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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Reference
Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
key study
Study period:
from 20 April to 20 July 2012
Reliability:
1 (reliable without restriction)
Qualifier:
according to
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Deviations:
yes
Remarks:
EC medium used instead of OECD medium. EC medium can be considered as a modified OECD medium and EC medium is compliant with the elemental composition of the OECD medium. It was considered that this deviation did not impact the validity of the study.
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
yes
Details on sampling:
Sampling at T = 0 h (fresh media) and at T = 72 hours (old media)
Details on test solutions:
Due to the complex and insoluble nature of the test substance (UVCB), a Water Accommodated Fraction (WAF) approach was considered to be the most suitable method of test media preparation.
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Strain: 278/4
- Source (laboratory, culture collection): Culture Collection of Algae and Protozoa (CCAP), Oban, UK
- Method of cultivation: EC cultivation medium (nutrients salts in reconstituted water)

ACCLIMATION
- Acclimation period: pre-culture prepared for at least 72 hours before initiation
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Test temperature:
22.4 - 22.8°C
pH:
7.86 - 7.88 (start) ; 8.00 - 10.1 (end)
Dissolved oxygen:
not specified
Details on test conditions:
TEST SYSTEM
- Initial cells density: 1*10^4 cells/mL
- No. of vessels per concentration (replicates): 4
- No. of vessels per control (replicates): 7

GROWTH MEDIUM
- Standard medium used: EC cultivation medium

OTHER TEST CONDITIONS
- Photoperiod: permanent illumination
- Light intensity and quality: 4440 - 8880 lux

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: particle counter

TEST CONCENTRATIONS
- Test concentrations: nominal loading rates of 0, 0.22, 0.46, 1.0, 2.2, 4.6 and 10 mg/L (Water accomodated fraction).
Duration:
72 h
Dose descriptor:
EL50
Effect conc.:
1.3 mg/L
Nominal / measured:
nominal
Conc. based on:
other: WAF
Basis for effect:
other: yield
Duration:
72 h
Dose descriptor:
EL50
Effect conc.:
1.3 mg/L
Nominal / measured:
nominal
Conc. based on:
other: WAF
Basis for effect:
biomass
Duration:
72 h
Dose descriptor:
EL50
Effect conc.:
1.7 mg/L
Nominal / measured:
nominal
Conc. based on:
other: WAF
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EL20
Effect conc.:
0.87 mg/L
Nominal / measured:
nominal
Conc. based on:
other: WAF
Basis for effect:
other: yield
Duration:
72 h
Dose descriptor:
EL20
Effect conc.:
0.82 mg/L
Nominal / measured:
nominal
Conc. based on:
other: WAF
Basis for effect:
biomass
Duration:
72 h
Dose descriptor:
EL20
Effect conc.:
1.2 mg/L
Nominal / measured:
nominal
Conc. based on:
other: WAF
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
NOELR
Effect conc.:
0.46 mg/L
Nominal / measured:
nominal
Conc. based on:
other: WAF
Basis for effect:
other: yield
Duration:
72 h
Dose descriptor:
NOELR
Effect conc.:
0.46 mg/L
Nominal / measured:
nominal
Conc. based on:
other: WAF
Basis for effect:
biomass
Duration:
72 h
Dose descriptor:
NOELR
Effect conc.:
1 mg/L
Nominal / measured:
nominal
Conc. based on:
other: WAF
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
1.1 mg/L
Nominal / measured:
estimated
Conc. based on:
test mat.
Basis for effect:
other: yield
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
1 mg/L
Nominal / measured:
estimated
Conc. based on:
test mat.
Basis for effect:
biomass
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
1.4 mg/L
Nominal / measured:
estimated
Conc. based on:
test mat.
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.66 mg/L
Nominal / measured:
estimated
Conc. based on:
test mat.
Basis for effect:
growth rate
Details on results:
Measured TOC concentrations above the limit of quantification (LOQ), considered to be 0.5 ppm, were not determined for the 0.22, 0.46 and 1.0 mg/L loading rate WAFs. Based on the results of the TOC analysis of the 2.2, 4.6 and 10 mg/L loading rate WAFs, the estimated exposure concentrations of CAE were 2.0, 4.0 and 9.0 mg/L, respectively. Given that TOC analysis is not compound specific, these values are only an estimation of test substance concentration, therefore the results were based on both nominal loading rates and estimated CAE concentrations.
Reported statistics and error estimates:
The area under the growth curve, the average specific growth rate and the final yield over specified time intervals were analysed using the Bonferroni adjusted t-test.

Table 1     Inhibition of growth of P. subcapitata exposed to WAFs of CAE during 72 hours

Nominal loading rate (mg/L)

0-72 h reduction (%) in

Yield

Growth (biomass)

Growth rate

0

-

-

-

0.22

-6.82

-4.72

-1.44

0.46

-7.37

-3.53

-1.54

1.0

21.9

26.6

4.94

2.2

98.7

96.7

79.3

4.6

99.3

98.4

86.0

10

99.5

98.7

90.4

- not applicable

Negative percentage inhibition values relative to the common control represent an increase in growth relative to the control.

Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of the test, CAE was considered to inhibit the growth of Pseudokirchneriella subcapitata at loading rate > 0.46 mg/L (lowest NOELR determined as the highest loading rate below the ExL20). The 72 hour EyL50, EbL50 and ErL50 values were calculated to be 1.3, 1.3 and 1.7 mg/L, respectively. The corresponding estimated CAE concentrations values were 1.1, 1.0 and 1.4 mg/L, respectively.
Executive summary:

In a static toxicity test performed according to OECD guideline No.201, the alga Pseudokirchneriella subcapitatawas exposed for 72 hours to nominalloading rates ranging between 0.22 and 10 mg CAE/L in EC water. A control group was also included. The initial cell concentration was approximately 1 * 104cells/mL. Due to the complex and insoluble nature of the test substance (UVCB), a Water Accommodated Fraction (WAF) approach was considered to be the most suitable method of test media preparation.

Samples of test media were analysed for Total Organic Carbon (TOC), as a measure of the dissolved test substance concentration in fresh and old test media. Given that TOC analysis is not compound specific, the results represent only an estimation of test substance concentration. Therefore the endpoints were based on both nominal loading rates and estimated CAE concentrations.

Based on nominal loading rates, the 72 hours EyL50, EbL50and ErL50values were calculated to be 1.3, 1.3 and 1.7 mg/L, respectively. The corresponding NOELR values after 72 hours, determined asthe highest loading rate below the ExL20,were0.46, 0.46 and 1.0 mg/L, respectively.

Based on estimated CAE concentrations, the 72 hours EyC50, EbC50and ErC50values were calculated to be 1.1, 1.0 and 1.4 mg/L, respectively.

The NOEC values for yield and biomass after 72 hours exposure could not be determined given that measured TOC concentrations above the LOQ were not observed. The NOEC value for specific growth rate after 72 hours was equal to 0.66 mg/L.

Description of key information

The 72 hour EyL50, EbL50 and ErL50 values were calculated to be 1.3, 1.3 and 1.7 mg/L, respectively. The corresponding estimated CAE concentrations values were 1.1, 1.0 and 1.4 mg/L, respectively.

Key value for chemical safety assessment

EC50 for freshwater algae:
1.3 mg/L

Additional information