Hexane, 1,6-diisocyanato-, homopolymer, 2-hydroxyethyl acrylate- and propylene glycol monoacrylate-blocked

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

Study period:

From January 19, 2017 to February 9, 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

yes

Remarks:

see 'Any other information on materials and methods'

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

Deviations:

yes

Remarks:

see 'Any other information on materials and methods'

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Remarks:

Measurement of the O2-concentration

Vehicle:

no

Details on test solutions:

Due to the poor solubility of the test substance, the test substance was weighed directly into the test vessels.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Activated sludge from a biologic sewage treatment plant was used. The chosen plant treats mostly domestic sewage. Source: the sludge was taken from the activation basin of the ESN (Stadtentsorgung Neustadt) sewage treatment plant in D-67435 NW-Lachen-Speyerdorf. Pre-Treatment: Upon arrival in the test facility, the sludge was filtered, washed with tap water 3 times and re-suspended in tap water. The activated sludge was aerated until usage in the test and fed daily with 50 mL synthetic sewage feed /L. inoculum. The dry matter was determined as 3.2 g suspended solids/L, giving a concentration of 1.6 g suspended solids/L in the test.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Hardness:

0.83 mmol/L

Test temperature:

19.3 – 20.8°C (first experiment (pre-test))
19.1 – 20.5°C (second experiment (main test))
19.5 – 20.5°C (third experiment)

pH:

8.16

Dissolved oxygen:

Aeration: purified air, using Pasteur pipettes

Salinity:

sodium concentration: 4.7 mg/L

Conductivity:

228 μS/cm (at 25°C)

Nominal and measured concentrations:

Nominal: 4 concentrations ranging from 1000 to 1 mg/L

Details on test conditions:

Replicates:
1 replicate/concentration (positive control, all experiments)
1 replicate/concentration test substance 100 / 10 / 1 mg/L (first experiment)
5 replicates/concentration test substance 1000 mg/L (first experiment)
5 replicates/concentration test substance (second and third experiment)
Blank Control 2 replicates before and 2 after measuring positive control and test substance, respectively.

On the day before each experiment, the inoculum was taken from its source, washed, aerated and the dry matter was determined. Volume was adapted to the desired content of dry matter. The nutrient solution was thawed and the sludge was fed with 50 mL nutrient solution / L sludge. On the day of the experiment, the dry matter was determined once more. The stock solution of the positive control was prepared.

In the blank control vessels, 16 mL nutrient solution was mixed with 234 mL water. The positive control vessels and the treatments were prepared by putting the appropriate amount of positive control solution respectively test substance into the respective test vessel, adding 16 mL nutrient solution and water to reach a total volume of 250 mL. Then, 250 mL inoculum was added in 5 min intervals and the mixtures were aerated. After 3 h of incubation, the content of the first vessel was poured in a 250 mL narrow-neck bottle and the respiration rate was determined by measurement of the O2-concentration over a period of max. 5 min. The following vessels were measured likewise in 5 min intervals.

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

22 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Key result

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

360 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Results with reference substance (positive control):

3,5-Dichlorophenol (CAS No. 591-35-5) was used as positive control. Stock solutions in deionised water containing 500 mg/L (first experiment), 501 mg/L (second experiment) and 500 mg/L (third experiment) were freshly prepared for each experiment.

Validity criteria fulfilled:

yes

Conclusions:

Under the study conditions, the 3 h EC50 and NOEC of the substance to sludge microorganisms were determined to be >1000 mg/L and 22 mg/L (nominal) respectively.

Executive summary:

A study was conducted to determine the toxicity of the substance on the respiration of sludge microorganisms according to OECD Guideline 209 and EU Method C.11, in compliance with GLP. The dry matter of the inoculum was determined to be 3.2 g suspended solids/L, giving a concentration of 1.6 g suspended solids/L in the test. The sludge was exposed to the test substance at concentrations ranging from 1 to 1000 mg/L for 3 h. Due to the poor solubility of the test substance in water, the test substance was weighed directly into the test vessels to which sludge was added later. Inhibition of respiration at the lowest treatment concentration was significant in the two initial tests, and a third experiment was performed to determine the NOEC at lower concentrations. In the third experiment the test substance was tested using 3 concentrations ranging from 22 to 4.6 mg/L (nominal concentration). Under the study conditions, the 3 h EC50 and NOEC of the substance to sludge microorganisms were determined to be >1000 mg/L and 22 mg/L (nominal) respectively (Muckle, 2017).

Key value for chemical safety assessment

EC50 for microorganisms:

1 000 mg/L

EC10 or NOEC for microorganisms:

22 mg/L

Additional information

A study was conducted to determine the toxicity of the substance on the respiration of sludge microorganisms according to OECD Guideline 209 and EU Method C.11, in compliance with GLP. The dry matter of the inoculum was determined to be 3.2 g suspended solids/L, giving a concentration of 1.6 g suspended solids/L in the test. The sludge was exposed to the test substance at concentrations ranging from 1 to 1000 mg/L for 3 h. Due to the poor solubility of the test substance in water, the test substance was weighed directly into the test vessels to which sludge was added later. Inhibition of respiration at the lowest treatment concentration was significant in the two initial tests, and a third experiment was performed to determine the NOEC at lower concentrations. In the third experiment the test substance was tested using 3 concentrations ranging from 22 to 4.6 mg/L (nominal concentration). Under the study conditions, the 3 h EC50 and NOEC of the substance to sludge microorganisms were determined to be >1000 mg/L and 22 mg/L (nominal) respectively (Muckle, 2017).