2,3-epoxypropyl isopropyl ether

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

2012-10-10 - 2013-06-04

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Well documented GLP OECD TG 201 study without deviations on suitable read-across substance

Justification for type of information:

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
The structural analogue 1,2,3-Propanetriol, glycidyl ethers is a mixture of different components with average 2-3 epoxy functional groups per molecule, to be more accurate, with 2,3-epoxypropyl side chains. Those are identical to the side chain of 2,3-epoxypropyl isopropyl ether, which is considered to be the toxicologically more relevant functional group. Also, the isopropyl chain is related to the partially substituted propane moiety of 1,2,3-Propanetriol, glycidyl ethers. Both substances are rather small molecules, indicating a similar distribution pattern, which is supported by the liquid state, high water solubility, and low logPow, especially in ecotoxicity tests. They are both not readily biodegradable and sufficiently hydrolytically stable over the usual short-term exposure period in ecotoxicity testing. In consequence, 1,2,3-Propanetriol, glycidyl ethers may serve as a read-across substance for 2,3-epoxypropyl isopropyl ether.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Source Chemical: 1,2,3-Propanetriol, glycidyl ethers, CAS 90529-77-4
Target Chemical: 2-(isopropoxymethyl)oxirane, CAS 4016-14-2

3. ANALOGUE APPROACH JUSTIFICATION
As stated above, the analogue (source) consists of components with average 2-3 2,3-epoxypropyl side chains. Those are identical to the side chain of 2,3-epoxypropyl isopropyl ether, which is considered to be the toxicologically more relevant functional group. Both substances are rather small molecules, indicating a similar distribution pattern, and especially relevant for ecotoxicity tests, they both have a high water solubility and low logPow. There is in general no indication that both substances may not pass biological membranes except a possible direct protein binding via nucleophilic addition via the epoxy group, which is however a common mechanism. Both substances are sufficiently stable during the average duration of short-term ecotoxicity tests or when performed in a flow-through design: They are both not readily biodegradable and sufficiently hydrolytically stable.
With regard to the comparability of the ecotoxicity data, ECOSAR Version 1.11 by US EPA predictions were used for comparison as these values are easily available for both substances. For IPGE, there are Class-specific Estimations available, both enormous differing in the magnitude of the values. However, in general, the values obtained for the source chemical are in between the values derived for IPGE (Epoxides, mono, or Neutral Organics), showing that there is no definitive reason to believe that the values derived from actual IPGE testing would largely differ frim the current ones for CAS 90529-77-4.
In consequence, 1,2,3-Propanetriol, glycidyl ethers may serve as a read-across substance for 2,3-epoxypropyl isopropyl ether.

4. DATA MATRIX
See Attachment

Reason / purpose for cross-reference:

read-across source

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Qualifier:

according to guideline

Guideline:

EU Method C.3 (Algal Inhibition test)

GLP compliance:

yes (incl. QA statement)

Remarks:

Swiss Federal Public of Health, Bern

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
PHYSICO-CHEMICAL PROPERTIES
- Melting point: < -20°C
- Boiling point: substance decomposes before boiling occurs: decomposition temperature ≥ 181°C (at 101.325 kPa)
- Vapour pressure: 0.0392 Pa (estimated)
- Water solubility (under test conditions): 20 -30 g/L
- Henry's law constant: 2.15E-9 Pa*m³/mol (Bond Method), 2.37E-14 Pa*m³/mol (Group Method) (estimated)
- log Pow: -1.94 (estimated)

OTHER PROPERTIES (if relevant for this endpoint)
- Results of test for ready biodegradability: not readily biodegradable
- Other: hydrolytically stable (estimated)

Analytical monitoring:

yes

Details on sampling:

A small volume of the algal suspension was withdrawn daily from each test flask for the measurement of the biomass, and was not replaced.
The algal biomass in the samples was determined by fluorescence measurement (BIO-TEK(R) Multi-Detection Microplate Reader, Model FLx800, wavelength: excitation 440 nm, emission 680 nm). The measurements were performed at least in triplicate.
At the end of the test, a sample was taken from the control and from the test concentration of nominal 100 mg/L to determine a potential influence of the test item on the algal cells. The shape and size of the algal cells were visually inspected.

Vehicle:

no

Details on test solutions:

50 mL Erlenmeyer flasks were used per replicate containing 15 mL of test solution. Each test flask was covered with a glass dish. The test flasks were labeled with the study number and all necessary additional information to ensure unique identification. During exposure, the test solutions were continuously stirred by magnetic stirrers.

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Details on test organisms:

TEST ORGANISM
- Common name: Pseudokirchneriella subcapitata (formerly: Selenastrum capricornutum)
- Strain: 61.81 SAG
- Source: Collection of Algal Cultures (SAG, Institute for Plant Physiology, University of Göttingen, Germany)
- Culture: The inoculum culture was set up three days before start of the exposure. The algae were cultivated under the test conditions and were kept in the exponential growth phase until inoculation of the test solutions.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Post exposure observation period:

No post exposure observation period described.

Hardness:

0.15 mmol/L (= 15 mg/L as CaCO3)

Test temperature:

22 °C (temperature controlled water bath)

pH:

start: 7.4 - 7.5
end: 8.4

Dissolved oxygen:

Not reported.

Salinity:

Not applicable.

Nominal and measured concentrations:

0.32, 1.0, 3.2, 10, 32 and 100 mg/L (nominal)

Details on test conditions:

TEST SYSTEM
- Test vessel: 50 mL Erlenmeyer flasks
- Initial cells density: 5000 cells/mL (nominal)
- No. of vessels per concentration: 3
- No. of vessels per control: 6

TEST WATER PARAMETERS
- Type: reconstituted test water (AAP Medium)
- Macro-nutrients: 15 mg/L NaHCO3, 1.044 mg/L K2HPO4, 14.6 mg/L MgSO4 x 7 H2O, 12.165 mg/L MgCl2 x 6 H2O, 4.41 mg/L CaCl2, 25.5 mg/L NaNO3
- Trace elements: 186.0 µg/L H3BO3, 415.0 µg/L MnCl2 x 4 H2O, 3.27 µg/L ZnCl2, 1.43 µg/L CoCl2 x 6 H2O, 0.012 µg/L CuCl2 x 2 H2O, 7.26 µg/L Na2MoO4 x 2 H2O, 160.0 µg/L FeCl3 x 6 H2O, 300.0 µg/L Na2EDTA x 2 H2O

DOSAGE
The test medium of the highest nominal concentration of 100 mg/L was prepared by dissolving 40.13 mg of the test item completely in 400 mL of test water under intense stirring for 15 minutes at room temperature. The test medium of the highest test concentration was used in a series of dilutions with test water to prepare the test media of the lower test concentrations. The test media were prepared just before the start of the test.

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Mean measured light intensity: 7000 lux (range: 6150 - 7590 lux)
- Deviation: +/- 15 % from the average light intensity as recommended by the guideline
- Illumination: fluorescent tubes (Philips TLD 36 W/840)

TEST CONCENTRATIONS
- Range finding study: yes, mentioned in the study report

Reference substance (positive control):

yes

Remarks:

Potassium dichromate

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

21 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

21 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

LOEC

Effect conc.:

69 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

LOEC

Effect conc.:

69 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

> 120 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

7.7 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

EC20

Effect conc.:

> 120 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC20

Effect conc.:

120 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Remarks on result:

other: extrapolated value

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 120 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 120 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Remarks on result:

other: extrapolated value

Details on results:

Defined values for EC10 (growth rate), EC20 and EC50 (growth rate and yield) could not be calculated due to the low toxicity of the test item for the algae. Confidence intervals could not be calculated.

Results with reference substance (positive control):

The result of the latest positive control test performed in April 2013 showed that the sensitivity of the test system was within the internal historical range (72-hour EC50 for the growth rate: 1.5 mg/L (Harlan Study Number D74222), range of the 72-hour EC50 for the growth rate from 2000 to 2013: 0.71 - 1.7 mg/L).

Reported statistics and error estimates:

Williams t-test, alpha = 0.05

Validity criteria fulfilled:

yes

Remarks:

Validity criteria of the applied guideline were fulfilled.

Conclusions:

The study report describes a valid guideline study conducted under GLP compliance. Based on growth rate and biomass, the extrapolated EC50(72h) values were determined to be 120 mg/L and > 120 mg/L, respectively, thus the test substance can be regarded as non-toxic to aquatic algae. The test item was considered suitable for read-across to 2,3-epoxypropyl isopropyl ether, hence, it can be concluded that 2,3-epoxypropyl isopropyl ether can be regarded as non-toxic to aquatic algae, too.

Executive summary:

The effects of 1,2,3-Propanetriol, glycidyl ethers on the growth of the freshwater green algal species Pseudokirchneriella subcapitata was investigated according to OECD Guideline 201 / EU Method C.3. The study was conducted under certificated GLP compliance. Exponentially growing cultures of the test organisms were exposed to the different concentrations of the test substance over a period of 72 hours and the inhibition of algal growth in relation to control cultures was assessed over several generations. The selection of the test concentrations was based on the results of a range-finding test and on results of a pre-experiment to determine the solubility of the test substance. The following nominal concentrations were chosen: 0.32, 1.0, 3.2, 10, 32 and 100 mg/L (three replicates per concentration). Additionally, a control was tested in parallel (six replicates). The initial cell density was 5000 cells/mL (nominal). A static test design was applied. A small volume of the algal suspension was withdrawn daily from each test flask for the measurement of the biomass, and was not replaced. The concentrations of the test substance were determined in one of the duplicate test medium samples from the nominal test concentrations of 32 and 100 mg/L. The samples from the nominal test concentrations of 0.32 to 10 mg/L were not analyzed, since these concentrations were below the NOEC determined in this test. From the control samples, one of the duplicate samples was analyzed per sampling time. The measured concentrations in the test media of the nominal test concentrations of 32 and 100 mg/L were 77 and 79 % of the nominal values at the start of the test, respectively. During the test period of 72 hours, a decrease of test item concentration in the test media occurred. At the end of the test, 58 and 61 % of the nominal values were found, respectively. The microscopic examination of the algal cells at the end of the test showed no difference between the algae growing at the nominal test concentration of 100 mg/L and the algal cells in the control. The shape and size of the algal cells were obviously not affected by the test item up to at least this concentration. No remarkable observations were made concerning the appearance of the test media. All test media were clear solutions throughout the test period. The biological results based on growth rate can be summarized as follows: ErC10(72h), ErC20(72h) as well as ErC50(72h) were found to be > 120 mg/L. Based on yield, the results were reported as: EbC10(72h): 7.7 mg/L, EbC20(72h): 120 mg/L (extrapolated) and EbC50(72h) > 120 mg/L (extrapolated). The NOEC was found as 21 mg/L and the NOEC as 69 mg/L after 72 hours exposure duration, respectively. Defined values for EC10 (growth rate), EC20 and EC50 (growth rate and yield) could not be calculated due to the low toxicity of the test item for the algae. Confidence intervals could not be calculated.

Description of key information

Toxicity to aquatic algae: NOEC = 21 mg/L (growth rate / biomass), LOEC = 69 mg/L (growth rate / biomass), EC50 > 120 mg/L (growth rate / biomass), EC10 > 120 mg/L (growth rate), EC10 = 7.7 mg/l (biomass), EC20 > 120 mg/l (growth rate), EC20 = 120 mg/L (biomass), 72 h, for Pseudokirchnerella subcapitata (OECD 201, GLP, on 1,2,3-Propanetriol, glycidyl ethers)

Key value for chemical safety assessment

EC50 for freshwater algae:

120 mg/L

EC10 or NOEC for freshwater algae:

120 mg/L

Additional information

There is a valid, well-documented GLP OECD 201 guideline study without relevant deviations on the structural analogue 1,2,3-Propanetriol, glycidyl ethers available, assessed with Klimisch 2. In this study, the following values were determined after 72h: OEC = 21 mg/L (growth rate / biomass), LOEC = 69 mg/L (growth rate / biomass), EC50 > 120 mg/L (growth rate / biomass), EC10 > 120 mg/L (growth rate), EC10 = 7.7 mg/L (biomass), EC20 > 120 mg/L (growth rate), EC20 = 120 mg/L (biomass). The results can be considered as sufficiently reliable to assess the toxicity of 2,3-epoxypropyl isopropyl ether to aquatic algae. Due to limitations of the IUCLID entry field, the EC50 and EC10 values will be stated as 120 mg/L, are however very likely much higher.

With regard to the CLP Regulation 1272/2008, the results do not trigger classification of 2,3-Propanetriol, glycidyl ethers and hence 2,3-epoxypropyl isopropyl ether as hazardous to the aquatic environment. The database is of high quality, and the tonnage-driven data requirements under REACH are fully met, hence, no data gap was identified.