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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:
1998-05-25 to 1998-05-29
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline study without restrictions. The study was conducted according to the appropriate OECD test guideline, and in compliance with GLP.
Qualifier:
according to guideline
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Details on sampling:
- Concentrations: 0 (Control), 625, 2500 and 10000 mg/L

- Sampling method: Samples of the test media were taken at the start and end of the test.

- Sample storage conditions before analysis: not reported.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: The test substance was a poorly soluble complex mixture and therefore the test media were water-accommodated fractions (WAF) prepared by stirring for 23 hours with a vortex depth not exceeding 10% of the liquid depth. The media were then allowed to stand for 1 hour before drawing off the WAFs for testing.

WAFs were prepared at nominal loading rates of 625, 1250, 2500, 5000 and 10000 mg/L. The WAFs were renewed after each successive 24 hour exposure period.

- Controls: Dilution water
Test organisms (species):
Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)
Details on test organisms:
TEST ORGANISM

- Strain: SAG 86.81

- Source (laboratory, culture collection): Laboratory stock culture maintained on a sterile sloped agar tube (OECD-Medium, 0.8% Agar), transferred to new agar tube every 2 months.

- Age of inoculum (at test initiation): ca. 72 hours

- Method of cultivation: Incubation on a shaker in 250 ml Erlenmeyer flasks, seterile, at 25ºC, 100-130 rpm, 10000 lux (Gro-Lux-Aquarstar) continuous illumination.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Hardness:
not reported
Test temperature:
25+/-2.0 ºC
pH:
6.3 – 10.3 (The deviation exceeded the guideline maximum of 1.5 units but this was a consequence of the high levels of algal growth (algal cell density increased by a factor of 116 in 72 hours in the Controls) achieved in the test.
Dissolved oxygen:
not applicable
Salinity:
not applicable
Nominal and measured concentrations:
Nominal loading rates (first series): 75, 150, 300, 625 and 1250 mg/L

Nominal loading rates (second series): 0 (Control), 625, 1250, 2500, 5000 and 10000 mg/L.

Concentrations of total organic carbon were measured in the Control and 625, 2500 and 10000 mg/L WAFs at the start and end of the test. The corresponding measured concentrations were 0.9, 8.5, 16.1 and 34.1 mg/L at the start of the test and 1.6, 7.5, 16.9 and 34.0 mg/L at the end of the test (Table 3). The results indicate that the exposure concentrations were stable over the course of the test.

The test results are reported with reference to nominal loading rates.
Details on test conditions:
TEST SYSTEM

- Test vessel: 250 mL Erlenmeyer flasks.

- Aeration: none

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

- Initial cells density: 10000 cells/mL

- Control end cells density: 1160000 cells/mL

- No. of vessels per concentration (replicates): 3

- No. of vessels per control (replicates): 3

GROWTH MEDIUM

- Standard medium used: yes

TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: OECD 201 prepared in demineralised water

- Culture medium different from test medium: no

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

OTHER TEST CONDITIONS

- Sterile test conditions: yes

- Adjustment of pH: no

- Photoperiod: continuous

- Light intensity and quality: 1000 lux (Gro-Lux Aquastar) continuous

EFFECT PARAMETERS MEASURED: cell densities after 24, 48 and 72 hours

- Determination of cell concentrations: counting chambers (Fuchs-Rosenthal: chamber factor 80000; Neubauer: chamber factor 4000000)

TEST CONCENTRATIONS

- Spacing factor for test concentrations: 2
Reference substance (positive control):
no
Key result
Duration:
72 h
Dose descriptor:
EL50
Effect conc.:
ca. 3 300 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
water-accommodated fraction loading rate
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
EL50
Effect conc.:
ca. 2 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
water-accommodated fraction loading rate
Basis for effect:
biomass
Key result
Duration:
72 h
Dose descriptor:
NOELR
Effect conc.:
ca. 300 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
water-accommodated fraction loading rate
Basis for effect:
other: growth rate and biomass
Details on results:
- Exponential growth in the control (for algal test): yes

- Observation of abnormalities (for algal test): none reported

- Any stimulation of growth found in any treatment: no

- Effect concentrations exceeding solubility of substance in test medium: The tested loading rates exceeded the solubility of the test substance
Reported statistics and error estimates:
The EL50 values were estimated from plots of percentage inhibion of biomass or growth rate against log concentration. The NOELR was estimated directly from the raw data.

Table 1. Test results - first series of test media - 72 hours

Nominal loading rate (mg/L) Mean cell concentration (cells/mL) Average specific growth rate Inhibition of average specific growth rate (%) Area under the growth curve Inhibition of area under the growth curve (%)
 Control  1160000  0.07  -  24652000  -
 625  709333  0.06  10  17020000  31
 1250
 909333  0.06  5.1  21260000  14
 2500  264000  0.05  31  6508000  74
 5000  34833  0.02  74  906000  96
 10000 163000  0.04  41  3508000  86

Table 2. Test results - second series of test media - 72 hours

Nominal loading rate (mg/L) Inhibition of area under the growth curve (%)
 Control  -
 75  0
 150
16
 300 3.4
 625 27
 1250  29

Table 3. Results of TOC analysis of test media

 Time (h)  Control  625 mg/L  2500 mg/L  10000 mg/L
 0  0.9  8.5  16.1  34.1
 72  1.6  7.5  16.9  34.0
Validity criteria fulfilled:
yes
Conclusions:
A 72 h EL50 of circa 3300 mg/L and NOELR of circa 300 mg/L have been determined for the effects of the test substance on growth rate of Scenedesmus subspicatus. A 72 h EL50 of circa 2000 mg/L has been determined for effects on biomass in the same test.

Description of key information

The results for toxicity to algae and aquatic plants are summarised in Table 7.4. A 72h EL50 of approximately 3300 mg/L and NOELR of approximately 300 mg/L have been determined for the effect of DTO on growth rate of Scenedesmus subspicatus. These values are the lowest of those obtained in three reliable tests conducted on different samples of DTO.

DTO is a UVCB substance and compositional information has been used in conjunction with validated QSARs to derive No Observed Effect Concentrations (NOECs) for its constituent blocks. Calculation of long-term PNECs for the aquatic compartment will be based on data for the constituent blocks rather than on data for the whole substance. Further testing for long-term toxicity to aquatic algae will therefore not contribute to the database that is required to complete the assessment of the substance.

Key value for chemical safety assessment

Additional information