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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:
weight of evidence
Study period:
From October 24, 2017 to November 24, 2017
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)
Deviations:
not specified
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
other: Aerobic sludge, mixed treatment plant of urban (66%) and industrial (34%)
Details on inoculum:
Method of mud sampling
For the preparation of the inoculum a sample of aerobic sludge has been selected by the mixed treatment plant of urban (about 66%) and industrial (about 34%) liquid sewage situated at San Rocco - Monza (MB), Italia. The plant of treatment is managed by "BRIANZACQUE SRL (Monza)".

Mud preparation
In the laboratory the sampled muds, have been mixed and let settle, keeping them in aerobic conditions. The mud samples, before their use, have been analysed to check its ability to form colony units. Then it has been centrifuged, washed and analyzed to quantify the suspended solids concentration for the inoculum preparation. The inoculum was prepared in order to have a concentration of suspended solid of about 4 mg/L.

Medium preparation:

Solution A
Anhydrous potassium dihydrogen phosphate (KH2P04): 8.50 g/L
Anhydrous dipotassium hydrogen phosphate (K2HP04): 21.75 g/L
Disodium hydrogen phosphate dihydrate (Na2HP04.2H20): 33.40 g/L
Ammonium chloride (NH4Cl): 0.50 g/L
pH = 7.53

Solution B
Calcium chloride dihydrate (CaCI2.2H20): 36.40 g/L

Solution C
Magnesium sulphate heptahydrate (MgSO4.7H20): 22.50 g/L

Solution D
Iron chloride (Ill) hexahydrate (FeCl3.6H20): 0.25 g/L
All solutions has been made with deionized water (MilliQ Millipore). Then for each litre of medium 10 mL of Solution A have been transferred into a 1000 mL volumetric flask and diluted with 800 mL of deionised water; 1 mL of Solution B, 1 mL of Solution C and 1 mL of Solution D have been added and the solution has been diluted to volume with deionised water. For higher volumes the medium has been prepared according to the same proportion. The preparation of the solutions has been reported in an internal laboratory logbook.

Duration of test (contact time):
ca. 28 d
Initial conc.:
ca. 39.73 mg/L
Based on:
TOC
Parameter followed for biodegradation estimation:
inorg. C analysis
Reference substance:
benzoic acid, sodium salt
Remarks:
18.61 mg/L of TOC
Key result
Parameter:
% degradation (inorg. C analysis)
Remarks:
Test substance
Value:
ca. 118
Sampling time:
28 d
Remarks on result:
other: Readily biodegradable
Results with reference substance:
Percentage biodegradation of reference substance at 14 d was determined to be 101%, therefore the assay fulfilled the validity criteria.

Results

Quality criteria of the test were satisfied. The mean amount of TIC present in the blank controls at the end of the test was < 3 mg C/L. The trend of the inorganic carbon and related biodegradation percentages in the bottle contained both the test sample and the reference substance confirm the absence of inhibitory effect of the test sample on inoculum. The biodegradation percentage of the test substance during the test was as follow:

Check point (d)

% of Biodegradation

Reference substance

% of Biodegradation

Test substance

% of Biodegradation

Reference + Test substance

0

0

0

0

1

3

3

7

7

90

35

-

14

101

58

-

21

102

88

-

28

127

118

90

 

Conclusions

On the basis of results obtained, interpreted in accordance to OECD 310:2014, the test substance was considered readily biodegradable in aerobic condition.

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
Under the study conditions, the test substance was determined to be readily biodegradable.

Executive summary:

A study was conducted to determine the ready biodegradability of the test substance, ''Phosphoric acid, hexadecyl esters, potassium salts with cetyl alcohol and isostearyl isostearate', using Headspace test method (CO2 in sealed vessels), according to OECD Guideline 310, in compliance with GLP. Aerobic sludge inoculum was prepared with mixed treatment plant of urban (66%) and industrial (34%) liquid sewage and in order to have a concentration of suspended solid of about 4 mg/L. In the study, 17 replicates of blanks (containing only culture medium), positive control (sodium benzoate at 18.61 mgTOC/L) and test substance (39.73 mg TOC/L) and 8 replicates of toxicity control (i.e., Test and reference substances (49.77 mg TOC/L)) were used. All treated samples were kept at the temperature of 20°C for 28 d. The calculation of biodegradation as total inorganic carbon (TIC) was determined at each sampling time (i.e., 0, 1, 7, 14, 21 and 28 d) for the reference substance, test sample and blank. For toxicity control, calculation of biodegradability as total inorganic carbon (TIC) was determined on Day 1 and 28. The trend of the inorganic carbon and related biodegradation percentages in the bottle containing both the test sample and the reference substance, confirmed the absence of inhibitory effect of the test sample on inoculum. At 28 d, the biodegradability of the test substance was determined to be 118%. At 14 d biodegradability for reference substance was determined to be 101%. The mean amount of TIC present in the blank controls at the end of the test was < 3 mg C/L. Based on the study results, the test had satisfied all the validity criteria. Therefore, under the study conditions, the test substance was considered to be readily biodegradable (Eurofins, 2017).

Description of key information

Based on the available weight of evidence from studies on read across substances representative of the main constituents,the test subsatance is considered to be readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable
Type of water:
freshwater

Additional information

In absence of biodegradation study with the test substance,the endpoint has been assessed based on studies for read across substances representative of the main constituents, which can be categorised as phosphate esters (PSE i.e., mono- and di C16 PSE, K+), alcohols (i.e., C16-18 linear and branched alcohol) and esters (i.e., C16-18 linear and branched fatty acid esters). The results are presented below:

Constituents: PSE and Alcohol (linear) and Esters (branched) - read across study

A study was conducted to determine the ready biodegradability of the read across substance, 'phosphoric acid, hexadecyl esters, potassium salts with cetyl alcohol and isostearyl isostearate', using Headspace test method (CO2 in sealed vessels), according to OECD Guideline 310, in compliance with GLP. Aerobic sludge inoculum was prepared with mixed treatment plant of urban (66%) and industrial (34%) liquid sewage and in order to have a concentration of suspended solid of about 4 mg/L. In the study, 17 replicates of blanks (containing only culture medium), positive control (sodium benzoate at 18.61 mgTOC/L) and read across substance (39.73 mg TOC/L) and 8 replicates of toxicity control (i.e., Test and reference substances (49.77 mg TOC/L)) were used. All treated samples were kept at the temperature of 20°C for 28 d. The calculation of biodegradation as total inorganic carbon (TIC) was determined at each sampling time (i.e., 0, 1, 7, 14, 21 and 28 d) for the reference substance, test sample and blank. For toxicity control, calculation of biodegradability as total inorganic carbon (TIC) was determined on Day 1 and 28. The trend of the inorganic carbon and related biodegradation percentages in the bottle containing both the test sample and the reference substance, confirmed the absence of inhibitory effect of the test sample on inoculum. At 28 d, the biodegradability of the read across substance was determined to be 118%. At 14 d biodegradability for reference substance was determined to be 101%. The mean amount of TIC present in the blank controls at the end of the test was < 3 mg C/L. Based on the study results, the test had satisfied all the validity criteria. Therefore, under the study conditions, the read across substance was considered to be readily biodegradable (Eurofins, 2017).

Constituent: Esters (linear) - read across study

A study was conducted to determine the biodegradability of the read across substance 'tetradecyl myristate' (Purity: 99.4%), according to the OECD Guideline 301C, modified MITI method, in compliance with GLP. An activated sludge inoculum (suspended solids concentration of 30 mg/L) was treated with test substances (100 mg/L) and reference substance (aniline) at 25°C for 28 d. Degradation was followed over 28 d by determining the oxygen consumption, TOC removal and test material analysis. The test substance attained 67% and 94% degradation over the test period by oxygen consumption and test material analysis methods respectively. The oxygen consumption for aniline in the above used test system reached 58% and 75% degradation after 7 d and 14 d, respectively. It was confirmed that the test conditions of this test were effective. Under the study conditions, the read across substance was determined to be readily biodegradable (CIA, 1992).

Further, the presence of branched alcohols in the test substance, are not expected to show difference in degradation potential compared to the linear alcohols. Therefore, overall based on the available weight of evidence from studies on read across substances representative of the main constituents, the test substance is considered to be readily biodegradable.