Oxalic acid

Biodegradation in water and sediment: simulation tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: sediment simulation testing

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.

Key value for chemical safety assessment