Registration Dossier

Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

Administrative data

Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Well conducted Guideline study conducted under GLP.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2005
Report Date:
2005

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Deviations:
no
GLP compliance:
yes

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Type:
Constituent
Type:
Constituent
Details on test material:
-Test substance (name as cited in study report): Eastman TXIB
-Source of test material: Eastman Chemical Company
-Purity: >98%
-Production date: 4/26/07
-Date of receipt: 7/26/07
-Stability: 1 year
-Storage: Room temperature and humidity
-Description: Clear liquid
-Specific gravity: 0.92

Sampling and analysis

Analytical monitoring:
yes
Details on sampling:
- Concentrations: 5.92, 8.89, 13.3 20, 30 mg/L nominal
- Sampling method: Samples analyzed at 0, 24, 48, and 72 hours. At time 0 aliquots of nominal exposure solutions were analyzed along with a media control solution. At 24, 48 and 72 hours 3 separate aliquots of each test exposure solution were analyzed along with single aliquots of the light and dark 30 mg/L control solutions. At72 hours three media control solutions were also analyzed.

Test solutions

Vehicle:
no

Test organisms

Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Source (laboratory, culture collection): Lab cultures originating from American Type Culture Collection, Rockville, MD
- Age of inoculum (at test initiation): 3-day culture (passage 5)
- Method of cultivation: liquid algal medium


ACCLIMATION
- Acclimation period: Several previous passages were performed in order to confirm expotential growth under the conditions of the test.
- Culturing media and conditions (same as test or not): same
- Any deformed or abnormal cells observed: none reported

Study design

Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h

Test conditions

Test temperature:
23.8 +or- 0.58 (+ or - SD)
pH:
Conc. Initial Final
30 7.466 7.887
20 7.466 7.939
13.3 7.470 7.950
8.89 7.468 7.942
5.92 7.476 7.963
medium control 7.480 7.981
Nominal and measured concentrations:
Nominal Measured (geometric mean)
5.92 1.57
8.89 1.76
13.3 2.25
20 3.56
30 7.49
Details on test conditions:
TEST SYSTEM
- Test vessel:
- Type (delete if not applicable): open (with foam stoppers)
- Material, size, headspace, fill volume: 250 mL glass Erlenmeyer flasks, ~100 mL of algal growth medium
- Initial cells density: 1e4 cells/mL
- Control end cells density: 1.15e6 cells/mL
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 2



GROWTH MEDIUM
- Standard medium used: yes



TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: distilled or deionized water free of toxic substances
- Intervals of water quality measurement: intial and final test solutions


OTHER TEST CONDITIONS
- Sterile test conditions: yes
- Adjustment of pH: none
- Photoperiod: continuous light
- Light intensity and quality: mean illumination of 742.3 + or - 0.96 foot-candles maintained



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



TEST CONCENTRATIONS
- Spacing factor for test concentrations: 0.66x

Results and discussion

Effect concentrationsopen allclose all
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 7.49 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 7.49 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
biomass
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
3.56 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks:
(see conclusions and attachment)
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
2.25 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
biomass
Details on results:
- Exponential growth in the control (for algal test): yes
- Observation of abnormalities (for algal test): none
- Any stimulation of growth found in any treatment: none
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: Known to absorb to algae and glassware
- Effect concentrations exceeding solubility of substance in test medium: yes
Reported statistics and error estimates:
EC50 calculations were conducted emperically as there was not a 50% reduction in the growth rate or biomass in any test concentration. The NOEC was calculated using MINITAB statistical software. Data were examined using tests for equal variances, ANOVA, and t-tests.

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Conclusions:
Study was conducted on a difficult substance known to absorb to algal cells and glassware. With this known, an effort to attain a mean measured concnetration at the determined water solubility of the test substance in algal medium was made by utilizing a number of concentrations that exceeded the water solubility of the test substance. Glassware was also briefly conditioned. Despite these measures, absorbtion to glassware and algal cells, and losses due to centrifugation of un-dissolved material, the geometric means of the measured test solutions were significantly lower than the nominal concentrations. Losses from flasks containing algae ranged from 75.7% to 93.4%. Losses from the chemical control flask without algae were 76.9% in the light exposed controls and 95.9% in the light shielded controls. The geometric mean of the highest test concentration (7.49 mg/L) did not achieve the estimated water solubility of the test substance in algal medium (8.7 mg/L). However, at this highest test concentration there was not a 50% reduction in either growth rate or biomass production. Growth rate inhibition in the highest concentration was only reduced by a mean of 14.9%. This result supports a conclusion that the EC50 is greater than the water solubility of the test substance. The report also indicated that the NOEC was the mean measured concentration of 2.25 mg/L. The study indicated that this was calculated by ANOVA and t-tests. The most recent version of the 201 guidline indicates that the statistical analyses for the NOEC should be ANOVA with an appropriate multiple comparison test. The data was re-analyzed using appropriate tests for data normality and homogeneity (passed both) followed by ANOVA and a parametric multiple comparison test (Dunnett's and Williams). The results of this re-analyses shows that the NOEC for growth rate is different than that reported in the study. The re-analyses of the data indicates that the NOEC should be the mean measured 3.56 mg/L level coresponding to the 20 mg/L nominal concentration (statistical analyses attached). In addition, the two highest mean measured concentrations, 7.49 and 3.56 mg/L, exhibited only 14.9% and 5% inhibition respectively. The 201 guideline indicates that there is a recomendation of abandoning the concept of NOEC and replacing it with a regression based point estimate EC value. The appropriate EC value has not been established for the algal study but a range of 10 to 20% appears to be appropriate. In this study the highest concentration (30 mg/L nominal, 7.49 mg/L mean measured) resulted in ~14.9% inhibition of growth rate which approximates an EC15. While there was difficulty in accurately measuring exposure concentrations due to the test material sorbing to algal cells and glassware, and conducting the test with 4 of the 5 initial exposure levels at or above the solubility of the material, the data tends to support a conclusion that there are no adverse effects at or near the water solubility of the substance.