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

Toxicity to soil microorganisms

Link to relevant study record(s)

Reference

Endpoint:

toxicity to soil microorganisms

Type of information:

experimental study

Adequacy of study:

key study

Study period:

14 Jan 1998 to 27 Feb 1998

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

BBA Part VI, 1-1

Version / remarks:

1990

Qualifier:

according to guideline

Guideline:

other: SETAC-Europe, Procedures for assessing the environmental fate and ecotoxicity of pesticides

Version / remarks:

1995

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 216 (Soil Microorganisms: Nitrogen Transformation Test)

Version / remarks:

OECD Draft: Soil Microorganism: Nitrogen and Carbon Mineralisation test (1996)

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on preparation and application of test substrate:

APPLICATION OF TEST SUBSTANCE TO SOIL
- Method: Soil samples were treated with the test substance at two doses. The test concentrations related to a soil depth of 5 cm and a soil density of 1.5 g/cm3.

Test organisms (inoculum):

soil

Total exposure duration:

28 d

Test temperature:

- Respiration test: 20 - 24 °C
- Nitrification test: < -18 °C

Moisture:

Not reported

Details on test conditions:

TEST SYSTEM
- Test container: 150 mL Erlenmeyer flasks with a cotton wool stopper
- Amount of soil: Not reported
- No. of replicates per concentration: 3
- No. of replicates per control: 3

SOURCE AND PROPERTIES OF SUBSTRATE
- Soil type (USDA): Loamy sand, not further specified
- pH: Test start: 7.5 to 7.8; test end: 6.7 to 7.3

OTHER CONDITIONS
- Photoperiod: Constant darkness

EFFECT PARAMETERS MEASURED: nitrogen conversion
Nitrogen conversions were determined by measuring the content of NH3H, NO3N and NO2N. Post application measurements for nitrogen conversions were performed in powdered Lucerne amended soil. Measurements for substrate induced respiration were performed in soil not amended with Lucerne meal.

Nominal and measured concentrations:

- Nominal concentrations: 0 (soil mixed with Lucerne meal for N-mineralisation ), 0.27 and 2.67 mg a.s./kg dry soil (corresponding to 1 and 10 fold the maximum field application rate, respectively).

Reference substance (positive control):

yes

Remarks:

Dinoseb (at 1.5 - 2.5 kg a.i./ha nominal)

Key result

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

2.67 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

nitrate formation rate

Details on results:

The test substance showed no significant effects in the tested soil on short-term respiration rates at the one and ten-fold application rate. N-mineralisation was not affected in the loamy sand.
An overview of the short-term respiration rates and carbon transformation results is presented in 'Any other information on results incl. tables'.

Reported statistics and error estimates:

For the statistical evaluation of soil short term respiration rates during the constant initial respiration phase and the Nitrite, Nitrate and Ammonium-N concentrations the assumption of a constant relative error was made, i.e. concentrations were assumed to be approximately normally distributed with a constant variance over groups for each point of sampling. Therefore, concentrations were used to compare treatment groups and positive control to negative control, for each point of time, using Dunnett’s Test. The SAS procedure GLM and the probmc function were used to calculate Dunnett’s p-values. Results for respiration and nitrogen- mineralisation were compared and classified using the scheme given by Malkomes (1990).

Table: Rates of short term respiration in control, test substance and positive control treated soil samples

Sanple	Control (mL CO2/h)	1 fold field rate		10 fold field rate		Dinoseb 5 fold field rate
		(mL CO2/h)	%	(mL CO2/h)	%	(mL CO2/h)	%
0-3 hours	1.858	1.882	1.3	1.845	-0.7	1.669	-10.2
Day 14	2.067	2.000	-3.2	1.971	-4.6	1.396	-32.5
Day 28	1.633	1.587	-2.8	1.524	-6.7	0.960	-41.2

Table: Effects on Carbon Transformation in Soil after Treatment with the test substance

Sample	Incubation
	0-3 hours			14 days			28 days
	NO3N	NH4N	Total N	NO3N	NH4N	Total N	NO3N	NH4N	Total N
	(mg/100g soil dry weight)
Control	4.70	0.93	5.7	6.50	1.30	7.8	8.15	0.55	8.7
1 fold	4.57	0.90	5.6	6.33	0.93	7.3	8.23	0.40	8.6
10 fold	4.47	0.97	5.5	6.07	0.87	6.9	7.97	0.43	8.4
Dinoseb	4.40	0.87	5.4	8.13	0.50	8.6	10.03	0.37	10.4

NO2 values are not listed.

Total N= sum of NO3 and NO2and NH

Validity criteria fulfilled:

yes

Remarks:

See 'Any other information on materials and methods incl. tables.'

Conclusions:

The test substance has shown no significant effects in the tested soil on short-term respiration rates at the one and ten-fold application rate. N-mineralisation was not affected in the loamy sand. Therefore, it can be concluded that the substance showed no long lasting effects on N-mineralisation of the tested agricultural soil. Based on these results, the 28-d NOEC value is determined to be 2.67 mg/kg soil dw.

Executive summary:

The toxicity to soil microorganisms was determined in a GLP-compliant study according to BBA part VI, 1-1. In this study, soil (loamy sand) was incubated for 28 days with test substance concentrations of 0 (control), 0.27 and 2.67 mg/kg soil dw. Soil was mixed with Lucerne meal for N-mineralisation. Nitrogen conversions were determined by measuring the content of NH3H, NO3N and NO2N. Post application measurements for nitrogen conversions were performed in powdered Lucerne amended soil. Measurements for substrate induced respiration were performed in soil not amended with Lucerne meal. The test method was calibrated with Dinoseb as a reference substance. The test substance has shown no significant effects in the tested soil on short-term respiration rates at the one and ten-fold application rate. N-mineralisation was not affected in the loamy sand. Therefore, it can be concluded, that the substance showed no long lasting effects on N-mineralisation of the tested agricultural soil. Based on these results, the 28-d NOEC value is determined to be 2.67 mg/kg soil dw.

Description of key information

All available data were assessed and the studies representing the worst-case effects were included as key or weight-of-evidence studies. Other studies are included as supporting information. The key studies are considered to be worst-case and were selected for the CSA.

The 28-d NOEC value is determined to be 2.67 mg/kg soil dw.

Key value for chemical safety assessment

Long-term EC10 or NOEC for soil microorganisms:

2.67 mg/kg soil dw

Additional information

Several studies investigated the toxicity of the substance to soil microorganisms. In a GLP-compliant study according to BBA part VI, 1-1, soil (loamy sand) was incubated for 28 days with test substance concentrations of 0 (control), 0.27 and 2.67 mg/kg soil dw. Exposure to the test substance had no significant effects on short-term respiration rates at the selected doses. N-mineralisation was not affected in the loamy sand. Therefore, it can be concluded, that the substance showed no long lasting effects on N-mineralisation of the tested agricultural soil. Based on these results, the 28-d NOEC value was determined to be 2.67 mg/kg soil dw.