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BIODEGRADATION IN WATER: SCREENING TESTS

Read across justification for the of use the Diglyme test

Dimethylated glycols and polyglycols are not readily biodegradable. Obviously microorganism can not easily cleave the O-Methyl bond. Nevertheless Diglyme can be biodegraded under inherent conditions, e.g. Zahn-Wellens test OECD 302 B.

Monomethylated glycols on the other hand can be biodegraded rapidly. An example is the monomethylated triglycole (TEGME,CASNo 112-35-6) which is readily as well as inherently biodegradable ((MSDS Dow, 2007, Hoechst 1986, W 86-223).

Based on the facts given above it is reasonable to use the data on inherent biodegradation of Diglyme also for Triglyme.

It can be concluded from these facts that rapid biodegradation of dimethylated glycols can occur when one of the methylgroups is cleaved off. This also means that Triglyme is not a recalcitrant substance.

Details on the biodegradation sceening test of Diglyme

The primary and inherent biodegradability were determined in the Zahn-Wellens-Test / EMPA Test with a non adapted activated sludge for the test item Diethylenglykoldimethylether over a period up to 36 days. The study was conducted from 2010-03-08 to 2010-05-19 with the definitive exposure phase oft the main test from 2010-04-13 to 2010-05-19 according to OECD 302 B at Dr.U.Noack-Laboratorien.

For the determination of the primary biodegradation the test item was tested at a concentration of 600 µg/L in duplicates. The primary biodegradation was determined by SPME GC/MS analysis of the test item. For the determination of the inherent biodegradation the test item was tested at a concentration of 95 mg/Lin duplicates, corresponding to a DOC of 51.3mg C/L in the test vessel. The inherent biodegradation of the test item was followed by determination of DOC. The ratio of eliminated DOC, corrected for the control at each time interval to the initial DOC value is expressed as the percentage biodegradation at each sampling date.

In order to check the activity of the test system diethylene glycole in a concentration of 120 mg/L was used as functional control. After 14 days a degradation rate of 100 % was reached.

The physico-chemical elimination (volatilisation) of the test item was monitored in separate sterile controls. At the test item concentration of 95 mg/L a sterile control without inoculum and poisoned with HgCl2was used. For determination of the primary biodegradation sterile controls (with inoculum and poisoned with HgCl2) with a test item concentration of 300 µg/L and 600 µg/L were tested. No physico-chemical elimination (volatilistion) occurred in the sterile controls until test end.

The primary degradation started after an adaptation phase of 16 days. The biodegradation was fast and on day 23 the pass level of 70 % was reached. After 28 days the primary degradation came to 95 %.

The inherent degradation started after a long lasting adaption phase of 21 days. The biodegradation was fast and the biodegradation reached the 70 % pass level after 29 days. After 36 days a biodegradation of 99 % was reached.

The test item is classified as primary biodegradable after 23 days
and inherent biodegradable after 29 days.


Table 1:         Primary and Inherent Biodegradability of the Test Item Diethylenglykoldimethylether in Comparison to the Functional Control and the Sterile Control

Inherent Biodegradation / Elimination [%]

Day

7

14

21

28

36

test item
95 mg/L

0

3

4

67

99

functional control
120 mg/L

97

100

100

95

95

Sterile control*
95 mg/Ltest item

0

0

0

0

0

Primary Biodegradation / Elimination [%]

Test item
600 µg/L

9

01)

60

95

Sterile control*
600 µg/L test item

4

01)

0

2

Sterile control*
300 µg/L test item

0

01)

0

7

BIODEGRADATION IN WATER: SIMMULATION TESTS

Triglyme is not readily but inherently biodegradable. It is not expected that the DT90 of Triglyme in an OECD 308 or 309 would indicate a rapid biodegradation in sediment and surface water e.g. < 100 d. Due to the fact that Triglyme is classified R62 strict risk reduction measures have to be applied which means that release to the environmental compartments have to be minimized. Based on these facts the simulation tests according OECD 308 and 309 are not warranted.

BIODEGRADATION IN SOIL

The US EPA property estimation program KOCWIN V2.00 calculates for the Koc of Triglyme 10 L/kg (Molecular Connectivity Index) or 1.4 L/kg (based on Log Kow of -0.52. Due to the low estimated Koc of Triglyme a transfer to agricultural soil via sewage sludge can be neglected. Indirect exposure via deposition from air is unlikely as Triglyme is readily photodegraded in air. Because of the low soil exposure by Triglyme a soil biodegradation study is not warranted. The statement given above fulfills the requirement for waiving as given in 1907/2006/EC Annex IX, Column 2, 9.2.1.3: "The study need not be conducted if direct and indirect exposure of soil is unlikely.""