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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

Study period:

from 12 October 2001 to 17 January 2002

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)

Deviations:

yes

Remarks:

The temperature in the culture room dropped below 20°C during short time periods (< 1 hour each) between days 4 and 6 of the test (minimum of 19°C). This minor deviation was not considered to have compromise the validity or the integrity of the study.

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge: inoculum was collected from a water treatment plant (Evreux, france) containing effluent from a predominantly domestic origin.
- Laboratory culture: under laboratory conditions in reconstituted water at 22°C
- Preparation of inoculum for exposure: the inoculum was prepared by initially sieving sewage sludge. The sludge was then centrifuged for 5 minutes, the supernatant was rejected and the pellet was redispersed in the mineral medium.
In order to wash out the dissolved organic carbon (DOC) and to lower the carbon organic content, the inoculum was preconditioned for 6 days before use at 22 +/- 2 °C. Air was bubbled through the inoculum during the preconditioning period.
- Concentration of sludge: 12 mg/L of suspended solids (d.w.)
- Water filtered: yes

Duration of test (contact time):

28 d

Initial conc.:

22.7 mg/L

Based on:

test mat.

Initial conc.:

10 mg/L

Based on:

other: TOC

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

TEST CONDITIONS
- Composition of medium: reconstituted water (OECD and EEC recommended) using deionised water.
- Additional substrate: /
- Test temperature: between 19 and 24°C
- pH: 7.54 in the mineral medium before the start of the test, 7.83 to 8.13 measured in the test flasks at the end of the test.
- pH adjusted: no
- Aeration of dilution water: air was bubbled through each parallel at the rate of 30 – 100 mL/min during the test
- Suspended solids concentration: 12 mg/L (dry weight)
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: dark glass bottles fitted with dark glass stoppers
- Number of culture flasks/treatment: 1 (reference item, air control, abiotic sterile control treatments) and 2 (blank and test item treatments)
- Method used to create aerobic conditions: aeration (air bubbled during the test)
- Measuring equipment: titration

SAMPLING
- Sampling frequency: on days 1, 4, 6, 8, 11, 13, 15, 18, 22, 25 and 29
- Sampling method: see "Details on analytical method"
- Sample storage before analysis: data not available

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes (2.4 L of mineral medium + inoculum at 12 mg/L of suspended solids (dry weight))
- Abiotic sterile control: yes (2.4 L of mineral medium + test item at 10 mg TOC/L + sterilizing item (sodium azide) at 30 mg/L)
- Toxicity control: no
- Other:
* procedure control: 2.4 L of mineral medium + inoculum at 12 mg/L of suspended solids (dry weight) + reference item (sodium acetate) at 10 mg TOC/L,
* air control: only 2.4 L mineral medium

Reference substance:

acetic acid, sodium salt

Remarks:

10 mg TOC/L

Key result

Parameter:

% degradation (CO2 evolution)

Value:

22.18 - 50.35

Sampling time:

28 d

Remarks on result:

other: Flask 1: 50.35 % Flask 2: 22.18 %

Details on results:

TEST ITEM TREATMENT:
Biodegradation values of test item replicates deviated by more than 20% at the end of the test (50% and 22% of degradation in the first and second replicates, respectively). The same problem was observed in a previous study. It was probably due to the very low water solubility of the test item (11.9 µg/L). ). It was therefore considered, in view of the hazard assessment, that the test item biodegradation result retained for data interpretation would be those obtained in the replicate where the degradation percentage was the lower after 28 days. The 10-day window started on the 11th day. Biodegradation of the test item cerium and iron oxide isostearate totalled 16% at the end of this 10-day window (21th day) and 22% at the end of the test.

ABIOTIC CONTROL TREATMENT:
The test item degradation percentage reached 24% in the abiotic sterile control at the end of the test and was therefore similar to that obtained in the test solution. Consequently, it was assumed that the degradation of the test item in the test solution (in presence of activated sludge) came completely or at least partly from an abiotic reaction.

Results with reference substance:

The reference compound degraded normally under the test conditions (81.33 % biodegradation after 28 days). Such results confirmed the presence of an acceptable microbial community and confirmed the system integrity.

Table 1: cumulative percentage of biodegradation

	Test item		Reference	Abiotic
Day	No. 1	No. 2	item	Control
1 4 6 8 11 13 15 18 22 25 28	13.79 26.73 35.52 40.51 43.11 44.66 45.91 47.56 49.50 50.20 50.35	1.50 7.74 8.34 9.74 10.04 11.29 12.94 14.79 16.93 18.63 22.18	1.10 22.83 42.91 54.30 63.39 69.24 73.48 77.83 80.18 80.18 81.33	0.40 1.65 5.89 7.49 8.19 8.79 9.79 11.99 15.09 16.78 24.18

Validity criteria fulfilled:

no

Remarks:

Biodegradation of reference item and control flasks were valid. However biodegradation values of test item replicates deviated by more than 20% at the end of the test. See more details in results.

Interpretation of results:

other: non readily biodegradable

Conclusions:

Under the experimental conditions, cerium and iron oxide isostearate is non readily biodegradable in the 28-day modified Sturm test.

Executive summary:

The ready biodegradability of cerium and iron oxide isostearate was evaluated using a 28-day modified Sturm test according to OECD guideline 301B and GLP.

7 flasks were used to determine the quantity of carbon dioxide evolved by the degradation of the test item: 2 inoculum blanks, 2 inoculum with the test item (10 mg TOC/L), 1 procedure control (with the reference item), 1 air control and one abiotic sterile control.

The inoculum consisted of domestic, non-adapted, activated sludge (12 mg/L dw)

 

The 10-day window started on the 11th day. Biodegradation of the test item cerium and iron oxide isostearate totalled 16% at the end of this 10-day window (21th day) and 22% at the end of the test.

On the other end, the test item degradation percentage reached 24% in the abiotic sterile control at the end of the test and was therefore similar to that obtained in the test solution. Consequently, it was assumed that the degradation of the test item in the test solution (in presence of activated sludge) came completely or at least partly from an abiotic reaction.

 

Biodegradation values of test item replicates deviated by more than 20% at the end of the test (50% and 22% of degradation in the first and second replicates, respectively). The same problem was observed in a previous study. It was probably due to the very low water solubility of the test item (11.9 µg/L).

 

Under the experimental conditions, cerium and iron oxide isostearate is non readily biodegradable in the 28-day modified Sturm test.

Reference 2

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

See attached document in section 13 "Assessment report" for justification and rationale of the analogy approach.
Original letters from the French Competent Authorities requiring the read across to be done with cerium and iron oxide isostearate are attached below.

Reason / purpose for cross-reference:

read-across source

Key result

Parameter:

% degradation (CO2 evolution)

Value:

22.18 - 50.35

Sampling time:

28 d

Remarks on result:

other: Flask 1: 50.35 % Flask 2: 22.18 %

Conclusions:

Iron oxide isostearate is to be considered as cerium and iron oxide isostearate as non readily biodegradable.

Executive summary:

The source and target substances present similar characterization (nanoparticles of very similar parameters), and similar physico-chemical and ecotoxicological properties (high melting point, low vapour pressure, very low water solubility, no expected bioaccumulation potential when considering cerium and iron elements and isostearate parts, no acute toxicity to daphnids up to and including the saturation concentration). This similarity supports the relevance of the read-across.

Thus, the ready biodegration potential is expected to be the same for the source and target substances.

Iron oxide isostearate is to be considered as cerium and iron oxide isostearate as non readily biodegradable.

Description of key information

By analogy with cerium and iron oxide isostearate, iron oxide isostearate should be considered as non readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Additional information

In the absence of data on iron oxide isostearate and as validated by the French Competent Authorities in September 2005 (see the document attached in the target endpoint study record), the biodegradation was assessed based on data on the analogue cerium and iron oxide isostearate. This GLP-compliant study was performed according to OECD test guideline 301B, quoted as reliability 1 according to Klimisch criteria and flagged as a key study.