Mesitylene

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:

other: Study carried out was GLP compliant and followed standard guidelines

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
Not applicable

Oxygen conditions:

aerobic

Inoculum or test system:

mixture of sewage, soil and natural water

Details on inoculum:

Mixed inoculum of the aqueous phase of non-adapted activated sludge and pre-treated, non-adapted standard soil.
Activated sludge from the sewage plant at Hildesheim that receives predominantly municipal sewage and hardly any industrial chemical waste. The activated sludge was washed twice with chlorine free tap water. After second washing the settled sludge was resuspended in mineral salts medium and was maintained in an aerobic condition by aeration for 2 hours. Thereafter the sludge was homogenised with a blender. After sedimentation the supernatant was decanted and maintained in aerobic conditions with CO2-free air for 5 days. 10mL/L was used to initiate inoculation.
The standard soil was obtained from LUFA at Speyer. It is well suited as it is a certified and field fresh soil established for biodegradation studies. The soil was mixed with mineral salts medium and shaken on an overhead shaker overnight. Subsequently, the soil was allowed to settle for 3 hours and the supernatant was used as inoculum. The supernatant was maintained in an aerobic condition by aeration with CO2 free air until test start. 7mL/L were used to initiate inoculation.

Duration of test (contact time):

28 d

Initial conc.:

24.2 mg/L

Based on:

test mat.

Initial conc.:

76.2 mg/L

Based on:

ThOD/L

Parameter followed for biodegradation estimation:

other: Biological Oxygen Demand

Details on study design:

- Test vessel: 250 mL test solution in 500 mL brown glass bottle fitted with a rubber sleeve with soda lime to absorb evolved CO2. Bottles were closed with OxiTop measuring heads.
- Test medium: OECD 301F mineral salts medium
- Temperature: 21.3-21.5°C
- pH: 7.64 at start and 7.57 to 7.63 at end in test vessel, 7.65 to 7.69 at start and 7.57 to 7.87 at end in control vessels
- Conditions: Continual stirring in an incubator in the dark
- Observations: Oxygen consumption was measured every 112 minutes. The difference between the test and inoculum control replicates was used to determine the oxygen depletion, with biodegradation calculated as the relation of the BOD to the ThOD. Results were calculated using Sigma Plot SPSS software.
- Replicates: 3 per test treatment
- Functional control: 1 replicate
- Inoculum control: 2 replicates of test medium without test or reference item
- Toxicity control: 1 replicate of test medium with test and reference item

Reference substance:

benzoic acid, sodium salt

Key result

Parameter:

other: ThOD

Value:

61

Sampling time:

28 d

Remarks on result:

other: Mean of three replicates

Details on results:

The first two test item replicates reached the 10% level (beginning of biodegradation) within 12 days and the 3rd test item replicate reached the 10% level on day 15. The 1st test item replicate reached the 60% pass level on day 23 and the 2nd and 3rd test item replicates did not reach the 60% pass level. The mean biodegradation on day 28 was 61% (1st test item replicate was 65% and the 2nd and 3rd test item replicates were 59%). After 28 days, the test item is classified as readily biodegradable but without complying with the 10-day window within the 28-day period of the study.

Results with reference substance:

Functional control reached the pass level for degradation (>60%) within 3 days and came to a maximum of 89% biodegradation after 28 days.
The toxicity control reached 53% after 14 days and 74% biodegradation after 28 days. The validity criterion that the test item should not inhibit the degradation of the reference item was fulfilled.

		Biodegradation [%]
		Study Day [d]
	Replicate	7	14	21	28
Test Item	1	1	25	56	65
	2	1	19	49	59
	3	0	7	41	59
	Mean	1	17	49	61
Functional Control    45 mg/L		75	86	87	89
Toxicity Control       24.2 mg/L Test Item + 45 mg/L Reference Item		38	53	67	74

Validity criteria fulfilled:

yes

Remarks:

Functional control reached 60% by day 3 and toxicity control reached 25% degradation by day 2. On day 28, mean O2 depletion of inoculum control was 28.1 mg/L (<60), pH of all replicates was 6.0-8.5 and difference between test item replicates was 6% (<20).

Interpretation of results:

readily biodegradable, but failing 10-day window

Conclusions:

The test item showed a mean biodegradation of 61 % after 28 days but did not fulfil the 10-day window criterion.

Executive summary:

The testing was carried out following OECD 301F testing guidelines. A mixed inoculum of soil, non-adapted sludge, and water was used. The biodegradation rate was calculated from the biological oxygen demand. A functional control and a toxicity control were carried out. The functional control reached 89 % degradation after 28 days and the toxicty control reached 74 % degradation after 28 days, demonstrating the biodegradation was not inhibited by the test item. The mean biodegradation of the test item was measured to be 61 % after 28 days. 3 replicates were carried out, the 1st achieved 65 %, the 2nd and 3rd achieved 59 % biodegradation after 28 days.

Description of key information

1,3,5-trimethylbenzene is considered to be readily biodegradable but failing the 10 day window (Dr Noack 2016). The mean biodegradation of the test item was measured to be 61 % after 28 days, with the first of the 3 replicates achieving 65 % and the 2nd and 3rd replicates achieving 59 % biodegradation after 28 days.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable but failing 10-day window

Additional information

A GLP-compliant ready biodegradation study following OECD 301F testing guideline is available for 1,3,5-trimethylbenzene (Dr Noack 2016). The study used a mixed inoculum of soil, non-adapted sludge and water and the biodegradation rate was calculated from the biological oxygen demand. The mean biodegradation of the test item was measured to be 61 % after 28 days, with the first of the 3 replicates achieving 65 % and the 2nd and 3rd replicates achieving 59 % biodegradation after 28 days. 1,3,5-trimethylbenzene is considered to be readily biodegradable but failing the 10 day window.

Biodegradation data are also available from a number of other non-standard studies but the results are variable and the studies either did not follow a standard test guideline or are not available for review. Therefore, as a new, GLP-compliant study following OECD 301F was conducted at Dr Noack (2016), this study is considered to be the key study for risk assessment purposes and the non-standard studies have been disregarded.