Diethyl (hydroxymethyl)phosphonate

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:

2015

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.3 (Algal Inhibition test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Batch Number: 540-1013-14

Analytical monitoring:

yes

Details on sampling:

Samples were taken from control and test flasks at 24, 48 and 72 hours and the cell densities were measured using a Coulter Z Series Particle Count and Size Analyser. The estimate of cell numbers in each sample was based on the mean of three consecutive counts, corrected for
background counts of uninoculated dilution medium. The presence of any abnormal cells was also recorded during screening of the media from the control and test groups.

Vehicle:

no

Details on test solutions:

Algal nutrient medium (OECD):
Four stock solutions were prepared, using filtered, dechlorinated tap water which had been softened and treated by reverse osmosis, before microfiltration and purification (resistivity of 18 Megohm/cm). Stock solutions were sterilised by autoclaving (solutions 1 and 3) or by membrane filtration (solutions 2 and 4)
before being stored at 4degrees Celsius in the dark. Aliquots of stock solutions 1 and 3 were further diluted with the same diluent and autoclaved again to produce the working strength nutrient medium. Stock solutions 2 and 4 were added to the medium prior to (stock 2) or on the day of use (stock 4).

The determination of E06-16 in OECD medium:
Samples were diluted with OECD medium, prior to quantitation by LC-MS. A weighed amount of E06-16 was dissolved in methanol to produce a 10 mg/mL stock standard solution. Aliquots of the stock standard solution were diluted with methanol to give standard fortification solutions. The appropriate standard fortification solution was further diluted with OECD medium to produce a series of calibration solutions in the range 1 to 50 ng/mL.

Test organisms (species):

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

Details on test organisms:

Strain No. CCAP 278/4.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

72 h

Remarks on exposure duration:

n/a

Post exposure observation period:

no

Test temperature:

21 to 24°C

pH:

8

Nominal and measured concentrations:

100 & 112 mg/L

Details on test conditions:

Conical flasks (250 mL) each containing control or test culture (ca. 100 mL) were placed in an illuminated orbital incubator according to a random number sequence. The cultures were incubated, without renewal of medium for 72 hours under continuous illumination (nominally 4440 to 8880 lux.) provided by 7 x 30 W “cool white” 1 metre fluorescent tubes. The temperature was maintained at 21 to 24°C.The light intensity was monitored daily at four corner positions and in a central position of the random block design within the test area. To minimise the impact of differences in light intensity across the test area on algal growth, control and test flasks were re-positioned in the test area each day during the definitive test.

Key result

Duration:

72 h

Dose descriptor:

other: EC50 & NOEC

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks:

Average specific growth rate

Key result

Duration:

72 h

Dose descriptor:

other: EC50 & NOEC

Effect conc.:

> 112 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

After 72 hours, analysis of samples of media containing E06-16 at 100 mg/L, which had been incubated without algal cells, gave similar results to test media incubated in the presence of algal cells. This finding indicated that the presence of algal cells did not affect the stability of the test substance.

Reported statistics and error estimates:

The mean coefficient of variation (CoV) for section by section daily growth rates in the control cultures was 9.1% during the definitive test and the CoV for the average specific growth rates of the control culture was 1.77% during the 72 hour exposure period.

Validity criteria fulfilled:

yes

Conclusions:

After 72 hours of exposure, algal growth was reduced by 3% for growth rate and 14% for yield; neither reduction was found to be statistically significant. Therefore, the ErC50 and EyC50 could not be determined, but must be greater than 100 mg/L (nominal) or greater than 112 mg/L (mean measured). The “no observed effect concentration” (NOEC) for growth rate and yield was 100 mg/L (nominal) or 112 mg/L (mean measured).

Executive summary:

The effect of E06-16 on the growth of the unicellular green alga Pseudokirchneriella subcapitata was assessed under non-axenic conditions. Cell numbers were counted daily to monitor growth. After 72 hours of exposure to E06-16, algal growth was reduced by 3% for growth rate and 14% for yield, compared to the control group; this was not found to be statistically significant. Therefore, the ErC50 and EyC50 could not be determined, but both must be greater than 100 mg/L (nominal) or greater than 112 mg/L (mean measured). The “no observed effect concentration” (NOEC) for growth rate and yield was 100 mg/L (nominal) or 112 mg/L (mean measured).

Key value for chemical safety assessment

EC50 for freshwater algae:

112 mg/L

EC10 or NOEC for freshwater algae:

112 mg/L