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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
Study period:
1997-03-04
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
no guideline followed
Principles of method if other than guideline:
A 48-hour static range-finding test was conducted at nominal concentrations of 0.01, 010, 1.0, 10, 100 and 1000 mg/L prior to performing the definitive test. Twenty water fleas were tested at each concentration. After 48 hours of exposure, mortality of water fleas in the range-finding test was five perscent in the control and at 0.10 mg wm/L. Mortality was 60% at 1.0 mg wm/L and 100% at test concentration >= 10 mg wm/L. Based upon these preliminary results, nominal test concentrations of 0.25, 0.50, 1.0, 2.0, 4.0 and 8.0 mg wm/L were selected for the definitive test.

The 48-hour test was initiated on January 28 1997 with the impartial addition of water fleas, by ones and twos, to all test chambers until 5 water fleas were distriuted to each chamber. Four replicates of the control and test treatments were established, resulting in a total of 20 water fleas per treatment. The water fleas were added following the monitoring of the initial water quality parameters. The test chambers were 300-mL glass crystallizing dishes (10-cm diameter x 5-cm height) containing 200 mL of dilution water which provided a water depth of 3.2 cm. All test chambers were covered throughout the exposure period to reduce evaporation. The test chambers were positioned in an environmental chamber under fluorescent lighting regulated to a photoperiod of 16 hours light and 8 hours darkness. The light intensity ranged between 16.7 to 30.8 microEinsteins per square meter per second.

Survival of daphnids was monitored daily and any dead or immobilized animals removed. Any abnormalities in the behavior or physical appearance of daphnids were also noted. Daphnids were not fed during the test, nor were test solutions aerated.

At test initiation, water quality measurements (i.e. temperature, dissolved oxygen and pH) were measured in the control and test solution composites prior to distribution into each replicate. Test water temperature was monitored in one control replicate on day 1 and one replicate from each control and treatment on day 2 of the test. The diurnal range of the environmental chamber temperature was continuously monitored using a minimum/maximum thermometer and recorded daily. At test termination, dissolved oxygen concentrations and pH were measured in all control and test solution replicates. Specific conductivity, total alkalinity, and total hardness of the dilution water were measured at test initiation.
GLP compliance:
yes
Specific details on test material used for the study:
Lot: 96-1
Purity: 80%
Analytical monitoring:
no
Details on sampling:
No water samples were collected or analyzed during the test. Nominal concentrations were used during both the range-finding and definitive tests.
Vehicle:
no
Details on test solutions:
A primary stock (1005 mg wm/L) was prepared by adding 0.2513 g of neat test substance to a 250-mL volumetric flask and bringing it to volume with laboratory freshwater. Composite test solutions were prepared by adding appropriate amounts of the stock solution to 1L volumes of dilution water. A dilution water control was maintained concurrently with the test solutions.
Test organisms (species):
Ceriodaphnia dubia
Details on test organisms:
Cerodaphnia dubia used for testing were obtained from Toxikon Environmental Sciences' cultures which originated from animals received from Sachs Systems Aquaculture, St. Augustine, Florida in November 1996. A subculture of adults was isolated from these cultures and maintained prior to testing. The cultures were fed the green algae, Selenastrum capricornutum, and a solution (YCT) prepared from yeast, cereal leaves (Cerophyll) and trout chow daily.
Less than 24 hours prior to test initiation, the adults were re-isolated in dilution water. Neonates (< 24 hours old) were collected for test initiation in January 1997. Ceriodaphnia dubia were cultured and isolated in moderately hard freshwater. No ephippia were produced during culture and organisms appeared in good physical condition at test initiation.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
48 h
Hardness:
78 mg/L as CaCO3
Test temperature:
19.4 - 20.3 °C
pH:
6.9 - 7.0 (initiation)
7.2 - 7.3 (termination)
Dissolved oxygen:
8.6 - 9.0 mg/L (92-98% saturation)
Conductivity:
442 µmhos/cm
Nominal and measured concentrations:
Nominal: 0.25, 0.50, 1.0, 2.0, 4.0 and 8.0 mg wm/L
Key result
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
1.5 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Conclusions:
Mortality of water fleas exposed for 48 hours to the test substance ranged from 0% at 0.5 and 1.0 mg/L to 100% at 8.0 mg wm/L. Mortality was 0% in the control. The 48-hour EC50 was 1.5 mg wm/L with 95% CL of 1.0 and 2.0 mg wm/L. The NOEC was 1.0 mg/L based on the lack of significant mortality and sublethal effects at this and lower test concentrations.
Executive summary:

In this study, the acute toxicity of the substance to daphnids was investigated. A final test was performed based on the results of a preceding combined limit/range-finding test. Twenty daphnids per group (four replicates, five daphnids per replicate) were exposed to an untreated control and to nominal concentrations of 0.25, 0.50, 1.0, 2.0, 4.0 and 8.0 mg wm/L. The total exposure period was 48 hours and under the conditions of the present study, the 48h-EC50 was 1.5 mg/L based on nominal concentrations (95% confidence interval between 1.0 and 2.0 mg/L).

Description of key information

A 48h-EC50 of 1.5 mg/L was determined for the substance, based on nominal concentrations.

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
1.5 mg/L

Additional information

In this study, the acute toxicity of the substance to daphnids was investigated. A final test was performed based on the results of a preceding combined limit/range-finding test. Twenty daphnids per group (four replicates, five daphnids per replicate) were exposed to an untreated control and to nominal concentrations of 0.25, 0.50, 1.0, 2.0, 4.0 and 8.0 mg wm/L. The total exposure period was 48 hours andunder the conditions of the present study, the 48h-EC50 was 1.5 mg/L based on nominal concentrations (95% confidence interval between 1.0 and 2.0 mg/L).