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

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

Study period:

19 May - 17 June 2016

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)

Version / remarks:

July 1992

GLP compliance:

yes (incl. QA statement)

Remarks:

Landesanstalt für Umwelt, Messungen und Naturschutz Baden-Württemberg, Germany

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Municipal wastewater treatment plant Breisgauer Bucht (sampled on 17 May 2016)
- Storage conditions: The sludge was sealed and aerated with CO2-free overnight. The reactors were kept mixed with magnetic stirrers.
- Storage length: 2 d
- Preparation of inoculum for exposure: Based on the determined dry weight, defined amounts of the activated sludge suspension were added to mineral medium to obtain a final concentration of 30 mg dry material per liter
- Pretreatment: The activated sludge was washed twice with tap water by settling the sludge, decanting the supernatant and re-suspending the sludge
- Concentration of sludge: 30 mg dry solids per litre

Duration of test (contact time):

29 d

Initial conc.:

>= 19.8 - <= 20.4 mg/L

Based on:

TOC

Initial conc.:

>= 35.6 - <= 36.6 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

TEST CONDITIONS
- Composition of medium: according to the guideline
- Test temperature: 22.3 - 23.6 °C
- Aeration of dilution water: aeration rate was kept at a rate of 30 - 100 mL/min (1.6 - 5.5 bubbles/second)
- Suspended solids concentration: Dry solid of the activated sludge was determined as 4.95 g/L by weight measurements after drying at 105 °C
- Continuous darkness: diffuse light
- other: For the CO2 adsorption medium 64.04 g NaOH was dissolved in 8000 mL deionised water in closed recipients (0.2 M NaOH). The inorganic carbon concentration of the 0.2 M NaOH was determined.

TEST SYSTEM
- Culturing apparatus: 2 L gas wash bottles with lateral connecting pieces for butyl rubber septums were used (fill volume: 1500 mL).
- Number of culture flasks/concentration: 3 (per test item, blank and reference) and 1 reactor (toxicity control)
- Method used to create aerobic conditions: The day before incubation the flasks were filled with mineral medium and inoculum and aerated overnight with CO2-free synthetic air. The CO2-free air production system consists of an air compressor, three 1000 mL gas wash bottles filled with dry soda lime in series followed by one bottle filled with 0.1 M NaOH (sodium hydroxide). At the end of the system was one gas wash bottle filled with demineralised water, followed by an empty one to catch any drops of condensation water. A colour change of the soda lime from white to blue indicates that the CO2 absorption capacity is depleted. The CO2-free air is passed on to an air distributor with two input and 22 output channels and through PE-tubes.
- Measuring equipment: IC measurement was performed with a total carbon analyser (TOC-5050A Shimadzu with an autosampler ASI-5000A) by purging the inorganic carbon with H3PO4 (25%) using a non dispersive infrared (NDIR) detector.
- Test performed in open system: yes
- Details of trap for CO2 and volatile organics if used: 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 butyl rubber septum using 5 mL PE syringes.

SAMPLING
- Sampling frequency: On the 4th, 8th, 11th, 14th, 21st and 28th day
- Sampling method: 4 mL NaOH from the first of two CO2-absorber flasks connected in line was sampled. The vials were immediately closed with sealing film in order to avoid CO2 uptake from the air. On the 28th day 2 mL of 4 M hydrochloric acid (HCl) was added into each reactor to release the CO2 dissolved in water. On day 29 the IC was determined in both CO2-absorber flasks in line.

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes, 3 reactors
- Toxicity control: yes, 1 reactor
- Reference control: yes, 3 reactors

Reference substance:

benzoic acid, sodium salt

Remarks:

20 mg C/L

Parameter:

% degradation (CO2 evolution)

Value:

0

Sampling time:

29 d

Remarks on result:

other: after acidification

Results with reference substance:

The biodegradation of the reference compound reached the pass level of 60% ThCO2 by day 4.

There was no degradation of the test item within 28 days. The criterion for ready biodegradation (degradation 60%, 10-d-window) was therefore not met. The test item didn’t reach the pass level for ready biodegradability.

Table 1: Ultimate biodegradation after x days [% of ThCO2]

Day	0	4	8	11	14	21	28	29
Test flasks	0	2.3	1.8	2.0	3.1	2.1	2.7	2.8
	0	1.7	1.4	1.9	2.0	0.0	0.6	0.6
	0	-1.9	-2.7	-2.6	-2.4	-5.6	-4.6	-3.5
Reference flasks	0	71.1	83.0	86.6	92.0	93.9	94.3	94.2
	0	77.3	89.0	94.9	100.8	105.4	107.4	107.2
	0	74.7	86.8	87.9	92.1	96.6	98.4	98.4
Toxicity control	0	39.1	43.8	44.7	46.5	46.2	46.2	46.7

Table 2: Mean CO2-evolution of blank flask after x days

Day	0	4	8	11	14	21	28	29
CO2-evolution [mg/L]	0	8.9	13.8	16.3	18.6	24.9	28.6	29.5

Validity criteria fulfilled:

yes

Interpretation of results:

under test conditions no biodegradation observed

Description of key information

Not readily biodegradable (0% in 28 d, OECD 301 B)

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Additional information

There is one experimental study available, in which the ready biodegradability of Hexamethylene diisocyanate, trimers, reaction products with 2-hydroxyethyl acrylate (CAS 162492-01-5) was investigated according to OECD guideline 301 B and GLP.

A test item concentration corresponding to 19.8 – 20.4 mg organic carbon/L was inoculated with activated sludge (30 mg dry solids/L) from a municipal sewage treatment plant treating predominantly domestic wastewater for 28 d under aerobic conditions in diffuse light. A reference, toxicity and inoculum control were run in parallel. Degradation was followed by measuring inorganic carbon to determine the produced CO2 absorbed to sodium hydroxide and expressed as percentage of ThCO2.

After 28 d, degradation of the test item reached 0%. Therefore, the test item did not reach the criteria for ready biodegradability. The procedural control confirmed the suitability of the test system. Degradation in the toxicity control was 46.5% after 14 d. Thus, the test item is not toxic to microorganisms of activated sludge according to the guideline criteria.