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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
Study period:
11.09.2006 - 19.01.2007
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Version / remarks:
1992
Deviations:
yes
Remarks:
see field "any other information on results incl. tables"
GLP compliance:
no
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: the activated sludge was collected from the secondary treatment system of an integrated system for liquid effluent treatment from South Petrochemical Complex Triunfo- RS- Brazil.
- Preparation of inoculum for exposure: 1 L of activated sludge was aerated for 5 to 7 days and subsequently filtered.
- Initial cell/biomass concentration: 6.4 x 10^6 colony forming units/mL
- Other: 50 mL inoculum/3 L mineral medium was used
Duration of test (contact time):
28 d
Initial conc.:
42.5 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium:
KH2PO4 8.50 g/L
K2HPO4 21.75g/L
Na2HPO4.2H2O 33.40 g/L
NH4CI 0.50 g/L
MgSO4.7H20 22.50 g/L
FeCI3.6H20 0.25 g/L
CaCl2.2H2O 36.40 g/L
- Suspended solids concentration: 9.08 g/L
- Test temperature: 19.7 - 24.6 °C
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 4 L flasks
- Number of culture flasks/concentration: 2 (0.1276 g test substance + 50 mL inoculum + 3 L mineral medium)
- Method used to create aerobic conditions: continuous air-flow system
- Details of trap for CO2 and volatile organics if used: by titration of sodium hydroxide 0.9917 M (CO2 absorbent) with chloridric acid 0.2556 N

CONTROL AND BLANK SYSTEM
- Inoculum blank: 1 (inoculum + mineral medium)
- Toxicity control: 1 (0.0633 g test substance + 0.1273 g reference substance + 50 mL inoculum + 3 L mineral medium)
- Procedure control: 1 (0.0635 g reference substance + 50 mL inoculum + 3 L mineral medium)
Reference substance:
other: potassium hydrogen phthalate
Parameter:
% degradation (CO2 evolution)
Value:
7.7
Sampling time:
4 d
Parameter:
% degradation (CO2 evolution)
Value:
7.7
Sampling time:
28 d
Results with reference substance:
85.9% after 10 days

The test could not properly investigate possible ready biodegradability since the test substance was inhibitory to microorganisms.

Biodegradation in the toxicity control was 37.7% within 14 days since test initiation.

DEVIATIONS:

The temperature reached a min. of 19.7°C and a max. of 24.6°C, which is higher than the deviation specified by the guideline (22 +/-2°C). However the temperature was within the range of 22 +/-2°C for 98.5% of the experimental time. Therefore, it is not expected that the short time would have affected the organisms and the test result.

The number of viable cells and suspended solids concentration of the inoculum was different that specified in the guideline. The concentrations were 10^7 - 10^8 and <<30 mg/L, respectively. The procedure control reached the acceptability criteria of the study. Therefore it is concluded that this incident did not affect the final result of the study.

VALIDITY CRITERIA:

Table 1: Validity criteria for OECD 301.

Criterion from the guideline

Outcome

Validity criterion fulfilled

Difference of extremes of replicate values of the removal of the test chemical at the plateau, at the end of the test or at the end of the 10-d window, as appropriate, is less than 20%.

7.7% difference

 

yes

Percentage degradation of the reference compound reached the pass level by day 14 (≥ 60%).

85 - 86.8%

yes

The toxicity control should degrade to at least 35% (based on DOC) or at least 25% (based on ThOD or ThCO2) within 14 d.

37.7% after 4 d and 14 d

yes

The IC content of the test substance suspension in the mineral medium at the beginning of the test must be less than 5% of the TC.

Not specified

Not specified

The total CO2 evolution in the inoculum blank at the end of the test should not normally exceed 40 mg/L medium.

0.0293 g

yes

Validity criteria fulfilled:
yes
Remarks:
For details refer to field "Any other information on results incl. tables"
Interpretation of results:
other: not readily biodegradable

Description of key information

Zinc bis dimethyldithiocarbamate (CAS No. 137-30-4) is not readily biodegradable: 7.7% (CO2 evolution) in 28 days (OECD 301 B)

Key value for chemical safety assessment

Biodegradation in water:
not biodegradable
Type of water:
freshwater

Additional information

One study investigating the ready biodegradability of zinc bis dimethyldithiocarbamate (CAS No. 137-30-4) is available (2007). This test was conducted according to the OECD Guideline No. 301B (1992). Non-adapted activated sludge was exposed for 28 days to a test substance concentration of 42.5 mg/L. A procedure and a toxicity control were run in parallel. The test substance reached a maximum of 7.7% biodegradation after 28 d and therefore, it is considered as not readily biodegradable. In the toxicity control 37.7% degradation was observed within 14 days. Some inhibition occurred during that study as stated by the authors.