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BIODEGRADATION IN WATER: SCREENING TESTS, Sipos (2015)

The test material was investigated for its ready biodegradability in a Closed Bottle Test over a period of 28 days. The study was conducted under GLP conditions and in accordance to the standardised guidelines OECD 301D, EPA OPPTS 835.3110 and EU Test Method C.4-E.

The study has therefore been assigned a reliability score of 1 in line with the principles for assessing data quality as defined by Klimisch et al. (1997).

The biodegradation was followed by the oxygen uptake of the microorganisms during exposure. As a reference material Sodium benzoate was tested simultaneously under the same conditions as the test material, and functioned as a procedure control.

The test system was a microbial inoculum of good quality, collected from a sewage plant for domestic sewage. The sludge was washed by centrifugation, filtered through cotton wool and aerated until use. Based on the determined dry weight content, the washed sludge suspension contained 4 g dry material per litre.

Under the test conditions the percentage biodegradation of the test material reached a mean of 4.2 % after 28 days based on the measured COD of the test material. Therefore the test material is considered not readily biodegradable.

According to the test guidelines the pass level for ready biodegradability is removal of 60 % COD.

The reference material Sodium benzoate was sufficiently degraded to a mean of 87.5 % after 14 days, and to a mean of 93.3 % after 28 days of incubation, based on ThODNH4, thus confirming the suitability of the used activated sludge inoculum.

In the toxicity control containing both, the test material and the reference material Sodium benzoate, a mean of 40.5 % biodegradation was noted within 14 days and 41.7 % biodegradation after 28 days of incubation.

According to the test guidelines the test material can be assumed to be not inhibitory at the applied concentration level of 6.3 mg/L on the activated sludge microorganisms because degradation was >25 % within 14 days.

Under the conditions of this study, the test material was determined not to be inherently biodegradable.