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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, and the 14-day window which applies to closed bottle tests was met. 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'.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

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. Graphical interpolation indicated that the 14 -day window applicable to this test had been met. As such, the substance is considered to be readily biodegradable.

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.

QSAR estimation of biodegradability

A QSAR estimation of the biodegradability of hexyl acetate was conducted using Biowin v4.10. The following SMILES and chemical structure was used: O=C(OCCCCCC)C

All of the models within Biowin v4.10 predict that hexyl acetate will biodegrade quickly. Hence, Biowin v4.10 predicts that the substance is readily biodegradable. This indicates that the structure of hexyl acetate is susceptible to rapid breakdown by environmental microorganisms.