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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:
18th September 1989 to 22nd September 1989
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Deviations:
no
GLP compliance:
yes
Analytical monitoring:
no
Details on sampling:
- Concentrations: all concentrations and the controls at test initiation
Vehicle:
yes
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: A primary stock solution of 40 mg/mL was created with serial dilutions to create primary stock solutions of 20, 10, 5 and 2.5 mg/mL.
- Chemical name of vehicle (organic solvent, emulsifier or dispersant): acetone
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Source (laboratory, culture collection): Carolina Biological Supply Company, Burlington, North Carolina
- Age of inoculum (at test initiation): 4 days
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
96 h
Test temperature:
24-26 ºC
pH:
7.1-9.3
Nominal and measured concentrations:
0.25, 0.5, 1.0, 2.0 and 4.0 mg/L (nominal)

0.14, 0.21, 0.38, 1.01 and 1.08 mg/L (Measured)
Details on test conditions:
TEST SYSTEM
- Test vessel: 125 mL flasks
- Initial cells density: 1 x 10E+4/mL
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 3
- No. of vessels per vehicle control (replicates): 3

GROWTH MEDIUM
- Standard medium used: no
- Detailed composition if non-standard medium was used:
CaCl2.2H2O - 36.76 mg/L
MgSO4.7H20 - 36.97 mg/L
NaHCO3 - 12.6 mg/L
K2HPO4 - 8.71 mg/L
NaNO3 - 85.01 mg/L
FeCl3.6H20 - 1.575 mg/L
CuSO4.5H20 - 0.01 mg/L
CoCl2.6H20 - 0.01 mg/L
ZnSO4.7H20 - 0.022 mg/L
MnCl2.4H20 - 0.18 mg/L
NaMoO4.2H20 - 0.006 mg/L
H3BO3 - 1 mg/L
Na2EDTA - 4.36 mg/L

TEST MEDIUM / WATER PARAMETERS
- Conductivity: 250-260 µmhos/cm

OTHER TEST CONDITIONS
- Adjustment of pH: yes to 7.5 ± 0.1 with 0.1 N HCl
- Photoperiod: continuous illumination
- Light intensity and quality: 4000-4500 lux at solution surface

EFFECT PARAMETERS MEASURED (with observation intervals if applicable)
- Other: reduction in average growth rate over 96 hours (based on cell density) relative to the control

TEST CONCENTRATIONS
- Range finding study
- Results used to determine the conditions for the definitive study: yes
Reference substance (positive control):
no
Key result
Remarks on result:
other: EbC50 values could not be calculated
Details on results:
Cell densities increased with time over all replicates. Statistical analysis indicated that there was no significant difference in growth rate between any of the test concentrations and the controls. Therefore, the test material had no adverse effects at the maximum concentration achievable (1.08 mg/L). On that basis, adverse effects on algae are not expected at concentrations at or below the water solubility of the test material. The calculation of an EbC50 was not possible on the basis of the lack of consistent dose-response data.
Reported statistics and error estimates:
The average specific growth rate (µave) for each replicate was calculated as the average of the µ values for all observation intervals. The NOEC was determined from the µave. The µave values from the controls and solvent controls were compared using a t-test; if no significant difference was found between the controls and solvent controls, data from the two groups was pooled. If a significant difference was found, data from the blank controls was discarded.

The NOEC was determined using one-way analysis of variance and Dunnett's Procedure if all treatment groups had the same number of replicates or Bonferroni's Test if treatment groups had unequal number of replicates. Before conducting the analysis of variance, the data were checked for normality using the Chi-square test and for homogeneity of variance using the Hartley test. If the assumptions of normality and homogeneity of variance were not met, the NOEC was determined using the Kruskal-Wallis test rather than the Dunnett's Procedure.

EbC10, EbC50 and EbC90 values were determined by linear regression of response. Four linear regressions were estimated based on (a) untransformed data, (b) untransformed response vs. logarithim-transformed concentration, (c) probit-transformed response and (d) probit-transformed response vs. logarithim-transformed concentration. The regression that best fitted the data was selected on the basis of the highest coefficient of determination. The regression equation was then applied to estimate the EbC values.
Validity criteria fulfilled:
not specified
Conclusions:
Under the conditions of the test, exposure to propargite in a 96 hour static test at 1.08 mg/L did not cause any adverse effects on growth of the Selenastrum capricornutum. On this basis, adverse effects on algae are not expected at concentrations equal to or below the water solubility of propargite. EbC50 values could not be calculated due to the lack of consistent dose-response data.
Executive summary:

The acute toxicity of propargite to freshwater algae was assessed by determining the EbC50 over a 96 hour period. Propargite was added to the test system at nominal concentrations of 0, 0.25, 0.5, 1, 2 and 4 mg/L (respective mean measured concentrations are 0, 0.14, 0.21, 0.38, 1.01 and 1.08 mg/L) with a solvent and non-solvent control also included. Observations on the reduction in average growth rate over 96 hours (based on cell density) relative to the control were made every 24 hours.

Exposure to propargite did not cause any adverse effects on growth. On this basis, adverse effects on algae are not expected at concentrations equal to or below the water solubility of propargite. EbC50 values could not be calculated due to the lack of consistent dose-response data.

Description of key information

No adverse effects on growth; study conducted in accordance with OECD Guideline 201; Giddings, 1990

Key value for chemical safety assessment

Additional information

The acute toxicity of propargite to freshwater algae was assessed by determining the EbC50 over a 96 hour period. Propargite was added to the test system at nominal concentrations of 0, 0.25, 0.5, 1, 2 and 4 mg/L (respective mean measured concentrations are 0, 0.14, 0.21, 0.38, 1.01 and 1.08 mg/L) with a solvent and non-solvent control also included. Observations on the reduction in average growth rate over 96 hours (based on cell density) relative to the control were made every 24 hours.

Exposure to propargite did not cause any adverse effects on growth. On this basis, adverse effects on algae are not expected at concentrations equal to or below the water solubility of propargite. EbC50 values could not be calculated due to the lack of consistent dose-response data.

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