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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
Remarks:
The test addresses both the surface water and sediment compartments
Type of information:
experimental study
Adequacy of study:
key study
Study period:
18 September 2003 to 26 May 2004
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:
yes
Remarks:
(the study integrity was not affected by the deviations)
GLP compliance:
yes
Radiolabelling:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
natural water / sediment
Details on source and properties of surface water:
System Goorven Englese Dijk
Total N 2.8 mg/L 1.4 mg/L
Total P 0.1 mg/L 0.1 mg/L
Hardness: 29 mg/L CaCO3 126 mg/L CacO3
DOC: 14.6 mg/L (start); 9.7 mg/L (end) 19.5 mg/L (start); 4.9 mg/L (end)
pH: 5.44 7.46
Temperature: 18 ºC 16.7 ºC
Redox potential: 157 mV 39 mV
Oxygen: 7.9 mg/L 7.19 mg/L
Details on source and properties of sediment:
System Goorven Englese Dijk
Sand (63µm-2mm) 99.37 % 17.97 %
Silt (2µm-63µm) 0.56 % 49.97 %
Clay (<2µm) 0.07 % 32.06 %
Texture Sand Silty clay loam
Organic carbon 1.2% (start); 0.5 % (end); 0.8 % (mean) 5.4% (start); 7.2 % (end); 6.3 % (mean)
pH (water) 6.2 (start); 5.4 (end) 7.5 (start); 7.3 (end)
pH (KCl) 5.2 (start); 4.6 (end) 7.3 (start, end)
pH (CaCl2) 5.7 (start); 4.6 (end) 7.5 (start); 7.1 (end)
CEC 1.1 mEq/100g 45.2 mEq/100g
Total N 448 mg/kg 922.5 mg/kg
Total P 36.4 mg/kg 2165.4 mg/kg
Duration of test (contact time):
100 d
Initial conc.:
2.7 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
test mat. analysis
Details on study design:
EQUILIBRATION:
For the Goorven system, approximately 250 g wet sediment and 450 mL water were each placed in 24 1 L Brown metabolism flasks. For the Engelse Dijk system, approximately 125 g wet sediment and 470 mL water were each placed in 24 1 L Brown metabolism flasks. The wet sediment weights and water volumes were each chosen so that a sediment later of approximately 2 cm and a water layer of approximately 6 cm was obtained. The metabolism flasks were placed in a climatised room at ~20ºC and the next day connected to an air stream which was allowed to bubble gently through the upper layer of the water during the equilibration period. The equilibration period last 12 days for the Goorven system and 20 days for the Engelse Dijk system.

INCUBATION
450 µL of a spiked solution (equivalent to 2.7 mg test material/L) was added to 18 metabolism flasks for each system. Immediately after spiking, the metabolism flasks were placed in the climatised room in the dark and connected to a series of traps: (1) a polyurethane foam flask inserted in the neck of the flask, (2) a liquid trap containing 2-methoxyethanol and (3) two liquid traps containing 2N NaOH. During incubation, aeration took place twice daily for 30 minutes. The ingoing air was allowed to bubble gently through the upper part of the water layer so as to not disturb the sediment layer (see Figure 1).

SAMPLING
Two flasks of each system were harvested at T=0 (30 minutes after spiking), 3, 7, 15, 30, 59 and 100 days after spiking. At sampling, the polyurethane foam plugs and liquid traps were also analysed and replaced in the flasks not being sampled to avoid saturation.

WATER LAYER
The water layer was carefully decanted and weighed. Radioactivity in the water and extracts generated by extraction with dichloromethane were analysed by LSC.

SEDIMENT LAYER
The sediment later was added to a centrifuge bottle and the metabolism flask rinsed with 100 mL methanol which was added to the sediment for 30 minutes extraction on a shaker. The supernatant was centrifuged for 5 minutes at 1761 g. This procedure was repeated twice more. Radioactivity was determined in the methanol extracts by LSC. The post-extraction sediment was transferred to a Soxhlet apparatus and extracted with 250 mL methanol for 3 hours. Total radioactivity in the Soxhlet extract was determined by LSC. The remaining sediment was air-dried for combustion analysis.

POLURETHANE PLUGS
The plugs were twice extracted with acetonitrile and radioactivity in the extracts determined by LSC.

LIQUID TRAPS
Total radioactivity was determined by LSC.
Test performance:
Redox potential and oxygen concentration measurements indicated aerobic conditions in the water layer and anaerobic conditions in the sediment throughout the test.

The mass balances for the Goorven system ranged from 97.20 to 100.18 % of applied radioactivity and from 97.54 to 101.45 % for the Engelse Dijk system and fulfil the guideline criteria of 90-110 %.
Key result
Compartment:
water
DT50:
>= 10.1 - <= 10.9 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Key result
Compartment:
water
DT50:
>= 3.5 - <= 6.3 d
Type:
other: hockystick model
Temp.:
20 °C
Transformation products:
yes
No.:
#1
Details on transformation products:
Metabolites in the water layer were 2,6-dichlorobenzamide (maximum 4.46 (GV) - 5.32 % (ED) of applied), 2-chlorobenzoic acid (maximum 9.13 % of applied in ED system only) and eight unidentified minor metabolites, none of which exceeded 10 % of applied radioactivity or 5 % of applied radioactivity at two consecutive time points (individual maximum 0.48 (GV) and 4.86 % (ED)). One minor metabolite was tentatively identified as hydroxyl-dichlobenil (maximum 0.26 %, ED system only).

Metabolites in the sediment were 2,6-dichlorobenzamide (maximum 1.73 (GV) - 2.04 % (ED) of applied) and four unidentified minor metabolites (in ED system only), none of which exceeded 10 % of applied radioactivity or 5 % of applied radioactivity at two consecutive time points (individual maximum 3.86 % (ED)). See Tables 3 and 4.
Evaporation of parent compound:
yes
Volatile metabolites:
not specified
Residues:
not specified
Details on results:
The fate of the test material in water/sediment systems can be described as follows: Upon addition to the water, a rapid partitioning of the test material between water and sediment took place in both water/sediment systems. The test material in the water phase was removed through volatilisation (major process, 27.08 (ED) - 36.40 % (GV)) and degradation (7.80 (GV) - 20.78 % (ED)), which caused a continuous repartitioning of the test material from the sediment to the water. Some degradation of the test material in the sediment was observed (1.73 (GV) - 9.29 % (ED)). Bound residues accounted for 3.03 (GV) - 7.83 % (ED) and complete mineralisation accounted for 0.63 (GV) - 4.51 % (ED) of applied radioactivity after 100 days.

The rate of test material dissipation in the water, sediment and combined water and sediment compartments could be described by first order kinetics and/or multi-compartment first order kinetics and/or the hockey stick model (see Table 1 and 2).

Table 1: Degradation rates of the test substance in the 'Goorven' water/sediment test system

 Compartment  Process  DT50 (days)  DT75 (days)  DT90 (days)  r2 *
 Water  Volatilisation + transfer to sediment + degradation  10.9  21.7  36.1  0.814
     3.521, 39.4, 3.52  7.041, 78.8, 35.8  11.71, 131, 87.7  0.988
   Degradation  233  467  775  0.989
 Water + Sediment  Volatilisation + degradation  100  201  333  0.997
   Degradation  3582, 307  7172, 614  11912, 1020  0.999, 0.973
 Sediment  Degradation + repartitioning to water  152  304  505  0.948
   Degradation  737  1475  2450  0.989

1hockey stick model: before hinge point, after hinge point, overall

2based on 1st order multi-compartment model, and normalised data/1st order

*coefficient of determination

Table 2: Degradation rates of the test material in the 'Engelse Dijk' water/sediment test system

 Compartment  Process  DT50(days)  DT75(days)  DT90(days)  r2 *
 Water  Volatilisation + transfer to sediment + degradation  10.1  20.3  33.7  0.934
     6.261, 28.6, 6.26  12.51, 57.3, 26.8  20.71, 95.1, 64.6  0.991
   Degradation  56.6  113  188  0.986
 Water + Sediment  Volatilisation + degradation  47  94  156  0.975
   Degradation  72.62, 65.6  1452, 131  2412, 218  0.990, 0.962
 Sediment  Degradation + repartitioning to water  68.6  137  228  0.925
   Degradation  119  237  394  0.986

1hockey stick model: before hinge point, after hinge point, overall

2based on 1st order multi-compartment model, and normalised data/1st order

*coefficient of determination

Table 3: Summary of the quantitation of [14C]-dichlobenil and metabolites in water, sediment and polyurethane foam (PUF) for the Goovern system (% of applied)

     Water  Sediment extractables  Volatiles (PUF)
 Time (days)  Replicate  Test material  BAM  others  Test material  BAM others  Test material  Others
 0  A  97.30  0.00  1.45  1.32  0.00  0.00  0.00  0.00
   B  97.65  0.00  1.28  1.51  0.00  0.00  0.00  0.00
   mean  94.78  0.00  1.36  1.41  0.00  0.00  0.00  0.00
 3  A  54.12  0.00  0.68  41.29  0.00  0.00  2.97  0.00
   B  53.88  0.00  0.67  40.72  0.00  0.00  4.01  0.00
   mean  54.00  0.00  0.67  41.00  0.00  0.00  3.49  0.00
 7  A  44.96  0.00  0.54  48.61  0.00  0.00  5.41  0.00
   B  45.88  0.00  1.19  47.11  0.00  0.00  5.28  0.00
   mean  45.42  0.00  0.87  47.86  0.00  0.00  5.34  0.00
 15  A  30.35  0.56  0.85  55.95  0.00  0.00  9.90  0.00
   B  30.43  0.30  0.73  55.19  0.00  0.00  9.06  0.00
   mean  30.39  0.43  0.79  55.57  0.00  0.00  9.48  0.00
 30  A  23.53  1.17  1.03  58.50  0.00  0.00  12.87  0.00
   B  25.31  1.17  1.12  51.99  0.00  0.00  18.03  0.00
   mean  24.42  1.17  1.08  55.24  0.00  0.00  15.45  0.00
 59  A  17.80  2.96  2.53  50.85  0.00  0.00  22.46  0.00
   B  15.79  2.68  2.43  46.55  0.00  0.00  28.15  0.00
   mean  16.80  2.82  2.48  48.70  0.00  0.00  25.31  0.00
 100  A  11.44  4.11  2.85  38.93  1.30  0.00  36.37  0.00
   B  10.84  4.82  3.83  36.20  2.16  0.00  36.44  0.00
   mean  11.14  4.46  3.34  37.56  1.73  0.00  36.40  0.00

BAM = 2,6-dichlorobenzamide

others = includes residual (post-extraction) radioactivity in the water layer and up to four individual metabolites all ≤0.61% of applied

Table 3: Summary of the quantitation of [14C]-dichlobenil and metabolites in water, sediment and polyurethane foam (PUF) for the Englese Dijk system (% of applied)


     Water  Sediment extractables  Volatiles (PUF)
 Time (days  Replicate  Test material  BAM  others  2-CBA  Test material  BAM  others  Test material  others
 0  A  97.69  0.00  2.13  0.00  2.50  0.00  0.00  0.00  0.00
   B  98.99  0.00  2.05  0.00  1.63  0.00  0.00  0.00  0.00
   mean  98.34  0.00  2.09  0.00  2.07  0.00  0.00  0.00  0.00
 3  A  61.04  0.00  0.92  0.00  27.64  0.00  2.57  5.74  0.18
   B  66.77  0.00  1.05  0.00  26.04  0.00  1.46  3.73  0.00
   mean  63.90  0.00  0.98  0.00  26.84  0.00  2.02  4.74  0.09
 7  A  47.22  0.36  1.82  0.00  42.20  0.00  1.01  6.95  0.00
   B  48.33  0.26  1.92  0.00  42.53  0.00  1.44  6.83  0.00
   mean  47.77  0.31  1.87  0.00  42.36  0.00  1.23  6.89  0.00
 15  A  31.77  0.79  4.39  0.00  46.97  0.00  36.7  10.21  0.23
   B  34.40  0.62  3.62  0.00  47.14  0.00  1.87  10.79  1.03
   mean  33.08  0.70  4.00  0.00  47.06  0.00  2.77  10.50  0.63
 30  A  21.33  2.39  8.07  2.10  41.60  1.44  4.54  15.39  0.00
   B  20.13  4.38  7.12  4.60  38.42  2.09  2.29  17.80  0.00
   mean  20.73  3.38  7.59  3.35  40.01  1.76  3.41  16.59  0.00
 59  A  11.54  2.53  14.77  4.79  29.02  0.00  7.36  20.81  0.00
   B  8.08  5.71  6.69  13.47  21.29  3.82  6.28  21.00  0.00
   mean  9.81  4.12  10.73  9.13  25.15  1.91  6.82  20.91  0.00
 100  A  7.84  4.20  7.44  43.8  25.44  2.18  7.78  25.60  2.43
   B  6.64  6.45  7.66  11.45  20.03  1.90  6.72  26.13  0.00
   mean  7.24  5.32  7.55  7.91  22.74  2.04  7.25  25.87  1.21

                                                                                       

BAM = 2,6-dichlorobenzamide

2 -CBA = 2-chlorobenzoic acid

others = includes residual (post-extraction) radioactivity in the water layer and up to four individual metabolites all ≤0.61% of applied

Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of the study, the test material in the water phase is removed through volatilisation (major process) and degradation. The dissipation half-life of the test material in the aqueous phase ranges from 10.1 - 10.9 days, based on first order kinetics and 3.5 - 6.3 days, based on the hockystick model.

Metabolites in the water layer were 2,6-dichlorobenzamide, 2-chlorobenzoic acid (only in one of two test systems) and eight unidentified minor metabolites, none of which exceeded 10 % of applied radioactivity or 5 % of applied radioactivity at two consecutive time points.
Executive summary:

In a GLP compliant water/sediment study conducted in line with standardised guideline OECD 308, the degradation of the test material in two water/sediment systems was determined. The test material was incubated in the laboratory in two non-contaminated water/sediment systems at 20 ± 2 ºC for 100 days. The initial test material concentration in the water layer was approximately 2.7 mg/L. Replicate samples of each water/sediment system were taken at 0, 3, 7, 15, 30, 59 and 100 days. The test material in the water phase is removed through volatilisation (major process) and degradation.

The dissipation half-life of the test material in the aqueous phase ranges from 10.1 - 10.9 days, based on first order kinetics and 3.5 - 6.3 days, based on the hockystick model.

Metabolites in the water layer were 2,6-dichlorobenzamide, 2-chlorobenzoic acid (only in one of two test systems) and eight unidentified minor metabolites, none of which exceeded 10 % of applied radioactivity or 5 % of applied radioactivity at two consecutive time points.

Description of key information

The half-life of the test material was determined to be 10.1-10.9 days (first order kinetics) or 3.5-6.3 days (hockystick model) according to a study performed in line with OECD Guideline 308.

Key value for chemical safety assessment

Additional information

See 'Environmental Fate and Pathways' endpoint summary.