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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Reference
Endpoint:
biodegradation in water and sediment: simulation testing, other
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: See remarks
Remarks:
In this literature publication, the materials and methods and results are sufficiently reported. The aim of the study is to demonstrate the presence of oxalate in plants and sediments and the occurrence of anaerobic microbial degradation in aquatic habitats, therefore the mineralization rates are presented as the rate of product formed (14CO2).
Qualifier:
no guideline followed
Principles of method if other than guideline:
In this literature publication, the materials and methods and results are sufficiently reported. The aim of the study is to demonstrate the presence of oxalate in plants and sediments and the occurrence of anaerobic microbial degradation in aquatic habitats, therefore the mineralization rates are presented as the rate of product formed (14CO2).

Mineralization of [14C]oxalate in sediment was measured using sediment from three different lakes.
Additional experiments: the oxalate content in several aquatic plants was determined, and degradation of oxalate present in aquatic plants was measured using litter bag experiments.
GLP compliance:
not specified
Specific details on test material used for the study:
Mineralization experiment:
- Name of test material (as cited in study report): [14C]oxalate
- Physical state: N2 sparged solution
- Specific activity (if radiolabelling): 50 Ci/mol
- Source: New England Nuclear
Radiolabelling:
yes
Oxygen conditions:
anaerobic
Inoculum or test system:
natural sediment
Duration of test (contact time):
ca. 6.5 h
Initial conc.:
ca. 3.6 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
CH4 evolution
CO2 evolution
test mat. analysis
% Degr.:
>= 90
Parameter:
test mat. analysis
Sampling time:
175 d
Mineralization rate (in CO2):
1 d-1
Other kinetic parameters:
pseudo-first order rate constant
other: turnover time (1/rate constant) can be substantially less than 1 day
Transformation products:
yes
No.:
#1
No.:
#2

The production rates of 14CO2 in anaerobic sediments amended with [14C]oxalic acid are summarized in the following table (reproduced from the publication).

Sediment sample (type)

Total sediment oxalate concentration (µmol/liter of sediment)

Oxalate mineralization rate (µCi of 14CO2 produced/liter of sediment/day)

Rate constant (per day)

Searsville Lake, eutrophic reservoir

Pelagic SVL

688

27.3

0.55

15.4

0.31

Littoral SVL

533

272.7

5.45

86.3

1.73

Intermediate SVL

98.2

1.96

Big Soda Lake

Pelagic BSL

100

0.2

0.004

Littoral BSL

110

10.8

0.22

San Fransisco Bay, tidal mud flat

Salt marsh

367

20.6

0.41

46.2

0.92

Tidal mud flat

235

37.8

0.76

lake Tahoe, oligotrophic lake

Pelagic LT

78

0.54

0.01

Near shore LT

297

6.62

0.13

The following table contains the oxalate content of potential detrital inputs to aquatic sediments, and is also reproduced from the publication.

Sample

Description

% oxalic acid by dry wt

Brown hickory

Senescent leaves

5.01

Brown oak

Senescent leaves

2.22

Sea grass (Zostera sp.)

Whole plant

1.02

Pickle grass (Salicornia sp.)

Leaves

1.99

Cord grass (Spartina sp.)

Whole plant

0.08

Waterlily (Nuphar sp.)

Leaf blades

3.34

Petioles

5.02

Water milfoil (Myriophyllum sp.)

Whole plant

2.54

Widgeon grass (Ruppia sp.)

Whole plant

0.07

Algal mat

Littoral zone ( )

0.21

Seston

Pelagic zone ( )

0.04

The oxalate content in litter bags containing Myriophyllum sp samples decreased with time when burien in littoral sediment. The net loss was the result of a decrease in both the total plant mass remaining in the litter bag and the oxalate concentration of that plant material (7% of the initial total oxalate remained in the litter bag after 175 days, compared to 16% of the initial plant mass). In the litter bags placed in the aerobic water column, the exalate content remained relatively constant. The oxalate concentration of the litter bag contents was 2.54 mg/g dry wt initially, and after 175 days 2.06 mg/g dry wt for the water column-placed litter bags and 0.75 for the sediment-placed litter bags.

Validity criteria fulfilled:
not specified
Conclusions:
[14C]oxalic acid was anaerobically degraded to 14CO2 and traces of CH4 in all sediment types tested. In littoral and near-shore sediments the rate of 14CO2 production ranged from 6.6 to 273 µCi of 14CO2 produced/liter of sediment/day, and in pelagic sediments the rate was 0.2 to 27.3 µCi of 14CO2 produced/liter of sediment/day, under the current test conditions. The turnover time of the added [14C]oxalate can be substantially less than 1 day in some sediments.
Executive summary:

The anaerobic degradation of oxalate was determined in different sediment samples. [14C]oxalic acid was anaerobically degraded to 14CO2 in all sediment types tested. In littoral and near-shore sediments the rate of 14CO2 production ranged from 6.6 to 273 µCi of 14CO2 produced/liter of sediment/day, and in pelagic sediments the rate was 0.2 to 27.3 µCi of 14CO2 produced/liter of sediment/day. Rate constants were 0.01 to 0.5 per day in pelagic sediments and 0.13 to 5.4 per day in littoral sediments. The turnover time of the added [14C]oxalate was less than 1 day in the sediment from the Searsville Lake.

The anaerobic degradation of oxalate appears to be a widespread phenomenon, occurring in every sediment tested.

The oxalate concentration of several plant species which are potential detrital inputs to the tested aquatic sedmients ranged from 0.1 to 5.0% (dw). In experiments with litter bags, the oxalate content of Myriophyllum sp. samples buried in freshwater littoral sediments decreased to 7% of the original value in 175 days.

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