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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Several Ready test results are available which will be presented one by one in the additional information section.

Closed Bottle test OECD TG 301D: Not ready biodegradable

Extended Closed Bottle test (OECD TG 301D, non-GLP: Not persistent

MITI test (OECD TG 301C: Not readily biodegradable but full primary degradation into the substance respective acid and alcohol

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed
Type of water:
other: activated sludge

Additional information

Ready biodegradability test, Closed Bottle test in activated sludge

The ready biodegradability was determined in the Closed Bottle test (OECD TG 301D) under GLP. Activated sludge is exposed to 2 mg/l of test substance. At day 7, 14, 21 and 28 days the following degradation rates were measured 0, 0. 2 and 3%, respectively. The substance should therefore be classified as not readily biodegradable. The substance caused a slight inhibition of the endogenous respiration. This test in activated sludge was prolonged (non-GLP) and the test substance was biodegraded by 29% at day 60.

Ready biodegradability test, Closed Bottle test in river water and activated sludge

Introduction and method: The ready biodegradability of Pinyl isobutyraldehyde was investigated in a series of Closed Bottle tests according to OECD TG301D, not under GLP. The goal of this study was to investigate the influence of the source of inoculum and test substance concentration on the biodegradability of the substance. Tests were performed with activated sludge and river water as inocula, and with test substance concentrations of 1 and 2 mg/L.

Results: Inhibition of the endogenous respiration of the inoculum during the first 2 weeks was detected in the presence of the substance independent on the type of inoculum and concentration, except in river water and 1 mg/l concentration no inhibition was seen. The following results were seen at day 7,14, 21, 28, 42, 56 and 70.

Activated sludge 2 mg/l: -2, -2, 1, 5, 12, 32, 66%, respectively;

River water 2 mg/l: -3,-1, 6, 14, 32, 47 and 66%, respectively;

River water 1 mg/l: -1, 0, 2, 18, 54, 73 (at 56 days) and last time point not measured, respectively (key value is underlined).

Discussion and Conclusion: Biodegradation percentages of < 20 were found at day 28 with both river water and activated sludge as inocula. The substance is therefore not readily biodegradable. After 56 to 70 days biodegradation percentage in excess of 60 were found in a prolonged Closed Bottle test. Higher biodegradation rates were found with river water compared to the tests performed with activated sludge as inoculum. A result of >60% was obtained with river water and an initial test substance concentration of 1.0 mg/L and therefore the substance is not persistent.

Ready biodegradability in MITI test:

In order to assess the biodegradation of the substance a modified MITI test according to OECD 301C was performed and a "Method for Testing the Biodegradability of Chemical Substances by Microorganisms" stipulated in the "Testing Methods for New Chemical Substances", was applied under GLP conditions. In this study a mixture of activated sludge (containing samples from surface water and surface soil of rivers, lakes and inland sea, and return sludge from sewage plants) was exposed to 100 mg/L of the substance for 28 days. The validity criteria of the test were met. Though it needs to be noted that in the concentration of the test item in the test exceeded its water solubility (100 versus 10 mg/l, respectively) and the pH was not measured to limit the volatilisation from the test vessels. The test item was measured and ca 85% could be recovered, the ca 15% loss was probably due to volatilisation. The test item was not biodegraded (-1%) during the 28 -days and is therefore not readily biodegradable. The substance slightly decreased the oxygen consumption of the bacteria, which is an indication of the toxicity of the substance or its metabolites. The test item was fully primary degraded and the metabolites were identified: the aldehyde functional group was converted to an acid and/or an alcohol. The concentration of these two could not be quantified and not be distinguished. The pH was not measured to limit the volatilisaton of the test item.