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Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
other: Only a summary report was available for review.
Qualifier:
no guideline followed
Principles of method if other than guideline:
20-day BOD test using procedures which generally follow the biochemical oxygen demand (BOD) method published in Standard Methods for the Examination of Water and Wastewater, 14th ed., Am. Public Health Association, Washington, DC (1975)
GLP compliance:
not specified
Oxygen conditions:
aerobic
Inoculum or test system:
sewage, domestic, non-adapted
Duration of test (contact time):
20 d
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
Method changes from those in Standard Methods for the Examination of Water and Wastewater, 14th ed., Am. Public Health Association, Washington, DC (1975):
Test period extended to 20 days;
Three seed control bottles (2ml domestic sewage/bottle) were maintained through the test period for calculating seed oxygen demand;
Reaeration, if needed, was accomplished by dividing the BOD bottle contents between two BOD bottles, sealing, shaking 20 times and returning to the original bottle, reading oxygen level, resealing and returning to the incubator.
Discussion of these modifications appear in Price, Waggy, Conway, "Brine Shrimp and Seawater BOD of petrochemicals" published in J. Water Poll. Control Fed., January 1974.
Key result
Parameter:
% degradation (O2 consumption)
Value:
61
Sampling time:
20 d
Interpretation of results:
not readily biodegradable
Conclusions:
A biodegradation rate of 61% in 20 days is reported in a summary report.
Endpoint:
biodegradation in water: screening test, other
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
2005-04-21 to 2005-04-19
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
Guideline study (OECD 306) and in compliance with GLP
Qualifier:
according to
Guideline:
other: OECD 306: Biodegradability in Seawater, Closed Bottle Method
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
other: natural sea water
Details on inoculum:
The test method uses natural seawater both as the aqueous phase and as the source of microorganisms. Natural seawater from an unpolluted site at about 80 m depth in Byfjord was collected from a tap at Akvamiljo. This seawater had a salinity of 34%. Prior to use the seawater was decanted to remove coarse particles and aged under aerobic conditions at room temperature for about 10 days. Nutrients were added to the test system as described in the OECD Guideline 306. To prevent possible oxygen consumption by nitrification processes, a nitrification inhibitor (allylthiourea) was added to the test system as described in the Norwegian standard method NS-ISO 1899-1, 1998)
Duration of test (contact time):
28 d
Initial conc.:
2.82 mg/L
Based on:
test mat.
Initial conc.:
5.1 mg/L
Based on:
ThOD/L
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
Preparation of test solution:
Glass fibre filters with a diameter of 25 mm were used as an inert carrier for the test substance. 84.7 mg of the test substance was dissolved in 10 ml of acetone. 100 µl of the solution was applied to the filters. For one hour the solvent was dried off and the filters wereadded to the test system.
The reference substance was added by a stock solution to a final concentration of 2.44 mg/l. This corresponds to 3.93 mg ThOD/litre in the reference substance solution.
The possible inhibition of bacterial growth was tested in bottles containing a mixture of the test substance and reference substance. The test substance was added at the same concentration as when tested alone (2.82 mg/l) and the reference substance was added in half of the concentration (1.22 mg/l)
Experimental set-up:
Sets of BOD bottles were filled with test solutions:
13 bottles containing the test substance,
13 bottles containing reference substance,
7 bottles containing inhibition control mixture
13 bottles serve as blanks, containing enriched seawater without neither test or reference substance. Filters treated with acetone only were added to the blanks.
Incubation:
The study was run for 28 days, and the test bottles were incubated in the dark at a temperature of 19.6-21.1 °C
Reference substance:
benzoic acid, sodium salt
Remarks:
BDH, dok.id: 114858
Key result
Parameter:
% degradation (O2 consumption)
Value:
75
Sampling time:
28 d
Details on results:
The specific oxygen demand of the test subsatnce after 28 days was 1.364 mg BOD/mg sample, which corresponds to adegradation of about 75% relative to the theoretical oxygen demand.

The results from the inhibition control indicated that the test substance did not inhibit the bacterial growth at the concentration tested.
Results with reference substance:
The lag time before onset of degradation was short and the time to reach 50% of the final oxygen uptake was about 5 days. The degradation after 28 days was 100% relative to the ThOD. This indicates that the bacterial activity in the test system, seawater, was normal.

Oxygen determination for the test substance, the reference substance and the inhibition control.

Dissolved oxygen

determination

 

 

 

Bottle no.

mg O2/l after n days

                                                            

      0           7          14          21            28

Blank

(seawater with nutrients,

but without test material)

a)

b)

mean blank

7.40        6.60       6.50      6.40        7.20

               6.70       6.40      6.40        7.10

7.40        6.65       6.45       6.40        7.15

Test substance

(seawater with nutrients

and test substance)

a)

b)

mean test

subst.

7.40        4.80       4.60      3.20        2.80

               4.80       4.20      3.40        3.80

 

 7.40        4.80       4.40      3.30        3.30

Reference substance

(seawater with nutrients

and reference substance)

a)

b)

meanref.

subst.

7.40        3.70       3.30      3.00        3.20

               3.80       3.30      3.00        3.20

 

 7.40        3.75       3.30      3.00        3.20

Inhibition control

a)

b)

meaninhib.

control

7.40        2.30       2.80      2.00        1.40

 

 

7.40        2.30       2.80      2.00        1.40

 

Biochemical oxygen demand and calculation of degradation for the test and reference substances.

 

Dissolved oxygen depletion and degradation

BOD after n days

     7          14            21          28

Test substance: Dynasylan AMEO

Oxygen demand (mg BOD/l)

Specific oxygen demand (mg BOD/mg sample)

  

   1.85        2.05        3.10      3.85

  0.655     0.726       1.098   1.364

Degradation (%)

     36         40            61         75

Test substance: Sodium benzoate

Oxygen demand (mg BOD/l)

Specific oxygen demand (mg BOD/mg sample)

 

   2.90        3.15        3.40      3.95

  1.188     1.290       1.393   1.618

Degradation (%)

     74         80            87         101

 

Biochemical oxygen demand and calculated percentage of degradation for the test and reference substances in the inhibition control.

 

Inhibition control

(mixture of test and reference substance)

BOD after n days

   7             14             21              28

Oxygen demand of mixture (mg BOD)/l)

 4.350        3.650       4.400         5.750

If oxygen demand of test subst. is assumed as for test subst. alone:

Assumed O-demand test subst.(mgBOD/l)

Resulting O-demand ref. subst. (mgBOD/l)

 

 

 1.85            2.05         3.10         3.85

2.502          1.602       1.303       1.904

Estimated degradation of ref. subst. (%)

 127             82              66             97

If oxygen demand of ref. subst. is assumed as for ref. subst. alone:

Assumed O-demand ref. subst.(mgBOD/l)

Resulting O-demand test subst. (mgBOD/l)

 

 

1.45            1.57         1.70         1.97

2.901          2.076       2.701       3.776

Estimated degradation of test. subst. (%)

 57               41            53             74

 

Validity criteria fulfilled:
yes
Interpretation of results:
other: there is a potential for biodegradation in the marine environment
Conclusions:
The biodegradation of the test substance, 3-aminopropyltriethoxysilane after 21 days was calculated to be 61%. After 28 days the degradation was 75% and the test was closed. The result is considered to be reliable.

Description of key information

Biodegradation in water: screening tests:  75% in 28 days (OECD 306), read-across from an analogous substance. No significant biodegradation of the silanol hydrolysis product is expected.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed
Type of water:
marine water

Additional information

There are no reliable ready biodegradation data available for 3-(trimethoxysilyl)propiononitrile, therefore good quality data for the structurally-related substance, 3-aminopropyltriethoxysilane (CAS 919-30-2), have been read across. Both substances hydrolyse to structurally-related hydrolysis products, 3-(trihydroxysilyl)propiononitrile and 3-aminopropylsilanetriol respectively; the other hydrolysis products are methanol and ethanol respectively. In view of the rapid hydrolysis, it is the silanol hydrolysis product that is relevant for environmental risk assessment.

Ethanol and methanol are readily biodegradable (OECD 2004a and OECD 2004b).

3-(Trimethoxysilyl)propiononitrile (CAS 2526-62-7) and 3-aminopropyltriethoxysilane (CAS 919-30-2) are within a wider analogue group of organosilicon substances that exhibit no evidence of any significant biodegradation once hydrolysis and subsequent biodegradation of alkoxy/acetoxy groups has been taken into account.

This wider analogue group for the ready biodegradability endpoint consists of a number of sub-classes of substances. However, read-across is carried out between substances with the same sub-class in most cases. In this case, however, no data are available for substances containing a nitrile functional group, so data are read across from a substance in a related sub-class of amino-functional silanes.

The table below presents ready biodegradation data for chlorosilanes, siloxanes, silanes and alkoxysilanes etc. with amino group(s) inside the chain after any very rapid hydrolysis has been accounted for. 3-Aminopropyltriethoxysilane (CAS 919-30-2) is a member of this group of substances.

It is therefore considered valid to read-across the result of not readily biodegradable for 3-aminopropyltriethoxysilane (CAS 919-30-2) to fill the data gap for the registered substance. Additional information is given in a supporting report (PFA, 2013f) attached in Section 13.

 

Table : Ready biodegradation data available for relevant substances

CAS

Name

Main code

Readily biodegradable? Yes/no

Result: Biodegradation after 28 days (%)

Guideline

Klimisch code

Corrected % biodegradation once alkoxy/acetoxy biodegradation is accounted for[1]

27445-54-1

Cyclohexanamine,N-[(diethoxymethylsilyl)methyl]-

III-08

no

29% (26% taking into account nitrification)

OECD 301F

1

-7

919-30-2

3-aminopropyltriethoxysilane

III-08

No

76%

OECD 306

1

28

31024-56-3

N-[3-(trimethoxysilyl)propyl]butylamine

III-08

No

24.70%

OECD 301B

1

-5

227085-51-0

N-ethyl-3-trimethoxysilyl-2-methylpropanamine

III-08

No

16 - 18%

OECD 301F

1

-15

157923-74-5

2,2-dimethyl-4-(trimethoxysilyl)butylamine

III-08

No

36%

OECD 301F

1

3

3069-33-8

N-[3-(methoxydimethylsilyl)propyl]ethylenediamine

III-08

No

11.10%

OECD 301D

1

-1

1760-24-3

N-(3-(trimethoxysilyl)propyl)ethylenediamine

III-08

No

39%

Annex V C4-A

1

2

82985-35-1

Bis(trimethoxysilylpropyl)amine

III-08

No

11-20%

OECD 301D

2

-33

13497-18-2

Bis(triethoxysilylpropyl)amine

III-08

Yes

64.5% in 28 days, 71% in 60 days

OECD 306

1

-2

[1]The negative values in this column are where the biodegradation rate observed in the test is less than that expected assuming only alkoxy/acetoxy parts biodegrade. This could be due to low solubility of parent substance or low rates of hydrolysis. These values should in effect be considered as zero.

In the study with 3-aminopropyltriethoxysilane (CAS 919-30-2), a biodegradation of 75% in 28 days (M-lab 2005) was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP (OECD 306, Biodegradability in seawater). A biodegradation of 67% in 28 days (not readily biodegradable (Schoerberl 1994) was determined in a second reliable study conducted according to an appropriate test protocol, and in compliance with GLP (EU Method C.4-A).

A study with the registered substance, (3-(trimethoxysilyl)propiononitrile (CAS 2526-62-7) resulted in a 61% biodegradation (O2 consumption) in 20 days (BOD test). However, a reliability could not be assigned to this study as only a summary report is available. Therefore, the study with 3-aminopropyltrietoxysilane (CAS 919-30-2) is used as weight-of-evidence.

3-Aminopropyltriethoxysilane (CAS 919-30-2) hydrolyses within the timescale of the biodegradation study to 3-aminopropylsilanetriol and ethanol. The registered substance hydrolyses within the timescale of biodegradation study to 3-(trihydroxysilyl)propiononitrile and methanol. The biodegradation observed in the studies are attributable to the biodegradation of the ethanol or methanol hydrolysis products.

Ethanol is readily biodegradable (OECD 2004b) and constitutes 67% of the carbons in the test substance, 3-aminopropyltriethoxysilane.

Methanol is readily biodegradable (OECD 2004a) and constitutes 50% of the carbons in the registered substance.

No significant biodegradation is expected for the silanol hydrolysis product.

 

References: 

OECD (2004a): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18-20 October 2004, Methanol, CAS 67-56-1.

OECD (2004b): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 19-22 October 2004, Ethanol, CAS 64-17-5.

PFA (2013f). Peter Fisk Associates, Biodegradation Main Analogue Group report, PFA.300.005.007