Potassium hexadecyl hydrogen phosphate

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2012-05-22 until 2012-05-24

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

Version / remarks:

2008-05-30

Deviations:

no

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Version / remarks:

adopted 2010-07-22

Deviations:

no

Qualifier:

according to guideline

Guideline:

ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

Adequate amounts of the test item were directly weighed into each test flask. 3 replicates of the test item flasks were prepared (nominal 100 mg test item/L) and six controls (tap water, synthetic sewage and inoculum, but without addition of the test item) were tested in parallel. In parallel to the study with the test item, the reference item 3,5-dichlorophenol was tested at the nominal test concentrations of 3.2, 10 and 32 mg/L under otherwise identical test conditions. One test solution with a final volume of 500 mL was tested per treatment in a glass flask (>500 mL). Samples were prepared in about 15-minute intervals.

Test organisms (species):

activated sludge, domestic

Details on inoculum:

Origin:
Activated sludge microorganisms from a domestic waste water treatment plant were supplied by the municipal sewage treatment plant Bensheim, Germany.

Conditioning:
The activated sludge used for this study was used as collected, but coarse particles were removed by settling for a short period and then the upper layer decanted. During holding prior to use the sludge was fed daily with 50 mL synthetic sewage (see below) per litre and kept aerated at room temperature overnight.
An aliquot of the final sludge suspension was weighed, dried and the ratio of wet sludge to its dry weight determined. Based on the sludge dry matter, calculated amounts of wet sludge were suspended in tap water to yield a concentration equivalent to 2.5 g/L on dry weight basis. This level gave a concentration of 1.0 g/L suspended solids in the test medium. The pH of the activated sludge was 7.4 and therefore no adjustment was necessary.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Test temperature:

20 - 22 °C during pre-incubation (3 hours)
18 - 23 °C during evaluation period
The water temperature was measured in one control medium at the start and the end of the incubation period.

pH:

The pH of the activated sludge inoculum was determined to be pH 7.4. The pH was determined at the start and at the end of the incubation period in all test concentrations and controls.

Dissolved oxygen:

The oxygen concentrations were determined at the start and at the end of the incubation period in all test concentrations and controls.

Nominal and measured concentrations:

Nominal 100 mg test item/L

Details on test conditions:

TEST SYSTEM
- Test vessel: Glass flasks of approximately 1 litre volume and Karlsruher flasks of 250 mL volume
- Aeration: compressed air (1.026 litre per minute)
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6 controls, 1 replicate. Positive control: 3 controls, 1 replicate (3 different concentrations of 3,5-Dichlorophenol were examined, 3.2, 10 and 32 mg/L)
- Synthetic sewage was used:
16 g peptone
11 g meat extract
3 g urea
0.7 g NaCl
0.4 g CaCl2 · 2H2O
0.2 g MgSO4 · 7H2O
2.8 g K2HPO4
Filled up to 1 L with deionised water. The pH of this solution was 7.1

OTHER TEST CONDITIONS
- Adjustment of pH: no

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

The respiration rates of the activated sludge treated with the test item at a concentrations of 100 mg/L differed by 10.2 % from control. The respiration rate of the activated sludge to potassium hexadecyl hydrogen phosphate at the rate of 100 mg/L was not statistically significant reduced when compared to the control. The NOEC is established above 100 mg/L.

Results with reference substance (positive control):

The 3-hour EC50 of the reference item 3,5-Dichlorophenol was determined to be 2.5 mg/L and was thus in the range of 2 to 25 mg/L for the activated sludge batch which was used.

Reported statistics and error estimates:

Student t-test for homogenous variances with Bonferroni-Holm Adjustment, α = 0.05

Validity criteria fulfilled:

yes

Conclusions:

Under the study conditions, the determined NOEC was above 100 mg/L

Executive summary:

The influence of the test item potassium hexadecyl hydrogen phosphate on the activity of activated sludge was evaluated by measuring the respiration rate under defined conditions according to EU Method C.11 and OECD Guideline 209. The respiration rate (oxygen consumption) of an aerobic activated sludge fed with a standard amount of synthetic sewage was measured in the presence of one concentration of the test item, 100 mg/L (limit test) after an incubation period of 3 hours. 6 controls (tap water, synthetic sewage and inoculum, but without addition of the test item) were tested in parallel and a reference item 3,5-dichlorophenol was tested at the nominal test concentrations of 3.2, 10 and 32 mg/L under otherwise identical test conditions.

The respiration rates of the activated sludge treated with the test item at a concentrations of 100 mg/L differed by 10.2 % from control. The respiration rate of the activated sludge to potassium hexadecyl hydrogen phosphate at the rate of 100 mg/L was not statistically significant reduced when compared to the control. The determined NOEC was above 100 mg/L.

The positive control 3,5-Dichlorophenol was tested in the same way as the test item. The 3-hour EC50 was found to be 2.5 mg/L, thus, laying in the range of 2 - 25 mg/L recommended by the test guidelines. The result confirms the suitability of the activated sludge used.

Description of key information

In accordance with OECD TG 209 the NOEC was determined to be greater than 100 mg/L.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

100 mg/L

Additional information

The influence of the test item potassium hexadecyl hydrogen phosphate on the activity of activated sludge was evaluated by measuring the respiration rate under defined conditions according to EU Method C.11 and OECD Guideline 209. The respiration rate (oxygen consumption) of an aerobic activated sludge fed with a standard amount of synthetic sewage was measured in the presence of one concentration of the test item, 100 mg/L (limit test) after an incubation period of 3 hours. 6 controls (tap water, synthetic sewage and inoculum, but without addition of the test item) were tested in parallel and a reference item 3,5-dichlorophenol was tested at the nominal test concentrations of 3.2, 10 and 32 mg/L under otherwise identical test conditions.

The respiration rates of the activated sludge treated with the test item at a concentrations of 100 mg/L differed by 10.2 % from control. The respiration rate of the activated sludge to potassium hexadecyl hydrogen phosphate at the rate of 100 mg/L was not statistically significant reduced when compared to the control. The determined NOEC was above 100 mg/L.

The positive control 3,5-Dichlorophenol was tested in the same way as the test item. The 3-hour EC50 was found to be 2.5 mg/L, thus, laying in the range of 2 - 25 mg/L recommended by the test guidelines. The result confirms the suitability of the activated sludge used.