the basis of acute toxicity data, and the substance is classified accordingly.

A comparison of the lowest acute toxicity value LC₅₀ = 7.3 mg/L with the environmental classification criteria shows that the substance does not qualify for classification as hazardous to the aquatic environment, based on acute (short-term) aquatic hazards: The LC₅₀ is in the range of >10 to ≤100 mg/L, but the substance including its hydrolysis products neither fulfils the “not rapidly degradable” provision nor are there indications of a log Pow ≥ 4, based on QSAR calculations. Likewise, there are no indications suggesting the need for a “safety net” classification (category “Chronic 4”).