4,4'-cyclohexylidenedi-o-cresol

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

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

yes

Remarks:

- modifications to the study guidelines included the use of an industrial sludge in addition to a municipal sludge and the use of a larger sludge inoculum than is specified in the guidelines.

GLP compliance:

yes

Analytical monitoring:

yes

Vehicle:

yes

Details on test solutions:

For those bottles which were to receive DMBPC, the inhibitory reference substance or benzoate, 200 mL of the bottle contents were first poured into a beaker. The neat chemicals were weighed into an aluminium weigh pan and the weights recorded. The powder was gently tapped into a small glass funnel that rested in the neck of the bottle and several streams of the reserved medium was directed into the weigh pan from a Pastuer pipette to wash any remaining powder into the funnel. The remaining reserved medium was poured into the funnel to wash all remaining powder into the bottle. At this point, all bottles were place in the water baths and stirring was initiated. The bottles were equilibrated approximately 2 hours until the test was initiated.

Test organisms (species):

activated sludge of a predominantly industrial sewage

Details on inoculum:

Activated sludge, from the Waste Water Treatment Plant (WWTP) of an industrial facility in manufacturing site (MF Site), which consisted of a return activated sludge system from which return sludge, influent and effluent were used in this study. In addition, a sample of return sludge from the Schenectady City Water Pollution Control Facility was used in this study.

Inoculum preparation: Biomass (return sludge) was obtained from the Sponsor’s industrial facility in MF Site and aerated immediately before packaging on ice with overnight shipment to the testing facility. Samples of influent and effluent (from clarifiers) were also shipped. Upon arrival to the test facility aeration to the sludge was initiated. Return sludge was obtained from the Schenectady municipal plant the morning the MF Site samples arrived. Time elapsed from sampling of the Schenectady sludge until aeration began was approximately 30 minutes. After aeration for an hour, samples of each sludge were taken and prepared for the MLVSS determination (missed liquor volatile suspended solids, an estimate of the biomass solids).

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

30 d

Remarks on exposure duration:

20-30 days

Post exposure observation period:

none

Test temperature:

24 ± 1°C

Nominal and measured concentrations:

50 and 200 mg/L (Nominal)

Details on test conditions:

A Challenge Environmental Systems, Inc. respirometer with the capability of running 16 vessels simultaneously was used to measure the oxygen uptake rate of the biomass automatically over time. Each vessel held 500 mL and was held in place in a water bath situated over synchronized stirrers. A small trap was suspended in the top of each vessel and held potassium hydroxide solution to trap the carbon dioxide that was generated during active respiration.

In the Challenge system, oxygen demand was quantified by counting oxygen bubbles that were generated by precisely milled flow measuring cells. As the biomass depleted oxygen and the carbon dioxide was adsorbed by the potassium hydroxide, pure oxygen was pulled into the flow measuring cell through a manifold. Oxygen bubbles of a fixed volume were formed in an inert silicone oil in the lower section of the cell and passed through a detection section which activated a counter in the interface module. Each of the 16 cells was calibrated for the bubble size it produced and the mass of oxygen the bubble contained. The oxygen flowed from the cell into a flexible tube which was attached to a needle inserted into the vessel through a butyl rubber septum. The system was controlled by a computer and the collected data were stored as the accumulated oxygen uptake over time. The test was run at 24 ± 1°C. A test was performed to qualify the respirometer prior to use which demonstrated that all 16 cells functioned identically.

Reference substance (positive control):

yes

Remarks:

Sodium benzoate (Benzoic acid, sodium salt; Aldrich Chemical Company, Milwaukee, WI) was used as the reference substrate to confirm that the municipal sludge inoculum was active.

Duration:

30 d

Dose descriptor:

NOEC

Effect conc.:

> 100 mg/L

Remarks on result:

other: Typical municipal sludge

Duration:

30 d

Dose descriptor:

NOEC

Effect conc.:

> 200 mg/L

Remarks on result:

other: Industrial sludge

Validity criteria fulfilled:

not specified

Conclusions:

Under the conditions of this study, the 30 d NOEC was > 100 mg/L for typical municipal sludge and >200 mg/L for industrial sludge.

Executive summary:

The potential of the test material to undergo inhibit the microorganisms in activated sludge under aerobic conditions was investigated in accordance with the standardised guideline OECD 209 under GLP conditions.

Modifications to the study guideline included the use of an industrial sludge in addition to a municipal sludge and the use of a larger sludge inoculum than is specified. The activated sludge was exposed to the test material for a contact period of 20 to 30 days under static conditions at initial nominal concentrations of 50 and 200 mg/L. Analytical monitoring took place by HPLC.

Under the conditions of this study it was determined that DMBPC is not inhibitory to the normal activity of an industrial sludge at concentrations as high as 200 mg/L; DMBPC is not inhibitory to the tested municipal sludge as high as 100 mg/L.

Description of key information

Under the conditions of this study, the 30 d NOEC was > 100 mg/L for typical municipal sludge and >200 mg/L for industrial sludge.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

100 mg/L

Additional information

The potential of the test material to undergo inhibit the microorganisms in activated sludge under aerobic conditions was investigated in accordance with the standardised guideline OECD 209 under GLP conditions. The study was awarded a reliability score of 1 in accordance with the criteria set forth by Klimisch et al. (1997).

Modifications to the study guideline included the use of an industrial sludge in addition to a municipal sludge and the use of a larger sludge inoculum than is specified. The activated sludge was exposed to the test material for a contact period of 20 to 30 days under static conditions at initial nominal concentrations of 50 and 200 mg/L. Analytical monitoring took place by HPLC.

Under the conditions of this study it was determined that DMBPC is not inhibitory to the normal activity of an industrial sludge at concentrations as high as 200 mg/L; DMBPC is not inhibitory to the tested municipal sludge as high as 100 mg/L.