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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Ethanol:
Fresh water: Readily biodegradable (2 studies), inherently biodegradable (1 study)
Salt water: readily biodegradable (1 study)
Anaerobic conditions: degradable, complete mineralisation (1 study)
Isopropanol:
The substance has a BOD5/ThOD ratio of 0.50, and is therefore considered to be readily degradable.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

There are no data available for the reaction mass.

Ethanol:

The biodegradation of ethanol was assessed at a number of concentrations using a non-adapted domestic sewage inoculum in a freshwater medium using a 20 day study. Rapid degradation was observed. In a study that used a method based on a proposed improvement to a Sturm guideline study to make it more suitable for volatile substances, ethanol was shown to be readily biodegradable. In both cases, degradation well in excess of 60% was seen with 5 days. Based on the results of these studies, ethanol meets the criteria to be classified as readily biodegradable.

The biodegradation of ethanol was assessed at a number of concentrations using an inoculum prepared from natural salt water and boosted with non-adapted domestic sewage inoculum in an artificial salt water medium. Degradation was observed to a level of 75% over 20 days and 68% in 10 days. This results shows it meets the requirement for designation as readily biodegradable in sea water.

In a study to assess the biodegradability of ethanol under anaerobic conditions, ethanol was exposed to methanogenic bacteria derived from an aquifer slurry. Degradation was followed by measuring the pressure increase through emissions of CH4 and CO2 and, at the end of the study, by GC analysis to quantify the amount of methane produced. After a lag time of 25 -30 days, methane emissions equivalent to 91% mineralisation was eventually seen (after an unquantified time) indicating biodegradability under anaerobic conditions.

The biodegradation data suggests a half life of around 3 days in water, which compares to other an estimated river half life of 6.5 -26 hours and a half life for aerobic degradation of 26 -104 hours.

Isopropanol:

The BOD5 (non-adapted), BOD5 (adapted) and COD of the substance were reported by Bridié et al. (1979) to be 1.19 g O2/g, 1.72 g O2/g and 2.23 g O2/g, respectively.  The BOD test was conducted in accordance with the standard dilution method (APHA "Standard Methods" No. 219 (1971)) at 20 ± 1ºC for a period of 5 days. The only deviation from the APHA standard was the addition of 0.5 mg/l allylthiourea in each test to prevent nitrification. 500 ml test solutions were seeded with a filtered 10 ml volume of the effluent from a biological sanitary waste treatment plant. The authors reported that in some cases an adapted seed was prepared and used, although in no case was inducement of adaptation tried exhaustively. Duplicate tests were run on a mixture of glucose and glutamic acid, as recommended in the APHA method, as a means of checking the activity of the inoculum. The COD test was conducted in accordance with the standard potassium dichromate method described in ASTM D 1252 -97 (reapproved 1974). The BOD5/COD ratios from these results are 0.53 (non-adapted) and 0.77 (adapted). As indicated in the REACH Endpoint Specific Guidance section R.7.9.5.1; whereno other measured degradability data are available,BOD5 datacan be used for classification purposes, but where the chemical structure is known, a calculated theoretical oxygen demand (ThOD) value should be used instead of the COD. According to Annex IV of OECD 301, the ThOD of this substance can be calculated to be 2.40 g O2/g, which gives BOD5/ThOD ratios of0.50 (non-adapted) and 0.72 (adapted). The value for non-adapted seed equals 0.5, at which level or above a substance can be considered to be readily degradable.

Therefore it can be concluded that the reaction mass also can be considered readily biodegradable.