Hexamethylene diisocyanate, trimers, reaction products with 2-hydroxyethyl acrylate

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

toxicity to microorganisms, other

Remarks:

toxicity control of ready biodegradability test

Type of information:

experimental study

Adequacy of study:

key study

Study period:

19 May - 17 June 2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

July 1992

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Landesanstalt für Umwelt, Messungen und Naturschutz Baden-Württemberg, Germany (29.06.2016)

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: 52.4 mg test item and 5.15 mL of the reference stock (10 g/L sodium benzoate) were added to the test vessel, corresponding to a concentration of 40 mg/L total organic carbon. Mixing was performed with a magnetic stirrer with 2 cm stir bars. The final test volume in the test vessel was 1500 mL, consisting of 1490.9 mL mineral medium and 9.1 mL activated sludge (30 mg/L dry solids). The test vessels (containing mineral medium and activated sludge) were prepared 1 d before test start, sealed, aerated with CO2-free air and mixed with a magnetic stirrer overnight. The following day, the absorber bottles were filled with 0.2 M NaOH (CO2 trap) and the test item and reference compound were introduced and the test started.
- Controls: Only inoculum (blank)

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Name and location of sewage treatment plant where inoculum was collected: Municipal wastewater treatment plant Breisgauer Bucht, Germany (sampled 17 May 2016)
- Preparation of inoculum for exposure: The activated sludge was washed twice with tap water by settling the sludge, decanting the supernatant and re-suspending the sludge.
- Initial biomass concentration: 4.95 g/L mean dry solid content of activated sludge, determined after drying at 105 °C

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

28 d

Test temperature:

22.3 - 23.6 °C

Nominal and measured concentrations:

34.9 mg/L (nominal)

Details on test conditions:

TEST SYSTEM
- Test vessel: Gas wash bottles (2000 mL); Fill volume: 1500 mL
- Aeration: With CO2-free air overnight
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 3
- Sludge concentration (weight of dry solids per volume): 30 mg/L dry solids

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Mineral medium

OTHER TEST CONDITIONS
- Light intensity: diffuse light
- Details on termination of incubation: The CO2 produced in the reactors was absorbed in two 250 mL gas wash bottles in series each filled with 200 mL 0.2 M NaOH. Sampling was performed through the lateral connecting pieces through the butlyl rubber septum using 5 mL PE syringes.

EFFECT PARAMETERS MEASURED:
Degradation was followed by determining the amount of CO2 produced and absorbed to sodium hydroxide via IC-measurement (IC = inorganic carbon) on Days 0, 4, 8, 11, 14, 21, 28, and 29.

TEST CONCENTRATIONS
- Justification for using fewer concentrations than requested by guideline: Toxicity control of ready biodegradability test (Modified Sturm Test)

Reference substance (positive control):

yes

Remarks:

sodium benzoate

Duration:

14 d

Dose descriptor:

NOEC

Effect conc.:

>= 34.9 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: degradation

Remarks on result:

other:

Remarks:

46.5% degradation; 52.4 mg test item in 1500 mL test medium

The degradation in the toxicity control after 14 d was 46.5% and thus above the criterion for inhibition effects to the inoculum. The test item had no toxic effect on the inoculum according to the validity criteria of OECD 301 on ready biodegradability.

Validity criteria fulfilled:

yes

Description of key information

NOEC (14 d) ≥ 34.93 mg/L (nominal, OECD 301)

Additional information

The microbial toxicity of Hexamethylene diisocyanate, trimers, reaction products with 2-hydroxyethyl acrylate (CAS 162492-01-5) was inferred from the toxicity control of a standard ready biodegradability test conducted according to OECD 301 B and GLP, as recommended by the Guidance document “Chapter R.7b Endpoint specific Guidance on Information Requirements and Chemical Safety Assessment” (ECHA, 2017) in absence of a microbial toxicity test according to OECD 209.

 

In the CO2 evolution test (Modified Sturm Test), the toxicity control was prepared by inoculating 52.4 mg test item (corresponding to approximately 34.93 mg test item/L) and 5.15 mL of the reference compound stock solution (sodium benzoate), with activated sludge (30 mg/L dry solids) under aerobic conditions in diffuse light for 28 d. Degradation was followed by quantification of the produced CO2 trapped by sodium hydroxide, and expressed as blank corrected percentage of the theoretical CO2 demand (ThCO2).

After 14 d, degradation of the reference compound and test item in the toxicity control was 46.5% and thus above the criterion (< 25% degradation in 14 d) for inhibition effects to the inoculum. Based on this result, the test item had no toxic effect on the inoculum and a NOEC (14 d) of ≥ 34.93 mg/L was derived according to the Guidance document “Chapter R.7b Endpoint specific Guidance on Information Requirements and Chemical Safety Assessment” (ECHA, 2017).