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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:
2016-02-12 to 2016-05-24
Reliability:
1 (reliable without restriction)
Qualifier:
according to
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Deviations:
yes
Remarks:
Minor deviation on temperature which lasted less than 1 hour. The study integrity was not affected by the deviation.
GLP compliance:
yes
Specific details on test material used for the study:
CP2684
Analytical monitoring:
yes
Remarks:
samples of the test medium were taken for orthophosphate analysis
Details on sampling:
5.0 mL samples taken at 0, 24 and 72 hour.
Vehicle:
yes
Details on test solutions:
Water Accommodated Fractions (WAF) were prepared separately at loading rates ranging from 1.0 to 100 mg/L applying a 30 minute period of ultrasonic waves followed by a two-day period of magnetic stirring. Thereafter, the resulting mixtures were filtered over a 0.45 µm membrane filter. Where applicable, the pH was set to 8.5 with 1 M HCl. The resulting solutions were clear and colourless and used as test solutions.
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
strain NIVA CHL 1. In-house laboratory culture
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
72 h
Hardness:
(Ca+Mg) 0.24 mmol/L
Test temperature:
21-24 C
pH:
8.5
Nominal and measured concentrations:
Water Accommodated Fractions. Loading rates nominally between 1.0 and 100 mg/L.
Details on test conditions:
All test solutions were prepared separately at loading rates ranging from 1.0 to 100 mg/L applying a
30 minute period of ultrasonic waves followed by a two-day period of magnetic stirring. Thereafter, the
resulting mixtures were filtered over a 0.45 µm membrane filter (Whatman; RC55). The resulting
Water Accommodated Fractions (WAFs) were clear and colourless and used as test solutions.

The pH of the highest WAF in the combined limit/range finding test was set from 10.5 to 8.5. In the
final test, the pH of the four highest concentrations were set from a range of 9.3-10.6 to 8.5. All pH
adjustments were done using with 1 M HCl (Merck, Darmstadt, Germany).

After preparation, volumes of 50 mL were added to each replicate of the respective test concentration.
Subsequently, 1 mL of an algal suspension was added to each replicate providing a cell density of
104 cells/mL.
Reference substance (positive control):
yes
Remarks:
potassium dichromate
Key result
Duration:
3 d
Dose descriptor:
NOEC
Effect conc.:
32 mg/L
Nominal / measured:
nominal
Conc. based on:
other: WAF
Basis for effect:
growth rate
Key result
Duration:
3 d
Dose descriptor:
EL50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
other: WAF
Basis for effect:
growth rate

Summary of effect parameters:

   Parameter (mg/L)  NOEL  EL10  EL20  EL50
 Growth rate  Value  32  61  >100  >100
   Lower 95%-cl    53  n.d  n.d.
   Upper 95%-cl    68  n.d.  n.d.
 Yield  Value  18  16  28  84
    Lower 95%-cl    12  23  74
    Upper 95%-cl    20  33  99
Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of the present study with Pseudokirchneriella subcapitata, Silicic acid (H4SiO4), zirconium (4+) salt (1:1), reaction products with sodium hydroxide reduced growth rate of this fresh water algae species significantly at loading rates of 56 mg/L and higher.
The EL 50 for growth rate inhibition (72h-E R L 50 ) was beyond the range tested.
The EL 50 for yield inhibition (72h-E Y L 50 ) was 84 mg/L with a 95% confidence interval ranging from 74 to 99 mg/L.
The 72h-NOEL for growth rate inhibition was 32 mg/L based on biological relevance. The 72h-NOEL for yield inhibition was 18 mg/L.
Executive summary:

The study procedures described in this report were based on the OECD guideline No. 201, 2006; Annex 5 corrected 28 July 2011. In addition, the procedures were designed to meet the test methods of the Commission Regulation (EC) No 440/2008, Part C.3, 2008; Amended by EC No. 761/2009 and the OECD series on testing and assessment number 23, 2000. The batch of test item tested was a brown powder not completely soluble in test medium at the loading rates initially prepared. The test item was a UVCB substance. No correction was made for the purity/composition of the test item. Water Accommodated Fractions (WAF) were prepared separately at loading rates ranging from 1.0 to 100 mg/L applying a 30 minute period of ultrasonic waves followed by a two-day period of magnetic stirring. Thereafter, the resulting mixtures were filtered over a 0.45 µm membrane filter. Where applicable, the pH was set to 8.5 with 1 M HCl. The resulting solutions were clear and colourless and used as test solutions. A final test was performed based on the results of a preceding combined limit/range-finding test. Six exponentially growing algal cultures were exposed to an untreated control, whereas three replicates per group were exposed to WAFs prepared at 10, 18, 32, 56 and 100 mg/L. The initial cell density was 10 4 cells/ml. The total exposure period was 72 hours and samples for analytical confirmation of orthophosphate concentrations were taken at the start, after 24 hours of exposure and the end of the exposure period. Samples taken from the control and the highest concentration were analysed. The expected concentration of orthophosphate in medium was 0.82 mg/L. The concentration measured in the control treatment was in line with this theoretical value at the start of the test (0.85 mg/L), whereas in the highest WAF was 20% lower (0.69 mg/L) indicating that part of the phosphate was removed by the test item. The measured concentrations decreased to 0.50 and 0.59 mg/L in the control and the highest WAF after 24 hours of exposure, respectively. At the end of the exposure the measured concentrations were 0.20 and 0.23 mg/L, respectively. The study met the acceptability criteria prescribed by the study plan and was considered valid.

Summary of effect parameters:

   Parameter (mg/L)  NOEL  EL10  EL20  EL50
 Growth rate  Value  32  61  >100  >100
   Lower 95%-cl    53  n.d  n.d.
   Upper 95%-cl    68  n.d.  n.d.
 Yield  Value  18  16  28  84
    Lower 95%-cl    12  23  74
    Upper 95%-cl    20  33  99

Description of key information

Under the conditions of the present study with Pseudokirchneriella subcapitata, Silicic acid (H4SiO4), zirconium (4+) salt (1:1), reaction products with sodium hydroxide reduced growth rate of this fresh water algae species significantly at loading rates of 56 mg/L and higher. The EL 50 for growth rate inhibition (72h-E R L 50 ) was beyond the range tested. The EL 50 for yield inhibition (72h-E Y L 50 ) was 84 mg/L with a 95% confidence interval ranging from 74 to 99 mg/L. The 72h-NOEL for growth rate inhibition was 32 mg/L based on biological relevance. The 72h-NOEL for yield inhibition was 18 mg/L.

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:
32 mg/L

Additional information

The EL 50 for growth rate inhibition (72h-E R L 50 ) was beyond the range tested