Ethoprophos

Toxicity to aquatic algae and cyanobacteria

Administrative data

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

from 1999-03-30 to 1999-08-19

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1999

Report date:

1999

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Version / remarks:

1984

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method C.3 (Algal Inhibition test)

Version / remarks:

EU DIRECTIVE 92/69/EEC

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

Ethoprophos

EC Number:

236-152-1

EC Name:

Ethoprophos

Cas Number:

13194-48-4

Molecular formula:

C8H19O2PS2

IUPAC Name:

ethyl bis(propylsulfanyl)phosphinate

Test material form:

liquid

Sampling and analysis

Analytical monitoring:

yes

Details on sampling:

- Samples were collected from each replicate test chamber at approximately 24-hour intervals during the test to determine cell densities, which were subsequently used to calculate areas under the growth curve and growth rates. A single aliquot of each sample collected during the test was diluted with an electrolyte solution (Isoton®) before doing the cell count.
- Approximately 5 mL samples were collected at approximately 24-hour intervals during the 72-hour exposure and were held for a maximum of three days under refrigerated conditions sufficient to inhibit growth until cell counts could be performed on the last day of the test.
- Samples of test solutions were collected at approximately 0 and 72 hours to measure concentrations of the test substance. Samples at test initiation were collected from the individual batches of test solution prepared for each treatment and control group prior to addition of the algae. At test termination, samples were collected from the pooled replicates from each treatment and control group. All samples were collected in glass jars and analysed immediately without storage.

Test solutions

Vehicle:

yes

Details on test solutions:

A primary stock solution was prepared by dissolving the test item in freshwater dimethylformamide (DMF) at a nominal concentration of 30 mg a.i./mL. The primary stock was inverted at least 20 times to mix and appeared clear and colourless. Working stock solutions then were prepared in DMF at nominal concentrations of 0.26,0.56,1.2,2.7,6.0 and 13 mg a.i./mL by serial dilution from the primary stock. The test solutions were prepared at nominal concentrations of 0.026,0.058,0.13,0.28,0.62,1.4 and 3.0 mg a.i./L by diluting appropriate aliquots of the primary or working stock solutions with freshwater algal medium and inverting the solutions to mix. The final concentration of DMF in the test solutions and the solvent control solution was 0.1 mL/L. All resultant test solutions appeared clear and colourless.

Test organisms

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Details on test organisms:

TEST ORGANISM
- Common name: freshwater green algae
- Strain: Chodat (CCAP 276/22)
- Source: culture medium at Wildlife International Ltd., Easton, Maryland, USA
- Origin: CCAP - The Culture Collection of Algae and Protozoa, U.K.
- Age of inoculum (at test initiation): 2 weeks

ACCLIMATION
- Acclimation period: no, in-house culture
- Culturing media and conditions: same as test

Study design

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Test conditions

Test temperature:

23.1 - 26.0 °C

pH:

7.8 to 7.9 at test initiation
8.1 to 8.4 at test termination

Nominal and measured concentrations:

Nominal concentrations: control, solvent control, 0.026, 0.058, 0.13, 0.28, 0.62, 1.4 and 3.0 mg a.i./L
Measured concentrations: control, solvent control, 0.028, 0.059, 0.12, 0.26, 0.60, 1.3 and 3.0 mg a.i./L

Details on test conditions:

TEST SYSTEM
- Test vessel: Erlenmeyer flasks
- Type: closed, plugged with foam stoppers
- Material, size, headspace, fill volume: glass, 250 mL, 100 mL fill volume
- Aeration: none
- Initial cells density: 1E4 cells/mL
- Control end cells density: 1 066 803 cell/mL
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 3
- No. of vessels per vehicle control (replicates): 6

GROWTH MEDIUM
- Standard medium used: yes

TEST MEDIUM / WATER PARAMETERS
- Total organic carbon: <1 mg/L
- Particulate matter: 286 mg/L

OTHER TEST CONDITIONS
- Sterile test conditions: no
- Adjustment of pH: no
- Light intensity and quality: cool-white fluorescent lighting, 6620 to 9170 lux

EFFECT PARAMETERS MEASURED:
- Determination of cell concentrations: Cell counts were performed using an electronic particle counter (Coulter Electronics, Inc.).

Reference substance (positive control):

no

Results and discussion

Effect concentrations

Effect concentrations 1

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

2.4 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

act. ingr.

Basis for effect:

biomass

Effect concentrations 2

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

1.3 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

act. ingr.

Basis for effect:

biomass

Effect concentrations 3

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 3 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

act. ingr.

Basis for effect:

growth rate

Effect concentrations 4

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

1.3 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

act. ingr.

Basis for effect:

growth rate

Details on results:

After 72 hours of exposure, inhibition of area under the growth curve in the 0.028, 0.059, 0.12, 0.26, 0.60, 1.3 and 3.0 mg a.i./L treatment groups was 8.4, 2.9, -22, 5.7, -1.5, 18 and 67 %, respectively, relative to the pooled control.
After 72 hours of exposure, inhibition of growth rate in the 0.028, 0.059, 0. 12, 0.26, 0.60, 1.3 and 3.0 mg a.i./L treatment groups was 2.9, -0.57, -5.0, 0.098, -0.93, 2.2 and 23 %, respectively, relative to the pooled control.

Reported statistics and error estimates:

Bonferroni's test indicated that areas under the growth curve were significantly reduced (p<0.05) in the 3.0 mg a.i./L treatment group. The 72-hour NOEC for area under the growth curve was 1.3 mg a.i./L.
Bonferroni's test indicated that growth rates were significantly reduced (p<0.05) in the 3.0 mg a.i./L treatment group. The 72-hour NOEC for growth rates was 1.3 mg a.i./L.

Any other information on results incl. tables

Analytical measurements

Samples collected at the beginning of the test had measured concentrations that ranged from 93.0 to 103 % of nominal concentrations. Samples collected at test termination ranged from 90.3 to 114 % of nominal concentrations, respectively. When measured concentrations of the samples collected at 0 and 72 hours were averaged, the mean measured test concentrations for this study were 0.028, 0.059, 0. 12, 0.26, 0.60, 1.3 and 3.0 mg a.i./L. Mean measured concentrations were used in the calculation of EC50 values.

 

Table 1: Summary of Analytical Chemistry Data

Nominal Concentration (mg a.i./L)	Replicate	Measured Concentration (mg a.i./L)	Mean Measured Concentration (mg a.i./L)	Mean Measured Percent of Nominal
Negative Control	0 72	<LOQ^1 <LOQ	--	--
Solvent Control	0 72	<LOQ <LOQ	--	--
0.026	0 72	0.0269 0.0295	0.028	108
0.058	0 72	0.0588 0.0588	0.059	102
0.13	0 72	0.121 0.117	0.12	92.3
0.28	0 72	0.264 0.263	0.26	92.9
0.62	0 72	0.616 0.589	0.60	96.8
1.4	0 72	1.31 1.28	1.3	92.9
3.0	0 72	3.02 2.92	3.0	100
^1 The limit of quantitation (LOQ) was 0.0150 mg a.i./L.

 

Biological results

Table 2: EC50 Values Over the 72-Hour Exposure Period

Time	Area Under the Growth Curve			Growth Rate
	EbC50 (mg a.i./L)	95 % Confidence Limits (mg a.i./L)		ErC50 (mg a.i./L)	95 % Confidence Limits (mg a.i./L)
24 Hours	2.9	2.2 and 3.0		>3.0	--^1
48 Hours	2.3	1.5 and 2.7		>3.0	--^1
72 Hours	2.4	2.0 and 2.6		>3.0	--^1
^1 Confidence limits could not be calculated from the data obtained.

 

Applicant's summary and conclusion

Validity criteria fulfilled:

not specified

Conclusions:

The 72-hour EbC50 value, based on area under the growth curve, for Scenedesmus subspicatus exposed to the test item was 2.4 mg a.i./L with 95 % confidence limits of 2.0 and 2.6 mg a.i./L. The 72-hour ErC50 value, based on growth rate, was greater than 3.0 mg a.i./L, the highest concentration tested. The NOEC based on area under the growth curve and growth rate at 72 hours was 1.3 mg a.i./L.

Executive summary:

The objective of this study was to determine the toxicity of the test itme to the freshwater green alga, Scenedesmus subspicatus according to OECD 201 (1984). The green alga, Scenedesmus subspicatus, was exposed to a geometric series of seven test concentrations, a negative (culture medium) control and a solvent (dimethylformamide) control under static conditions for 72 hours. Nominal test concentrations selected were 0.026, 0.058, 0.13, 0.28, 0.62, 1.4 and 3.0 mg active ingredient of the test item per liter of test solution (mg a.i./L). Samples collected at the beginning of the test had measured concentrations that ranged from 93.0 to 103 % of nominal concentrations. Samples collected at test termination ranged from 90.3 to 114 % of nominal concentrations, respectively. When measured concentrations of the samples collected at 0 and 72 hours were averaged, the mean measured test concentrations for this study were 0.028, 0.059, 0. 12, 0.26, 0.60, 1.3 and 3.0 mg a.i./L. Mean measured concentrations were used in the calculation of EC50 values. The 72-hour EbC50 value, based on area under the growth curve, for Scenedesmus subspicatus exposed to the test item was 2.4 mg a.i./L with 95 % confidence limits of 2.0 and 2.6 mg a.i./L. The 72-hour ErC50 value, based on growth rate, was greater than 3.0 mg a.i./L, the highest concentration tested. The NOEC based on area under the growth curve and growth rate at 72 hours was 1.3 mg a.i./L.