Sodium 4-chloro-3-[4-[[5-chloro-2-(2-chlorophenoxy)phenyl]azo]-4,5-dihydro-3-methyl-5-oxo-1H-pyrazol-1-yl]benzenesulphonate

Toxicity to aquatic plants other than algae

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic plants other than algae

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 221 (Lemna sp. Growth Inhibition Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Vehicle:

yes

Test organisms (species):

Lemna minor

Details on test organisms:

Test organism: Exponential growing plant monoculture of Lemna minor (Umweltbundesamt, FGIII 2.5, Überwachungsverfahren Abwasserentsorgung, Schichauweg 58, D-12307 Berlin)
Culture: all-glass vessel containing sterile Swedish Standard (SIS) medium (Table 2) and the exponentially growing plant monoculture. Healthy Lemna minor plants consist of colonies comprising 2-5 fronds.
Cultivation: At least seven days before testing, sufficient colonies were transferred aseptically into fresh sterile medium and cultured for 7-10 days under the conditions of the test.
Illumination: continuous (6500–10000 lux) from Osram Fluora L18W77 (Osram AG, Winterthur, Switzerland) and CH Lighting F18T8/6500K EUP (CH Lighting CO., Ltd., China)
Temperature: 24 ± 2 °C
Control of sensitivity: Yearly, with 3,5-dichlorophenol

Test type:

static

Water media type:

freshwater

Total exposure duration:

7 d

Test temperature:

24 ± 2 °C

pH:

6.5 at the beginning of the test.

Nominal and measured concentrations:

Prior to the definitive test a non-GLP range finding test with the nominal concentrations of 10, 100 and 500 mg/l of active ingredient was performed.
Based on the results of this non-GLP range finding test, the test concentrations for the definitive test were 316, 100, 31.6, 10.0 and 3.16 mg/l nominal concentration of the active ingredient (i.e.to 379, 120, 37.9, 12.0 and 3.79 mg/l of test item).

Details on test conditions:

Test vessel: 400 ml beakers, all-glass, with 200 ml of test medium. The beakers were covered with black paper up until the 200 ml mark to ensure that illumination comes only from above and not from the sides.
Test medium: Recommended Swedish Standard (SIS) medium (Table 2), prepared with ultra-pure water
Pre-culture: Exponentially growing plant monoculture of Lemna minor (the culture was visibly free from contamination by other organisms such as algae and protozoa).
Illumination: Intensity: continuous (6500–10000 lux) from Osram Fluora L18W77 (Osram AG, Winterthur, Switzerland) and CH Lighting F18T8/6500K EUP (CH Lighting CO., Ltd., China)
Homogeneity: ±15% (target; but see Deviations in section 1.10.2)
Incubation: Beakers were incubated on a black non-reflecting surface.

Reference substance (positive control):

no

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

19.3 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

frond number

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

30 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: dry weight

Details on results:

Effects on frond numbers
With respect to growth rate inhibition, the following effects as compared to the untreated controls were observed: 94% at 316 mg/l, 89% at 100 mg/l, 78% at 31.6 mg/l, 14% at 10.0 mg/l and 15% at 3.16 mg/l.
Based on these effects and the measured concentrations of the test item, the median effect concentration with respect to the frond number’s growth rate (frond number ErC50) of Acid Yellow 110 to Lemna minor was calculated to be 19.3 mg/l (95% confidence limits: 3.85–43.3 mg/l). The ErC10 was 5.79 mg/l (n.d..–11.9) mg/l; while the NOErC was determined to be <3.67 mg/l.


Effects on dry weight
With respect to growth rate inhibition, the following effects as compared to the untreated controls were observed: 64% at 316 mg/l, 66% at 100 mg/l and 86% at 31.6 mg/l. No significant effects were observed at the nominal concentrations of 10.0 and 3.16 mg/l.
No significant dose-response relationship between these effects and the measured concentrations of the test item was found by the statistical program. Therefore, the effect concentrations were estimated based on the observations made and inhibitions calculated. The median effect concentration with respect to the dry weight’s growth rate (dry weight r ErC50) of the tested substance to Lemna minor was estimated to be ca. 30 mg/l. The NOErC was determined to be 9.99 mg/l.

Appearance of the plants at the end of the test

In the blank control the plants looked healthy with roots reaching to the bottom of the test vessel.

At 3.16 mg/l, the plants looked healthy with roots reaching to the bottom of the test vessel.

At 10.0 mg/l, the plants were light green colored and smaller as compared to the blanks. The roots reached to the bottom of the test vessel.

At 31.6 mg/l, the plants were partially yellow and some roots were missing.

At 100 and 316 mg/l, the plants were yellow and all the roots were missing.

Validity criteria fulfilled:

yes

Conclusions:

EC50 = 19.3 mg/l with respect of frond number

Executive summary:

The toxicity to the aquatic plant Lemna Minor were determined following OECD 221.

The results showed some toxic effects to Lemna minor under the test conditions.

Description of key information

EC50 = 19.3 mg/l

Key value for chemical safety assessment

EC50 for freshwater plants:

19.3 mg/L

Additional information

A test was performed on the tested substance following OECD 221.

The tested substance showed some toxic effects on Lemna Minor. EC50 value was set to 19.3 mg/l

Lemna minor is an aquatic plant that develops his leaves on the surface of the water, while nourishing substances are taken from the water solution. With this tests the observed effect is only related to the potential toxicity of the substance and not to the potential shading effect of a classical Alga study. A deviation to the protocol has been applied to the test recommended for dyes (Michael Cleuvers a, Hans-Toni Ratte, Phytotoxicity of coloured substances: is Lemna Duckweed an alternative to the algal growth inhibition test? Chemosphere 49 (2002) 9–15): "Beakers will be incubated on a black non-reflecting surface. Additionally, the walls of the incubation chambers will also be covered with black fabric in order to avoid reflection".