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Biodegradation in water: screening tests

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Description of key information

Readily biodegradable

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

No reliable studies on the ready biodegradability is available on the the target substance. For this reason data on Similar Substamce 01 was taken into account. More details about the similarity between the two substances is reported in the assessment attached.

A study on the Target Substance is however available on its inherent biodegradability and an additional study, with insufficient details (Muller 2001), is also available confirming the readily biodegradability of the Target Substance.

In the study of Mendel (2002), considered as the key study of this end-point, the authors assessed the ready biodegradability and the biodegradability with adapted bacteria of Similar Substance 01. The study was performed in accordance with the later published guideline OECD 301D (Ready Biodegradability - Closed bottle test).

The concentrations of test substance used were 2.4, 8.0, 24 and 80 mg/L. During the testing period the biodegradation was followed based on the reduction of dissolved oxygen. The degree of biodegradation was calculated by the amount of oxygen taken up by the micro-organisms under these testing conditions (corrected with the uptake of the blank inoculum) and expressed as a percentage of the theoretical oxygen demand (ThOD). Furthermore also an inoculum blank, procedure control and emulsifier W control were included.

At concentrations of 8 mg/L and higher toxic effects were observed after 20 days (without adaptation) and after 10 days (with adaptation). Furthermore, the dissolved oxygen was emaciated with the adapted inoculum at concentrations of 24 and 80 mg/L of test substance after 10 days and at concentrations of 8 mg/L and greater after 20 days.

The percentage of degradation , concentration 2.4 mg/L, with the non-adapted inoculum was 0, 0 and 72.7 % after 5, 10 and 20 days respectively, thus confirming the 10 -day window. Consequently the test substance can be considered as readily biodegradable.

In an inherent biodegradability test (Voelskow 2009), the authors tested an hydrolyzed solution of 4 -chloro-benzotrichloride under aerobic conditions according to DIN 38 412 Part 25, which is similar to the OECD Guideline 302B (Inherent Biodegradability: Zahn-Wellens/ EVPA Test). As an inoculum, non adapted activated industrial sludge was used and exposed to 821.2 mg/L of 4 -chloro-benzotrichloride. In total the DOC removal in three vessels was followed during 21 days. One vessel contained the test substance and inoculum (start concentration 821.2 mg/L test material), a second vessel contained inoculum alone, and a third contained reference compound and inoculum.

Under the test conditions biodegradation of the reference substance diethylene glycol wa smore than 80% after only 6 days and for the test substance a biodegradation was observed above 70%. Thus, at this level of information the test substance can be considered as inherently biodegradable.