[No public or meaningful name is available]

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

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

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Justification for type of information:

The substance reaction mass of stearic acid and stearic anhydride contains of the acid and the anhydrid. Under environmental conditions the anhydride will dissociate into the acid. Thus it is sufficient to evaluate the toxicity towards microorganisms of stearic acid.

Reason / purpose for cross-reference:

read-across source

Qualifier:

according to guideline

Guideline:

other: Bewertung wassergefährdender Stoffe, III Bestimmung der akuten Bakterientoxizität

Qualifier:

equivalent or similar to guideline

Guideline:

ISO 10712 (Water quality – Pseudomonas putida growth inhibition test (Pseudomonas cell multiplication inhibition test

GLP compliance:

yes

Analytical monitoring:

yes

Details on sampling:

- Sampling method: 50 mL of the test substance stock solutions were taken after filtration of the saturated stock solution
- Sample storage conditions before analysis: frozen at -20 °C

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: A saturated test substance solution with a nominal concentration of 10 mg/L was prepared by sonication for 30 minutes and a subsequent 24 h lasting mixing with a magnetic stirrer. Afterwards the solution was filtered and neutralised to a pH of 7.1 with NaOH
- Controls: 10 with inoculum without test substance to determine turbidity and for each test concentration 1 control without inoculum to determine possibly occuring colouration

Test organisms (species):

Pseudomonas putida

Details on inoculum:

- Preparation of inoculum for exposure: Bacteria from 7 days old stock culture were inoculated in a fluid nutrient medium in Erlenmeyer flasks and incubated for 16-20 h at 25 °C. Afterwards the extinction of the monochromatic radiation at 436 nm was determined for a 10 mm layer of the bacterial suspension by photoelectric measurement.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

16 h

Remarks on exposure duration:

16 - 20 h

Test temperature:

23 - 27 °C

pH:

pH was neutralised to 7.1 with NaOH

Nominal and measured concentrations:

nominal: 3.9, 7.8, 15.6, 31.3, 62.5, 125.0, 250.0, 500.0, 1000.0, 2000.0, 4000.0, 8000.0 mg/L (mean measured)
actual: (0.11 % of the nominal concentrations)

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Type (delete if not applicable): closed with aluminum foil caps
- Material, size, headspace, fill volume: 300 mL Erlenmeyer flasks
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 10

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Milli-Q water: water was first purified by reverse osmosis and thereafter passed over activated carbon and ion exchange cartridges

OTHER TEST CONDITIONS
- Adjustment of pH: with NaOH to 7.1

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : extinction of monochromatic radiation at 436 nm in a 10 mm layer after 16 - 20 h

Reference substance (positive control):

yes

Remarks:

Methanol

Key result

Duration:

18 h

Dose descriptor:

EC10

Effect conc.:

883 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth inhibition

Remarks on result:

other: given as TT (toxicity threshold)

Results with reference substance (positive control):

The toxicity threshold value of the reference substance was in the usual range known at RCC Notox

Table 1: Extinction of the test substances solutions after 16 - 20 h

 

Concentration [mg/L]	Extinction at 436 nm
	Replicate I	Replicate II	Replicate III	Arithm. mean of replicates	Replicate without inoculum	Corrected arithmetic mean*
3.9	0.822	0.910	0.927	0.886	0.001	0.885
7.8	0.760	0.745	0.827	0.777	0.000	0.777
15.6	0.801	0.836	0.842	0.826	0.000	0.826
31.3	0.823	0.829	0.843	0.832	0.000	0.832
62.5	0.849	0.815	0.827	0.830	0.000	0.830
125.0	0.845	0.816	0.832	0.831	0.000	0.831
250.0	0.843	0.834	0.833	0.837	0.000	0.837
500.0	0.796	0.807	0.852	0.818	0.000	0.818
1000.0	0.775	0.740	0.699	0.738	0.001	0.737
2000.0	0.672	0.658	0.654	0.661	0.009	0.652
4000.0	0.680	0.694	0.703	0.692	0.024	0.668
8000.0	0.746	0.731	0.781	0.753	0.057	0.696

* corrected with extinction values from replicate without inoculum

 

The resulting nominal toxicity threshold (TT), determined graphically at 883 mg prod./L. However, due to the DOC and TCC measurements only 0.11 % of the added test substance persist in the test medium. Thus, the actual TT (which is equivalent to the EC10) must be 0.97 mg prod./L.

 

Table 2: Extinction after 16 - 20 h in the reference substance and the blank control

 

Concentration [mg prod./L]	Extinction at 436 nm
	Reference substance	Blank controls
3950.0	0.775	0.855
7900.0	0.695	0.901
15800.0	0.490	0.912
31600.0	0.220	0.903
63200.0	0.057	0.830
		0.810
		0.790
		0.788
		0.803
		0.809
Arithmetic mean		0.840

 

With respect to the historical test with the reference substance methanol, it can be concluded that the test conditions were optimal and the results are valid.

Validity criteria fulfilled:

yes

Conclusions:

The EC10 of stearic acid towards Pseudomonas putida can be stated to be 883 mg/L.

Description of key information

The EC10 of stearic acid towards Pseudomonas putida can be stated to be 883 mg/L.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

883 mg/L