Dibutyl [[bis[(2-ethylhexyl)oxy]phosphinothioyl]thio]succinate

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:

Initiation (not specified) to 30 May 2006

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Version / remarks:

v 7.6.84

Deviations:

no

Principles of method if other than guideline:

Limit test with 100 mg/L loading rate WAF

GLP compliance:

not specified

Specific details on test material used for the study:

Sample storage: at room temperature

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Details on test organisms:

Test organism: Desmodesmus subspicatus CHODAT
Origin: Pflanzenphysiol. lnstitut der Universitat Gbttingen, Stamm-Nr.: 8681

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

72 h

Test temperature:

24 +/- 1 °C

pH:

7.84 - 10.01

Nominal and measured concentrations:

10 and 100 mg/L (nominal)

Details on test conditions:

APPLICATION METHOD
The test substance was tested on algae toxicity at a concentration of 100 mg/L. For this purpose, the test substance was dissolved in demineralised water. Since the test item is poorly soluble in water, 125 mg of the substance were suspended in deionized water and shaken for 24 h on the shaker at about 130 rpm before the start of the test. It is assumed that during this time an equilibrium between water-soluble and water-insoluble part of the substance is established. After this the suspension was filtered through a folded filter which had been previously rinsed with deionized water. The clear filtrate (eluate) was used directly without further dilution in the algae test.
The eluate was spiked with the necessary nutrients for the algae and inoculated with the active growing, 3-day-old algae pre-culture. In the same way parallel replicates were prepared for the purpose of blind value correction, which contained a corresponding amount of non-inoculated algae medium instead of the algae pre-culture. The test mixtures were then incubated at a temperature of 25 ± 1 ° C under continuous illumination. In order to ensure the uniform distribution of the algae in the test mixture, these were stirred 15 minutes each hour. After 24, 48 and 72 hours, a determination was made of the algal cell number in the test batches using the photometer. The inhibition of algal growth is given in comparison to a control batch without test substance. Accompanying, the pH was determined at the beginning and at the end of the incubation.
72 hours before the start of the experiment, a pre-culture is prepared, which is produced as a control batch without test substance and incubated under the same conditions as in the test batch.
At time t0, the test assays are prepared. Each test solution is inoculated with an algal suspension adjusted from the 72h active growth pre-culture to an initial cell concentration of ca. 10E5 algae per mL. From this algae suspension, 5 ml per 50 ml final volume are added to the test mixture. As inoculated control without test substance (reference value for the calculation of the percentage-wise inhibition) 7 test series are prepared. For the test substance assay, 5 ml algal pre-culture inoculations are obtained. In addition, 3 incubation vessels without algal suspension are used for blind value correction. The extinction of these non-inoculated assays is determined before testing and after each 24h, 48h, and 72h and subtracted from the final value (mean of the 5 parallels with test substance).
The incubation of the test and control mixtures is carried out according to the OECD guideline for 72 h at 25 ± 1 ° C with an illumination of 8000 lux (measured with a spherical collector in a range of 400-700 nm). To ensure the introduction of CO2, the test mixtures are stirred with the aid of magnetic stirrers for 15 minutes every hour.
The increase in biomass is determined by means of a spectrophotometer after 24, 48 and 72 h. The algal biomass is given as extinction of the algal culture measured at 578 nm.

Reference substance (positive control):

no

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

Since the growth rate is expressed by the logarithm of cell number change, EbC (biomass) and ErC (growth rate) values are not directly comparable.

Results

Cell number (biomass)

Cell number at test start: ca. 1.81 x 10^4 algae cells per ml assay

Concentration of the test substance	Cell number       (n/mL)
(mg/L)	23.5 h	47.5 h	72 h
Control (0)*	1.14 x 10^5	5.21 x 10^5	2.18 x 10^7
100 mg/L*	1.36 x 10^5	6.10 x 10^5	1.93 x 10^7

*Cell numbers = Mean value from 7 parallel test series

Inhibition values (growth rate)

Concentration of the test substance	% Inhibition		pH value
(mg/L)	Cell proliferation	Growth rate	At the start	after 72h
Control (0)^1	-	-	7.96	9.71
100 mg/L^1	0.7	8.1	7.84	10.01

¹Cell numbers = Mean value from 7 parallel test series

Validity criteria fulfilled:

not specified

Remarks:

The biomass in the control cultures increased exponentially by a factor of at least 16 within the 72-hour test period, but coefficients of variation for growth rates in the control cultures were not specified.

Conclusions:

The test item had no inhibitory effect on the test organism, D. subspicatus, at the nominal limit concentration of 100 mg/L. Exact values for EbC10 or EbC50 and ErC10 or ErC50 can not be determined in the limit test. These inhibition values are expected at concentrations above 100 mg/L.

Executive summary:

The chronic toxicity on algae of the test item was investigated according to OECD 201 in a limit test at 100 mg/L over 72 hours.

The biomass production and thus the growth rate of the algae after 72-hour exposure was determined for the test item. A corresponding control without test substance is carried out as comparison. As a result, the inhibitory effects of biomass production and growth rate are calculated compared to uninhibited control.

E_bC_x corresponds to the x-percent inhibition of biomass production and E_rC_x to x-percent inhibition of growth rate. The algal biomass is given as extinction of the algal culture measured at 578 nm.

The test item showed no inhibitory effect on the test system under the conditions of this method at the selected concentration of 100 mg/L over 72 hours:

E_bC₁₀ > 100 mg/L

E_bC₅₀ > 100 mg/L

E_rC₁₀ > 100 mg/L

E_rC₅₀ > 100 mg/L

Since the growth rate is expressed by the logarithm of cell number change, E_bC and E_rC values are not directly comparable. The test was carried out without chemical analysis (quantification) of the test substance in solution.

Description of key information

In an OECD 201 study, the effect of the test substance on the growth of Pseudokirchneriella subcapitata was investigated and the 72-hour EC50 value based on growth rate was determined to be greater than 100 mg/L loading rate WAF (SGS INSTITUT FRESENIUS GmbH, 2006).