p-cymene

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

June 1999

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

other: OECD 301 F

Deviations:

no

Principles of method if other than guideline:

Toxicity control used in OECD Guidelines for Testing of Chemicals, Method No. 301F

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Details on test solutions:

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.

Test organisms (species):

activated sludge of a predominantly domestic sewage

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.
Activated sludge dry weight = 2.421 g/l - To obtain a concentration of 30 mg/l (dry weight) in a 250 ml flask, 3.1 ml of sludge was required.

Test type:

static

Water media type:

freshwater

Total exposure duration:

28 d

Test temperature:

22°C

pH:

initial pH: 7.5

Nominal and measured concentrations:

Nominal concentrations
- test substance: p-cymene100 mg/l
- reference substance : sodium benzoate 100 mg/l

Details on test conditions:

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 (positive control):

yes

Remarks:

Sodium benzoate

Key result

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other:

Remarks:

Inhibition of biodegradation of reference substance

Details on results:

The oxygen consumption curves for the reference substance alone and the reference substance plus p-cymene showed no toxic effects to the micro-organisms at the test concentration (100 mg/l nominal).

Validity criteria fulfilled:

not specified

Conclusions:

The oxygen consumption curves for the reference substance alone and the reference substance plus p-cymene showed no toxic effects to the micro-organisms at the test concentration (100 mg/l nominal).

Description of key information

The oxygen consumption curves for the reference substance alone and the reference substance plus p-cymene showed no toxic effects to the micro-organisms at the test concentration (100 mg/l nominal).

Key value for chemical safety assessment

EC50 for microorganisms:

100 mg/L