Hexadecyl palmitate

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

activated sludge respiration inhibition testing

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

Refer to analogue justification provided in IUCLID section 13.

Reason / purpose for cross-reference:

read-across source

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other:

Remarks:

Source: CAS 36078-10-1, activated sludge, 3 h

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other:

Remarks:

Source: CAS 36078-10-1, activated sludge, 3 h

Conclusions:

No inhibition of the respiration rate of activated sludge occurred up to the limit concentration of 1000 mg/L (nominal, OECD 209).

Reference 2

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

17 Oct 2012

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

yes (incl. QA statement)

Remarks:

Landesanstalt für Umwelt, Messungen und Naturschutz Baden-Württemberg, Karlsruhe, Germany

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: 586 µL of the test item were added into the test vessels to obtain final concentrations of 1000 mg/L. Three parallel vessels of the test item were prepared.
- Eluate: no
- Differential loading: yes
- Controls: yes, blank control

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Source: Activated sludge from the municipal wastewater treatment plant Staufener Bucht (Germany) was used as test system. The treatment plant clarifies predominantly domestic wastewater of the region of Staufen and has a capacity of 140 000 inhabitant equivalents. Sampling date of activated sludge was 16 Oct 2012.
- Laboratory culture: no
- Preparation of inoculum for exposure: The activated sludge was kept aerated and fed with synthetic sewage (50 mL per litre and day) until use. Dry solids of the activated sludge was determined as 5.3 g/L by weight measurements before and after 3 h drying at 105°C (mean of triplicate measurements). The activated sludge was washed twice by settling the sludge, decanting the supernatant, and re-suspending the sludge in aerated tap water. Before using, the activated sludge was diluted to 3 g/L dry solids with tap water, in order to obtain a final concentration of 1.5 g/L dry solids in the test.
- Initial biomass concentration: 1.5 g/L (dry solids)

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Test temperature:

18 - 20 °C

pH:

7.7

Nominal and measured concentrations:

nominal: blank, 1000 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: BOD bottles
- Fill volume: 500 mL
- Aeration: All vessels were stirred and aerated throughout the contact time with room air at a rate of 0.5 - 1 L/min using a membrane pump.
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: according to guideline (demineralised water)

EFFECT PARAMETERS MEASURED: respiration rate was measured every 15 min to allow a contact time of 3 h

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Results with reference substance (positive control):

- Results with reference substance valid? yes
- Relevant effect levels: EC50 (3 h): 22.48 mg/L. The EC50 was calculated with ToxRat version 2.09 (ToxRat Solutions GmbH, Alsdorf, Germany) by probit analysis using linear max. likelihood regression.

The validity criteria set out in the Guideline are met.

Table 1: Respiration rate of activated sludge after application of the test substance of the definite test.

Vessel	O2 concentration [mg/L]		Consumption rate [mg/(L*h)]	Inhibition [%]
	First measurement	Last measurement
Blank 1	7.77	6.15	38.9
Blank 2	7.50	6.07	34.3
Blank 3	7.88	6.66	29.3
Blank 4	7.44	6.15	31.0
Blank 5	7.80	6.53	30.5
Blank 6	8.59	7.77	19.7
Test item 1	5.22	3.65	37.7	-23
Test item 2	5.85	4.55	31.2	-2
Test item 3	8.09	3.75	32.2	-5

Coefficient of variation of blanks: 0.19

The results of a first test with a concentration of 1000 mg/L showed high negative inhibitions (until -53%) and a relative low start value of oxygen at the beginning of the measurement. Therefore, the aeration of the test was optimized and the test was repeated. The data of the first test are not shown in detail in the report. In the repetition the values of oxygen at the start of measurement were considerably higher and the evaluation showed conclusive results.

Description of key information

No effects up to the limit of water solubility (OECD 209, activated sludge microorganisms); read-across

Additional information

The endpoint for the toxicity ofhexadecyl palmitate (CAS 540-10-3) to activated sludge microorganisms was covered by read-across to the structurally related source substance lauryl oleate (dodecyl oleate, CAS 36078-10-1), in accordance with Regulation (EC) No 1907/2006 Annex XI, 1.5. The source substance is characterized by a fatty acid as well as fatty alcohol of similar chain lengths as the target substance, which is an ester of a C16 fatty acid and alcohol. The source substance dodecyl oleate (CAS 36078-10-1) is an ester of a C18 fatty acid and a C12 fatty alcohol. Therefore, the source substance is considered a suitable representative for the assessment of the toxicity of the target substance to microorganisms. A detailed read-across justification is provided in in the analogue justification in IUCLID section 13.

The available study with dodecyl oleate (CAS 36078-10-1) was performed according to OECD guideline 209 and GLP. In a limit test, a nominal concentration of 1000 mg/L test item was inoculated with 1.5 g/L activated sludge (dry solids) from a predominantly domestic sewage treatment plant for 3 h. It was found that the respiration rate of the activated sludge microorganisms was not inhibited, resulting in a NOEC (3 h) of ≥ 1000 mg/L.

Based on the structural and chemical similarity of the target and source substance, the target substance is expected to exhibit a similar ecotoxicological profile as the source substance. Therefore, it can be concluded that hexadecyl palmitate (CAS 540-10-3) will not exhibit toxic effects on microorganisms from activated sludge up to the limit of water solubility (< 0.846 µg/L).