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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

OECD 301C_modified MITI test: 2 % degradation after 28 days - not readily biodegradable
RA_1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol_EU Method C.4-D: 0 % degradation after 28 days - not readily biodegradable
RA_1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol_OECD 301C: not readily biodegradable
RA_CAS 50530-43-3_OECD 301C: not readily biodegradable

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

The target substance 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-nonanethiol (CAS 91648-65-6) as well as its read across substances 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol (No CAS, no EC) and 5-(dodecyldithio)-1,3,4-thiadiazole-2(3H)-thione (CAS 50530-43-3) were investigated for their biodegradability.

1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-nonanethiol (CAS 91648-65-6) was evaluated as described in OECD Guideline 301C (Katsuura, 1990). Based on the insoluble nature of the test substance, a modified MITI test was carried out. Standard activated sludge was used as inoculum and the initial concentration of test substance was 100 mg/L. After an incubation period of 28 days at 25 °C there was only 2 % biodegradability observed during the test using BOD (Biological Oxygen Demand) as degradation parameter. Using the HPLC method 5 % biodegradability was measured. The test substance was found to be stable under the experimental conditions and can be considered as "not readily biodegradable". The reference substance, aniline, attained 80 % biodegradation during the exposure period in this experiment.

The biodegradability of 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol (No CAS, no EC) was investigated according EU Method C.4-D (“Determination of ‘ready’ biodegradability – Manometric Respirometry”) with GLP compliance (Müller, 1999). The test was performed aerobic with activated test sludge, that was taken from an aeration tank of sewage treatment works Bürrig and pre-adapted with 100 mg/L test substance for 4 weeks immediately before the study was conducted. The sludge was incubated for 28 days with 100 mg/L of the test item in three replicates. Benzoic acid, sodium salt (100 mg/L) served as reference substance, inoculum blanks and toxicity control were also performed. After 28 days, the test substance showed no degradation, whereas the positive control was degraded by 92 % (14 d) and 96 % (28 d), respectively, measured by biochemical oxygen demand. The test substance was non-toxic in the test system, but attained 0 % degradation after 28 days. Although the activated sludge was pre-adapted, no increase of the BOD of the sludge treated with the test item could be observed and hence, no biodegradation of the test item. So, the pre-adaption is negligible in order to assess the validity of the test and the results can be considered reliable. As conclusion, the test substance can be considered as not readily biodegradable.

The same result was attained with this read-across substance in an experiment according to OECD Guideline 301 C ("Ready Biodegradability: Modified MITI Test (I)") (Rheinchemie, no date given). The study was performed on sludge (no more details were given) over 28 d, aniline served as positive control, blank was included and biodegradability was determined by measuring biochemical oxygen demand (BOD) (for 28 days) and dissolved organic carbon (DOC) (at day 28). The positive control was shown to be readily biodegradable (63% on day 7), whereas the test substance must be considered as "not readily biodegradable". The full reliability of the test could not be assigned because it was only available as a short summary

5-(dodecyldithio)-1,3,4-thiadiazole-2(3H)-thione (CAS 50530-43-3) was evaluated using a similar procedure to that described in the current OECD Guideline 301C (Takagi, 1984). Standard activated sludge was used as inoculum and the initial concentration of test substance was 100 mg/L.After an incubation period of 28 days at 25 +/- 1 °C there was no ready biodegradability observed during the test.