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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:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
2006
Justification for type of information:
see analogue justification attached to chapter 13
Reason / purpose:
read-across source
Qualifier:
according to
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
- Concentrations: control and 100 mg/L. Samples were taken after 0 and 72 hours.
The concentration oftest substance in the test solution was analyzed at the beginning (0 hr) and at the end (72 hrs) ofthe study. About 15 mL was taken from triplicate flask of each test concentration and pooled. 30 mL sample (10 mL x 3 replicate) was taken from pooled solution and put into 20 mL volume vial. 0.3 mL of nitric acid solution (61%) was added into the samples then the samples were sent to the chemical analysis laboratory at Korea Research Institute of Chemical Technology for analysis of calcium. Samples at 0 hour were not filtered additionally because the undissolved test substance in the test solutions were filtered using 0.45 um membrane filter (advantec, Inc., USA) when the test solutions were prepared. Samples at 72 hours were centrifuged slightly (5000 rpm, 10 min) to remove grown algae and preparation process was same as above.
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: After 100 mg of the test substance (purity: 99.9%) was added in 1,000 mL beaker and dilution water (OECD nutrient medium) was added up to the mark of the beaker to produce the nominal concentration of 100 mg/L. For the control group, only the dilution water was used.
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Strain: Strain No. ATCC 22662; UTEX 1648
- Source: The culture collection of algae, The University of Texas at Austin, USA (UTEX)- Strain No.: UTEX1648

ACCLIMATION
- Culturing media and conditions: An OECD culture medium was diluted to produce the biomass of 1×104 cells/mL and then sub-cultured continuously at intervals of 3 to 4 days. For pre-cultivation, the test algae were inoculated into the OECD culture medium at a biomass of 0.5-1.0×104 cells/mL 2 to 4 days prior to study initiation.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Test temperature:
23.7 ± 0.5 ℃
pH:
Control: 9.06 (0 hour) - 8.36 (72 hours)
0.3 mg/L: 8.83 (0 hours) - 8.39 (72 hours)
1.0 mg/L: 8.84 (0 hours) - 8.37 (72 hours)
3.1 mg/L: 8.87 (0 hours) - 8.35 (72 hours)
9.8 mg/L: 8.89 (0 hours) - 8.30 (72 hours)
31.3 mg/L: 8.79 (0 hours) - 8.32 (72 hours)
100.0 mg/L: 8.57 (0 hours) - 8.44 (72 hours)
Nominal and measured concentrations:
Nominal test substance concentrations: control, 0.3, 1, 3.1, 9.8, 31.3, and 100 mg/L
Measured test concentrations at 0 h: 0.3, 0.4, 0.3, 0.8, 1.7, and 4.4 mg/L
Measured test concentrations at 72 h: n.d., n.d., n.d., 0.3, 1.6, and 4.7 mg/L.
Details on test conditions:
TEST SYSTEM
- Initial cells density: 0.5-1.0×104 cells/mL (2-4 days prior to test initiation)
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 1


GROWTH MEDIUM
- Standard medium used: yes


TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: OECD culture medium


OTHER TEST CONDITIONS
- Light intensity and quality: 4,440-8,880 Lux


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
Morphological changes of algal cells were observed including expansion, aggregation, atrophy, and decoloration at 72 hours after exposure. Cell densities were determined by direct counts using a BECKMAN COULTER Multisizer 3 particles analyzer.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 3.2
- Range finding study
- Test concentrations: control, 0.1, 1, 10, and 100 mg/L.
- Results used to determine the conditions for the definitive study: tthe average specific growth rate was inhibited by 13.5% and by 51.4% for the area under growth curve method at the highest dose of 100 mg/L.
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 4.4 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
growth rate
Details on results:
Algal cells were observed to maintain a similar shape to the control in all test solutions.

Table 1. Growth inhibition rates based on mean value during the test period

(1) Average growth rate

Nominal concentration (mg/L)

Mean measured concentration (mg/L)

Average growth rate

Relative inhibition (%)

Mean relative inhibition (%)

Control

ND

1.7038

-

-

0.3

0.3

1.7084

-0.3

0.0

1.6861

1.0

1.7180

-0.8

1

0.4

1.6385

3.8

4.2

1.598

6.2

1.6619

2.5

3.1

0.3

1.7464

-2.5

-3.4

1.8030

-5.8

1.7356

-1.9

9.8

0.8

1.8378

-7.9

-3.4

1.7358

-1.9

1.7090

-0.3

31.3

1.7

1.7674

-3.7

-2.2

1.7312

-1.6

1.7263

-1.3

100.0

4.4

1.7609

-3.4

-3.3

1.7747

-4.2

1.7453

-2.4

Description of key information

Key value for chemical safety assessment

Additional information

Data on the acute toxicity of magnesium hydrogen orthophosphate (CAS 7757-86-0) to aquatic algae are not available. The assessment was therefore based on studies conducted with the analogue substance calcium hydrogen orthophosphate (7757-93-9) as part of a read across approach, which is in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5.

The acute toxicity of calcium hydrogen orthophosphate to aquatic algae was investigated in a study following OECD guideline 201 (Kim et al. 2013). Pseudokirchnerella subcapitata was exposed to nominal test substance concentrations of 0.3, 1, 3.1, 9.8, 31.3, and100 mg/L. The mean measured test concentrations at test start were 0.3, 0.4, 0.3, 0.8, 1.7, and 4.4 mg/L. Based on the algal growth rate an EC50(72 h) >4.4 mg/L (measured) was determined (nominal: EC50(72 h) >100 mg/L). Based on the study results for the read across substance calcium hydrogen orthophosphate the assessed substance magnesium hydrogen orthophosphate is considered not acutely toxic to aquatic algae.