Registration Dossier

Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Reference
Endpoint:
bioaccumulation in aquatic species: fish
Data waiving:
other justification
Justification for data waiving:
the study does not need to be conducted because direct and indirect exposure of the aquatic compartment to the substance is unlikely
Justification for type of information:
The performance of a study on bioaccumulation in fish was considered scientifically not justified.

REACH Regulation No. 1907/2006, Annex IX, Sect. 9.3.2, Col. 2, states as follows: “9.3.2: The study need not to be conducted: - if the substance has a low potential for bioaccumulation (for instance a log Kow ≤ 3) and/or a low potential to cross biological membranes, or direct and indirect exposure of the aquatic compartment is unlikely. ”

Direct and indirect exposure of the test item to surface water is highly unlikely. Due to the unstable nature of organic peroxides, it can be assumed that upon contact with water and organic matter, the test item undergoes degradation resulting in the formation of respective alcohols and acids. Hydrolysis half-life of TBPND was determined to be < 24 or even 12 h at different pH values and 25 °C. Therefore, an abiotic degradation of the test item in the environment is expected.

In addition, TBPND is considered as inherently biodegradable based on a Closed Bottle Test according to OECD 301 D (26 % degradation after 28 days, 53 % after 140 days, please refer to IUCLID section 5.2.1). New data for other peroxyesters were recently generated. Those revealed that surface water does not change the degradation products or behavior compared to hydrolysis studies in water/buffer. It is therefore proposed to first invest more in clarifying the biodegradation potential of the compound before considering further testing on bioaccumulation properties.
For this reason a new prolonged closed bottle test was initiated. Preliminary results of a non-GLP enhanced closed bottle test revealed 65 % degradation after 28 days. In ready biodegradability tests, the time window concept has been introduced as a simple alternative to quantify the rate of biodegradation. However, this concept is only applicable and valid for single water-soluble chemical substances. TBPND is a chemical in which two moieties are linked together. Upon hydrolysis tert-butanol and 7,7-dimethyloctanoic acid require the concerted action of at least two microorganisms as a single organism usually lacks the full complement of enzymatic capabilities. It can be expected that those two moieties usually do not have identical lag periods. Instead, sequential degradation is the case. Biodegradation curves of peroxyesters, such as TBPND, should therefore not be used to assess a 10- or 14- day effect.
The new data on biodegradation will be included in the dossier as soon as the GLP compliant study is concluded and study report is available. A second test with the respective hydrolysis product (neo¬decanoate, UVCB) will be performed depending on the outcome of the first test, as the data for the registered mono-constituent neodecanoic acid are not applicable and sufficient data for tert-butanol are available. Depending on the outcome in a second step a Zahn-Wellens test is foreseen as positive results for other organic peroxides were noted. According to ECHA Guidance on Information Requirements and Chemical Safety Assessment Chapter R11: PBT/vPvB Assessment inherent biodegradability of a substance is proof enough for considering the substance as not P or vP. Based on preliminary results, TBPND could even be considered as readily biodegradable.


The very low exposure of the water compartment is further based on the following facts:
Organic peroxides, when released into the sewage of a plant production or a downstream user’s plant, are treated with other substances in dedicated sewage treatment plants. The activated sludge stemmed from these sewage treatment plants are then extracted and treated as chemical waste. From the production plant, the release of organic peroxide into the sewage is very limited, not to say completely negligible. The waste water from production plant can be treated on site (at least a physical/chemical treatment, which will neutralize potential residual organic peroxide), which is usually followed by a biological treatment. Regarding the rest of the lifecycle, organic peroxides are mainly used as cross-linking agent/polymerization initiator for the production of resins/rubbers/polymers. Based upon the fact that organic peroxides are totally consumed during the process (>99%, which is confirmed by the release factor to sewage for curing agents from ESD n°3), the surface water is not exposed to organic peroxides via the waste water system. As a consequence, the surface water is not considered to be significantly exposed by the test item.

In addition, bioaccumulation potential was estimated by QSAR calculation for the parent compound. The substance was within the applicability domain of the model and thus fulfilling validity criteria of the QSAR calculation. A calculated BCF value of 925 L/kg was obtained, being well below the threshold value of 2000 L/kg for the B criterion. This further indicates no concern in regards to bioaccumulating potential of TBPND. The first hydrolysis product, tert-butanol (CAS 75-65-0), was not investigated for its bioaccumulating potential. However, its logPow was determined to be 0.3. Tert-butanol is therefore not considered of concern in regards to bioaccumulation (logPow < 4.5, please also refer to disseminated information of REACH Registration Dossier of tert-butanol). A BCF study is available for 7,7-dimethyloctanoic acid, the other hydrolysis product, stating a BCF of < 225. Therefore, no bioaccumulating potential is expected for both hydrolysis products.

In conclusion, according to REACH Annex IX, Sect. 9.3.2, Col. 2 the study does not need to be conducted as exposure to the aquatic environment is unlikely, as outlined above. Further, the substance is at least inherently, but likely readily, biodegradable (see preliminary non-GLP study results described above) and thus not considered to be P or vP. Therefore, testing on bioaccumulation properties in regards to PBT or vPvB assessment is also not applicable. In addition, QSAR calculation of the parent compound as well as available data of the hydrolysis products indicate no concerns in regards to bioaccumulation potential.
Based on these points testing for bioaccumulation is considered neither scientifically justified nor reasonable. And for animal welfare reasons no test is proposed for bioaccumulation in fish.

Description of key information

The performance of a test for bioaccumulation in aquatic species, preferably fish, is scientifically unjustified. REACH Regulation No. 1907/2006, Annex IX, Sect. 9.3.2, Col. 2, states as follows: “9.3.2 The study need not be conducted if:

- the substance has a low potential for bioaccumulation (for instance a logKow<= 3) and/or a low potential to cross biological membranes, or

- direct and indirect exposure of the aquatic environment is unlikely. ” Direct and indirect exposure of the test item to water is highly unlikely. Due to the unstable nature of organic peroxides, it can be assumed that upon contact with water and organic matter, the test item undergoes rapid degradation resulting in the formation of respective alcohols and acids. Therefore, TBPND was considered to have no bioaccumulation potential. Using EPIWIN 4.1 a BCF of 925 L/Kgwwtwas calculated indicating no potential for bioaccumulation.

Key value for chemical safety assessment

Additional information