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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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biodegradation in water: simulation testing on ultimate degradation in surface water
Data waiving:
study scientifically not necessary / other information available
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other:
Justification for type of information:
The performance of simulation test on biodegradation in surface water was considered scientifically not justified.

REACH Regulation No. 1907/2006, Annex IX, Sect. 9.2 Col. 2, states as follows: “9.2. Further biotic degradation testing shall be proposed by the registrant if the chemical safety assessment according to Annex I indicates the need to investigate further the degradation of the substance and its degradation products."

The chemical safety assessment does not indicate the need to further investigate the biodegradation of the substance for the following reasons:

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 20 °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 a simulation test.

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.

Based on the hydrolysis study, t1/2 at pH4 and pH7 is 8 and 9 h at 25°C, respectively. Thus at the relevant temperature and pH values of aquatic toxicity tests the t1/2 is below 12 h.
Taken together, this is also the reason to elaborate the bio-degradation potential further.

Further, Environmental Risk Assessment revealed safe use of the substance throughout its whole life cycle due to very low exposure of the water compartment which is especially 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 conclusion, simulation testing on ultimate degradation in surface water is considered not scientifically justified since the chemical safety assessment does not indicate the need to further investigate the degradation properties of the substance according to REACH Regulation No. 1907/2006, Annex IX, Sect. 9.2 Col. 2. Further, the substance´s inherently biodegradability is recently further assessed and testing strategy will be depending on the studies outcome.

Description of key information

The performance of simulation tests for biodegradation in water and sediment is scientifically unjustified. REACH Regulation No. 1907/2006, Annex IX, Sect. 9.2.1.2, Col. 2, states as follows: “9.2.1.2: The study need not to be conducted: - if the substance is readily biodegradable, or - if direct and indirect exposure of sediment is unlikely. ” Direct and indirect exposure of the test item to water and sediment 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.Furthermore,TBPND was considered to be inherently biodegradable, therefore simulation testing for biodegradation in water was considered not scientifically justified.

Key value for chemical safety assessment

Additional information