Dichlobenil

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:

25 July 2002 to 15 November 2002

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.3110 (Ready Biodegradability)

Deviations:

no

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

sewage, predominantly domestic (adaptation not specified)

Details on inoculum:

- Source of inoculum/activated sludge: final effluent stage at Severn Trent Water plc sewage treatment plant at Loughborough, Leicestershire, UK
- Storage conditions: filtered through course filer paper (first 200 mL discarded) and maintained on aeration at 21 ± 1 ºC

Duration of test (contact time):

28 d

Initial conc.:

50 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS
- Composition of medium:
SOLUTION A
KH2PO4: 8.50 g/L
K2HPO4: 21.75 g/L
Na2HPO4.2H2O: 33.40 g/L
NH4Cl: 0.50 g/L

SOLUTION B
CaCl2: 27.50 g/L

SOLUTION C
MgSO4.7H2O: 22.50 g/L

SOLUTION D
FeCl3.6H2O: 0.25 g/L

To 1 L of purified water was added 10 mL of solution A and 1 mL each of solutions B to D.

TEST SYSTEM
The following were prepared and inoculated in 500 mL bottles:
(a) four replicates containing inoculated culture medium to act as the control. These bottles contained 5 mL of inoculum and 495 mL of culture medium.
(b) three replicates containing inoculated culture medium and aniline at a concentration of 100 mg/L.
(c) three replicates containing inoculated culture medium and the test substance at a concentration of 50 mg/L.
(d) two replicates containing inoculated culture medium, aniline at a concentration of 100 mg/L and test substance at a concentration of 50 mg/L.

All bottles were inoculated with the prepared inoculum at a rate of 1 % v/v.

- Culturing apparatus: sample flask sealed by a sensor head/CO2 trap immersed in a temperature controlled water bath.
- Test performed in closed vessels due to significant volatility of test substance: yes

SAMPLING
On day 28, two control, one standard material, two test material and one toxicity control vessel that were considered to have given the most consistent BOD values were selected for pH and DOC analysis.

STATISTICAL METHODS:
A Students t-test was carried out for the control and test substance vessels to determine any statistically significant differences between the BOD values on day 28 for the control and test groups.

Reference substance:

aniline

Preliminary study:

An initial experiment in which dispersed test material was exposed to sewage sludge microorganisms at a concentration of 100 mg/L showed no biodegradation in the toxicity control vessel (test material plus the standard material, aniline) after 14 days. However, results obtained from the standard material vessel indicated that sufficient biodegradation (68 %) had occurred after 14 days, therefore satisfying the validation criterion given in the test guidelines and confirming the suitability of the inoculum used and culture conditions.

Under the definition given in the test guidelines, this would indicate that the test material, at a concentration of 100 mg/L, exhibited an inhibitory effect on the sewage sludge microorganisms. However results obtained from the test material and toxicity control vessels indicated that although no biodegradation had occurred, the oxygen consumption values obtained were similar to those obtained from the control vessels. This suggests that although the test material was exhibiting an inhibitory effect on biodegradation of the standard material in the toxicity control vessel, as the oxygen consumption values in the test material vessels are similar to those in the control vessels, the test material was not exhibiting a toxic effect.

Key result

Parameter:

% degradation (O2 consumption)

Value:

0

Sampling time:

28 d

Details on results:

Following the recommendations of the test guidelines, dispersed test material was exposed in the definitive test to sewage sludge micro-organisms at a reduced test concentration of 50 mg/L with culture medium in sealed culture vessels in the dark at 21 ± 0.7 °C for 28 days. The degradation of the test material was assessed by the measurement of daily oxygen consumption values. Control solutions with inoculum and the standard material, aniline, together with a toxicity control were used for validation purposes.

No degradation of the test material was observed after 28 days and therefore it cannot be considered to be readily biodegradable.

Results with reference substance:

The standard material vessels indicated that sufficient biodegradation (68 %) had occurred after 14 days, therefore satisfying the validation criterion given in the test guidelines and confirming the suitability of the inoculum used and culture conditions.

Validity criteria fulfilled:

yes

Interpretation of results:

under test conditions no biodegradation observed

Conclusions:

Under the conditions of the test, no degradation of the test material was observed after 28 days and the test material is not considered to be readily biodegradable.

Executive summary:

In a GLP compliant ready biodegradability study conducted in line with standardised guidelines OECD 301F, EU Method C.4 -D and EPA OPPTS 835.3110, the biodegradability of the test material was determined. Under the conditions of the test, no degradation of the test material was observed after 28 days and the test material is not considered to be readily biodegradable.

Description of key information

The test material was determined to be not ready biodegradable according to a study performed in line with OECD Guideline 301F, EU Method C.4-D and EPA OPPTS 835.3110.

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Additional information

See 'Environmental Fate and Pathways' endpoint summary.