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Environmental fate & pathways

Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: ready biodegradability
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
weight of evidence
Justification for type of information:
REPORTING FORMAT FOR THE CATEGORY APPROACH
Please refer also to the read-across statement attached in section 13

1. HYPOTHESIS FOR THE CATEGORY APPROACH (ENDPOINT LEVEL)
The target and the source substances are structurally similar substances that share the common organometallic core structure consisting of a central zinc metal bonded to four alkyldithiophosphate esters (ligands) by coordinate covalent bonds -Zn[(S2P(OR)2]2. Structural variations between the target and the source substances are related only to the alkyl (R) groups of the alkyldithiophosphate ligands. The substances in this category give thus rise to an (identical) common compound Phosphorodithioic acid moiety that can be released by the breakage of ester bonds and dissociation from the Zinc complex to which the organism would be exposed if the target substance was tested in the toxicity studies. Exposure to the parent compounds (non-transformed constituents) and to the counter alkyl alcohols, possibly released by hydrolysis of P-O bonds – non-common compounds – would not influence the prediction of the (eco)toxicological properties because they are considered to have the same biological targets and to cause the same type of effects through a common underlying mechanism due to the same functional groups (zinc cation, phosphorodithioic cation and aliphatic alcohol anionic moieties). The impurities of the target and the source substances are not expected to impact the prediction because they are identical or, if slightly structural different, belong to the same class of compounds with the same functional groups and their percentages are very low.

2. CATEGORY APPROACH JUSTIFICATION (ENDPOINT LEVEL )
The target substance is considered to follow similar biodegradation pattern as the source substance because it has the same structural features. Moreover, there is a sufficient weight of evidence that the entire range of substances of ZDDP category including the source substance are not biodegradable, it is therefore a high probability that the target substance is also not readily biodegradable. There are no other structural alerts of the target substance pointing to a different from the source substance biodegradation pattern. The source substance (CAS 4259-15-8) with longer alkyl rests (ethylhexyl) represents rather worst-case for the target substance with shorter alkyl rests (isopropyl-, isobutyl and pentyl). Therefore, it is predicted that the target substance would possess the same biodegradation rate as the source substance if it was tested in a biodegradation study.
Parameter:
% degradation (O2 consumption)
Value:
< 5
Sampling time:
5 d
Remarks on result:
other: mean of 2 test concentrations
Parameter:
% degradation (O2 consumption)
Value:
< 5
Sampling time:
15 d
Remarks on result:
other: mean of 2 test concentrations
Parameter:
% degradation (O2 consumption)
Value:
< 5
Sampling time:
27 d
Remarks on result:
other: mean of 2 test concentrations
Details on results:
The biological oxygen demand was <5% of the chemical oxygen demand in both test concentrations at all sampling dates.

Sodium acetate in the inhibition test (medium contained test substance as well as reference substance) was degraded by 80% at day 27 which indicates that the test concentration did not have inhibitory effects on the inoculum.
Results with reference substance:
The biodegradation of sodium acetate was >95% .

TEST SUBSTANCE

Results of oxygen measurements during the test

 

 

Oxygen content [mg O2/L ]

Test duration [d]

0

5

15

27

Medium without test substance, without inoculum

1

2

mean

8.77

8.86

8.82

8.73

8.80

8.77

8.79

8.51

8.65

8.50

8.48

8.49

Medium without test substance, with inoculum

1

2

mean

8.72

8.80

8.76

8.67

8.74

8.71

8.63

8.70

8.67

8.55

8.42

8.49

Medium with 2.49 mg test substance/L and inoculum

1

2

mean

8.91

8.95

8.93

8.72

8.73

8.73

8.68

8.71

8.70

8.43

8.56

8.50

Medium with 3.91 mg test substance/L and inoculum

1

2

mean

8.92

8.91

8.92

8.67

8.70

8.69

8.58

8.63

8.61

8.40

8.27

8.34

Decrease in oxygen content of test medium

Test substance concentration [mg/L]

Biological oxygen demand [mg/L]

Day 5

Day 15

Day 27

2.49

-0.02

-0.03

-0.01

3.91

0.02

0.06

0.15

 

Biodegradation of test substance

Test substance concentration [mg/L]

%BOD of COD [mg/L]

Day 5

Day 15

Day 27

2.49

<5

<5

<5

3.91

<5

<5

<5

Mean

<5

<5

<5

COD: Chemical oxygen demand of test substance (2.26 mg O2/mg)

REFERENCE SUBSTANCE (SODIUM ACETATE)

Results of oxygen measurements during the test

 

 

Oxygen content [mg O2/L ]

Test duration [d]

0

5

15

27

Medium without test substance, without inoculum

1

2

mean

8.77

8.86

8.82

8.73

8.80

8.77

8.79

8.51

8.65

8.50

8.48

8.49

Medium without test substance, with inoculum

1

2

mean

8.72

8.80

8.76

8.67

8.74

8.71

8.63

8.70

8.67

8.55

8.42

8.49

Medium with 5.0 mg reference substance/L and inoculum

1

2

mean

8.83

8.80

8.82

5.87

5.85

5.86

5.48

5.49

5.49

3.90

4.05

3.98

Medium with 10.0 mg reference substance/L and inoculum

1

2

mean

8.84

8.82

8.83

2.90

2.88

2.89

2.41

2.32

2.37

0.95

0.87

0.91

 

Decrease in oxygen content of test medium

Reference substance concentration [mg/L]

Biological oxygen demand [mg/L]

Day 5

Day 15

Day 27

5.0

2.85

3.18

4.51

10.0

5.82

6.30

7.58

 

Biodegradation of reference substance

Reference substance concentration [mg/L]

% BOD of ThOD [mg/L]

Day 5

Day 15

Day 27

5.0

73

81

>95

10.0

75

81

>95

Mean

74

81

>95

ThOD: theoretical oxygen demand (0.78 mg O2/mg for sodium acetate

The test is considered to be valid as validity criteria were fulfilled (more than 60 % of the reference substance was degraded after 27 days; the oxygen consumption in the test medium (blank control) did not exceed 0.4 mg/L and was < 0.6 mg/L in the inoculum control after 14 and 27 d).

Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
Under test conditions no biodegradation observed.
Executive summary:

Biodegradation of the substance was tested in a non-GLP study according to EU Method C.6 (Degradation: Chemical Oxygen Demand), similar to OECD Guideline 301D. Under the test conditions no biodegradation was observed. Therefore, the substance is considered to be not ready biodegradable.

Endpoint:
biodegradation in water: ready biodegradability
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
weight of evidence
Justification for type of information:
REPORTING FORMAT FOR THE CATEGORY APPROACH
Please refer also to the read-across statement attached in section 13

1. HYPOTHESIS FOR THE CATEGORY APPROACH (ENDPOINT LEVEL)
The target and the source substances are structurally similar substances that share the common organometallic core structure consisting of a central zinc metal bonded to four alkyldithiophosphate esters (ligands) by coordinate covalent bonds -Zn[(S2P(OR)2]2. Structural variations between the target and the source substances are related only to the alkyl (R) groups of the alkyldithiophosphate ligands. The substances in this category give thus rise to an (identical) common compound Phosphorodithioic acid moiety that can be released by the breakage of ester bonds and dissociation from the Zinc complex to which the organism would be exposed if the target substance was tested in the toxicity studies. Exposure to the parent compounds (non-transformed constituents) and to the counter alkyl alcohols, possibly released by hydrolysis of P-O bonds – non-common compounds – would not influence the prediction of the (eco)toxicological properties because they are considered to have the same biological targets and to cause the same type of effects through a common underlying mechanism due to the same functional groups (zinc cation, phosphorodithioic cation and aliphatic alcohol anionic moieties). The impurities of the target and the source substances are not expected to impact the prediction because they are identical or, if slightly structural different, belong to the same class of compounds with the same functional groups and their percentages are very low.

2. CATEGORY APPROACH JUSTIFICATION (ENDPOINT LEVEL)
The target substance is considered to follow similar biodegradation pattern as the source substance because it has the same structural features. Moreover, there is a sufficient weight of evidence that the entire range of substances of ZDDP category including the source substances are not biodegradable, it is therefore a high probability that the target substance is also not readily biodegradable. There are no other structural alerts of the target substance pointing to a different from the source substance biodegradation pattern. The source substance (CAS 84605-29-8) with longer alkyl rests (1,3-dimethylbutyl and in addition iso-Propyl)) represents rather worst-case for the target substance with shorter alkyl rests (isopropyl-, isobutyl and pentyl). Therefore, it is predicted that the target substance would possess the same biodegradation rate as the source substance if it was tested in a biodegradation study.
Parameter:
% degradation (CO2 evolution)
Value:
1.5
Sampling time:
28 d
Details on results:
The mean percent theoretical CO2 evolved for the test substance was 1.5% (range 0.6 to 2.0%). The control chambers evolved an average of 6.5 milligrams of CO2 over the test period. The mean percent theoretical CO2 evolved for the reference substances was 99%. The temperature range recorded during the test was 18 to 20 °C. The average measured total suspended solids concentration of the inoculum was 78.6 mg/L. The result of the standard plate count performed on the inoculum was 1.37 x 10E6 CFU/mL. The measured pH values ranged from 5.2 to 6.9. The control chambers evolved an average of 6.5 milligrams of CO2 over the test period.
Results with reference substance:
The mean percent theoretical carbon dioxide evolved for sodium benzoate was 99%

Cumulative Percent of Theoretical Carbon Dioxide Evolved

Day

Benzoate

Replicate values

Test item

Replicate values

1

0.0; 0.0; 0.0

0.0; 0.1; 0.0

4

13.1; 34.8; 50.0

1.2; 0.5; 0.0

8

64.4; 46.8; 73.2

1.1; 0.5; 0.0

11

85.6; 94.9; 94.5

1.3; 0.5; 0.1

14

91.1; 100.4; 98.4

1.2; 1.0; 1.8

19

92.9; 101.5; 100.4

1.8; 0.6; 1.9

21

92.7; 102.1; 100.9

2.0; 0.8; 2.0

25

94.1; 103.4; 101.2

2.2; 0.8; 2.2

29

94.6; 103.0; 100.4

2.0; 0.6; 1.9

Validity criteria fulfilled:
yes
Interpretation of results:
other: not readily biodegradable under test conditions
Conclusions:
The mean percent theoretical CO2 evolved for the test substance was 1.5% (range 0.6 to 2.0%). The control chambers evolved an average of 6.5 milligrams of CO2 over the test period. The mean percent theoretical CO2 evolved for the reference substances was 99%.
Executive summary:

The objective of the study was to measure the amount of carbon dioxide produced from the biodegradation of the test substance under the conditions tested. The test contained a blank control group, a reference group, and a treatment group, and each contained three replicate test chambers. The study was conducted according to procedures specified by the OECD Guideline for Testing of Chemicals, Method 301B and EEC Method C.4-C. The test substance was administered to the treatment group test chambers by direct weight addition at a concentration of 10 mg Carbon per liter. After 28 days the cumulative percent of theoretical carbon dioxide evolved for the test material was 1.5%. The solids concentration of the test solution was within the acceptable limit specified I the test guideline. The standard plate count result indicated that the inoculum used in this study contained an acceptable number of viable microbes according to the guidelines.

Description of key information

Biodegradation of the source substance Zinc bis[O,O-bis(2-ethylhexyl)] bis(dithiophosphate) (CAS 4259 -15 -8) was tested in a non-GLP study according to EU Method C.6 (Degradation: Chemical Oxygen Demand), similar to OECD Guideline 301D. The study quality of the study was assessed with Klimisch 1. Under the test conditions no biodegradation was observed. Therefore, the target substance is also considered to be not ready biodegradable.

Biodegradation of the source substance Phosphorodithioic acid, mixed O,O-bis(1,3-dimethylbutyl and iso-Pr) esters, zinc salts (CAS 84605 -29 -8) was tested in a GLP study according to EU EU Method C.4 -C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test) and OECD Guideline 301B. The study quality of the study was assessed with Klimisch 1. Under the test conditions no biodegradation was observed. Therefore, the target substance is also considered to be not ready biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

[Type of water: freshwater]


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