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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

In a ready biodegradability test the substance was found to be 66% degraded after 28 days, but failed to meet the 10-day window. An inherent biodegradability test was conducted and the substance was found to be 85% degraded after 28 days. Thus, the substance is considered to be 'readily biodegradable, but failing 10-day window' and has also been shown to be inherently biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable but failing 10-day window

Additional information

Ready biodegradability

A 28-day ready biodegradability study was conducted according to OECD guidelines in order to determine the biodegradability of the n-hexyl acetate. The test substance was suspended in a mineral medium at a concentration of 2.9 mg/l with an activated sludge inoculum. Blank inoculum, reference substance and toxicity control treatments were also used during this test. Test vessels were incubated in the dark at 20 ± 1oC and the dissolved oxygen content was measured on days 7, 14, 21 and 28. The biodegradation of the substance was determined based on the depletion of dissolved oxygen during this time.

The results for the reference substance and toxicity controls proved the test was valid. After 28 days the test substance was found to be 66% degraded. However the 10-day window was not achieved. As such the test substance falls into the category of 'readily biodegradable, but failing 10-day window'.

Inherent biodegradability

The inherent biodegradability of hexyl acetate was determined by a manometric respirometry test according to OECD guideline 302 C. Dilutions of 30 mg/l hexyl acetate were created using inoculated medium. These were stirred and incubated at 25oC for 28 days and the rate of oxygen consumption measured using a Bioscience BI-1000 respirometer. The amount of oxygen taken up by the microbial population during biodegradation of the test substance was expressed as a percentage of the theoretical oxygen demand (ThOD) in order to determine the percentage of the test substance degraded.

The reference substance was 95% degraded within 14 days, confirming the activity of the inoculum. The test substance was found to be 85% degraded after 28 days. As such the substance can be classified as inherently biodegradable.