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

Biodegradation in soil

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

05 Apr 1995 to 09 Aug 1996

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: US EPA Pesticide Assessment Guidelines, Subdivision N, Chemistry, Environmental Fate, Series 164-1

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: BBA Guidelines "Richtlinien fiir die Priifung von Pflanzenschutzmitteln im Zulassungsverfahren" Teil IV 4-1

Version / remarks:

December 1986

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test type:

field trial

Radiolabelling:

yes

Remarks:

14C-labelled at position 2 of thiazole ring

Oxygen conditions:

aerobic

Soil classification:

not specified

Year:

1995

Soil type:

other: not reported

% Clay:

21

% Silt:

31.6

% Sand:

47.4

% Org. C:

3.1

pH:

7.2

CEC:

17.1 meq/100 g soil d.w.

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: The plot was located at in Switzerland.
- Pesticide use history at the collection site: In the year 1993 the original soil was removed and replaced by fresh, untreated soil. Until preparation of the plot prior to application, grass was grown (no pesticide treatments).
- Plot preparation prior to application: Three soil cores (depth 30 cm, diameter of 5cm) were taken before application, analyzed according to standard procedures and compared with background samples. No radioactivity beyond background level was found. The plot was leveled and hand-weeded before application.

PROPERTIES OF THE SOILS
- Water capacity: 49% (0.05 bar)

Duration:

492 d

Initial conc.:

207 g/ha d.w.

Based on:

test mat.

Remarks:

See 'Details on experimental conditions'.

Parameter followed for biodegradation estimation:

CO2 evolution

radiochem. meas.

Details on experimental conditions:

PESTICIDE APPLICATION
- On April 5, 1995, plot 1.2aN (6 m2) was treated with 300 ml of spraying suspension using a small plot sprayer KFA1 with 4 TeeJet nozzles (even flat spray tip #8001E) with a flow of ca 0.39 I/min each at ca 3 bar overpressure. In order to ensure that the total amount of radioactivity was applied onto the plot, the vessel was washed with 300 ml of water sprayed and the washing was sprayed onto the plot. A total amount of 124 mg [thiazol-2-14C] test substance (124 MBq) were applied, corresponding to a rate of 20.7 mg a.i./m2 or 207 g a.i. / ha.
- Post treatment crop maintenance: The field was surrounded with a fence and marked with appropriate labels. The bareground plot was divided into six sections in which the rotational crops were subsequently planted and harvested according to the schedule given in. From October 25, 1995 until December 11, 1995, i.e. part time of the growing period of spring wheat_2, the plot was covered with a plastic roof equipped with a heating to prevent the plant culture from freeze.

SAMPLING
- Samplng intervals: Soil samples were taken 1 hour, 29, 63, 89, 119, 180, 362, and 492 days after treatment.
- Sampling method for soil samples: Soil samples (diameter of 5cm) were taken at various intervals (systematically in the spraying direction at the position of the nozzles) throughout the area of the plot using a Humax2
electrical sample collector. Five soil cores 00 - 30 cm were taken at interval 1 to 6. Five cores 00 - 60 cm were taken at the last two intervals.
- Sample handling: The soil cores were divided into three to six 10 cm layers, 00-10 cm, 10-20 cm, 20-30 cm, 30 - 40 cm, 40 - 50 cm, 50 - 60 cm and. At interval 1 and 2 the top soil layers (00-10 cm) were extracted after sampling without drying. The total residues in these soil layers were determined by the sum of extractable and non-extractable radioactivity. All other soil samples were air dried and homogenized in a disk mill before analysis.
- Sample retention: The soil samples are kept at location for one year after the testing period.
- Storage stability: To evaluate the stability of the test substance and its metabolites during air drying (RT) and storage (-20°C), soil fortifications were prepared using fresh untreated soil from the control plot and soil extract of interval 4.

Key result

DT50:

51 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: field study; no standard temperature

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

No.:

#4

Details on transformation products:

Results on the radioactivity of the transformation prodcuts thoughout the study are tabulated in 'Any other information on materials and methods incl. tables'

CHARACTERISATION IN RADIOACTIVITY IN SOIL
- 0 - 10 cm soil layer: Analysis of the extracts by 2-dim TLC (ss 160 / ss 79) revealed apart unchanged test substance at least 6 different metabolite fractions. The parent content in the 0 - 10 cm soil layer declined from 0.186 ppm just after treatment to 0.002 ppm at interval 8, i.e 492 days later. A DT50 of 51 days and a DT 90 of 170 days were determined assuming first order kinetics. M4 was found to be the major metabolite throughout the study. Its amount in percent of recovered radioactivity continuously increased and reached 36% after 492 days. M4 reached its maximum concentration (16.2 ppb or 8.7% of total residues at day 0) at Day 180 and thereafter declined to 10.3 ppb after 492 days after application. M1 accounted for 4.1 % of total radioactivity (5.9 ppb or 3.2% of total residues at day 0) at interval 2, i.e. 29 days after treatment and thereafter continuously declined to 0.2 ppb after 492 days. In addition minor amounts of M8 were detected. Its maximum concentration was found between Day 180 and Day 492, accounting for 1.1 - 1.4 ppb. Non-extractable residues in the 0 - 10 cm soil layer expressed in percent of recovered radioactivity continuously increased to 49% at the end of the experimental period. Maximum concentration of non-extractable residues (21.5 ppb) was found after 119 days and declined to 13.9 ppb at the end of the study.
- 10 - 20 cm soil layer: The metabolite pattern in the 10 - 20 cm soil layer, analyzed 492 days after treatment, was similar to the pattern of the top layer. M2 was found as major metabolite, accounting for 62% of total radioactivity or 4.5 ppb. No thiazol specific metabolite fractions were detected so far in relevant amounts, whereas one oxadiazin specific metabolite was found in minor amounts.

Evaporation of parent compound:

no

Volatile metabolites:

not specified

Residues:

yes

Remarks:

See 'Details on results'

Details on results:

Results on dissipation and storage stability are tabulated in 'Any other information on results incl. tables'.

TOTAL RESIDUE LEVELS IN THE FIELD SOIL
- 0 - 10 cm soil layer: The total residue level in the 0 - 10 cm layer decreased from 0.186 ppm after application to 0.072 ppm 89 days later. After that time the decrease proceeded slower and finally reached 0.029 ppm 492 days after application. Curve fitting was achieved using a two compartment model, assuming slow and fast first order reactions contributing to the dissipation of radioactivity. On the basis of this model an overall DT so for the dissipation of total radioactivity in the 0 - 10 cm soil layer of about 92 days was calculated.
- 10 - 20 and 20 - 30 cm soil layers: Some downward movement of radioactivity with time was observed. Radioactivity in the 10 - 20 cm and 20 - 30 cm soil layers was below 0.001 ppm until interval 4, i.e. 89 days after treatment. Total radioactivity in the 10 - 20 cm layer increased to 0.003 ppm at interval 5, i.e. 119 days after treatment, reached 0.007 ppm at Day 362 and remained at 0.007 ppm until the end of the experimental period (492 days after treatment). The amount of radioactivity found in the 10 - 20 cm at 362 days and 492 days after application corresponded to about 4.5% of the radioactivity found in the 0 - 10 cm layer just after treatment. Total radioactivity in the 20 - 30 cm soil layer never exceeded 0.002 ppm and was found to be 0.001 ppm after 492 days.
- 30 - 40 cm, 40 - 50 cm and 50 - 60 cm soil layers: At the end of the experimental period the radioactivity in the 30 - 40 cm, 40 - 50 cm and 50 - 60 cm soil layers was below 0.001 ppm.

STORAGE STABILITY
To evaluate the stability of the test substance and its metabolites during air drying (room temperature) and storage (-20°C), soil fortifications were prepared using fresh untreated soil from the control plot. Fresh soil aliquots were treated with a concentrate of soil extract of interval 4. Two samples were extracted just after fortification and analyzed by 1-dim TLC. Stability of parent and its metabolites during air drying was evaluated after drying period of 7 and 14 days at room temperature. Freezer storage stability was demonstrated after a storage period of one, 6 and 12 months, respectively. No significant changes in the TLC pattern were observed during air drying or freezer storage.

Table: Dissipation of Radioactivity and Residual Test Substance in Soil after Bareground Application 

Days after Treatment	Soil Layers	Total Residues			Parent [ppm](1)	Extr. Radioactivity [%](3)	NE Rad. [%](3)	Total [%](3)
		[ppm](1)	sd[%]	[%](2)
0	SOIL
	00-10 cm	0.186	20.6	100	n.a.	87.6	12.4	100
29	SOIL
	00-10cm	0.143	47.7	98.7	0.107	87.7	12.3	100
	10-20cm	<0.001	56.1	0.7	n.a.	n.a.	n.a.
	20-30 cm	<0.001	31.2	0.6	n.a.	n.a.	n.a.
	SOIL TOTAL			100
63	SOIL
	00-10 cm	0.134	30.5	99.2	0.101	90.4	12.8	103.2
	10-20 cm	<0.001	43	0.4	n.a.	n.a.	n.a.
	20-30 cm	<0.001	70.7	0.4	n.a.	n.a.	n.a.
	SOIL TOTAL			100
89	SOIL
	00-10 cm	0.072	25.9	98.7	0.045	83.9	20	103.9
	10-20 cm	<0.001	43	0.9	n.a.	n.a.	n.a.
	20-30 cm	<0.001	39.1	0.4	n.a.	n.a.	n.a.
	SOIL TOTAL			100
119	SOIL
	00-10cm	0.086	35.8	96.2	0.042	78.9	24.9	103.8
	10-20 cm	0.003	181.1	3.7	n.a.	n.a.	n.a.
	20-30 cm	<0.001	136.9	0.1	n.a.	n.a.	n.a.
	SOIL TOTAL			100
180	SOIL
	00-10 cm	0.055	26.1	86.6	0.012	63.8	39.1	102.9
	10-20 cm	0.006	35.8	9.6	n.a.	n.a.	n.a.
	20-30 cm	0.002	27.9	3.8	n.a.	n.a.	n.a.
	SOIL TOTAL			100
362	SOIL
	00-10 cm	0.041	37.7	76.3	0.006	56	43.2	99.1
	10-20cm	0.007	94.3	13.5	n.a.	n.a.	n.a.
	20 30cm	0.002	35.1	3.9	n.a.	n.a.	n.a.
	30-40cm	0.001	26.7	3	n.a.	n.a.	n.a.
	40-50cm	0.001	47.5	2	n.a.	n.a.	n.a.
	50-60cm	<0.001	41.6	1.3	n.a.	n.a.	n.a.
	SOIL TOTAL			100
492	SOIL
	00-10 cm	0.029	28.2	71.8	0.002	54.6	48.5	103.1
	10-20 cm	0.007	33	20.7	0.0001	79.3	26.3	105.6
	20-30 cm	0.001	14.6	3.2	n.a.	n.a.	n.a.
	30-40cm	<0.001	20.4	1.7	n.a.	n.a.	n.a.
	40-50cm	<0.001	21.1	1.7	n.a.	n.a.	n.a.

1) In equivalents of test substance combustion

2) In % of the total radioactivity found in the sub-balanced soil layer, determined by combustion

3) In % of the total radioactivity found in the soil layer, determined by combustion

Limit of quantification for combustion: 0.001 ppm

Table: Quantitation of metabolites as a function of time (expressed in % of the radioactivity totally found in the soil layers)

Interval /Soil layer (Days after Treatment)	Metabolite Fractions(%)									NE (%)	Total (%)
	Unidentified compound 1	M8	M4	Unidentified compound 2	Test substance	Unidentified compound 3	M1	unres.	subtot.
29 d: 0 - 10 cm	n.d.	n.d.	3.4	n.d.	74.6	1.9	4.1	3.7	87.7	12.3	100.0
63 d: 0 - 10 cm	n.d.	n.d.	6.0	n.d.	75.4	1.2	2.8	5.0	90.4	12.8	103.2
89 d: 0 - 10 cm	1.2	0.6	11.7	0.8	62.9	1.5	3.0	2.2	83.9	20.0	103.9
119 d: 0 -10 cm	3.0	1.0	17.0	1.8	49.3	1.1	2.2	3.4	78.8	24.9	103.7
180 d: 0 - 10 cm	1.6	2.5	29.7	1.2	22.6	1.6	1.0	3.6	63.8	39.1	102.9
362 d: 0 - 10 cm	0.5	2.7	32.0	0.8	14.6	2.0	0.8	2.7	56.1	43.2	99.3
492 d: 0 - 10 cm	n.d.	4.4	35.8	0.5	8.4	1.5	0.6	3.4	54.6	48.5	103.1
492 d: 10 - 20 cm	n.d.	9.9	62.3	n.d.	1.8	0.5	n.d.	4.8	79.3	26.3	105.6

 

Table: Storage Stability

Initial pattern in spiked soil(1) [%](2)	Pattern after air drying [%](2)		Pattern after freezer storage [%](2)
Fractions/Time	0 Days	7 Days	14 days	1 Month	6 Months	12 Months
1 = start	3.9	2.9	2.9	3.8	4.1	3.6
2	0.9	0.7	1.0	0.9	0.8	0.9
3	3.1	3.1	3.3	3.1	3.1	2.8
4	13.4	13.0	14.0	13.0	13.1	12.8
5 = test substance	71.1	74.9	73.1	73.7	73.4	70.0
6	1.4	1.0	1.2	1.0	1.4	2.0
7	4.9	4.2	4.5	4.2	3.7	5.2
8	1.2	0.2	0.2	0.3	0.4	3.0

1) The soil was extracted just after spiking

2) Given in % of extracted

Conclusions:

The total residue level in the 0 - 10 cm soil layer decreased from 0.186 ppm (immediately after application) to 0.029 ppm within 492 days. The DT50 and DT90 values for the test substance in the 0 - 10 cm layer were 51 days and 170 days, respectively.

Executive summary:

The degradation of the test substance in soil was investigated in a field study according to US EPA 164-1 and BBA part IV, 4-1 and in compliance with GLP criteria. The dissipation of the parent compound in soil (47.4% sand, 31.6% silt, 21.0% clay) under field conditions was determined along with the rate of formation and dissipation of major metabolites and the downward movement of parent as a function of time. Therefore, a bareground spray application of formulated [Thiazol-2-14C]-radiolabelled test substance at a rate of 207 g a.i. / ha was performed on a plot which was conjointly used to grow the rotational crops. The soil was subject to realistic environmental conditions with a pH of 7.2, an organic carbon content of 3.1%, a CEC potential of 17.1 meq/100g soil and a water capacity of 49%. Soil samples were taken 1 hour, 29, 63, 89, 119, 180, 362, and 492 days after treatment. Five soil cores at 00 - 30 cm were taken at interval 1 to 6. Five cores at 00 - 60 cm were taken at the last two intervals. Samples were extracted and radioactivity of the combusted samples or in extracts and silica gel removed from TLC was measured by liquid scintillation counting. Total radioactivity in soil samples, as well as non-extractable radioactivity was determined by combustion with subsequent liquid scintillation counting of the evolved carbon dioxide.

The total residue level in the 0 - 10 cm soil layer decreased from 0.186 ppm (immediately after application) to 0.029 ppm within 492 days. The DT50 and DT90 values for the test substance in the 0 - 10 cm layer were 51 days and 170 days, respectively. Some downward movement of radioactivity with time was observed. Total radioactivity in the 10 - 20 cm layer increased to 0.003 ppm at Day 119 and reached 0.007 ppm at Day 362 and remained at 0.007 ppm until the end of the experimental period (492 days after treatment). Total radioactivity in the 20 - 30 cm soil layer never exceeded 0.002 ppm and was found to be 0.001 ppm after 492 days. At the end of the experimental period the radioactivity in the 30 - 40 cm, 40 - 50 cm and 50 - 60 cm soil layers was below 0.001 ppm. M4 and M1 were found as major metabolites. The concentration of M1 amounted to 5.9 ppb at interval 2, i.e. 29 days after treatment and thereafter continuously declined to 0.2 ppb after 492 days. Maximum concentration of M4 (16.2 ppb) was found after 180 days and declined to 10.3 ppb after 492 days. Non-extractable residues in the 0 - 10 cm soil layer expressed in percent of recovered radioactivity continuously increased to 49% at the end of the experimental period. Maximum concentration of non-extractable residues (21.5 ppb) was found after 119 days and declined to 13.9 ppb at the end of the study.

Description of key information

DT50 = 51 days, in field soil under realistic environmental conditions, US EPA 164-1 and BBA IV, 4-1, Sandmeier 1997. The study by Sandmeier is considered representative of the soil degradation properties of the test substance.

Key value for chemical safety assessment

Half-life in soil:

51 d

at the temperature of:

20 °C

Additional information

Overview of available data for the test item on biodegradation in soil (Sandmeier 1997)
The degradation of the test substance in soil was investigated in a wide range of simulation studies. In a representative GLP study according to US EPA 164-1 and BBA part IV, 4-1, the dissipation of the parent compound in soil (47.4% sand, 31.6% silt, 21.0% clay) was determined under field conditions along with the rate of formation and dissipation of major metabolites. The [Thiazol-2-14C]-radiolabelled test substance was applied by spraying at a rate of 207 g/ha on a plot which was conjointly used to grow rotational crops. The soil was representative of realistic environmental conditions with a pH of 7.2, an organic carbon content of 3.1%, a CEC potential of 17.1 meq/100g soil and a water capacity of 49%. Radioactivity of the combusted samples or in extracts and silica gel removed from TLC was measured by liquid scintillation counting. Total radioactivity in soil samples, as well as non-extractable radioactivity was determined by combustion with subsequent liquid scintillation counting of the evolved carbon dioxide. The DT50 and DT90 values for the test substance in the 0 - 10 cm layer were 51 days and 170 days, respectively.

N-[(2-chloro-1,3-thiazol-5-yl)methyl]-N'-methyl-N''-nitroguanidine and 3-[(2-chloro-1,3-thiazol-5-yl)methyl]-5-methyl-1,3,5-oxadiazinan-4-one were identified as major metabolites. Further metabolites were N-[(2-chloro-1,3-thiazol-5-yl)methyl]-N'-methylurea and N-[(2-chloro-1,3-thiazol-5-yl)methyl]-N'-nitroguanidine. Non-extractable residues in the 0 - 10 cm soil layer expressed in percent of recovered radioactivity continuously increased to 49% at the end of the experimental period. A maximum concentration of non-extractable residues (21.5 ppb) was found after 119 days and declined to 13.9 ppb at the end of the study.

Soil dissipation
A large number of soil dissipation studies were conducted with the test material. As information on soil dissipation is outside the scope of REACH, the studies are not summarized as individual endpoint study entries, but briefly discussed here: The test material was tested for different application types in different crops and bare grounds with an application rate ranging from 26.3 to 336 g ai/ha for broadcast application and 70 to 200 g ai/ha for seed treatment. The DT50 values reported in the original reports as calculated with first order kinetic modelling were between 5.9 - 72 days for broadcast application and 5 - 31 days for seed treatment. The DT50 values as recalculated with first order kinetic modelling were between 7.15 - 109 days for broadcast application and 11.5 - 54.5 days for seed treatment. (Hayes, 2015a,b,c; Ford, 2015; Mair, 1996; Hardy, 2015; Pointurier, 1997a,b,c,d,e,f; Smith, 1998a,b; Mair, 1998a,b; Balluff, 2003; Sandmeier, 1997; Finger, 2015a,b,c,d; Gezahegne and Ahrens, 2015; Tribolet, 2001; Purdy, 2004; Speth, 1999a,b; Wiepke, 1999a,b; Wiepke, 1998; Stolze, 2001a,b,c; Nagra, 2004a,b; Nagra, 2007 and Gezahegne and Arhens, 2015).