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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:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)
Deviations:
no
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
Samples of the test and control solutions were collected for chemical analysis in 50-mL polypropylene centrifuge tubes at test initiation and termination.
Details on test solutions:
Test solutions were prepared from a stock solution containing 10 mg of the test substance in 1 L dilution water. The stock solution was serially diluted with laboratory dilution water to obtain the remaining test concentrations (5.0, 2.5, 1.3, 0.6, 0.3, and 0.2 mg/L; nominal concentrations). The control was laboratory dilution water. Four 50-mL volumes of each test solution were dispensed to replicate test vessels (100-mL glass beakers) and an additional 50 mL was archived for chemical analysis.
Test organisms (species):
Daphnia magna
Details on test organisms:
The test organism was Daphnia magna. The test was initiated with young daphnids less than 24 hours old from in-house cultures. The culture vessels were incubated in a temperature-controlled room at 20 ± 1 °C, under a photoperiod of 8 hours of darkness and 16 hours of light. Light intensity at the water surface was 410 to 460 lux provided by cool white florescent lights. Stock cultures were fed a 50:50 (volume to volume) mixture of a green alga and a solution of yeast, alfalfa powder, and fermented trout chow three times weekly. Culture vessels were cleaned on Monday and Friday and the culture turned over on Wednesday. On these days the number of adults and young were counted and recorded for each jar. Young for testing were collected from 3- to 4-week-old adults. Mortality in the stock culture was 2.5 % in the week prior to test initiation.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
48 h
Hardness:
Dilution water was dechlorinated City of Calgary tap water (charcoal filtered and aerated). The dilution water had a hardness of 196 mg CaCO3/L.
Test temperature:
20 ± 1 °C
pH:
The pH was 8.1 to 8.2 at initiation and 8.2 to 8.3 at termination.
Dissolved oxygen:
The concentration of dissolved oxygen was between 7.7 and 8.2 mg/L (95 to 100 % saturation at the test temperature corrected for altitude).
Nominal and measured concentrations:
- Nominal concentrations: 0.2, 0.3, 0.6, 1.3, 2.5, 5.0 and 10 mg/L
- Measured concentrations: <0.2, 0.3, 0.6, 1.1, 2.2, 4.5 and 9.2 mg/L
Details on test conditions:
TEST MEDIUM / WATER PARAMETERS
- Water quality measurement: The pH was measured with an Oakton pH meter equipped with a combination glass electrode with temperature compensation. Dissolved oxygen was measured with a YSI 9501 probe equipped with temperature compensation connected to a Model 95 Dissolved Oxygen meter. Temperature was measured with the probe connected to the dissolved oxygen meter. All instruments were calibrated daily against appropriate standards.

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
The test vessels were examined at 24 and 48 hours, and the number of immobilised organisms recorded along with any observations of unusual behaviour.
Duration:
24 h
Dose descriptor:
EC50
Effect conc.:
1.6 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
mobility
Remarks on result:
other: 1.4 to 1.8 mg/L
Key result
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
0.9 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
mobility
Remarks on result:
other: 0.8 to 1.2 mg/L
Duration:
24 h
Dose descriptor:
NOEC
Effect conc.:
1.1 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
mobility
Key result
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
0.6 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
mobility
Details on results:
At test initiation, dissolved oxygen, temperature, and pH ranged from 7.7 to 8.2 mg/L, 19.0 to 20.0 °C, and 8.1 to 8.2 units, respectively. At test termination, dissolved oxygen and temperature were 7.9 mg/L and 20 °C in all test solutions, respectively. The pH ranged from 8.2 to 8.3.

Dead organisms were considered immobilised. The organisms in the two highest test concentrations (4.5 and 9.2 mg/L) were confirmed dead at 24 hours. Ninety percent of the organisms in the next lowest concentration (2.2 mg/L) were alive but immobile at 24 hours. There was an immobile daphnid in one replicate of the 1.1 mg/L concentration. The daphnids in the other replicates of this and the lower test concentrations and controls were all mobile. At test termination (48 hours), the daphnids in the 2.2 mg/L test concentration were immobile. Seventy percent of the daphnids in the 1.1 mg/L concentration were immobile. The daphnids in the lower test concentrations (<0.2, 0.3, and 0.6 mg/L) and controls were mobile.
The concentrations (and 95 % confidence limits) that immobilised 50 % of the daphnids at 24 and 48 hours were 1.6 mg/L (1.4 to 1.8 mg/L) and 0.9 mg/L (0.8 to 1.2 mg/L), respectively.
The highest concentrations that produced no significant immobility relative to controls at 24 and 48 hours were 1.1 and 0.6 mg/L, respectively (NOEC).
The lowest concentrations that produced significant immobility relative to controls at 24 and 48 hours were 2.2 mg/L and 1.1 mg/L, respectively (LOEC). The lowest concentrations that produced 100 % immobility at 24 and 48 hours were 4.5 mg/L and 2.2 mg/L, respectively. The highest concentration that produced no immobility at 24 and 48 hours was 0.6 mg/L.

At test initiation, the difference between measured and nominal concentrations ranged from 5.0 to 23.1 % (average of 11.5 %; standard deviation 8.2 %). The difference in the values at test termination ranged from 8.0 to 16.0 % (average of 8.6 %; standard deviation of 7.2 %). Differences between measured concentrations at test initiation and termination ranged from 4.5 to 10.0 % in five of the seven treatments. The concentration of p-Cumylphenol in the sample at test initiation for the lowest treatment (0.2 mg/L) was less than the detection limit. The difference between the measured concentrations at test initiation and termination in the 0.6 mg/L treatment was 20.0 %. The average difference for all treatments was 6.9 % (standard deviation was 8.6 %). The difference between measured concentrations at test initiation and termination was consistent and, on average, below 20 %. Measured concentrations less than the nominal concentrations were expected because no corrections were made for purity. The toxicity values were derived from an average of the measured concentrations for each treatment at test initiation and termination. The mean measured concentrations were <0.2, 0.3, 0.6, 1.1, 2.2, 4.5 and 9.2 mg/L.

Table 1: Average Number of Daphnia Immobilised After a 24- or 48-hour Exposure to p-Cumylphenol

Nominal p-Cumylphenol Concentration (mg/L)

Measured p-Cumylphenol Concentration (mg/L)

Average Immobilisation (%)

24 h

48 h

Control

Control

0

0

0.2

Less than 0.2

0

0

0.3

0.3

0

0

0.6

0.6

0

0

1.3

1.1

5

70

2.5

2.2

90

100

5.0

4.5

100

100

10

9.2

100

100

Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of this study, the 48 hour EC50 concentration (and 95% confidence limits) was 0.9 mg/L (0.8 to 1.2 mg/L) and the NOEC was 0.6 mg/L.
Executive summary:

An acute immobilisation test was conducted with Daphnia magna according to OECD Guideline 202.

Daphnia were exposed to concentrations of p-Cumylphenol ranging from <0.2 to 9.2 mg/L for 48 hours under static conditions with a 16/8 light/dark cycle.

Under the conditions of this study, the EC50 concentrations at 24 and 48 hours were 1.6 and 0.9 mg/L, respectively. The NOECs at 24 and 48 hours were 1.1 and 0.6 mg/L, respectively. The LOECs at 24 and 48 hours were 2.2 and 1.1 mg/L, respectively.

Description of key information

The 48 hour EC50 of p-cumylphenol to Daphnia magna was 0.9 mg/L.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Effect concentration:
0.9 mg/L

Additional information