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

Toxicity to terrestrial plants

Link to relevant study record(s)

Reference

Endpoint:

toxicity to terrestrial plants: short-term (with study design considered suitable for long-term assessment)

Type of information:

experimental study

Adequacy of study:

key study

Study period:

30 Nov 2012 to 10 Jan 2013

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 208 (Terrestrial Plants, Growth Test)

Version / remarks:

July 2006

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Species:

Zea mays

Plant group:

Monocotyledonae (monocots)

Details on test organisms:

- Common name: Corn

Species:

Allium cepa

Plant group:

Monocotyledonae (monocots)

Details on test organisms:

- Common name: Onion

Species:

Lolium perenne

Plant group:

Monocotyledonae (monocots)

Details on test organisms:

- Common name: Perennial ryegrass

Species:

Avena sativa

Plant group:

Monocotyledonae (monocots)

Details on test organisms:

- Common name: Oat

Species:

Phaseolus vulgaris

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: Common bean

Species:

Cucumis sativus

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: Cucumber

Species:

Glycine max (G. soja)

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: Soybean

Species:

Brassica napus

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: Oilseed rape

Species:

Pisum sativum

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: Pea

Species:

Beta vulgaris

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: Sugar beet

Test type:

seedling emergence and seedling growth test

Study type:

laboratory study

Substrate type:

artificial soil

Limit test:

no

Total exposure duration:

21 d

Remarks:

14 days after 50% of the control seeds had emerged.

Test temperature:

19-33 °C; 16-39 °C for sugar beet

pH:

Not reported

Moisture:

Not reported

Details on test conditions:

TEST SYSTEM
- Test container: Polypropylene pots (12 cm tall, 14 cm diameter top, 12 cm diameter bottom)
- Amount of soil: The test container was filled to a depth of 10 cm
- Method of seeding: Not reported
- No. of seeds per container: Not reported
- No. of plants (retained after thinning): Not reported
- No. of replicates per treatment group: 10
- No. of replicates per control: 10

GROWTH CONDITIONS
- Photoperiod: 8 hours dark / 16 hours light
- Light source: Not reported
- Light intensity and quality: Not reported
- Day/night temperatures: Not reported
- Relative humidity (%): 15 to 89%
- Volume applied: 100 L/ha
- Interval of applications: Not reported
- Method of application: Laboratory sprayer

EFFECT PARAMETERS MEASURED: emergence, morphological abnormalities, shoot length, tallest new growth (dicots), longest leaf length (monocots), dry weight
Each pot was observed on days 0, 7 and 14 days (test termination) after 50% of the control seeds had emerged to determine percent emergence and to record any morphological abnormalities (e.g., chlorosis of leaves) of the emerged shoots. Observations of morphological abnormalities were reported as the percentage of plants exhibiting the abnormality. Shoot length was measured at test termination. The dicotyledons were measured to the tallest new growth and the monocotyledons were measured to the longest leaf length using a ruler and measuring to the nearest 0.5 cm. Additionally, at test termination, the shoots within a pot were cut at the soil surface and placed in labelled, prepared container. Shoots were dried in an oven at approximately 70 ± 5 ºC for a minimum of three days before determining shoot dry weights. Weights were measured using a four place balance (Sartorius). Plants that died during the exposure were not included in statistical calculations.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 2

Nominal and measured concentrations:

- Nominal concentrations: 0 (control), 18.63, 37.25, 74.5, 149 and 298 g a.s./ha

Reference substance (positive control):

no

Species:

other: all species

Duration:

21 d

Dose descriptor:

ER50

Effect conc.:

> 298 g/ha

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

other: survival, emergence, shoot length and shoot dry weight

Remarks on result:

other: see 'Any other information on results incl. tables' for an overview of the results.

Key result

Species:

other: all species

Duration:

21 d

Dose descriptor:

ER50

Effect conc.:

> 0.4 mg/kg soil dw

Nominal / measured:

meas. (geom. mean)

Conc. based on:

act. ingr.

Basis for effect:

other: survival, emergence, shoot length and shoot dry weight

Remarks on result:

other: recalculation to mg/kg soil dry weight unit by the registrant

Details on results:

Of the ten crops tested, only one displayed signs of toxicity: Cucumis sativa (cucumber) showed a decrease in shoot length at study termination. However, data is insufficient to determine an ER50 and no other effects were observed for this crop throughout the study. A detailed overview of all effects values is provided in 'Any other information on results incl. tables'.

Reported statistics and error estimates:

The No-Observed-Effect Concentration (NOEC) on day 14 for percentage emergence, survival, shoot length and shoot dry weight when compared to the control data were determined. The data were first checked for normality using Shapiro-Wilks' Test and for homogeneity of variance using either Levene’s Equality of Variance Test or Bartlett's Test. If the data sets passed the tests for homogeneity and normality, Dunnett's Multiple Comparison Test or Bonferroni’s adjusted t-Test were used to determine the NOEC. If the data did not pass the tests for homogeneity and normality, then Steel’s Many-One Rank Sum Test was used to determine the NOEC.
The EC05, EC25 and EC50 values (concentrations of test substance which reduced the day 14 percent emergence survival, shoot length or shoot dry weight by 5, 25 and 50%, respectively) and the 95% confidence limits were calculated. The EC values and their 95% confidence limits were determined by linear interpolation of the biological response versus the nominal application rate.

Table: Effect rates of the test substance on 21-day emergence and survival

Species	Survival (g a.s./ha)				Percentage emergence (g a.s./ha)
	LOEC	NOEC	EC25	EC50	LOEC	NOEC	EC25	EC50
Monocots
Zea mays (corn)	> 298	298	> 298	> 298	> 298	298	> 298	> 298
Avena sativa (oat)	> 298	298	> 298	> 298	> 298	298	> 298	> 298
Allium cepa (onion)	> 298	298	> 298	> 298	> 298	298	> 298	> 298
Lolium perenne (perennial ryegrass)	> 298	298	> 298	> 298	> 298	298	> 298	> 298
Dicots
Phaseolus vulgaris (common bean)	> 298	298	> 298	> 298	> 298	298	> 298	> 298
Cucumis sativa (cucumber)	> 298	298	> 298	> 298	> 298	298	> 298	> 298
Brassica napus (oilseed rape)	> 298	298	> 298	> 298	> 298	298	> 298	> 298
Pisum sativum (pea)	> 298	298	> 298	> 298	> 298	298	> 298	> 298
Glycine max (soybean)	> 298	298	> 298	> 298	> 298	298	> 298	> 298
Beta vulgaris (sugar beet)	> 298	298	> 298	> 298	> 298	298	> 298	> 298

 Table: Effect rates of the test substance on 21-day shoot length and shoot dry weight

Species	Shoot length (g a.s./ha)				Shoot dry weight (g a.s./ha)
	LOEC	NOEC	EC25	EC50	LOEC	NOEC	EC25	EC50
Monocots
Zea mays (corn)	> 298	298	> 298	> 298	> 298	298	> 298	> 298
Avena sativa (oat)	> 298	298	> 298	> 298	> 298	298	> 298	> 298
Allium cepa (onion)	> 298	298	> 298	> 298	> 298	298	> 298	> 298
Lolium perenne (perennial ryegrass)	> 298	298	> 298	> 298	> 298	298	> 298	> 298
Dicots
Phaseolus vulgaris (common bean)	> 298	298	> 298	> 298	> 298	298	> 298	> 298
Cucumis sativa (cucumber)	18.63	< 18.63	28	> 298	> 298	298	> 298	> 298
Brassica napus (oilseed rape)	> 298	298	> 298	> 298	> 298	298	> 298	> 298
Pisum sativum (pea)	> 298	298	> 298	> 298	> 298	298	> 298	> 298
Glycine max (soybean)	> 298	298	> 298	> 298	> 298	298	> 298	> 298
Beta vulgaris (sugar beet)	> 298	298	> 298	> 298	> 298	298	> 298	> 298

 

 

Validity criteria fulfilled:

yes

Remarks:

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

Conclusions:

Ten crop species were tested (four monocotyledons and six dicotyledons) for sensitivity to the test substance. A pre-emergent application of the test substance, at rates up to 298 g a.s./ha resulted in ER50 values of > 298 g a.s./ha for all species. All species were equally unaffected by the test item, with most NOECs being the highest rate tested, 298 g a.s./ha, equivalent to 0.4 mg/kg soil dw.

Executive summary:

The toxicity to terrestrial plants was determined in a Seedling Emergence and Seedling Growth Test according OECD guideline No 208 and in compliance with GLP criteria. In this study, ten plant species (six dicotyledonous and four monocotyledonous species, representing ten plant families) were exposed to nominal test concentrations of 0 (control), 18.63, 37.25, 74.5, 149 and 298 g a.s./ha. The test item was applied by a laboratory sprayer with a volume of 100 L/ha. Test concentrations were not analytically verified and thus test concentrations are given as nominal. The exposure time was 14 to 21 days after 50% germination in the control, depending on the growth of the seedlings. Emergence and morphological abnormalities were determined during the test and shoot length, tallest new growth (dicots), longest leaf length (monocots) and dry weight were determined at study termination. Of the ten crops tested, only one displayed signs of toxicity; Cucumis sativa (cucumber) showed a decrease in shoot length at study termination. However, insufficient to determine a ER50 and no other effects were observed for this crop throughout the study. Based on these results, the overall 21-d ER50 was determined to be > 298 g a.s./ha for all species, equivalent to 0.4 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 21-d ER50 value is >298 g a.i/ha, equivalent to 0.4 mg/kg soil dw, determined by OECD TG 208, Martin, 2013

No quantitative acute effect value (ER50) can be determined as no ≥50% effect was reached in the study.

Additional information

The toxicity of the substance to terrestrial plants was investigated under GLP in a growth test conducted to OECD TG 208. Four monocot species (corn, oat, onion, perennial ryegrass) and six dicot species (common bean, cucumber, oilseed rape, pea, soybean, sugar beet) were exposed for a period of 21 days to an application rate of 298 g/ha. This application rate was recalculated by the registrant to a soil concentration of 0.4 mg/kg soil dw. No significant adverse effect on emergence, survival shoot length and shoot dry weight was observed in any of the tested species.