2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole)

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Oct. 2015

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 211 (Daphnia magna Reproduction Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Remarks:

An analytical method, via HPLC, was investigated. Due to the low water solubility (<10 μg/L) of the test substance, the method was not sufficiently sensitive for determining the test substance in test water up to its saturation limit.

Vehicle:

no

Details on test solutions:

The test substance is poorly water soluble; therefore a saturated stock solution was prepared following general guidance provided in OECD 23. The saturated stock solution was prepared by directly adding 10 mg of test substance to 1L of test medium (10 mg/L, loading). The mixture was treated in an ultrasonic bath for 10 minutes then stirred on a magnetic plate for about 2 days to ensure that a saturated test solution was obtained. Undissolved test substance was removed by centrifugation or filtration with a membrane filter (pore width 0.45 μm). The first 50-100 mL of filtered solution was discarded (used to condition the filter). The exposure was started after separation of the undissolved material. The aqueous fraction of the test solution, after separation of the undissolved material, was considered 100% saturated in test media. According to OECD 23, test solutions of poorly soluble substances separated from the remaining undissolved fraction were considered equivalent to the nominal or loading concentration used to prepare them. In order to maintain constant exposure conditions to the soluble fraction of the test substance, fresh test solutions was prepared daily.

Test organisms (species):

Daphnia magna

Details on test organisms:

Test species : Daphnia magna STRAUS
Reason for selection of the test species: Recommended species in the test guidelines.
Origin : The clone of Daphnia magna STRAUS 1820 used was supplied by the Institut National de Recherche Chimique Appliquée, France, in 1978. From this date on this clone was cultured and bred continuously in the Ecotoxicology Laboratory of Experimental Toxicology and Ecology, BASF SE, Ludwigshafen Germany.
Culture conditions: Daphnia brood stock are kept in mass cultures consisting of approx. 20–30 individuals for a maximum of 4 weeks. All individuals in the mass culture originate from a single female. After approximately 14 days the adults have produced at least 3 broods and the young can be used in tests. Offspring are removed from the mass cultures at least once daily during the normal work week to ensure that young daphnia are <24-h old (first instar) at test initiation. Detailed records are kept (in test facility archives) to monitor the health of Daphnia brood stock cultures including observations of young production, mortality, ephippia, and measurement of water chemistry parameters. Only young from healthy cultures without signs of stress are used for testing.
Acclimatization: The Daphnia are cultured under the identical conditions as the test including test media (Elendt M4), water quality, temperature (20 ±1°C), and diet.
Age at test initiation: < 24 h
Reference substance testing: In order to verify that the Daphnia magna culture is responding normally to toxic stress, acute toxicity tests with a reference substance are conducted monthly. Reference substance tests are conducted generally according to the OECD 202 guideline and in accordance with GLP, but without a GLP status. The EC50(48 h) of the reference substance sodium chloride (NaCl) was 4.06 g/L (experiment date: 02 Sep 2015). This result is within the range of 3.88–7.22 g/L, which represents ±2 standard deviations from the published EC50(48 h) of 5.55 g/L and indicates that the culture of Daphnia magna used in this study is responding normally to toxic stress.

Test type:

semi-static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

22 d

Hardness:

2.41 - 2.46 mmol/L total hardness

Test temperature:

20 - 21 deg. C

pH:

7.7 - 8.5

Dissolved oxygen:

6.2 - 9.2 mg/L

Salinity:

n/a

Nominal and measured concentrations:

10 mg/L nominal (loading rate, saturated solution)

Details on test conditions:

Test medium: A synthetic fresh water (Elendt M4) is used as media for culture and test purposes. For the composition of this M4 medium see OECD 211.
Test vessels : Numbered glass beakers (nominal volume 100 mL), covered with glass Petri plates to slow evaporation.
Test volume: 50 mL
Biological loading: 1 animal / test vessel (0.02 animals / mL)
Light intensity / Photo period: 763–810 lux at a wave length of 400–750 nm. The light intensity did not exceed 1000–1500 lux for cool white light (equivalent to 15–20 μE•m-2•s-1 according to the test guideline). 16 hours light : 8 hours darkness
Aeration: None
Test solution renewal: Semi-static, daily renewal
Diet: During the test daphnids were fed daily a diet of live green algae Desmodesmus subspicatus, cultured in a synthetic medium. The algae were separated from their culture medium by centrifugation, resuspended in daphnid's medium (M4) corresponding to concentrations of 110 mg and 145 mg TOC/L (respectively) in the algal concentrates used. The daphnids were fed a defined volume (≤145 μL) of the concentrate to reach the amount of food defined in the table below. The algae were stored in a refrigerator (dark, about 4-8°C) for maximum 21 days
Test groups : 0 (control), 10 mg/L as nominal concentrations (loading concentration) on test substance mass not corrected for purity.
Replicates / test group: 10 replicates (1 parent animal each)
Reason for the selection of the test concentrations : The test concentrations for this study were selected based on the results of an acute Daphnia study. In the acute study, a nominal (loading) concentration of 100 mg/L caused no immobilization after 48 hours). Based on the acute test results, this chronic study is conducted as a limit test at the recommended chronic limit concentration of 10 mg/L.

Reference substance (positive control):

yes

Key result

Duration:

22 d

Dose descriptor:

NOEC

Effect conc.:

>= 10 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat. (total fraction)

Basis for effect:

reproduction

Duration:

22 d

Dose descriptor:

LOEC

Effect conc.:

> 10 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat. (total fraction)

Basis for effect:

reproduction

Conclusions:

No significant mortality or any other additional significant adverse effects or abnormal behavior were observed in any of the test treatments. The data were not sufficient to calculate ECx values for reproduction or mortality. The test substance had no observable chronic effect on Daphnia magna up to its saturation limit in test media and under test conditions. The given water solubility limit of the test substance is <10 μg/L. The concentration of test substance in test media could not be verified analytically. According to guidance in OECD 23, for tests with chemicals that cannot be quantified by analytical methods at the concentrations causing effects, the effect concentration can be expressed based on the nominal concentrations. The results in this study are consistent with all validity criteria and the test is valid according to the guidelines of this study. No deviations from test guidelines or other incidents occurred during the course of the reported test which may have influenced the results.

Description of key information

Based on long-term (chronic) toxicity study data, the product is very likely not harmful to aquatic organisms.

Additional information

The long-term toxicity was assessed in a chronic toxicity study to Daphnia magna according to OECD TG 211 and under consideration of GLP. No effects could be recorded at a test concentration of 10 mg/L. The NOEC was thus determined to be >= 10mg/L.