3,5-xylenol

Biodegradation in water: screening tests

Administrative data

Endpoint:

biodegradation in water: screening tests

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Not carried out to modern guidelines but an experienced laboratory carried out the experiment using a developed standard test.

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

1976

Materials and methods

Principles of method if other than guideline:

On the basis of experience obtained the Department of Water Technology and Environmental Engineering has developed a standard test for the comparison of biological degradability of organic substances.

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

3,5-xylenol

EC Number:

203-606-5

EC Name:

3,5-xylenol

Cas Number:

108-68-9

Molecular formula:

C8H10O

IUPAC Name:

3,5-dimethylphenol

Details on test material:

Not stated.

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
Biological medium prepared by adding 1 mL each of solutions of calcium chloride (25g in 1L distilled water), magnesium sulphate (22.5 g in 1L) and ferric chloride (0.25g in 1L) with 5 ml ammonium sulphate solution (10g in 1 L), 20 ml of pH 7.2 phosphate buffer and 100 ml tapwater to ca 800 ml of distilled water, then made up to 1000 ml with distilled water.

Study design

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, adapted

Details on inoculum:

Activated sludge taken from sewage treatment plant is cultivated in a 1000ml volumetric cyclinder and aerated with pressure air. Every day 200 ml of the mixture is driven off so that the sludge age is 5 days. After driving off the 200 ml aeration is interrupted, and after sedimentation ca 600 ml of the liquid phase is driven off. The residue (200 ml of thickened activated sludge) is diluted to ca 800 ml and 600 mg/l starch or glucose, 600 mg/L peptone, 25 mL phosphate buffer pH 7.2 and the solution of the tested compound are added. Then the mixture is made up to 1000 ml with tap water and aerated for 23 h. After this period the procedure is repeated. The concentration of the tested substance is gradually increased so that after 20 days of adaptation it reaches the equivalent value of 200 mg/L COD.

Duration of test (contact time):

ca. 1 - ca. 20 d

Initial test substance concentration

Initial conc.:

ca. 200 mg/L

Based on:

COD

Parameter followed for biodegradation estimation

Parameter followed for biodegradation estimation:

inorg. C analysis

Details on study design:

To 1000-1500ml of the biological medium such amount of the solution of the substance tested is added that the intial COD is 200 mg/L. Then an amount of the adapted activated sludge is dosed to the medium that the concentration of the dry matter is 100 mg/L. Simultaneouly a blank test is prepared to verify the activity of the inoculum. With volatile substances a test without the inoculum is carried out as well to differentiate the actual biological degradation and the losses due to volatilization. 50-80 ml of the mixture are taken, and after filtration through a medium porosity filter paper, the inital vlaues of COD or organic carbon of the liquid phase are determined. Initial levels in the beakers are marked and afterwards placed in a dark room at 20 +/- 3 degrees C on magnetic stirrers. The oxygenation capacity of this device was ca 11 mg oxygen h/L at 800 rev/min. At regular time intervals ca 50-80 ml of the sample are taken for analysis. The experiment was carried out until there is no decrease in COD. After that time the total percentage of COD removed and the rate of degradation are evaluated. If 90% of the initial COD is removed in 120h of incubation (degradation rate being more than 15 mg of COD g/h) then the test substance can be considered to be biologically readily decomposable.

Results and discussion

Test performance:

For 3,5-Dimethylphenol 89.3% COD was removed with a rate of biodegradation of 11.0 mg COD g/h.

% Degradation

Parameter:

other: COD removal

Value:

ca. 89.3

Sampling time:

2 d

Remarks on result:

other: sampling time approximate

Details on results:

This result is < than the 15 mg COD g/h rate required to be classified as Readily Biodegradable in this paper.

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable, but failing 10-day window

Conclusions:

The results show that 3,5-dimethylphenol is biodegradable with 89.3% COD removed. The rate of biodegradation is 11.0 mg COD g/h which is less than the 15 mg COD g/h stated to be readily biodegradable in this paper.

Executive summary:

The author carried out experiments on the degree and rate of biological degradation of 123 organic compounds including 3,5 -dimethylphenol (3,5 -xylenol) with respect to the decrease of organic substance in terms of COD. The organic substances were the sole source of carbon for the microbes of the inoculum, adapted activated sludge being the inoculum. Samples were taken at regular intervals and the COD measured until there was no more decrease in COD. After that time the total percentage of COD removed and the rate of degradation were evaluated.

For 3,5 -dimethylphenol 89.3% COD was removed with a degradation rate of 11 mg COD g/h. To be considered readily biodegradable according to this experiment 90% of the initial COD had to be removed in 120 hours with the degradation rate being over 15 mg COD g/h.