Chlorhexidine dihydrochloride

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:

2002

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge: Municipal sewage treatment plant, STP Marl-Ost, Germany
- Preparation of inoculum for exposure: Sewage sludge was treated in accordance with standard procedures of the laboratory (SOP), no further detail
- Pretreatment: None
- Initial cell/biomass concentration: Content of dry matter in the inoculum was 4.172 g/L

Duration of test (contact time):

14 d

Initial conc.:

5.7 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

TEST CONDITIONS
- Composition of medium: mineral medium
- Additional substrate: no
- Test temperature: 21.7-22.5°C
- Aeration of dilution water: medium aerated overnight
- Suspended solids concentration: 4.172 g/L dw (110exp4 CFU/mL)
- Continuous darkness: yes

TEST SYSTEM
- Number of culture flasks/concentration: 2

SAMPLING
Degradation measured via TIC analysis after 0, 2, 5, 9, and 14 days

CONTROL AND BLANK SYSTEM
- Inoculum blank: 2 vessels
- Toxicity control: 1 vessel

Reference substance:

benzoic acid, sodium salt

Parameter:

% degradation (CO2 evolution)

Value:

-76

Sampling time:

14 d

Remarks on result:

other: mean of 2 determinations

Details on results:

The degree of degradation was -76 %. The negative value is due to mathematical calculation. The toxicity control (test plus reference item) reached -5 % in the course of 14 days. It can be assessed that the test item is inhibitory in the concentrations used here, because in the toxicity control batch less than 25 % degradation occurred within 14 days (see OECD 301). Therefore, the test was broken off after 15 days.
With the plate count determination in the batches a selection of species could be observed.
The normal diversity of species was reduced to max. two different, probably less sensitive types. The number of colony forming units was significantly higher as in the control item batch, but this may be due to the fact that the plate count determination was performed on a full medium.

Degradation products: not measured

Validity criteria fulfilled:

yes

Interpretation of results:

under test conditions no biodegradation observed

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed