2,2-dimethyl-1,3-propanediyl didecanoate

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

04 Jul - 05 Jul 2012

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: GLP-guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Version / remarks:

adopted 2010

GLP compliance:

yes (incl. QA statement)

Remarks:

The Department of Health of the Government of the United Kingdom

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: Amounts of test item (5, 50 and 500 mg in triplicate) were each separately dispersed in approx. 200 mL of deionised reverse osmosis water and subjected to ultrasonication for approx.. 15 min followed by magnetic stirring for 24 h in order to maximise the dissolved test item concentration. All test vessels were shielded from light during mixing. Synthetic sewage (16 mL), activated sewage sludge (250 mL) and water were added to a final volume of 500 mL to give the required concentrations of 10, 100 and 1000 mg/L (3 replicates).

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Source of inoculum: A mixed population of activated sewage sludge micro-organisms was obtained on 04 July 2012 from the aeration stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, UK, which treats predominantly domestic sewage.
- Preparation of inoculum for exposure: The activated sewage sludge sample was maintained on continuous aeration in the laboratory at a temperature of approx. 21 °C overnight prior to use in the test. On the day of collection the activated sewage sludge (5 L) was fed synthetic sewage sludge (250 mL).
- Initial suspended solids concentration: 3.0 g/L prior to use

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

20 ± 2 °C

pH:

at test start: 6.9 - 7.3
at test end: 7.3 - 7.8

Dissolved oxygen:

Control vessels: 5.6 - 6.3 mg/L
Test item vessels: 5.0 - 5.3 mg/L
Reference vessels: 5.5 - 6.1 mg/L

Nominal and measured concentrations:

Nominal: 0, 10, 100 and 1000 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: 500 mL conical flask
- Measuring vessel: 250 mL darkened glass BOD bottle
- Aeration: air flow of 0.5 - 1 L per minute
- No. of vessels per concentration (replicates): 1 vessel for 10 and 100 mg/L each, 3 vessels for 1000 mg/L
- No. of vessels per control (replicates): 4
- Respiratory substrate: Synthetic sewage with composition as recommended by OECD guideline 209.

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: The test water used was deionised reverse osmosis water containing less than 1 mg/L dissolved organic carbon (DOC).
- Intervals of water quality measurement: The pH of all test solutions was measured at 0 h and after 3 h prior to the measurement of the respiration rate. The oxygen concentrations in all vessels were measured after 30 min contact time.

OTHER TEST CONDITIONS
- Adjustment of pH: yes
- Light intensity: normal laboratory lighting

EFFECT PARAMETERS MEASURED (with observation intervals if applicable):
- The rate of respiration for each flask was measured after 3 hours of incubation.
- Observations were made on the test preparations throughout the test period.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 10
- Range-finding test: The test reported was planned as range-finding test. As no statistically significant toxic effects were shown at all of the test concentrations employed, it was considered justifiable not to perform a definitive test.

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

- In some instances, the initial and final dissolved oxygen concentrations were outside those recommended in the test guideline. This was considered to have had no adverse effect on the result of the study given that in all cases the oxygen consumption rate was determined over the linear portion of the oxygen consumption trace.

Results with reference substance (positive control):

- Results with reference substance valid? yes
- Relevant effect levels: EC50 (3h) = 7.1 mg/L, 95% CL: 5.6 - 9.0 mg/L

Reported statistics and error estimates:

The percentage inhibition values were plotted against concentration for the reference item only, a line fitted using the Xlfit software package (IDBS) and the effect concentration values determined from the equation for the fitted line.
95% confidence limits were calculated for the reference item EC50 value using the method of Litchfield and Wilcoxon (1949).
One way analysis of variance incorporating Bartlett’s test for homogeneity of variance and Dunnett’s multiple comparison procedure for comparing several treatments with a control was carried out on the oxygen consumption data after 3 h for the control and all test concentrations to determine any statistically significant differences between the test and control groups. All statistical analyses were performed using the SAS computer software package (SAS, 1999 – 2001).

Table 1: Oxygen consumption rates and percentage inhibition values after 3 h contact time

 

Nominal concentration (mg/L)	Initial O2 reading (mg O2/L)	Measurement period (min)	Final O2 reading (mg O2/L)	O2 consumption rates (mg O2/L*h)	% Inhibition
Control (1)	3.9	3	1.5	48	-
Control (2)	3.2	2	1.6	48	-
Control (3)	3.5	2	2.0	45	-
Control (4)	3.1	2	1.5	48	-
10	3.2	2	1.5	51	[8]
100	n.d.	n.d.	n.d.	n.d.	n.d.
1000 (1)	n.d.	n.d.	n.d.	n.d.	n.d.
1000 (2)	2.6	1	1.7	54	[14]
1000 (2)	2.7	1	1.7	60	[27]

 

n.d., not determined; it was not possible to measure a response over a linear portion of the trace

[Increase in respiration rate as compared to controls]

Table 2: Observations on the test preparations at test start (prior to the addition of activated sewage sludge) and test end

 

Nominal concentration (mg/L)	Observations on test preparations
	0 hours	3 hours
Control	pale yellow/brown dispersion	dark brown dispersion
10	pale yellow/brown dispersion with slight oily film of test item visible on surface	dark brown dispersion, no undissolved test item visible
100	pale yellow/brown dispersion with oily film of test item visible on surface	dark brown dispersion,oily film of test item visible on surface
1000	pale yellow/brown dispersion, large oily globules of test item visible on surface	dark brown dispersion,oily slick of test item visible on surface
Reference	pale yellow/brown dispersion, no undissolved reference item visible	dark brown dispersion, no undissolved reference item visible

Reference 2

Endpoint:

activated sludge respiration inhibition testing

Type of information:

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

Remarks:

Summary of available data used for the endpoint assessment of the target substance

Adequacy of study:

key study

Justification for type of information:

Refer to analogue justification document provided in IUCLID section 13.

Reason / purpose for cross-reference:

read-across source

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: Source: RA-A, CAS 68855-18-5, Croda, 2012, Activated sludge, 3 h, RL2

Description of key information

NOEC (3 h)≥1000 mg/L (nominal; total respiration; activated sludge); no effects up to the limit of water solubility; read-across

Additional information

There is no study available in which the toxicity of Neopentyl glycol dicaprate (CAS No. 27841-06-1) to microorganisms was assessed. Therefore, read-across to the structurally and chemically closely related source substance Heptanoic acid, ester with 2,2-dimethyl-1,3-propanediol (CAS 68855-18-5) was performed in accordance with Regulation (EC) No 1907/2006 Annex XI, section 1.5 in order to fulfill the data requirements for this substance. The source substance is characterized by similar chemical structure and is therefore considered a suitable representative for the assessment of the toxicity of the target substance to microorganisms. A detailed read-across justification in provided in IUCLID section 13.

The study conducted with the source substance acid, ester with 2,2-dimethyl-1,3-propanediol (CAS 68855-18-5) to microorganisms was performed under static conditions and according to OECD guideline 209, using activated sludgeof a predominantly domestic sewage as test organism. Test solutions of 10, 100 and 1000 mg/L, plus blank control were prepared. No respiration inhibition was observed in the treatments or control during the 3 h exposure period. Hence, the NOEC (3 h) was determined as≥1000 mg/L (nominal; total respiration).

Based on the available result from a structurally related read-across substance (in accordance with Regulation (EC) No 1907/2006 Annex XI, 1.5) which is characterized by a similar ecotoxicological profile and comparable structure, it can be concluded that the target substance Neopentyl glycol dicaprate (CAS No. 27841-06-1) is not toxic to microorganisms.