Hexamethylene diisocyanate

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: GLP guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)

Qualifier:

equivalent or similar to guideline

Guideline:

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

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic (adaptation not specified)

Details on inoculum:

TEST ORGANISM:
- mixed population of aquatic organism, origin from an aeration tank of a waste water treatment plant treating predominantly domestic sewage (Wupper area water authority, Germany)
- pretreatment: none
- activated sludge concentration in test flasks: 30 mg ss/l

Duration of test (contact time):

28 d

Initial conc.:

100 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

INITIAL CONCENTRATION:
- Direct weighing
- Test substance: 100 mg/l
- Reference substance: 100 mg/l

The test was run triplicate

Composition of the test medium according to guideline.

EXPOSURE CONDITION:
- 28 days incubation at 20 +/- 1 °C

TOXICITY CONTROL (run in parallel):
- Test concentration test substances: 100 mg/l
- Theoretical oxygen demand test substance: mg 1617 O2/g
- Test concentration reference compound: 100 mg/l
- Theoretical oxygen demand reference substance: mg 1665 O2/g

Reference substance:

benzoic acid, sodium salt

Remarks:

purity 99 %, initial concentration 100 mg/l

Test performance:

- A suspension of 100 mg/L test item in a mineral medium was inoculated and incubated under aerobic conditions in the dark.
- The endogenous activity of the inoculum was checked running parallel blanks with inoculum but without test item.
- A reference substance was run in parallel to check the operation of the procedures.
- The oxygen uptake was calculated from the readings taken at regular and frequent intervals.

Parameter:

% degradation (O2 consumption)

Value:

42

Sampling time:

28 d

Details on results:

Kinetics of Desmodur H rein: 8 day(s) 7 %
14 day(s) 20 %
20 day(s) 33 %

Results with reference substance:

Kinetics of Benzoic acid, sodium: 8 day(s) 77 %
14 day(s) 86 %

No oxygen consumption by nitrification occured in the units with the test substance.

Validity criteria fulfilled:

yes

Remarks:

All validity criteria were met (see "conclusions", below)

Interpretation of results:

other: not readily biodegradable

Conclusions:

All validity criteria were met:
- reference compound reached the level for ready biodegradability within 14 days
- no toxicity of the test item was observed in the toxicity control.
- at the end (or plateau, or the end of the 10-days-window) of the test, biodegradation (%) in parallels with test item did not differ by more than 20 percentage points
- oxygen uptake of the inoculum blank was ≤ 60 mg/L

Executive summary:

A ready biodegradation test was carried out on HDI according to EU Method C.4 which is similar to OECD Guideline 301F. Experimental units consisted of 250 –Ml test bottles.

Activated sludge from domestic sewage treatment plant was used as biological inoculum. The following treatments were applied: control (inoculum), test material (inoculum + test substance), reference material (inoculum + benzoic acid, sodium salt), and toxicity control.

The initial test concentration was 100 mg/L. All test solutions were incubated for 28 days at 20°C ± 1°C. The O₂-consumption was measured during this period. The concentrations of test substance did not induce toxicity effects on bacteria. The percentage of biodegradation of test substance attained 0% on Day 4, 20 % on Day 14 % and 42 % on Day 28 based on O₂-consumption.

This ready biodegradation study is classified as acceptable and satisfies the guideline requirement. Under the conditions of this study, HDI is considered as not readily biodegradable in accordance with the classification system of the EU (Directive 67/548/EC).

 

Results Synopsis:

Ready biodegradation

A mixed population of microorganisms in activated sludge coming from STEP effluents (domestic, adaptation not specified)

Aerobic % of biodegradation after 28 days: 42 % (based on O₂-consumption)

Description of key information

Hexamethylenediisocyanate  is not readily biodegradable. After 28 days 42 % of the test substance had been degraded in a manometric respiratory test according Directive 92/69/EEC, C.4-D. (Bayer AG, 2000a). 

Additional information

A biodegradation test was carried out on hexamethylene diisocyanate according to OECD Guideline 302 C (Inherent Biodegradability: Modified MITI Test (II)). The percentage of biodegradation of test substance attained 0% after 28 days based on O₂-consumption (Bayer AG, 1992).

The test was carried out with industrial, activated sludge,origin from an industrial sewage treatment plant treating industrial sewage (Bayer AG, Leverkusen Germany). This test may not be used for classification or PBT assessment as this situation does not reflect normal environmental conditions. Therefore the test result can onlybe used for assessment of HDI in industrial STPs.