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Three acute aquatic studies with Diisobutyryl peroxide according to OECD guidelines, performed under GLP, but without chemical analyses are available for three trophic levels.

Due to the extremely short half-life of the test material determined in the hydrolysis study, the degradation products of the test material were deemed the most relevant for aquatic toxicity. For this reason the test material was loaded to the test medium agitated gently for 24 hours and then used directly for testing. All test concentrations were prepared separately as Water Accommodated Fractions to allow the determination of the toxicity of the resulting degradation mixture as a whole to be determined. It is known that the test chemical degrades to multiple degradation products and is itself present in an isododecane solvent. The effects cannot therefore be attributed to a single component with 100% certainty. However the main degradation product isobutryic acid is the most likely cause of any toxicity that may be observed.  

An acute fish study with Danio rerio according to OECD 203 is available. A loading of 100 mg/L of test material left to degrade for 24 hours resulted in no visible toxicity to the test organisms. A 96h-LL50 could therefore not be determined and may be expressed as LL50 >100 mg/L.

An acute study with Daphnia magna according to OECD 202 is available. A loading of 100 mg/L of test material left to degrade for 24 hours resulted in no visible toxicity to the test organisms in an open system. A 48h-EL50 could therefore not be determined and may be expressed as EL50 >100 mg/L.

In closed conditions the test material was shown to affect invertebrates significantly. In open conditions however no effects were observed. Following identical procedures with identical concentrations of test material. A supporting study was conducted testing open and closed conditions in parallel  to allow direct comparison of these conditions. Supporting studies confirmed that the test substance induced no significant effects up to 100 mg/L loading in open conditions but caused significant effects in closed conditions these were however not sufficient to result in classification.  

A freshwater algae study with Pseudokirchneriella subcapitata according to OECD 201 is available. Effects to algae were observed and a 72h-ErL10 and a 72h-ErL50 were determined. The test material is not of high concern to algae species as the EL50 is 151.2 mg/L of test material, the EL10 is 35.0 mg/L of test material.

For an ErL50 of 151 mg/L a theoretical maximum of 60.4 mg/L of Isobutyric Acid can be formed based  on a diisobutyryl peroxide purity of 40%. However measured company data  indicates that in fully degraded state (in water) 32.4 % of the original peroxide is actually degraded to isobutyric acid. This results in a theoretical 20 mg/L of isobutyric acid present at the ErC50 concentration of 151 mg/L diisobutyryl peroxide. The theoretical ErC50 is 20 mg/L for isobutyric acid, derived from this study. This is a worst case approach as can be concluded from the data summarized below.

Aquatic toxicity data for Isobutyric acid:

Acute fish study with Leuciscus idus 96h-LC50 = 146.6 mg/L (ECHA dossier CAS 79 -31 -2)

Acute Daphnia according to US EPA guideline (EPA-660/3 75 -009, 1975), 48h-EC50 = 51.25 mg/L (SIDS dossier Isobutyric acid, April 2008: BASF AG. (1989) Determination of the acute toxicity of isobutyric acid to the waterflea Daphnia magna Straus. Report 1/0244/2/89-0244/89)

Freshwater algae study 72h-EC50 = 45.1 mg/L (biomass), 72h-EC50 = 44.7 mg/L (fluorescence) (ECHA dossier CAS 79 -31 -2)

An OECD 209 with Diisobutyryl peroxide under GLP is available. The EC50 is 115 mg/L and the EC10 is 47 mg/L. This indicates that the substance is not highly toxic for sewage treatment microorganisms. Due to the instability of the test substance in water and the readily biodegradable degradation products formed, removal is expected to be complete and a sewage treatment plant is unlikely to be adversely affected.

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