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

Sediment toxicity

Link to relevant study record(s)

Reference

Endpoint:

sediment toxicity: long-term

Type of information:

experimental study

Adequacy of study:

key study

Study period:

24 Feb 1998 to 05 May 1998

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: OECD Guidelines for the Testing of Chemicals, Proposal for Toxicity Test with Chironomidae

Version / remarks:

November 1997

Qualifier:

according to guideline

Guideline:

other: Proposal for a BBA-Guideline: Effects of Plant Protection Products on the Development of Sediment-Dwelling Larvae of Chironomus riparius in a Water-Sediment System

Version / remarks:

1995

GLP compliance:

yes

Analytical monitoring:

yes

Details on sampling:

WATER
Sacrificial replicates were used to determine the concentration of test material for the overlying water in the 40 and 20 µg a.s./L treatments, and in the sediment at 40 µg a.s./L, on days 0, 7 and 30. Analysis of the sediment at 20 µg a.s./L was performed on day 30.

SEDIMENT
Sacrificial replicates were used to determine the concentration of test material for the overlying water in the 400 and 200 µg a.s./kg dry sediment treatments, and in the sediment at 400 µg a.s./kg dry sediment, on days 0, 7 and 30. Analysis of the sediment at 200 µg a.s./kg dry sediment was performed on day 30.

Vehicle:

yes

Remarks:

acetone for Scenario B (sediment)

Details on sediment and application:

PREPARATION OF SPIKED WATER (SCENARIO A)
A solution was prepared by dissolving 70.0 mg of test material in 1000 mL of M4 medium to give a nominal concentration of 70 mg/L. From this, six stock solutions (one per treatment) were prepared by making appropriate aliquots of the 70 mg/L solution up to 1000 mL with M4 medium. Then appropriate volumes of each stock solution were added to the appropriate treatment replicates to produce the test dilutions. A dilution water control was also prepared.

PREPARATION OF SPIKED SEDIMENT (SCENARIO B)
A solution was prepared by dissolving 20.01 mg of test material in 100 mL of acetone to give a nominal concentration of 200 mg/L. Six stock solutions (one per treatment) were prepared by making appropriate aliquots of the 200 mg/L solution up to 25 mL with acetone. Then appropriate volumes of each stock solution were added to 15.5 g sand, mixed and the solvent evaporated off. Each batch of spiked sand was then mixed with 760.6 g (dry weight) of aged sediment for about 30 minutes to produce the spiked sediment for the six test treatments. A solvent control was also prepared in the same manner as the test treatments, using acetone and sand, along with a negative control using sand alone.

Test organisms (species):

Chironomus riparius

Details on test organisms:

TEST ORGANISM
- Common name: Harlequin fly larvae
- Instar: first instar
- Source: Continuous laboratory cultures

Study type:

laboratory study

Test type:

static

Water media type:

freshwater

Type of sediment:

artificial sediment

Limit test:

no

Duration:

30 d

Exposure phase:

total exposure duration

Remarks:

For the water and sediment scenarios

Hardness:

- Scenario A (water): 272 mg/L as CaCO3
- Scenario B (sediment): 297 mg/L as CaCO3

Test temperature:

- Scenario A (water): 19.7 - 21.4°C
- Scenario B (sediment): 19.7 - 21.4°C

pH:

- Scenario A (water): 7.7 - 9.2
- Scenario B (sediment): 7.7 - 8.2

Dissolved oxygen:

- Overlying water Scenario A (water): 95 to 110% saturation value
- Overlying water Scenario B (sediment): 78 to 104% saturation value

Conductivity:

- Scenario A (water): 701 µS/cm
- Scenario B (sediment): 720 µS/cm

Nominal and measured concentrations:

- Nominal concentrations in water: 0 (control), 1.25, 2.5, 5, 10, 20 and 40 µg a.s./L
- Nominal concentrations in sediment: 0 (control), 0 (solvent control), 12.5, 25, 50, 100, 200 and 400 µg a.s./kg dry sediment
- Mean measured concentrations: See 'Any other information on materials and methods incl. tables'. for an overview of the measured concentrations in water and sediment per scenario.

Details on test conditions:

TEST SYSTEM
- Test container scenario A: 1 L tall-form glass beakers 9 cm diameter, covered with parafilm
- Test container scenario B: 1 L tall-form glass beakers 9 cm diameter, covered with parafilm. Separation of sediment ingredients avoided when adding water by placing styropore layer on sediment before pouring water. The styroscope was then removed.
- Weight of wet sediment scenario A: 86 g of wet sediment (1.6 - 2 cm layer)
- Weight of wet sediment scenario B: 120 g of wet sediment
- Overlying water volume scenario A: 536 mL (8 cm layer) of test medium.
- Sediment volume: 510 mL of test medium
- Depth of sediment and overlying water: 9.6 - 10.0 cm
- Aeration: Yes, gentle aeration was applied for both scenarios.

EXPOSURE PREPARATIONS
- Scenario A: 12 days before application of the test item, three replicate test and control replicate vessels were prepared (water and sediment added) and gently aerated. Larvae were introduced to the test vessels 24 hours before application of test item to water column.
- Scenario B: Artificial sediment was conditioned in flowing water for 13 days before application of the test item (spiked onto sand using acetone as a solvent). Replicates were prepared about 20 hours before test start and gently aerated. Then, larvae were introduced randomly per vessel and the aeration halted for 24-h. Aeration then re-started. Test system kept in temperature controlled room.

EXPOSURE REGIME
- No. of organisms per container: 20
- No. of replicates per treatment group: 3
- No. of replicates per control / vehicle control: 3
- Feeding: Fish food (Tetramin) suspension (2g Tetramin in 40 ml medium); equivalent to about 1.0 mg fish food per larva per day on days 0 and 1, doubled to 2 mg fish food per larva per day on the remaining feeding days.
- Feeding regime: For both scenarios, food was supplied on days 0, 1, 3, 7, 8, 10, 13, 15, 17, 20, 22, 24, 27 and 29.

OVERLYING WATER CHARACTERISTCS
- Type of water: Elendt M4

CHARACTERIZATION OF (ARTIFICIAL; delete if not applicable) SEDIMENT
- % dry weight of sphagnum moss peat: 10
- Particle size distribution : >50% of the particles between 50 and 200µm
- % industrial sand: 68
- % koalin clay: 20
- Oganic carbon content: 3 - 4%
- Adjustment of pH: Yes, calcium carbonate was used to adjust the pH.

OTHER TEST CONDITIONS
- Light quality: Fluorescent (both scenarios)
- Photoperiod: 16 hours light and 8 hours dark with 30 minute dawn and dusk transition periods (both scenarios)
- Light intensity: 800 - 1000 lux (both scenarios)

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : behaviour, mortalities, emergence and dry weight
Visual assessments of behaviour, mortalities and emergence were made daily (except on days 4, 5, 12, 19, 25 and 26) for both scenarios. Emerged adults were removed from the test vessels when seen, recorded and sexed before being discarded. The emergence and development rates, and the gender ratio were calculated from the total numbers of emerged male and female adults, and from the time to emergence. On day 7 a sacrificial replicate at each treatment and control, set up at the same time as the three test replicates, was sieved to remove the larvae. After drying at 60 °C the larvae were weighed.

TEST CONDITIONS MEASURED
The pH and dissolved oxygen were measured in each test vessel on different days. Water temperature was recorded continuously. The hardness and conductivity of the batches of M4 medium were measured after preparation. For Scenario A, sacrificial replicates were used to determine the concentration of test material for the overlying water in the 40 and 20 µg a.s./L treatments, and in the sediment at 40 µg a.s./L, on days 0, 7 and 30. Analysis of the sediment at 20 µg a.s./L was performed on day 30. For Scenario B, sacrificial replicates were used to determine the concentration of test material for the overlying water in the 400 and 200 µg a.s./kg dry sediment treatments, and in the sediment at 400 µg a.s./kg dry sediment, on days 0, 7 and 30. Analysis of the sediment at 200 µg a.s./kg dry sediment was performed on day 30.

VEHICLE CONTROL PERFORMED: yes

Reference substance (positive control):

no

Key result

Duration:

30 d

Dose descriptor:

NOEC

Effect conc.:

10 µg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

emergence rate

Remarks on result:

other: in water (scenario A)

Duration:

30 d

Dose descriptor:

NOEC

Effect conc.:

10 µg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

development rate

Remarks on result:

other: in water (scenario A)

Key result

Duration:

30 d

Dose descriptor:

NOEC

Effect conc.:

100 µg/kg sediment dw

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

emergence rate

Remarks on result:

other: in sediment (scenario B)

Duration:

30 d

Dose descriptor:

NOEC

Effect conc.:

100 µg/kg sediment dw

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

development rate

Remarks on result:

other: in sediment (scenario B)

Duration:

30 d

Dose descriptor:

EC50

Effect conc.:

11.4 µg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

emergence rate

Remarks on result:

other: in water (scenario A)

Duration:

30 d

Dose descriptor:

EC50

Effect conc.:

> 10 µg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

development rate

Remarks:

sexes pooled

Remarks on result:

other: in water (scenario A)

Duration:

30 d

Dose descriptor:

EC50

Effect conc.:

114 µg/kg sediment dw

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

emergence rate

Remarks on result:

other: in sediment (scenario B)

Duration:

30 d

Dose descriptor:

EC50

Effect conc.:

> 100 µg/kg sediment dw

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

development rate

Remarks on result:

other: in sediment (scenario B)

Details on results:

For the water and sediment tests, no signs of toxicity were observed up to 10.0 µg/L and 100 µ/kg dry sediment, respectively, throughout the test. Therefore, the two highest concentrations in both scenarios were used as sacrificial replicates and were therefore not used for determination of toxic effects of the test substance. The complete results are tabulated in 'Any other information on results incl. tables'.

Reported statistics and error estimates:

Not reported

Table: Effects of the test substance on emergence and development of Chironomus riparius after 30 days exposure for Scenario A

Nominal concentrations (µg a.s./L)	Mean number emerged	Mean emergence rate	Mean gender rate	Mean development rate/vessel	Day to first hatch
Control	17.7	0.88	0.40	0.09	13
1.25	17.7	0.88	0.45	0.08	13
2.50	18.0	0.90	0.52	0.07	13
5.00	19.0	0.95	0.53	0.08	13
10.0	16.7	0.83	0.54	0.07	13
20.0	0	0	0	0	-
40.0	0	0	0	0	-

  

Table:Effects of the test substance on emergence and development of Chironomus riparius after 30 days exposure for Scenario B

Nominal concentrations (µg a.s./kg dry sediment)	Mean number emerged	Mean emergence rate	Mean gender rate	Mean development rate/vessel	Day to first hatch
Control	17.0	0.85	0.40	0.07	14
Solvent control	17.7	0.88	0.51	0.07	13
12.5	18.0	0.90	0.56	0.07	14
25	15.0	0.75	0.52	0.07	14
50	16.3	0.82	0.63	0.07	14
100	15.3	0.77	0.55	0.07	13
200	0	0	0	0	-
400	0	0	0	0	-

 

Table: Summary of the effects of the test substance on growth of Chironomus riparius after 7 days exposure for Scenario A 

Concentration (µg a.s./L)	Average dry weight of larvae (mg)	No. larvae found
0 (control)	0.59	19
1.25	0.69	19
2.5	0.33	14
5.0	0.78	19
10	0.45	20
20	0.20	19
40	0.35	15

 

Table: Summary of the effects of the test substance on growth of Chironomus riparius after 7 days exposure for Scenario B

Concentration (µg a.s./kg dry sediment)	Average dry weight of larvae (mg)	No. larvae found
0 (control)	0.25	15
0 (solvent control)	0.24	18
12.5	0.22	11
25	0.38	15
50	0.29	10
100	0.32	14
200	0.48	12
400	0.25	15

 

Validity criteria fulfilled:

yes

Remarks:

most criteria were met, see 'Any other information on materials and methods incl. tables'.

Conclusions:

Based on nominal concentrations of the test substance, the 30 day EC50 for emergence rate was 11.4 µg a.s./L when exposed via the water column (Scenario A), and 114 µg a.s./kg dry sediment when exposed via the sediment (Scenario B). For development rate the 30 day EC50 was >10 µg a.s./L when exposed via the water column (Scenario A), and >100 µg a.s./kg of dry sediment when exposed via the sediment (Scenario B). The 30 day NOECs for emergence rate and development rate were 10 µg a.s./L (Scenario A), and 100 µg a.s./kg dry sediment (Scenario B).

Executive summary:

The toxicity to sediment-dwelling organisms was determined in a GLP-compliant study according to OECD Proposal for toxicity test with Chironomidae. In this study, harlequin fly larvae (60 per treatment; Chironomus rapirius) were exposed through a water (Scenario A) and sediment (Scenario B) system to nominal test substance concentration of 0 (control), 1.25, 2.5, 5, 10, 20 and 40 µg a.s./L and 0 (control), 0 (vehicle control) 12.5, 25, 50, 100, 200 and 400 µg a.s./kg dry sediment, respectively for 30 days. For scenario A, the substance was dissolved in the medium. For scenario B, the test substance was spiked in artificial soil that contained 68% industrial sand, 20% koalin clay and 10% sphagnum peat moss. Visual assessments of behaviour, mortalities and emergence were made on most days for both scenarios. Emerged adults were removed from the test vessels when seen, recorded and sexed before being discarded. The emergence and development rates, and the gender ratio were calculated from the total numbers of emerged male and female adults, and from the time to emergence. On day 7 a sacrificial replicate at each treatment and control, set up at the same time as the three test replicates, was sieved to remove the larvae. After drying at 60 °C the larvae were weighed. For the water and sediment tests, no signs of toxicity were observed up to 10.0 µg/L and 100 µ/kg dry sediment, repsectively, throughout the test. The the two highest concentrations in both scenarios were used as sacrificial replicates and were therefore not used for determination of toxic effects of the test substance. Based on these findings, the 30-d NOEC values for emergence rate were determined to be > 10 µg a.s./L and 100 µg a.s./kg dry sediment, for scenario A and B respectively. The derived 30-d EC50 values for emergence rate were determined to be 11.4 a.s./L and 114 µg a.s./kg dry sediment, for scenario A and B respectively.

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.

30-d NOEC = 100 µg a.s./kg dry sediment, Chironomus riparius, emergence rate, OECD Proposal for toxicity test with Chironomidae (1997), Grade 1998

Key value for chemical safety assessment

EC50 or LC50 for freshwater sediment:

114 µg/kg sediment dw

EC10, LC10 or NOEC for freshwater sediment:

100 µg/kg sediment dw

Additional information

In a GLP study conducted to OECD draft guidelines, harlequin fly larvae (60 per treatment; Chironomus rapirius) were exposed to a series of test substance concentrations via water or sediment for 30 days, by dissolving the substance in the medium or spiking artificial sediment that contained 68% industrial sand, 20% kaolin clay and 10% sphagnum peat moss. The emergence and development rates, and the gender ratio were calculated from the total numbers of emerged male and female adults, and from the time to emergence. One sacrificial replicate of each concentration and control sieved to remove the larvae, which were dried at 60 °C and weighed. No signs of toxicity were observed up to 10.0 µg/L and 100 µ/kg dry sediment, respectively. The 30-day NOEC values for emergence rate were determined to be >10 µg/L and 100 µg/kg dry sediment. The derived 30-day EC50 values for effects on the emergence rate were determined to be 11.4 µg/L and 114 µg/kg dry sediment.