3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1999-09-21 to 1999-09-24

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Guideline study with acceptable restrictions: Test substance not stable under test conditions

Qualifier:

according to guideline

Guideline:

EU Method C.3 (Algal Inhibition test)

Version / remarks:

Cited as Directive 92/69/EEC, C.3

GLP compliance:

yes

Analytical monitoring:

yes

Details on sampling:

At test start and after 72 hours of exposure 

Vehicle:

no

Details on test solutions:

STOCK AND TEST SOLUTION AND THEIR PREPARATION
- 125 mg/l stock solution
- Dispersion: ultra-turrax treatment for 60 seconds at 8000 rpm, followed  by stirring with a magnetic stirrer for 24 hours and filtration 
(folded  filter) at pore size 7-12 µm

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Details on test organisms:

TEST ORGANISMS
- Strain: Desmodesmus subspicatus CHODAT
- Source/supplier: Institute of Plant Physiology, University of Göttingen
- Method of cultivation: In a light chamber at 23 +/- 2 °C and with a  quantum flux which equals 120 uE/m2 x s

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Test temperature:

- Test temperature: 23 +/- 2 degree C

pH:

- 8.0-8.1 at 0 hours; 
- 9.5-10.2 at 72 hours   
- control: 7.8 at 0 hours; 10.2 at 72 hours

Nominal and measured concentrations:

1.1; 2.2; 4.4; 8.8; 17.5; 35; 70 mg/l (nominal concentrations)
3; 6; 12; 25; 48 mg TOC/L (0 hours; concentrations at 1.1 and 2.2 mg/L were not analysed)
5; 7; 18; 24; 45 mg TOC/L (72 hours; concentrations at 1.1 and 2.2 mg/L were not analysed)
TOC has to be multiplied with 1.5 to correspond with test substance.

Details on test conditions:

TEST SYSTEM
- Exposure vessel type: 300 ml Erlenmeyer flasks with stoppers with 100  ml of test medium; light chamber with shaker
- Number of replicates: 3 (control: 6)
- Controls: Inoculum in nutrient medium and dilution water
- Initial cell concentration: 10 000 cells/ml
- Intensity of irradiation: 120 uE/m2 x s

DILUTION WATER
- Source: deionized water

TEST PARAMETER
- Counting with microcellcounter Sysmex F-300 Digitana at  every 24 hours

STATISTICAL METHODS
- Williams test for NOEC, LOEC

Reference substance (positive control):

not specified

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

4.4 mg/L

Nominal / measured:

nominal

Conc. based on:

other: TOC measurement

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

LOEC

Effect conc.:

8.8 mg/L

Nominal / measured:

nominal

Conc. based on:

other: TOC measurement

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 70 mg/L

Nominal / measured:

nominal

Conc. based on:

other: TOC measurement

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Remarks:

biomass

Effect conc.:

> 70 mg/L

Nominal / measured:

nominal

Conc. based on:

other: TOC measurement

Basis for effect:

biomass

Remarks:

expressed as growth (integral of biomass)

Details on results:

- Effect data / endpoints: 
- EC50 (biomass as well as growth rate) > highest test concentration (70 mg/l nominal/measured); 
- NOEC / LOEC (growth rate) = 4.4 / 8.8 mg/l;
- NOEC / LOEC (biomass) >= 70 / > 70 mg/l

After 2 days of undisturbed growth, cell counts suddenly stayed constant (17.5 mg/l nominal) or even dropped markedly (> 17.5 mg/l nominal)
leading to an inhibition of growth rate of 8.3 % at 17.5 mg/l and higher concentrations compared to 0 % inhibition at all lower concentrations. In  total however, EC50 values based on both biomass (area under the growth curve) and growth rate are above the highest test concentration.

Results with reference substance (positive control):

no data available

- Nominal/measured concentrations: 
nominal / 24 hours / 72 hours
test s.   /  TOC       /   TOC
4.4           3               5 mg/l
8.8           6               7 mg/l
17.5         12            18 mg/l
35            25            24 mg/l
70            48            45 mg/l
TOC has to be multiplied with 1.5 to correspond with the amount of test  substance.

- Cell density data: 
concn.  / biomass / % inhibition / growth rate (% inhibition)
control / 426000  /      0.0        /    1.2/d (0.0)
 1.1     / 481000  /    -12.9       /    1.2/d (0.0)
 2.2     / 445000  /     -4.5        /    1.2/d (0.0)
 4.4     / 416000  /      2.3        /    1.2/d (0.0)
 8.8     / 356000  /     16.4       /    1.2/d (0.0)
17.5    / 455000  /     -6.8        /    1.1/d (8.3)
35       / 427000  /     -0.2        /    1.1/d (8.3)
70       / 436000  /     -2.3        /    1.1/d (8.3)

Validity criteria fulfilled:

not specified

Conclusions:

The EC50 (both biomass and growth rate) was determined as >70 mg/L. On the basis of these results it cannot be excluded that the test substance
may be harmful to algae.

Executive summary:

The toxic effects of isophorone diisocyanate on the green alga Scenedesmus subspicatus were investigated by Bayer AG (2000) according to EU method C.3. Seven concentrations ranging from 1.1 to 70 mg/L were tested over a period of 72 hours. The following endpoints were derived for growth rate (based on nominal concentrations)

EC50 (72h): >70 mg/L

NOEC: 4.4 mg/L

LOEC: 8.8 mg/L

Due to fast hydrolysis it is assumed that the observed effect is rather attributed to the hydrolysis product than to the parent substance.

The study was assessed as "reliable with restrictions".

Description of key information

The toxic effects of isophorone diisocyanate on Scenedesmus subspicatus were investigated by Bayer AG (2000) according to EU method C.3. Seven concentrations ranging from 1.1 to 70.0 mg/L were tested over a period of 72 hours. The EC50 (72 hours, growth rate) was determined as >70 mg/L and the NOEC as 4.4 mg/L.

Additional information

In view of the low solubility in water (see chapter 4.9) and the liability towards hydrolysis (see chapter 5.1.2) of 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate, exposure to well-defined aquatic concentrations is difficult to achieve. Due to fast hydrolysis, the observed effect is expected to be the effect of the hydrolysis product. In the aquatic environment, only the chemically less reactive hydrolysis product is expected to be relevant. The method for the determination of the test substance concentration (TOC) does not differentiate between parent substance and hydrolysis product. Hence the analytical results should be treated with caution.