Methylthiouracil

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)

GLP compliance:

yes

Specific details on test material used for the study:

Batch manufactured and supplied by : Korde Chemicals Pvt Ltd.
W-13, TTC Pawane,
Navi Mumbai 400705 INDIA

Test item : 6-Methyl-2-thiouracil

CAS No. : 56-04-2

Chemical name (IUPAC) : 6-Methyl-2-sulfanylidene-1H-pyrimidin-4-one

Physical appearance : White powder

Molecular formula : C5H6N2OS

Molecular weight : 142.18 g/mol

Purity as per CoA : 98.46%

Batch No. : 151117

pH 0.1 % : 6.20

Manufactured date : 15 November 2017

Expiry date : 14 November 2019

Recommended storage condition : Ambient (+15 to +25°C)

Notes: a) Date of receipt of test item at test facility: 24 November 2017
b) Test Item code by test facility: K010-01

Oxygen conditions:

aerobic/anaerobic

Inoculum or test system:

activated sludge, domestic, adapted

Details on inoculum:

The inoculum was secondary effluent, collected from a treatment plant receiving predominantly domestic sewage. This effluent was used as test system as it is recommended in the guideline. A fresh sample of secondary effluent was collected from the treatment plant and was kept aerobic during transport.

This effluent was allowed to settle for one hour, decanted and the decanted effluent was used in the test.

Source of the Inoculum

Sewage Treatment Plant
Eurofins Advinus Limited
Bengaluru – 560 058
India

Determination of Bacterial Population in the Inoculum

The bacterial population in the inoculum was determined as colony forming units (CFU/mL) by diluting the inoculum to an appropriate dilution and then plating on nutrient agar plates.

Preconditioning of the Inoculum

The decanted effluent was preconditioned by aerating for 6 days at 22 to 24C.

Parameter followed for biodegradation estimation:

CO2 evolution

Key result

Parameter:

% degradation (CO2 evolution)

Value:

ca. 31.65

St. dev.:

5.07

Sampling time:

10 d

Key result

Parameter:

% degradation (CO2 evolution)

Value:

ca. 29.79

St. dev.:

1.12

Sampling time:

29 d

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

Based on the results, it was concluded that the test item, 6-Methyl-2-Thiouracil is biodegradable but not readily biodegradable as 29.79% mean degradation was achieved at the end of test which is less than 60% pass level in 10-day window period within the 28-d period of the test.

Executive summary:

The ready biodegradability of 6-Methyl-2-Thiouracil was tested using the CO₂Evolution Test. The test item was added to two test vessels at the concentration of 36 mg/L (equivalent to 15.2 mg of Total Organic Carbon/L). Two control treatments containing only the inoculum, one reference item treatment and one toxicity control treatment containing the test item and the reference item were also tested. All the treatments were added with equal volume of inoculum which was collected from the secondary effluent treatment plant receiving predominantly domestic sewage.

 

Treatment mixtures were aerated for 29 days with carbon dioxide (CO₂) free air. The CO₂released was trapped in a series of bottles containing barium hydroxide, which were connected to the outlet of each test vessel. The residual barium hydroxide was measured on Days 3, 6, 8, 10, 13, 16, 20, 24, 27 and 29 after the initiation of the test.

 

The mean per cent degradation of test item was 29.79% at the end of test while, the percent degradation of reference item was 122.67% and the toxicity control was 94.34% at the end of the test. It was observed that the mean degradation of test item,6-Methyl-2-Thiouracilwas 29.79% which is less than 60% pass level in 10-day window period within the 28-d period of the test.

 

The test fulfilled all the validity criteria.

 

Based on the results, it was concluded that the test item,6-Methyl-2-Thiouracilis biodegradable but not readily biodegradable as 29.79% mean degradation was achieved at the end of test which is less than 60% pass level in 10-day window period within the 28-d period of the test.

Description of key information

Based on the results, it was concluded that the test item, 6-Methyl-2-Thiouracil is biodegradable but not readily biodegradable as 29.79% mean degradation was achieved at the end of test which is less than 60% pass level in 10-day window period within the 28-d period of the test.  

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Type of water:

freshwater