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Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Biodegradation in water

The test material was determined not to be readily biodegradable in both a CO2 evolution test and in a manometric respirometry test but was considered to be inherently biodegradable in the manometric respirometry test.

Additional information

Two studies were conducted to assess the ready biodegradability of the test material in water. Both studies were conducted in accordance with standardised guidelines and under GLP conditions. Therefore both were assigned a reliability score of 1 in accordance with the criteria for assessing data quality set forth by Klimisch et al. (1997).

The ready biodegradability of the test material was investigated in accordance with the standardised guideline OECD 301 F under GLP conditions using the manometric respirometry method.

Fresh activated sludge collected from a biological waste water plant for domestic sewage was washed three times in the mineral medium (by centrifuging at 1000 g for 10 minutes, discarding the supernatant and re-suspending in mineral medium) and kept aerobic until being used on the same day. The sludge was exposed to the test material in duplicate at a nominal concentration of 100 mg/L for a period of 28 days at 22 ± 1 °C. The biodegradation was followed by the oxygen uptake of the microorganisms during exposure.

As reference, sodium benzoate was tested simultaneously under the same conditions and functioned as a procedure control. Additionally, flasks containing both the test and reference materials were run in parallel and acted as toxicity control.

The test material undergoes 66 % biodegradation after 29 days (65 % after 28 days) in the test conditions. Biodegradation really starts on day 14 and reaches only 56 % at the end of the 10-day window (days 14 to 24). Thus, test material should be regarded as not readily but inherently biodegradable according to this test.

No toxic effect of test material to the micro-organisms at the test concentration was observed. Degradation of sodium benzoate exceeds 40 % after 7 days and 65 % after 14 days: the activity of the inoculum is thus verified and the test is considered as valid.

Under the conditions of this study, the test material was determined not to be readily biodegradable but it is considered to be inherently biodegradable.

The ready biodegradability of the test material was investigated in a CO2-evolution test conducted in accordance with the standardised guidelines OECD 301 B and EU Method C.4-C under GLP conditions.

The test system was a microbial inoculum of activated sludge obtained from a municipal sewage treatment plant. The sludge (suspended solids concentration 3.4 g/L) was exposed to the test material in duplicate for a period of 28 days at 22 ± 1 °C. The biodegradation was followed by the carbon dioxide evolution of the microorganisms during exposure. As reference, sodium acetate was tested simultaneously under the same conditions and functioned as a positive control. Blank and toxicity controls were run concurrently.

Since the solubility of the test material was below 1 g/L, weighed amounts of the test material were added to test bottles. Approximately 10 mL of Milli-RO water was added to each weighing bottle and after thoroughly mixing (vortex) the resulting suspension was added quantitatively to the test medium. The test was started by bubbling CO2-free air through the solution at a rate of approximately 1-2 bubbles per second (ca. 30-100 mL/min). The solutions were continuously stirred throughout the test period. The CO2 evolved was trapped by Ba(OH)2 and measured by titration with HCl. Titrations were made every second or third day during the first 10 days, and thereafter at least every fifth day until the 28th day. On the 28th day, 1 mL of concentrated HCl was added to each bottle. The bottles were aerated overnight to drive off CO2 present in the test suspension. The final titration was made on day 29.

The relative degradation values calculated from the measurements performed during the test period revealed 29 and 19 % degradation of the test material for replicates A and B respectively. Thus, the criterion for ready biodegradability (at least 60 % biodegradation was not reached within ten days of biodegradation exceeding 10 %) was not met.

In the toxicity control more than 25 % degradation occurred within 14 days (based on ThCO2). Therefore, the test material was assumed to be not inhibitory on microbial activity. The positive control had achieved 64 % degradation after 7 days and 96 % degradation by the end of the test period.

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