Paraquat-dichloride

Biodegradation in water and sediment: simulation tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water and sediment: simulation testing, other

Remarks:

water and sediment system

Type of information:

experimental study

Adequacy of study:

key study

Study period:

25 Oct 1995 - 02 Feb 1996

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: BBA Guidelines for the Official Testing of Plant Protection Products; Part IV, 5-1 "Degradability and Persistence of Plant Protection Products in the Water/Sediment System"

Version / remarks:

December 1990

Deviations:

no

GLP compliance:

yes

Radiolabelling:

yes

Remarks:

Uniformly [14C]-labelled at both pyridine rings

Oxygen conditions:

aerobic

Inoculum or test system:

natural water: freshwater

Details on source and properties of surface water:

- Details on collection: Overlying water was collected at two sites in South East England and are identified as Virginia water and Old Basing. Before collection of the sediments, the pH, temperature and dissolved oxygen in the surface waters were determined and recorded. A sample of the surface water at each site was collected and stored in a 25 L plastic bottle prior to sampling of the sediment.

VIRGINIA WATER
- Location: The Great Park, Windsor, Berkshire, England
- Water depth: 0.1 m
- Width of stream: 1 m
- Approximate flow reate: 0.07 m/s
- Water temperature: 15 °C
- Water pH: 7.2
- Dissolved oxygen (5 cm above sediment): 8.0 mg/L

OLD BASING
- Location: River Loddon, Old Basing, Basingstoke, Hampshire, England
- Water depth: 0.25 - 0.75 m
- Width of stream: 5 m
- Approximate flow reate: 0.1 m/s
- Water temperature: 12 °C
- Water pH: 7.5
- Dissolved oxygen (5 cm above sediment): 8.0 mg/L

Physical characteristics of the sediments at the start and end of the study are presented in 'Any other information on materials and methods incl. tables'.

MEASUREMENTS
- pH: The pH of the water above the sediment was measured using a temperature compensated portable pH meter which had been calibrated at pH 7 and pH 4.
- Dissolved oxygen: The dissolved oxygen in the surface water at each site was determined prior to sampling. A portable dissolved oxygen meter, previously calibrated in the laboratory, was immersed into the water until a stable reading was obtained (approximately 1 minute). This meter automatically compensated for temperature.
- Temperature: The temperature of the water at each sampling site was determined using a mercury in glass thermometer which was immersed into the water until a stable reading was obtained (approximately 1 minute).
- Redox potential: The redox potential was monitored within control vessels, one of each sediment type. The redox probe was a Russell, type CMPtDL/S7/Hg/320 positioned approximately 10 mm below the sediment-water interface.

Details on source and properties of sediment:

- Details on collection: Sediments were collected at two sites and are identified as Virginia water and Old Basing. The sediments were collected from the top 5 cm with a shovel. The sediment was stored at 20 ± 2°C overnight before setting up the test vessels.
- Sediment samples sieved: Yes; The sediment collected was passed through a 2 mm stainless steel sieve to remove large stones and plant material. The sediment passing through the sieve was collected in a plastic container and mixed thoroughly. The material retained in the sieve was discarded. The water samples were filtered through a 0.2 mm filter and stored in the containers in which they were collected until required for use.

VIRGINIA WATER
- Location: The Great Park, Windsor, Berkshire, England
- Dissolved oxygen (5 cm below surface): 8.8 mg/L
- Sampling depth: 0-5 cm

OLD BASING
- Location: River Loddon, Old Basing, Basingstoke, Hampshire, England
- Dissolved oxygen (5 cm below surface): 9.2 mg/L
- Sampling depth: 0-5 cm

Physical characteristics of the sediments at the start and end of the study are presented in 'Any other information on materials and methods incl. tables'.

Duration of test (contact time):

100 d

Initial conc.:

500 µg/L

Based on:

test mat.

Remarks:

in water

Initial conc.:

1.1 other: kg/ha

Based on:

test mat.

Remarks:

in sediment

Parameter followed for biodegradation estimation:

CO2 evolution

radiochem. meas.

Details on study design:

ACCLIMATION
The incubation vessels were acclimatised for 63 days to allow the sediment to enable an equilibrium to be established with respect to pH and oxygen concentration in the water and redox potential of the sediment.

TEST CONDITIONS
- Test vessel: Each test vessel consisted of a 250 mL polycarbonate centrifuge tube fitted with an adapted lid with an inlet and outlet port. All flexible tubing in the test system was made of butyl rubber to minimise losses of gaseous substances.
- Volume of test solution/treatment: Each incubation vessel contained an amount of wet sediment equivalent to approximately 40 g (dry weight basis) of Virginia Water sediment or approximately 20 g (dry weight basis) of Old Basing sediment plus a total of 150-200 g of water. The sediment weights are based upon the remaining sediment after digestion. The water weights are based upon the volunes determined upon analysis of the samples. This was sufficient to five a minimum depth of sediment of 2 cm and a minimum depth of water of 6 cm.
- Composition of medium: Physical characteristics of the sediments at the start and end of the study are presented in 'Any other information on materials and methods incl. tables'.
- Test temperature: The test systems were incubated at 20 ± 2°C.
- Aeration of dilution water: Each vessel was then connected to a common inlet manifold through which CO2-free, humidified air, was drawn. The exhaust from the last trap was connected via a needle valve, to control the air flow through each vessel, to an exhaust manifold along with three other vessels. Each exhaust manifold was connected to a vacuum pump which pulled the air through the test system. This slight negative pressure minimised losses of radioactive gases from the test system in the event of a leak.
- Continuous darkness: Yes

TEST SYSTEM
- Number of culture flasks/concentration: 2
- Measuring equipment:
- Details of trap for CO2 and volatile organics if used: The CO2 free, humidified air, was produced by passing the air through 2M sodiwn hydroxide to remove CO2 and then the air was bubbled through water to humidify it The CO2-free, humidified air, entered each test vessel just above the surface of the water. The exhaust gases from each vessel were passed through a series of traps: solid adsorbents to trap volatile organics and 2 x 50 ml traps of 2M sodium hydroxide to trap [14C]O2.

DESCRIPTION OF CONTROL AND/OR BLANK TREATMENT PREPARATION CONTROL AND BLANK SYSTEM
- Abiotic sterile control: Replicate control vessel was used to monitor the dissolved oxygen in the surface water above each sediment and to measure the pH of the water. In this way the redox potential of the sediment was not perturbed during the study. The measurement of the sediment redox potential and the surface water dissolved oxygen were used to confirm the aerobic to anaerobic transition in the sediment.

MEASUREMENTS QUALITY PARAMETERS
Throughout the incubation period of the study the redox potential, pH and dissolved oxygen of the control vessels were measured on each day that samples were removed for analysis. The dissolved oxygen and pH of test vessels removed for analysis were also measured. At day 0 and 0.25 the dissolved oxygen and pH of the test vessels were not determined because of the likelihood of contamination of the probes leading to a low recovery of applied radioactivity.
- Determination of dissolved oxygen in surface water: Control vessels not containing a redox probe were used to measure the surface water dissolved oxygen each time vessels were removed for analysis. The vessel closure containing the flushing ports was removed whilst a calibrated hand-held dissolved oxygen probe was gently lowered into the surface water layer and agitated slowly without disturbing the sediment layer. After a stable reading was obtained (approximately 2 minutes) it was recorded and the probe was removed. The dissolved oxygen in those vessels removed for analysis was detennined in the same manner.
- Determination of pH in the aqueous phase: After the dissolved oxygen had been determined, the pH of the control vessels and those vessels to be analysed were determined using a calibrated pH stick.
- Determination of the Redox potential: The control vessels containing a redox probe were used to measure the redox potential below the sediment-water interface. The output signals from the redox probes were continuously logged over the course of the study on a Squirrel data-logger. The redox potential of the vessels to be analysed was not determined because of the likelihood of sedimentous particles containing the test substance adhering to the probe leading to a low recovery of applied radioactivity.

Compartment:

natural water: freshwater

Remarks on result:

other: Old Basing: Total radioactive recoveries varied between 92.9% and 99.2%

Remarks:

see 'Any other information on results incl. tables'

Compartment:

natural sediment: freshwater

Remarks on result:

other: Virginia water: Total radioactive recoveries varied between 91.6 to 98.7%

Remarks:

see 'Any other information on results incl. tables'

Remarks on result:

other: No degradation was detected

Remarks on result:

other: No estimation of the DT50 and DT90 was possible, because no degradation of paraquat when adsorbed to sediment was observed during the exposure period.

Remarks:

see 'Any other information on results incl. tables'

Transformation products:

no

Evaporation of parent compound:

no

Volatile metabolites:

no

Residues:

yes

Remarks:

see 'Details on results'

Details on results:

Physical parameters of sediments and waters are presented in 'Any other information on results incl. tables'.

RADIOACTIVITY IN THE AQUEOUS PHASE
Summaries of the total amount of applied radioactivity in the aqueous phases for both Old Basing and Virginia Water are shown in 'Any other information on results incl. tables'. At no point during the course of the study was the radioactivity in the aqueous phase greater than 5%, therefore no characterisation was performed. The amount of radioactivity in the aqueous phases from both Old Basing and Virginia Water varied slightly with time. At time 0 the aqueous phase contained a mean of 3.0% and 0.3% of the applied radioactivity for Old Basing and Virginia Water, respectively. By day 100 the aqueous phase contained 0.1 % and 0.2% of the applied radioactivity for Old Basing and Virginia Water, respectively.

RADIACTIVITY EXTRACTED FROM THE SEDIMENTS
Summaries of the total amount of recovered radioactivity and the amount of test substance, (expressed as a % of applied radioactivity) in the sediment extracts for both Old Basing and Virginia Water are shown in 'Any other information on results incl. tables', respectively. At time 0 the sediment extracts contained 89.5% and 92.4% of the applied radioactivity for Old Basing and Virginia Water, respectively. At day 0 98.5% or more of the radioactivity in the sediment extracts from Old Basing and Virginia Water was identified as the test substance. By day 100 the radioactivity in the sediment extracts of the Old Basing sediment-water system accounted for approximately 94.9% of the applied radioactivity. The test substance accounted for 99.4% of this radioactivity, equivalent to 94.3% of the applied radioactivity. By day 100 the radioactivity in the sediment extracts of the Virginia Water sediment-water system accounted for approximately 92.9% of the applied radioactivity. The test substance accounted for 99.2% of this radioactivity, equivalent to 92.1 % of the applied radioactivity.

RESIDUAL RADIOACTIVITY IN THE SEDIMENTS
The radioactivity remaining in the sediment after solvent extraction and air drying was determined by ball-milling the sediment and then combusting subsamples. Initially < 5 % of the applied radioactivity was found in the sediment from both sediment-water systems after solvent extraction. As the exposure phase continued the amount of radioactivity remaining in the sediment fluctuated slightly. At the end of the 100 days exposure, the Old Basing sediment contained a mean of 4.2% and the Virginia Water sediment contained a mean of 4.5% of the applied radioactivity.

RADIOACTIVITY IN THE COMBINED WATER AND SEDIMENT EXTRACTS
At the beginning of the exposure period the radioactivity in the combined water and sediment extracts of the Old Basing sediment-water system was 92.5%. The test substance accounted for 99.3% of the radioactivity in the sediment extract, equivalent to at least 88.8 % of the total radioactivity applied on day 0, although there was no characterisation of the water samples due to the low amount of radioactivity in the samples. At the end of the 100 day test period the amount of radioactivity in the combined water and sediment extracts was 95.0% of the applied radioactivity. The test substance accounted for 99.4% of radioactivity in the sediment extract, equivalent to at least 94.3% of the total radioactivity applied on day 0. At the beginning of the exposure period the radioactivity in the combined water and sediment extracts of the Virginia Water sediment-water system was 92.7%. The test substance accounted for 98.7% of the radioactivity in the sediment extract, equivalent to at least 91.2 % of the total radioactivity applied on day 0, although there was no characterisation of the water samples due to the low amount of radioactivity in the samples. At the end of the 100 day test period the amount of radioactivity in the combined water and sediment extracts was 93.1 % of the applied radioactivity. The test substance accounted for 99.2% of radioactivity in the sediment extract, equivalent to at least 92.1 % of the total radioactivity applied on day 0.

Table: Extraction and recovery of radioactivity from Old Basing sediment-water system after application of radiolabelled test substance at a nominal rate of 500 μg/L (results expressed as a % of the applied radioactivity)

Time after application (days)	Aqueous phase	Sed iment		Total sediment	volatiles	Total recovery
		Extractable	Non-extractable
0	4.1 1.8	88.3 90.6	1.7 1.5	90.0 92.1	<0.1 <0.1	94.1 93.9
0.25	2.1 1.4	89.1 91.7	1.7 1.6	90.8 93.3	<0.1 <0.1	92.9 94.7
1	1.4 0.8	90.4 92.2	1.2 1.4	91.5 93.6	<0.1 <0.1	92.9 94.4
2	0.5 0.3	92.3 95.8	2.2 1.9	94.5 97.7	<0.1 <0.1	95.0 98.0
7	0.8 0.1	92.4 72.0	2.3 1.5	94.7 73.5	<0.1 <0.1	95.5 73.6
14	0.2 0.3	95.3 95.4	3.6 3.2	98.9 98.6	<0.1 <0.1	99.1 98.9
30	0.1 0.2	92.7 93.7	2.2 2.5	94.9 96.2	<0.1 <0.1	95.0 96.4
54	0.1 0.1	88.1 91.6	9.1 5.8	97.2 97.4	<0.1 <0.1	97.3 97.5
100	0.1 0.1	95.0 94.8	4.1 4.2	99.1 99.0	<0.1 <0.1	99.2 99.1

Table: Extraction and recovery of radioactivity from Virginia Water sediment-water system after application of radiolabelled test substance at a nominal rate of 500 μg/L (results expressed as a % of the applied radioactivity)

Time after application (days)	Aqueous phase	Sediment		Total sediment	volatiles	Total recovery
		Extractable	Non- Extractable
0	0.2 0.4	91.9 92.8	3.3 3.2	95.2 96.0	<0.1 <0.1	95.4 96.4
0.25	0.9 1.0	92.3 92.1	2.0 2.2	94.3 94.3	<0.1 <0.1	95.2 95.3
1	0.9 1.8	91.3 93.0	2.6 2.0	93.9 95.0	<0.1 <0.1	94.8 96.8
2	0.3 0.9	94.7 93.9	2.1 2.3	96.8 96.2	<0.1 <0.1	97.1 97.1
7	0.5 0.6	93.5 88.7	2.0 2.4	95.5 91.0	<0.1 <0.1	96.0 91.6
14	0.4 0.6	94.4 95.3	3.4 2.6	97.8 98.1	<0.1 <0.1	98.2 98.7
30	0.2 0.1	94.5 91.1	2.0 4.9	96.5 96.0	<0.1 <0.1	96.7 96.1
54	0.2 <0.1	92.1 94.2	4.7 4.4	96.8 98.6	<0.1 <0.1	97.0 98.6
100	0.2 0.1	92.5 93.2	4.8 4.2	97.3 97.4	<0.1 <0.1	97.5 97.5

Table: Mean distribution of the test substance in the aqueous phase and sediment extracts from Old Basingh sediment after application at a nominal rate of 500 μg/L (results expressed as a% of the applied radioactivity)

Time after application (days)	Water	Sediment		Total
		% of applied	% as test substance	% of applied	% as test substance
0	3	89.5	88.8 (99.3)	92.5	88.8
0.25	1.8	90.4	88.1 (97.5)	92.2	88.1
1	1.1	91.3	89.9 (98.5)	92.4	89.9
2	0.4	94.1	93.1 (99.0)	94.5	93.1
7	0.5	92.4	92.0 (99.6)	92.9	92
14	0.3	95.4	94.1 (98.6)	95.7	94.1
30	0.2	93.2	91.6 (98.2)	93.4	91.6
54	0.1	89.9	87.7 (97.6)	90	87.7
100	0.1	94.9	94.3 (99.4)	95	94.3

Figures in brackets () are the percentage of the extracted radioactivity characterised as the test substance

 

Table: Mean distribution of the test substance in the aqueous phase and sediment extracts from Virginia Water sediment after application at a nominal rate of 500 μg/L (results expressed as a% of the applied radioactivity)

Time after application (days)	Water	Sediment		Total
		% of applied	% as test substance	% of applied	% as test substance
0	3	92.4	91.2 (98.7)	92.7	91.2
0.25	1.8	92.2	90.8 (98.4)	93.2	90.8
1	1.1	92.2	91.3 (99.1)	93.6	91.3
2	0.4	94.3	92.9 (98.5)	94.9	92.9
7	0.5	91.1	89.8 (98.6)	91.7	89.8
14	0.3	94.9	93.1 (98.1)	95.4	93.1
30	0.2	92.8	92.0 (99.2)	93	92
54	0.1	93.2	91.9 (98.6)	93.4	91.9
100	0.1	92.9	92.1 (99.2)	93.1	92.1

Figures in brackets () are the percentage of the extracted radioactivity characterised as the test substance

Validity criteria fulfilled:

not specified

Conclusions:

The aquatic degradation of the test substance in two sediment-water systems has been studied at a nominal application rate of 1.1 kg test substance/ha. No degradation of the test substance was detected in either of the two systems during the exposure period.

Executive summary:

The degradation of the radiolabelled test substance has been studied in two different sediment-water systems. The sediments used in the study were collected from two sites in England: Virginia Water and Old Basing. Both sediment-water systems were set up in cylindrical polycarbonate vessels in the dark at 20 ± 2°C. The test systems were allowed to acclimatise for 63 days to enable an equilibrium to be established with respect to pH and oxygen concentration of the water and redox potential of the sediment. Following acclimatisation of the test system, radiolabelled test substance was applied to the water surface of each vessel in a small volume of deionised water. The nominal application rate was equivalent to 1.1 kg test substance/ha uniformly distributed in a 30 cm depth of water which is equivalent to a concentration of 500 μg/L in the water overlaying the sediment. Each test system was continuously aerated from above the air-water interface by drawing CO2-free, humidified air through the system. The air stream was then passed through two traps containing solid adsorbent to trap organic volatile products, and sodium hydroxide solution to trap carbon dioxide. Duplicate incubation units were removed for analysis at intervals of 0 (immediately after test substance application), 0.25, 1, 2, 7, 14, 30, 54 and 100 days after test substance application. The total recovery of applied radioactivity from each test system ranged from 91.6 - 99.2%. After 100 days incubation the distribution of the applied radioactivity in the Virginia Water sediment-water system showed that only 0.2% remained in the aqueous phase, while 92.9% was extractable from the sediment Volatile products accounted for <0.1 % of the applied radioactivity. The total amount of radioactivity associated with the aqueous phase and sediment extracts from the Virginia Water sediment-water system accounted for 93.1 % of the applied radioactivity. Of this, the test substance was the major component accounting for 92.1 % of the applied radioactivity. After 100 days incubation the distribution of the applied radioactivity in the Old Basing sediment-water system showed that only 0.1 % remained in the aqueous phase, while 94.9% was extractable from the sediment. Volatile products accounted for <0.1 % of the applied radioactivity. The total amount of radioactivity associated with the aqueous phase and sediment extracts from the Old Basing sediment-water system accounted for 95.0% of the applied radioactivity. Of this, the test substance was the major component accounting for 94.3% of the applied radioactivity. No degradation products were detected.

Description of key information

The aquatic degradation of the test substance in two sediment water systems has been studied. No degradation of the test substance was detected in either of the two systems during the exposure period (BBA Part IV, 5 -1, Long 1996)

Additional information

Table: Overview of available data on biodegradation in water and sediment of the test substance

Compartment	Guideline / GLP	Endpoint	Value	Comment	Reference
Natural water: freshwater (Old Basing)	BBA Part IV, 5-1/ GLP	DT50	-	No estimation of the DT50 and DT90 was possible, because no degradation of the test substance when adsorbed to sediment was observed during the exposure period. No metabolites were detected.	Long, 1996
Natural water: freshwater (Virginia Water)		DT50	-
Natural water / sediment: freshwater (Old Basing)		DT50	-
Natural water / sediment: freshwater (Virginia Water)		DT50	-