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Environmental fate & pathways

Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
15 May 2018 to 5 Sept 2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 310 (Ready Biodegradability - CO2 in Sealed Vessels (Headspace Test)
Version / remarks:
2014
Deviations:
yes
Remarks:
TOC measurement was carried out on Day 8 instead of Day 7, however this has no impact on the validity or outcome of the study.
Principles of method if other than guideline:
Test was conducted according to a standard OECD guideline.
GLP compliance:
yes
Specific details on test material used for the study:
Identification: Thio Isocyanate Adduct
Appearance: Colourless liquid
Batch number: BZA13778
Test item storage: At room temperature container flushed with nitrogen
Expiry date: 13 July 2018
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge (adaptation not specified)
Remarks:
Predominantly domestic
Details on inoculum:
Activated sludge was freshly obtained from a municipal sewage treatment plant: ''Waterschap Aa en Maas', 's-Hertogenbosch, The Netherlands, receiving predominantly domestic sewage.

The freshly obtained sludge was kept under continuous aeration until further treatment. The concentration of suspended solids was determined to be 3.5 g/L in the concentrated sludge. Before use, the sludge was allowed to settle (31 minutes) and the liquid was decanted for use as inoculum at the amount of 10 mL/L of mineral medium.
Duration of test (contact time):
28 d
Initial conc.:
20 mg/L
Based on:
TOC
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
Preparation of Test Item Solutions:
The test item, Thio Isocyanate Adduct, was added to the mineral medium to give a final organic carbon concentration of 20 mg C/L. The carbon content was based on the results of TOC-analysis. Aliquots of 4.0 μL Thio Isocyanate Adduct (equalling 4.1 mg) were added directly to the test vessels containing 107 mL medium with microbial organisms and mineral components. Any residual volumes were discarded.


Test Procedure and Conditions:
The test item was incubated in inoculated mineral salts medium, in which 1 litre of mineral medium contains; 10 mL of solution (A), 1 mL of solutions (B) to (D) and Milli-RO water. Milli-RO water used in mineral medium was tap-water purified by reverse osmosis (Milli-RO) and subsequently passed over activated carbon and ion-exchange cartridges (Milli-Q) (Millipore Corp., Bedford, Mass., USA) and contained carbon levels <500 ppb.

The test was performed in sealed glass serum vessels (TFE/silicone septa and Teflon seals) and were filled to give a headspace to liquid ratio of 1:2 (107 mL test medium in 160 mL-capacity vessel). The test consisted of five groups:
1. Inoculum blank: containing inoculated medium.
2. Procedure control: containing inoculated medium and reference item.
3. Test item: containing inoculated medium and test item.
4. Toxicity control: containing inoculated medium, reference item and test item.
5. Abiotic control: containing untreated medium, test item and sterilising agent

Sampling was conducted at the following points for each test type:
- Inoculum blank: day 1, 8, 14, 21 and 28
- Procedure control: day 1, 8 and 14
- Test item: day 1, 8, 14, 21 and 28
- Toxicity control: day 1, 8 and 14
- Abiotic control: day 1 and 28

Three parallel reserve vessels for each test series were prepared. These vessels were not used and were removed at the end of the test. Furthermore, an additional vessel of each test series was prepared for pH measurement. The vessel was prepared identically to the test vessels. Test vessels were incubated in the dark on an orbital shaker, with a shaking rate sufficient to keep the vessel well mixed and in suspension.

Samples were pre-treated with 1 mL 7 M NaOH (Merck KGaA, Darmstadt, Germany) (prepared freshly at the start of the test) via injection through the septum of each vessel, the vessels were then returned to the orbital shaker for 1 hour. Vessels were subsequently removed from the shaker and allowed to settle. The supernatant was used for IC analysis.

The CO2 evolution resulting from the aerobic biodegradation of the test item was determined by determining the inorganic carbon (IC) produced in the test vessels in excess of that produced in inoculum blank. Biodegradation was expressed as a percentage of the ThIC based on the quantity of test item initially added.
Reference substance:
other: 1-octanol
Preliminary study:
NA
Test performance:
The reference item (1-octanol) was biodegraded by at least 60% (62%) within 14 days. The mean amount of Total Inorganic Carbon (TIC) present in the inoculum blanks at the end of the test was < 3 mg C/L (1.6 mg C/L). Since all criteria for acceptability of the test were met, this study was considered to be valid.
Key result
Parameter:
% degradation (CO2 evolution)
Value:
12
Sampling time:
28 d
Details on results:
The relative biodegradation values calculated from the measurements performed during the test period revealed 12% biodegradation of Thio Isocyanate Adduct (mean value), thus the criterion for ready biodegradability (at least 60% biodegradation within a 10-day window) was not met.

In the toxicity control less than 25% biodegradation occurred within 14 days (19%, based on ThIC). Therefore, there may have been limited inhibitory effects of the test item, however the presence of biodegradation in the test item vessels indicated sufficient microbial activity.
Remarks on result:
not measured/tested
Results with reference substance:
The reference substance (1-octanol) showed 62% biodegradation within 14 days.

Mean Biodegradation in Percentage of the Theoretical maximum IC Production (ThIC)

 

Nominal day

Microbial degradation in percentage of the ThIC

Degradation

Reference Item

Test Item

Toxicity Control

Abiotic Control

1

0

5

3

2

7

43

8

18

-

14

62

5

19

-

21

-

17

-

-

28

-

12

-

2

- = Not measured 

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
Thio Isocyanate Adduct showed 12% biodegradation during the test period, thus the criterion for readily biodegradability was not met under the test conditions and is therefore concluded to be not readily biodegradable. It is noted however, that in the toxicity control Thio Isocyanate Adduct was found to possible have a slight inhibiting effect on microbial activity.
Executive summary:

The ready biodegradability of Thio Isocyanate Adduct was assessed via an OECD Guideline 310 (‘Ready Biodegradability - CO2 in Sealed Vessels (Headspace Test’)) study. The study was performed at a GLP accredited laboratory, fulfilled the validity criteria described by the guideline and is well documented and is therefore considered to be reliable.  

Thio Isocyanate Adduct showed 12% biodegradation during the test period, thus the criterion for readily biodegradability (at least 60% biodegradation within a 10 -day window) was not met under the test conditions and is therefore concluded to be not readily biodegradable. It is noted however, that in the toxicity control Thio Isocyanate Adduct was found to possible have a slight inhibiting effect on microbial activity.

Description of key information

The ready biodegradability of Thio Isocyanate Adduct was assessed via an OECD Guideline 310 (‘Ready Biodegradability - CO2 in Sealed Vessels (Headspace Test’)) study. The study was performed at a GLP accredited laboratory, fulfilled the validity criteria described by the guideline and is well documented and is therefore considered to be reliable.  

Thio Isocyanate Adduct showed 12% biodegradation during the test period, thus the criterion for readily biodegradability (at least 60% biodegradation within a 10 -day window) was not met under the test conditions and is therefore concluded to be not readily biodegradable. It is noted however, that in the toxicity control Thio Isocyanate Adduct was found to possible have a slight inhibiting effect on microbial activity.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed
Type of water:
freshwater

Additional information