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Environmental fate & pathways

Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Deviations:
no
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, adapted
Details on inoculum:
inoculum consisti of mixed population of aquatic microorganisms (activated sludge). The origin is an aeration tank of a wastewater plant treating predominantly domestic sewage (Wupper Area water authority, STP Odenthal). The concentration of the inoculum is 30 mg/L. The sludge was washed twice by adding mineral medium and centrifuging for 10 min at 200 rpm and 20 °C and decanting off the supernatant. 1.014 g of the wet sludge was dried in order to determine the wet weight/dry weight ratio of the sludge and to prepare a stock suspension of 3g dw/L. The mineral medium consist of 10ml minearal salt solution (KH2PO4, K2HPO4, Na2HPO4 2H2O, NH4Cl) , 800 mL deionised water and 1ml of each of the magnesium sulphate-, calciumchloride- and the iron (III) chloride solution and filled up to 1 L with deionised water. The inoculum was stored at room temperature under continuous shaking with aeration until use for two days.
Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
ThOD/L
Parameter followed for biodegradation estimation:
other: nitrite nitrogen and nitrate nitrogen
Reference substance:
benzoic acid, sodium salt
Parameter:
% degradation (O2 consumption)
Value:
2
Sampling time:
7 d
Parameter:
% degradation (O2 consumption)
Value:
4
Sampling time:
14 d
Parameter:
% degradation (O2 consumption)
Value:
6
Sampling time:
21 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
8
Sampling time:
28 d

Description of key information

Zinc bis(dibenzyldithiocarbamate) is characterised as “not readily biodegradable”.

Key value for chemical safety assessment

Additional information

A GLP-compliant OECD 301F (Manometric Respirometry Test) is available for zinc bis(dibenzyldithiocarbamate). After 28 days 8% degradation was observed (Currenta GmbH & Co., 2010d). Therefore, in the assessment zinc bis(dibenzyldithiocarbamate) is characterised as “not readily biodegradable”.

In view of the overall low, but steadily increasing degradation rate it is hypothesized that the categorisation ofzinc bis(dibenzyldithiocarbamate) as “not readily biodegradable” is partly due to slow solution kinetics of this poorly soluble substance. This statement starts from the assumption that the dissolved part of organic substances is generally regarded to be available for biodegradation more easily than undissolved test item particles are.