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Biodegradation in water and sediment: simulation tests

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Endpoint:
biodegradation in water: simulation testing on ultimate degradation in surface water
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1996
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
test procedure in accordance with national standard methods with acceptable restrictions
Qualifier:
according to guideline
Guideline:
other: BBA, part IV, section 5.1 (1990)
Deviations:
no
GLP compliance:
yes
Remarks:
Rhône-Poulenc Agriculture Ltd, Essex, UK
Specific details on test material used for the study:
Radiochemical purity: 98.8%
Optical purity: 98.3%
Radiolabelling:
yes
Oxygen conditions:
anaerobic
Inoculum or test system:
natural water
Details on source and properties of surface water:
Samples of sediment and water were collected from two sites, a stream located on Aldhams Farm, Manningtree, Essex U.K. (system 96/03 (Manningtree)) and from the River Roding, Boarded Barns Farm, Ongar, Essex U.K. (system 96/04 (Ongar)).
Details on source and properties of sediment:
Immediately prior to sample collection the water temperature (measured just below the water surface), oxygen content (measured immediately below the water surface and at 5 cm above the sediment), pH and redox potential were measured. The water was then transferred to 60 litre plastic drums and the sediment was collected using a spade. The sediments were sieved to 5 mm at the collection site and transferred to large plastic bags. The sediment and water were then maintained in the dark at 4 °C prior to use.
Details on inoculum:
- The sediments were sieved to 2 mm and added to individual glass flasks (ca. 7.5 cm internal diameter) to a depth of 2 - 2.5 cm; 0.2 mm filtered water was added to an approximate depth of 5 cm above the sediment. This level was maintained throughout the study by addition of de-ionised water, as necessary. Approximately 80 flasks were prepared to fulfil protocol requirements and provide spares.
- The experiment was initiated after pre-incubation of the incubation flasks for approximately 6 weeks in the dark at 20 ± 2 °C, to enable acclimatisation of the systems with respect to oxygen content, pH, redox potential and complete phase separation. Throughout the acclimatisation and experimental period a continuous flow of moistened, carbon dioxide-free air was passed through the water, at a rate sufficient to allow aeration and gentle movement and at the same time avoiding mixing of the two phases. The passage of air was controlled by the use of flow restrictors, these consisted of lengths of glass with a capillary along their whole length. This narrow hole allows sufficient air to pass into each flask and for flask to be disconnected without disrupting the flow through others.
Duration of test (contact time):
100 d
Initial conc.:
992 g/L
Based on:
act. ingr.
Initial conc.:
0.992 other: mg/mL
Based on:
act. ingr.
Parameter followed for biodegradation estimation:
CO2 evolution
radiochem. meas.
Details on study design:
- An acetonitrile solution containing 0.992 mg/mL of [14C]-MCPP-P equivalent to 1.123 kg ai/ha was dispensed in aliquots of 100 µL (0.099 mg) dropwise on a single occasion, into the water (approx. 300 mls) of each flask. The quantity of MCPP-P per flask was 99.2 µg compared to the theoretical value of 132.54 µg.
- The aquatic incubation units were maintained in the dark at 20 ± 2 °C. Moistened carbon dioxide-free air was passed through the water in each unit and the effluent air current evolved passed through an ethylene glycol and two 2 M potassium hydroxide traps to trap volatiles and 14-CO2, respectively.
Reference substance:
not required
Compartment:
other: Mannintree aquatic system
% Recovery:
110
Compartment:
other: Ongar aquatic system
% Recovery:
105.5
Key result
Compartment:
entire system
DT50:
61 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: 96/03 (Manningtree)
Key result
Compartment:
entire system
DT50:
23 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: 96/04 (Ongar)
Key result
Compartment:
water
DT50:
49 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: 96/03 (Manningtree)
Key result
Compartment:
water
DT50:
24 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: 96/04 (Ongar)
Transformation products:
not measured
Evaporation of parent compound:
not measured
Volatile metabolites:
not measured
Residues:
not measured
Details on results:
- MCPP-P was identified as the main extractable component of the sediment. The amounts of MCPP-P in the extracts reached a maximum at 14 days for both sediment systems.
- The DT50 for the water of both systems was different, approximately 49 days for 96/03 (Manningtree) and 23 days for 96/04 (Ongar). The main differences occured in the DT50 of the total system, where system 96/03 (Manningtree) showed a less rapid DT50 than system 96/04 (Ongar). The onset of decline of MCPP-P in the extracts of sediment from system 96/03 (Manningtree) is at day 61 rather than at day 30 for the sediment of system 96/04 (Ongar).

Mineralisation: 58 % and 55 % after 100 days in the stream and river system, respectively.

Water:

DT50 (days)

DT90 (days)

96/03 (Manningtree)

49

156

96/04 (Ongar)

24

33

Entire system:

DT50 (days)

DT90 (days)

 96/03 (Manningtree)

61

175

96/04 (Ongar)

23

26

Validity criteria fulfilled:
yes
Conclusions:
MCPP-P is readily degraded in the aerobic aquatic systems and is therefore unlikely to persist in the aquatic environment.
Executive summary:

MCPP-P was degraded in both the aquatic sediment systems falling to 20 % (96/03 (Manningtree)) and 2 % (96/04 (Ongar)) of applied radioactivity after 100 days. Degradation is via several minor unknowns with ultimate mineralisation to carbon dioxide, which accounted for an overall maximum of 58 % (range 42.36 -73.43 %) of applied radioactivity after 100 days.

The DT50 values of MCPP-P in the water phases of both aquatic sediments were different, being 49.23 days in system 96/03 (Manningtree) and 24.25 days in system 96/04 (Ongar). The corresponding DT90 values for the water are 155.47 days in system 96/03 (Manningtree) and 33.27 days system 96/04 (Ongar). For the total systems marked differences occur, the DT50 calcuated for system 96/03 (Manningtree) was 60.66 days and for system 96/04 (Ongar) was 22.97 days. These differences may be due to the differences in the sediment types. Mineralisation of MCPP-P acid was 58 % and 55 % after 100 days in the stream and river system, respectively.

MCPP-P is readily degraded in the aerobic aquatic systems and is therefore unlikely to persist in the aquatic environment.

Endpoint:
biodegradation in water: simulation testing on ultimate degradation in surface water
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
Please refer to section 13 for "Read Across justification".
Reason / purpose for cross-reference:
read-across source
Key result
Compartment:
entire system
DT50:
61 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: 96/03 (Manningtree)
Key result
Compartment:
entire system
DT50:
23 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: 96/04 (Ongar)
Key result
Compartment:
water
DT50:
49 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: 96/03 (Manningtree)
Key result
Compartment:
water
DT50:
21 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: 96/04 (Ongar)
Transformation products:
not measured
Evaporation of parent compound:
not measured
Volatile metabolites:
not measured
Residues:
not measured
Endpoint:
biodegradation in water: sediment simulation testing
Data waiving:
exposure considerations
Justification for data waiving:
the study does not need to be conducted because direct and indirect exposure of sediment is unlikely

Description of key information

As the main hydrolysis product of MCPP-P 2-EHE, MCPP-P acid was used as a source substance in a read-across approch for the biodegradation in water. MCPP-P is readily degraded in the aerobic aquatic systems and is therefore unlikely to persist in the aquatic environment.

The study on sediment screening does not need to be conducted becasue direct and indirect exposure of the sediment is unlikely.

Key value for chemical safety assessment

Half-life in freshwater:
24.05 d
at the temperature of:
20 °C
Half-life in freshwater sediment:
22.97 d
at the temperature of:
20 °C

Additional information

MCPP-P was degraded in both the aquatic sediment systems falling to 20 % (96/03 (Manningtree)) and 2 % (96/04 (Ongar)) of applied radioactivity after 100 days. Degradation is via several minor unknowns with ultimate mineralisation to carbon dioxide, which accounted for an overall maximum of 58 % (range 42.36 -73.43 %) of applied radioactivity after 100 days.

The DT50 values of MCPP-P in the water phases of both aquatic sediments were different, being 49.23 days in system 96/03 (Manningtree) and 24.25 days in system 96/04 (Ongar). The corresponding DT90 values for the water are 155.47 days in system 96/03 (Manningtree) and 33.27 days system 96/04 (Ongar). For the total systems marked differences occur, the DT50 calcuated for system 96/03 (Manningtree) was 60.66 days and for system 96/04 (Ongar) was 22.97 days. These differences may be due to the differences in the sediment types.Mineralisation of MCPP-P acid was 58 % and 55 % after 100 days in the stream and river system, respectively.

MCPP-P is readily degraded in the aerobic aquatic systems and is therefore unlikely to persist in the aquatic environment.