Estr-5(10)-en-17-one, 3,3-dimethoxy-

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:

2000

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)

Deviations:

no

Principles of method if other than guideline:

not relevant

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic (adaptation not specified)

Duration of test (contact time):

28 d

Initial conc.:

10 mg/L

Based on:

DOC

Key result

Parameter:

% degradation (CO2 evolution)

Value:

69

Sampling time:

29 d

Parameter:

% degradation (CO2 evolution)

Value:

17

Sampling time:

11 d

Details on results:

The reference compound sodium acetate was degraded to > 80% on day 14. In the toxicity control, the reference compound (sodium acetate) plus
the test compound ZK 235382, was degraded to 80% on day 29.

Table 1: Biological degradation (cumulative) in percent (corrected for blank CO2 production) of ZK 235382

Test	Nominal	Day of sampling
compound	concentration of carbon	4	7	11	14	18	22	27	29
ZK 235382	10 mg/L	0	2	17	28	43	56	64	69
Reference (sodium acetate)	10 mg/L	32	59	76	81	87	91	93	95
T oxicity control (ZK 235382 + sodium acetate)	10 mg/L + 10 mg/L	16	32	51	59	66	71	75	80

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable, but failing 10-day window

Conclusions:

In accordance with the OECD guideline, the test compound ZK 235382 is not readily biodegradable under the conditions of the test, since the
stringent criteria for "ready biodegradability", i.e. degradation of 60% within a 10 day window, were not met. However, ZK 235382 is expected
to be inherently biodegradable. It was not toxic to the microbes of activated sludge.

Executive summary:

The purpose of this study was to determine the ready biodegradability of Dimethoxyketal (ZK 235382), which is an intermediate of the synthesis of Dienogest. The study was conducted in agreement with the OECD test guideline no. 301 B.

The test substance was incubated in an aqueous solution including nutrients with microorganisms from a municipal sewage treatment plant for 28 days (start of treatment = day 1). The nutrient solutions were made up of phosphates, magnesium sulphate, iron chloride, ammonium chloride and calcium chloride.

The test substance was incubated at a concentration of 10 mg carbon/L in triplicate.

Additionally, a reference substance (sodium acetate) was tested in a single set according to the same procedure, in order to verify the viability and activity of the degrading microorganisms. One further set was incubated with sodium acetate at 10 mg carbon/L (reference substance) plus ZK 235382 at 10 mg carbon/L representing a toxicity control. Furthermore, a blank control

was tested in triplicate without any test or reference substance. The biological degradation of the test and reference substances was evaluated by measurement of the carbon dioxide (CO2) produced during the test period. CO2 production was determined

on days 4, 7, 11, 14, 18, 22, 27, and 29. On day 28 the solutions were acidified in order to expel all dissolved CO2 and CO2 was determined on day 29. The CO2 production was calculated as the percentage of total CO2 that the test material could theoretically have produced, based on carbon content. The blank CO2 production was subtracted for correction.

The test compound was degraded to 69% on day 29 (~ 28 days of incubation). This indicates that the test compound was degradable under the test conditions.

Description of key information

In accordance with the OECD guideline, the test compound ZK 235382 is not readily biodegradable under the conditions of the test, since the

stringent criteria for "ready biodegradability", i.e. degradation of 60% within a 10 day window, were not met. However, ZK 235382 is expected

to be inherently biodegradable. It was not toxic to the microbes of activated sludge.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable but failing 10-day window

Type of water:

freshwater