Hexanoic acid

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

toxicity to microorganisms, other

Remarks:

Pseudomonas putida growth inhibition test

Type of information:

migrated information: read-across based on grouping of substances (category approach)

Adequacy of study:

key study

Study period:

15 Mar - 16 Mar 1988

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Basic data given (comparable to guideline)

Qualifier:

equivalent or similar to guideline

Guideline:

other: ISO 10712

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: A saturated solution containing 680 mg prod./L and an oversaturated solution containing 1360 mg/L were prepared using sterile Milli-Q water which was mixed with an magnetic stirrer for 10 min. The pH was adjusted to 6.8 - 7.2 with NaOH.
- Controls: 10 with inoculum without test substance (series B) to determine turbidity and for each test concentration 1 control without inoculum to determine occuring colouration

Test organisms (species):

Pseudomonas putida

Details on inoculum:

- Laboratory culture: obtained from RIVM, Bilthoven, Netherlands
- Method of cultivation: kept in agar plant tubes with a nutrient stock solution, incubated at 25 °C
- Preparation of inoculum for exposure: 7 days old stock cultures were inoculated in a fluid nutrient medium in Erlenmeyer flasks for 16 - 20 h at 25 °C. Subsequently the extinction of the monochromatic radiation was measured at 436 nm in a 10 mm layer of the bacterial suspension by photoelectric measurement. On basis of the measured values the turbidity was adjusted with sterile saline to the value of the Formazin standard suspension (TU/F/436 nm = 10) with which the spectrophotometer was calibrated.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

18 h

pH:

6.8 - 7.2, adjusted with NaOH

Nominal and measured concentrations:

nominal: 0.266, 0.531, 1.063, 2.125, 4.25, 8.50, 17.00, 34.00, 68.00, 136.00, 272.00, 544.00, 1088.00 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Material, size, headspace, fill volume: 300 mL Erlenmeyer flasks stoppered with aluminum caps containing 100 mL test medium
- No. of vessels per concentration (replicates): 3 + 1 control (please refer to "details of test solution" above)
- No. of vessels per control (replicates): 10

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: sterile Milli-Q water (Milipore Corp., Bedford, USA)

OTHER TEST CONDITIONS
- Adjustment of pH: adjusted to 6.8 - 7.2 with NaOH solution

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : turbidity after 16 -20 h

Reference substance (positive control):

yes

Remarks:

Methanol

Duration:

18 h

Dose descriptor:

EC10

Effect conc.:

912 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: mean extinction value

Results with reference substance (positive control):

- Results with reference substance valid? yes

Reported statistics and error estimates:

The toxicity threshold (TT) is determined graphically. The mean extinction values of each dilution step were plotted against the logarithm of the mean values of the test substance concentration.

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

Concentration [mg prod./L]	Extinction at 436 nm
	Replicate I	Replicate II	Replicate III	Arithm. mean of replicates	Replicate without inoculum
0.226	0.490	0.500	0.470	0.487	0.000
0.531	0.471	0.480	0.469	0.473	0.000
1.063	0.463	0.460	0.456	0.460	0.000
2.125	0.452	0.450	0.460	0.454	0.000
4.250	0.458	0.430	0.466	0.451	0.000
8.500	0.447	0.450	0.459	0.452	0.000
17.000	0.469	0.434	0.463	0.455	0.000
34.000	0.458	0.450	0.470	0.459	0.000
68.000	0.525	0.512	0.497	0.511	0.000
136.000	0.588	0.580	0.570	0.579	0.000
272.000	0.710	0.740	0.745	0.732	0.000
544.000	0.985	0.979	0.990	0.985	0.000
1088.000	0.198	0.212	0.220	0.210	0.000

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
4937.500	0.488	0.449
9875.000	0.440	0.440
19750.00	0.415	0.452
39500.00	0.270	0.459
79000.00	0.155	0.458
		0.449
		0.433
		0.439
		0.440
		0.438
Arithmetic mean		0.446

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.

Description of key information

EC10 (18 h) = 912 mg/L (nominal, similar to ISO 10712), read across

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

912 mg/L

Additional information

For hexanoic acid (CAS 142-62-1) a cell multiplication inhibition test with inconsistent results and two short abstracts on toxicity to microorganisms are available (RL4). Both, the cell multipication inhibition test and the abstracts on further toxicity tests are insufficient for evaluation.

Therefore ecotoxicological effects are predicted from adequate and reliable data for source substance by read-across to the target substance within the group applying the group concept in accordance with Annex XI, Item 1.5, of Regulation (EC) No 1907/2006. Toxicity on microorganisms was not observed fro fatty acids independant from carbon chain length. Therefore a reliable GLP-study conducted with octanoic acid (CAS 124-07-2) is chosen as read across.

In the cell multiplication inhibition test with octanoic acid (Coenen, 1988), conducted similar to ISO 10712, an EC10 (18 h) of 912 mg/L (nominal) was determined.

Richterich and Mühlenberg (2002) conducted a cell multiplication inhibition test with hexanoic acid according to ISO 10712, but although the method described a test with measurement of the turbidity after an exposure time of 16 h, the results are given for inhibition of oxygen consumption after 30 min. With regard to this inconsistency the study was disregarded.

The two abstracts dealt with the toxicity of hexanoic acid towards different microrgansims: Bacillus subtilis (Freese, 1979) and six different bacetria, which were anaeribically incubated (Powell and May, 1981).

Resulting from the read across approach with octanoic acid, no adverse effects of hexanoic acid on microorganisms are expected.