Gum benzoin, Siam

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

14 March 2018 - 12 April 2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Identification (Trade Name): Benzoin resoid (UVCB)
Chemical (IUPAC) Name of UVCB: Benzoin resinoid obtained from the resin of Styrax tonkinensis by extraction with solvent
Batch no: SM17060068
CAS no UVCB: 9000-72-0
IPC number: 021601
EC Description for sameness purposes: Extractives and their physically modified derivatives. It is a product which may contain resin acids and their esters, terpenes, and oxidation or polymerization products of these terpenes. (Styrax, Styracaceae).
Appearance brown solid
Stability: not relevant in biodegradation tests
Storage: at ambient temperature in the dark

Oxygen conditions:

aerobic

Inoculum or test system:

natural water: freshwater

Details on inoculum:

River water was sampled from the Rhine near Heveadorp, The Netherlands (08-03-2018). The nearest plant (Arnhem-Zuid) treating domestic wastewater biologically was 3 km upstream. The river water was aerated for 7 days before use to reduce the endogenous respiration. River water without particles was used as inoculum. The particles were removed by sedimentation after 1 day while moderately aerating.

Duration of test (contact time):

28 d

Initial conc.:

2 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

Test bottles:
The test was performed in 0.30 L BOD (biological oxygen demand) bottles with glass stoppers.

Deionized water:
Deionized water containing no more than 1.0 mg/L of organic carbon was prepared in a water purification system.

Nutrients, and stocks:
The river water used in the Closed Bottle test was spiked per liter of water with 8.5 mg KH2PO4, 21.75 mg K2HPO4, 33.4 mg Na2HPO4·2H2O, 22.5 mg MgSO4·7H2O, 27.5 mg Ca-Cl2, 0.25 mg FeCl3·6H2O. Ammonium chloride was not added to the river water to prevent nitrification. Accurate administering of the poorly soluble test item was accomplished by preparing a solid stock of 3.0 mg of the test item per g of silica gel in a 50-mL serum flask. This was achieved by dissolving 73 mg of test substance in ~1 mL DCM. The DCM with test substance was then added to the top layer of the silica gel. The container was washed with ~ 3 mL of DCM also added to the top layer of the silica gel (24.3 g). Next the DCM was allowed to evaporate for ~6 hours. The serum flask was closed with a screw top and the content was mixed vigorously. Silica gel was also treated with DCM by adding ~4 mL of DCM to 20 g of silica gel. The DCM was allowed to evaporate (6 hours) and the serum flask was closed and mixed vigueurously. Subsequently 0.20 g of silica gel with the test item was added to the test bottles. Amounts of 0.20 g of silica gel (~4 mL of DCM added and evaporated) were added to control bottles. Finally the bottles were filled with nutrient medium with inoculum and closed. Sodium acetate was added to the bottles using a stock solution of 1.0 g/L.

Test procedure:
Use was made of 10 bottles containing only river water, 10 bottles containing river water and silica gel (DCM added and evaporated), 10 bottles containing river water and silica gel with test substance, 6 bottles with river water and sodium acetate. The concentrations of the test substance, and sodium acetate in the bottles were 2.0 and 6.7 mg/L, respectively. Each of the prepared solutions was dispensed into the respective group of BOD bottles so that all bottles were completely filled without air bubbles. The zero time bottles were immediately analyzed for dissolved oxygen using an oxygen electrode. The remaining bottles were closed and incubated in the dark. Two duplicate bottles of all series were withdrawn for analyses of the dissolved oxygen concentration at day 7, 14, 21, and 28.

Test conditions:
The pH of the media was 8.0 at the start of the test. The pH of the medium at day 28 was 8.0 (controls) and 7.9 (test). The temperature ranged from 22.6 to 23.0°C which is within the prescribed temperature range of 22 to 24°C.

Reference substance:

acetic acid, sodium salt

Remarks:

Purity: >99%

Test performance:

The validity of the test is demonstrated by an endogenous respiration of 1.4 mg/L at day 28. Furthermore, the differences of the replicate values at day 28 were less than 20%. The biodegradation percentage of the reference compound, sodium acetate, at day 14 was 81. Finally, the validity of the test is shown by oxygen concentrations >0.5 mg/L in all bottles during the test period.

Key result

Parameter:

% degradation (O2 consumption)

Value:

48

Sampling time:

28 d

Parameter:

% degradation (O2 consumption)

Value:

45

Sampling time:

21 d

Parameter:

% degradation (O2 consumption)

Value:

36

Sampling time:

14 d

Parameter:

% degradation (O2 consumption)

Value:

7

Sampling time:

7 d

Parameter:

% degradation (O2 consumption)

Value:

0

Sampling time:

0 d

Details on results:

Benzoin resoid (UVCB) was biodegraded by 48% at day 28 in the Closed Bottle test. Benzoin resoid (UVCB) should as a consequence be classified as not readily biodegradable. The percentage reached indicates partial degradation.

Results with reference substance:

The biodegradation percentage of the reference compound, sodium acetate, at day 14 was 81 %

Toxicity

Inhibition of the degradation of a well-degradable compound, e.g. sodium acetate by the test substance in the Closed Bottle test was not determined because possible toxicity of Benzoin resoid (UVCB) to micro­organisms degrading acetate is not relevant. Inhibition of the endogenous respiration of the inoculum by the test substance at day 7 was not detected. Therefore, no inhibition of the biodegradation due to the "high" initial test substance concentration is expected.

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

The substance was biodegraded by 48% at day 28 in the Closed Bottle test and should therefore be classified as not readily biodegradable.

Executive summary:

In order to assess the biodegradation of Benzoin resoid (UVCB), a screening test was performed according to OECD TG 301D (Closed Bottle test) and under GLP conditions. In this study, river water was exposed to 2 mg/L of the substance for 28 days. Benzoin resoid did not cause a reduction in the endogenous respiration. Furthermore, the validity criteria of the test were met. Benzoin resoid  was biodegraded by 48% at day 28 in the standard Closed Bottle screening test and should therefore not be classified as readily biodegradable.

Description of key information

In order to assess the biodegradation of Benzoin resoid (UVCB), a screening test was performed according to OECD TG 301D (Closed Bottle test) and under GLP conditions. In this study, river water was exposed to 2 mg/L of the substance for 28 days. Benzoin resoid did not cause a reduction in the endogenous respiration. Furthermore, the validity criteria of the test were met. Benzoin resoid  was biodegraded by 48% at day 28 in the standard Closed Bottle screening test and should therefore be classified as not readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Type of water:

freshwater