p-cymene

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 C (Ready Biodegradability: Modified MITI Test (I))

GLP compliance:

not specified

Oxygen conditions:

aerobic

Inoculum or test system:

mixture of sewage, soil and natural water

Details on inoculum:

- Source of inoculum/activated sludge: collected from 10 sites in Japan (sludge, sewage, soil surface water)
- Concentration of sludge: 30 mg/L

Initial conc.:

100 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Parameter followed for biodegradation estimation:

TOC removal

Parameter followed for biodegradation estimation:

test mat. analysis

Details on study design:

- Test temperature: 25 +- 1 °C
- Concentration of test substance 100 mg/L
- Concentration of activated sludge 30 mg/L (as the concentration of suspended solid)
- Volume of testing solution 300 mL
- Duration of test 14 days
- Number of culture flasks/concentration: 6 container (1 x water + test substance, 3 x sludge + test substance, 1 x sludge + reference substance, 1 x blank)

Reference substance:

aniline

Key result

Parameter:

% degradation (O2 consumption)

Value:

88

Sampling time:

14 d

Parameter:

% degradation (TOC removal)

Value:

88.6

Sampling time:

14 d

Parameter:

% degradation (test mat. analysis)

Value:

100

Sampling time:

14 d

Results with reference substance:

Biodegradation rates of aniline after 7 and 14 days determined based on BOD were 53% and 87%, respectively, so the validity of the test conditions was confirmed.

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

The test item is readily biodegradable.

Reference 2

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

June 1999

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic (adaptation not specified)

Details on inoculum:

Fresh activated sludge from a biological waste water treatment plant treating predominantly domestic sewage (City of Geneva Aire) was used. The sludge is collected in the morning, washed 3 times in the mineral medium (centrifuging at 1000g for 10 minutes, discarding the supernatant and resuspending in mineral medium) and kept aerobic until being used on the same day.

The dry weight and suspended solids is determined by taking 50 ml samples of the homogenised sludge, evaporating the water on a steam bath, drying in an oven at 105-110 °C for two hours and weighing the residue.

Duration of test (contact time):

29 d

Initial conc.:

100 mg/L

Based on:

test mat.

Initial conc.:

3.22 mg/L

Based on:

ThOD

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

Equipment
Respirometer: SAPROMET D12, made by J.M VOITH Gmbh, D-7920 Heidenheim.

The water used in the study was deionised water containing <10 mg/l dissolved organic carbon.

Mineral medium preparation
Stock solution A, made up to 1 litre of water:
KH2PO4: 8.5 g
K2HPO4: 21.75 g
Na2HPO4.2H2O: 33.4 g
NH4Cl: 0.5 g
Stock solution B, made up to 1 litre of water:
CaCl: 27.5 g
Stock solution C, made up to 1 litre of water:
MgSO4.7H2O: 22.5 g
Stock solution D, made up to 1 litre of water:
FeCl3.6H2O: 0.25 g
HCl conc.: one drop
Prepared by mixing 50 ml of solution A and 2000 ml deionised water and adding 5 ml of each of solutions B, C and D. The pH is measured and if necessary adjusted to 7.4+-0.2 with phosphoric acid or potassium hydroxide.

Two replicate 250 ml flasks were filled with 250 ml of mineral medium and the following test solution concentrations:
- test substance at a concentration of 100 mg/l;
- positive control or reference substance (sodium benzoate) at a concentration of 100 mg/l; and
- control blank.

A volume of suspended sludge corresponding to 7.5 mg dry weight was then added to each flask. The pH of the resulting test solution was only then measured if the test substance is of acid of alkaline character, if not measured then the pH was assumed to be the same as the mineral medium. Neutral test substances such as sodium benzoate do not tend to alter the pH of the test solution by more than 0.1 pH unit. About 2 g of soda lime is place in the attachment of the stopper and the flasks are closed and place in the water bath of the SAPROMAT. After temperature and pressure equilibration, the oxygen meters of the instrument are set to zero (time zero of the experiment).

Oxygen consumption was recorded daily alongside temperature and stirrer checks. At the end of the test the pH is measured again.

A concurrent study examining the toxicity of the test substance to the inoculum was conducted according to the OECD 301 F technical guidance. Two replicate 250 ml flasks were filled with 250 ml of mineral medium and the test substance and the reference substance (sodium benzoate), at concentrations of 100 mg/l each. These were incubated alongside the other test items and had their daily oxygen consumption readings recorded. If the daily oxygen readings of these flasks were below that of the positive control/reference substance then the test chemical can be assumed to be inhibitory to the inoculum used.

Reference substance:

benzoic acid, sodium salt

Test performance:

Degradation of sodium benzoate (reference substance) exceeded 40% after 7 days and 65% after 14 days therefore the activity of the inoculum was verified and the test considered valid.

Parameter:

% degradation (O2 consumption)

Value:

65

Sampling time:

29 d

Key result

Parameter:

% degradation (O2 consumption)

Value:

64

Sampling time:

28 d

Details on results:

Oxygen uptakes as read on the SAPROMAT meters are corrected:
- by deducting the basic oxygen uptake of the sludge (blank control)
- proportionally to account for the small difference between actual and nominal concentrations of the test and reference substances.

The means of identical flasks were used to derive the final results.

Results with reference substance:

Degradation of sodium benzoate exceeds 40% after 7 days and 65% after 14 days. At 28 days degradation was 98%.

ThOD = 3.22 mg O₂/l

Para Cymene - BOD mg O2/l, adjusted to nominal concentrations

		Days	3	7	13	21	28	29
BOD Sludge	1st Flask	B1	5	7	11.0	13.0	15.0	15.0
	2nd Flask	B2	4.0	7.0	10.0	13.0	17.0	17.0
	mean	B	4.5	7.0	10.5	13.0	16.0	16.0
BOD Test Substance	1st flask	C1	90.2	156.4	190.0	213.1	223.8	225.7
	2nd flask	C2	109.1	161.7	195.4	212.3	222.3	224.3
	1st fl. corr.	C1 -B	85.7	149.4	179.5	200.1	207.8	209.7
	2nd fl. corr.	C2 -B	104.6	154.7	184.9	199.3	206.3	208.3
% degr.	1st flask	D1	27	46	56	62	65	65
	2nd flask	D2	32	48	57	62	64	65
	mean	D	30	47	57	62	64	65

B=(B1 + B2) / 2

D1 = 100 * (C1 - B) / ThOD * [S]

D2 = 100 * (C2 - B) / ThOD * [S]

D = (D1 + D2) / 2

where [S]: initial test substance concentration.

Validity criteria fulfilled:

yes

Interpretation of results:

inherently biodegradable

Conclusions:

p-Cymene undergoes 65% biodegradation after 29 days. p-Cymene should be regarded as not readily but inherently biodegradable according to this test.

Executive summary:

The biodegradability of p-cymene was tested according to OECD TG 301 F. p-Cymene should be regarded as inherently biodegradable according to this test and the guideline.

The test item undergoes 65% biodegradation after 29 days (64% after 28 days) in the test conditions. Biodegradation starts on day 3 and reaches 57% at the end of the 10 day window (days 3 to 13). Therefore, the test item should be regarded as not readily but inherently biodegradable. The curves obtained with the reference substance alone and with p-cymene and reference substance show no toxic effect of the test item to the micro-organisms at the test concentration.

Description of key information

readily biodegradable (88% after 14 days, OECD 301C)

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Type of water:

freshwater

Additional information

Two biodegradation test are available. The first study was performed according to OECD 301C. A mixture microorganisms obtained from sludge, sewage, surface water and soil was epxposed to 100 mg/L of the test substance. Based on BOD a bidegradation rate of 88 % wasobserved after 14 days. Based on this result the test item can be considered as readily biodegradable.

The second study the biodegradability of the test item was tested according to OECD TG 301 F and GLP. The test item undergoes 65% biodegradation after 29 days (64% after 28 days) in the test conditions. Biodegradation starts on day 3 and reaches 57% at the end of the 10 day window (days 3 to 13) and supports the results of the first study. The results of the toxicity control show no toxic effect of the test item to the micro-organisms up to a concentration of 100 mg/L.