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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 308 (Aerobic and Anaerobic Transformation in Aquatic Sediment Systems)
Deviations:
no
Qualifier:
according to
Guideline:
EPA OPPTS 835.4400 (Anaerobic Aquatic Metabolism)
Deviations:
no
GLP compliance:
yes
Radiolabelling:
yes
Oxygen conditions:
anaerobic
Inoculum or test system:
natural water / sediment
Duration of test (contact time):
100 d
Initial conc.:
5 other: µg/g
Based on:
act. ingr.
Parameter followed for biodegradation estimation:
CO2 evolution
radiochem. meas.
Compartment:
other: Loamy Sand system
% Recovery:
102.87
St. dev.:
1.15
Remarks on result:
other: treated with [fused pyrimidine-3-14C]-test substance
Compartment:
other: Silt loam system
% Recovery:
105.2
St. dev.:
0.87
Remarks on result:
other: treated with [fused pyrimidine-3-14C]-test substance
Compartment:
other: Loamy Sand system
% Recovery:
102.82
St. dev.:
0.89
Remarks on result:
other: treated with [pyridine-2,6-14C]-test substance
Compartment:
other: Silt loam system
% Recovery:
104.77
St. dev.:
1.24
Remarks on result:
other: treated with [pyridine-2,6-14C]-test substance
Key result
Compartment:
other: Loamy Sand Surface Water
DT50:
67.3 d
Type:
other: DFOP
Temp.:
20 °C
Key result
Compartment:
other: Loamy Sand Total System
DT50:
692.1 d
Type:
other: SFO
Temp.:
20 °C
Key result
Compartment:
other: Silt Loam Surface Water
DT50:
42.7 d
Type:
other: DFOP
Temp.:
20 °C
Key result
Compartment:
other: Silt Loam Total System
DT50:
512 d
Type:
other: SFO
Temp.:
20 °C
Transformation products:
yes
Remarks:
No major degradation products formed
Volatile metabolites:
no
Residues:
yes
Conclusions:
The test system degraded slightly in the water compartment and partitioned to the sediment where it was further degraded to other metabolites that eventually were incorporated into the sediment as non-extractable residue (NER). Multiple metabolites were observed in the water/sediment systems none of which accounted for more than 5% applied radioactivity. Dissipation of the test system from the overlying water from both systems occured with DT50 values of 67.3 and 42.7 days for loamy sand and silt loam water compartments, respectively. Dissipation from the total system was slow, with DT50 values of 692.1 and 512 days for loamy sand and silt loam systems, respectively.
Executive summary:

The fate of the test substance under anaerobic conditions was studied in two aquatic sediment test systems. The sediments and overlying waters were collected from two natural locations: Swiss Lake, Chatsworth, Derbyshire, UK and Calwich Abbey Lake, Calwich, Ashbourne, Staffordshire, UK. The Swiss Lake sediment was characterised as a loamy sand (USDA) with an organic carbon level of 1.1% and a pH of 5.8. The overlying water had a pH of 6.4 and a dissolved organic carbon level of 8.9 mg/L. The Calwich Abbey Lake sediment was characterised as silt loam (USDA) with an organic carbon level of 5.4% and a pH of 7.5. The overlying water had a pH of 7.8 and a dissolved organic carbon level of 1.8 mg/L. In the laboratory, the sediment/water systems were allowed to acclimatize for 26 days prior to test item application.

Two radiolabelled forms of the test substance were used separately, radiolabelled with carbon-14 in either the fused pyrimidine or pyridine rings. Each form of the radiolabelled test item was applied to the two sediment systems at a nominal rate of 5.0 μg a.i./g of water. The sediment (dry weight): water (total water) ratio was 1:4.2 based on weight for the loamy sand sediment/ water system and 1:13 based on weight for silt loam sediment/ water system. Treated vessels were incubated for up to 100 days under anaerobic conditions in the dark at 20 ± 2 ºC. This study was conducted in accordance with the OECD Guideline 308 (2002).

The test system consisted of four sets of glass incubation vessels (one for each sediment/ water system and each type of radiolabel) containing vessels of sediment with overlying water. The vessels were connected to air flow-through systems with traps for the collection of CO2 and non specific volatile organic compounds. Samples were analysed immediately following test item application (Day 0) and after the following periods of incubation: 1, 14, 28, 60, 75 and 100 days. The water phase was removed from the sediment and analyzed without additional extraction. The sediments were extracted four times by adding acetonitrile and placing on a shaker for ca two hours. Extracts and residues were separated by centrifugation (ca 3,000 g for ca 15 minutes). Surface water and extractable sediment radioactivity were quantified by liquid scintillation counting (LSC). Radioactive components in sediment extracts and surface waters were quantified separately by reversed phase high performance liquid chromatography (HPLC) with on-line radiodetection. Non-extractable 14C-residues were quantified by combustion analysis.

In the loamy sand sediment/water system material balances were quantitative (100.57-104.13% AR, mean = 102.85% AR) for all samples. The total 14C-residues in the water phase decreased from mean values of 100.16% AR at Day 0 to 42.48% AR at Day 100. Solvent extractable 14C-residues in the sediment increased from mean values of 2.84% AR at Day 0 to a maximum mean value of 51.85% AR at Day 100. Bound residues increased to a maximum mean value of 7.93% AR at Day 100. Radiolabelled volatile organics were below the limit of quantification throughout the study. 14CO2 accounted for a maximum mean value of 0.24% AR at Day 100.

The amount of [14C]-test substance in the water phase of the loamy sand system decreased from a mean value of 100.16% AR at Day 0 to 40.88% AR at Day 100.

The amount of test item in the sediment of the loamy sand system, following application of [14C]-test substance, increased to a mean value of 50.80% AR at Day 100. Up to 9 minor unidentified degradation products were observed in the loamy sand system, none of which individually accounted for >5% AR at any sampling interval.

In the silt loam sediment/water system material balances were quantitative (102.26-106.44% AR, mean = 104.99% AR) for all samples. The total 14C-residues in the water phase decreased from a mean value of 98.33% AR at Day 0 to 38.11% AR at Day 100. Solvent extractable 14C-residues in the sediment increased from mean values of 6.64% AR at Day 0 to a maximum mean value of 57.32% AR at Day 100. Non-extractable residues increased to a maximum mean of 7.30% AR at Day 100. Radiolabelled volatile organics were below the limit of quantification throughout the study. 14CO2 accounted for a maximum mean value of 0.57% AR at Day 100.

The amount of [14C]-test substance present in surface water of the silt loam system declined from a mean value of 98.33% AR at Day 0 to 36.30% AR at Day 100. The amount of test item in the sediment of the silt loam system, following application of [14C]-test substance, increased to a maximum mean of 55.14% AR at Day 100. Up to 6 minor unidentified degradation products were observed in the silt loam system, none of which individually accounted for >5% AR at any sampling interval.

Dissipation of the test system from the overlying water from both systems occured with DT50 values of 67.3 and 42.7 days for loamy sand and silt loam water compartments, respectively. Dissipation from the total system was slow, with DT50 values of 692.1 and 512 days for loamy sand and silt loam systems, respectively.

Endpoint:
biodegradation in water and sediment: simulation testing, other
Remarks:
Outdoor Water Sediment Study
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
no guideline followed
Principles of method if other than guideline:
The degradation of the test system was studied in two irradiated water/sediment systems (silt loam and sand) using pyridine ring and fused pyrimidine labeled [14C]-test substance by incubating the water/sediment samples outdoors for 30 days under natural sunlight in optical grade quartz vessels with optical grade quartz lids.
GLP compliance:
yes
Radiolabelling:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
natural water / sediment
Duration of test (contact time):
30 d
Initial conc.:
0.5 other: mg/kg
Based on:
act. ingr.
Parameter followed for biodegradation estimation:
CO2 evolution
radiochem. meas.
Compartment:
other: Silt Loam outdoor
% Recovery:
96.3
Remarks on result:
other: treated with [fused pyrimidine-14C]-test substance
Compartment:
other: Sand outdoor
% Recovery:
95.7
Remarks on result:
other: treated with [fused pyrimidine-14C]-test substance
Compartment:
other: Silt loam outdoor
% Recovery:
97.6
Remarks on result:
other: treated with [pyridine-14C]-test substance
Compartment:
other: Sand outdoor
% Recovery:
97.1
Remarks on result:
other: treated with [pyridine-14C]-test substance
Key result
Compartment:
other: Silt loam outdoors total system
DT50:
35.5 d
Type:
other: SFO
Remarks on result:
other: Temperature: 17.6 to 26.1°C
Key result
Compartment:
other: Silt loam outdoors water phase
DT50:
5.14 d
Type:
other: SFO
Remarks on result:
other: Temperature: 17.6 to 26.1°C
Key result
Compartment:
other: Sand, outdoors total system
DT50:
32.9 d
Type:
other: SFO
Remarks on result:
other: Temperature: 17.6 to 26.1°C
Key result
Compartment:
other: Sand, outdoors water phase
DT50:
8.54 d
Type:
other: SFO
Remarks on result:
other: Temperature: 17.6 to 26.1°C
Transformation products:
yes
Remarks:
IN-RUB93
Residues:
yes
Conclusions:
DT50: 35.5 and 32.9 days in the silt loam and sand systems, respectively (corresponding parent only total system DT90: 118 and 109 days in the silt loam and sand systems, respectively)
Significant metabolite identified in the natural sunlight irradiated sand water/sediment system: IN-RUB93
Executive summary:

The degradation of [14C]-test substance was studied in two irradiated water/sediment systems (silt loam and sand) using pyridine ring and fused pyrimidine labeled [14C]-test substance. The test item was applied to the water/sediment systems at a nominal rate of 0.5 μg a.i./g total system weight.

The study incorporated natural sunlight to better understand the environmental behaviour of the test substance in an outdoor environment.

The test system consisted of a flow through apparatus. Water/sediment samples were incubated outdoors for 30 days under natural sunlight at 22.3 ± 4.7°C in optical grade quartz vessels with optical grade quartz lids. For each water/sediment type the vessels were connected via side-arms to a series of two communal traps, containing sodium hydroxide, for the collection of 14CO2. Samples for each water/sediment type were extracted immediately following test substance application (zero time) and after the following periods of incubation under natural sunlight: 1, 2, 3, 4, 7, 10, 14 and 30 days. Trapping solutions were sampled and replenished at the same time intervals. Dark control and sun-light control (pH 7 phosphate buffer only) samples were incubated under the same conditions as the irradiated samples and were removed for analysis immediately following test substance application (zero time) and after 7, 14 and 30 days incubation.

At each sampling occasion, the appropriate sediment/water samples were removed from the apparatus. The sediment and water were separated by decanting the surface water. The radioactivity content of the surface water was determined by LSC analysis. Sub-samples were taken for HPLC. The sediment was extracted twice with acetonitrile (Extracts 1 and 2). Day 2 to Day 30 samples were subjected to a third extraction using acetonitrile: 0.1% formic acid in water (9:1 v/v) (Extract 3).

Mass balance was maintained throughout the duration of the study for both sediment/water systems. Extracts were combined and concentrated to a small volume prior to HPLC analysis. Radioactive components in sediment extracts were quantified using reverse-phase HPLC with fraction collection and LSC by TopCount. Non-extractable 14C-residues were quantified using LSC following combustion.

Thebtest substance degrades significantly faster in outdoor water sediment systems than in the indoor aqueous metabolism study, with total system DT50 values of 35.5 and 32.9 days in the silt loam and sand systems, respectively. The corresponding parent only total system DT90 values were 118 and 109 days in the silt loam and sand systems, respectively.

One significant metabolite was identified in the natural sunlight irradiated sand water/sediment system: IN-RUB93. However, formation of numerous minor metabolites, such as IN-SBV06, IN-RPD47 and IN-RPA19 indicated that all aerobic sediment degradation pathways were also operational in concert with the photodegradation of the parent and metabolites.

Photodegradation played an important role in degradation in this outdoor study, as evidenced by the formation of significant amounts of IN-RUB93.

Formation of one significant metabolites in the natural sunlight irradiated pH 7 buffer solution, IN-RUB93, was consistent with the photodegradation expected in aqueous only environment exposed to light. Formation of these products was consistent with other laboratory photolysis studies.

The rate of photolysis in light controls solution was considerably slower than the continuous irradiation laboratory aqueous photolysis study, probably due to lower intensity of the outdoor radiation.

Description of key information

OECD Guideline 308

Key value for chemical safety assessment

Additional information

In the aerobic water sediment study, the DT50 values were 40.6 and 22.9 days for sandy and silt loam water compartments. The DT50s were 319.8 and 282.9 days for the sandy and silt loam total compartments. In water sediment systems, test substance degrades forming multiple minor components. In the anaerobic water sediment study, the DT50 values were 67.3 and 42.7 days for loamy sand and silt loam water compartments. The DT50s were 692.1 and 512 days for the loamy sand and silt loam total compartments. The test system degraded slightly in the water compartment and partitioned to the sediment where it was further degraded to other metabolites that eventually were incorporated into the sediment as non-extractable residue (NER). Multiple metabolites were observed in the water/sediment systems none of which accounted for more than 5% applied radioactivity. Based on the results from the water sediment studies, the test substance would dissipate slowly from the water-sediment systems under aerobic and anaerobic conditions.