Sodium chlorate

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:

other: Study generated according to generally valid and internationally accepted testing guideline and performed under GLP.

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 221 (revised draft document 2002)

Deviations:

yes

Remarks:

Swedish Standard (SIS) medium. Modified: NH4Cl was given as inorganic nitrogen source instead of NaNO3 to get sufficient recovery rates of concentration control analysis. growth sp. inhibition test"

GLP compliance:

yes

Analytical monitoring:

yes

Details on sampling:

At the start and the end of the test samples were taken for analyses.

Vehicle:

no

Details on test solutions:

- Dispersion treatment: Agitation
- Procedures: 320 mg/L prepared with dilution water

Test organisms (species):

Lemna minor

Details on test organisms:

- Source/supplier: OekoTox Moser & Pickl Gbr, Stuttgart, Germany
- Laboratory culture: yes
- Method of cultivation: in 900 ml crystallization dishes, filled with 500 ml Swedish Standard (SIS) Medium.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

7 d

Test temperature:

24 ± 1 °C

pH:

6.60-6.64 at the start of the test and 5.23-5.95 at the end

Nominal and measured concentrations:

- Nominal test concentrations: 0.0, 3.2, 10, 32, 100, 320 mg/L
- The measured concentrations of the test substance were between 90 and 107% of the nominal concentrations, therefore the nominal values were
used for the calculations

Details on test conditions:

Swedish Standard (SIS) medium, modified GROWTH/TEST MEDIUM CHEMISTRY: Swedish Standard (SIS) medium
- pH: 6.5 ± 0.2
- Exposure vessel type: Crystallization dishes with a volume of 500 ml, covered with glass tops and filled with 200 ml test solution.
- Number of replicates, plants per replicate: 3, 3 plants with 4 fronds each
- Intensity of irradiation: 6500-10000 lx (85-125 µmol/m2*s)
- Photoperiod: continuous fluorescent light
- Number of plants (start and end of the test), number of fronds (on day 0, 2, 5 and 7) and dry weight (at the end of the test).
On each observation day the pigmentation, destruction of roots etc. were determined.

Reference substance (positive control):

yes

Remarks:

Zinc chloride, 99.2% pure

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

134 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 33.7- > 320 mg/L

Duration:

7 d

Dose descriptor:

NOEC

Effect conc.:

10 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

Details on results
Biomass growth (number of fronds):
EC50 = 73.7 mg/L (95% c.i. 34.5-158 mg/L)
LOEC = 32 mg/L NOEC = 10 mg/L
Growth rate (number of fronds):
EC50 = 134 mg/L (95% c.i. 33.7- > 320 mg/L)
LOEC = 32 mg/L NOEC = 10 mg/L
Biomass dry weight:
EC50 = 128 mg/L (95% c.i. 28.0- > 320 mg/L)
LOEC = 32 mg/L
NOEC = 10 mg/L
- Evaluation after day 7 (mean and standard deviation in brackets):

Conc (mg/L) log biomass Inhibition of integral log biomass (%)
control 7.49 (0.49)
3.2 8.37 (0.29) -11.74 (3.88)
10 8.30 (0.29) -10.75 (3.82)
32 6.12 (0.44) 18.31 (5.81)
100 3.25 (0.47) 56.58 (6.27)
320 0.24 (0.11) 96.83 (1.50)

Conc (mg/L) Specific Inhibition of growth rate specific growth rate (%)
control 0.350 (0.020)
3.2 0.366 (0.020) -4.45 (5.08)
10 0.355 (0.000) -1.44 (1.31)
32 0.289 (0.010) 17.29 (3.15)
100 0.204 (0.010) 41.74 (2.04)
320 0.099 (0.20) 71.70 (6.18)

Conc (mg/L) Doubling Biomass dw Inhibition of time of (mg) biomass dw (%) fronds (d)
control 1.98 (0.12) 26.0 (2.1)
3.2 1.90 (0.09) 29.5 (0.6) -4.87 (0.79)
10 1.95 (0.03) 23.4 (0.9) 4.21 (1.52)
32 2.39 (0.09) 15.4 (2.0) 20.37 (4.95)
100 3.40 (0.12) 8.4 (0.6) 43.92 (2.81)
320 7.00 (1.86) 4.2 (0.6) 70.78 (5.41)

- Other observations: In the three highest concentrations the fronds were lighter green and partly covered with white spots at day 2.
At day 5 the fronts in 320 and 100 mg/L were partly without pigmentation and in 32 mg/L fronds were partly covered with white spots.
At day 7 fronds in the three highest concentrations were partly without pigmentation.

Results with reference substance (positive control):

- Concentrations: 0.0, 0.32, 1, 3.2, 10, 32 mg/L
- Results:
- EC50 (biomass growth) = 9.5 mg/L (95% c.i. 1.8-50.2 mg/L)
- EC50 (growth rate) = 5.2 mg/L (95% c.i. 1.1-24.6 mg/L)
- EC50 (biomass dry weight) = 10.9 mg/L (95% c.i. 3.2-37.1 mg/L)

Reported statistics and error estimates:

ANOVA and Dunnett's test were used for determination of significant differences compared control replicates.
If normality of equal variance failed Bonferroni t-test was carried out. Probit analysis for calculation of EC50, confidence intervals
are calculated using.

Validity criteria fulfilled:

yes

Conclusions:

Test conducted under GLP with analysis, analysis certificate and to relevant guideline. This study can be considered reliable without restrictions.
The NOEC based on biomass dry weight is 10 mg/l. The lowest EC50 is based on biomass growth and is 73.7 mg/L (95% c.i. 34.5-158 mg/L).

Executive summary:

The effects of the test item Sodium Chlorate on growth of the monocotyledon species Lemna minor were determined according to the principles of OECD-Guideline 221 (Revised Draft Document July 2002), from October 29 to November 05, 2003 at DR.U.NoACK-LABORATORIEN, Sarstedt, Germany. The test item (batch number 1E01 03WF) contained 99.66 % Sodium Chlorate. The aim of the study was to determine the effects of the test item on the growth of Lemna minor over 7 days under static exposure conditions. On the basis of a preliminary test, 5 concentration levels were chosen in a geometrical series with a dilution factor of √1 0: nominal: 3.2 - 10 - 32 - 100 - 320 mg/L. Three replicates were investigated for the test concentrations and the control. Frond numbers were assessed on days 0, 2, 5 and 7. Inhibition of log biomass growth. specific growth rate and biomass dry weight were determined. The concentrations of sodium chlorate were analysed on day 0 (freshly prepared solutions) and on day 7 (old solutions) via HPLC. The recovery rates of the active ingredient chlorate were> 80 % at start and end of the study (for details of the analytical method and results please refer to chapter 10). Environmental parameters like water temperature and pH-value were determined to be within the acceptable limits. The effects of sodium chlorate, based on nominal concentrations, are summarised in table 1. Table 1: Effects on Lemna minor after 2, 5 and 7 d (based on nominal concentrations of the test item)    2d 5d  7d    Inhibition of log biomass growth [mg/L]          Elog bC50value  91.3 60.5 73.7  95 % confidence interval for ElogbC50values  68.6 -122  38.6 -95.0   34.5 -158  LOEC 100 100  32   NOEC 32  32  10  Inhibition of specific growth rate [mg/L]            ErC50value  91.3  57.8  134  95 % confidence interval for ErC50values  68.6 -122 35.8 -93.3  33.7 - >320   LOEC 100  100  32   NOEC 32  32  10  Inhibition of log biomass dry weight [mg/L]            ElogdwC50value n.a  n.a  128   95% cofidence interval forElogdwC50value n.a  n.a  28.0- >320   LOEC n.a  n.a  32   NOEC n.a  n.a  10  n.a. =not applicable

Description of key information

The NOEC for fresh water aquatic plants is 10 mg/l.

Key value for chemical safety assessment

EC10 or NOEC for freshwater plants:

10 mg/L

Additional information

One valid study was found for freshwater aquatic plants. The NOEC for fresh water aquatic plants is 10 mg/l.

The lowest value for chronic toxicity to freshwater plants is 10 mg/l based on Lemna minor. Lemna minor is the most sensitive freshwater species tested to sodium chlorate.