Registration Dossier

Administrative data

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

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2015
Report Date:
2015

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation))
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid
Specific details on test material used for the study:
Identification: Tungstosilicic-acid
Physical state/Appearance: white crystalline solid
Batch: MKBR8664V
Purity: ≥99.9%
Expiry Date: 11 February 2016
Storage Conditions: room temperature in the dark over silica gel

Sampling and analysis

Analytical monitoring:
no

Test solutions

Vehicle:
no
Details on test solutions:
A nominal amount of test item (2500 mg) was dissolved in water and the volume adjusted to 1 liter to give a 2500 mg/L stock solution from which dilutions were made to give 250 and 25 mg/L stock solutions. An aliquot (200 mL) of the 25 mg/L stock solution was dispersed with synthetic sewage (16 mL), activated sewage sludge (250 mL) and water, to a final volume of 500 mL, to give the required concentration of 10 mg/L. Similarly, aliquots (200 mL) of the 250 mg/L and 2500 mg/L stock solutions were used to prepare the test concentrations of 100 and 1000 mg/L.

Test organisms

Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Name and location of sewage treatment plant where inoculum was collected: Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK.
- Method of cultivation: continuous aeration at 21 ºC - used on the day of collection.
- Preparation of inoculum for exposure:
- Pretreatment: aeration with oil free compressed air.
- Initial biomass concentration: 3.0g/L

Study design

Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
3 h

Test conditions

Test temperature:
20C approximately
pH:
7.1
Dissolved oxygen:
The dissolved oxygen concentrations after 30 minutes contact time in all vessels were above 60 to 70% of the dissolved oxygen saturation level of 8.9 mg O2/L.
Details on test conditions:
TEST SYSTEM
- Aeration: no
- No. of vessels per control (replicates): 3 (lower concentrations only 1)
- No. of vessels per abiotic control (replicates): 4
- Nutrients provided for bacteria: synthetic sewage.

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water:
- Particulate matter:
OTHER TEST CONDITIONS
- Adjustment of pH: yes, pH adjusted to 7.1 using 1M NaOH solution.

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : As each vessel reached 3 hours contact time an aliquot was removed from the conical flask and poured into the measuring vessel (250 mL darkened glass Biological Oxygen Demand (BOD) bottle) and the rate of respiration measured using a Yellow Springs dissolved oxygen meter fitted with a BOD probe.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: geometric
- Justification for using fewer concentrations than requested by guideline: upper limit of 1000mg/L used
- Range finding study
- Test concentrations: up to 2500mg/L
Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenol

Results and discussion

Effect concentrationsopen allclose all
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Duration:
3 h
Dose descriptor:
EC10
Effect conc.:
> 10 - < 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Results with reference substance (positive control):
- Results with reference substance valid? yes
- Relevant effect levels: EC50=7.0mg/L

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Executive summary:

In a guideline study to assess the toxicity to activated sludge, the EC50 value was in excess of the maximum tested concentration of 1000mg/L. The EC10 value was in the range 10 -100mg/L, which suggests that the dose response curve that is quite shallow and that the EC10 figure should be used as a conservative basis for establishing the PNEC.