imidacloprid (ISO); 1-(6-chloropyridin-3-ylmethyl)-N-nitroimidazolidin-2-ylidenamine

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:

22 Feb - 13 Apr, 2001

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 219 (Sediment-Water Chironomid Toxicity Test Using Spiked Water)

Version / remarks:

2001

Deviations:

no

GLP compliance:

yes

Analytical monitoring:

yes

Details on sampling:

Water for analysis was taken from all beakers of one concentration, mixed and transferred to the analytical laboratory. The samples were stored frozen until they were analysed.
Due to the high concentration this sample had to be 50-fold diluted with test water OE containing 0.1% acetic acid. The injection volume was 220 µL. The sample was injected in duplicate.

Vehicle:

yes

Remarks:

M7 test medium

Details on sediment and application:

The test concentrations were set up as follows: 38.8 mg test substance was dissolved in 1.0 L M7 medium to obtain the stock solution. The stock solution was treated in an ultrasonic bath for 2 minutes and was stirred on a magnetic stirrer for 5 minutes. To obtain the application solution 10 mL of the stock solution was made up to 1 L with M7 medium and was stirred on a magnetic stirrer for 2 minutes.

Test organisms (species):

Chironomus riparius

Details on test organisms:

Test specimen of Chironomus riparius were obtained from a in-house culture maintained since 1991.
For the study, animals of the first larval stage (L1), the parents of which stem from an approximately 21 - 28 day old synchronous culture, were used. 20 larvae were placed in each test container (0.6 L glass beakers). The hatched larvae are fed with green algae and an aqueous suspension of a vegetable fish food.
The L1 larvae used in the study were obtained by introducing some fresh egg masses in small dishes with culture medium. 2 to 3 days after hatching the identification of the species was confirmed using a stereo microscope, and the L1 larvae were transferred carefully with a blunt pipette to the test vessels. The aeration of the water was stopped for 24 hours after insertion of test organisms.
During the study the test organisms were fed with a commercial ornamental fish food extract as used for the breeding. An appropriate amount of this suspension (about 1 mg/Larvae/day) was added to each test container on days: -1, 0, 3, 4, 5, 6,7, 10, 11, 12, 13, 14, 17, 18, 19, 20, 21, 24, 25, 26 and 27.

Study type:

laboratory study

Test type:

static

Water media type:

freshwater

Remarks:

M7 medium

Type of sediment:

artificial sediment

Remarks:

prepared 8 days before the start of the test. It consists of 74 % fine quartz sand, 5.0 % dried, finely ground peat, 20 % kaolin and around 1 % calcium carbonate to adjust the pH value to 7 ± 0.5.

Limit test:

no

Duration:

28 d

Exposure phase:

larvae from first generation (P)

Hardness:

267.0 - 302.6 mg/LCaCO3

Test temperature:

20.1 - 20.4°C

pH:

7.9 - 8.6

Dissolved oxygen:

7.4 - 8.8 mg/L

Salinity:

not applicable

Ammonia:

0.08 - 2.66 mg/L

Conductivity:

568 µS/cm

Nominal and measured concentrations:

Nominal: 0.35, 0.64, 1.14, 2.06, 3.70, 5.56 and 10.0 µg a.s./L
Measured: please refer to the table included in "Results and discussion - overall remark/ attached background material" field

Details on test conditions:

For acclimatization the test containers were prepared 7 days before the study commenced. One day prior to treatment (= day -1) the test organisms (L1 larvae) were transferred in a randomized procedure into the test containers (collectives of 5 larvae each).
Test and breeding water was prepared as "M7-medium". The medium is prepared using deionised water and adding mineral salts and vitamins. The content of particulate organic matter is checked at least once per year with being below 20 mg/L. The water was aerated and temperated to 20 °C in an in-house preparation tank. Test containers were 0.6 L glass beakers with an average diameter of about 9.5 cm. Any apparatus in contact with the test system was made of chemically inert material.
The water used in this study was free of contaminants which might influence the test.
The artificial sediment used in this study was free of contaminants which might influence the test.
The bottom of the test containers were covered with a 1.5 cm layer of sediment. To avoid a separation of the sediment ingredients, the sediment was covered by a sheet, and the test water poured slowly into the beaker (the beakers were filled with 0.38 L water). The sheet was removed carefully thereafter. The height of the water was 6.0 cm. Gentle aeration was provided through a glass Pasteur pipette situated about 2.5 cm above the sediment layer throughout the complete study. Test beakers were covered by clear plastic plates, preventing evaporation.

For chemical analysis of the active ingredient additional parallel replicates were prepared for analytical purposes only (control: 1 replicate; 0.35, 2.06 and 10.0 ug
a.s./L: 2 replicates). For measuring the temperature, pH and Oxygen-content of the test water during the study one replicate of each test concentration was prepared.

The test vessels were observed at least three times per week to make a visual assessment of any behavioral differences compared to the control. The sex, time
and number of emerged or not fully emerged adults were recorded daily during the period of emergence. As only fully emerged adults are relevant for the endpoints of this study, larvae which did not mature were not evaluated.

Key result

Duration:

28 d

Dose descriptor:

EC10

Effect conc.:

2.09 µg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

emergence rate

Key result

Duration:

28 d

Dose descriptor:

EC50

Effect conc.:

3.11 µg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

emergence rate

Details on results:

81.7 % of the inserted larvae maturated to adults in the control, fulfilling the guideline requirements. Also for the test concentrations of 0.35, 0.64, and 1.14 µg a.s./L high emergence ratio of 83.3, 81.7 and 83.8 % were recorded. At test concentrations of 2.06 and 3.70 µg a.s./L the emergence was reduced to 68.3 and 30 %. At the higher test concentrations of 5.56 and 10.0 µg a.s./L no larvae matured. The start of emergence was on day 13 for test concentrations of 0.35 to 2.06 ug a.s./L just like in the control, at 3.70 µg a.s./L the emergence was postponed for at least 2 days.
The EC15 (probit analysis) for the development rate was not calculable, as the influence on the development rate was below 15 % at all test concentrations with emergence (0.35 - 3.70 ug a.s./L) compared to control findings. Thus, the emergence ratio was more sensitive than the development rate and the EC15 of the development rate will be > 3.7 ug a.s./L and < 5.56 ug a.s./L.

Please refer to "overall remark/ attached background material" field for result tables.

Table 1. Validity criteria for OECD 219 (2004)

Criterion from the guideline	Outcome	Validity criterion fulfilled
The emergence in the control must be at least 70% at the end of the test.	81.7%	Yes
C. riparius emergence to adults from control vessels should occur between 12 and 23 d after their insertion into the vessels.	Mean of 15.4 days	Yes
At the end of the test, pH and the dissolved oxygen concentration should be measured in each vessel.	Measured on day 28	Yes
At the end of the test, the oxygen concentration should be at least 60% of the air saturation value (ASV) at the temperature used in all test vessels.	Min of 7.4 mg/L (corresponding to about 83%)	Yes
At the end of the test, the pH of the overlying water should be in the 6-9 range in all test vessels.	Ranged between 7.9 and 8.6	Yes
The water temperature should not differ by more than ± 1.0 °C.	Ranged between 20.1 and 20.4°C	Yes

Validity criteria fulfilled:

not specified

Remarks:

in the report, for further details please refer to “Any other information on results incl. tables”.

Conclusions:

The present guideline study was conducted in compliance with GLP. Under the test conditions used, the overall EC10 (28 d) was 0.00209 mg a.s./L and the overall EC50 was 0.00311 mg a.s./L.

Description of key information

From chronic toxicity key study, the 28-day EC₅₀ was 3.11 µg a.s./L and EC₁₀ was 2.09 µg a.s./L.

Additional information

In the key study (2001), the chronic toxicity of test material technical to sediment organisms was investigated. The study was conducted according to OECD Guideline No. 219, under GLP conditions, after 28 days of exposure to spiked water with the test substance. Chironomus riparius were exposed to the nominal concentrations of 0.35, 0.64, 1.14, 2.06, 3.70, 5.56 and 10.0 µg a.s./L, alongside with a control. Mean measured concentrations from day 0 and 1 hour after application ranged from 93.7% to 102.6 % of nominal concentration. Based on the nominal concentration 28-day EC₅₀ was 3.11 µg a.s./L and EC₁₀ was 2.09 µg a.s./L. Due to the low adsorption potential of the substance (log Kow < 3), the substance is not expected to adsorb to sediment or organic matter. Thus the available study with spiked water is considered suitable for the assessment.

 

There are three additional supportive studies available, conducted with the following species: (Gammarus pulex, Chirononmus riparius and Chironomus tentans) but not according to the OECD guideline, in which the LC₅₀ ranged from 3.17 µg a.s./L (after 10-d) to 55.2 µg a.s./L (after 24-h) and the NOEC (28-d) was 64 µg a.s./L.

 

In the first supporting study (2001), the chronic toxicity of test material to G. pulex was determined in a 28-d-static test according to OECD 219. The NOEC of the test material was determined to be 64 µg a.s./L based on nominal concentrations.

 

In the second supporting study (2002), the acute toxicity of test material to C. riparius was determined in a 24-h-static test with a method equivalent to OECD 202. The 24-h LC₅₀ of the test material was determined to be 55.2 µg a.s./L based on nominal concentrations.

 

In the third supporting study (1991), the acute toxicity of test material to C. tentans was determined in a 10-d semi-static test according to ASTM E1383 (Sediment Toxicity Test (Media: Sediment-freshwater)).The 10-d LC₅₀of the test material was determined to be 3.17 µg a.s./L based on measured concentrations.