Desmedipham

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:

1993-08-02 to 1993-10-12

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

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:

The test material is a beige colored powder.

Analytical monitoring:

yes

Details on sampling:

Samples of each concentration were taken for analysis of desmedipham and EHPC by HPLC at test initiation (prior to addition of algae), every 24 hours (±1 hour), and at test termination (96 hours).

Vehicle:

yes

Remarks:

0.1 mL DMF/L

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)

- Differential loading: Triplicate algal cultures with a cell count of approximately 1 x 10E4 cells/mL were exposed for 96 h to desmedipham technical in modified AAP algal medium at five nominal concentrations (i.e. 0.065, 0.11. 0.18, 0.3 and 0.5 mg/L).
- Controls: Six replicate control and solvent control cultures.
- Chemical name of vehicle (organic solvent, emulsifier or dispersant): modified AAP algal growth medium
- Concentration of vehicle in test medium (stock solution and final test solution(s) or suspension(s) including control(s)): AAP growth medium was modified by reducing the concentration of NaHCO3 to 7.5mg/L and increasing the concentration of K2HPO4 to 3.132 mg/L to reach pH of 6.
- Other relevant information: Each flask was also purged with 0.5% CO2: air. The cell density of each culture was measured under a microscope, using a haemocytometer, at 24-hour intervals during the test.

Test organisms (species):

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

Details on test organisms:

TEST ORGANISM
- Common name: Selenastrum capricornutum
- Strain: #1648
- Method of cultivation: Cultures were maintained in the laboratory at the test temperature and under continuous light. Algae were cultured and tested in AAP nutrient media utilizing aseptic technique. The media was prepared with distilled water and reagent grade chemicals.

Test type:

static

Water media type:

other: AAP algal growth medium

Limit test:

no

Total exposure duration:

96 h

Remarks on exposure duration:

Exposed over 96 hours. Desmedipham was however found on day 3 (72 hours) only, hence a 72 h ErC50 was estimated. Samples of all treatments were taken at test start (Day 0) prior to addition of the algae, at 24, 48, and 72 hours, and at test termination.

Test temperature:

Range: 23.5 to 23.8°C; mean temperature: 23.6°C

pH:

Test start: 6.0; Test end: 7.5 to 9.9

Dissolved oxygen:

Test start (6.8 - 7.3 ppm); test termination (8.1 8.2 ppm).

Nominal and measured concentrations:

A control of nutrient medium, solvent control and nominal concentrations of 0.065, 0.11. 0.18, 0.3 and 0.5 mg a.s./L.
Mean measured concentrations: 0.053, 0.084, 0.141, 0.178 and 0.619 mg a.s./L.

Details on test conditions:

Lighting: Continuous illumination at 8000 Lux
Test vessels: 250 mL glass Erlenmeyer flasks
Test medium: AAP algal growth medium
Replication: Six control, six solvent control and three replicates for each test concentration
Starting cell density: 1 x 10E4 cells/mL
Aeration: Each flask was also purged with 0.5% CO2: air

Key result

Duration:

72 h

Dose descriptor:

other: ErC50

Effect conc.:

0.064 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: based on re-calculated measured concentration, calculations were done by the Rapporteur member state (RMS)

Duration:

96 h

Dose descriptor:

other: ErC50

Effect conc.:

> 0.619 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: based on initial measured concentration

Duration:

72 h

Dose descriptor:

other: ErC50

Effect conc.:

0.228 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: based on initial measured concentration

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

< 0.05 mg/L

Nominal / measured:

meas. (not specified)

Conc. based on:

test mat.

Details on results:

The measured concentrations of test substance at day 0 were used in all data calculations. The initial measured concentrations of desmedipham were: 0.053, 0.084, 0.141, 0.178, and 0.619 mg/L. Desmedipham was found on day 3 only in the two highest treatment levels in concentrations of 7% and 3.2% of nominal, respectively. No desmedipham could be detected in any of the test treatments on day 4 due to degradation under test conditions, principally by hydrolysis and therefore results are based on initial measured concentrations. Therefore, the 72 h ErC50 was 0.228 mg/L (95% confidence limits 0.168 - 3.08 mg/L). The NOEC was less than 0.05 mg/L. However, according to the amended report M-146929-02-2, the 72-hour ErC50 estimated was 0.064 mg/L (based on geometric mean measured concentrations) .

Discussion

The objective of this study was to determine the EC₅₀ of desmedipham to algae at a pH ≤7.0 since desmedipham is hydrolytically unstable at higher pH Desmediphain has a half-life of 69.8 days, 19.6 hours, and 0.17 hours at 22°C and pH values of 5,7, and 9 respectively. Following preliminary investigations, modifications were made to the standard algal test in order to maintain a reduced pH. To determine the extent of hydrolysis of desmedipham in the algal study, the concentration of both desmedipham, and its major hydrolytic degradate (ie. EHPC) were measured analytically.Over the first 48 hours of the study, the pH in all replicates except the solvent control remained within the range of 6.0 to 7.1.

 

There was a substantial increase in cell growth after 48 hours of the test and the pH began to increase, indicating recovery of the algal cultures as desmedipham degraded. Since the pH was maintained at ≤7.0 for at least 48 hours, the EC₅₀ values for 24 and 48 hours would be the most relevant to a continuous desmedipham exposure. The actual environmental exposure would more likely be similar to the entire test period (i.e. 96 hours) with the algal growth increasing rapidly as the desmedipham degraded.

 

The maintenance of pH ≤7.0 beyond 48 hours is not practical in an algal growth study where biomass is increasing logarithmically over the course of the study. As the algae consume CO₂ the pH will rise. Attempts to change the buffering components of the growth medium so as to counteract the pH shift will also change the nutrient balance with unknown results. These changes to the study design have not been thoroughly tested or validated. Therefore, the data would not be comparable to that generated using standard methodology.

 

As can be determined from the analytical results, the mean percent degradation of desmedipham at 24 hours, across all concentrations, was 87%. At 48 hours approximately 90% had degraded The extent of degradation of desmedipham in this study is greater than would be anticipated on the basis of hydrolysis alone and may be attributable to absorption and/or metabolism by the algae, accelerated hydrolysis at the higher temperature used in the algal study (ie. 24°C), or photolysis due to the high light intensity (ie. 8000 lux). These chemically specific parameters also make it impractical to stabilize desmedipham concentrations in an algal test.

 

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

Table 1: Result of the sample analysis

Table 2: The E_bC₅₀ (biomass) and E_rC₅₀ (growth rate) of desmedipham technical to Selenastrum capricornutum

Validity criteria fulfilled:

yes

Remarks:

Cell density in the control replicates within 72 h (fold) = 16. Mean CV for section-by-section specific growth rates in control <35. CV of average specific growth rates during the whole test period in controls <7.

Conclusions:

Desmedipham technical was very toxic to Selenastrum capricornutum under the conditions of this test. Desmedipham was found on day 3 only in the two highest treatment levels of 0.178 (nom 0.3 mg/L) and 0.619 mg/L (nom 0.5 mg/L) in concentrations of 7% and 3.2% of nominal, respectively. The calculated 72 h ErC50 value (based on initial measured concentration) was 0.228 mg/L which is close to the test concentration of 0.178 mg/L. The 72 h geomean measured concentration of 0.178 mg a.s./L is 0.050 mg a.s./L. RMS has calculated the ratio between 0.228 mg a.s./L and 0.178 mg a.s./L which is 1.28. Hence, the estimated 72 h ErC50 would be 0.050 mg a.s./L * 1.28 = 0.064 mg/L. RMS considers this calculation adequately acceptable.

Executive summary:

The toxicity of desmedipham to Selenastrum capricornutum was determined. Algae were exposed to nominal concentrations of 0.065, 0.11. 0.18, 0.3 and 0.5 mg/L alongside a solvent control and culture medium control over a 96-hour period. However, desmedipham was found only on day 3 (72 hours). Therefore, the 72-hour E_rC₅₀ estimated was 0.064 mg/L (based on geometric mean measured concentrations) . 

Description of key information

A study was conducted to determine the influence of Desmedipham on exponentially growing Selenastrum capricornutum over 96 hours under static exposure. Based on mean measured concentrations, the 72-h E_rC₅₀ (base on growth rate) was determined to be 0.064 mg/L.

 

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
Selenastrum capricornutum (green algae)	72-h ErC50 = 0.228 mg a.s./L (initial measured) 72-h ErC50 = 0.064 mg a.s./L (re-evaluated, mean measured) 72-h NOEC <0.05 mg/L (initial measured)	Key study	Schupner & Stachura (1993) amended by Kern (2004)
Pseudokirchneriella subcapitata (green algae)	120-h EbC50 = 0.732 mg/L (initially measured) 120-h NOEC = 0.120 mg/L	This study is not considered valid since the cell counts did not fulfill the validity criteria for the control. Furthermore, the solvent control is 5 times higher than recommended in the TG.	Hughes & Williams (1993)
Pseudokirchneriella subcapitata (green algae)	96-h ErC50 = 0.0563 mg/L (mean measured) 96-h EbC50 = 0.0109 mg/L (mean measured) NOEC was not reported.	The study is not considered valid due to shortcomings no available information recarding the purity, missing CoA and based on the fact tht the results are partly based on extrapolated values.	Caley et al. (1991)
Desmodesmus subspicatus (green algae)	72-h ErC50 >5.23 mg/L (initially measured) 72-h ErC50 >0.051 mg/L (mean measured) 72-h ErC10 = 0.0128 mg/L (mean measured NOEC was not reported.	The study is not considered valid since no intermediate samples with measurable residues after 24 hours were present.	Scheerbaum (2005) amended by Herno (2017), Meller and Herno (2016)
Pseudokirchneriella subcapitata (green algae)	72-h ErC50 >0.032 mg/L (geomean measured)	The study is not considered valid since no intermediate samples with measurable residues after 24 hours were present.	Bruns (2011); amended by Herno (2017)
Anabaena flos-aquae (blue-green bacterium)	120-h ErC50 >0.833 mg/L (initial measured) 120-h EbC50 >0.833 mg/L (initial measured) NOEC was not reported.	Study is not considered valid since no intermediate samples with measurable residues after 24 hours were present.	Hughes & Williams (1993)
Navicula pelliculosa (freshwater diatom)	120-h EbC50 = 1.03 mg/L (initially measured) 120-h NOEbC < 0.06 mg a.s./L	Study is not considered valid due to shortcomings in the solvent control amount, the validity criteria, and endpoints are only based on cell density.	Hughes & Williams (1994)
Skeletonema costatum (marine diatom)	120-h EbC50 >1.16 mg/L (initially measured) 120-h ErC50 >0.27 mg/L (mean measured)	Study is not considered valid due to several shortcomings in the solvent control amount, endpoints based on cell density, no EC50 could be established as it was a limit test, and no intermediate samples with measurable residues after 24 hours were present.	Hughes & Williams (1993)
Navicula pelliculosa (freshwater diatom)	72-h ErC50 >0.041 mg/L (geomean measured) NOEC was not reported.	Study is not considered valid since no intermediate samples with measurable residues after 24 hours were present.	Scheerbaum (2005); amended by Herno (2016)
Anabaena flos-aquae (blue-green bacterium)	96-h ErC50 >0.00688 mg/L (geomean measured) 96-h ErC10 = 0.0011 mg/L (geomean measured) NOEC was not reported.	The study is not considered valid since no intermediate samples with measurable residues after 24 hours were present.	Banman & Moore (2013); amended by Herno (2017), Meller and Herno (2016)

Key value for chemical safety assessment

EC50 for freshwater algae:

0.064 mg/L

EC10 or NOEC for freshwater algae:

0.05 mg/L