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Biodegradation in water: screening tests

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Description of key information

The substance cannot be concerned to be readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

Regarding biodegradation in water (screening tests) only QSAR estimations are available for the substance Benzenepropanoic acid, 3,5 -bis(1,1 -dimethylethyl)-4 -hydroxy-,C7 -9 branched alkyl esters (CAS 125643 -61 -0). The first prediction was performed with the help of the EPIWIN software BIOWIN v4.10, developed by US-EPA (Chemservice S.A., 2011). The program calculates with seven different models: Linear Model (Biowin 1), Non-linear Model (Biowin 2), Ultimate Biodegradation Timeframe (Biowin 3), Primary Biodegradation Timeframe (Biowin 4), MITI Linear Model (Biowin 5), MITI Non-linear Model (Biowin 6) and Anaerobic Model (Biowin 7). The overall result gives the ready biodegradability prediction of the desired compound. According to the Linear Model the substance is biodegrading fast, whereas the non-linear Model predicts the opposite. The Ultimate Biodegradation Timeframe is given in months, and the Primary Biodegradation Timeframe shows weeks. Both MITI Models predict that the substance is not readily biodegradable, which is also the prediction as overall result. Also under anaerobic conditions the substance is suspected to be not biodegraded fast.

There are two structurally similar chemicals whose data on biodegradability were used in the read-across. For the first read-across substance, Butyl 3,5 -bis(1,1 -dimethylethyl)-4 -hydroxybenzenepropanoate (CAS 52449 -44 -2) three experimental results (key studies with reliability 1) are available, concluding that the substance is neither readily nor inherent biodegradable. All studies were conducted in compliance with the Principles of Good Laboratory Practice (GLP) and the validity criteria of the corresponding guidelines were met, respectively.

One study was conducted in compliance with the Guidelines for Testing of New Chemical Compounds (Kanhogyo No.5, Yakuhatu No.615, 49 Kikyoku No.392, 1974; revised in 1986 and 1987) under Japanese GLP compliance (Furukawa, 2000). The test substance was exposed to standard activated sludge in an automatic electrolytic BOD meter. Biochemical Oxygen Demand (BOD) was investigated for a period of 28 days and afterwards the Dissolved Organic Carbon (DOC) as well as the test substance in the bottles was measured. The test concentration was 100 mg/L, activated sludge was used as inoculum with a concentration of 30 mg/L. The average degradability was 13 % (based on BOD). The average disappearance rate of the test substance was 81 %. In conclusion, the test substance can be considered as not readily biodegradable. The test substance was hydrolyzed into water soluble carboxylic acid and alcohol, which was indicated by the fact that the measured DOCs were not zero and in HPLC chromatograms a new peak appeared and the peak of the test substance decreased. The produced alcohol was biodegraded by the activated sludge.

Another experiment to investigate the "readily biodegradable" potential of the substance was conducted according to OECD guideline 301B (Mead, 2000). As test species a mixed population of activated sewage sludge microorganisms was used, collected at a predominantly domestic sewage plant. The control as well as standard material (sodium benzoate) and test material vessels were prepared each in duplicate. The test material plus standard material in inoculated culture medium plus 100 mg silica gel acted as toxicity control (one vessel only). Each test vessel was inoculated with the prepared inoculum at a final concentration of 30 mg suspended solids (ss)/L. The study was carried out in a temperature controlled room at 21 °C, in darkness. The vessels were closed and CO2 -free air bubbled through the solution at a rate of approximately 40 mL/min with continuous stirring. CO2 as well as DOC (Dissolved Organic Carbon) analysis was performed during the study period. Sodium benzoate attained 71 % degradation after 28 days thereby confirming the suitability of the inoculum and test conditions. The toxicity control attained 33 % degradation after the study period thereby confirming that the test material was not toxic to the sewage treatment microorganisms used. The total CO2 evolution in the control vessels on day 28 was 40.14 mg/L ( = 120.41 mg/3 L). The test material attained 6 % degradation at day 28 and therefore cannot be considered as readily biodegradable.

An experiment concerning an inherent biodegradation potential was conducted under Japanese GLP compliance according to the "Guidelines for Testing of New Chemical Compounds (Kanliogyo No.5, Yakuhatsu No.615, 49 Kikyoku No.392, 1974; revised in 1998)", except that concentration of the test substance was 30 mg/L and that of the standard activated sludge was 100 mg/L (Furukawa, 2001). This method is also known as the "Inherent biodegradability test, Modified MITI test (II) in the OECD guidelines for the Testing of Chemicals No. 302 C. The test substance was exposed to standard activated sludge in an automatic electrolytic BOD meter. Biochemical Oxygen Demand (BOD) was investigated for a period of 28 days and afterwards, the Dissolved Organic Carbon (DOC) as well as the test substance in the bottles was measured. The average degradability was 27 % based on BOD, whereas the average degradability was 73 % based on the residual test substance concentration. In the test suspensions in the ready biodegradability test of the test substance (Furukawa, 2000; described before), the test substance remained about 20 % and HPLC chromatograms showed a new peak which was considered as the water soluble carboxylic acid derivative of the test substance. The inherently biodegradability test had been expected to accelerate biodegradation of the test substance and that the test substance would completely change to the water soluble carboxylic acid. However, this study unexpectedly revealed that on day 28, both peaks of the test substance and carboxylic acid appeared on HPLC chromatogram and the residual test substance concentration was about 30 % similar to in the ready biodegradability test and it can be concluded that the test substance is not inherently biodegradable.

The second read-across substance, Benzenepropanoic acid 3,5 -bis(1,1 -dimethylehtyl)-4 -hydroxy-2 -ethylhexylester (CAS 144429-84-5) met the criteria for "inherent and primary degradability" under the test conditions of the OECD guideline 302C (Zhang, 2009). The study was conducted under SEPA Good Laboratory Practice Standards (HJ/T 155-2004) and last for 28 days. As inoculum a mixed sample of sludge, surface oil, water etc. was collected at ten different sites, mainly in areas where a variety of chemicals were used and discharged (e.g. sewage plant works, rivers, and lakes). Aniline was chosen as reference, attaining 73.6 % degradation after the incubation period. The test vessel received the prepared inoculum at with a final concentration of 30 mg suspended solids (ss)/L. The study was carried out at 20 +/- 0.5 °C in darkness. As evaluation criterion the Biochemical Oxygen Demand (BOD) was chosen and was recorded daily. The test material attained 45.8 % degradation at day 28, thereby exceeding the pass level of 20 %.

Predictions by grouping chemicals in categories was performed with the OECD QSAR Toolbox by Chemservice S.A. (2011). There was one analogue substance found for which data on biodegradability was available. However, the read-across based on data of one chemical can not be considered as reliable and is therefore not considered in the risk assessment. Uploading the experimental results of two nearest analogues (CAS 52449 -44 -2 and CAS 144429 -84 -5) in the software the prediction resulted in 34.6 % degradation. According to the scaling of Toolbox such a result ends in "not ready biodegradable".

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