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Short-term toxicity to aquatic invertebrates

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Reference
Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
The study was conducted according to the appropriate OECD test guideline, and in compliance with GLP. However, there was no analysis of exposure concentrations, the solvent concentration was higher than recommended by the OECD guideline and exposure duration was only 24 hours rather than the guideline 48 hours.
Qualifier:
according to
Guideline:
OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)
Deviations:
yes
Remarks:
The concentration of tertiary butyl alcohol (TBA) used in the preparation of the test media (320 μl/l) exceeded the maximum (100 mg/l) recommended in the OECD guideline.
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
no
Vehicle:
yes
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: Stock solutions of the test substance were prepared in tertiary butyl alcohol at concentrations of 100, 180 and 320 g/l. The stock solutions were added to 100 ml of dilution water in amounts required to produce the desired test concentrations. The final concentration of TBA in the media (320 μl/l) exceeded the maximum concentration recommended in the OECD test guideline (100 mg/l).

- Controls: Dilution water and Dilution water+ Tertiary butyl alcohol at 100 μl/l.

- Chemical name of vehicle (organic solvent, emulsifier or dispersant): tertiary butyl alcohol (TBA)

- Concentration of vehicle in test medium (stock solution and final test solution(s) including control(s)): 320 μl/l.
Test organisms (species):
Daphnia magna
Details on test organisms:
TEST ORGANISM

- Source: Laboratory culture in the testing laboratory

- Age at study initiation (mean and range, SD): <24 hours

- Feeding during test: none
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
48 h
Hardness:
215 mg/l as CaCO3
Test temperature:
20 +/-1ºC
pH:
7.8-7.9
Dissolved oxygen:
≥8.4 mg/l
Nominal and measured concentrations:
Nominal concentrations: 0 (Control), 0+320 μl/l TBA (Solvent control), 10, 18, 32, 58 and 100 mg/l.

Test concentrations all contained 320 μl/l TBA
Details on test conditions:
TEST SYSTEM

- Test vessel: Beakers

- Type: open

- Material, size, headspace, fill volume: glass, 150 mL with 100 ml of test medium

- Aeration: none

- Renewal rate of test solution (frequency/flow rate): static

- No. of organisms per vessel: 5

- No. of vessels per concentration (replicates): 4

- No. of vessels per control (replicates): 4

- No. of vessels per vehicle control (replicates): 4

TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: Reconstituted freshwater (DSWL standard water) prepared by adding salts to groundwater from Linschoten, the Netherlands.

- Ca/mg ratio: 1.37 mmol/l Ca3+ : 0.78 mmol/l Mg3+

- Culture medium different from test medium: no

- Intervals of water quality measurement: Start and end of test

OTHER TEST CONDITIONS

- Adjustment of pH: no

- Photoperiod: 16 h light, 8 h dark

EFFECT PARAMETERS MEASURED: mobility after 24 and 48 hours

TEST CONCENTRATIONS

- Spacing factor for test concentrations: 1.8

- Range finding study: yes but results not reported.
Reference substance (positive control):
no
Key result
Duration:
24 h
Dose descriptor:
EC50
Effect conc.:
29 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Remarks on result:
other: 21-39
Duration:
24 h
Dose descriptor:
NOEC
Effect conc.:
10 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Duration:
24 h
Dose descriptor:
EC100
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Reported statistics and error estimates:
The EC50 values and their confidence intervals were calculated using a parametric model (Kooijman, 1981).

Kooijman, S.A.L.M. (1981). Parametric analyses of mortality rates in bioassays. Water Research, 15: 107-119.

Table 1. Test results

 Nominal test substance concentration (mg/l)  Mean percentage immobilisation after 24 hours
 0 (Control)  0
0 (TBA control)   0
 10  0
 18  55
 32  65
 58  55
 100  90
Validity criteria fulfilled:
yes
Conclusions:
A 24-hour EC50 value of 29 mg/l (21-39 mg/L) and NOEC of 10 mg/l have been determined for the effects of the test substance on mobility of Daphnia magna. The results are interpreted with reference to nominal concentrations of the test substance. However the test substance is susceptible to hydrolysis and it is likely that the test organisms were primarily exposed to a mixture of the parent compound and the hydrolysis products of the substance.

Description of key information

24 hr EC50 29 mg/l (nominal)

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
29 mg/L

Additional information

A 24 hour EC50 value of 29 mg/l and NOEC of 10 mg/l (nominal) have been determined for the effects of the registered substance on mobility of Daphnia magna. In view of the test media preparation method and exposure regime it is likely that the test organisms were exposed to a mixture of the parent substance and its hydrolysis products.

The exposure duration during this test was only 24 hours rather than 48 hours as recommended by OECD TG 202. It is therefore possible that the toxicity of the substance could have been underestimated and the EC50 value may have been lower, had the test duration been 48 hours. A test proposal is in place for a long-term toxicity to aquatic invertebrates study OECD TG 211. In this study it is proposed to conduct a Dose Range Finding study, the results of which will be compared with the current short-term aquatic invertebrate toxicity study by TNO (1990).

The test solution was prepared using tert-butyl alcohol (TBA) as a solvent. The recommended solvent concentration (100 mg/l) was exceeded during the test, with TBA at a concentration of approximately 250 mg/l (based on a density of 0.781 g/ml). However, according to the REACH registration dossier for TBA (2-methylpropan-2-ol), the lowest E(L)C50 value is 933 mg/l for invertebrates. It is therefore unlikely that TBA significantly affected the results of the test.

Above a concentration of approximately 100 mg/l, cross-linked condensation products could potentially form over time in the aqueous test media. No evidence of undissolved material (parent substance or precipitated products) has been reported in the study report for this test.