Dibutyl [(dipropoxyphosphinothioyl)thio]succinate

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

17 November 2017 to 16 December 2019

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)

GLP compliance:

yes

Specific details on test material used for the study:

-Description: Yellow, clear liquid
- Storage: room temperature, in the dark

Analytical monitoring:

yes

Details on sampling:

- Sampling method: Individual samples were collected by pipet at 0 and 24 Hour (new) and 24 and 48Hour (aged) from the approximate midpoint from the surface, bottom, and sides of the vessel
- Sample storage conditions before analysis: Analyzed upon collection; archived samples collected.
Quality Control (QC) Samples: Three samples per sampling interval were prepared in dilution water at nominal concentrations approximating the test concentration range.
- Sample processing: extraction in hexane with acetone rinse; extracts reconstituted in 50/50 acetonitrile/purified reagent water (v/v), then diluted into the calibration standard range with 50/50 acetonitrile/purified reagent water (v/v).

Vehicle:

no

Details on test solutions:

The primary stock solution (2.0 mg/L) was prepared as a water accommodated fraction (WAF) by adding the aliquot of test substance directly to the total volume of dilution water in a glass beaker. The solution was mixed slowly overnight for approximately 19.5 hours with a magnetic stir plate and Teflon covered stir bar. After mixing, the solution was allowed to settle for approximately 30 minutes. The solution was observed to be clear and colorless with undissolved oily globules of the test substance visible on the surface. The solution was then siphoned, avoiding the solution surface. The resulting solution was observed to be clear and colorless with no visible undissolved test substance.

Exposure solutions were prepared as dilutions of the stock water-accommodated fraction (WAF), as follows: 3.1, 6.3, 13, 25, 50, and 100% of a 2.0 mg/L water-accommodated fraction (WAF). The resulting exposure solutions were observed to be clear and colorless with no visible undissolved test substance following mixing with a glass rod for one minute. Control vessels were maintained under the same conditions as the treatment level solutions.

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
Species: Daphnia magna (water flea)
Source: Smithers Viscient culture (Wareham, Massachusetts)
Age: Less than 24 hours old; immature daphnids were removed from culture 24 hours prior to exposure initiation, isolating sexually mature adults. Young produced by the parent organisms were used for the exposure.
Culture Vessel: 1.0-L glass beaker containing 0.80 L of water
Food Type: Unicellular green algae, Ankistrodesmus falcatus (4 × 107 cells/mL); YCT suspension (yeast, cereal leaves, and flaked fish food)
Feeding Frequency: Once daily during culture; daphnids not fed during the definitive exposure
- Acclimation period: 2 weeks
- Acclimation conditions: same as the definitive exposure

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Hardness:

180 mg CaCO3/L

Test temperature:

20 +/- 2 °C

pH:

7.7 to 8.0

Dissolved oxygen:

7.8 to 8.7 mg/L

Salinity:

not applicable

Conductivity:

740 to 760 µS/cm

Nominal and measured concentrations:

Nominal: Control, 0.063, 0.13, 0.25, 0.50, 1.0 and 2.0 mg/L loading rate WAF
Geometric mean measured: Control, 0.00037, 0.00074, 0.0016, 0.0034, 0.0062, and 0.014 mg a.i./L

Details on test conditions:

TEST SYSTEM
- Test vessel: 250-mL glass beakers containing 200 mL of test medium
- Aeration: none
- No. of organisms per vessel: 5
- No. of vessels per test concentration or control (replicates): 4
- Biomass loading rate: 25 daphnids/L (5 daphnids per 200 mL)

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Fortified laboratory well water
- Total organic carbon: 1.1 mg/L
- Alkalinity: 84 to 86 mg CaCO3/L
- Culture medium different from test medium: same
- Intervals of water quality measurement: 0, 24 and 48 hours (in replicate A); temperature was also monitored continuously with a minimum/maximum thermometer

OTHER TEST CONDITIONS
- Adjustment of pH: none
- Photoperiod: 16 hours light: 8 hours dark
- Light intensity: 61 to 96 footcandles (660 to 1000 lux) measured

RANGE-FINDING STUDY
- Test concentrations: Control, 0.81, 2.7, 9.0, 30 and 100 mg/L loading rate WAF
- Results used to determine the conditions for the definitive study: 50% immobilization 0.81 mg/L loading rate WAF; 100% immobilization at/above 2.7 mg/L loading rate WAF.

Reference substance (positive control):

yes

Duration:

24 h

Dose descriptor:

EL50

Effect conc.:

> 2 other: mg/L loading rate WAF

Nominal / measured:

nominal

Basis for effect:

mobility

Key result

Duration:

48 h

Dose descriptor:

EL50

Effect conc.:

1 other: mg/L loading rate WAF

Nominal / measured:

nominal

Basis for effect:

mobility

Duration:

24 h

Dose descriptor:

EC50

Effect conc.:

> 0.014 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

act. ingr. (dissolved fraction)

Basis for effect:

mobility

Key result

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

0.006 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

act. ingr. (dissolved fraction)

Basis for effect:

mobility

Results with reference substance (positive control):

- Reference substance: Potassium Dichromate
- Duration: 24 Hours
- Age of Daphnids: less than 24 hours old
- Date Performed: 8 to 9 February 2018
- Result: EC50 was determined as a point estimate to be 2.4 mg/L (95% confidence interval, 2.0 to 2.7 mg/L)

Reported statistics and error estimates:

The 24-hour EC50 values were empirically estimated to be greater than the highest concentration tested since <50% immobilization was observed at this interval. The 48-hour EC50 values and 95% confidence interval were determined by Spearman-Kärber estimates using the CETIS version 1.8 software program.

Nominal Concentration (mg/L loading rate WAF)	Mean Measured Concentration (mg a.i./L)	Percent Immobilization *
		24-Hour						48-Hour
		A	B	C	D	Mean		A	B	C	D	Mean
Control	Control	0	0	0	0	0		0	0	0	0	0
		(0)	(0)	(0)	(0)			(0)	(0)	(0)	(0)
		--	--	--	--			--	--	--	--
0.063	0.00037	0	0	0	0	0		0	0	0	0	0
		(0)	(0)	(0)	(0)			(0)	(0)	(0)	(0)
		--	--	--	--			--	--	--	--
0.13	0.00074	0	0	0	0	0		0	0	0	0	0
		(0)	(0)	(0)	(0)			(0)	(0)	(0)	(0)
		--	--	--	--			--	--	--	--
0.25	0.0016	0	0	0	0	0		0	0	0	0	0
		(0)	(0)	(0)	(0)			(0)	(0)	(0)	(0)
		--	--	--	--			--	--	--	--
0.50	0.0034	0	0	0	0	0		0	0	0	0	0
		(0)	(0)	(0)	(0)			(0)	(0)	(0)	(0)
		--	--	--	--			--	--	--	--
1.0	0.0062	0	0	0	0	0		60	40	60	40	50
		(0)	(0)	(0)	(0)			(3)	(2)	(3)	(2)
		--	--	--	--			2L	--	--	--
2.0	0.014	40	20	40	20	30		100	100	100	100	100
		(2)	(1)	(2)	(1)			(5)	(5)	(5)	(5)
		--	--	--	1L			--	--	--	--

* The actual number of cumulative immobilized daphnids is presented in parentheses.

L = lethargic; -- = no adverse effects observed

 

Endpoint	Nominal Concentration (mg/L loading rate WAF)	Geometric Mean Measured Concentration (mg a.i./L)
48-Hour EL(C)50 [95% Confidence Intervals]	1.0 [0.86 -1.2]	0.0065 [0.0056 - 0.0077]
NOEL(C)	0.50	0.0034
LOEL(C)	1.0	0.0062
Highest concentration producing 0% immobilization	0.50	0.0034
Lowest concentration producing 100% immobilization	2.0	0.014

Validity criteria fulfilled:

yes

Conclusions:

The acute toxicity (EL50) of the test substance to Daphnia magna under static-renewal conditions after 48 hours was determined to be 1.0 mg/L loading rate WAF, and the No Observed Effect Loading rate (NOEL) was determined to be 0.50 mg/L loading rate WAF. Based on geometric mean measured concentrations, the 48-hour EC50 and NOEC were determined to be 0.0065 mg a.i./L and 0.0034 mg a.i./L, respectively.

Executive summary:

The study was conducted in accordance with the requirements of OECD Guideline No. 202 to assess the toxicity the 48-hour acute toxicity of the test substance to water fleas (Daphnia magna). Test solutions were prepared as Water Accommodated Fractions (WAFs) based on the recommendations of OECD Series on Testing and Assessment, No. 23. 

The definitive test was conducted under semi-static conditions (daily renewal) at 20 +/- 2 °C,employing nominal loading rates (WAF) of 0.063, 0.13, 0.25, 0.50, 1.0 and 2.0 mg/L (prepared as dilutions of the 2.0 mg/L loading rate WAF stock solution),with a concurrent control group. Each treatment or control consisted of 4 replicate 250 mL glass vessels each containing 200 mL of media and 5 juvenile daphnids. The daphnids in each test vessel were observed for immobilization and sub-lethal effects at 24-hour intervals throughout the 48-hour exposure period. The daphnids were not fed during the test. Analysis of test solutions collected at 0 and 24 hours (fresh media) and at 24 and 48 hours (old media) using liquid chromatography with tandem mass spectrometry detection (LC-MS/MS) resulted in geometric mean measured concentrations of0.00037, 0.00074, 0.0016, 0.0034, 0.0062, and 0.014 mg/L.

The acute toxicity (EL50) of the test substance to Daphnia magna after 48 hours under static-renewal conditions was determined to be 1.0 mg/L loading rate WAF, and the No Observed Effect Loading rate (NOEL) was determined to be 0.50 mg/L loading rate WAF. Based on geometric mean measured concentrations, the 48-hour EC50 and NOEC were determined to be 0.0065 mg a.i./L and 0.0034 mg a.i./L, respectively.

Description of key information

The acute toxicity (EL50) of the test substance to Daphnia magna under static-renewal conditions after 48 hours was determined to be 1.0 mg/L loading rate WAF, and the No Observed Effect Loading rate (NOEL) was determined to be 0.50 mg/L loading rate WAF. Based on geometric mean measured concentrations, the 48-hour EC50 and NOEC were determined to be 0.0065 mg a.i./L and 0.0034 mg a.i./L, respectively (Smithers Viscient, 2019).