thiamethoxam (ISO); 3-(2-chloro-thiazol-5-ylmethyl)-5-methyl[1,3,5]oxadiazinan-4-ylidene-N-nitroamine

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:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Test organisms (species):

Lemna gibba

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

> 90.2 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

frond number

At the start of the test, the concentrations of the test item were found to be in the range 97.6 to 99.2 % of the nominal values and at the end of the test were in the range 70.0 to 77.76%. Mean measured concentrations were used for the calculation and reporting of results.

Analytical results

Mean measured concentrations (mg a.s./L)	% of nominal measured on day 0	% of nominal        (old solutions) measured on day 3	% of nominal        (new solutions) measured on day 3	% of nominal measured on day 7
0 (control)	<LOD	<LOD	<LOD	<LOD
2.9	99.0	89.5	102.2	73.5
5.7	97.6	94.4	96.0	73.6
11.4	99.2	86.4	100.0	77.6
22.0	98.4	84.8	98.8	70.4
43.9	98.6	85.0	97.8	70.0
90.2	98.9	85.1	99.3	77.5

Data for frond number and dry weight were used to calculate growth rates for the control and each exposure concentration. Logit analysis was then used to calculate the 7-day ErC50, based on percent inhibition relative to the control. For the No Observed Effect Concentration and Lowest Observed Effect Concentration, a Dunnett’s Test was used to determine values significantly different to the control.

Mean frond numbers are presented below along with the growth rate, yield and respective inhibition values, alongside estimated EC₅₀values:

Effect of the test item on growth rate and yield (frond number) of Lemna gibba

Mean measured concentrations (mg test item /L)	Mean No. fronds/replicate (day 7)	Based on Frond Number (0-7 days)
		Growth Rate	Inhibition of Growth Rate (%)	Yield	Inhibition of Yield (%)
0 (control)	181	0.00	Not reported	Not reported	Not reported
2.9	169	4.51	Not reported	Not reported	Not reported
5.7	184	0.04	Not reported	Not reported	Not reported
11.4	172	4.14	Not reported	Not reported	Not reported
22.0	177	2.45	Not reported	Not reported	Not reported
43.9	185	0.91	Not reported	Not reported	Not reported
90.2	177	2.65	Not reported	Not reported	Not reported
EC50mg/L		>90.2 (mean measured)		n.d.
95% confidence limits		n.d.		n.d.
NOEC (mg/L)		90.2		n.d.
LOEC		n.d.		n.d.

Inoculum = 18 - 21 fronds
 n.d. – Not determined

Mean dry weights are presented below along with the growth rate, yield and respective inhibition values, alongside estimated EC50 values:

Effect of the test item on growth rate and yield (dry weight) of Lemna gibba

Mean measured concentrations (mg test item/L)	Dry Weight (mg) (day 7)	Based on Dry Weight (0-7 days)
		Growth Rate	Inhibition of Growth Rate (%)	Yield	Inhibition of Yield (%)
0 (control)	29.6	Not reported	Not reported	Not reported	Not reported
2.9	25.1	Not reported	Not reported	Not reported	Not reported
5.7	29.3	Not reported	Not reported	Not reported	Not reported
11.4	25.9	Not reported	Not reported	Not reported	Not reported
22.0	26.0	Not reported	Not reported	Not reported	Not reported
43.9	31.5	Not reported	Not reported	Not reported	Not reported
90.2	27.1	Not reported	Not reported	Not reported	Not reported
EC50mg/L		n.d.		n.d.
95% confidence limits		n.d.		n.d.
NOEC		90.2		n.d.
LOEC		n.d.		n.d.

Inoculum = Not reported

n.d. – Not determined

For frond number, the 7-day EC50 for growth rate (ErC50) for the test substance to Lemna gibba was >90.2 mg test substance/L, based on mean measured concentrations. For dry weight, the 7-day EC50 for growth rate (ErC50) was not stated. This study complies with the current validity criteria for toxicity testing with aquatic plants, despite more than the recommended number of fronds being added per vessel at test start. There is no impact on the reliability of the study and therefore it is still valid for use in the risk assessment

Validity criteria fulfilled:

not specified

Conclusions:

The 7-day EC50 for growth rate (ErC50) for the test substance to Lemna gibba was >90.2 mg test substance/L, based on mean measured concentrations.

Executive summary:

The toxicity of the test substance to the aquatic plant Lemna gibba was determined in a 7-day semi-static test according to the GLP compliantASTM Guideline E 1415 - 91study. The Lemn awere exposed to nominal concentrations of 3.13, 6.25, 12.5, 25, 50 and 100 mg test substance/L, equivalent to 2.90, 5.70, 11.4, 22.0, 43.9 and 90.2 mg test substance/L as mean measured concentrations. Assessments of frond number were made on days 0, 3, 5 and 7. Fronds were harvested for measurement of dry weight after 7 days. Temperature was measured continuously, light intensity was recorded at the start and end of the test and pH was recorded on days 0, 3 and 7. The test concentrations were verified by chemical analysis of the test substance on days 0, 3 (old and new solutions) and 7, using high performance liquid chromatography with ultra violet detection at 250 nm. For frond number, the 7-day EC50 for growth rate (ErC50) for the test substance to Lemna gibba was >90.2 mg test substance/L, based on mean measured concentrations. For dry weight, the 7-day EC50 for growth rate (ErC50) was not stated. This study complies with the current validity criteria for toxicity testing with aquatic plants, despite more than the recommended number of fronds being added per vessel at test start.

Description of key information

7-day EC50 for growth rate (ErC50) for the test substance to Lemna gibba was >90.2 mg test substance/L, ASTM E 1415 -91, Grade 1998