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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

In the present OECD 309 study the aerobic mineralisation of dimethyldiphenylether isomer mixture is investigated under aerobic conditions according to the OECD-Guideline 309 using surface water from a natural lake and 14C-labelled test item.

The current status of the study and the circumstances which have caused a temporal delay of the study are described in the attachment of the waiver entry for the OECD 309 study in this section as well as in the dossier header.

Key value for chemical safety assessment

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Status of 2015:

In accordance with REACH Annex IX, section, column 1, studies on sediment simulation testing are only needed for substances with a high potential for adsorption. Furthermore, in accordance to column 2 studies need not to be conducted if substances are either readily biodegradable or if direct and indirect exposure of soil is unlikely. Ditolyl ether has a log Koc of 4.0 which indicates a high potential for adsorption. Thus, according to column 1 soil simulation testing would in general be required. As ditolyl ether showed biodegradation with 2-3 % both in a study on ready as well as on inherent biodegradation this criterion of column 2 would also indicate the need of a soil simulation study.

The second criterion of column 2 is partly fulfilled. Ditolyl ether is manufactured and used at industrial sites only. There is no professional or consumer use. Thus, emissions can be assumed to be controlled and unintended release during normal operations can be excluded. Furthermore, manufacture and uses take place in a closed or strictly closed system which, in addition, makes emissions to the environment (in particular the soil compartment) even more unlikely. All waste from manufacturing and uses (including maintenance) has to be incinerated to completely eliminate the substance. Waste gas has to be incinerated or treated to completely remove the substance. There is no waste water from the use scenarios. However, there is waste water from manufacturing the substance which is transferred to an industrial STP. As described in CSR chapter 9.1 (Manufacture of ditolyl ether) there is no emission to air from the STP, and sewage sludge from the industrial STP is incinerated and not applied to land. As STP effluent concentrations were below the limit of quantitation a realistic worst case was used in the quantitative risk assessment assuming an emission of 1 kg ditolyl ether per day to surface water. The risk assessment in CSR chapter 9.1 demonstrated that the RCR = 0.001 and that the risk from manufacturing ditolyl ether is adequately controlled with respect to freshwater as well as marine sediment.

Although, formally the waiving criteria as defined in REACH Annex IX, section, column 1 and 2, are not fulfilled sediment simulation testing is not considered to be needed or justified anyway. An additional study on sediment simulation testing would only be essential if it was not possible to conclude on the persistence of ditolyl ether from the available data. However, with two screening studies being available demonstrating that the substance is neither readily nor inherently biodegradable (2-3% biodegradation) there is no need for clarification. The risk assessment being based on the assumption that the substance does not biodegrade is a worst case assessment.

Concluding, a sediment simulation study would not improve the database on ditolyl ether or clarify uncertainties. Such a study is, therefore, neither justified nor needed.