Desmedipham

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

2011-11-28 to 2012-09-07

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

Version / remarks:

2004

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 850.1010 (Aquatic Invertebrate Acute Toxicity Test, Freshwater Daphnids)

Version / remarks:

1996

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: ASTM Standard E729-96

Version / remarks:

2007 - ASTM Standard E729-96: Standard Guide for Conducting Acute Toxicity Tests on Test Materials with Fishes, Macroinvertebrates and Amphibians

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

The test material is in a solid form.

Analytical monitoring:

yes

Details on sampling:

Samples were collected from one test chamber of each treatment and control group four days prior to the start of the test after conditioning the diluter for approximately one and four days, respectively. Samples also were collected from alternating replicate test chambers in each treatment and control group at the beginning of the test and at 3, 24 and 48 hours (±1 hour) to measure concentrations of the test substance. The samples were collected from mid-depth, placed in glass vials, and processed immediately for analysis.

Vehicle:

yes

Remarks:

dimethylformamide

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Differential loading: The five test substance stock solutions were injected into the diluter mixing chambers at a rate of 3.10 µL/minute where they were mixed with dilution water delivered at a rate of 155 mL/minute to achieve the desired test concentrations.
- Controls: Negative control (dilution water only) and positive control (acidified HPLC-grade DMF)
- Other relevant information: All test solutions were adjusted to 100% active ingredient during preparation, based on the test substance purity (99.5%). Prior to stock solution preparation, HPLC-grade dimethylformamide (DMF) was acidified using 10% phosphoric acid to stabilize the test substance. The negative control received dilution water only. The solvent control was prepared by delivering acidified HPLC-grade DMF to the mixing chamber for the solvent control. The concentration of DMF in the solvent control and all desmedipham treatment groups was 0.02 mL/L, or 0.002% of DMF in the test solution at any given time.

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Common name: Daphnia magna
- Justification for species other than prescribed by test guideline: The cladoceran, Daphnia magna, was selected as the test species for this study. This species is representative of an important group of aquatic invertebrates and were selected for use in the test based upon past history of use in the laboratory.
- Age at study initiation (mean and range, SD): Daphnid neonates used in the test were less than 24 hours old.

METHOD FOR PREPARATION AND COLLECTION OF EARLY INSTARS OR OTHER LIFE STAGES, INCLUDING CULTURING CONDITIONS
The 5 adult daphnids used to supply neonates for the test were held for 20 days prior to collection of the juveniles for testing, and had each produced at least one previous brood. The adults were fed daily, a mixture of yeast, cereal grass media and trout chow (YCT), as well as a suspension of the freshwater green alga, Pseudokirchneriella subcapitata prior to test initiation. Adult daphnids in the culture had produced an average of at least three young per adult per day over the 7-day period prior to the test. The adults showed no signs of disease or stress and no ephippia were produced during the holding period. At test initiation, the juvenile daphnids were collected from the cultures and indiscriminately transferred one or two at a time to transfer chambers until each chamber contained 10 daphnids. Each group of daphnids then was transferred to the test compartment in an indiscriminately assigned test chamber to initiate the test. All transfers were made below the water surface using wide-bore pipettes.

Test type:

flow-through

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Remarks on exposure duration:

Exposed over 48 hours with observations carried out at regular intervals. Observations were made approximately 2, 24 and 48 hours after test initiation.

Hardness:

140 (mg/L as CaCO3)

Test temperature:

19.8 - 20.0°C

pH:

8.0 - 8.1

Dissolved oxygen:

7.6 - 8.4 mg/L

Salinity:

178 (mg/L as CaCO3)

Nominal and measured concentrations:

Nominal test concentrations: 0.13, 0.25, 0.50, 1.0, and 2.0 mg a.s./L, alongside a dilution water control and a solvent control (0.02 mL/L dimethylformamide).
Mean measured concentrations : 0.13, 0.24, 0.45, 0.82, and 1.1 mg a.s./L

Details on test conditions:

TEST SYSTEM
- Test vessel: 25-L Teflon-lined stainless steel aquaria filled with approximately 22 L of test water
- No. of organisms per vessel: 10 daphnids in each test chamber,
- No. of vessels per concentration (replicates): Two replicate test chambers
- No. of vessels per control (replicates): Two replicate test chambers

OTHER TEST CONDITIONS
- Photoperiod: 16 hours of light and 8 hours of darkness
- Light intensity: 738 Lux

Key result

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

> 0.33 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mobility

Details on results:

Measurement of Test Concentrations
Nominal concentrations selected for use in this study were 0.13, 0.25, 0.50, 1.0 and 2.0 mg a.s./L. During the course of the test, the appearance of the test solution at these nominal concentrations was observed in the test chambers, as well as in the diluter mixing chambers, where test substance stocks and dilution water were combined prior to delivery to the test chambers. The test solutions appeared clear and colorless, with no evidence of precipitation observed during the test, in the negative control, solvent control, 0.13 to 0.25 mg a.s./L test chambers, and in the diluter mixing chambers that delivered test solution for these concentrations. After conditioning the diluter test system for five days, white precipitate was observed in the diluter mixing chambers that delivered test solution for the 0.50 to 2.0 mg a.s./L test concentrations. Later, at test initiation, white precipitate was also noted in the test chambers for these test concentrations, increasing in amount with an increase in concentration. This white precipitate was also observed at study termination for the 0.50 to 2.0 mg a.s./L test concentrations in both the mixing and test chambers. This demonstrates that under these testing conditions, the functional limit of solubility is approximately 0.25 mg a.s./L. Due to the presence of a precipitate in the 0.50 to 2.0 mg a.s./L test chambers, all samples were centrifuged prior to analysis. The results of the study were based on the centrifuged mean measured concentrations.

Results of analyses to measure concentrations of desmedipham and EHPC in the pretest diluter verification samples are presented in Table 2 and Appendices 6 to 7. Combined (desmedipham and EHPC) measured concentrations of the samples ranged from approximately 46 to 100% of nominal. The recoveries of the metabolite of desmedipham (EHPC) were stoichiometrically converted to the desmedipham equivalent by dividing the measured concentration of EHPC by 0.6. Mean measured test concentrations of EHPC (after conversion) for this study were 0.088, 0.16, 0.31, 0.55 and 0.77 mg a.s./L, representing 67.9, 65.7, 62.2, 55.1 and 38.4% of nominal, respectively. Mean measured test concentrations of desmedipham were 0.040, 0.077, 0.14, 0.27 and 0.33 mg a.s./L, representing 30.4, 30.9, 28.2, 27.3 and 16.5% of nominal, respectively. To give overall accountability of the test substance, the total amount of desmedipham and the converted EHPC recoveries were added together to give a combined measured concentration. Results of analyses to measure concentrations of desmedipham and EHPC in the test solution samples collected during the test are presented in Table 3 and Appendices 8 to 9. When measured concentrations of the samples collected during the test were averaged, the mean measured test concentrations of desmedipham and EHPC combined for this study were 0.13, 0.24, 0.45, 0.82 and 1.1 mg a.s./L, representing 100, 96.0, 90.0, 82.0 and 55.0% of nominal concentrations, respectively. Samples were analyzed with and without centrifugation for all sampling intervals during the test. The results of the non-centrifuged analyses are presented in Appendices 10 to 11.

Observations and Measurements
Measurements of temperature, dissolved oxygen and pH of the water in the test chambers are presented in Table 4. Water temperatures were within the 20 ± 1°C range established for the test. Dissolved oxygen concentrations remained =7.6 mg/L (=84% of saturation) throughout the test. Measurements of pH ranged from 8.0 to 8.1. The measurements of hardness, alkalinity, specific conductance and TOC in the dilution water at test initiation were typical of Wildlife International, Ltd. well water (Table 5). Light intensity at test initiation was 738 lux at the surface of the water of one representative test chamber.

Daily observations for immobility and signs of toxicity during the test are presented in Table 6. Daphnia in the negative and solvent control groups appeared normal throughout the test. All daphnids in the 0.13 through 0.45 mg a.s./L treatment group also appeared normal throughout the test, with no immobility or overt signs of toxicity observed. Daphnids in the 0.82 mg a.s./L treatment group appeared normal with the exception of the two daphnids that appeared lethargic at the 24-hour observation interval. Percent immobility at test termination in the 1.1 mg a.s./L treatment group was 40%. The surviving daphnids in the 1.1 mg a.s./L treatment group appeared normal throughout the test, with the exception of four lethargic daphnids noted at test termination. The no-immobility concentration and the NOEC were 0.82 and 0.45 mg a.s./L, respectively. EC50 values at 24 and 48 hours were determined from the immobility data and are shown in Table 7.

See "Attachments" in "Overall remarks, attachments" for the tables and appendixes;

Validity criteria fulfilled:

yes

Conclusions:

The study fulfils the validity criteria set in the OECD TG 202 (1992); mortality in the controls <10% and dissolved oxygen = 3 mg/L. Since the metabolite EHPC is clearly less toxic than the parent the toxicity can be attributed to the active substance. Therefore, the study can be considered valid and a 48-hour EC50 value of >1.1 mg a.s./L was obtained based on mean measured test concentrations of sum of parent and metabolite. A 48-hour EC50 value of >0.33 mg a.s./L was obtained based on arithmetic mean measured concentrations of desmedipham.

The cladoceran, Daphnia magna, was exposed for 48 hours under flow-through conditions to five mean measured concentrations of the test item ranging from 0.13 to 1.1 mg a.s./L. White precipitate was present in the test solutions for both the mixing and test chambers in the 0.45, 0.82 and 1.1 mg a.s./L treatment groups. In this diluter test system, the functional limit of solubility was demonstrated to be 0.24 mg a.s./L. As evident in the precipitate in the three highest treatment groups, the test was conducted above the functional limit of solubility. Based upon the active substance desmedipham, the 48-hour EC50 value was >0.33 mg a.s./L, the highest concentration tested. Based upon the total concentration of desmedipham and its major metabolite EHPC, the 48-hour EC50 was >1.1 mg/L. Daphnids exposed to desmedipham at concentrations =0.45 mg a.s./L (=0.14 mg a.s./L for desmedipham only) appeared normal with no immobility or overt signs of toxicity. The 48-hour no-immobility concentration, NOEC and LOEC were 0.82, 0.45 and 0.82 mg a.s./L (0.27, 0.14 and 0.27 mg a.s./L for desmedipham only), respectively.

Executive summary:

The acute toxicity of Desmedipham Technical to Daphnia magna was determined under flow-through conditions.  Daphnids were exposed to nominal concentrations of 0.13, 0.25, 0.50, 1.0 and 2.0 mg a.s./L, alongside a dilution water control and a solvent control.  Based on mean measured desmedipham concentration, the 48-hour EC₅₀ was > 0.33 mg a.s./L.

Reference 2

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1995-10-24 to 1996-06-13

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

Version / remarks:

1989

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPP 72-2 (Aquatic Invertebrate Acute Toxicity Test)

Version / remarks:

1982

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

The test material is in a beige powder form.

Analytical monitoring:

yes

Details on sampling:

Samples of all replicates were taken at test initiation (Day 0), prior to addition of the daphnids, and at test termination (48 hours). Samples were preserved with one drop of phosphoric acid per 10 ml of sample volume at the time of collection. Desmedipham and EHPC were measured by HPLC.

Vehicle:

yes

Remarks:

Acetone (0.1 mL/L)

Details on test solutions:

Test solutions were prepared from a stock solution and delivered to duplicate test chambers via a proportional diluter. A concentrated stock solution of desmedipham technical in acetone was prepared by adding 1.6 grams of test material to 50 mL of acetone. Approximately five minutes before each diluter cycle, 0.25 mL of the stock solution was injected with a syringe pump into approximately 2.5 L of dilution water in the diluter mix box. This solution was allowed to mix via a magnetic stirrer using a Teflon stir bar until the diluter cycled. The proportional diluter is a modified Mount and Brungs8 diluter with solenoid valves. Materials of construction include Teflon, polyethylene, glass, and silicone rubber sealant. The diluter was calibrated prior to, and verified after testing. The diluter cycled approximately 48 cycles per day, at intervals of approximately 30 minutes between cycles. The diluter delivered approximately 250 mL of test solution per replicate chamber per cycle, or approximately 0.83 volume additions per cycle and approximately 40 volume additions per day. In order to provide a maximum diluter cycle rate, the splitter cups were modified to deliver approximately 23% of the total volume of test solution to each of the replicate chambers. The remaining 54% of the test solution was directed to the laboratory drain system to limit the test solution flow rate. This was done so as to limit stress to the test organisms as well as to limit degradation of solutions within the diluter system.

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Common name: Daphnia magna
- Age at study initiation (mean and range, SD): less than 24 hours old.

METHOD FOR PREPARATION AND COLLECTION OF EARLY INSTARS OR OTHER LIFE STAGES, INCLUDING CULTURING CONDITIONS
Daphnids were cultured in dilution water of identical composition and at the same temperature as was used in the test. Neonates were selected from a culture with adults 19 days old, a cumulative adult mortality less than or equal to 20%, no behavioral signs of stress, and no ephippia. Neonate mortality did not exceed 10% in the culture from which organisms were obtained for use in the study. Daphnids were cultured in 1 liter Pyrex beakers containing 800 mL of hard synthetic freshwater (hardness: 160 to 180 mg/L as CaC03). Culture beakers were maintained in a temperature controlled environmental chamber.

Test type:

flow-through

Water media type:

freshwater

Remarks:

A synthetic hard fresh water

Limit test:

no

Total exposure duration:

48 h

Hardness:

174 mg CaCO3/L

Test temperature:

20.3 ± 1°C

pH:

7.4-7.5

Dissolved oxygen:

99-101%

Conductivity:

600 µMhos/cm

Nominal and measured concentrations:

Nominal concentrations of 0.41, 0.69, 1.2, 1.9, and 3.2 mg a.s./L, alongside a dilution water control, and solvent control.
Mean measured concentrations were 0, 0 (solvent control), 0.16, 0.34, 0.61, 0.99 and 1.6 mg a.s./L.

Details on test conditions:

-20 daphnids per concentration, divided into2 groups of 10, were exposed to nominal concentration of 0, 0 (solvent control) 0.41, 0.69, 1.2, 1.9 and 3.2 mg a.s./L in a flow-throug test for 48 hours. The numbers of immobile daphnids per concentration were recorded at 3, 6 24 and 48 h.
- Desmedipham and EHPC were measured from test water at the beginning (0 h) and at the end of the test (48 h) by HPLC. LOD for both compounds were 0.01 µg/L. The mean measured concentrations were 0, 0 (solvent control), 0.16, 0.34, 0.61, 0.99 and 1.6 mg a.s./L.
- The pH of test water was 7.4-7.5 (hardness 160-180 mg CaCO3/l). Test water temperature within 20 ± 1°C and oxygen saturation was over 90%. A light cycle of 16 h light and 8 h dark was used.

Key result

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

0.35 mg/L

95% CI:

>= 0.28 - <= 0.42

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: based on recalculated EC50

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

0.78 mg/L

95% CI:

>= 0.67 - <= 0.91

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: based on initial reported EC50

Details on results:

Analytical results
The analytical results showed that test compound expressed as percents of nominal on day 0 were desmedipham (DMP): 39 - 52% and sum of DMP and EHPC: 39 - 73%, and on day 2 were DMP: 24 - 50%, and sum of DMP and EHPC: 41 - 83%. Even though the measured concentrations of sum of desmedipham and EHPC were not within ± 20% of nominal the study authors have based the results on nominal concentrations. The recalculated the test concentrations of desmedipham based on mean measured concentrations of desmedipham (See "Attachments" in "Overall remarks, attachments" for “Arithmetic mean measured concentrations of desmedipham”).

Biological results
Observations
No abnormal behavior or abnormal appearance was observed in the control treatments, or concentrations up to and including 0.41 mg a.s./L during the study.

Mortality
With a total number of 20 daphnids tested in each test level, cumulative number of immobilised daphnids was observed under flow-through conditions (See "Attachments" in "Overall remarks, attachments" for “Acute toxicity of desmedipham technical to daphnids, based on nominal concentrations”).
The 48 hour EC50 value based on nominal concentration was 0.78 mg a.s./L (with 95% confidence intervals of 0.67 - 0.91 mg a.s./L). However, in the amended report M-545523-01-1, the 48 hour EC50 was recalculated. This recalculation is based on arithmetic mean measured concentration of desmedipham, and the 48 hour EC50 obtained was 0.35 mg a.s./L (with 95% confidence intervals of 0.28 - 0.42 mg a.s./L).

Validity criteria fulfilled:

yes

Remarks:

Mortality in the controls < 10% and dissolved oxygen = 3 mg/L.

Conclusions:

The 48 hour EC50 value based on nominal concentration was 0.78 mg a.s./L (with 95% confidence intervals of 0.67 - 0.91 mg a.s./L). However, in the amended report, the 48 hour EC50 was recalculated. This recalculation is based on arithmetic mean measured concentration of desmedipham, and the 48 hour EC50 obtained was 0.35 mg a.s./L (with 95% confidence intervals of 0.28 - 0.42 mg a.s./L).

Executive summary:

The acute toxicity of Desmedipham Technical to Daphnia magna was determined under flow-through conditions.  Daphnids were exposed to nominal concentrations of of 0.41, 0.69, 1.2, 1.9, and 3.2 mg a.s./L, alongside a dilution water control and a solvent control.  Based on arithmetic mean measured concentration of desmedipham, the 48-hour EC₅₀ was 0.35 mg a.s./L.

Description of key information

An acute 48-h toxicity test was conducted to determine the influence of Desmedipham on the mobility of Daphnia magna. Based on arithmetic mean-measured concentrations of Desmedipham, the 48-h EC₅₀ for was determined to be 0.35 mg/L.

Even though the study by Claude et al. (2012) resulted in a lower endpoint (>0.33mg/L) compared to the endpoint from the study by Stachura (1996) (0.35 mg/L) the later study was identified as key study since the endpoint was a definitive endpoint instead of a greater than endpoint.

In the table below all available studies are listed. For some studies only the results are presented since they are not considered relevant due to the reasons given under “Assessment”. All available studies have been evaluated within the scope of Plant Protection Regulation in the respective Draft Renewal Assessment Report (DAR) under Regulation (EC) 1107/2009.

Test species	Result	Assessment	Reference
Daphnia magna	EC50 (48h) = 0.35 mg/L (arithmetic mean measured)	Key study	Stachura (1996)
Daphnia magna	EC50 (48h) > 0.33 mg/L (arithmetic mean measured)	Supporting study	Claude et al. (2012)
Daphnia magna	EC50 (48h) = 1.88 mg/L (nominal)	The study is considered invalid due to lack of analytic verification of the active substance.	Morrisey (1978)
Daphnia magna	EC50 (48h) = 0.45 mg/L (mean measured)	The study is not considered valid due to missing of purity and analytical method description.	Cameron et al. (1991)
Daphnia magna	EC50 (48h) = 1.34 mg/L (nominal)	The study is not considered valid due to missing analytical report and questionable analytical results.	Mathai (1998)

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Dose descriptor:

EC50

Effect concentration:

0.35 mg/L