2-methyl-2H-isothiazol-3-one

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

17 June - 20 September 1996

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP/Guideline study

Qualifier:

according to guideline

Guideline:

other: US FIFRA Subdivision J, 122-2

Deviations:

not specified

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Deviations:

not specified

Qualifier:

according to guideline

Guideline:

EU Method C.3 (Algal Inhibition test)

Deviations:

not specified

GLP compliance:

yes

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
Not applicable

Analytical monitoring:

not specified

Details on sampling:

Analytical determination of RH-573 Technical concentration (active ingredient) was performed with 40 ml samples collected from each test concentration and the stability blank prior to its addition into the triplicate test vessels at the beginning of the test and the stability blank. Approximately 40 ml from each concentration (pooled replicate test vessels) and the stability blank were sampled at the end of the test. The fourth replicate of each treatment and the fifth control vessel were sampled at 72 hours.

Vehicle:

no

Details on test solutions:

The test substance was liquified in a waterbath at approximately 57C for 35 minutes. The liquified test substance was used to prepare a 10 mg a.i./L primary stock solution by adding 0.0102 g of test substance to a 1-liter glass, class-A, volumetric flask and adjusting the final volume to 1000 ml with sterile dilution media. Appropriate amounts of the primary stock solution were added directly to sterile media to formulate test concentrations without the use of a solvent.

Test organisms (species):

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

Details on test organisms:

Source/supplier: original culture from culture collection of algae, University of Texas at Austin, TX, June 25, 1996
- Laboratory culture: yes
- Method of cultivation: culture transferred to sterile enriched media identical to media used for this test and maintained at test conditions for more than 14 days before initiating the definitive test. The subsample of algae used to inoculate media at the start of the definitive test came from a 9 day old culture.
- Pretreatment: 14 day accumulation period
- Controls: deionized water
- Initial cell concentration: about 10,000 cells per ml

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

120 h

Post exposure observation period:

The determination of whether toxic effcts were algistatic or algacidal was performed at 72 and 120 hours. At each of these times, a 0.5 ml subsample of test media from each flask with an initial measured concentration of 0.407 mg a.i./L RH-573 Technical was combined in a flask with 100 ml of fresh media.

Hardness:

Not described

Test temperature:

24C

pH:

7.5

Dissolved oxygen:

No data.

Salinity:

Not described

Nominal and measured concentrations:

0, 0.05, 0.10, 0.20, 0.40 and 0.80 mg a.i./L (nominal)

Details on test conditions:

A range-finding test was conducted from 17 June to 22 June 1996 with a control and five nominal concentrations of RH-573 Technical. At the conclusion of the test, the number of cells per milliliter in the test vessels equalled the following percents of the number of cells per milliliter in the control vessels: 0.05 mg a.i./L RH-573 Technical = 119%; 0.1 mg a.i./L RH-573 Technical = 94%; and 0.5, 1.0, and 5.0 mg a.i./L RH-573 Technical = 1%. A definitive test was initiated on August 23, 1996 with a control and five nominal concentrations of test substance: 0.05, 0.10, 0.20, 0.40 and 0.80 mg a.i./L RH-573 Technical. This test was determined to be invalid and was terminated due to unacceptable 0-hour analytical data.

The final definitive test was conducted for 120 hours from September 13 to 18, 1996. The test was conducted at 24 +/-1C with five concentrations of test substance and a dilution water control. Nominal concentrations of RH-573 Technical were 0 mg a.i./L (control), 0.050, 0.10, 0.20, 0.40 and 0.80 mg/a.i./L.

The test substance was liquified in a waterbath at approximately 57C for 35 minutes. The liquified test substance was used to prepare a 10 mg a.i./L primary stock solution by adding 0.0102 g of test substance to a 1-liter glass, class-A, volumetric flask and adjusting the final volume to 1000 ml with sterile dilution media. Appropriate amounts of the primary stock solution were added directly to sterile media to formulate test concentrations without the use of a solvent.

Freshwater algae were distributed among three replicates of each treatment at the rate of ~10,000 cells per milliliter. The same inoculation rate was used for a fourth replicate of each treatment and five extra control replicates. These extra replicates were established for the sole purpose of providing 72 and 120 hour sampling. Test vessles were 250 ml glass erlenmeyer flasks that contained 100 ml of test solution with an approximate depth of 3 cm. A stability blank was established at 0.20 mg a.i./L RH-573 Technical to monitor the influence of algae on any los of test substance during the toxicity test. This test vessel was not inoculated with algae. The stability blank was incubated with test vessles under test conditions.

Test vessels were capped with inverted glass beakers and randomly arranged on a rotary shaker that was adjusted to 100 rpm and located in an incubator during the test (a random numbers table was used to select the location of each test vessel, not sampling vessels). A 24 hour light and 0 hour dark photoperiod was automatically maintained with cool-white fluorescent lights that provided a light intensity of ~50 uEin/m(2)sec.

The number of algal cells/ml in each test vessel and the occurrence of relativ esize differences, unusual cell shapes, colors, flocculations, adherence of cells to test containers, or aggregation of cells was determined microscopically using a haemocytometer after 24, 48, 72, 96 and 120 hours of exposure. Temperature of the incubator was measured and recorded daily (thermometer number 3794), and pH (Beckman model pHI 12 mether, instrument number 154 pHT 5) was determined in each test vessel at hours 0, 72 and 120. The temperature of a representative flask of water incubated among the test vessels was recorded continuously.

After 72 hours of exposure, a 0.5 ml subsample of test media from each flask with an initial measured concentration of 0.407 mg a.i./L RH-573 Technical was combined with 100 ml of fresh media to determine whether algicidal or algistatic effects had occurred. This flask was incubated under test conditions for 168 hours and examined for the presence of algal cells. This procedure was repeated after 120 hours of exposure, with the inoculated flask of fresh media being incubated for 144 hours before being examined for the presence of algal cells.

Reference substance (positive control):

not specified

Duration:

120 h

Dose descriptor:

NOEC

Effect conc.:

0.05 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

act. ingr.

Basis for effect:

other: number of cells and growth rate

Duration:

120 h

Dose descriptor:

EC50

Effect conc.:

0.138 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

act. ingr.

Basis for effect:

cell number

Duration:

120 h

Dose descriptor:

EC50

Effect conc.:

0.22 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

act. ingr.

Basis for effect:

growth rate

Details on results:

Insoluble material was not observed in any test vessel during the test. Nominal concentrations of the active ingredient of RH-573 Technical were 0 mg a.i./L (control), 0.050, 0.10, 0.20, 0.40 and 0.80 mg a.i./L. Measured concentrations of RH-573 Technical ranged from 89 to 100% of nominal concentrations at the beginning of the test. Initial measured concentrations were <0.0100 mg a.i./L (control), 0.0503, 0.104, 0.202, 0.407 and 0.708 mg a.i./L. Because all but one of the measured concentrations at 72 hours, and again at 120 hours, were less than 70% of the corresponding nominal values, initial measured concentrations were used for all calculations. Measured concentrations of test substance in the stability blank (established at 0.20 mg a.i./L RH-573 Technical without algae) decreased to 78% and 63% of the nominal concentration after 72 and 120 hours, respectively, indicating that some loss of test substance from solution occurred without the influence of algae. Loss from this solution was not as great as loss in the presence of algae (measured concentrations of test substance in test vessels with a nominal concentration of 0.20 mg a.i./L decreased to 64% and 1.8% of nominal after 72 and 120 hours, respectively).

The algal population in the control vessels grew well, increasing from an average of 10,000 cells per milliliter to an average of 2,337,000 cells/ml after 120 hours of exposure. Water quality throughout the test was within acceptable limits. The range of incubator temperatures was 23.0 to 23.5C and the pH of test media was not affected by the test substance at the beginning of the test.

Exposure of Selenastrum capricornutum to RH-573 Technical for 72 hours resulted in a median effective concentration (EC50 of 0.103 mg a.i./L (95% confidence interval = 0.0693 to 0.152 mg a.i./L) when calculated using the number of cells/ml and of 0.158 mg a.i./L (95% confidence interval = 0.142 to 0.176 mg a.i./L) when calculated using the average specific growth rate. The 72 hour NOEC is 0.0503 mg a.i./L when calculated using either the number of cells/ml or the average specific growth rate.

The exposure of Selenastrum capricornutum to RH-573 Technical for 120 hours resulted in an EC50 of 0.138 mg a.i./L (95% confidence interval = 0.119 to 0.160 mg a.i./L) when calculated using the number of cells/ml and of 0.220 mg a.i./L (95% confidence interval = 0.212 to 0.228 mg a.i./L) when calculated using the average specific growth rate. The 120 hour NOEC is 0.0503 mg a.i./L when calculated using either the number of cells/ml or the average specific growth rate. The slope of the dose-response curve was 5.5 at 120 hours.

The determination of whether toxic effects were algistatic or algicidal was performed at 72 hours and at 120 hours. At each of these times, a 0.5 ml subsample of test media from each flask with an initial measured concentration of 0.407 mg a.i./L RH-573 Technical was combined in a flask with 100 ml of fresh media. After being incubated under test conditions for 168 hours, the algae in the 72 hour flask increased from <10,000 cells/ml to 1,116,000 cells/ml. After being incubated for 144 hours, the algae in the 120 hour flask increased from <10,000 cells/ml to 704,000 cells/ml. These results indicate that the effects of RH-573 Technical at this concentration were algistatic rather than algicical.

Results with reference substance (positive control):

Not applicable

Reported statistics and error estimates:

Both the 72 hour and 120 hour no observed effect level concentration (NOEC) is 0.050 mg a.i./L when calculated using either the number of cells/ml or the average specific growth rate.

Table 1 Nominal/measured concentrations

Nominal	Measured
RH287	0 hour	72 hour	120 hour
0 (control)	ND*	ND	ND
0.05	0.0503	ND	ND
0.10	0.104	0.0193	ND
0.20	0.202	0.127	0.0367
0.40	0.407	0.233	0.235
0.80	0.708	0.685	0.583

             

Table 2 Number of Cells Per Milliliter             

Time Period (Hours)	EC50 (95% Confidence Limits) mg/a.i./L
24	0.615 (0.237 - 0.708)
48	0.103 (0.061 - 0.172)
72	0.103 (0.069 - 0.152)
96	0.135 (0.090 - 0.201)
120	0.138 (0.119 - 0.160)

Table 3 Average Specific Growth Rate

Time Period (Hours)	EC50 (95% Confidence Limits) mg/a.i./L
24	0.089 (<0.050 - 0.238)
48	0.138 (0.120 - 0.158)
72	0.158 (0.142 - 0.176)
96	0.206 (0.203 - 0.209)
120	0.220 (0.212 - 0.228)

Table 4 Cell density data

Test Material	Hours
mg/L	24	48	72	96	120
Control	1.9	10.4	47.6	111.9	233.7
0.05	1.9	9.3	46.3	103.4	230.5
0.10	1.4	6.5	30.8	98.5	177.4
0.20	<1.0	1.3	2.4	12.9	47.7
0.41	<1.1	<1.0	<1.0	<1.0	<1.0
0.71	<1.1	<1.0	<1.0	<1.0	<1.0

Validity criteria fulfilled:

yes

Conclusions:

The exposure of Selenastrum capricornutum to RH-573 technical resulted in a 120-h EC50 of 0.138 mg/l based on number of cells and 0.22 mg/l based on growth rate. Both the 72 hour and 120 hour no observed effect level concentration (NOEC) is 0.050 mg a.i./L when calculated using either the number of cells/ml or the average specific growth rate.

Executive summary:

The toxicity of MIT to Selenastrum capricornutum was examined in a 120 hour study. Algae were exposed to 0, 0.05, 0.10, 0.20, 0.40 and 0.80 mg a.i./L. The exposure of Selenastrum capricornutum to RH-573 technical resulted in a 120-h EC50 of 0.138 mg/l based on number of cells and 0.22 mg/l based on growth rate. Both the 72 hour and 120 hour no observed effect level concentration (NOEC) is 0.050 mg a.i./L when calculated using either the number of cells/ml or the average specific growth rate.

Reference 2

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

21-25 June 2004

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP/Guideline study

Qualifier:

according to guideline

Guideline:

EPA OPPTS 850.5400 (Algal Toxicity, Tiers I and II) (January 2012)

Deviations:

not specified

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Deviations:

not specified

GLP compliance:

yes

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
Not applicable.

Analytical monitoring:

yes

Details on sampling:

Test solution samples were collected from all control and treatment levels at test initiation (0 hour) and test termination (96 hours). At each sample point, 10 ml were collected from each treatment. Quality control fortifications of dilution water (Saltwater algal nutrient medium, SWAM) were prepared at this time. Any dilutons were made with SWAM. The samples were then analyzed by HPLC.

Vehicle:

yes

Details on test solutions:

For the definitive test, a 0.00625 mg a.i./ml primary standard was prepared by dissolving 0.01220 g of 2-Methyl-4-isothiazolin-3-one in 1000 ml of saltwater algal nutrient medium. The test concentrations were prepared individually by diluting appropriate volumes of the primary standard with saltwater algal nutrient medium and transferring aliquots of the resulting solutions to the exposure flasks.

Test organisms (species):

Skeletonema costatum

Details on test organisms:

The parent stock of Skeletonema costatum was obtained from the Department of Botany, Culture Collection of Algae, University of Texas at Austin, on 6 April 2004. The parent stock was identified as Skeletonema costatum. The prepared cultures were maintained in a temperature-controlled environmental chamber under continuous light. Periodically, new Skeletonema cultures were cloned from an existing culture derived from the parent stock. All cultures were maintained under the same conditions as those used for testing. The algal culture used for this test was six days old at test initiation.

Test type:

static

Water media type:

saltwater

Limit test:

no

Total exposure duration:

96 h

Post exposure observation period:

No data

Hardness:

No data

Test temperature:

ranged from 20.6 to 21.8C.

pH:

ranged from 8.0 to 8.8 during the 96 hours

Dissolved oxygen:

No data

Salinity:

No data.

Nominal and measured concentrations:

Nominal concentrations selected for the definitive exposure were 0 (control, 0.0033, 0.0065, 0.013, 0.025, 0.050, and 0.10 mg a.i./l.

Measured concentrations of 2-methyl-4-isothiazolin-3-one concentrations at 0-hour were
All test solutions appeared clear and colorless with no visible particulates, surface film, undissolved test substance or precipitate throughout the duration of the exposure.

Details on test conditions:

The first 96-hour range-finding test was conducted from May 7 to 11, 2004 at nominal concentrations of 0 (control), 0.10, 1.0, 10, 100, and 1000 mg a.i./l. All treatments consisted of two exposure flasks. All test solutions appeared clear and colorless with no visible particulates, suface film, undissolved test substance or precipitate throughout the duration of the exposure. After 96 hours of exposure, percent differences in cell density, as compared to the control, for the 0.10, 1.0, 10, 100 and 1000 mg a.i./l treatments were -83, -100, -100, -100, and -100%, respectively. Based on the findings of this range-finding test, a second range-finding test was deemed necessary.

The second 96-hour range-finding test was conducted from May 14 to 18, 2004 at nominal concentrations of 0 (control), 0.0010, 0.010, and 0.10 mg a.i./l. All treatments consisted of two exposure flasks. All test solutions appeared clear and colorless with no visible particulates, surface film, undissolved test substance or precipitate throughout the duration of the exposure. After 96 hours of exposure, percent differences in cell density, as compared to the control, for the 0.0010, 0.010, and 0.10 mg a.i./l treatments were -6, -43, and -53%, respectively. Based on the results of this range-finding test, nominal concentrations selected for the definitive exposure were 0 (control, 0.0033, 0.0065, 0.013, 0.025, 0.050, and 0.10 mg a.i./l.

For the definitive test, a 0.00625 mg a.i./ml primary standard was prepared by dissolving 0.01220 g of 2-Methyl-4-isothiazolin-3-one in 1000 ml of saltwater algal nutrient medium. The test concentrations were prepared individually by diluting appropriate volumes of the primary standard with saltwater algal nutrient medium and transferring aliquots of the resulting solutions to the exposure flasks. For water quality (temperature and pH) at 72 hours, an additional replicate was prepared in a 100 ml volume. All water quality replicates were maintained under the same temperature and lighting conditions as the flasks described below.

The definitive study was conducted from June 21 to 25, 2004 in 250 ml Erlenmeyer flasks. The flasks were randomly positioned using a computer-generated random number table and incubated for 96 hours at a temperature of 20.0 to 20.4C, based upon a continuous temperature recording. Continuous lighting was provided at an average light intensity of 4571 +/- 95.6 lux. The flasks were hand-swirled at least twice per day throughout the test. Each flask was inoculated with 1.0 ml of an algal concentrate containing approximately 1.0 x 10(6) cells/ml, resulting in a final density of approximately 1.0 x 10(4) cells/ml for each flask. At 24, 48, 72, and 96 (+/-) hours, cell density was measured in replicates A, B, and C in each treatment by direct microscopic counting with a hymacytometer.

At test initiation, temperature and pH were measured in all parent solutions prior to distribution to exposure flasks. At 72 and 96 hours, temperature and pH were measured in replicates D and A of the control and all test substance treatment, respectively. Temperature and pH were measured wiht a Denver Instruments pH meter. A continuous temperature recording of one uninoculated blank flask in the environmental chamber was made using an electronic datalogger with thermistor probe. Light intensity was measured daily with a LI-CO Model LI-189 light meter equipped with a LI-COR photometric sensor.

Reference substance (positive control):

not specified

Duration:

96 h

Dose descriptor:

EC50

Effect conc.:

0.069 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

act. ingr.

Basis for effect:

cell number

Duration:

96 h

Dose descriptor:

EC50

Effect conc.:

0.07 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

act. ingr.

Basis for effect:

biomass

Duration:

96 h

Dose descriptor:

EC50

Effect conc.:

> 0.072 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

act. ingr.

Basis for effect:

growth rate

Details on results:

After 96 hours of exposure, mean cell density in the control was 101 x 10(4) cells/ml, or 101 times the initial inoculum. The coefficient of variation was 6% for the control. The mean cell density in the 2-methyl-4-isothiazolin-3-one treatments ranged from a low of 38 x 10(4) cells/ml at a concentration of 0.0725 mg a.i./l to a high of 109 x 10(4) cells/ml at a concentration of 0.0170 mg a.i./l. Percent inhibition in algal growth ranged from -62% at a concentration of 0.0725 mg a.i./l to +8% at a concentration of 0.0170 mg a.i./l. After 72 and 96 hours of exposure, no statistically significant reduction in cell density was observed at any test substance concentration. After 72 and 96 hours of exposure, a statistically significant reduction in area under the growth curve was observed at the 0.0725 mg a.i./l test substance concentration. After 72 and 96 hours of exposure, no statistically signifcant reduction in growth rate was observed at any test substance concentration.

Results with reference substance (positive control):

No data.

Reported statistics and error estimates:

The 72- and 96-hour EC50's based on cell density, were estimated to be >0.0725 mg a.i./l (95% CL could not be calculated) and 0.0689 mg a.i./l (0.0682- 0.0695 mg a.i./l), respectively. The 72-and 96-hour EbC50's, based on area under the growth curve, were estimated to be 0.0689 mg a.i./l (95% CL = 0.0274 - 0.110 mg a.i./l) and 0.0697 mg a.i./l (95% CL = 0.0688 - 0.0705 mg a.i./l), respectively. The 72- and 96-hour ErC50's, based on growth rate, were both estimated to be >0.0725 mg a.i./l (95% CL could not be calculated). The 72-and 96-hour no-observed-effect concentrations (NOEC) for cell density, area under the growth curve, and growth rate were 0.0725, 0.0358, and 0.0725 mg/l, respectively.

No additional information available.

Validity criteria fulfilled:

yes

Conclusions:

The 72- and 96 -hour EC50 values based on cell density, were estimated to be >0.0725 and 0.0689 mg a.i./l, respectively. The 72- and 96 -hour EC50 values, based on area under the growth curve (EbC50), were estimated to be 0.0689 and 0.0697 mg a.i./l, respectively. The 72 -and 96 -hour EC50 values, based on growth rate (ErC50), were both estimated to be >0.0725 mg a.i./l. The 72- and 96 -hour no-observed-effect concentration (NOEC) for cell density and growth rate was 0.0725 mg a.i./l. The 72- and 96 -hour NOEC for area under the growth curve was 0.0358 mg a.i./l.

Executive summary:

A toxicity test was conducted to evaluate the potential toxicity of 2 -methyl-4 -isothiazolin-3 -one (supplied as a 50% solution in water known as Kordek 573F Industrial Microbiocide) to the marine diatom, Skeletonema costatum. Algal cells were exposed for 96 hours under static conditions to nominal concentrations of 0 (control), 0.0033, 0.0065, 0.013, 0.025, 0.050, and 0.10 mg a.i./l of 2 -methyl-4 -isothiazolin-3 -one (Lot No. 0000454102, purity of 51.252%). The guidelines followed were the US Environmental Protection Agency, Office of Prevention Pesticides and Toxic Substance (OPPTS), Ecological Effects Test Guideline 850.5400 and OECD method 201 of the OECD Guidelines for Testing of Chemicals.

Analytical confirmation of 2 -methyl-4 -isothiazolin-3 -one exposure concentrations was conducted at 0 and 96 hours. Measured concentrations of 2 -methyl-4 -isothiazolin-3 -one concentrations at 0 -hour were <MQL (control), 0.00294, 0.00476, 0.00948, 0.0170, 0.0358, and 0.0725 mg a.i./l which represents 89, 73, 73, 68, 72, and 73% of the nominal treatment concentrations. Measurements at 96 hours indicated that the test substance had degraded over the period of 96 hours. EC50 estimates were based on 0 -hour measured concentrations. All test solutinos appeared clear and colorless with no visible particulates, surface film, undissolved test substance or precipitate throughout the duration of the exposure. Water quality characteristics of temperature and pH were within acceptable limits throughout the exposure.

The 72- and 96 -hour EC₅₀ values based on cell density, were estimated to be >0.0725 and 0.0689 mg a.i./l, respectively. The 72- and 96 -hour EC₅₀ values, based on area under the growth curve (E_bC₅₀), were estimated to be 0.0689 and 0.0697 mg a.i./l, respectively. The 72- and 96 -hour EC₅₀ values, based on growth rate (E_rC₅₀), were both estimated to be >0.0725 mg a.i./l. The 72- and 96 -hour no-observed-effect concentration (NOEC) for cell density and growth rate was 0.0725 mg a.i./l. The 72 -and 96 -hour NOEC for area under the growth curve was 0.0358 mg a.i./l.

Description of key information

the following 2 studies - freshwater and marine algae were identified as key studies.

Freshwater algae - The toxicity of MIT to Selenastrum capricornutum was examined in a 120 hour study. Both the 72 hour and 120 hour no observed effect level concentration (NOEC) is 0.050

mg a.i./L when calculated using either the number of cells/ml or the average specific growth rate. Exposure of Selenastrum capricornutum to RH-573 Technical for 72 hours resulted in a median eff

ective concentration (EC50 of 0.103 mg a.i./L (95% confidence interval = 0.0693 to 0.152 mg a.i./L) when calculated using the number of cells/ml and of 0.158 mg a.i./L (95% confidence interval = 0.142 to 0.176 mg a.i./L) when calculated using the average specific growth rate. The 72 hour NOEC was 0.0503 mg a.i./L when calculated using either the number of cells/ml or the average specific growth rate.

Marine water algae - A toxicity test was conducted to evaluate the potential toxicity of 2 -methyl-4 -isothiazolin-3 -one (supplied as a 50% solution in water known as Kordek 573F Industrial Microbiocide) to the marine diatom, Skeletonema costatum. The 72- and 96 -hour EC50 values based on cell density, were estimated to be >0.0725 and 0.0689 mg a.i./l, respectively. The 72- and 96 -hour EC50 values, based on area under the growth curve (EbC50), were estimated to be 0.0689 and 0.0697 mg a.i./l, respectively. The 72 -and 96 -hour EC50 values, based on growth rate (ErC50), were both estimated to be >0.0725 mg a.i./l. The 72- and 96 -hour no-observed-effect concentration (NOEC) for cell density and growth rate was 0.0725 mg a.i./l. The 72- and 96 -hour NOEC for area under the growth curve was 0.0358 mg a.i./l.

Key value for chemical safety assessment

EC50 for freshwater algae:

0.103 mg/L

EC50 for marine water algae:

0.072 mg/L

EC10 or NOEC for freshwater algae:

0.05 mg/L

EC10 or NOEC for marine water algae:

0.072 mg/L