Tetrakis(diethyldithiocarbamato-S,S')tellurium

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:

04 Sep 2018 to 07 Sep 2018

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:

July 2011

Qualifier:

according to guideline

Guideline:

EU Method C.3 (Algal Inhibition test)

Version / remarks:

1992

GLP compliance:

yes

Specific details on test material used for the study:

- Name of test material (as cited in study report): Perkacit® TDEC pdr
- Batch No.: 60701019
- Appearance: Solid
- Tellurium content: 17.6%
- Date of manufacture: 09 Feb 2017
- Storage conditions: Ambient

Analytical monitoring:

yes

Details on sampling:

Samples of the test solutions were collected to measure concentrations of the test substance at 0, 24, 48, and 72 hours. In addition, the stock solutions prepared in DMF at test initiation were also analyzed. Duplicate samples were collected at each sampling interval with one set of samples processed immediately for analysis and the other set stored refrigerated for potential future analysis if deemed necessary. Samples collected at test initiation (0 hour) were collected from the individual batches of test solution prepared for each treatment and control group prior to distribution into the test chambers. Samples collected at 24 and 48 hours were collected from surrogate replicates included in each treatment and control group. At exposure termination (72 hours), samples were collected from the pooled replicates from each treatment and control group. At each sampling interval, 10 mL of test solution was added to 20 mL glass scintillation vials containing 10 mL of acetonitrile. The samples collected from the dimethylformamide stocks consisted of approximately 5.0 mL of stock added to a 20 mL glass scintillation vial.

Vehicle:

yes

Remarks:

0.1 mL dimethylformamide/L

Details on test solutions:

A primary stock solution was prepared by mixing 0.0634 g of the test substance in 10 mL of DMF, to achieve a nominal concentration of 6.34 mg/mL. The primary stock was inverted at least 20 times to mix and appeared clear and orange in color at the time of preparation. The primary stock was serially diluted with DMF to prepare four additional stocks at nominal concentrations of 396, 793, 1585, and 3170 μg/mL. The 396, 793, 1585, and 3170 μg/mL stocks were mixed by inversion. Final nominal test concentrations were prepared by diluting 100 μL of each stock solution to a final volume of 1000 mL with freshwater OECD medium. The test solutions were sonicated for 10 minutes and inverted to mix. The test solutions appeared clear and colorless and otherwise unremarkable at the time of preparation. The 634 μg/L test solution was sonicated for 30 minutes and inverted to mix. Very fine particulates were observed in the 634 μg/L test solution after mixing. A solvent control was prepared by diluting 100 μL of DMF to a final volume of 1000 mL with freshwater OECD medium. The concentration of solvent in the treatment groups and solvent control was 0.1 mL DMF/L. The negative control solution consisted of freshwater OECD medium without test substance added.

Test organisms (species):

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

Details on test organisms:

TEST ORGANISM
- Common name: Green algae
- Source: Original algal cultures were obtained from the University of Texas at Austin, and have been maintained in culture medium at the test facility since June 2017.
- Method of cultivation: Algal cells for this study were taken from a culture that had been transferred to fresh medium five days prior to test initiation.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Test temperature:

23.18 - 23.31

pH:

- At study initiation: 7.9 - 8.0
- At study termination: 7.9 - 8.5

Nominal and measured concentrations:

- Nominal concentrations: 0 (negative control), 0 (solvent control), 40, 79, 159, 317 and 634 µg/L
- Mean measured concentrations:

Details on test conditions:

TEST SYSTEM
- Test vessel: Test chambers were sterile, 250 mL glass Erlenmeyer flasks. Test chambers were indiscriminately positioned on mechanical shaker tables in an environmental chamber and were shaken continuously at approximately 100 rpm.
- Type: closed, vessels were plugged with foam stoppers.
- Fill volume: 100 mL
- Aeration: No
- Initial cells density: 10,000 cells/mL
- Control end cells density:
- No. of organisms per vessel:
- No. of vessels per concentration: 3
- No. of vessels per control: 6
- No. of vessels per vehicle control: 3

GROWTH MEDIUM
- Standard medium used: yes; the algal cells were cultured and tested in freshwater OECD medium. Stock nutrient solutions were prepared by adding reagent-grade chemicals to purified EAG Laboratories-Easton well water (NANOpure® water). The test medium then was prepared by adding appropriate volumes of the stock nutrient solutions to NANOpure® water. The pH of the medium was adjusted to 8.0 with 10% hydrochloric acid and/or 0.1 N sodium hydroxide, as needed. The medium was sterilized by filtration (0.22 µm) and stored refrigerated prior to use.
- Detailed composition if non-standard medium was used:

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: EAG Laboratories-Easton well water (NANOpure® water).
- Culture medium different from test medium: Same

OTHER TEST CONDITIONS
- Sterile test conditions: yes
- Adjustment of pH: Yes, the pH of the medium was adjusted to 8.0 ± 0.1 using 10% HCl 0.1 N NaOH.
- Photoperiod: Continuous illumination
- Light intensity and quality: 6000 lux ± 10%. Light intensity was measured at test solution level at five locations surrounding the test flasks at test initiation using a SPER Scientific 840006C light meter.

WATER QUALITY MEASUREMENTS
- Temperature: The temperature of a container of water adjacent to the test chambers in the environmental chamber was monitored continuously using an Amegaview Scientific centralized monitoring system.
- pH: The pH of the medium in each treatment and control group was measured at test initiation and exposure termination using a Thermo Orion Model A214 pH/ISE meter, or equivalent. At test initiation, pH was measured in the individual batches of test solution prepared for each treatment and control group. At exposure termination, pH was measured in pooled samples of test solution collected from each of the replicates of each treatment and control group.

EFFECT PARAMETERS MEASURED: algal cell density, morphology
One test medium sample was collected from each replicate of the treatment and control groups at each sampling interval for the determination of algal cell densities, excluding the surrogate replicates included for analytical sampling. Samples were collected at approximately 24 hour intervals during the 72 hour exposure and were held in the dark for a maximum of two days under refrigerated conditions sufficient to inhibit growth until cell counts could be performed. Cell counts were performed using an electronic particle counter (Beckman Coulter® Z2 Series). Prior to conducting cell counts, the linearity of the instrument response was determined at settings previously established for R. subcapitata. A primary counting standard containing R. subcapitata cells was prepared at a nominal concentration of 100,000 cells/mL, and the density was verified using a hemacytometer and a microscope. The standard was subsequently diluted to provide a series of seven counting standards for the determination of instrument linearity. Theoretical densities were assigned to each secondary counting standard based upon the verified density of the primary counting standard and the dilution ratio. The cell densities of the counting standards were measured using the electronic particle counter and were compared to the theoretical densities by performing a least squares regression analysis. Cell counts for samples collected during the test were conducted once instrument linearity was demonstrated (i.e., the R squared values obtained through the regression analysis was 0.99912). A single aliquot of each sample collected during the test was diluted with an electrolyte solution (Isoton® II). Three 0.5-mL volumes of the diluted sample were counted, and the resulting counts were averaged. The cell density of the sample was determined by adjusting the mean cell count (cells/mL) obtained using the particle counter, based upon the Y intercept and slope calculated through the regression analysis, and the dilution factor. At the end of the exposure period, samples of test solution were collected from each of the replicates per treatment and control group, pooled within their respective treatments, and subsamples were removed and examined microscopically for atypical cell morphology (e.g., changes in cell shape, size or color). Cells in the replicate test chambers also were assessed for aggregation or flocculation of cells, and adherence of the cells to the test chamber.

RANGE FINDING STUDY
An exploratory non-GLP range-finding toxicity test was conducted at nominal concentrations of 0.634, 6.34, 63.4, and 634 μg/L, and yielded 3, 9, 3, and 38 inhibition of mean cell density, respectively, after 72 hours of exposure, relative to the mean negative control response.

Reference substance (positive control):

no

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 171 µg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: See 'Any other information on resutls incl. tables' for an overview of additional effect values

Key result

Duration:

72

Dose descriptor:

EC10

Effect conc.:

34 µg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 95% C.I.: <26 - 51 µg/L

Remarks:

See 'Any other information on resutls incl. tables' for an overview of additional effect values

Details on results:

An overview of the results is tabulated in 'Any other information on resutls incl. tables'.
- Cell density: After 72 hours of exposure, inhibition of cell density in the 26, 38, 56, 95, and 171 μg/L treatment groups was -1, 29, 70, 77, and 84%, respectively, relative to the pooled control.
- Yield: Inhibition of yield in the 26, 38, 56, 95, and 171 μg/L treatment groups was -1, 29, 70, 78, and 84%, respectively, relative to the pooled control.
- Growth rate: Inhibition of growth rate in the 26, 38, 56, 95, and 171 μg/L treatment groups was 0, 6, 22, 28, and 34%, respectively, relative to the pooled control.

Mean cell density and mean yield were significantly reduced (Dunnett’s test; p < 0.05) in the 38, 56, 95, and 171 μg/L treatment groups at 72 hours, when compared to the pooled control. Mean growth rate was significantly reduced (Jonckheere Terpstra Step-Down Trend test; p < 0.05) in the 38, 56, 95, and 171 μg/L treatment groups at 72 hours, when compared to the pooled control.

- Morphology: After 72 hours of exposure, aggregation, flocculation, or adherence to the test chambers was not observed in the controls or in any treatment groups. There were no noticeable changes in cell morphology in any of the treatment groups when compared to the control replicates during the microscopic examinations of the cells.

Reported statistics and error estimates:

See 'Any other information on materials and methods incl. tables'.

Table: Mean Cell Density, Mean Yield, and Percent Inhibition

Geometric Mean, Measured Test Concentration (μg/L)	24 Hours		48 Hours		72 Hours		0-72 Hours
	Mean Cell Density (cells/mL)	Percent Inhibition (1,2)	Mean Cell Density (cells/mL)	Percent Inhibition (1,2)	Mean Cell Density (cells/mL)*	Percent Inhibition (1,2)	Mean Yield (cells/mL)*	Percent Inhibition (1,2)
Negative Control	59,002	--	409,324	--	2,203,235	--	2,193,235	--
Solvent Control	56,909	--	367,737	--	2,224,067	--	2,214,067	--
Pooled Controls	58,304	--	395,461	--	2,210,179	--	2,200,179	--
26	58,060	0	385,606	2	2,225,385	-1	2,215,385	-1
38	55,142	5	299,171	24	1,575,730*	29	1,565,730*	29
56	48,057	18	200,711	49	664,358*	70	654,358*	70
95	47,606	18	165,266	58	498,953*	77	488,953*	78
171	44,207	24	131,964	67	355,281*	84	345,281*	84

1) Calculations were performed using SAS Version 9.4. Manual calculations may differ slightly.

2) Inhibition was calculated relative to the mean pooled control response.

* Treatment group mean was significantly reduced (Dunnett’s test, p < 0.05) when compared to the pooled control mean. Significance only evaluated for cell density at 72 hours of exposure.

 

Table: Mean Growth Rate (per Hour) and Percent Inhibition

Geometric Mean, Measured Test Concentration (μg/L)	0-24 Hours		0-48 Hours		0-72 Hours
	Mean Growth Rate (hour-1)	Percent Inhibition (1,2)	Mean Growth Rate (hour-1)	Percent Inhibition (1,2)	Mean Growth Rate (hour-1)*	Percent Inhibition (1,2)
Negative Control	0.0738	--	0.0773	--	0.0749	--
Solvent Control	0.0724	--	0.0751	--	0.0751	--
Pooled Controls	0.0733	--	0.0766	--	0.0750	--
26	0.0733	0	0.0760	1	0.0751	0
38	0.0711	3	0.0708	8	0.0702*	6
56	0.0654	11	0.0625	18	0.0583*	22
95	0.0650	11	0.0584	24	0.0542*	28
171	0.0619	16	0.0537	30	0.0496*	34

1) Calculations were performed using SAS Version 9.4. Manual calculations may differ slightly.

2) Inhibition was calculated relative to the mean pooled control response.

* Treatment group mean was significantly reduced (Jonckheere-Terpstra Step-Down Trend test (p < 0.05) when compared to the pooled control mean. Significance only evaluated at 72 hours of exposure.

ADDITIONAL EFFECT VALUES

Table: NOEC, EC50, ErC50 and EyC50 Values, Based on Geometric Mean, Measured Concentrations

Endpoint	0-24 Hours(1)	0-48 Hours(1)	0-72 Hours(1)
Cell Density
EC50	>171 μg/L	82 μg/L	47 μg/L*
95% Confidence Interval	(n/a)	67 to 100 μg/L	46 to 49 μg/L*
NOEC	--(2)	--(2)	26 μg/L
Growth Rate
ErC50	>171 μg/L	>171 μg/L	>171 μg/L
95% Confidence Interval	(n/a)	(n/a)	(n/a)
ErC20	>171 μg/L	85 μg/L	72 μg/L
95% Confidence Interval	(n/a)	69 to 104 μg/L	56 to 92 μg/L
ErC10	84 μg/L	38 μg/L	34 μg/L
95% Confidence Interval	52 to 134 μg/L	27 to 54 μg/L	<26 to 51 μg/L
NOEC	--(2)	--(2)	26 μg/L
Yield
EyC50	--(3)	--(3)	47 μg/L*
95% Confidence Interval			45 to 49 μg/L*
EyC20	--(3)	--(3)	34 μg/L*
95% Confidence Interval			32 to 38 μg/L*
EyC10	--(3)	--(3)	30 μg/L*
95% Confidence Interval			28 to 32 μg/L*
NOEC	--(2)	--(2)	25 μg/L

1) ECx values were calculated, when possible, using non-linear regression with replicate data (cell density, growth rate, and yield) and geometric mean, measured test concentrations.

2) NOEC values determined only at 72 hours of exposure per study protocol. NOEC values were based on the results of statistical comparisons between the treatment responses and pooled control response.

3) EyCx values were only calculated at 72 hours of exposure.

* Linear interpolation was used to estimate the 72-hour EC50, EyC10, EyC20, and EyC50 values and their corresponding 95% confidence intervals.

Validity criteria fulfilled:

yes

Remarks:

See 'Any other information on materials and methods incl. tables'

Description of key information

The 72-h ErC50 and ErC10 values were determined to be >171 and 34 µg/L, respectively, in a GLP-compliant OECD TG 201 study.

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:

34 µg/L

Additional information

The toxicity towards freshwater algae was determined in a study according to OECD TG 201 and in compliance with GLP criteria (EAG Laboratories, 2018).

In this study, exponentially growing freshwater alga (Raphidocelis subcapitata) were exposed to nominal test substance concentrations of0 (negative control), 0 (solvent control), 40, 79, 159, 317 and 634 µg/Lfor 72 hours under static conditions. The test was performed in 3 replicates per test concentration and 6 replicates in the negative control treatment. Test concentrations were analytically verified and determined to be<LOQ (negative control), <LOQ (solvent control),  26, 38, 56, 95 and 171 µg/L(geometric mean). At the start of the test and after 24, 48 and 72 hours exposure duration, the algae were scored for number of cells and for microscopic abnormalities.

Mean cell density and mean yield were significantly reduced in the 38, 56, 95, and 171 μg/L treatment groups at 72 hours, when compared to the pooled control. Mean growth rate was significantly reduced in the 38, 56, 95, and 171 μg/L treatment groups at 72 hours, when compared to the pooled control. There were no noticeable changes in cell morphology in any of the treatment groups when compared to the control replicates during the microscopic examinations of the cells.Based on these findings, the 72-h EC50 values for growth rate and yield are determined at >171 and 47 µg/L, respectively. The 72-h EC10 values are 34 and 30 µg/L, respectively.