Undecanal

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:

2018-12-11 to 2018-12-21

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Version / remarks:

adopted March 2006; corrected July 2011

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.3 (Algal Inhibition test)

Version / remarks:

Council Regulation (EC) No. 266/2016

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

All concentration levels and the control were analytically verified via LC-MS at the start (0 hours), after 24 hours and at the end of the exposure (72 hours) with algae.

Vehicle:

no

Details on test solutions:

A saturated solution with a nominal loading of 10 mg/L of the test item was prepared once at room temperature 1 hour prior to the start of the exposure in a closed glass bottle. An appropriate volume of the test item (the density of 0.828 g/cm3 at 20 °C was taken into account) was placed by pipette onto the surface of the sterile demineralized water and the bottle was closed with the screw cap. The headspace in the glass flask was minimized. The test item solution was stirred with a magnetic stirrer at approximately 1100 rpm for 1 hour at room temperature. After completion of stirring, the water phase (saturated solution) was removed by siphoning from the center of the water body after a short settling period not exceeding 10 minutes. The test item solution was checked via laser beam (Tyndall effect) for undissolved test item (formation of an emulsion). A slightly positive Tyndall effect was observed in the saturated solution. Then the components of the dilution water were added to the saturated solution. The saturated solution was used as a stock solution for the preparation of further dilution levels by dilution with dilution water.
The preparation method for the saturated solution was based on results of a preliminary experiment outlined within the attached illustration under the heading "17.1 1st Stability Test in Demineralized Water". It was a compromise between the aim of obtaining saturation level and keeping the reaction product undecanoid acid as low as practically possible.

Test organisms (species):

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

Details on test organisms:

Synonyms: Selenastrum capricornutum; Ankistrodesmus subcapitata; Raphidocelis subcapitata; Ankistrodesmus bibraianus (Experimental Phycology and Culture Collection of Algae at the University of Goettingen 2014).
Origin: Culture Collection of Algae and Protozoa (CCAP) SAMS Research Services Ltd Dunstaffnage Marine Laboratory Dunbeg, OBAN; Argyll PA37 1QA; Scotland, UK;
Cultivation at test facility: Fresh stocks are prepared every month on Z-Agar. Light intensity amounts to 2590 - 5180 lux corresponding to 35 - 70 μE m^(-2) s^(-1) for 24 hours per day.
Culture medium: Nutrient medium Z according to LÜTTGE et al. (1994);

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Post exposure observation period:

no

Hardness:

nominal hardness: 0.24 mmol Ca+Mg/L.

Test temperature:

min: 23.0 °C
max: 24.0 °C
mean value: 23.5 °C

pH:

pH range over all concentration groups during the study (0 h to 72 h): 7.85 to 8.38

Dissolved oxygen:

not applicable

Salinity:

not applicable, fresh water

Conductivity:

max. 0.1 μS/cm for ultrapure water used to prepare the dilution water

Nominal and measured concentrations:

Six concentrations were tested in a geometric series with a dilution factor of √10:
0.252 – 0.800 – 2.52 – 8.00 – 25.2 – 80.0% of the saturated solution, corresponding to the summed up time weighted mean measured concentrations of the test item and the degradation product of 3.22 – 6.40 – 23.5 – 81.1 – 284 – 1333 μg/L.
Dilution water without test item incubated under the same conditions as the test groups served as the control. Six control replicates were tested under the same test conditions as the test vessels.

Details on test conditions:

See IUCLID section "Any other information on materials and methods incl. tables" below.

Reference substance (positive control):

yes

Remarks:

potassium dichromate

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

132 µg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

other: n-undecanal and n-undecanoic acid

Basis for effect:

growth rate

Remarks on result:

other: 95% CI: 119 – 149 µg/L

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

49.1 µg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

other: n-undecanal and n-undecanoic acid

Basis for effect:

growth rate

Remarks on result:

other: 95% CI: 38.5 – 60.0 µg/L

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

23.5 µg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

other: n-undecanal and n-undecanoic acid

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

LOEC

Effect conc.:

81.1 µg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

other: n-undecanal and n-undecanoic acid

Basis for effect:

growth rate

Details on results:

See IUCLID section "Any other information on results incl. tables" below.

Results with reference substance (positive control):

The toxicity of potassium dichromate (SIGMA-ALDRICH, batch number MKBV0900V, purity 99.0 %, CAS RN 7778-50-9) to the unicellular freshwater green alga Pseudokirchneriella subcapitata was determined over a period of 72 hours from 2018-09-25 to 2018-09-28 (with headspace) and 2018-07-10 to 2018-07-13 (without headspace), respectively. The reference item toxicity is in the valid range which was established by calculation of the average of the historic reference data since 2005, and the limits were set using the threefold standard deviation of these values.
The following results were obtained (0 h to 72 h), with headspace (+hs) and without heaspace (-hs):

ErC50 (+hs) = 0.799 mg/L (95% CI: 0.707 - 1.30); ErC50 (-hs) = 0.244 mg/L (95% CI: 0.175 - 0.350*) - valid range (average ± 3 x SD): 0.744 ± 0.626

EyC50 (+hs) = 0.607 mg/L (95% CI: 0.404 - 0.694); EyC50 (-hs) = 0.236 mg/L (95% CI: 0.175 - 0.350*) - valid range (average ± 3 x SD): 0.409 ± 0.333

SD = Standard deviation
* = The highest concentration level without statistical significance and the lowest concentration level with statistical significance were used as confidence limits.

Reported statistics and error estimates:

Dose response modelling was performed using four parameter logistic equation i.e. sigmoidal dose-response with variable slope.
The following equation was applied:
Y=Bottom + (Top-Bottom)/(1+10^((LogEC50-X)*HillSlope))
 
Reported parameters for goodness of fit are the following (72 h exposure, growth rate):
 
R^2 (goodness of fit - between 0 and 1, the closer to 1 the better): 0.9922
 
Standard deviation of residuals, Sy.x = [(sum over all squared residuals)/(n-k)]^0.5, n-k being degrees of freedom (14):
Sy.x = 4.091;
Replicates test for lack of fit: the scatter of replicates for Xi is quantified by SD_replicates, the SD_lack of fit quantifies how close the curve approaches the mean of replicates. F compares these values: F= (SD_lack of fit / SD_replicates)^2. The p-value gives the probability of finding the F value under the presumption that all scatter is Gaussian (i.e. the model correct). A small p-value indicates that the model is wrong.
SD_replicates: 3.378;
SD_lack of fit: 6.976;
Discrepancy (F): 4.264;
P value: 0.0399;
 
Conclusion:
Based on the replicates test for lack of fit, the model would be inadequate: the scatter of replicates (SD) is low compared to SD_lack of fit (relatively high F-value), indicating a non-optimal fit. However, while other functions yielded better goodness of fit parameters, the actual fit as judged from plotting data with fitting function was unacceptable. In contrast, fitting data with sigmoidal dose-response with variable slope yielded acceptable confidence intervals and a scientifically valid representation of actual data in the plot (see graphical representation of dose-response curve in attached illustration.

For details on statistical testing, please see section "Overall remarks, attachments".

Measured Exposure Concentrations during the Definitive Test

The concentrations of the test item n-Undecanal and the degradation product n-undecanoic acid were determined at the start of exposure (0 h), after 24 hours and at the end of exposure in the test item treatments and the control via LC-MS/MS.

Details on measurements are given in tables 8 (n-undecanal), 9 (undecanoic acid) and 10 (sum of n-undecanal and undecanoic acid, time weighted mean meassured concentrations) within the attached illustration.

In summary, the following time weighted mean measured concentrations were obtained for the test item:

Nominal test item concentration [% of saturated solution]	Summed up time-weighted mean measured test item and degradation product concentration [µg/L]
80.0	1333
25.2	284
8.00	81.1
2.52	23.5
0.800	6.40
0.252	3.22

Biological results:

Determined cell densities at the start (0 h), after 24 h, 48 h, and 72 h for all single replicates is given in Table 4 within the attached illustration.

Microscopic evaluation of the cells at the start and at the end of the exposure revealed no morphological abnormalities in the test item treatments and the control. All effect values are given based on the summed up time-weighted mean measured concentrations of the test item and the degradation product.

A plot of the cell densities for the test item treatments and the control (0-72 hours) is given in figure 3 within the attached illustration.

Accordingly, the following (No)effect concentrations were derived based on the time-weighted mean measured test item concentrations (sum of n-undecanal and undecanoic acid):

NOEC, LOEC, ECx-values and 95% Confidence Intervals of n-Undecanal (0 - 72 hours) based on summed up time-weighted mean concentrations of the test item and the degradation product [μg/L]:

	Growth Rate Inhibition Time-weighted mean measured test item and degradation product concentration [µg/L]
NOEC	23.5
LOEC	81.1
ErC10	49.1 (38.5 – 60.0)
ErC20	73.9 (64.7 – 84.3)
ErC50	132 (119 – 149)
	Yield Inhibition Time-weighted mean measured test item and degradation product concentration [µg/L]
NOEC	23.5
LOEC	81.1
EyC10	n.d.
EyC20	67.9 (22.6 – 237)
EyC50	78.5 (25.7 – 245)

Validity

All validity criteria of the guideline were met:

Increase of the cell growth in the control cultures: 40-fold (>=16), with a specific growth rate 1.23 day^(-1).

Mean coefficients of variation for section-by-section specific growth rates (days 0-1, 1-2 and 2-3) in the control cultures: 27.9% ( ≤ 35%).

Coefficient of variation of average specific growth rates during the whole test period in replicate control cultures: 1.05% ( ≤ 7%).

Validity criteria fulfilled:

yes

Conclusions:

OECD TG 201 (GLP), Growth Inhibition Test with Pseudokirchneriella subcapitata with n-Undecanal:
The EC50-values for inhibition of growth rate and yield after 72 hours were 132 µg/L (95% CI: 119 – 149 μg/L) and 78.5 µg/L (95% CI: 25.7 – 245 μg/L), respectively. The NOEC-values for both inhibition of growth rate and yield after 72 hours were 23.5 μg/L.The EC10 (72 h; growth rate) was determined as 49.1 µg/L (38.5 – 60.0)

Executive summary:

For the test item n-undecanal a growth inhibition test on the unicellular freshwater green alga Pseudokirchneriella subcapitata was performed over 72 h according to OECD 202 (2004) compliant with GLP.

The study was conducted under static conditions with an initial cell density of 6442 cells/mL.

A saturated solution with a nominal loading of 10.0 mg test item/L was prepared once at room temperature 1 hour prior to the start of the exposure. After stirring for 1 hour the water phase (saturated solution) was removed by siphoning from the centre of the water body. This procedure was based on preliminary testing and is a compromise between the aim of obtaining saturation level and keeping the reaction product undecanoid acid as low as practically possible. After addition of the components of the dilution water the saturated solution was used as a stock solution for the preparation of further dilution levels.

With regard to the volatility of the test item, glass flasks without headspace were used in the test.

Six concentrations were tested in a geometrical series with a dilution factor of √10 (nominal): 0.252 - 0.800 - 2.52 - 8.00 - 25.2 - 80.0% of the saturated solution, corresponding to the summed up time-weighted mean measured concentrations of the test item and the degradation product of 3.22 – 6.40 – 23.5 – 81.1 – 284 – 1333 μg/L.

Three replicates were tested for each test item concentration and six replicates for the control. The environmental conditions were within the acceptable limits.

The test media were clear throughout the test period. The concentrations of n-Undecanal in the test item solutions and the control were analytically verified via LC-MS/MS at test start, after 24 and the end of exposure. The measured concentrations of the test item n-Undecanal were in the range of < LOQ to 971 μg/L at test start and between < LOQ and 562 μg/L at the end of the exposure. Additionally, the concentrations of the degradation product undecanoic acid were analyzed and calculated as n-Undecanal concentrations by conversion for molecular weight. The measured concentration of Undecanoic acid given as n-Undecanal equivalents were in the range of < LOQ to 622 μg/L at test start and between < LOQ and 722 μg/L at the end of the exposure. All effect values are based on the summed up time-weighted mean measured concentrations of the test item and the degradation product.

The following (no)effect concentrations were derived:

EC50 (72 h; growth rate) = 132 µg/L (95% CI: 119 – 149 μg/L);

EC50 (72 h; yield) = 78.5 µg/L (95% CI: 25.7 – 245 μg/L);

NOEC (72 h; growth rate and yield) = 23.5 μg/L;

EC10 (72 h; growth rate) = 49.1 µg/L (95% CI: 38.5 – 60.0 µg/L).

All validity criteria of the guideline were met.

Description of key information

OECD TG 201 (GLP), Growth Inhibition Test with Pseudokirchneriella subcapitata with n-Undecanal - the following (no)effect concentrations were derived:

EC50 (72 h; growth rate) = 132 µg/L (95% CI: 119 – 149 μg/L);

EC50 (72 h; yield) = 78.5 µg/L (95% CI: 25.7 – 245 μg/L);

NOEC (72 h; growth rate and yield) = 23.5 μg/L;

EC10 (72 h; growth rate) = 49.1 µg/L (95% CI: 38.5 – 60.0 µg/L).

Key value for chemical safety assessment

EC50 for freshwater algae:

0.132 mg/L

EC10 or NOEC for freshwater algae:

0.049 mg/L

Additional information

In the valid key study (NOACK, 2019), n-undecanal was tested in a growth inhibition test on the unicellular freshwater green alga Pseudokirchneriella subcapitata over 72 h according to OECD 202 (2004) compliant with GLP.

The study was conducted under static conditions with an initial cell density of 6442 cells/mL.

A saturated solution with a nominal loading of 10.0 mg test item/L was prepared once at room temperature 1 hour prior to the start of the exposure. After stirring for 1 hour the water phase (saturated solution) was removed by siphoning from the centre of the water body. This procedure was based on preliminary testing and is a compromise between the aim of obtaining saturation level and keeping the reaction product undecanoid acid as low as practically possible. After addition of the components of the dilution water the saturated solution was used as a stock solution for the preparation of further dilution levels.

With regard to the volatility of the test item, glass flasks without headspace were used in the test.

Six concentrations were tested in a geometrical series with a dilution factor of √10 (nominal): 0.252 - 0.800 - 2.52 - 8.00 - 25.2 - 80.0% of the saturated solution, corresponding to the summed up time-weighted mean measured concentrations of the test item and the degradation product of 3.22 – 6.40 – 23.5 – 81.1 – 284 – 1333 μg/L.

Three replicates were tested for each test item concentration and six replicates for the control. The environmental conditions were within the acceptable limits.

The test media were clear throughout the test period. The concentrations of n-Undecanal in the test item solutions and the control were analytically verified via LC-MS/MS at test start, after 24 and the end of exposure. The measured concentrations of the test item n-Undecanal were in the range of < LOQ to 971 μg/L at test start and between < LOQ and 562 μg/L at the end of the exposure. Additionally, the concentrations of the degradation product undecanoic acid were analyzed and calculated as n-Undecanal concentrations by conversion for molecular weight. The measured concentration of Undecanoic acid given as n-Undecanal equivalents were in the range of < LOQ to 622 μg/L at test start and between < LOQ and 722 μg/L at the end of the exposure. All effect values are based on the summed up time-weighted mean measured concentrations of the test item and the degradation product.

The following (no)effect concentrations were derived:

EC50 (72 h; growth rate) = 132 µg/L (95% CI: 119 – 149 μg/L);

EC50 (72 h; yield) = 78.5 µg/L (95% CI: 25.7 – 245 μg/L);

NOEC (72 h; growth rate and yield) = 23.5 μg/L;

EC10 (72 h; growth rate) = 49.1 µg/L (95% CI: 38.5 – 60.0 µg/L).

All validity criteria of the guideline were met.