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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:
12 to 16 November 1990
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:
yes
Vehicle:
no
Test organisms (species):
Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
96 h
Key result
Duration:
96 h
Dose descriptor:
EC50
Effect conc.:
1.6 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
biomass
Remarks:
cell densities: reduction in area under the curves
Remarks on result:
other: 95% CL (1.3 to 2.0 mg/L)
Key result
Duration:
96 h
Dose descriptor:
NOEC
Effect conc.:
0.2 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
biomass
Remarks:
cell densities: reduction in area under the curves
Remarks on result:
other: 95% CL 1.3 to 2.0 mg/L
Key result
Duration:
96 h
Dose descriptor:
EC50
Effect conc.:
11.6 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks:
Median effective concentration, growth rate (ErC50)
Remarks on result:
other: 95% CL 95% 6.4 to 18 mg/L
Key result
Duration:
96 h
Dose descriptor:
NOEC
Effect conc.:
0.8 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks:
No observed effect (P=0.05) concentration (NOEC), growth rate
Remarks on result:
other: 95% CL 6.4 to 18 mg/L

Analysis of solutions: Measured concentrations of captan in the test solutions at the start of the test ranged from 86 to 104% of the nominal values and so the results are presented as nominal values. The physical and chemical parameters of the test solutions remained at expected values during the study. The nominal 6.4 and 12.8 mg/L media were fine, white homogenous, but transparent suspensions; the other media were clear and colourless.

Algal densities: The results are summarised in Table 6.1.5-1.

Table 6.1.5-1 Summary of effects of captan on Selenastrum capricornutum following a 96-hour exposure

Captan concentration

(mg/L)1

Mean cell density

after 96 hours

(x104)

Mean area under

growth curve

(0 - 96 hr)

Mean growth rate

(0 - 96 hr)

Control

328

287.2 (100)

1.431 (100)

0.2

312

273.1 (95)

1.419 (99)

0.4

289

252.5* (88)

1.400 (98)

0.8

284

241.5* (84)

1.395 (97)

1.6

201

157.9* (55)

1.308* (91)

3.2

103

75.7* (26)

1.142* (80)

6.4

31.7

25.8* (9)

0.847* (59)

12.8

10.7

7.7* (3)

0.576* (40)

1Nominal concentrations.

* Significantly different from control at P = 0.05.

Figures in parenthesis are % of control values.

Validity criteria fulfilled:
yes
Remarks:
Biomass increase exponentially by a factor of 16 within the 72-hour test period = a specific growth rate of 0.92 day (control group)
Conclusions:
The 96-hour EbC50 of captan to Selenastrum capricornutum was 1.6 mg/L and the NOEC was 0.2 mg/L based on the reduction in area under the curves recorded at 0.4 mg/L. The 96-hour ErC50 was 11 mg/L and the NOEC was 0.8 mg/L based on the reduction in growth rate observed at 1.6 mg/L.
Executive summary:

The toxicity of captan technical (90% w/w) to the green alga Selenastrum capriconutum was determined. The procedures employed were based on the relevant OECD Guideline 201 (1984). The nominal exposure concentrations used in this study were 0.2, 0.4, 0.8, 1.6, 3.2, 6.4 and 12.8 mg per litre together with a dilution water control.The test organism was the unicellular green alga Selenastrum capriconutun Printz, (Strain ATCC 22662) from laboratory cultures maintained under axenic conditions. A culture of the alga in the exponential growth phase was used as inoculum for the test.

The culture was grown in the medium, and under the environmental conditions, described for the test.The algae cell densities of the inoculum and test cultures were determined by electronic particle counting.The area under the growth curve (Days 0 to 4) was calculated for each replicate culture, according to the formula given in OECD 201 (1984). The mean areas under the growth curve and the significant differences identified together with the areas expressed as percentages of that of the control were transformed to probability scale and analysed by linear regression against log concentration, to estimate the median effective concentration (based on biomass curve area, EbC50) and its 95% confidence limits.

 

The results obtained from these statistical analyses were as follows:

No observed effect (P = 0.05) concentration (NOEC) = 0.2 mg/L

Lowest significant effect (P = 0.05) concentration = 0.4 mg/L

Median effective concentration, biomass (EbC50) =1.6 mg/L

95% confidence limits = 1.3 to 2.0 mg/1

These values were based on the nominal concentrations of captan technical. Measured concentrations at the test start confirmed the nominal values.

 

The average (Days 0 to 4) growth rate of each replicate culture was calculated according to the formula as described for the area method. The results obtained from these growth rate analyses expressed on the basis of nominal concentrations were:

No observed effect (P = 0.05) concentration (NOEC) = 0.8 mg/L

Lowest significant effect (P = 0.05) concentration = 1.6 mg/L

'Median effective concentration, growth rate (ErC50) = 11 mg/L

95% confidence limits = 6.4 to 18 mg/L

Because the growth rate at each concentration was relatively constant throughout the test period, it was not considered necessary to analyse growth rates over shorter intervals.

Description of key information

NOEC (biomass, 96h) = 0.2 mg/L, NOEC (growth rate, 96 h) = 0.8 mg/L, EbC50 (biomass), 96 h) = 1.6 mg/L, ErC50 (average specific growth rate, 96 h) = 11 mg/L, the NOEC was 0.8 mg/L for Pseudokirchneriella subcapitata (Selenastrum capriconutun Printz, Strain ATCC 22662), OECD 201 (1984)

Key value for chemical safety assessment

EC50 for freshwater algae:
1.6 mg/L
EC10 or NOEC for freshwater algae:
0.2 mg/L

Additional information

Algae toxicity of captan was determined according to OECD 201 (1984). Based on cell density the NOEC (biomass, 96h) was found at 0.2 mg/L and the EbC50 (biomass), 96 h) at 1.6 mg/L. The growth rate effects were lower and determined to NOEC (growth rate, 96 h) = 0.8 mg/L and ErC50 (average specific growth rate, 96 h) = 11 mg/L.