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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

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

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

A study was conducted to evaluate the ready biodegradability of the test material in accordance with the standardised guideline OECD 301B under GLP conditions. The study was assigned a reliability score of 1 in accordance with the criteria for assessing data quality set forth by Klimisch et al. (1997).

The test substance was added as a solid adsorbed to silica dispersed through the test system. Buffered mineral salts medium was added to give a test substance concentration equivalent to 15 mg organic carbon/L. The medium was inoculated with microorganisms (30 mg/L) derived from a sample of activated sludge not previously intentionally exposed to the test substance. Test vessels were incubated in darkness at 22 ± 2 °C for 28 days and their contents continuously sparged with a supply of CO2-free air. The exhaust air from each vessel was passed through a series of traps containing a barium hydroxide solution, to trap evolved CO2.

At regular intervals during the incubation, traps were detached and their contents titrated with hydrochloric acid to determine the quantity of CO2 evolved from the respective test vessels. At the end of incubation, 28 days, the test vessel contents were acidified to release any residual CO2 that may have remained in solution. Titration of the traps was performed following overnight aeration.

The procedure and the activity of the inoculum were checked by measuring the CO2 evolved from vessels containing a reference substance, sodium benzoate. An additional vessel containing a combination of the test and reference substances served as a toxicity control to assess whether the test substance was inhibitory to biodegradation at the test concentration. Two blank control vessels were also prepared containing inoculated medium only. The results of these vessels were used to check the validity of the test and to correct the evolved CO2 values.

The test material showed a mean 2 % biodegradation at the end of the incubation and acidification. As a result, the test material cannot be considered readily biodegradable.

Mean total CO2 production in the blank control vessels was 45.5 mg (30.3 mg/L) at the end of the test (Day 28), satisfying the validity criterion of < 40 mg/L.

Mean biodegradation of the reference substance had exceeded 60 % by Day 6 and had reached a maximum of 97 % by the end of the incubation (day 28). The rate of biodegradation of the reference substance in the presence of the test material (46 % at

Day 6, 92 % by the end of the test) was subject to a slight initial lag phase but comparable to the reference substance alone by the end of the test. This suggests that the test material had only a minor inhibitory effect on the sludge microorganisms over the full duration of the test.

All validity criteria were satisfied excluding the inorganic carbon content of the test medium to be less than 5 % of the total carbon which did not affect the outcome of the study.

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