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Biodegradation in water: screening tests

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Description of key information

Not readily or inherently biodegradable

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

A study was performed to assess the ready biodegradability of Thiazol Blau.

The study was conducted in accordance with the OECD Guideline for Testing of chemicals No. 301 F 'Manometric respirometry Test' (adopted July 17, 1992).

A suspension of Thiazol Blau in a mineral medium was inoculated and incubated for 28 d under aerobic conditions. During this period, degradation was followed by BOD determinations.

Test item showed: 4 % degradation after 28 days

Therefore, Thiazol Blau is considered to be "Not Readily Biodegradable".

The control substance monoethylene glycol showed 82 % degradation after 14 days, proving the validity of the test system.

In addition, a study for inherent biodegradability of Thiazol Blau was performed according to the OECD Guidelines for the Testing of Chemicals, Inherent Biodegradability: Modified MITI Test.:OECD, Adopted 12 May 1981.

30 mg/L Thiazol Blau was dissolved with acetone, and some acetone solution of test substance was added to the flask. The acetone volatized completely and the test substance remained absorbed to the bottom and inner surface of the flask uniformly.

At the end of the test, BOD of inoculum blank and volatile solvent control was 53.44 mg O2and 54.33 mg O2respectively, with little difference. The results revealed that there was no biodegradation occurred in the volatile solvent control group, which proved that the solvent acetone was volatile completely and did not affect the test system. Therefore, the data of the data of volatile solvent control was used to calculate the percentage biodegradation. In order to investigate the effect of the volatility of acetone on the test substance, the recovery of the test substance was measured as 102%, so the test substance was not lost evidently during the volatile process. And the residual amount of the test substance could meet the requirement of the test guideline.

At the start of the test,NO2--Nconcentrations of the test suspensions,inoculum blank andvolatile solvent control were <0.03mg/L.NO3--Nconcentrations of the test suspensions,inoculum blank andvolatile solvent control were 0.04mg/L. At the end of the test,NO3--N concentrations of the three test suspensions, inoculum blank andvolatile solvent controlwere6.31mg/L, 5.85mg/L, 5.69mg/L (3 replicates), 6.56mg/L and 6.06mg/L, respectively;NO2--N concentrations of the test suspensions, inoculum blank andvolatile solvent control were <0.03mg/L.Theresultsrevealed that there was nitrification in test suspensions 1 while not nitrification in test suspensions 2, 3.

Results of recovery tests showed that the percent recovery of the test substance from water + test substance was 88.4% and the recovery from test medium + inoculum + test substance was 84.0% at start of the study.

At the end of the test, the residual content of test substance of abiotic control and the three test suspensions were 13.9mg and 14.2mg, 14.0mg and 13.6mg (3replicates), respectively. Considering the extracting efficiency,the reduction of the test substance in abiotic control might be due to the loss during extraction process of test substance but not non-biodegradation. The percentage primary biodegradation of test suspensions was 0%.

The percentage primary biodegradation of test suspensions were 0%, 0% and 2.0% (3replicates).

The percentage biodegradation at the end of the test by BOD was 0%

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