Mesitylene

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: GLP, guideline study, result taken from toxicity control of biodegradation study

Qualifier:

according to guideline

Guideline:

other: 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

Analytical monitoring:

no

Details on sampling:

Not applicable

Vehicle:

no

Details on test solutions:

- Test medium: OECD 301F mineral salts medium

Test organisms (species):

other: 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.
- Standard soil: 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.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

28 d

Post exposure observation period:

None

Hardness:

Not reported

Test temperature:

- Temperature: 21.3-21.5°C

pH:

- pH: 7.65 at start and 7.87 at end in toxicity control, 7.64 to 7.69 at start and 7.57 to 7.83 at end in the other vessels

Dissolved oxygen:

Not applicable

Salinity:

Not applicable

Nominal and measured concentrations:

- Nominal: 24.2 mg test item/L

Details on test conditions:

- 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.
- 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.
- Toxicity control: 1 replicate of test medium with test and reference item
- Other replicates: 3 for test item degradation, 1 for functional control and 2 for inoculum control (test medium without test or reference item)

Reference substance (positive control):

yes

Remarks:

sodium benzoate

Key result

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

24.2 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

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.

Results with reference substance (positive control):

Functional control reached the pass level for degradation (>60%) within 3 days and came to a maximum of 89% biodegradation after 28 days.
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%).

Reported statistics and error estimates:

No data reported

Validity criteria fulfilled:

not specified

Remarks:

Validity criteria of biodegradation study fulfilled

Conclusions:

No inhibition of biodegradation was observed in the toxicity control of the biodegradation study. The 28 day NOEC for the toxicity of 1,3,5-trimethylbenzene to a mixture of sewage sludge, soil and water is 24.2 mg test item/L.

Executive summary:

The toxicity of 1,3,5 -trimethylbenzene to aquatic micro-organisms has been taken from the results for the toxicity control in the biodegradation study. The biodegradation study is GLP compliant and follows OECD guideline 301F, ready biodegradability manometric respiration test. The toxicity control, containing 24.2 mg test item/L and sodium benzoate, showed no inhibition in respiration, reaching 53 % degradation after 14 days and 74 % biodegradation after 28 days, and therefore it is concluded that the test item does not inhibit the degradation of the reference item. The 28 day NOEC is 24.2 mg test item/L, the only concentration tested.

Description of key information

No inhibition of biodegradation was observed in the toxicity control of the biodegradation study. The 28 day NOEC for the toxicity of 1,3,5-trimethylbenzene to a mixture of sewage sludge, soil and water is 24.2 mg test item/L.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

24.2 mg/L

Additional information

The toxicity of 1,3,5 -trimethylbenzene to aquatic micro-organisms has been taken from the results for the toxicity control in the biodegradation study (Dr Noack 2016). The biodegradation study is GLP compliant and follows OECD guideline 301F, ready biodegradability manometric respiration test. The toxicity control, containing 24.2 mg test item/L and sodium benzoate, showed no inhibition in respiration, reaching 53 % degradation after 14 days and 74 % biodegradation after 28 days, and therefore it is concluded that the test item does not inhibit the degradation of the reference item. The 28 day NOEC is 24.2 mg test item/L, the only concentration tested.