Dipotassium oxalate

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

26 - 29 Jul 2016

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:

2006

GLP compliance:

yes (incl. QA statement)

Remarks:

Department of Health of the government of the United Kingdom

Specific details on test material used for the study:

Storage conditions: ambient temperature (10 to 30 °C) "

Analytical monitoring:

yes

Details on sampling:

- Concentrations and sampling method: samples of test media of all concentrations and the control were analysed at 0 (fresh media), 24, 48 and 72 h. At 72 h, inoculated replicate test vessels at each treatment level were pooled prior to sampling.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: a 100 mg/L solution was prepared by diluting the substance directly in the medium. The remaining test concentrations were prepared through serial dilution of this solution.

Test organisms (species):

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

Details on test organisms:

TEST ORGANISM
- Common name: green algae
- Strain: 278/4
- Source: laboratory culture

ACCLIMATION
- Acclimation period: prior to testing, duplicate cultures were prepared and incubated under test conditions for at least 72 h
- Culturing media and conditions: same as test

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Hardness:

-

Test temperature:

21.0 – 21.9 °C

pH:

7.45 - 7.95

Dissolved oxygen:

-

Salinity:

-

Conductivity:

-

Nominal and measured concentrations:

Nominal concentrations: 0 (control), 10, 18, 32, 56 and 100 mg/L
Mean measured:

Details on test conditions:

TEST SYSTEM
- Test vessel: 250 mL conical flasks
- Fill volume: 100 mg/L
- Initial cells density: 1 x 10^4 cells/mL
- Control end cells density: 54.8 cells x 10^4/mL
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6

GROWTH MEDIUM
- Standard medium used: yes
- Detailed composition if non-standard medium was used:

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: according to guideline
- Ca/Mg ratio: 18 mg/L CaCl2 2H2O per 15 mg/L MgSO4 7H2O
- Intervals of water quality measurement: temperature was recorded continuously

OTHER TEST CONDITIONS
- Sterile test conditions: no
- Adjustment of pH: no
- Photoperiod: continuous light conditions
- Light intensity and quality: 4440-8880 Lux (LED lights)
- Agitation: at ca 100 rpm

EFFECT PARAMETERS MEASURED
- Determination of cell concentrations: every 24 h with a particle counter (Z2 Coulter Counter®)

TEST CONCENTRATIONS
- Range finding study; yes
- Test concentrations: 0 (control), 1.0, 10 and 100 mg/L
- Results used to determine the conditions for the definitive study: the results of the range-finding test suggested that the 72-h EC50 value would be greater than 100 mg/L and the NOEC may be between 10 and 100 mg/L

Reference substance (positive control):

no

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 78 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

> 78 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

- Exponential growth in the control (for algal test): yes (54 fold)
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: freshly prepared media appeared as colourless solutions however, the 100 mg/L test concentration was slightly cloudy a period of time. After 24 h, slight precipitates were observed at concentrations
of 32, 56 and 100 mg/L. However, after gentle shaking the precipitate re-dissolved.

Table 1: Analytical results.

Nominal concentration (mg/L)	0 h	% nominal	24 h	% nominal	48 h	% nominal	72 h	% nominal	Time weighted mean measured concentration (mg/L)
Control	<LOQ	-	<LOQ	-	<LOQ	-	<LOQ	-	-
10	8.88	89	8.35	84	11.42	114	6.45	65	8.8
18	17.46	97	19.74	110	13.92	77	12.86	71	16
32	20.69	65	25.25	79	24.25	76	33.24	104	26
56	47.71	85	42.23	75	56.63	101	52.21	93	50
100	76.1	76	82.4	82	75.99	76	77.68	78	78

Since some of the measured concentrations were < 80% of the nominal value, it was considered appropriate to base the results on mean measured test concentrations.

Table 2: Cell concentrations of Pseudokirchneriella subcapitata during exposure time.

Measured concentration (mg/L)	Mean cell concentration (cells x 10^4/mL)
	24 h	48 h	72 h
Control	3.02	13.4	54.8
8.8	2.44	12.7	54.8
16	2.77	13	59.4
26	2.7	12.4	57
50	2.32	12.1	51.6
78	2.79	14.5	69.9

Table 3: % Inhibition of growth rate of Pseudokirchneriella subcapitata relative to the control.

Measured concentration (mg/L)	Reduction in average area under the growth curve relative to the control (%)			Reduction in average specific growth rates relative to the control (%)
	0-24 h	0-48 h	0-72 h	0-24 h	0-48 h	0-72 h
Control	-	-	-	-	-	-
8.8	29	11	3	19	2	0
16	12	5	-4	8	1	-2
26	16	10	1	10	3	-1
50	35	17	9	24	5	2
78	11	-4	-20	7	-3	-6

The mean coefficient of variation for section-by-section specific growth rates (0-24, 24-48 and 48-72 h) in the control culture was 8.51%.

The coefficient of variation for average specific growth rates during the whole test period in replicate control culture was 3.17%.

Table 4: Further toxicity results.

	Toxicity values (mg/L)
	72-hour
Parameter
Yield	>78
EyC10	>78
EyC20	>78
EyC50	>78
NOEC	≥78
Biomass
EbC10	>78
EbC20	>78
EbC50	>78
NOEC	≥78
Growth Rate
ErC20	>78
NOEC	≥78

Validity criteria fulfilled:

yes

Reference 2

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

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

Adequacy of study:

key study

Justification for type of information:

Please refer to the analogue justification provided in IUCLID section 13.

Reason / purpose for cross-reference:

read-across source

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 78 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

> 78 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Description of key information

ErC50 (72 h) > 78 mg/L and NOErC (72 h) ≥78 mg/L (geom. mean meas., OECD 201) based on read across from CAS 6009-70-7

Additional information

No data are available on the toxicity of dipotassium oxalate anhydrate (CAS 583-52-8) to algae. Therefore, a read across was performed to the analogues substance diammonium oxalate monohydrate (CAS 6009-70-7). Details on the read across justification are provided in section 13 of the IUCLID dossier.

The study was conducted according to the OECD guidance 201 and GLP standards (reference: 6.1.5-1). In a static system the test organism Pseudokirchneriella subcapitata was exposed for 72 h to nominal test concentrations of 0 (control), 10, 18, 32, 56 and 100 mg/L (corresponding to <LOQ, 8.8, 16, 26, 50 and 78 mg/L geom. mean meas.). An analytical monitoring was performed via LC-TOF/MS. Analysis of the test media samples was conducted after 0, 24, 48 and 72 h. The recovery of the test substance was between 65% and 114% of the nominal values. Therefore the results refer to geom. mean measured concentration. No toxic effects were observed up to the highest tested concentration resulting in an ErC50 (72 h) of > 78 mg/L and a NOErC (72 h) ≥ 78 mg/L (geom. mean meas.).

Based on the results of the read across substance, no toxic effects to algae are expected by dipotassium oxalate.