Hexan-1-ol

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2005-01-10 to 2005-01-28

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

Good study conducted following OECD guideline 201 and conducted according to GLP (certified).

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Concentrations: all nominal concentrations were tested at time 0, 24 and 72 h.

- Sampling method: samples were taken from the vessels with algae and vessels prepared without algae.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: A stock solution was prepared by adding 180 mg of the test substance to sterilised test medium and adjusting the volume to 1 L. The solution was stirred for 24 hours. The stock solution was diluted with sterilised growth medium to obtain the nominal test concentrations under sterile conditions: 7.7, 17, 37, 82 and 180 mg hexanol/L.

- Controls: standard control using dilution water.

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Details on test organisms:

TEST ORGANISM

- Common name: freshwater green alga

- Strain: Pseudokirchneriella subcapitata

- Source (laboratory, culture collection): SAG, Culture Collection of Algae at Pflanzenphysiologisches Institut of the University at Göttingen, Albrecht von Haller Institut, Untere Klarspüle 2, D-37073 Göttingen, Catalog No 61.81.


ACCLIMATION

- Culturing media and conditions: The stock cultures were maintained fulfilling the criteria of the OECD guidelines. Prior to testing a pre-culture was established in test medium to obtain exponentially growing algae for the test.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Post exposure observation period:

None

Hardness:

N.R.

Test temperature:

22.0 - 22.2 °C

pH:

8.52 - 8.58 (Controls), 8.08 - 8.40 (test concentrations)

Dissolved oxygen:

N.R.

Salinity:

N.A.

Nominal and measured concentrations:

Nominal: 7.7, 17, 37, 82 and 180 mg hexanol/L
Mean measured (with algae): 4.72, 11.3, 31.2, 50.1 and 111.2 mg hexanol/L
Mean measured (without algae present): 5.48, 12.3, 29.3, 54.9 and 105.5 mg hexanol/L 

Details on test conditions:

TEST SYSTEM

- Test vessel: glass flask, with cultures being resuspended continuously by shaking on a laboratory shaker (Incubation Shaker Multitron ®, INFORS, Switzerland).

- Type: closed

- Material, size, headspace, fill volume: Test vessels are 250 mL conical glass flasks covered with silicone-sponge caps. The vessels and caps were  sterilized prior to use (autoclaving or heating). 

- Aeration: none

- Initial cells density: 10,000 cells/mL

- Control end cells density: 143.3x10^4 cells/mL

- No. of vessels per concentration: 3

- No. of vessels per control: 6


GROWTH MEDIUM

- Standard medium used: yes


TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: A sterilized synthetic growth medium according to OECD 201

- Culture medium different from test medium: no

- Intervals of water quality measurement: daily


OTHER TEST CONDITIONS

- Sterile test conditions: yes

-Adjustment of pH: none

- Photoperiod: continuous

- Light intensity and quality: 8000 Lux



EFFECT PARAMETERS MEASURED:

- Determination of cell concentrations: Cell concentrations were determined using an electronic particle counter (CASY 1 Model TT Schärfe System
Reutlingen, Germany) from time 0h to 72h every 24h. The correctness of the electronic counts was checked by microscopically counting following internal operation procedures. 


TEST CONCENTRATIONS

- Spacing factor for test concentrations: five concentrations arranged in a geometric series, spaced by a factor of 2.2

- Range finding study: yes, details not reported.

Reference substance (positive control):

no

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

11.3 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

LOEC

Effect conc.:

31.2 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

19.8 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

79.7 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

< 4.72 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

LOEC

Effect conc.:

< 4.72 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

4.97 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

20.5 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

biomass

Details on results:

- Exponential growth in the control: yes

Reported statistics and error estimates:

Calculation of the percent inhibition of growth rate, yield (cell counts) and biomass integral was performed according to the OECD guideline.
A concentration-effect relationship was observed and statistically analyzed to obtain effect concentrations.
The test results were statistically analyzed to determine EC10 and EC50 values together with 95 % confidence intervals using Probit-analysis assuming lognormal distribution of the values by using the computer program ToxRat.
The NOEC and LOEC values for yield and biomass were determined by the Welch t-test.

Table 1. Cell densities, biomass and growth rate, and percentage inhibition of the test organism treated at a range of concentrations of the test substance. Biomass and growth rate are the mean at 72 h, the percentage inhibition are expressed relative to the period 0 -72 h.

Treatment concentration (measured concentration average mg/L)				Cell density					Biomass	Biomass % inhibition	Growth rate	Growth rate % inhibition
Control 0		Replicate #		24 h		48 h	72 h			-	-	-
		1		5.0		27.0	136.3		-	-	-	-
		2		4.5		27.0	138.6		-	-	-	-
		3		4.6		29.3	148.6		-	-	-	-
		4		4.9		30.2	148.1		-	-	-	-
		5		4.6		29.7	140.4		-	-	-	-
		6		5.1		27.8	147.7		-	-	-	-
Mean (± SD)		-		4.8 ± 0.2		28.5 ± 1.4	143.3 ± 5.5		102.4 ±3.8	0	1.655 ± 0.013	0
4.72 mg/L		1		3.7		26.2	154.5		-	-	-	-
		2		3.1		21.6	137.8		-	-	-	-
		3		1.4		12.1	72.4		-	-	-	-
Mean (± SD)				2.7 ± 1.2		20.0 ± 7.2	121.6 ± 43.4		81.0 ± 30.0	20.9	1.583 ± 0.136	4.3
11.3 mg/L		1		3.0		23.8	145.7		-	-	-	-
		2		3.0		17.5	118.5		-	-	-	-
		3		2.6		16.6	117.0		-	-	-	-
Mean (± SD)				2.9 ± 0.2		19.3 ± 3.9	127.1 ± 16.2		83.2 ± 12.1	18.7	1.613 ± 0.041	2.5
31.2 mg/L		1		1.6		2.2	78.5		-	-	-	-
		2		1.7		6.5	43.5		-	-	-	-
		3		2.0		8.8	27.5		-	-	-	-
Mean ± SD				1.7 ± 0.2		5.8 ± 3.4	49.8 ± 26.1		30.0 ± 9.5	70.7	1.272 ± 0.175	23.1
50.1 mg/L		1		1.8		7.4	32.6		-	-	-	-
		2		2.0		7.7	36.0		-	-	-	-
		3		1.9		7.1	32.6		-	-	-	-
Mean (± SD)		-		1.9 ± 0.1		7.4 ± 0.3	33.8 ± 2.0		23.6 ± 1.4	76.9	1.173 ± 0.019	29.1
111.2 mg/L		1		1.6		4.0	7.8		-	-	-	-
		2		1.7		2.4	4.8		-	-	-	-
		3		1.5		3.5	6.0		-	-	-	-
Mean (± SD)		-		1.6 ± 0.1		3.3 ± 0.8	6.2 ± 1.5		5.5 ± 1.5	94.6	0.063 ± 0.079	63.6

Growth rate was significantly reduced between 50.1 and 111.2 mg/L. The calcuated ErL50 was 79.7 mg/L.

Table 2. Results of analytical monitoring (mg/L).

Nominal conc. (mg/L)	Sample	Replicate #	0h (initial)	24 h	24 h % of initial	72 h	72 h % of initial	Avergae of all measurements
7.7	with algae	1	4.38	5.4	123	3.7	85
		2		5.5	126	3.7	85
		3		6.0	136	5.0	115
		Mean		5.6	128	4.1	95	4.72
	without algae	4	5.34	5.5	102	5.2	97
		5		6.00	111	5.7	106
		mean		5.7	107	5.4	102	5.48
17	with algae*	1	13.6	11.9	88	7.9	58
		2		12.9	95	8.7	64
		3		13.6	100	7.53	56
		mean		12.8	94	7.53	56	11.3
	without algae	4	13.6	13.3	98	8.0	59
		5		16.8	124	8.6	64
		mean		15.0	120	24.1	61	12.3
37	with algae**	1	32.5	39.0	120	24.1	74
		2		24.4	75	30.1	94
		3		40.4	124	26.5	82
		mean		34.6	107	26.5	81.6	31.2
	without algae	4	32.5	26.3	81	25.7	79.2
		5		39.4	121	19.4	60
		mean		32.8	101	22.5	69	29.3
82	with algae	1	54.7	51.0	92	28.7	26
		2		62.2	113	31.5	58
		3		71.1	130	34.2	63
		mean		61.3	112	34.2	63	50.1
	without algae	4	52.5	78.8	150	42.9	82
		5		64.6	123	38.4	73
		mean		71.7	137	40.7	77	54.9
180	with algae	1	112.9	120.9	107	104.3	92
		2		86.5	77	113.6	101
		3		84.9	75	152.2	135
		mean		97.4	86	123.4	109	111.2
	without algae	4	120.0	70.6	59	121.9	102
		5		75.6	63	124.7	104
		mean		73.1	61	123.3	103	105.5

* 0 h measured: 32.0 mg/L; regarded as outlier, omitted from evaluation.

** 0 h measured : 13.5 mg/L; regarded as outlier, omitted from evaluation.

Above are results if the analytical monitoring of the test substance (1 -hexanol) over the experimental duration in all test concentrations with and without algae. The mean measured test concentrations varied in some cases by more than +/-20% of the nominal values. The results are therefore interpreted with respect to the mean measured values. The values in bold are the values effectively used. All values at time 0 h were taken from the test solution prior to the addition of algae. Samples at time 48h and 72h were taken from the exposure vessels.

Validity criteria fulfilled:

yes

Conclusions:

A 72h ErC50 value of 79.7 mg/L and NOEC value of 11.3 mg/L have been determined for the effect of the test substance on growth rate of Pseudokirchnerella subcapitata.

Description of key information

(72 h) ErC₅₀ 79.7 mg/L, NOEC 11.3 mg/L, ErC₁₀ 19.8 mg/l freshwater algae P. subcapitata.

Key value for chemical safety assessment

EC50 for freshwater algae:

79.7 mg/L

EC10 or NOEC for freshwater algae:

19.8 mg/L

Additional information

A 72h ErC₅₀ of 79.7 mg/L, NOEC of 11.3 mg/L and ErC₁₀ of 19.8 mg/L have been determined for the effect of hexan-1-ol on growth rate of Pseudokirchneriella subcapitata. This study has been chosen as key as it reflects the lowest reliable value available for this endpoint.

A study (Bringmann and Kuhn, 1977) has determined a Toxicity Threshold value of 30 mg/L.

Other studies which have been assigned reliability 4 have determined LOECs in the range 18 to 75 mg/L.

Biodegradation by algae

Rapid degradation in water is indicated by the difficulties encountered in long-term toxicity to invertebrates (Daphnia reproduction) test for long chain aliphatic alcohols (Section 6.1.4). Alcohols in the range C10-C15 were found to be rapidly removed from the test medium. This was attributed to metabolism by algae present as a food source in tests, and in later stages of the 21-day tests to bacterial degradation by microbes adsorbed onto the carapace of the test daphnids, despite daily cleaning of the animals.

Discussion of trends in the Category of C6-24 linear and essentially-linear aliphatic alcohols:

The data for single carbon chain length LCAAs show toxicity to increase from an ErC₅₀ of 80 mg/L for C6 to 0.33 mg/L for C12. The C14 and C16 LCAAs were not toxic to algae, indicating a toxicity cut-off at C14 and above. Two of the studies determined NOECs that are suitable for assessing long-term toxicity. A NOEC of 11 mg/L has been reported for hexan-1-ol based on measured exposure concentrations. A test with dodecanol resulted in a 72-h EC₀ (equivalent to a NOEC) value of 0.085 mg/L.

Other algal studies used a WAF methodology and/or used test concentrations greater than the limit of water solubility and/or did not report a NOEC or equivalent statistic.

The data for mixed carbon chain length LCAAs (commercial products) shows that substances containing LCAAs with carbon numbers in the ranges of C7-9 to C12-15 exerted toxicity at concentrations of between 3.1 and 0.043-0.092 mg/L. At these concentrations all the constituents are likely to have been fully dissolved. For the C12-18 and C14-15 multi-constituent substances there was evidence of toxic effects in tests conducted on water-accommodated fractions prepared at loading rates that will have exceeded the solubility of some constituents.