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Environmental fate & pathways

Biodegradation in water: screening tests

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Administrative data

Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
26 March 1998 - 12 November 1998
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline study; well documented study report

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1998
Report date:
1998

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)
Deviations:
no
GLP compliance:
yes

Test material

Constituent 1
Reference substance name:
Phosphorodithioic acid, mixed O,O-bis(1,3-dimethylbutyl and iso-Pr) esters, zinc salts
EC Number:
283-392-8
EC Name:
Phosphorodithioic acid, mixed O,O-bis(1,3-dimethylbutyl and iso-Pr) esters, zinc salts
Cas Number:
84605-29-8
IUPAC Name:
Phosphorodithioic acid, mixed O,O-bis(1,3-dimethylbutyl and iso-Pr) esters, zinc salts
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
PHYSICO-CHEMICAL PROPERTIES
- Melting point: liquid at room temperature
- Boiling point: decomposes before boiling
- Vapour pressure: 0.0069 Pa at 25 deg. C
- Henry's law constant (for volatile substances): low vapour pressure 0.0069Pa at 25 C
- Water solubility (under test conditions): 2764 ppm at 22 deg. C
- Solubility in organic solvents: no data
- log Pow: 0.56
- pKa: no data
- Base or acid catalysis of test material: no data
- UV absorption: no data
- Stability of test material at room temperature: stable
- pH dependance on stability: hydrolytically stable at pH 4 and 7 for 5 days at 50 deg. C (OECD 111, Tier 1 preliminary study)

OTHER PROPERTIES (if relevant for this endpoint)
- Toxicity to microorganisms: EC50 > 10,000 mg/L (OECD 209)

Study design

Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
Activated sludge was collected from the Prospect Bay Wastewater Treatment Facility in April 1998. The sludge was sieved using a 2 mm screen and then aerated for approximately 4 hours. The sludge was homogenized in a blender at medium speed for approximately 2 minutes and then was allowed to settle for approximately 30 minutes. The supernatant was used as the inoculum for this study and was used the same data that it was prepared. A total suspended solids measurement and standard plate count were performed on the inoculum using procedures based on Standard Methods. The average measured total suspended solids concentration of the inoculum was 78.6 mg/L. The plates were incubated at 20 degrees C for approximately 48 hours and then the number of colony forming units was enumerated. The result of the standard plate count performed on the inoculum was 1.37x10^6 CFU/mL. The standard plate count result indicated that the inoculum used in this study contained an acceptable number of viable microbes according to the guideline.
Duration of test (contact time):
28 d
Initial test substance concentration
Initial conc.:
10 other: mg carbon/liter Carbon determined by elemental analysis
Parameter followed for biodegradation estimation
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: The test medium was a modified biochemical oxygen demand test dilution water. The test medium contained the following standard reagent solutions per liter of high quality Nanopure water: 1mL ammonium sulfate solution 4%; 1 mL of calcium chloride solution (2.75%); 4 mL of ferric chloride solution (0.025%); 1 mL of magnesium sulfate solution (2.25%); 2 ml of phosphate buffer solution (pH 7.2).

- Test temperature: 20C
- pH: The pH values ranged from 5.2 to 6.9.
- pH adjusted: yes/no

- Suspended solids concentration: The solids concentration of the test solution was 0.786 mg/L


TEST SYSTEM
- Culturing apparatus: The test chambers were ambered 4 liter bottles. The air entering the chambers was passed through Drierite to remove ambient moisture and then through Ascarite to produce CO2 free air. The air exiting the test chambers was passed through a series of three gas washing bottles each containing KOH to trap the CO2 that had evolved within the chamber. All chambers were aerated with CO2 free air for 24 hours at a rate of 50 to 100 mL per minute to purge the system of CO2. After the aeration period, the flow of CO2 was stopped and three CO2 traps each containing KOH were connected to the exit air lines of each chamber. An amount of test substance necessary to deliver 10 mg C/L was added to the treatment group test chambers by direct weight addition. An amount of reference substance necessary to deliver 10 mg C/L was added to the reference group test chambers by direct weight addition. The biodegradation was started by bubbling CO2 free air through each of the test chambers at a rate of 50 to 100 mL per minute. The CO2 produced from the degradation of organic carbon sources within the test chamber was trapped as K2CO3 in the KOH solution and the amount of inorganic carbon in the trapping solution was measured at various intervals during the study using a Shimadzu TOC 5000 carbon analyzer.

- Number of culture flasks/concentration: 3 Replicates


SAMPLING
The CO2 traps were removed for analysis on days 1, 4, 8, 11, 14, 19, 21, 25, and 29. The CO2 trap nearest the chamber was removed and analyzed for inorganic carbon. The two remaining traps were placed one position closer to the test chamber and a new trap was placed on the end of the series. On the 28h day of the test, an aliquot of the contents of each test chamber was removed and the pH determined. The contents of each chamber then were acidified by the addition of 3 mL of concentrated hydrochloric acid to drive off inorganic carbonate. The chambers were aerated overnight after which the trapping solutions closest to the test chambers were analyzed for inorganic carbon.

CONTROL AND BLANK SYSTEM
The test contained a blank control group, a reference group, and a treatment group. The blank control, reference, and treatment groups each contained three replicate test chambers
Reference substance
Reference substance:
benzoic acid, sodium salt

Results and discussion

% Degradation
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 20C. 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 10^6 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.

BOD5 / COD results

Results with reference substance:
The mean percent theoretical carbon dioxide evolved for sodium benzoate was 99%

Any other information on results incl. tables

Results based on read across and Justification for read across:

Cumulative Percent of Theoretical Carbon Dioxide Evolved (EC 283 -392 -8)

Day

Benzoate

Replicate values

CAS 84605-29-8

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

Justification for Read Across from EC 283-392 (Data Source) to EC 270-608-0 (Target)

Common Manufacturing Process: The test substance (EC 270-608-0) and the analogue (EC 283-392-8) are produced under a common manufacturing process in which a phosphorodithioic acid ester intermediate, (RO)2PS2H,is produced by the reaction of phosphorus pentasulfide with a mixture of two alcohols of a similar class - branched alcohols containing C4 and C5 carbons (test substance) and C3 and C6 carbons (analogue ). The intermediate is neutralized with zinc oxide to produce the final multicomponent substance.The reaction is performed in the presence of a highly refined base oil which accounts for 8 – 10 % of the final products. 

 

Impurities: The level of impurities in the submission substance and the analogue is minimal (0.09 % wt and < 0.15% wt, respectively). Impurities have been identified as residual, unreacted alcohols from the production of the phosphorodithioic acid ester intermediates (isobutyl alcohol and pentyl alcohol isomers in the submission substance and isopropyl and 1,3-dimethylbutyl alcohols in the analogue).

 

Same Chemical Category: The submission substance (EC 270-608-0) and the analogue (EC 283-392-8), generically referred to as ZDDPs, have been shown to have sufficient structural similarities to be included in the Zinc Dialkydithiophosphate Category (ZDDPs) in the United States Environmental Protection Agency High Production Volume (HPV) Chemical Challenge Program.

 

Structural Similarity: The primary feature accounting for the similarity of the test substance (EC 270-608-0) and the analogue (EC 283-392-8) is 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 test substance and the analogue are related to the alkyl (R) groups of the alkyldithiophosphate ligands.

 

Both substances contain a distribution of several different zinc dialkyldithiophosphates (ZDDPs). 

The type and distribution of the zinc dialkyldithiophosphates is determined by the alcohol mixture and charge ratios of the alcohols used in the manufacturing process.

 

The test substance (EC 270-608-0) is a mixture of ZDDPs containing all isobutyldithiophosphate ligands, all pentyldithiophosphate ligands, and components containing both isobutyldithiophosphate and isomeric pentyldithiophosphate ligands resulting in a multicomponent substance with a molecular weight range of 548 – 604 (for monomers).            

 

The analogue (EC 283-392-8) is a multicomponent mixture of ZDDPs containing all isobutyl dithiophosphate ligands, all pentyl dithiophosphates ligands and ZDDPs containing both isobutyl and isomeric pentyl dithiophosphates with a molecular weight range of 492 – 660 (for monomer).

 

Tanimoto Fingerprint (ToxMatch Version 1.06 software) gives a similarity index greater than 0.8 (values range from 0, no similarity to 1, identical). Peer reviewed literature indicates that values greater than 0.6 are significantly similar. DSSTox similarity was 80% between the submission substance and the analogue.

 

Similarity of Physicochemical Properties: In addition to the structural similarities, similar physicochemical properties further support the justification for read across from the analogue. Both the test substance and analogue have similar physical states, densities and the same order of magnitude of vapour pressures and partition coefficients (logPow). Both were shown to be hydrolytically stable at pH 4, 7 and 9 in an OECD 111 preliminary hydrolysis study.

 

In evaluating the evidence for read across, significant consideration was given to water solubility. Water solubility studies conducted on the test substance and the analogue show the lower molecular weight ZDDP monomers are preferrentially dissolved in water with solubility decreasing with increasing alkyl chain lengths (molecular weights) of the alkyldithiophosphate ligands.  In this respect, the water soluble composition of the test substance (EC 270 -608 -0) and the analogue (EC 283 -392 -8) are considered to be sufficiently close to reasonably expect similar behaviour toward mircobial degradation.

 

      

Data Matrix for Read Across from Analogue                                       

Property

Submission Substance (Target)

Analogue    (Data Source) 

EC

270-608-0

283-392-8

CAS

68457-79-4

84605-29-8

Chemical Name

Phosphorodithioic acid, mixed O,O-bis(iso-Bu and pentyl) esters, zinc salts

Phosphorodithioic acid, mixed O,O-bis(1,3-dimethylbutyl and iso-Pr) esters, zinc salts

Physical

Viscous liquid

Viscous liquid

Boiling Point

Decomposes before boiling

Decomposes before boiling

Density @ 15.6 deg. C 

(ASTM D4052)

1.17 mg/L

1.2 mg/L

Vapour Pressure @ 25 C 

 (EU method A.4)

0.0023 Pa

0.0069

Water Solubility @ 22 deg. C (OECD 105)

1658 mg/L

2764 mg/L

Identity of water soluble components (% = GC area %)

ZDDPs containing 76% isobutyl (C4) dithiophosphate ligands + 24% containing mixed isobutyl (C4) and pentyl (C5) dithiophosphate ligands

ZDDP containing 95% isopropyl (C3) dithiophosphate ligands + 5% containing mixed isopropyl and 1,3 -dimethylbutyl dithiophosphate ligands

Average molecular weight of water solubles (weighted average based on GC peak area %)

562

500.4

Partition Coefficient, logPow (OECD 107)

0.69

0.56

Hydrolysis as a function of pH (OECD 111, Tier 1 preliminary study at pH 4,7 and 9)

 

Hydrolytically stable at pH 4, 7 and 9

Hydrolytically stable at pH 4, 7 and 9

Applicant's summary and conclusion

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