3,4-xylenol

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:

2019

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Freshwater Alga and Cyanobacteria, Growth Inhibition Test)

Version / remarks:

2011 (Annex 5 corrected: 28 July 2011)

GLP compliance:

yes (incl. QA statement)

Remarks:

Date certificate: 3 Jan 2017

Analytical monitoring:

yes

Vehicle:

no

Test organisms (species):

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

Details on test organisms:

TEST ORGANISM
- Strain: CCAP 278/4
- Source: Culture Collection of Algae and Protozoa (CCAP), SAMS Research Services Ltd, Dunstaffnage Marine Laboratory, Dunbeg, OBAN; Argyll PA37 1QA; Scotland, UK
- Method of cultivation: Fresh stocks are prepared every month on Z-Agar

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Test temperature:

21-24 °C

Nominal and measured concentrations:

nominal: 0 - 0.0500 – 0.158 – 0.500 – 1.58 – 5.00 – 15.8 – 50.0 mg/L
The highest, the lowest concentration, the concentration level 1.58 mg/L and the control were determined in fresh media (0 h) and at the end of the exposure interval (72 h) via GC-MS.
measured (0 h): < LOQ - 0.0524 - 1.65 - 52.4 mg/l
measured (72 h): < LOQ - 0.0529 - 1.53 - 47.8 mg/l

Details on test conditions:

TEST SYSTEM
- Test vessel: Sterile headspace flasks, volume: 59 mL, with aluminium tops with PTFE seals
- Type: closed
- Material, size, headspace, fill volume: without headspace
- Initial cells density: nominal: approximately 5 x 103 - 104 cells/mL, actual: 5416 cells/mL

GROWTH MEDIUM/DILUTION WATER
- OECD201 medium + additional NaHCO3 (250 mg/l)) and MES monohydrate (2665.6 mg/l) to enable sufficient growth under conditions without headspace

OTHER TEST CONDITIONS
- Photoperiod: 24 h/day light
- Light intensity and quality: approximately 4440 to 8880 lux, corresponding to 60 to 120 µE*m-2*s-1

EFFECT PARAMETERS MEASURED
- Determination of cell concentrations: fluorometer
- Chlorophyll measurement: the cell density was measured daily via Chlorophyll a-fluorescence, excitation at 436 nm, emission at 685 nm.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: √10
- Range finding study: test concentrations: 0.1, 1, 10 and 100 mg/l

Reference substance (positive control):

yes

Remarks:

potassium dichromate

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

9.32 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

1.58 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

< 0.05 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

cell number

Remarks:

yield

Details on results:

- Exponential growth in the control: yes
- Microscopic evaluation of the cells at the start and at the end revealed no morphological abnormalities

Results with reference substance (positive control):

- Results with reference substance valid? yes
- ErC50: 0.244
- EyC50: 0.236

Validity criteria fulfilled:

yes

Remarks:

(1) specific growth rate: 1.46 day-1 (2) mean coefficient of variation for section-by-section specific growth rates in control: 10.7% (3) coefficient of variation of average specific growth rates during the whole test period in replicate control: 1.65%

Executive summary:

The study was conducted under static conditions with an initial cell density of 5416 cells/mL. A stock solution with a nominal concentration of 50.0 mg/L was freshly prepared with dilution water. The dispersion was treated with ultrasound for 10 minutes at room temperature. Seven concentration levels were tested in a geometrical series with a spacing factor of √10. Three replicates were tested for each test item concentration and six replicates for the control. The environmental conditions were within the acceptable limits.

At the start of the exposure the measured concentrations were in the range of 104 to 105% of the nominal values. At the end of exposure after 72 hours, the measured concentrations were in the range of 96 to 106% of the nominal test item concentrations.

The EC₅₀-values with 95% confidence intervals for inhibition of growth rate (E_rC₅₀) and yield (E_yC₅₀) after 72 hours were 9.32 (8.80 – 9.86) mg/L and 3.98 (3.08 – 4.75) mg/L, respectively. The NOEC for inhibition of growth rate and yield was 1.58 mg/L and < 0.0500 mg/L, respectively. The preferred observational endpoint in this study is algal growth rate inhibition because it is not dependent on the test design, whereas biomass depends both on growth rate of the test species as well as test duration and other elements of test design.

Key value for chemical safety assessment