N-cyclohexylbenzothiazole-2-sulfenamide

Short-term toxicity to fish

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

short-term toxicity to fish

Type of information:

experimental study

Adequacy of study:

key study

Study period:

May 21, 1997 - May 25, 1997

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 203 (Fish, Acute Toxicity Test)

Deviations:

no

GLP compliance:

yes

Analytical monitoring:

yes

Remarks:

HPLC

Details on sampling:

Approximately 1.0 mL of test water was collected from each test tank at the start of the test and 24 hours later and analyzed. In the analysis of the test water, the standard solution (concentration 0.05, 1.0, 4.0 mg/L) was measured every day of sample measurement, and the calibration coefficient was obtained to measure the test substance concentration.

Vehicle:

yes

Remarks:

Hardened castor oil (HCO-40)

Details on test solutions:

Preparation of test solution
- Since the test substance is poorly soluble, a test solution was prepared using hardened castor oil (HCO-40), which is less toxic to medaka.
- A required amount of a test stock solution of a 35 mg/L aqueous solution of the test substance was prepared.
- A control group containing only diluted water was provided.
- An dispersant control group having the maximum concentration (100 mg/L) of the dispersant used was provided.
- The state (appearance, etc.) of the test solution was observed. It was colorless and transparent, and no precipitation was observed.

Test organisms (species):

Oryzias latipes

Details on test organisms:

The body length (scale body length) of the test fish was 2.0 cm ± 0.5 cm.

1) Common name : Himedaka
2) Scientific name : Oryzias latipes
3) Body length : 1.914 cm (1.52～2.21 cm), n = 10
4) Weight : 0.07415 (0.0308～0.1116 g), n = 10
5) Lot number : 970312
6) Purchased by : Rokuoto fish farm
7) Purchased item : March 12, 1997

It was acclimated to breeding for 12 days or more under the same conditions as the test conditions (water quality, temperature, etc.). The diet was fed with commercially available tetramine. No feeding was started 24 hours before the start of exposure. Healthy, macroscopically normal individuals were used in the study. The mortality rate for 7 days before the start of exposure was 0.0%. In addition, the result of the acute toxicity test using the reference substance (copper sulfate (II) pentahydrate, reagent special grade) of the test fish was 0.36 mg/L for 96 hours LC50.

Test type:

flow-through

Water media type:

freshwater

Limit test:

no

Total exposure duration:

96 h

Hardness:

21.8 mg/L (CaCO3 equivalent)

Test temperature:

23.7 to 24.2 °C

pH:

6.7-7.2

Dissolved oxygen:

6.75 to 8.51 mg/L

Salinity:

n.a.

Conductivity:

No data

Nominal and measured concentrations:

0.11 mg/L, 0.22 mg/L, 0.44 mg/L, 0.88 mg/L, 1.75 mg/L and 3.50 mg/L (nominal values)

Details on test conditions:

I. Test conditions
- Exposure method: Running water type (water change rate 5 times/eye)
- Test water temperature: 24+1 °C
- Exposure period: 96 hours
- Number of organisms: 10 fish / concentration group
- Test volume: 3 L
- Number of stations: 1 station per concentration group
- Feeding: None
- Aeration: None
- Illumination: Room light, 16 hours light / 8 hours dark

II. Dilution water
Nagoya city tap water was dechlorinated by passing it through activated carbon. The main water quality of the diluted water was 21.8 mg / L (CaCO3 equivalent) and pH 6.8.

III Test container, constant temperature bath, etc.
- Running water type test equipment : Continuous diluting device using metering pump
- Test container: 3 L glass beake
- Constant temperature bath: Constant temperature water tank and water circulation device (Yamato Scientific Coolline CL100 type)
- Coolant temperature gauge:: pH meter built-in thermometer (HORIBA, Ltd. Castany LAB pH meter F-22
- pH meter: HORIBA, Ltd. Caskuni 1 LAB pH meter F-22
- Dissolved oxygen meter: Toa Denpa DO METER DO-14P

IV Test concentration setting
As a result of the preliminary test, the 96-hour median lethal concentration (LC50) was 1.5 mg/L or more. With reference to this result, in this study, the concentration ratio was 2.0. Six test concentrations of 0.11 mg/L, 0.22 mg/L, 0.44 mg/L, 0.88 mg/L, 1.75 mg/L and 3.50 mg/L were prepared.

Reference substance (positive control):

yes

Remarks:

Copper sulfate (H) pentahydrate, reagent special grade

Key result

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

2.13 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Remarks on result:

other: 95 % confidence limit: 1.63 mg/L to 3.02 mg/L

Details on results:

The concentration of the test substance in the test water was measured at the start of the test and 24 hours later. The concentration of the test substance at the start of the test was 0.041～3.10 mg/L, and the concentration of the test substance 24 hours after the start of the test was 0.036～3.09 mg/L. The ratio of the measured concentration to the nominal concentration (0.11～3.50 mg/L) was 32.6～88.6%. Since the measured concentration exceeded ± 20% of the set concentration, all test results were expressed as the arithmetic mean value of the measured concentration.

Results with reference substance (positive control):

The result of the acute toxicity test using the reference substance (copper sulfate (II) pentahydrate, reagent special grade) of the test fish was 0.36 mg/L for 96 hours LC50.

Validity criteria fulfilled:

yes

Conclusions:

The mortality to fish was investigated in a flow-through GLP study following OECD 203. After 96 hours exposure, the median lethal concentration (LC50) based on measured concentration was 2.13 mg/L or more (95 % confidence limit: 1.63 mg/L to 3.02 mg/L).

Executive summary:

This test is based on the OECD Guidelines for Testing of Chemicals No. It was conducted in accordance with 203 “Fish Toxicity Test" (1992). For N-Cyclohexyl-2-benzothiazolylsulphenamide, an acute toxicity test against medaka (Oryzias latipes) was performed to determine the median lethal concentration (LC50) for 96 hours under flow through exposure conditions. At the start of exposure, the weight and scale length of 10 fish acclimatized in the same tank as the test fish were measured. No feeding was done during the dew. After measuring the pH, dissolved oxygen concentration, and water temperature of the test solution in each test container, 10 fish under test were placed in the test container per concentration group. The pH, dissolved oxygen concentration and water temperature were measured once daily during the exposure period. Deaths were recorded 24, 48, 72 and 96 hours after the start of exposure and any signs or abnormalities of toxicity observed were recorded. Other specific cases (bending of the back, bleeding, change in body color, secretion of mucus, etc.) are described separately when observed. When dead individuals were found, they were promptly removed to prevent deterioration of water quality. As a result of the preliminary test, the 96-hour median lethal concentration (LC50) was 1.5 mg/L or more, the maximum 0% mortality concentration was 0.60 mg/L, and the minimum 100% mortality concentration was 1.5 mg/L or more. With reference to this result, in this study, the concentration ratio was 2.0. Six test concentrations of 0.11 mg/L, 0.22 mg/L, 0.44 mg/L, 0.88 mg/L, 1.75 mg/L and 3.50 mg/L were prepared. After 96 hours exposure, the median lethal concentration (LC50) based on measured concentration was 2.13 mg/L or more. The mortality rate for 7 days before the start of exposure was 0.0%. In addition, the result of the acute toxicity test using the reference substance (copper sulfate (II) pentahydrate, reagent special grade) of the test fish was 0.36 mg/L for 96 hours LC50. This toxicity study is classified as acceptable and satisfies the guideline requirements for the acute fish toxicity study.

Reference 2

Endpoint:

short-term toxicity to fish

Remarks:

prolonged test 14 days

Type of information:

experimental study

Adequacy of study:

key study

Study period:

June 4, 1997 to June 18, 1997

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 204 (Fish, Prolonged Toxicity Test: 14-day Study)

Deviations:

no

GLP compliance:

yes

Analytical monitoring:

yes

Remarks:

HPLC

Details on sampling:

At the start (day 0), on the 2nd, 5th, 8th, 12th and 14th days, 1.0 mL of test water was collected from each test tank and analyzed. The standard solution (0.010, 0.10, 0.50, 2.00, 3,000 mg/L) was measured every day of sample measurement, and the calibration coefficient was obtained from the standard solution to measure the concentration of the test substance.

Vehicle:

yes

Remarks:

Hardened castor oil (HCO-40)

Details on test solutions:

Preparation of test solution
1) Since the test substance is poorly soluble, a stock solution of the test substance was prepared using hardened castor oil (HCO-40), which is less toxic to medaka. The prepared stock solution was colorless and
transparent, and no insoluble matter was found.
2) A test solution was prepared by mixing 3.0 mg/L or 30 mg/L of the test substance supply solution and diluted water with a continuous diluting device.
3) Since this test substance decomposes to about half at room temperature in an aqueous solution state, the feed solution was stored in a refrigerator and reprepared daily.
4) A control group containing only diluted water was provided.
5) A dispersant control group was provided in which the highest concentration (100.0 mg/L) of the dispersant used was added to the diluent.

Test organisms (species):

Oryzias latipes

Details on test organisms:

The body length (scale body length) of the test fish was 2.0 cm ± 0.5 cm.

1) Common name : Himedaka
2) Scientific name : Oryzias latipes
3) Body length : 1.910 cm (1.53～2.26 cm), n = 10
4) Weight : 0.0859 (0.0344～0.1321 g), n = 10
5) Lot number : 970312
6) Purchased by : Rokuoto fish farm
7) Purchased item : March 12, 1997

Under the same conditions (water quality, temperature, etc.) as the critical test conditions, the animals were habituated for 12 hours or more. The diet was fed with commercially available tetramine. No feeding was started 24 hours before the start of exposure. Healthy, macroscopically normal individuals were used in the study. The mortality rate for 7 days before the start of exposure was 0.0%. In addition, the result of the acute toxicity test using the reference substance (copper sulfate (II) pentahydrate, reagent special grade) of the test fish was 0.36 mg/L for 96 hours LC50.

Test type:

flow-through

Water media type:

freshwater

Limit test:

no

Total exposure duration:

14 d

Hardness:

23.8 mg/L (CaCO3 equivalent)

Test temperature:

23.9 to 24.3 °C

pH:

6.9 to 7.2

Dissolved oxygen:

6,37-8.48 mg / L
Saturated dissolved oxygen concentration at 24.0 °C: 8. 25 mg/L

Salinity:

n.a.

Conductivity:

No data

Nominal and measured concentrations:

Test concentration (n): 0.16, 0.29, 0.51, 0.93, 1.67, and 3.00 mg/L

Details on test conditions:

I. Test conditions
- Exposure method: Flow through (using a continuous dilution device using a metering pump)
- Exposure period: 14 days
- Number of stations: 1 station per concentration group
- Number of organisms: 10 fish / concentration group
- Test aquarium: Constant temperature water tank
- Test water temperature: 24+2 °C
- Feeding: Commercially available tetramine was given daily at 2% of fish body weight
- Aeration: None

II. Dilution water
Nagoya city tap water was dechlorinated by passing it through activated carbon. The main water quality of the diluted water was 23.8 mg/L (CaCO3 equivalent) and pH 6.9.

III. Test container, constant temperature bath, etc.
- Running water type test equipment: Continuous diluting device using metering pump
- Test container: 3L glass beake
- Constant temperature bath: Constant temperature water tank and water circulation device (Yamato Scientific Coolline CL100 type)
- Coolant temperature gauge: pH meter built-in thermometer (HORIBA, Ltd. Castany LAB pH meter F-22
- pH meter: HORIBA, Ltd. Caskuni 1 LAB pH meter F-22
- Dissolved oxygen meter: Toa Denpa DO METER DO-14P

IV. Test concentration setting
As a result of the acute toxicity test, the median lethal concentration (LC50) was 2.13 mg/L. The maximum 0% mortality concentration and the minimum 100% mortality concentration were 0.45 mg/L and 2.95 mg/L, respectively. Therefore, in this test, 6 concentration groups of 0.16, 0.29, 0.51, 0.93, 1.67, and 3.00 mg/L were set at a common ratio of 1.8.

Reference substance (positive control):

yes

Remarks:

copper sulfate (II) pentahydrate (reagent special grade)

Key result

Duration:

14 d

Dose descriptor:

LC50

Effect conc.:

0.78 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Remarks on result:

other: 95% confidence limit: 0.51 mg/L～1.31 mg/L

Key result

Duration:

14 d

Dose descriptor:

NOEC

Effect conc.:

0.14 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Details on results:

Toxic symptoms and feeding status
- Decreased food intake was seen in the 0.67, 1.24 and 2.84 mg/L (measured) concentrations.
- Swimming incompetence was observed in the 1.24 and 2.84 mg/L (measured value) concentration groups.
- No abnormal symptoms were observed during the test period in the lower concentration group and the control group.

Results with reference substance (positive control):

The result of the acute toxicity test using the reference substance (copper sulfate (II) pentahydrate, reagent special grade) of the test fish was 0.36 mg/L for 96 hours LC50.

Validity criteria fulfilled:

yes

Conclusions:

The mortality of N-Cyclohexyl-2-benzothiazolylsulphenamidel (95-33-0) to fish was investigated in a flow-through GLP study following OECD 204. After 14 days of exposure, the median lethal concentration (LC50) was 0.78 mg/L and the NOEC was 0.14 mg/L. The above concentrations are all based on the arithmetic mean of the measured concentrations.

Executive summary:

This test is based on the OECD Guidelines for Testing of Chemicals No. It was conducted in accordance with 204 “Fish Toxicity Test" (1992). For N-Cyclohexyl-2-benzothiazolylsulphenamide, an prolonged toxicity test on medaka (Oryzias latipes) is conducted for 14 days to determine the threshold value and maximum no action concentration (NOEC) of lethality and other observed effects on medaka. At the start of exposure, the weight and scale length of each of the 10 fish acclimatized in the same tank as the test fish were measured, and it was confirmed that the scale length was 2.0 ± 0.5 cm. After measuring the pH, dissolved oxygen concentration, and water temperature of the test solution in each test tank, 10 fish to be tested were put into the test tank per concentration group. After the start of exposure, the water temperature, pH, and dissolved oxygen concentration of the test solution in each test tank were measured three times a week. During the exposure period. Food was given 2% of the individual weight per fish. If the population decreased due to death, the amount of feed was reduced accordingly. Daily deaths were recorded and observed signs of toxicity or abnormalities were recorded after the start of exposure. When dead individuals were found, they were promptly removed to prevent deterioration of water quality. At the end of exposure, the weight and scale length of all surviving fish were measured and recorded. As a result of the acute toxicity test, the median lethal concentration (LC50) was 2.13 mg/L. The maximum 0% mortality concentration and the minimum 100% mortality concentration were 0.45 mg/L and 2.95 mg/L, respectively. Therefore, in this test, 6 concentration groups of 0.16, 0.29, 0.51, 0.93, 1.67, and 3.00 mg/L were set at a common ratio of 1.8. After 14 days of exposure, the median lethal concentration (LC50) was 0.78 mg/L and the NOEC was 0.14 mg/L. The above concentrations are all based on the arithmetic mean of the measured concentrations. The result of the acute toxicity test using the reference substance (copper sulfate (II) pentahydrate, reagent special grade) of the test fish was 0.36 mg/L for 96 hours LC50. This toxicity study is classified as acceptable and satisfies the guideline requirements for the prolonged fish toxicity study.

Reference 3

Endpoint:

short-term toxicity to fish

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 203 (Fish, Acute Toxicity Test)

Deviations:

no

Principles of method if other than guideline:

continuous flow conditions

GLP compliance:

not specified

Analytical monitoring:

yes

Vehicle:

yes

Details on test solutions:

stock solution: 10 g test substance in 100 ml N,N-dimethylformamide (DMF)
The concentration has been confirmed by analytics.

Test organisms (species):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Details on test organisms:

Juveline rainbow trout were obtained from Mt. Lassen Trout Farm and maintained at SRI for at last two weeks prior testing.

Test type:

flow-through

Water media type:

freshwater

Limit test:

no

Total exposure duration:

13 d

Hardness:

28 mg/L CaCO3

Test temperature:

13 °C

pH:

7.1 - 8.6

Dissolved oxygen:

mean 8.9 mg/L

Nominal and measured concentrations:

Nominal Concetrations tested (mg/L): 0; 0.9; 1.9; 3.8; 7.5; and 15
Only samples (n=6) from the highest concentrations were taken for chemical analysis, and the measured concentrations were below the level of detection, which probably contained less than 1 mg/L Thiofide.

Sublethal observations / clinical signs:

No mortalities related to the toxicant occured in fish exposed to Thiofide at the highest nominal concentrations (15 mg/L) tested. However, all samples from highest concentration were below the detection level and probably contained less than 1 mg/l test substance. Because the actual stock concentraitons agreed very well with the nominal concentrations and syringe pumps and diluter were functioning properly, the test substance must have entered the test system at close to nominal levels. The water in test vessels were observed to be slightly cloudy in the highest concentration, and hence the test substance is suspected to be not fully soluble under the test temperature 13 °C (water solubility at 25 °C: 0.27 -0.37 mg/L). The result can be interprated as LC0 higher than the water solubility of the MBTS at 13 °C.

Validity criteria fulfilled:

not specified

Conclusions:

No acute toxicity of MBTS was observed to Oncorhynchus mykiss up to its water solubility (<1mg/L) during 96 hours exposure in a flow-through system according to OECD Guideline 203 (Monsanto, 1981).

Executive summary:

No acute toxicity of MBTS was observed to Oncorhynchus mykiss up to its water solubility (<1mg/L) during 96 hours exposure in a flow-through system according to OECD Guideline 203 (Monsanto, 1981).

Reference 4

Endpoint:

short-term toxicity to fish

Type of information:

experimental study

Adequacy of study:

other information

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

secondary literature

Remarks:

EU-RAR Document

Principles of method if other than guideline:

EU-risk assessment

GLP compliance:

not specified

Sublethal observations / clinical signs:

A flow-through test on the acute toxicity of BT to Pimephales promelas was conducted by Geiger et al. (1990). The fish were exposed in Lake Superior water to 5 test substance concentrations in the range of 27.7 to 155 mg/l. Analytical measurements revealed that the applied concentrations were >80% of the nominal during the test period. Based on measured concentrations a 96h-LC50 of 64 mg/l was obtained. The affected fish lost schooling behaviour, were hypoactive and underreactive to external stimuli, were darkly coloured and lost equilibrium prior to death. Considering these sub-lethal effects, a 96h-EC50 of 60.7 mg/l was determined.

Evans et al. (2000) tested lethal and sublethal effects of BT on larvae of sheepshead minnow (Cyprinodon variegatus). The fish were exposed over 5 days to 5 concentrations in the range of 3.7 to 60.0 mg/l. The 96h-LC50 value was calculated to 53 mg/l. Significant decreases in larval growth were noted at all exposure concentrations, the weight ranged from 53.6 to 64.9% of control. It has to be noted that larval growth was not dependent to the applied test substance concentrations. Analytical measurements were not performed, because of the volatility of BT the effective concentrations are expected to be lower.

A flow-through test on the acute toxicity of BT to juvenile Oncorhynchus mykiss was carried out by SRI International (1981). No standard guideline was applied but the study is adequately documented. The measured test concentrations were 0 mg/l, 1.6 mg/l, 4.4 mg/l. 8.1 mg/l, 14.9 mg/l and 22.9 mg/l and the duration altogether 14 days. The measured concentrations were over 95 % of the nominal concentrations. For each dose level and controls two test tanks were run with 10 fish each. Temperature varied between 13.0-14.0 ºC, Hardness was 28 mg CaCO3 /l, alkalinity 29 mg CaCO3/l and the pH varied during the test between 6.8 and 8.2. In the control tanks, no mortality was observed. Oxygen concentration varied between 9.4 and 10.8 mg/l. The fish were adapted to the test conditions for two weeks prior to test. A LC50 of 8.1 mg/l at 96 h and a LC50 of 5.6 mg/l at day 14 resulted.

The table below presents an overview of the studies which are considered plausible. In addition to the tests prescribed above, four such static acute fish tests are available where mortality was observed as the endpoint and only nominal concentrations were reported. These tests are also presented in brief in the table below. It should be noted, that their validity is questionable while test concentrations may be < 80% of the nominal concentrations.

Species	Test type	Exposure time	Effect conc.	Reference
Pimephales promelas	flow-through	96 h	LC50 = 64.0 mg/l (e) EC50 = 60.7 mg/l (e)	Geiger et al. (1990)
Brachydanio rerio	Static	96 h	LC0 = 65.5 mg/l (n) LC100 = 66.0 mg/l (n)	Bayer AG (1984)
Oryzias latipes	Static	48 h	LC50 = 87.2 mg/l (e)	MITI (1992)
Cyprinodon variegatus	Static or semi-static	96 h	LC50 = 53 mg/l (n)	Evans et al. (2000)
Cyprinodon variegatus	Static	96 h	LC50 = 36 mg/l (n)	Analytical Bio-Chemistry Laboratories, Inc. (1985)
Oncorhynchus mykiss	flow-through	96 h	LC50 = 8.1mg/l (e)	SRI International (1981)
Oncorhynchus mykiss	flow-through	14 d	LC50 = 5.6 mg/l (e)	SRI International (1981)
Pimephales promelas	Static	96 h	LC50 = 47 mg/l (n)	Analytical Bio-Chemistry Laboratories, Inc. (1980)

(n): nominal concentrations; (e) effective concentrations.

Validity criteria fulfilled:

not specified

Executive summary:

A flow-through test on the acute toxicity of BT to Pimephales promelas was conducted by Geiger et al. (1990). The fish were exposed in Lake Superior water to 5 test substance concentrations in the range of 27.7 to 155 mg/l. Analytical measurements revealed that the applied concentrations were >80% of the nominal during the test period. Based on measured concentrations a 96h-LC50 of 64 mg/l was obtained. The affected fish lost schooling behaviour, were hypoactive and underreactive to external stimuli, were darkly coloured and lost equilibrium prior to death. Considering these sub-lethal effects, a 96h-EC50 of 60.7 mg/l was determined.

Evans et al. (2000) tested lethal and sublethal effects of BT on larvae of sheepshead minnow (Cyprinodon variegatus). The fish were exposed over 5 days to 5 concentrations in the range of 3.7 to 60.0 mg/l. The 96h-LC50 value was calculated to 53 mg/l. Significant decreases in larval growth were noted at all exposure concentrations, the weight ranged from 53.6 to 64.9% of control. It has to be noted that larval growth was not dependent to the applied test substance concentrations. Analytical measurements were not performed, because of the volatility of BT the effective concentrations are expected to be lower.

A flow-through test on the acute toxicity of BT to juvenile Oncorhynchus mykiss was carried out by SRI International (1981). No standard guideline was applied but the study is adequately documented. The measured test concentrations were 0 mg/l, 1.6 mg/l, 4.4 mg/l. 8.1 mg/l, 14.9 mg/l and 22.9 mg/l and the duration altogether 14 days. The measured concentrations were over 95 % of the nominal concentrations. For each dose level and controls two test tanks were run with 10 fish each. Temperature varied between 13.0-14.0 ºC, Hardness was 28 mg CaCO3 /l, alkalinity 29 mg CaCO3/l and the pH varied during the test between 6.8 and 8.2. In the control tanks, no mortality was observed. Oxygen concentration varied between 9.4 and 10.8 mg/l. The fish were adapted to the test conditions for two weeks prior to test. A LC50 of 8.1 mg/l at 96 h and a LC50 of 5.6 mg/l at day 14 resulted.

The table below presents an overview of the studies which are considered plausible. In addition to the tests prescribed above, four such static acute fish tests are available where mortality was observed as the endpoint and only nominal concentrations were reported. These tests are also presented in brief in the table below. It should be noted, that their validity is questionable while test concentrations may be < 80% of the nominal concentrations.

Reference 5

Endpoint:

short-term toxicity to fish

Type of information:

experimental study

Adequacy of study:

other information

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

secondary literature

Remarks:

EU-RAR Document

Principles of method if other than guideline:

EU-risk assessment

GLP compliance:

not specified

Validity criteria fulfilled:

not specified

Executive summary:

Static tests on the acute toxicity to Brachydanio rerio and Pimephales promelas resulted in 96h-LC50 values of 1.6 mg/l for B. rerio (geometric mean of LC0 and LC100) and 11 mg/l for P. promelas (Bayer AG, 1988; Monsanto, 1979). The results should be interpreted with caution because no analytical monitoring was performed and the test substance concentrations were probably not stable due to photolytical degradation of MBT during the test period.

A flow-through test to juvenile Oncorhynchus mykiss was conducted by Monsanto (1981). The fish were exposed to nominal concentrations between 0.06 and 1.00 mg/l, the flow rate was set to provide five tank volumes per day. The analytical control (RP-LC) suggest that, except for the lowest concentration of 0.06 mg/l, agreement between nominal and actual test concentrations was reasonable good. The test was terminated after 8 days of exposure, at which time no death had occurred for three consecutive days. The resulting LC50 values (based on measured concentrations) were 0.73 mg/l after 4 days and 0.67 mg/l after 8 days. The authors interpreted the relatively small increase in mortality between 4 and 8 days and the fact that no death occurred on day 6-8 suggest that the material does not show substantial cumulative toxicity under conditions of acute exposure.

Description of key information

The acute toxicity and the prolonged toxicity of CBS to fish (Oryzias latipes) were tested according to OECD TG 203 "Fish, acute toxicity test" and OECD TG 204 "Fish, prolonged toxicity test: 14-day Study", respectively. After 96 hours of exposure a LC50 of 2.1 mg/L was obtained for acute effect and after 14 days of exposure a LC50 of 0.78 mg/L and a NOEC of 0.14 mg/l were obtained for prolonged effect (MOE Japan, 1997). For both studies effect concentratinos are based on arithmethic means of measured CBS concentrations. The studies were conducted under flow through test conditions.
CBS is rapidly degraded by hydrolysis and benzothiazole (BT) is the main degradation product appearing during the time frame of acute tests. The most sensitive results of the acute toxicity of BT to fish (96h-LC50=8.1 mg/l) and the prolonged toxicity of BT to fish (14d-LC50=5.6 mg/l) are reported by SRI International (1981) using a flow-through sys-tem with Oncorhynchus mykiss.
Some further data are available for another main metabolite from CBS, like MBT and MBTS. The most sensitive results of the toxicity of MBT to fish (4d-LC50=0.73 mg/l and 8d-LC50=0.67 mg/l) are reported by Monsanto (1981) using a flow-through system with Oncorhynchus mykiss. For MBTS no toxic effect was observed to fish (Oncorhynchus mykiss) up to its water solubility (Monsanto, 1981).
Regarding the data summarized here, the described metabolites of CBS are less toxic to fish than CBS itself.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Dose descriptor:

LC50

Remarks:

prolonged effect, 14 d

Effect concentration:

0.78 mg/L

Additional information

A hydrolysis half-life time of CBS of 13.4 h was observed in deionized water at pH 7.0 and at 20°C (Currenta 2022). In the key studies (acute and prolonged, MOE Japan, 1997) for both studies effect concentratinos are based on arithmethic means of measured CBS concentrations. The studies were conducted under flow through test conditions. The reported LC50 is higher than the water solubility of CBS (i.e. 0.32 mg/l). In both studies hardened castor oil (HCO-40) was used as a vehicle.

 

Two Monsanto studies from 1979 with Pimephales promelas and from 1976 with Salmo gairdneri and Lepomis macrochirus are considered as invalid. The reason for Monsanto (1979) is the lack of analytical monitoring and the observable precipitation. The reason for Monsanto (1976) is the lack of aeration inducing that the oxygen saturation at the end of the study was less than 30%.