O,O,O-triphenyl phosphorothioate

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2013-01-21 to 2013-01-24

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
In the definitive test, a water accomodated fraction (WAF) was used. Thus, 100 mg/L of the test item was weighed and transferred with an appropriate amount of dilution water into a brown glass flask. This dispersion was stirred for 72 hours with 1100 rpm at room temperature. Thereafter, undissolved particles were removed by membrane filtration (0.45 µm, RC, MACHEREY-NAGEL). The saturated solution was clear and colourless and used as a stock solution.
The solubility of the test item in water under test conditions turned out to be lower than the limit of quantification of the analytical system of 0.1 mg test item/L.
- Controls: Negative controls (water) were performed in 6 Replicates

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Details on test organisms:

TEST ORGANISM
- Common name: Green Algae
- Source (laboratory, culture collection): Sammlung von Algenkulturen (SAG), Pflanzenphysiologisches Institut der Universität Göttingen, Nikolausberger Weg 18, D-37073 Göttingen
- Method of cultivation: Fresh stocks are prepared every month on Z-Agar. Light intensity amounts to 35-70 µE m2/s for 24 h per day

ACCLIMATION
- Acclimation period: A three day old preculture, prepared in dilution water (according to OECD 201 medium), was used as inoculum.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

72 h

Hardness:

0.24 mmol Ca+Mg/L

Test temperature:

21.75 ± 0.25°C

pH:

Negative controls: 0 hours: 8.22; 72 hours: 8.36
Test concentration: 0 hours: 8.24; 72 hours: 8.31

Nominal and measured concentrations:

100 mg/L nominal (WAF)

Details on test conditions:

TEST SYSTEM
- Test vessel: Sterile Erlenmeyer flasks (vol. 250 mL) with cotton wool plugs
- Type (delete if not applicable): open
- Material, size, headspace, fill volume: 250 mL filled with 100 mL test solution
- Initial cells density: 4332 cells/mL
- Control end cells density: 704668 cells/mL
- No. of vessels per concentration (replicates): 6
- No. of vessels per control (replicates): 6

GROWTH MEDIUM
- Standard medium used: yes

OTHER TEST CONDITIONS
- Sterile test conditions: no
- Adjustment of pH: no
- Photoperiod: continuous
- Light intensity and quality: 60 - 120µE m2/s, Fluorescent tubes, Osram L36 W/11-865, cool daylight

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: The cell density was measured at 24, 48 and 72 hours exposure using via Chlorophyll-a fluorescence excitation at 436 nm and emission at 685 nm. Dilution water was used as background signal.

TEST CONCENTRATIONS
- Test concentrations:
- 100 mg/L nominal concentration (WAF)

Reference substance (positive control):

yes

Remarks:

Potassium dichromate (CAS: 7778-50-9)

Key result

Duration:

72 h

Dose descriptor:

EL10

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat. (dissolved fraction)

Remarks:

100 mg/L loading rate WAF

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EL50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat. (dissolved fraction)

Remarks:

100 mg/L loading rate WAF

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EL10

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat. (dissolved fraction)

Remarks:

100 mg/L loading rate WAF

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

EL50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat. (dissolved fraction)

Remarks:

100 mg/L loading rate WAF

Basis for effect:

biomass

Details on results:

- Exponential growth in the control (for algal test): yes (163-fold)
- Flocculation: Since after preparation of the stock solution, all undissolved particles were removed by membrane filtration, no floccation was observed in the study
- Other: No analytical evaluation of the limit concentration and the control was carried out. The solubility of the test item in water under test conditions turned out to be lower than the limit of quantification of the analytical system of 0.1 mg test item/L.

Results with reference substance (positive control):

- Results with reference substance valid? - yes
- EC50: 0.631 mg/L (growth rate inhibition); 0.256 mg/L (yield inhibition)

Validity criteria fulfilled:

yes

Description of key information

The substance is not harmful to algae up to the limit of solubility in water.

Additional information

Two studies are available investigating the toxicity of O,O,O-triphenyl phosphorothioate to aquatic algae.

In the key study Desmodesmus subspicatus was exposed to O,O,O- triphenyl thiophosphate for 72h at saturation concentration (undiluted filtrate of the test item with a nominal loading rate of 100mg/L) under static conditions (Noack 2013). Due to its low solubility in water, the test item was tested by preparing Water-Accommodated-Fractions (WAFs). The EL50 (growth rate) and EL50 (yield) values were above saturation concentration (undiluted filtrate of the test item with a nominal loading rate of 100mg/L). There was no significant growth inhibition in the test item concentration. EL10 (growth rate) and EL10 (yield) is determined to be equal or higher than the saturated solution of the substance.

In a supporting study conducted with O,O,O-triphenyl phosphorothioate in a lower purity (purity > 25%; RCC 1997), the 72h-ErL50 and 72h-EbL50 was determined to be above the saturation concentration ((WAF) undiluted filtrate of the test item with a nominal loading rate of 100mg/L). The NOErL and NOEbL was determined to be equal or above saturation concentration ((WAF) undiluted filtrate of the test item with a nominal loading rate of 100mg/L). Based on these results, it can be expected that the poorly soluble constituents of the test item do not exhibit adverse effects to algae.

It can be concluded that O,O,O- triphenyl thiophosphate is not harmful to algae up to the limit of solubility in water.