Trihexyl phosphate

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:

27 - 30 Mar 2017

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:

adopted 2004

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.2 (Acute Toxicity for Daphnia)

Version / remarks:

2008

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Landesamt für Umwelt, Wasserwirtschaft und Gewerbeaufsicht, Rheinland-Pfalz, Germany

Analytical monitoring:

yes

Details on sampling:

- Concentrations: all test item concentration and control
- Sampling method: samples were taken at test start, after 24 h (old), 24 h (new) and 48 h

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: Saturated solution was prepared by pipetting 106 μL/L corresponding to the nominal load 100 mg/L (based on a density of 0.94 g/mL, stated in the MSDS provided by the sponsor) on the surface of dilution water and stirring slowly for 24.5 h (first solution) resp. 24 h (second solution). The lower phase was used as highest concentrated test solution and for preparation of the lower concentrated treatments. At the beginning and for medium renewal, the necessary solutions were freshly prepared.
- Controls: yes, medium

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Common name: water flea
- Source: Umweltbundesamt Berlin; in-house breeding since 27 Sep 2007
- Age of test animals: between 0 and 24 hours
- Feeding during test: no
- Food type: unicellular green algae (Desmodesmus subspicatus)
- Frequency: twice a week

ACCLIMATION
- Acclimation conditions (same as test or not): same
- Type and amount of food: unicellular green algae (Desmodesmus subspicatus)
- Feeding frequency: twice a week

METHOD FOR PREPARATION AND COLLECTION OF EARLY INSTARS OR OTHER LIFE STAGES: 18 h before the start of the test, the adult animals were separated from the young. 0.5 h before test start, the adults were caught with the help of a glass tube, and the newborn Daphnia, aged between 0 and 17 h, were sieved from the medium and immediately placed into a 250 mL-beaker containing dilution water. After a settling-in period of 30 min, animals which showed no apparent damage were used for the test.

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Hardness:

2.502 mmol/L
250 mg CaCO3/L

Test temperature:

20.0 – 21.8 °C

pH:

7.7 - 7.8 (control)
7.6 - 7.9 (test concentrations)

Dissolved oxygen:

8.5 - 8.7 mg/L (control)
8.5 - 9.0 mg/L (test concentrations)

Nominal and measured concentrations:

control, 4.6, 10, 22, 46 and 100 mg/L (nominal)
control, 7.1, 18.8, 42.3, 101.4 and 215.8 µg/L (geometric mean)

Details on test conditions:

TEST SYSTEM
Test vessel:
- Type: open
- Material, size, headspace, fill volume: glass beakers 100 mL volume, tall shape, 50 mL test volume, 50 mL headspace
- Renewal rate of test solution (frequency/flow rate): after 24 h
- No. of organisms per vessel: 5
- No. of vessels per concentration (replicates): 4
- No. of vessels per control (replicates): 4

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Deionised water with an enrichment of certain minerals (dilution water as demanded in the guidelines) was used in the test. M4-Medium according to the OECD guideline.
- pH: 7.7
- Culture medium different from test medium: no
- Intervals of water quality measurement: every 24h during the test

EFFECT PARAMETERS MEASURED: mobility

RANGE-FINDING STUDY: no range-finding test was performed

Reference substance (positive control):

yes

Remarks:

Potassium dichromate

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

76 µg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

lower phase of saturated test solution was tested

Basis for effect:

mobility

Duration:

48 h

Dose descriptor:

NOEC

Effect conc.:

19 µg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

lower phase of saturated test solution was tested

Basis for effect:

mobility

Details on results:

- Behavioural abnormalities: no abnormalities were detected
- Mortality of control: 0% mortality in the control
- Other: Analytical and biological results are summarized within the tables 1-5 in the section "Any other information on results incl tables"

Results with reference substance (positive control):

- EC50 (24h): 1.8 mg/L (within the range of 0.6 – 2.1 mg/L of the OECD guideline)

Reported statistics and error estimates:

The estimation of the biological results was accomplished using the software ToxRat® Professional, version 3.2.1.

Table 1: Validity criteria

Criterion from the guideline	Outcome	Validity criterion fulfilled
In the control, including the control containing the solubilising agent, not more that 10% of the daphnids should have been immobilized.	0%	Yes
The dissolved oxygen concentration at the end of the test should be ≥ 3 mg/L in control and test vessels.	8.7 mg/L	Yes

 

Table 2: Biological Results Test Item

Parameter	Value	95%-confidence interval
24h EC50	104 μg/L	n d. *
48h EC50	76 μg/L	59 – 99 μg/L
48h NOEC	19 μg/L	--
48h LOEC	42 μg/L	--

* not determined either due to mathematical reasons or value is beyond the tested concentrations by more than factor 1000.

Table 3: Immobility

Nominal Concentration in mg/L	Immobility 24 hours absolute				Immobility 48 hours absolute
Blank control	0	0	0	0	0	0	0	0
4.6	0	0	0	0	0	0	0	0
10	0	0	0	0	0	0	0	0
22	0	0	0	0	0	3	3	0
46	3	2	3	1	4	2	3	1
100	5	5	5	5	5	5	5	5

 

Table 4: Analytical Results: Measured Concentrations

Nominal Concentration Test Item	Measured Concentrations t = 0 h	Measured Concentrations t = 24 h old	Measured Concentrations t = 24 h new	Measured Concentrations t = 48 h
mg/L	μg/L	μg/L	μg/L	μg/L
Blank control	< LOD	< LOD	< LOD	< LOD
4.6	9.02	3.37	13.38	6.35
10	23.33	16.54	25.82	12.49
22	46.01	31.25	57.38	38.69
46	101.98	87.58	123.05	96.21
100	234.75	198.40	*	*

LOQ (Limit of quantification) = 2.8μg/L; *not measured because all Daphnia were found dead after 24 hours

Validity criteria fulfilled:

yes

Description of key information

EC50 (48h) = 76 µg/L (Daphnia magna, OECD 202, geometric mean)

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

76 µg/L

Additional information

One experimental study is available investigating the toxicity of the substance to aquatic invertebrates. The study was conducted according to OECD 202 (GLP) using the water flea Daphnia magna (LAUS GmbH, 2017d). The study was performed using 5 test item concentrations ranging from 4.6 to 100 mg/L (nominal). For each test concentration 20 Daphnia were exposed to the test item for 48 hours in a semi-static test system. The content of the test item in the test solutions was measured using GC/MSD at the beginning and at the end of the test and at medium renewal in the new and old test solution. Because of the poor solubility of the test item, the correlation between nominal and measured concentration was weak. Therefore, the determination of the results was based on the geometric mean of the measured concentrations. The EC50 (48h) was determined at 76 µg/L and a NOEC (48h) was observed at 19 µg/L based on the measured concentration (based on the geometric mean) and thus below the highest measured test concentration of 215.8 µg/L.