Potassium niobate

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:

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

Adequacy of study:

key study

Justification for type of information:

For details and justification of read-across please refer to the attached report in section 13 of IUCLID.

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

72 h

Dose descriptor:

EL50

Effect conc.:

533 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: (95%-CI: 393 – 725 mg/L)

Duration:

72 h

Dose descriptor:

EL20

Effect conc.:

164 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: (95%-CI: 79.5 – 242 mg/L)

Duration:

72 h

Dose descriptor:

EL10

Effect conc.:

88.3 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: (95%-CI: 31.6 – 149 mg/L)

Duration:

72 h

Dose descriptor:

LOELR

Effect conc.:

<= 125 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

NOELR

Effect conc.:

< 125 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EL50

Effect conc.:

102 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Remarks on result:

other: (95%-CI: 65 – 136 mg/L)

Duration:

72 h

Dose descriptor:

LOELR

Effect conc.:

<= 125 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

NOELR

Effect conc.:

< 125 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Details on results:

- Exponential growth in the control (for algal test): yes
- Observation of abnormalities (for algal test): no abnormalities observed.
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: Precipitation and agglomeration

- Exponential growth in the control (for algal test): yes
- Observation of abnormalities (for algal test): No
- After pH adjustment the measured Nb5+ concentrations were low and showed high variability. Therefore, no concentration-response relationship could be established. Concentrations of the test sample varied due to precipitation, agglomeration and adsorption reactions. In addition, slight changes in pH had profound impact on the test concentrations. Observed effects may therefore predominantly refer to elevated NaCl concentrations originated from neutralization, than released Nb5+ ions. Hypothetical Nb5+ related effects cannot be distinguished from NaCl induced inhibition in the conducted test. Therefore, only nominal effect levels, respectively nominal loading rates, were calculated.

Results with reference substance (positive control):

- ErC50: 0.74 mg/L (0.73 – 0.76 mg/L 95%-CI)
- EyC50: 0.36 mg/L (0.35 – 0.36 mg/l 95%-CI).

Table 2: Mean growth rates and yields as well as their mean inhibition in comparison to the controls after 72 h, recorded pH at 0 and 72 h.

		Control	A	B	C	D	E
Nominal loading rate [mg/L]		0	125	250	500	1000	2000
Number of replicates		6	3	3	3	3	3
Mean growth rate		1.09	0.82	0.77	0.63	0.49	-0.07
Mean yield		1.77	0.75	0.65	0.39	0.23	-0.01
Mean inhibition of growth rate [%]		-	24.9	29.2	42.5	55.3	106.4
Mean inhibition of yield [%]		-	57.9	63.2	78.1	86.9	100.7
pH	0 h	6.4	6.5	6.6	6.6	6.7	6.7
	72 h	7.1	7.1	7.2	7.2	7.2	7.2

Table 3: Parameters derived from concentration-response calculations for inhibition of growth rate and yield after 72 h of exposure.

	Specific Growth Rate 72 h nominal loading rate	Yield 72 h nominal loading rate
EL50	533 mg/L	102 mg/L
95% CI	393 – 725 mg/L	65.1 – 136 mg/L
EL20	164 mg/L	n.d.
95% CI	79.5 – 242 mg/L
EL10	88.3 mg/L.	n.d.
95% CI	31.6 – 149 mg/L
Slope of the curve	1.642	1.186
P(Chi²)	1.000	1.000
r²	0.744	0.825
LOELR	≤ 125 mg/L	≤ 125 mg/L
NOELR	< 125 mg/L	< 125 mg/L

95% CI: 95%-confidence limit
The data presented were calculated using the statistical software ToxRat (ToxRat solutions, Alsdorf, Germany)

n.d.: not determined by statistical analysis with ToxRat

Table 4: Results of the chemical analysis of the samples.

		NC	A	B	C	D	E
Nominal loading rate [mg/L]		0	125	250	500	1000	2000
Measured concentration [µg/L]
Time [h]	0	< LOQ	16	50	149	117	382
	24	< LOQ	2.04	3.36	6.19	8.58	111
	48	< LOQ	0.82	1.25	2.25	4.06	27.2
	72	< LOQ	10.6	10.9	55.0	34.2	62.8
	72*	< LOQ	7.32	17.3	21.4	69.6	74.0
Recovery rate after 72 h from measured test concentration at 0 h [%]		-	66.3	21.8	36.9	29.2	16.4

LOQ (Limit of quantification) = 0.5 μg/L

*from test vessels with algae

72 h samples were analysed after chemical digestion

Validity criteria fulfilled:

yes

Conclusions:

For the conducted static algae growth inhibition test with Pseudokirchneriella subcapitata, applying nominal concentrations of of 0 (control), 125, 250, 500, 1000 and 2000 mg/L niobium pentachloride, results based on growth rate after 72 h were as follows: EL50: 533 mg/L (95 % C.I. 393 – 725 mg/L); LOELR: ≤ 125 mg/L; NOELR: < 125 mg/L. The values indicate effects at nominal loading rates. Due to methodological constraints, it was not possible to determine effect levels based on measured test item concentrations.

Executive summary:

In a 72-h growth inhibition test, cultures of Pseudokirchneriella subcapitata (Strain No. 61.81 SAG) were exposed to niobium pentachloride at nominal concentrations of 0 (control), 125, 250, 500, 1000 and 2000 mg/L under static conditions in accordance with the OECD Guideline 201 (March 2006) and under GLP. The % growth inhibition in the treated algal culture as compared to the control ranged from 57.9 % at a nominal concentration of 125 mg/L to 100.7 % at a nominal concentration of 2000 mg/L. Specific results based on growth rate after 72 h were as follows:

- EL₅₀: 533 mg/L (95 % C.I. 393 – 725 mg/L);

- EL₂₀: 164 mg/L (95 % C.l. 79.5 – 242 mg/L);

- EL₁₀: 88.3 mg/L (95 % C.l. 31.6 – 149 mg/L);

- LOELR: ≤ 125 mg/L;

- NOELR: < 125 mg/L.

The values indicate effects at nominal loading rates. Due to methodological constraints, it was not possible to determine effect levels based on measured test item concentrations. After pH adjustment the measured Nb⁵⁺ concentrations were low and showed high variability. Therefore, no concentration-response relationship can be delineated. Concentrations of the test sample varied due to precipitation, agglomeration and adsorption reactions. In addition, slight changes in pH had profound impact on the test concentrations. Observed growth inhibition effects may therefore rather predominantly refer to elevated NaCl concentrations, originated from neutralization, than released Nb⁵⁺ ions.

Reported effects of sodium chloride concerning the freshwater alga P. subcapitata vary but inhibitory concentrations of 2.5 g/L, respectively 0.87 g/L have been determined (Geis et al., 2000 and Santos et al., 2007, in Heisterkamp, 2015). Due to a concentration of approximately 2.92 g/L NaCl, present at the highest loading rate of 2000 mg/L test substance, and the sensitivity of P. subcapitata to salinity, any hypothetical Nb⁵⁺ related effects cannot be distinguished from NaCl induced inhibition in the conducted test. This study is classified as acceptable and satisfies the guideline requirements for an algae growth inhibition toxicity study.

Results Synopsis

 

Test Organism: Pseudokirchneriella subcapitata (Strain No. 61.81 SAG)

Test Type: Static 

	Specific Growth Rate (72 h, nominal loading rate)	Yield (72 h, nominal loading rate)
EL50	533 mg/L	102 mg/L
EL20	164 mg/L	n.d.
EL10	88.3 mg/L.	n.d.
Slope of the curve	1.642	1.186
LOELR	≤ 125 mg/L	≤ 125 mg/L
NOELR	< 125 mg/L	< 125 mg/L

n.d.: not determined by statistical analysis with ToxRat

Endpoint(s) Effected: Growth rate and Biomass

This information is used in a read-across approach in the assessment of the target substance.

For details and justification of read-across please refer to the attached report in section 13 of IUCLID.

Reference 2

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

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

Adequacy of study:

supporting study

Justification for type of information:

For details and justification of read-across please refer to the attached report in section 13 of IUCLID.

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

120 h

Dose descriptor:

EC50

Effect conc.:

ca. 1 337 other: ppm

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Validity criteria fulfilled:

not specified

Conclusions:

Within testing of 18 different substances the 120-h EC50 for Nitzscheria linearis was determined with 1337 ppm.

Executive summary:

In a 120-h growth inhibition test, cultures of Nitzscheria linearis were exposed to potassium chloride. The 120-h EC₅₀ for Nitzscheria linearis was determined with 1337 ppm.

This information is used in a read-across approach in the assessment of the target substance.

For details and justification of read-across please refer to the attached report in section 13 of IUCLID.

Description of key information

 

Heisterkamp (2015) conducted a static algae growth inhibition test with Pseudokirchneriella subcapitata, applying nominal concentrations of 0 (control), 125, 250, 500, 1000 and 2000 mg/L niobium pentachloride. The ELr₅₀ after 72-h was 533 mg/L.  

The values indicate effects at nominal loading rates. Due to methodological constraints, it was not possible to determine effect levels based on measured test item concentrations. After pH adjustment the measured Nb⁵⁺ concentrations were low and showed high variability. Therefore, no concentration-response relationship can be delineated. Concentrations of the test sample varied due to precipitation, agglomeration and adsorption reactions. In addition, slight changes in pH had profound impact on the test concentrations. Observed growth inhibition effects may therefore rather predominantly refer to elevated NaCl concentrations, originated from neutralization, than released Nb⁵⁺ ions. Reported effects of sodium chloride concerning the freshwater alga P. subcapitata vary but inhibitory concentrations of 2.5 g/L, respectively 0.87 g/L have been determined (Geis et al., 2000 and Santos et al., 2007, in Heisterkamp, 2015). Due to a concentration of approximately 2.92 g/L NaCl, present at the highest loading rate of 2000 mg/L test substance, and the sensitivity of P. subcapitata to salinity, any hypothetical Nb⁵⁺ related effects cannot be distinguished from NaCl induced inhibition in the conducted test

 

In addition, information from a peer reviewed publication (Patrick et al., 1968) on potassium chloride is added to the dossier for potassium niobate. The determined 120-h EC₅₀ for the diatome Nitzscheria linearis is 1337 ppm (equaling approximately 1337 mg/L).

 

This information is used in a read-across approach in the assessment of the target substance.

For details and justification of read-across please refer to the attached report in section 13 of IUCLID.

 

The key value for chemical safety assessment is derived by calculating the EC₅₀ value of KNbO₃ for combined effects of niobium and potassium ions upon dissolution of the test substance KNbO₃ in water. According to information from the available water solubility study according to OECD 105, 441 mg/L and 143 mg/L of potassium and niobium, respectively, are released from a nominal loading of 20 g KNbO₃/L. The acute toxicity of KNbO₃ to algae can be calculated according to the following formula:

 

(Sum(Ci)) / EC_50m = Sum (C_i / EC_50i)

 

With

-       C_i = concentration of component i (weight percentage)

-       EC_50i = EC₅₀ value for component i

-       n = number of components

-       EC_50m = EC₅₀ of the part of the mixture with test data

The weight percentages of potassium and niobium correspond to 75.5 % and 24.5 %, respectively. Sum (Ci) corresponds to 100 %. Thus, the calculated EC₅₀ for KNbO₃ is approximately 976 mg/L. This value is carried forward in the risk assessment. 

Key value for chemical safety assessment

EC50 for freshwater algae:

976 mg/L