Registration Dossier

Environmental fate & pathways

Biodegradation in water: screening tests

Administrative data

Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2017-12 - 2018-03
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline study under GLP conditions

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2018
Report Date:
2018

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Version / remarks:
July 1992
Deviations:
no
GLP compliance:
yes (incl. certificate)
Remarks:
2016-06-29

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid: particulate/powder
Specific details on test material used for the study:
TEST SUBSTANCE: CYASORB® UV-24 Light Absorber
Main component: 2,2`-Dihydroxy-4-methoxybenzophenone CAS# 131-53-3
Molecular formula C14H12O4
Molecular Weight: 244.24 g/mol
Appearance: yellow powder
Batch number: CM70314A1
Expiration date: 14 March 2019

Study design

Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Activated sludge from the municipal wastewater treatment plant AZV Staufener Bucht; The treatment plant clarifies predominantly domestic wastewater and has a capacity of 140,000 inhabitant equivalents.
- Pretreatment: The activated sludge was washed twice with tap water by settling the sludge, decanting the supernatant and re-suspending the sludge.
- Concentration of sludge: 30 mg dry solids per litre
Duration of test (contact time):
28 d
Initial test substance concentration
Initial conc.:
ca. 20 mg/L
Based on:
TOC
Parameter followed for biodegradation estimation
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
Experimental set up
The CO2-free air production system consists of an air compressor, three 1000 mL gas wash bottles filled with dry soda lime in series followed by one bottle filled with 0.1 M NaOH (sodium hydroxide). At the end of the system is one gas wash bottle filled with demineralised water, followed by an empty one to catch any drops of condensation water. A color change of the soda lime from white to blue indicates that the CO2 absorption capacity is depleted. The CO2-free air is passed on to an air distributor with two input and 22 output channels and through PE-tubes. Gas wash bottles (2000 mL volume) with lateral connecting pieces for butyl rubber septa were used as reactors. The liquid volume was fixed as 1500 mL each. Mixing was performed by magnetic stirrers with 2 cm stir bars.
The CO2 produced in the reactors was absorbed in two 250 mL gas wash bottles in series each filled with 200 mL 0.2 M NaOH. Sampling was performed through the lateral connecting pieces through the butyl rubber septum using 5 mL PE syringes.

Procedure
In total two reactors containing the test item, three reactors containing only inoculum (blank), three reactors containing the reference compound, one reactor containing test item and reference compound (toxicity control) and one reactor without inoculum containing test item and a toxicant (abiotic control) were set up. 10.5 mL activated sludge was filled up to 1500 mL with 1489.5 mL mineral medium corresponding to 30 mg/L dry solids. Only the abiotic control vessel was filled with 1500 mL mineral medium without inoculum. The system was sealed and aerated with CO2-free air overnight. The reactors were kept mixed with magnetic stirrers. On the next day, the absorber wash bottles were filled with 0.2 M NaOH and the test substance was added into the two test vessels, into the toxicity control vessel and the abiotic control vessel. The reference compound was added into the reference vessels and into the toxicity control vessel and the toxicant into the abiotic control vessel. The aeration rate was kept at a rate of 30 - 100 mL / min (1.6 - 5.5 bubbles / second) and determined visually daily on working days. The determination by counting the gas bubbles over a defined period using a stop watch was made on days 11 and 29. The CO2-free air production system, the air-tightness of the whole experimental set-up, the aeration of the absorber flasks and the magnetic stirrers were controlled daily on working days. At the beginning of the study the IC concentration of the 0.2 M NaOH used for the CO2-absorption flasks was determined as 5.3 mg/L. The IC in the reactors at the beginning of the test was 0.865 mg/L. On the 4th, 7th, 11th, 14th, 21st and 28th day 4 mL NaOH from the first of two CO2-absorber flasks connected in line was sampled and the IC's were determined. The vials were immediately closed with sealing film in order to avoid CO2 uptake from the air. On the 28th day 2 mL of 4M hydrochloric acid (HCl) was added into each reactor to release the CO2 dissolved in water. On day 29 the IC was determined in both CO2-absorber flasks in line.
IC measurement was performed with a total carbon analyser (TOC-5050A Shimadzu) by purging the inorganic carbon with H3PO4 (25%) using a non-dispersive infrared (NDIR) detector.
Reference substance
Reference substance:
benzoic acid, sodium salt

Results and discussion

% Degradation
Parameter:
% degradation (CO2 evolution)
Value:
0
Sampling time:
28 d
Details on results:
No degradation could be observed within the test duration (28 days, after acidification). The biodegradation extent of the test item at the end of the test showed a negative value (-17.0%, mean of three replicates).

Toxicity control
The degradation extent in the toxicity control was 35.3% within 14 days. According to the guideline the test substance had no inhibitory effect on the inoculum.

Reference item
The reference compound sodium benzoate reached the pass level for ready biodegradability within 4 days

Blank
The mean CO2-evolution of the blank flasks was 29.8 mg/L on day 28 after acidification

Criteria of validity
The IC content in the test vessel was less than 5% of the TOC introduced with the test item.
The CO2 evolution in the inoculum blank at the end of the test was below 40 mg/L.
The difference of extremes of replicate values of the test item at the end of the test was less than 20%.
The biodegradation of the reference compound reached the pass level of 60% ThCO2 by day 4.
The degradation extent in the toxicity control was above 25% in 14 days based on ThCO2
The test is valid according to OECD Test Guideline 301 B (July 1992).

Any other information on results incl. tables

Table 1: Biodegradation after x days (% of ThCO2)

Reactor

Day

0

4

7

11

14

21

28

29

11

Test flasks

0

-4.4

-8.4

-10.8

-12.0

-14.1

-15.9

-16.0

12

0

-5.8

-9.8

-12.3

-13.5

-16.3

-18.5

-19.1

13

0

-2.9

-7.2

-9.5

-11.1

-13.5

-15.1

-15.8

4

Reference flasks

0

68.5

78.5

85.9

90.2

92.1

91.9

93.2

5

0

71.2

81.9

87.2

89.4

91.1

93.1

93.2

6

0

68.2

74.5

86.7

87.9

90.9

90.1

90.8

14

Toxicity control

Test item

Reference Item

0

31.7

32.3

35.2

35.3

35.4

35.6

34.6

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
The degradation of the test item at the end of the test was -17% (28 d after acidification, mean of three replicates).
The degradation of the toxicity control after 14 days was 35.3%. The test item had no inhibitory effect on the inoculum according to the criterion of the guideline.
Executive summary:

The ready biodegradability of dioxybenzone was tested in a CO2 evolution test according to OECD TG 301B. Activated sludge of a sewage treatment plant served as inoculum. Samples of the test substance and positive controls (sodium benzoate) were incubated for 28 days at 20.2 – 23.7 °C in diffuse light. Three replicates were set up. CO2 evolution was measured by IC measurements at days 0, 4, 7, 11, 14, 21, 28, 29.

After 28 days, dioxybenzone was degraded by 0%.

Based on the test results, dioxybenzone is not biodegradable according to criteria of OECD test guidelines on biodegradation.

The study is assessed as accepable. It satisfies the requirements of OECD test guideline 301B for ready biodegradability without restrictions.