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Sediment toxicity

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Reference
Endpoint:
sediment toxicity: long-term
Type of information:
experimental study
Adequacy of study:
key study
Study period:
chronic, 28 days
Reliability:
1 (reliable without restriction)
Qualifier:
according to guideline
Guideline:
other: OECD Guideline for testing of chemicals, Proposal for Toxicity Test with Chironomidae
Version / remarks:
1997
Deviations:
no
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
Samples of 30 mL of the aqueous test solution were taken from the centre of all test vessels and the control at day 0, 1, 7 14 and the end of exposure. At the beginning, after 7 days and at the end of the study, the concentration of test substance in the sediment was measured in the test vessels with dose levels of 4.0 and 8.0 mg/L.
Vehicle:
no
Details on sediment and application:
Artificial sediment was prepared according to the guideline recommendation, containing:
- 5.5% sphagnum peat
- 20% kaolin clay
- 74.5% industrial sand (find sand with more than 50% of the particles between 50 and 200 µm)
- pH was adjusted to 6.3 by adding pure calcium carbonate
- the content of organic carbon was determined to be ca. 2.5%

The sediment layer in each test vessel was about 2 cm thick.
Test organisms (species):
Chironomus riparius
Details on test organisms:
Larvae are reared in crystallising dishes spread at the bottom with a thin layer of Kieselgur of about 1-2 cm depth and covered with M4 medium to a height of about 6 cm. The vessels are kept in a suitable cage to prevent escape of emerging adults. Culturing is performed at a constant temperature of 20 ± 2 °C, a photo-period of 16 hours light and 8 hours darkness (transition period of 30 minutes) and relative air humidity of >70%. Gentle aeration is provided throughout the culturing period. Larvae are fed with a fish flake food (dry ground powder of TETRAMIN). Some green algae (Scenedesmus subspicatus) are added when new culture vessels are set up and sometimes throughout the culturing. Once adults are present in the breeding cage, all larvae rearing vessels are checked three times a week for deposition of the gelatinous egg masses, which are removed carefully if present. The eggs are transferred to new culturing dishes and cultured as described previously. The first instar larvae hatching from these eggs are transferred to test beakers when they are two to three days old. During the study the larvae are fed with commercial fish food (TETRAMINS) at about 1 mg food/day.
Study type:
laboratory study
Test type:
static
Water media type:
freshwater
Type of sediment:
artificial sediment
Limit test:
no
Duration:
28 d
Exposure phase:
total exposure duration
Hardness:
264 mg CaCO3/L
Test temperature:
20 - 22 °C
pH:
7.3 to 7.5 after application, 7.7 to 9.5 at test termination
Dissolved oxygen:
61 to 91% after application, 34 to 118% at test termination (the low oxygen content in one control vessel had no influence on the quality of the test, because all larvae had emerged after 16 days).
Conductivity:
723 µS/cm
Nominal and measured concentrations:
Nominal test concentrations in the water phase were 0.5, 1.0, 2.0, 4.0 and 8.0 mg/L (based on results of range finding test indicating that the NOEC will be higher than 10 mg/L)
Measured concentration at day 0 (1 to 3 hours after application) were 0.11, 0.18, 0.32, 0.82 and 1.9 mg/L. After 28 days all concentrations were less than the limit of detection of 0.006 mg/L in all test vessels.
The measured concentrations of the metabolite at day 0 were <0.009, <0.009, <0.009, 0.086 and 0.59 mg/L. The measured concentrations of the metabolite after 28 days were 0.094, 0.108, 0.281, 0.558 and 1.377 mg/L.
The concentration of cloquintocet-mexyl and its metabolite in sediment were measured for the two highest test concentrations in water of 4.0 and 8.0 mg/L. The following concentrations were determined (including interstitial water):
For test concentration 8.0 mg/L after 0, 7 and 28 days: 20.3, 14.3 and 27.1 mg/kg sediment (ww)
For test concentration 4.0 mg/L after 0, 7 and 28 days: 8.7, 18.5 and 8.9 mg/kg sediment (ww)
Details on test conditions:
TEST SYSTEM
Glass beakers (1L, tall form, 9 cm diameter) were filled with a layer of 1-2 cm of artificial sediment (corresponding to 110 g sediment (dw)). Sediment was overlaid with reconstituted wate (M4 medium according to guidance) of a height of approximately 8 cm (540 g water). The water level was marked outside on the test beaker. The vessel was then covered with parafilm with small holes to reduce evaporation throughout the test and to allow for the collection of emerged midges. Gentle aeration was provided through a glass Pasteur pipette situated about 2-3 cm above the sediment. Test beakers were prepared seven days before the start of the definitive experiment.

EXPOSURE REGIME
One day before treatment, 20 larvae of the first larval stage were allocated randomly to each test vessel with a blunt pipette. After addition of the larvae aeration was stopped for the following 25 hours. Substance was added to the test vessels by adding appropriate amounts of stock solution to the water column of the vessels below the water surface using a pipette and gently mixing the upper water layer.
For each concentration and for the control three replicates were carried out. The test system was kept in a temperature controlled room at about 20 °C, a relative air humidity of >70% under a light:darkness rhythm of 16 hours to 8 hours and a light intensity of 800 to 1000 Lux.
Reference substance (positive control):
no
Duration:
28 d
Dose descriptor:
NOEC
Effect conc.:
8 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Basis for effect:
emergence rate
Remarks:
of adult midges
Remarks on result:
other: cloquintocet-mexyl applied to water column
Duration:
28 d
Dose descriptor:
NOEC
Effect conc.:
8 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Basis for effect:
development rate
Remarks:
of larvae
Remarks on result:
other: cloquintocet-mexyl applied to water column
Duration:
28 d
Dose descriptor:
EC50
Effect conc.:
> 8 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Basis for effect:
emergence rate
Remarks:
of adult midges
Remarks on result:
other: cloquintocet-mexyl applied to water column
Duration:
28 d
Dose descriptor:
EC50
Effect conc.:
> 8 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Basis for effect:
development rate
Remarks:
of larvae
Remarks on result:
other: cloquintocet-mexyl applied to water column
Validity criteria fulfilled:
yes
Conclusions:
The 28-day NOEC for the development of the sediment-dwelling larval stages and the emergence of winged adults of Chironomus riparius exosed to cloquintocet-mexyl via the water column was 8.0 mg/L (nominal), the highest concentration tested.
Executive summary:

The toxicity of cloquintocet-mexyl and its main environmental metabolite was studied to a proposed OECD test guideline (1987) under GLP. The tests were carried out in glass beakers filled with a layer of 1-2 cm artificial sediment, overlaid by reconstituted water (M4-medium) at a height of circa 8 cm. Sediment-dwelling larvae of the midge Chironimus riparius were exposed for 28 days to cloquintocet-mexyl applied to the overlying water at nominal concentrations raning from 0.5 to 8.0 mg/L. There were no significant effects of exposure, relative to the untreated control, on the timing of the hatch of winged adults or on the emergence of male and female midges. The 28-day NOEC was considered to be 8.0 mg/L, the highest concentration tested.

Combined measurements of the concentration of the test substance and metabolite in sediment in this study were also taken at day 0, 7 and 28. The measured concentration in sediment at the start of the experiment (i.e. 1 to 3 hours after application) was 20.3 mg/kg wwt. After 28 days the measured concentration of cloquintocet-mexyl and its metabolite in sediment was 27.1 mg/kg wwt. Therefore, a 28-day sediment NOEC of 20.3 mg/kg wwt is proposed.

Description of key information

28-day NOEC = 8.0 mg/L (nominal, water phase), NOEC = 93.4 mg/kg dwt (sediment), Chironomus riparius (OECD TG 219, Grade 1998)

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater sediment:
93.4 mg/kg sediment dw

Additional information

Grade (1998) investigated the toxicity of cloquintocet-mexyl to the sediment-dwelling larvae of the midge Chironomus riparius in a GLP compliant 28-day study performed according to OECD Guideline 219 (Sediment-Water Chironomid Toxicity Test Using Spiked Water). The study is considered to be reliable without restrictions. There were no significant effects of exposure, relative to the untreated control, on the timing of the hatch of winged adults or on the emergence of male and female midges. The 28-day NOEC was therefore 8.0 mg/L, the highest concentration tested.

Combined measurements of the concentration of the test substance cloquintocet-mexyl and its metabolite [(5-chloro-8-quinolinyl)-oxy]-acetic acid in sediment in this study were also taken at day 0, 7 and 28. At day 0, where minimal metabolite is likely to have formed, the measured concentration in sediment was 20.3 mg/kg wwt. After 28 days this value was 27.1 mg/kg wwt. Therefore a sediment NOEC of 20.3 mg/kg wwt is proposed, or 93.4 mg/kg dwt (conversion factor= 4.6, EUSES v2.1.1).