Dibutyl hydrogen 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:

2012

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)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

Method of administration: direct weighing

Details on test solutions:

105.4 mg of the test item were added to 1 litre of dilution water and treated for 30 min. on a magnetic stirrer. The pH was measurd to be 6.5.
19 mL of the solution were taken and diluted with 1 mL of dilution water containing 10 daphnids resulting in a final concentration of 100 mg/L. For each test item concentration and the control 2 replicates were prepared.

Test organisms (species):

Daphnia magna

Details on test organisms:

Name: Daphnia magna STRAUS, parthenogenetic females
Source: Strain of Bundesgesundheitsamt Berlin
Maintenance and Acclimatisation: A population of parthenogenetic females of synchronized age structure has been maintained for more than 15 years in the test facility under constant temperature conditions (20 +/- 1 °C) at a 16 : 8 hour light-dark photoperiod (light intensity: < 20 μE x m-2 x s-1). The culture water (so-called 'M4 medium') was partly renewed once a week. The Daphnia were exclusively fed unicellular green algae (Desmodesmus subspicatus) 'ad libitum'. Mortalities of parent Daphnia during the culture period were recorded daily in a semi-quantitative way. The neonates were separated from their parent Daphnia by filtration prior to the acute test.

Test type:

semi-static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

48 h

Hardness:

14.8° dH (= 264 mg/L CaCO3)

Test temperature:

20.4 - 21.3°C

pH:

6.5 - 7.5

Dissolved oxygen:

8.5 - 8.9 mg/L ( 96 - 98 %)

Salinity:

Reconstituted water (so-called 'M4 medium' according to OECD 202) was used for the maintenance of the test animals and the preparation of stock and test solutions of the test item.

Nominal and measured concentrations:

- limit test concentration of nominally 100 mg/L

Details on test conditions:

Pre-treatment of test item and preparation of test item concentrations:
Direct weighings were prepared on 2012-02-28 and 2012-02-29 to produce the only test concentration. 105.4 mg of the test item were added to 1 litre of dilution water on both days and treated for 30 min. on a magnetic stirrer. The pH was measurd to be 6.5 for both solutions.
19 mL of the solution were taken and diluted with 1 mL of dilution water containing 10 daphnids resulting in a final concentration of 100 mg/L. For each test item concentration and the control 2 replicates were prepared.
Exposure conditions:
Test vessels: 50 mL glass beakers covered with watch glasses holding 10 neonates in 20 mL of test medium
Experimental design: 1 test concentration plus 1 control
10 neonates per vessel, 2 replicates per concentration/control
no feeding during the exposure period
neonates were placed in prepared media
Photoperiod: 16 h light : 8 h dark, semi static system
Temperature of incubation unit: 19.6 to 19.7°C

Key result

Duration:

24 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Key result

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Details on results:

The results are expressed in terms of nominal concentrations at 24 h and at 48 h.
Effective concentrations ranged from 105 % to 106.2 % in the freshly prepared media and correspond to 102.7 % in the media after 24 hours of exposure.

Chemical analysis	0 h 2012-02-28	24 h 2012-02-29	0 h 2012-02-29	24 h 2012 -03 -01
HPLC value [mg/L]	106.159	102.670	105.014	102.679

Validity criteria fulfilled:

yes

Remarks:

The immobilisation and other abnormalities in the controls did not exceed 10 % by the end of the test. The dissolved oxygen concentration remained above 3 mg/L throughout the exposure period

Conclusions:

The acute toxicity of dibutyl hydrogen phosphate to Daphnia magna was investigated in a semi-static test. After 48 hours of exposure an EC50 of >100 mg/L (nominal) was determined. No toxic effect was observed.

Executive summary:

A study was performed to assess the acute toxicity dibutyl hydrogen phosphate to Daphnia magna STRAUS under semi-static conditions. The study was conducted in accordance with the Council Regulation (EC) No 440/2008, Method C.2 ‘Acute toxicity for Daphnia’ (2008) which is equivalent to OECD Guideline for Testing of Chemicals No. 202 'Daphnia sp., Acute Immobilisation Test' (adopted April 13, 2004). A range finding test preceded the main test. It provided information about the range of concentrations which were used in the main test. The following nominal concentrations of the test item were tested in the range finding test: 1, 3.2, 10, 32 and 100 mg/L. In the main test, Daphnia were exposed to dibutyl hydrogen phosphate added to dilution water at a limit test concentration of nominally 100 mg/L for a period of 48 hours. At this concentration no toxic effects against Daphnia were observed at the end of the 48 hour study period, thus no statistical analysis was required to determine the EC50. Immobilisation rates were recorded at 24-hour intervals. Additionally any abnormal behaviour or appearance of the Daphnia was reported every 24 hours. The main test was conducted as a semi-static test with daily renewal of test medium. During the test a temperature range of 18 - 22 °C was maintained in the test vessels, with a maximum temperature fluctuation of +/- 1 °C in each individual test. The temperature, the pH and the oxygen values were measured every day in the freshly prepared media and in the media after 24 hours of exposure. After 48 hours of exposure an EC50 of >100 mg/L (nominal) for the substance was determined. Analytically determined values vary not more than 6.2 %, therefore the EC50 is given as nominal concentration. This toxicity study is classified as acceptable and satisfies the guideline requirements for the acute Daphnia study.

Description of key information

The acute toxicity of dibutyl hydrogen phosphate to Daphnia magna was investigated in a semi-static test. After 48 hours of exposure an EC50 of >100 mg/L (nominal) was determined. No toxic effect was observed.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Dose descriptor:

EC50

Effect concentration:

> 100 mg/L

Additional information

Data on toxicity of dibutyl hydrogen phosphate towards aquatic invertebrates was found for Daphnia magna. A 48h-EC50 of 64 mg/l conducted according OECD TG 202 Part II (1984) by the National Institute of Technology and Evaluation, Japan is reported.

This value is not taken into account for assessment, based on the following reason:

Dibutyl hydrogen phosphate was assessed within the scope of the ICCA/HPV-program. Preparing the OECD-SIDS dossiers the studies conducted by the National Institute of Technology and Evaluation, Japan were not available. Information on study design and results are only presented in the OECD-SIDS Report and the OECD-SIDS dossier. In the OECD-SIDS report, the composition of the assessed substance is reported to be a mixture of 64% dibutyl phosphate, 20% tributyl phosphate and 16% monobutyl phosphate. In the context of REACH, the assessed substance/mixture would be regarded as a multi-constituent substance. In the OECD-SIDS dossier, it is reported that dibutyl phosphate with a purity of 97.6% was used as test substance in ecotoxicity tests. It is not really clear, if the degree of purity refers to pure dibutyl hydrogen phosphate or to the assessed substance, which under REACH would be regarded as a multi-constituent substance. Therefore, it is concluded that sameness of both substances, the assessed substance within the OECD-SIDS dossiers and the substance to be registered cannot be proved/demonstrated.

The studies conducted by the National Institute of Technology and Evaluation, Japan are considered to be reliable, but show a high mortality of the daphnids in the control group at the beginning of the test. Also it is not clear, if the pH value was adjusted accordingly. Based on this they are not taken into account for assessment.

A new study was performed to assess the acute toxicity of dibutyl hydrogen phosphate to Daphnia magna STRAUS under semi-static conditions. The study was conducted in accordance with the Council Regulation (EC) No 440/2008, Method C.2 ‘Acute toxicity for Daphnia’ (2008) which is equivalent to OECD Guideline for Testing of Chemicals No. 202 'Daphnia sp., Acute Immobilisation Test' (adopted April 13, 2004). A range finding test preceded the main test. It provided information about the range of concentrations which were used in the main test. The following nominal concentrations of the test item were tested in the range finding test: 1, 3.2, 10, 32 and 100 mg/L. In the main test, Daphnia were exposed to dibutyl hydrogen phosphate added to dilution water at a limit test concentration of nominally 100 mg/L for a period of 48 hours. At this concentration no toxic effects against Daphnia were observed at the end of the 48 hour study period, thus no statistical analysis was required to determine the EC50. Immobilisation rates were recorded at 24-hour intervals. Additionally any abnormal behaviour or appearance of the Daphnia was reported every 24 hours. The main test was conducted as a semi-static test with daily renewal of test medium. During the test a temperature range of 18 - 22 °C was maintained in the test vessels, with a maximum temperature fluctuation of +/- 1 °C in each individual test. The temperature, the pH and the oxygen values were measured every day in the freshly prepared media and in the media after 24 hours of exposure. After 48 hours of exposure an EC50 of >100 mg/L (nominal) for dibtuyl hydrogen phosphate was determined. Analytically determined values vary not more than 6.2 %, therefore the EC50 is given as nominal concentration. This toxicity study is classified as acceptable and satisfies the guideline requirements for the acute Daphnia study.