Potassium thiosulphate

Toxicity to aquatic plants other than algae

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to aquatic plants other than algae

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

Study according to standard guideline. However, chemical analytics not given, replicate numbers not stated (except sub samples for fluorescentce measurement), important water quality parameters not given, control data missing (validity criteria unassessible).

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

other: U.S. EPA method 1003.0, 1994. Short-term methods for estimating the chronic toxicity of effluents and receiving waters to freshwater organisms

Version / remarks:

3rd ed. EPA/600/4-91/002. Environmental
Monitoring Systems Laboratory, Cincinnati, OH

Principles of method if other than guideline:

Duckweed Lemna minor was exposed to different concentrations of potassium in the form of potassium sulfate (K2SO4) diluted in 20% diluted duckweed medium according to U.S. EPA method 1003.0, 1994. The dilution of the medium was done to lower the background concentration of salts present in the medium. Lemna minor was exposed for up to 7 days in a static system and thereafter, the acute 48 h - EC10 and EC50 values on mortality as well as the chronic 7 d - EC10 and EC50 values for the number of fronds were determined.

GLP compliance:

not specified

Remarks:

publication

Analytical monitoring:

no

Details on sampling:

Live and dead fronds were counted after 2 d (acute test) and 7 d (chronic test). A frond was considered dead when no green pigment was visible.

Vehicle:

no

Details on test solutions:

Duckweed medium was preopared according to U.S. EPA method 1003.0, 1994 and thereafter was diluted to one-fifth (20% medium) of the normal concentration so that the background salt concentrations would be lower. Specific conductance of each solution was measured with a conductivity meter (Model 30, YSI) initially and at the end of the incubation.

Test organisms (species):

Lemna minor

Details on test organisms:

TEST ORGANISM
- Common name: duckweed
- Scientific name: Lemna minor
- Strain: not stated
- Source: Carolina Biological Supply
- Inoculum (start): 20 fronds per peaker
- Method of cultivation: in 20% duckweed medium with weekly renewal of the medium

ACCLIMATION
- Acclimation period: 4 weeks
- Media/conditions: the same for culturing and testing

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

7 d

Hardness:

not stated

Test temperature:

not stated

Dissolved oxygen:

not stated

Salinity:

not stated

Conductivity:

At 48 h - EC10 and EC50 (survival): 16 ± 0.90 mS/cm and 26 ± 1.2 mS/cm
At 7 d - EC10 and EC50 (Frond number): 2.4 ± 0.073 mS/cm and 11 ± 0.23 mS/cm

Nominal and measured concentrations:

nominal (target concentration):
0 (control), 0.002, 0.005, 0.01 0.04, 0.05, 0.07. 0.1 and 0.2 mol K2SO4/L
0 (control), 349, 871, 1743, 6970, 8713, 12198, 17425 and 34851 mg K2SO4/L

nominal (Background concentration, 20% duckweed nutrient medium):
0.0012 mol K+/L; 0.0004 mol SO42-/L
46.92 mg K+/L; 38.42 mg SO42-/L

nominal (initial concentration):
0 (control), 434, 957, 1828, 7056, 8798, 12283, 17511 and 34936 mg K2SO4/L

Details on test conditions:

TEST SYSTEM
- Test vessel: beaker (volume not stated)
- Type: closed
- Aeration: not stated
- System: static
- # of colonies per vessel:not stated
- # of fronds per colony: 20
- replicates: 5 (treatment), 5 control

GROWTH MEDIUM
- Standard medium used: yes, duckweed medium but diluted to one-fifth

OTHER TEST CONDITIONS
- Sterile test conditions: not stated
- Adjustment of pH: not stated
- Photoperiod: 12/12, light/dark
- Light intensity and quality:fluorescent lights, 2500 lux

EFFECT PARAMETERS MEASURED:
- frond number: manual counting after 2 and 7 days

Reference substance (positive control):

not specified

Duration:

2 d

Dose descriptor:

EC10

Effect conc.:

9 409.7 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

K2SO4

Basis for effect:

other: survival

Duration:

2 d

Dose descriptor:

EC50

Effect conc.:

15 857.1 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

K2SO4

Basis for effect:

other: survival

Duration:

7 d

Dose descriptor:

EC10

Effect conc.:

1 202.4 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

K2SO4

Basis for effect:

frond number

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

6 621.7 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

K2SO4

Basis for effect:

frond number

Duration:

2 d

Dose descriptor:

EC10

Effect conc.:

4 316.8 mg/L

Nominal / measured:

estimated

Conc. based on:

element

Remarks:

Potassium

Basis for effect:

other: survival

Remarks on result:

other: including medium background

Duration:

2 d

Dose descriptor:

EC50

Effect conc.:

7 209.7 mg/L

Nominal / measured:

estimated

Conc. based on:

element

Remarks:

Potassium

Basis for effect:

other: survival

Remarks on result:

other: including medium background

Duration:

7 d

Dose descriptor:

EC10

Effect conc.:

633.4 mg/L

Nominal / measured:

estimated

Conc. based on:

element

Remarks:

Potassium

Basis for effect:

frond number

Remarks on result:

other: including medium background

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

3 065.3 mg/L

Nominal / measured:

estimated

Conc. based on:

element

Remarks:

Potassium

Basis for effect:

frond number

Remarks on result:

other:

Remarks:

including medium background

Details on results:

Survival as well as frond number of control not given. It was not stated whether endpoints were calculated on target- or initial concentrations (for details see "Nominal and measured concentrations").

Results with reference substance (positive control):

not applicable

Reported statistics and error estimates:

The effective concentration for 10 and 50% (EC10 and EC50) values were estimated according to U.S. EPA method 1003.0, 1994. Briefly, linear regression was used to interpolate between the two experimental treatments that bracketed the EC10 or EC50. To determine the relative toxicity of individual cations and anions, a two-way analysis of variance (ANOVA) with replication using cation type and anion type as factors was applied to all of the results in which the anion concentrations were 0.1 M. Because the total anion concentration was identical for each salt, observed differences in end points could be attributed to the presence or absence of individual ion species. The two-way ANOVA also tested for interactions between cations and anions.

Validity criteria fulfilled:

not applicable

Remarks:

since important water parameters during the test as well as control growth/biomass have not been stated

Conclusions:

Duckweed Lemna minor was exposed to different concentrations of potassium in the form of potassium sulphate (K2SO4) for 7 days in a static system according to EPA method 1003.0, 1994. For the endpoint "survival", the 48 h - EC10 and EC50 values amounted to 9409.7 and 15857.1 mg K2SO4/L (nominal), which is equivalent to elemental potassium concentrations of 4222.6 and 7115.8 mg K/L. For the endpoint "frond number", the 7 d - EC10 and EC50 values amounted to 1202.4 and 6621.7 mg K2SO4/L (nominal), respectively, which is equivalent to elemental potassium concentrations of 539.6 and 2971.4 mg K/L, respectively. Since important water parameters during the test as well as frond numbers of control have not been stated, it was not possible to assess the test's validity.

Reference 2

Endpoint:

toxicity to aquatic plants other than algae

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

Study according to standard guideline. However, chemical analytics not given, replicate numbers not stated (except sub samples for fluorescentce measurement), important water quality parameters not given, control data missing (validity criteria unassessible).

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

other: U.S. EPA method 1003.0, 1994. Short-term methods for estimating the chronic toxicity of effluents and receiving waters to freshwater organisms

Version / remarks:

3rd ed. EPA/600/4-91/002. Environmental
Monitoring Systems Laboratory, Cincinnati, OH

Principles of method if other than guideline:

Duckweed Lemna minor was exposed to different concentrations of potassium in the form of potassium chloride (KCl) diluted in 20 % diluted duckweed medium according to U.S. EPA method 1003.0, 1994. The dilution of the medium was done to lower the background concentration of salts present in the medium. Lemna minor was exposed for up to 7 days in a static system and thereafter, the acute 48 h - EC10 and EC50 values on mortality as well as the chronic 7 d - EC10 and EC50 values for the number of fronds were determined.

GLP compliance:

not specified

Remarks:

publication

Analytical monitoring:

no

Details on sampling:

Live and dead fronds were counted after 2 d (acute test) and 7 d (chronic test). A frond was considered dead when no green pigment was visible.

Vehicle:

no

Details on test solutions:

Duckweed medium was preopared according to U.S. EPA method 1003.0, 1994 and thereafter was diluted to one-fifth (20% medium) of the normal concentration so that the background salt concentrations would be lower. Specific conductance of each solution was measured with a conductivity meter (Model 30, YSI) initially and at the end of the incubation.

Test organisms (species):

Lemna minor

Details on test organisms:

TEST ORGANISM
- Common name: duckweed
- Scientific name: Lemna minor
- Strain: not stated
- Source: Carolina Biological Supply
- Inoculum (start): 20 fronds per peaker
- Method of cultivation: in 20% duckweed medium with weekly renewal of the medium

ACCLIMATION
- Acclimation period: 4 weeks
- Media/conditions: the same for culturing and testing

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

7 d

Hardness:

not stated

Test temperature:

not stated

Dissolved oxygen:

not stated

Salinity:

not stated

Conductivity:

At 48 h - EC10 and EC50 (survival): 12 ± 0.65 mS/cm and > 27 mS/cm
At 7 d - EC10 and EC50 (Frond number): 1.5 ± 0.042 mS/cm and 6.3 ± 0.18 mS/cm

Nominal and measured concentrations:

nominal (target concentration):
0 (control), 0.002, 0.005, 0.01 0.04, 0.05, 0.07. 0.1 and 0.2 mol KCl/L
0 (control), 149, 373, 746, 2982, 3728, 5219, 7455 and 14910 mg KCl/L

nominal (Background concentration, 20% duckweed nutrient medium):
0.0012 mol K+/L; Cl-: trace
46.92 mg K+/L; Cl-: not determinable

nominal (initial concentration):
0 (control), 196, 420, 792, 3029, 3774, 5265, 7502 and 14957 mg KCll/L

Details on test conditions:

TEST SYSTEM
- Test vessel: beaker (volume not stated)
- Type: closed
- Aeration: not stated
- System: static
- # of colonies per vessel:not stated
- # of fronds per colony: 20
- replicates: 5 (treatment), 5 control

GROWTH MEDIUM
- Standard medium used: yes, duckweed medium but diluted to one-fifth

OTHER TEST CONDITIONS
- Sterile test conditions: not stated
- Adjustment of pH: not stated
- Photoperiod: 12/12, light/dark
- Light intensity and quality:fluorescent lights, 2500 lux

EFFECT PARAMETERS MEASURED:
- frond number: manual counting after 2 and 7 days

Reference substance (positive control):

not specified

Duration:

2 d

Dose descriptor:

EC10

Effect conc.:

6 038.6 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

KCl

Basis for effect:

other: survival

Duration:

2 d

Dose descriptor:

EC50

Effect conc.:

> 13 419.2 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

KCl

Basis for effect:

other: survival

Duration:

7 d

Dose descriptor:

EC10

Effect conc.:

715.7 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

KCl

Basis for effect:

frond number

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

3 205.7 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

KCl

Basis for effect:

frond number

Duration:

2 d

Dose descriptor:

EC10

Effect conc.:

3 213.9 mg/L

Nominal / measured:

estimated

Conc. based on:

element

Remarks:

Potassium

Basis for effect:

other: survival

Remarks on result:

other: including medium background

Duration:

2 d

Dose descriptor:

EC50

Effect conc.:

> 7 084.6 mg/L

Nominal / measured:

estimated

Conc. based on:

element

Remarks:

Potassium

Basis for effect:

other: survival

Remarks on result:

other: including medium background

Duration:

7 d

Dose descriptor:

EC10

Effect conc.:

422.3 mg/L

Nominal / measured:

estimated

Conc. based on:

element

Remarks:

Potassium

Basis for effect:

frond number

Remarks on result:

other: including medium background

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

1 728.1 mg/L

Nominal / measured:

estimated

Conc. based on:

element

Remarks:

Potassium

Basis for effect:

frond number

Remarks on result:

other: including medium background

Details on results:

Survival as well as frond number of control not given. It was not stated whether endpoints were calculated on target- or initial concentrations (for details see "Nominal and measured concentrations").

Results with reference substance (positive control):

not applicable

Reported statistics and error estimates:

The effective concentration for 10 and 50% (EC10 and EC50) values were estimated according to U.S. EPA method 1003.0, 1994. Briefly, linear regression was used to interpolate between the two experimental treatments that bracketed the EC10 or EC50. To determine the relative toxicity of individual cations and anions, a two-way analysis of variance (ANOVA) with replication using cation type and anion type as factors was applied to all of the results in which the anion concentrations were 0.1 M. Because the total anion concentration was identical for each salt, observed differences in end points could be attributed to the presence or absence of individual ion species. The two-way ANOVA also tested for interactions between cations and anions.

Validity criteria fulfilled:

not applicable

Remarks:

since important water parameters during the test as well as control growth/biomass have not been stated

Conclusions:

Duckweed Lemna minor was exposed to different concentrations of potassium in the form of potassium chloride (KCl) for 7 days in a static system according to EPA method 1003.0, 1994. For the endpoint "survival", the 48 h - EC10 and EC50 values amounted to 6038.6 and > 13419.2 mg KCl/L (nominal), which is equivalent to elemental potassium concentrations of 3166.9 and > 7037.6 mg K/L. For the endpoint "frond number", the 7 d - EC10 and EC50 values amounted to 715.7 and 3205.7 mg KCl/L (nominal), respectively, which is equivalent to elemental potassium concentrations of 375.3 and 1681.2 mg K/L, respectively. Since important water parameters during the test as well as frond numbers of control have not been stated, it was not possible to assess the test's validity.

Description of key information

Simmons (2012) investigated the effects of potassium in form of KCl and K2SO4 on duckweed Lemna minor after a 7-days static exposure; the overall lowest 7-day EC10 and EC50 values (frond number) amount to 422.3 and 1728.1 mg K+/L, respectively (KCl test), and are above the OECD test limit (Simmons, 2012).

Potassium is an essential macronutrient and most abundantly absorbed cation that plays an important role in the growth, metabolism and development of e.g. macrophytes. Plants suffering of potassium therefore show different symptoms (e.g. wilting, decolouration and growth disorders). It is among others involved in water balance, photosynthesis and the assembly of vegetable cell walls and is therefore present in media used for macrophyte tests (e.g. Modified Swedish Standard (SIS), 20X AAP (U.S. EPA) and modified STEINBERG medium (ISO 20079)). These media require the addition of potassium in form of K2HPO4, KH2PO4 and KNO3, resulting in final elemental concentrations of 3.9, 10.3 and 17.9 mg K/L, respectively. Potassium concentrations of the OECD test media are above the median background concentrations of potassium in European stream water of 1.65 mg K/L (FOREGS) indicating a high potassium demand of macrophytes and the corresponmding lack of a toxic potential.

In sum, potassium asessential element has a very low potential for toxicity to aquatic plants.