Hexadecyl dihydrogen phosphate

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:

72 hours

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

The substance that has been tested for this end point is the potassium salt of the hexadecyl hydrogen phosphate. Once in solution, the potassium ion will dissociate from the substance leaving the hexadecyl hydrogen phosphate anion as the organic species of relevance for the effect on aquatic species, which is basically the substance being registered.
The potassium ion in solution is ubiquitous in aquatic systems and known not to be toxic at low levels. The pH of the mono constituent substance being registered, which is >= 80% hexadecyl hydrogen phosphate, is reported to be around 5.0, slightly lower than the K salt in solution. Both the K salt and the acid substance are of very low solubility. The aquatic test for alga recognised this issue and testing was carried out as per insoluble substances.
The similarity in substances and properties have been assessed and read-across is considered valid.

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Freshwater Alga and Cyanobacteria, Growth Inhibition Test)

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Lot/Batch Number: 57387F17
Solubility (specified): 160mg/l, water 20°C (SDS)
Solubility (observed): The test substance was found to be insoluble in water at the concentration required for the test (100mg/l)

Analytical monitoring:

yes

Details on sampling:

Duplicate samples were taken at the start and end of the 72 hour exposure period. Samples were taken from remaining test media after filling test vessels for 0 hours and pooled replicate flasks for 72 hours. Analysis of these samples for the verification of exposure concentrations was performed using ICP-MS.

Vehicle:

no

Details on test solutions:

The test substance was found to be insoluble in water at the concentration required for the test (100mg/l) and was therefore tested as insoluble.
Both the preliminary range-finding test and the definitive test were prepared by the direct addition of measured amounts of test substance to dilution water and stirred.
The only practicable method to prepare the 0.1 and 1.0mg/l test concentration was by dilution (addition of 5 and 50ml of the 10mg/l preparation to 500ml of dilution water respectively). The
solution was then stirred for 23 hours and 05 minutes and settled for 4 hours and 55 minutes.
After settling the first 100ml (approximately) of aqueous phase was removed (avoiding all settled and floating material) and discarded after filtering through Whatman 54 filter paper. The remaining aqueous phase provided sufficient volumes for water quality measurements and testing

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Details on test organisms:

Species: Pseudokirchneriella subcapitata strain: CCAP 278/4 received 15 May 2018.
Source: Culture Collection of Algae and Protozoa SAMS Ltd, Scottish Marine Institute OBAN, Argyll PA37 1QA, Scotland, United Kingdom
Culture conditions: Temperature: 21.5 - 22.2C.
Illumination: 6500 - 7900 lux continuous white light.
Orbiting: set to 200rpm.
Culture media: Deionised water with added nutrients according to OECD 201

Test type:

static

Water media type:

freshwater

Total exposure duration:

72 h

Test temperature:

Temperature range within incubator throughout test: 20.9 - 22.2 °C
(Required: 21-24±2°C)

pH:

Initial pH at 0 Hours: 8.02 (Required: 8.1±0.1)
pH range in control and test concentrations throughout test: 7.25 - 8.02

Details on test conditions:

Illumination range within incubator throughout test: 6080 - 7910 Lux. (Required: 6x103-8x103 Lux ± 15% of recorded mean)
Orbital shaking: 200rpm (Required: 200-250rpm)

Reference substance (positive control):

yes

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

> 10.9 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

element

Remarks:

Potassium measured by ICP

Basis for effect:

growth rate

The 72 hour EC(r)50 and EC(y)50 of ColaFax CPE-K, 1-Hexadecanol, 1-(dihydrogen phosphate),potassium salt (1:1) to Pseudokirchneriella subcapitata were >10.9 mg/L and >10.9 mg/L (determined by Linear Interpolation) respectively.

The 0 to 72-hour NOEC(r) was >10.9 mg/L (Homoscedastic t Test indicates no significant differences) and the 0-72 hour LOEC was >10.9 mg/L (Homoscedastic t Test indicates no significant differences).

The algal cells were examined microscopically during the determination of cell concentration. All cells within the control and test concentrations appeared normal, no abnormalities were observed

Conclusions:

The definitive test was performed according to the OECD 201 (2011) guideline.
The nominal concentration of the test material (100 mg/L) and mean measured concentration of Potassium have been used in the determination of the EC50 and NOEC values
The algal cells were examined microscopically during the determination of cell concentration. All cells within the control and test concentrations appeared normal, no abnormalities were observed
All validity criteria for the definitive test were met.
A value of >100 mg/l has been assessed for both EC50 and NOEC values

Description of key information

The substance that has been tested for this end point is the potassium salt of the hexadecyl hydrogen phosphate. Once in solution, the potassium ion will dissociate from the substance leaving the hexadecyl hydrogen phosphate anion as the organic species of relevance for the effect on aquatic species, which is basically the substance being registered.

The potassium ion in solution is ubiquitous in aquatic systems and known not to be toxic at low levels. The pH of the mono constituent substance being registered, which is >= 80% hexadecyl hydrogen phosphate, is reported to be around 5.0, slightly lower than the K salt in solution. Both the K salt and the acid substance are of very low solubility. The aquatic test for alga recognised this issue and testing was carried out as per insoluble substances.

The similarity in substances and properties have been assessed and read-across is considered valid.

Key value for chemical safety assessment

EC50 for freshwater algae:

100 mg/L

EC10 or NOEC for freshwater algae:

100 mg/L