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

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

effects on growth of green algae

Type of information:

experimental study

Adequacy of study:

key study

Study period:

31 Mar - 06 Apr, 2000

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Version / remarks:

7 June 1984

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Delivered by : Ministerium fur Umwelt, Raumordnung und Landwirtschaft des Landes Nordrhein-Westfalen.

Analytical monitoring:

yes

Details on sampling:

Quantitative analyses of the test material in samples of the nutrient medium were made at the beginning and at the end of the experiment. The samples were stored in a refrigerator until they were analyzed.

Vehicle:

no

Details on test solutions:

A stock solution of the test substance was prepared by adding 0.150 g of technical grade active ingredient to a 1500 mL test beaker and bringing this up to volume with sterile, deionized water. Before use, the flask containing the stock solution was placed in an ultrasonic bath for 5 minutes and subsequently was agitated with a magnetic stirrer for 45 minutes.

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Details on test organisms:

The green algae, Selenastrum capricornutum, strain SAG 61.81 (Collection of Algal Cultures, Inst. for Plant Physiology, University of Gottingen, Nikolausberger Weg 18, 37077 Gottingen, Germany) was used in the experiments. Pre-cultures of the algae were inoculated with 1x 10 000 cells/mL. They were grown in 200 mL nutrient solution number 2 for 3 days in an incubator.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

72 h

Hardness:

Not reported

Test temperature:

23 ± 2°C

pH:

8,16 - 8,84

Dissolved oxygen:

Not reported

Salinity:

Not applicable

Conductivity:

Not reported

Nominal and measured concentrations:

Nominal concentration: 100 mg/L (98.6 mg a.s./L)
Mean measured concentration: 99.5 (start) and 98.6 (end) mg a.s./L

Details on test conditions:

Incubation was at 23 ± 2 °C and 8000 lux ± 20 %. Illumination in the incubator (24 h/day) was provided by 2 banks of lights containing 3 fluorescent lamps each. To help provide uniform illumination, the banks were attached to opposite walls of an incubator whose inner walls were covered with reflective metal. A dimmer was used to maintain light at the intensity stipulated in the guidelines. In the incubator, culture flasks were suspended by their necks from a series of transparent plastic disks supported in the middle by a central pole. The disks were spaced 18 cm apart. By intermittent turning of the pole (6.5 thrusts per revolution, 3 revolutions per minute), sedimentation of the cells and/or test substance was prevented, and exposure of individual flasks to light was made more uniform.

Reference substance (positive control):

yes

Remarks:

reagent grade K2Cr2o7 tested at concentrations of 0.1, 0.18, 0.32, 0.56, 1 and 1.8 mg/L.

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

< 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

< 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Details on results:

As compared to control, an inhibition of growth rate of 3.8% after 72 h of exposure to the test item was reported, indicating a statistically significant (p < 0.05) reduction in growth rate for the treated algae. Thus, the NOEC was below 100 mg/L.

Results with reference substance (positive control):

The 72 hour ErC50 determined for algal growth rate was 2.34 mg/L for the positive control substance; with respect to biomass, the EbC50 was 1.12 mg/L.

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

Table 1: Validity criteria for OECD 201 (2006)

Criterion from the guideline	Outcome	Validity criterion fulfilled
The biomass in the control cultures should have increased exponentially by a factor of at least 16 within the 72-hour test period.	Factor of 103.9	yes
The mean coefficient of variation for section-by-section specific growth rates (days 0-1, 1-2 and 2-3, for 72-hour tests) in the control cultures must not exceed 35%	26%	yes
The coefficient of variation of average specific growth rates during the whole test period in replicate control cultures must not exceed 7% in tests with Pseudokirchneriella subcapitata and Desmodesmus subspicatus. For other less frequently tested species, the value should not exceed 10%.	0.66%	yes

Validity criteria fulfilled:

yes

Remarks:

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 72-hour ErC50 for Selenastrum capricornutum was > 100 mg/L whereas the NOEC was < 100 mg/L, due to a statistical significant inhibitory effect of the test item on growth rate.

Description of key information

In a key study conducted according to OECD guideline 201, an ErC50 greater than 100 mg/L was derived for Pseudokirchneriella subcapitata after 72h exposure, whereas the NOEC was below 100 mg/L.

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:

100 mg/L

Additional information

In the key study (2000), the green algae Pseudokirchneriella subcapitata was exposed to the test item under static conditions for 72-hours according to the OECD testing guideline 201 (1984). The study was based on a limit test conducted with a nominal concentration of 100 mg/L of test item. Mean measured concentrations ranged from 100 to 102 % of nominal concentration. As compared to control, an inhibition of growth rate of 3.8% after 72 h of exposure to the test item was reported, indicating a statistically significant (p < 0.05) reduction in growth rate for the treated algae. Thus, the NOEC was below 100 mg/L. The ErC50 however was > 100 mg/L.  Similar results were obtained with respect to the biomass.

 

A further study conducted in 1986 according to the OECD guideline 201 is also available, which considered for purpose of support. This study also consisted of a limit test with the algae Scenedesmus subspicatus being exposed to a concentration of 10 mg/L of the test item for up to 96 hours.

After 72 hours, the resulting NOEC was set at 10 mg/L whereas the  ErC50 was > 10 mg/L, indicating no effects on  growth rate. Similar results were obtained with respect to the biomass.