Pirimiphos-methyl

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:

6 Oct 1988 to 7 Apr 1989

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

GLP compliance:

yes

Analytical monitoring:

yes

Details on sampling:

After 24, 48, 72 and 96 hours, samples were removed from each test and blank vessel. At the start of the test, samples were taken of each test solution, using
the excess remaining after: filling the test vessels, and were analysed for the concentration of the test substance.

Vehicle:

yes

Remarks:

Acetone

Details on test solutions:

The test substance had low solubility in water (approximately 5 mg/L) therefore stock solutions in acetone (HPLC grade) were prepared. Each test solution was prepared by the addition of an aliquot of the appropriate stock solution to sterile culture medium, with an equalizing addition of acetone to a volume of 1000 ml such that the final acetone concentration was 0.1 mL/L. The solvent control contained 0.1 mL acetone/L. The control solution consisted of culture medium only. After preparation, visual observation showed the highest nominal concentration (6.4 mg/L) test solution to be a transparent, faint, fine, white homogeneous suspension; all other test and control solutions were clear and colorless. Using aseptic techniques, 100 mL volumes of the appropriate test solution were dispensed to each test and blank vessel, and the remaining test solutions used for physical and chemical analysis. The nominal exposure concentrations used in this study were 0.2, 0.4, 0.8 , 1.6, 3.2 and 6.4 mg of test substance per L together with a control and solvent control. These were equivalent to 0.14, 0.30, 0.56, 1.3, 2.6 and 5.2 mg per L respectively, expressed as the individual means of the measured concentrations of test substance at the start and end of the study.

Test organisms (species):

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

Details on test organisms:

TEST ORGANISM
- Common name: Green algae
- Strain: Strain ATCC 22662
- Source: Brixham Laboratory archive.
- Culturing conditions: The algae were maintained under axenic conditions. A culture of the alga in the exponential growth phase was used as Inoculum for the test. The culture was grown in the medium, and under the environmental conditions which was described for the test.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

96 h

Test temperature:

24°C

pH:

7.0 - 9.4

Nominal and measured concentrations:

- Nomimal concentrations: 0.2, 0.4, 0.8, 1.6, 3.2 and 6.4 mg/L of the test substance
- Measured concentrations: 0.14, 0.30, 0.56, 1.3, 2.6 and 5.2 mg/L of the test substance
See Table 1 in "Any other information on materials and methods incl. tables"

Details on test conditions:

TEST SYSTEM
- Test vessel: The test vessels were borosilicate glass conical flasks of 250 mL nominal capacity.
- Type: Closed with polyurethane foam bungs
- Aeration: No
- Fill volume: Each flask contained 100 ml of test solution. The cultures were incubated at 24 +/- 1°C, under continuous illumination, with orbital shaking at 100 rpm
- Initial cells density: A nominal cell density of 1.0E+04 cells/mL
- Control end cell density: 4.25E+06 cells/mL
- No. of vessels per concentration: 3
- No. of vessels per control: 3
- No. of vessels per solvent control: 6

GROWTH MEDIUM
- Standard medium used: yes (AAP medium regarding OECD TG 201)

OTHER TEST CONDITIONS
- Adjustment of pH: No
- Photoperiod: Continuous
- Light intensity: 8100 Lux

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: Small volumes of all test concentrations and controls were taken from all test flasks after 24, 48, 72 and 96 hours of exposure. The algal cell densities in these samples were determined by counting with an electronic particle counter.

Reference substance (positive control):

no

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

0.3 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

act. ingr.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

3.38 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

act. ingr.

Basis for effect:

growth rate

Details on results:

No effects were observed in the controls vessels. At 0.56 mg/L, the mean growth rate over 72 hours was significantly inhibited compared to the control vessels. At 1.3, 2.6 and 5.6 mg/L, growth inhibition increased further in a dose-responsive manner. Overview of the results are provided in table 1 and table 2 at "Any other information on results incl. tables"

Results with reference substance (positive control):

Not applicable

Reported statistics and error estimates:

Probit analysis

Table 1. The result obtained from the statistical analyses

Nominal concentration of test substance(mg/L)	Meanmeasured concentration of test substance (0 to 96 hours) (mg/L)	Mean area under growth curve (0-72 hours)	Percentage of solvent control
Culture medium control	-	94.5	-
Solvent control	-	91.9	100
0.2	0.14	91.0	99
0.4	0.30	82.7	90
0.8	0.56	73.3	80*
1.6	1.3	47.8	52*
3.2	2.6	21.5	23*
6.4	5.2	2.93	3*

* Significant difference (P=0.05) from the solvent control

Table 2. Algal cell densities

Nominal concentration of the test substance inmg/L	Mean measured concentration ofthe test substance inmg/L	Replicate	Algal cell density (1.0E+04 cells/mL)
			Day 1	Day 2	Day3	Day 4
Control	-	1 2 3	4.13 4.05 3.82	22.2 21.7 20.3	149 146 135	445 446 383
		Mean	4.00	21.4	143	425
Solvent control	-	1 2 3 4 5 6	3.92 4.41 3.66 4.22 3.89 3.67	20.5 22.7 20.4 22.0 21.3 20.8	148 154 133 145 135 115	465 477 422 440 416 396
		Mean	3.96	21.3	138	436
0.2	0.14	1 2 3	4.37 4.21 4.15	23.3 22.5 21.6	138 146 117	424 435 397
		Mean	4.24	22.5	134	419
0.4	0.30	1 2 3	4.35 4.14 3.90	22.4 20.1 20.4	142 117 102	420 338 332
		Mean	4.13	21.0	120	363
0.8	0.56	1 2 3	3.84 4.19 4.10	18.8 21.8 20.7	102 104 102	367 351 345
		Mean	4.04	20.4	103	354
1.6	1.3	1 2 3	3.28 3.26 3.21	15.0 15.3 14.7	64.2 65.9 62.4	228 234 225
		Mean	3.25	15.0	64.2	229
3.2	2.6	1 2 3	2.29 2.28 2.27	7.78 7.39 7.59	27.2 28.6 29.2	99.8 108 117
		Mean	2.28	7.59	28.3	108
6.4	5.2	1 2 3	1.34 1.54 1.53	2.02 2.26 2.14	3.03 4.51 3.70	5.30 8.06 7.28
		Mean	1.47	2.14	3.75	6.88

Validity criteria fulfilled:

not specified

Conclusions:

Based on the findings, the 72-h ErC 50 and NOErC were determined to be 3.38 and 0.30 mg/L, respectively.

Executive summary:

The toxicity of the test substance to aquatic algae was determined in a study in accordance with OECD TG 201 and in compliance with GLP criteria. The freshwater green alga Raphidocelis subcapitata was cultured in a range of concentrations of the test substance for 96 hours. The cultures were incubated in a static regime at 24 ± 1°C, under continuous illumination (8100 Lux), with orbital shaking at 100 rpm. The test substance was of a low water solubility and acetone was therefore used as a solvent in the preparation of test solutions (0.1mL/L).Six vessels were used for the solvent control and three vessels for each test concentration and culture media control. One blank vessel, without algae, was incubated concurrently for each control and test item group.The nominal concentration of the test substance were 0.2, 0.4, 0.8, 1.6, 3.2 and 6.4 mg/L. The test concentrations were analytically verified by gas chromatography and were determined to be 0.14, 0.30, 0.56, 1.3, 2.6 and 5.2 mg/L, respectively. The starting cell density in all vessels was 4.0E+04 cells/mL. The algal cell densities were measured at 24, 48, 72 and 96 hours and the mean biomass and growth rate were calculated.

 

No effects were observed in the controls vessels. At 0.56 mg/L, the mean growth rate over 72 hours was significantly inhibited compared to the control vessels. At 1.3, 2.6 and 5.6 mg/L, growth inhibition increased further in a dose-responsive manner. Based on the growth rate inhibition, the 72-h NOErC was determined to be 0.30 mg/L and the 72-h ErC50 was determined to be 3.38 mg/L.

Description of key information

72-h ErC50 = 3.38 mg/L, static, Raphidocelis subcapitata, OECD TG 201, Smyth 1989

72-h NOErC = 0.30 mg/L, static, Raphidocelis subcapitata, OECD TG 201, Smyth 1989

Key value for chemical safety assessment

EC50 for freshwater algae:

3.38 mg/L

EC10 or NOEC for freshwater algae:

0.3 mg/L

Additional information

The toxicity of the test substance to aquatic algae was determined in a study in accordance with OECD TG 201 and in compliance with GLP criteria. The freshwater green alga Raphidocelis subcapitata was cultured in a range of concentrations of the test substance for 96 hours. The cultures were incubated in a static regime at 24 ± 1°C, under continuous illumination (8100 Lux), with orbital shaking at 100 rpm. The test substance was of a low water solubility and acetone was therefore used as a solvent in the preparation of test solutions (0.1mL/L).Six vessels were used for the solvent control and three vessels for each test concentration and culture media control. One blank vessel, without algae, was incubated concurrently for each control and test item group. The nominal concentration of the test substance were 0.2, 0.4, 0.8, 1.6, 3.2 and 6.4 mg/L. The test concentrations were analytically verified by gas chromatography and were determined to be 0.14, 0.30, 0.56, 1.3, 2.6 and 5.2 mg/L, respectively. The starting cell density in all vessels was 4.0E+04 cells/mL. The algal cell densities were measured at 24, 48, 72 and 96 hours and the mean biomass and growth rate were calculated.

 

No effects were observed in the controls vessels. At 0.56 mg/L, the mean growth rate over 72 hours was significantly inhibited compared to the control vessels. At 1.3, 2.6 and 5.6 mg/L, growth inhibition increased further in a dose-responsive manner. Based on the growth rate inhibition, the 72-h NOErC was determined to be 0.30 mg/L and the 72-h ErC50 was determined to be 3.38 mg/L.