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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
Remarks:
The study record is on source Benzyl acetate
Adequacy of study:
key study
Study period:
1991
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 310 (Ready Biodegradability - CO2 in Sealed Vessels (Headspace Test)
Deviations:
yes
Remarks:
, see principle of method
GLP compliance:
not specified
Remarks:
(not likely)
Oxygen conditions:
aerobic
Inoculum or test system:
other: secondary effluent from an activated sludge plant treating domestic sewage.
Details on inoculum:
The test was inoculated with secondary effluent from an activated sludge plant treating domestic sewage. The collected effluent was first passed through a coarse filter, Whatman No.l, to remove any gross particulate matter. The level of inorganic carbon in the inoculum was reduced before use by sparging with carbon dioxide-free air for about one hour while maintaining the pH at 6.5. In the tests reported here the CO2 produced in the control vessels, using the maximum inoculum concentration of 10% secondary effluent, was in the range 0.4 - 1.3 mg/L. Hence, in cases where positive results were obtained less than 10% of the carbon dioxide produced was derived from the control.

It has been shown that the biodegradation potential achieved by the use of secondary effluent as a source of micro-organisms is at least comparable to activated sludge.
Duration of test (contact time):
28 d
Initial conc.:
10 mg/L
Based on:
DOC
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
PROCEDURE
The test substance in a dilute mineral salts solution is incubated in sealed vessels with appropriate micro-organisms for a period of up to 28 days. Only about two thirds of the volume of the vessel is filled with liquid. At the test concentrations used only about 15% of the available oxygen in the headspace gas is required for the complete oxidation of all test compound carbon to carbon dioxide. Any carbon dioxide produced by the breakdown of the test material is distributed between the liquid and gaseous phases. Periodically a vessel is taken, a sample of the headspace gas withdrawn using a gas syringe and the concentration of carbon dioxide in the headspace gas determined. The seal is then broken and the concentration of dissolved inorganic carbon (DIC) in the solution is measured. Similar determinations are made for a control vessel which does not contain the test substance. The difference in the total inorganic carbon found in the test and control vessels allows the quantity of carbon dioxide produced from the test compound to be ascertained. From a knowledge of the quantity of test material added and its carbon content the extent of mineralisation can be calculated.
Using suitable volumetric apparatus 100±1 mL of the mineral salts media is dispensed into '125 mL' Hypo-Vial [Pierce Warriner (UK) Ltd]. The media is prepared so as to contain 0.5 to 10% by volume of inoculum and 2 to 10 mg/L of test substance as organic carbon. Controls containing the same inoculum concentration but no test compound are also prepared. The vials are sealed with butyl rubber septa and aluminium crimp seals and placed on an orbital shaker in a temperature controlled environment. To follow the course of biodegradation and to statistically evaluate the extent of biodegradation on the final day of the test a minimum of 12 vessels is required per test substance. This provides for a data point every fourth day and 6 replicates for the assessment of the final extent of biodegradation on the 28th day of the test.
A vessel is removed from the shaker as required, a sample of the headspace gas withdrawn using a gas syringe and the concentration of carbon dioxide determined. The seal is then broken and the concentration of dissolved inorganic carbon (DIC) in the solution is measured immediately, Similar determinations are made for a control vessel which does not contain the test substance. The difference in the total inorganic carbon found in the test and control vessels allows the quantity of carbon dioxide produced from the test compound to be ascertained.
MINERAL MEDIUM USED
The mineral medium used was adopted from that recommended in the 1988 OECD Ring Test of Ready Biodegradability. Stock solutions (a)-(d) were prepared by dissolving the following salts in 1 litre of deionised water: (a) 8.50 g KH2PO4, 21.75 g K2HPO4, 33.40 g Na2HPO4·2H20, 0.5 g NH4CI; (b) 36.4 g CaCI2·2H20; (c) 22.50 g MgSO4·7H20; (d) 0.2 g FeCI3·6H20, 0.4 g EDTA disodium salt. The test medium was prepared by diluting 10 mL of solution (a) and 1 mL of solutions (b)-(d) in 1 litre aliquots of water.
Key result
Parameter:
% degradation (CO2 evolution)
Value:
100.9
Sampling time:
28 d
Remarks on result:
other: 95% C.I.: 96.9-104-9%
Details on results:
The biodegradation curve shows that biodegradation is very rapid. After approx. 2 days 10% biodegradation was reached, within 5 days 60% biodegradation was reached and after ca. 12 days biodegradation was complete.
Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
Under the conditions of the test the substance was readily biodegradable.
Executive summary:

In this OECD TG 310 study the substance (10 mg/L as DOC) was inoculated for 28 days with secondary effluent from an activated sludge plant treating domestic sewage. Only about two thirds of the volume of the vessel was filled with liquid. Periodically a sample of the headspace gas was withdrawn using a gas syringe and the concentration of carbon dioxide in the headspace gas determined. The seal was then broken and the concentration of dissolved inorganic carbon (DIC) in the solution is measured. The extent of mineralisation was calculated from quantity of test material added and carbon content measured. After approx. 2 days 10% biodegradation was reached, within 5 days 60% biodegradation was reached and after ca. 12 days biodegradation was complete. Based on these findings the substance is assessed as readily biodegradable.

Description of key information

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

The ready biodegradation of Ylanganate was assessed using read across from Benzyl acetate. This section starts with the summary of the biodegradation test of Benzyl acetate. Thereafter the read across justification is presented.

Benzyl acetate Biodegradation summary

In this OECD TG 310 study the substance (10 mg/L as DOC) was inoculated for 28 days with secondary effluent from an activated sludge plant treating domestic sewage.Only about two thirds of the volume of the vessel was filled with liquid.Periodically a sample of the headspace gas was withdrawn using a gas syringe and the concentration of carbon dioxide in the headspace gas determined. The seal was then broken and the concentration of dissolved inorganic carbon (DIC) in the solution is measured. The extent of mineralisation was calculated from quantity of test material added and carbon content measured. After approx. 2 days 10% biodegradation was reached, within 5 days 60% biodegradation was seen.

The potential for (ready) biodegradability of Ylanganate (CAS 89-71-4) using read across fromBenzyl acetate (CAS 140-11-4)

Introduction:

Ylanganate is a benzylic acetate with a methyl group at the ortho-position for which no ready biodegradation information is available.In accordance with Article 13 of REACH,lacking information can be generated by means of applying alternative methods such asin vitrotests, QSARs, grouping and read-across. For assessing the ready biodegradation of the substance in water sediment the analogue approach is selected because for one closely related analogue reliable a ready biodegradation can be derived.

Hypothesis:Ylanganate has the same biodegradation potential as Benzyl acetate in the OECDTG 310 test.Benzyl acetate is very similar in structure. Both substances have a similar benzylic backbone and a similar functional group which makes read across feasible.

Available information:The biodegradation potential of the source chemical substance Benzyl acetate was tested in a well conducted study comparable to OECD TG 301B (Birch and Fletcher, 1991). In this study benzyl acetate was found to biodegrade ca. 100% within 28 days with the 10-day window criterion being met.

US-EPA Hazard Characterisation Document: Benzyl Derivatives Category:

The US-EPA has performed a category approach for benzyl derivatives which includes 10 chemicals that contain a substituted or unsubstituted benzene ring bonded directly to a single oxygenated carbon (US-EPA, 2010). Within this approach a sub-category was made for ‘benzyl and benzoate esters’ which consists of benzyl acetate (CAS 140-11-4), methyl benzoate (CAS 93-58-3), methylp-methylbenzoate (CAS 99-75-2) and benzyl benzoate (CAS 120-51-4). Experimental data are available for benzyl acetate, methyl benzoate and benzyl benzoate and all three are reported to be readily biodegradable (according to OECD criteria). Especially the ready biodegradability of methyl benzoate adds to the justification for read-across as it contains the methyl acetate group which is also present in Ylanganate.

Overview of data available for the US-EPA sub-group of ‘benzyl and benzoate esters’:

Substance

Benzyl acetate

(CAS 140-11-4)

 

Methyl benzoate

(CAS 93-58-3)

 

Methylp-methyl benzoate

(CAS 99-75-2)

Benzyl benzoate

(CAS 120-51-4)

 

Biodegradation data

100% in 28 days (OECD 301B)

95.3% after 28 days (OECD 301B)

no data

93% in 28 days (OECD 301B)

Target and source chemical

Chemical structures of the target and source are presented in the data matrix at the end of this document, including physico-chemical properties, though relevant for biodegradation.

Purity/Impurities

Ylanganate is a mono-constituent with a high purity and has no constituents that influence the biodegradation potential. Benzyl acetate

Analogue justification

According to Annex XI 1.5 read across can be used to replace testing when the similarity can be based on a common backbone and a common functional group. When using read across the result should be applicable for C&L and/or risk assessment and it should be presented with adequate and reliable documentation.

Benzyl acetate was selected as key analogue because this structure was considered closest in analogue and had relevant information.

Structural similarity:Ylanganate and Benzyl acetate have a similar benzylic backbone. Ylanganate has an additional methyl group attached to this benzylic ring which is not anticipated to influence the study result. Ylanganate and Benzyl acetate both have an acetate group attached to the ring but the ester group is reversed one. This will result in an acid after cleavage by carboxyl-esterases for Ylanganate. For Benzyl acetate the first degradation will be the benzylic alcohol. In view of the acid and alcohol can be reduced and oxidised, respectively these groups will not influence the ready biodegradability potential.

Bioavailability:The molecular weight and physico-chemical data of Ylanganate and Benzyl acetate are near identical presenting similar bioavailability. The only difference is that the log Kow of Ylanganate is slightly higher (log Kow = 3) than that of benzyl acetate (log Kow = 2). This difference in bioavailability is considered to not have a significant effect on the biodegradation potential of the two substances.

Reactivity:In view of the similar backbone and similar functional ester group the reactivity is considered similar. After cleavage of the ester bond, Ylanganate will turn into an acid, while benzyl acetate will at first become an alcohol. This alcohol can become an acid after auto-oxidation. These aspectis are thought not to make a difference in biodegradability between Ylanganate and Benzyl acetate.

Supporting information from QSAR predictions for both substances: When running EpiSuite-BIOWIN 5 and 6 the similarity in biodegradation potential is further supported, see the data in Table 1. If anything Ylanganate has a slightly higher potency for biodegradation than Benzyl acetate. BIOWIN 5 and 6 are selected because these models are based on ready biodegradability information.

Table 1               BIOWING 5 and 6 predictions for Ylanganate and Benzyl acetate.

Substance

Ylanganate

Benzyl acetate

Chemical structure

Cas no

89-71-4

140-11-4

 

Target

Source

BIOWIN 5

 

 

Ester

0.3437

0.3437

Aromatic-CH3

0.0415

 --

Aromatic-CH2

 

-0.0557

Aromatic-H

0.0329 (4x)

 0.0411 (5x)

Methyl – CH3

0.0004

0.0004

Molecular weight parameter

- 0.4468

- 0.4468

Equation constant

 0.7121

0.7121

RESULT

0.68

 0.59

BIOWIN 6

Ester

 2.4462

   2.4462

Aromatic-CH3

0.3072

 --

Aromatic-CH2

 --

- 0.1246

Aromatic-H

 0.4806 (4x)

 0.6007 (5x)

Methyl-CH3

 0.0194

 0.0194

MW parameter

-4.3355

-4.3355

RESULT

 0.81

 0.75

Uncertainty of the prediction:Based on the reasoning above there are no remaining uncertainties.

Data matrix

The data matrix is presented below in Table 2

Conclusion on biodegradation per endpoint for C&L

For Ylanganate no ready biodegradability information is available. For Benzyl acetate a well conducted ready biodegradation test is available showing ready biodegradation. In view of the similarities between Ylanganate and Benzyl acetate Ylanganate can be considered readily biodegradable.

Table 2Data matrix presenting Ylanganate and Benzyl acetate information that supports the read across

Common names

Ylanganate

Benzyl acetate *

Chemical structures

CAS no

89-71-4

140-11-4

Empirical formula

C9H10O2

C9H10O2

Physico-chemical data

Molecular weight

150.2

150.2

Physical state

liquid

liquid

Melting point,oC

< -20

< -20

Boiling point,oC

216.3

213.5

Vapour pressure, Pa

12.9      (23°C)

24 Pa    (25°C)

Water solubility, mg/L

2630     (22°C)

2660     (20°C)

Log Kow

3.0

1.96      (25°C)

* Physicochemical data of benzyl acetate are taken from the ECHA website (disseminated data).

 

Reference

US-EPA (2010). U.S. Environmental Protection Agency, Hazard Characterization Document. Screening-level hazard characterization - Benzyl Derivatives Category.