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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:
April - July 2020
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
July 1992
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
Activated sludge from a biologic sewage treatment plant was used. The chosen plant is treating mostly household sewage. The sludge was taken from the activation basin of the ESN (Stadtentsorgung Neustadt) sewage treatment plant, Im Altenschemel, NW-Lachen-Speyerdorf (Date of collection: 09. Jun. 2020, batch no: E20200609). The sludge was filtrated, washed with medium 2x, and resuspended in test medium. It was then aerated. The dry matter was determined as 4.80 g suspended solids/L.
Duration of test (contact time):
28 d
Initial conc.:
230 mg/L
Based on:
test mat.
Initial conc.:
99.64 other: ThOD/L
Based on:
ThOD
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
Preparation: The medium was prepared using the stock solutions. The dry matter of the inoculum was determined. A sufficient number of test vessels was provided. A stock solution of the positive control containing 599.8 mg/L in deionised water was freshly prepared. The test item was pipetted directly into the test vessels considering the density 2.571 g/cm³. Before the start of the test, the cartridge of the measuring heads was filled with soda lime and the program parameters (duration of the test, volume of the test flasks and volume of the test solution) were selected.
Experimental Parameters
Test item concentration: 230 mg test item/L (corresponding to 99.64 mg ThOD/L)
Positive control concentration: 60 mg /L sodium benzoate (corresponding to 99.77 mg/L ThOD)
Number of control flasks: 3 (medium and inoculum)
Number of positive control flasks: 3 (sodium-benzoate, medium and inoculum)
Number of test vessels: 3 (1,3-Diiodopropane, medium and inoculum)
Abiotic control: 1 (1,3-Diiodopropane and 10 mL 1% HgCl2 solution/L)
Toxicity control: 1 (200 mg/L ThOD, 100 mg/L ThOD each of 1,3-Diiodopropane and positive control nominal)
Volume of test vessels: 500 mL (600 mL total volume including measuring head)
Volume test solution: 250 mL (toxicity flask 125 mL)
Concentration of suspended solids: 25.0 mg/L
Temperature: 19.4 – 21.3 °C
Duration: 28 days
Start of the Test: The test vessels were filled with medium, then the positive control was added to the appropriate vessels and the pH was measured in all test vessels. Then the test item was added. After pH-adjustment, the inoculum was added, the vessels were connected to the OxiTop® measuring heads and they were started via the OxiTop® Controller.
Performance of the Test: The oxygen which was consumed by the content of the vessels was measured automatically by the test apparatus. After 28 days, the test was ended. Because the test item and positive control do not contain nitrogen, presence of nitrate and nitrite was not checked.
EVALUATION (Calculation of Degradation & Oxygen Demand): The oxygen demand of test item and positive control vessels and for each measuring point were calculated using the following equation:
O2-demand in mg/vessel = O2-demand in mg (vessel) – mean O2-demand in mg (blank controls)
For the abiotic control, the O2-demand of the blank controls was not subtracted.
Reference substance:
benzoic acid, sodium salt
Remarks:
60 mg/L (99.77 mg/L ThOD)
Preliminary study:
not performed
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
28 d
Details on results:
O2 Consumption: The values of the oxygen demand of the vessel which were used for evaluation of the results were automatically recorded and used for assessment.
Results and Assessment: The measured pH values at the start and the end of the test and the calculated percentage degradation values are presented in table 1 and 2.
Assessment
The degree of biodegradation reached 0 % after 28 days. The 10-day-window was not detected. The degradation phase is defined as interval between the end of the lag phase and the reaching of 90 %. Because there was no degradation this cannot be stated.
For the test item 1,3-Diiodopropane no biodegradation was observed after 28 days. The 10-day window could not be determined. The criterion of reaching 60% of degradation after 28 days is not met. 1,3-Diiodopropane is therefore considered as “not readily biodegradable and not ultimately biodegradable, within 28 days, as well”.
All validity parameters and values were as follows:
Degradation of positive control ≥ 60% (criterion ≤ 14 days): found 3 days  valid
Mean O2 demand of the controls (criterion < 60 mg/L): found 38.87 mg/L  valid
Degradation in the toxicity flask on day 14 (criterion > 25%): found 29.8 %*  non-toxic
pH at the end of the test (criterion 6.0 – 8.5): found 7.3 – 7.9  valid
In conclusion all validity criteria were met and the study is considered valid.

Note: All calculations are performed with unrounded values. Therefore, re-calculation with rounded values may lead to slightly different results.

* Biological degradation of xx % in the toxicity control on day 14 is calculated as follows:
D(T) =(O(A) – O(B))/(ThOD (T) *C(T) + ThOD(P) * C(P)) * 100%
with:
O(A): O2-uptake in the toxicity flask in mg O2/L on day 14 = 85.6 mg/L
O(B): Mean O2-uptake of the control in mg O2/L on day 14 = 25.7 mg/L
ThOD(T): Theoretical oxygen demand without nitrification test item = 0.433 mg O2 / mg test item
ThOD(P): Theoretical oxygen demand without nitrification positive control = 1.665 mg O2 / mg positive control
C(T): Concentration of the test item in the toxicity flask = 232 mg/L
C(P): Concentration of the positive control in the toxicity flask = 60 mg/L
Results with reference substance:
Degradation of positive control reached >60% within 3 days (see validity criteria in details on results).

Oxygen Demand and Degradation

Table 1: pH-values on day 0 and day 28, oxygen demand and degradation values on day 28
 (Blank and Positive Control)

Flask

Blank control 1

Blank control 2

Blank control 3

Positive control 1

Positive control 2

Positive control 3

pH at day 0

7.6

7.6

7.6

7.6

7.6

7.6

pH at day 28

7.5

7.5

7.5

7.9

7.9

7.9

Oxygen demand in mg/L at day 28

30.1

48.9

37.6

111

135

111

Oxygen demand in mg/L after deduction

--

--

--

72.1

*96.1

72.1

% biological degradation

--

--

--

72.3

n.e.

72.3

*Positive Control 2 was not used for evaluation. (n.e.: not evaluated)

 

 

Table 2: pH-values on day 0 and day 28, oxygen demand and degradation values on day 28
 (Test Item, Abiotic and Toxicity Control)

Flask

Test item 1

Test item 2

Test item 3

Mean Test item

Abiotic Control

Toxicity Control

pH at day 0

7.6

7.6

7.6

--

7.4

7.6

pH at day 28

7.6

7.6

7.6

--

7.3

7.7

Oxygen demand in mg/L at day 28

0

0

1.9

--

0

80.5

Oxygen demand in mg/L after deduction

-38.9

-38.9

-37.0

--

0.0

41.6

% biological degradation

-39.0

-39.0

-37.1

-38.4

0.0

20.7

 

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
For the test item 1,3-Diiodopropane no biodegradation was observed after 28 days.
Executive summary:

Findings and Results of the study, titled “Determination of the Ready Biodegradability of 1,3-Diiodopropane under aerobic conditions in the Manometric Respirometry Test following OECD 301F / EU C.4-D” were as follows:

The test item 1,3-Diiodopropane was tested using a concentration of 230 mg test item/L (equivalent to a theoretical oxygen demand of 99.64 mg O2/L). Activated sludge was used as inoculum. The test was left running for 28 days.

All validity criteria were met. The positive control reached the pass level of 60% on day 3 (criterion:≤14).

The following data could be determined for the test item 1,3-Diiodopropane:

10-day-window: was not detected

Degradation phase none

degradation at the end of 10-day-window none

degradation at the end of the test 0 %

Description of key information

1,3-Diiodopropane is classified as not readily biodegradable following OECD 301F/EU C.4-D.

Key value for chemical safety assessment

Biodegradation in water:
not biodegradable
Type of water:
freshwater

Additional information