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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Reference
Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
September 2013- April 2014
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Reliable experimental study following OECD Guideline 308 and compliant with GLP standards.
Qualifier:
according to guideline
Guideline:
OECD Guideline 308 (Aerobic and Anaerobic Transformation in Aquatic Sediment Systems)
GLP compliance:
yes
Radiolabelling:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
natural water / sediment
Details on source and properties of surface water:
The water/sediment systems were from Tift County, Georgia, USA, and Grand Forks County, North Dakota, USA. The Tift water/sediment was sampled on 16 September 2013 from a natural surface water pond. The only known chemical or fertilizer applications within the last four years to this site was of diquat dibromide in the years 2009, 2010, and 2012. The Goose River water/sediment was sampled on 08 October 2013. For this site there were no direct applications of chemicals or fertilizers within the last 4 years.
Details on source and properties of sediment:
The water/sediment systems were from Tift County, Georgia, USA, and Grand Forks County, North Dakota, USA. The Tift water/sediment was sampled on 16 September 2013 from a natural surface water pond. The only known chemical or fertilizer applications within the last four years to this site was of diquat dibromide in the years 2009, 2010, and 2012. The Goose River water/sediment was sampled on 08 October 2013. For this site there were no direct applications of chemicals or fertilizers within the last 4 years. Both sediment samples were taken from the below the overlaying water surfaces.
Duration of test (contact time):
100 d
Initial conc.:
0.356 other: ug/g water
Based on:
act. ingr.
Initial conc.:
0.293 other: ug/g water
Based on:
act. ingr.
Parameter followed for biodegradation estimation:
CO2 evolution
radiochem. meas.
Reference substance:
other: The reference substance was the non-radiolabeled test substance, DCDPS, provided by BASF, Ludwigshafen, Germany. The non-radiolabeled reference substance was stored at ambient temperature and was determined to have 99.9% purity.
Compartment:
other: water / sediment, material (mass) balance
Remarks on result:
other: The mean material balance for the Tift sediment/water system was 100.3 ± 1.9% of the applied radioactivity (%AR). The mean material balance for the Goose River sediment/water system was 99.5 ± 3.3% of the %AR
% Degr.:
4
Parameter:
radiochem. meas.
Sampling time:
100 d
Remarks on result:
other: Tift (sandy loam) total water/sediment system amount of extractable test substance decreased from 98.1% at 0 d to 94.1% at 100d.
% Degr.:
14.7
Parameter:
radiochem. meas.
Sampling time:
100 d
Remarks on result:
other: Goose River (clay loam) total water/sediment system amount of extractable test substance decreased from 96.9% at day 0 to 82.2% at 100 d.
Compartment:
water
DT50:
7.1 d
Type:
other: double first order in parallel (DFOP) using ModelMaker 4.0
Temp.:
20 °C
Remarks on result:
other: Tift (sandy loam) water layer
Compartment:
water
DT50:
6.2 d
Type:
other: double first order in parallel (DFOP) using ModelMaker 4.0
Temp.:
20 °C
Remarks on result:
other: Goose River (clay loam) water later
Compartment:
entire system
DT50:
1 287.2 d
Type:
other: single first order model (SFO) using ModelMaker 4.0
Temp.:
20 °C
Remarks on result:
other: Tift (sandy loam) entire system extrapolation beyond the 100 d study duration
Compartment:
entire system
DT50:
394.3 d
Type:
other: single first order model (SFO) using ModelMaker 4.0.
Temp.:
20 °C
Remarks on result:
other: Goose River (clay loam) entire system extrapolation beyond the 100 d study duration
Transformation products:
no
Details on transformation products:
No transformation products were detected.
Evaporation of parent compound:
no
Volatile metabolites:
no

In the sediment phase, the maximum levels of 4,4’-DCDPS were 81.8 and 79.8% AR (Day100) for the Tift and Goose River systems respectively. No known or unknown metabolites occurred at =3.4% AR in the sediment for either system.

For the total water/sediment system, the amount of extractable 4,4’-DCDPS in the Tift system generally decreased over the course of the study, from 98.1% AR at Day 0 to 92.7% AR at Day 50, and then slightly increasing to 94.1% AR at Day 100. The amount of extractable 4,4’-DCDPS in the Goose River system generally decreased over the course of the study, from 96.9% AR at Day 0 to 80.7% AR at Day 50 where it leveled off (81.2 and 82.2% AR at Days 75 and 100, respectively).

The DT50 values for 4,4’-DCDPS were calculated by the single first order model (SFO), first order multi-compartment model (FOMC), hockey stick (HS), and the double first order in parallel (DFOP) using ModelMaker® 4.0. The best fit visually and statistically for the data from the total system was obtained using the SFO model, and that for the water layer only was obtained using the DFOP model. The rate constants (kp), DT50values obtained for4,4’-DCDPS dissipation in the water phase (DFOP model) and overall degradation in the total system (SFO model) are summarized in the table below.

Water / Sediment Type

Layer

4,4’-DCDPS
Rate Constant 1
(Day-1)

4,4’-DCDPS
DFOP Rate Constant 2
(Day-1)

4,4’-DCDPS
DT50
(Days)

r2

Tift
(Sandy Loam)

Water layer

0.223

0.011

7.1

0.994

Total system

0.001

N/A

1287.2*

0.31

Goose River (Clay Loam)

Water layer

0.147

0.016

6.2

0.994

Total system

0.002

N/A

394.3*

0.64

* These values are extrapolations beyond the duration of the study (100 days)

No major degradation product, which is defined as =10% AR or at =5% AR at two consecutive sampling intervals, was observed during the course of the study in either of the test systems. No significant radioactivity (=10% AR) was found in the Tift sediment layer as non-extractable residues (NER). However, for the Goose River test system, the NER residues increased over time from 0.3% (Day 0) to over 10% AR by Day 30, reaching a mean maximum of 16.6% AR by Day 75.

For all practical purposes, no degradation of the 4,4’-DCDPS was observed in either test system over the course of this study, which indicates that 4,4’-DCDPS would show persistence in aerobic aquatic systems in the environment.

 

 

 

 

Validity criteria fulfilled:
yes
Remarks:
The processing/extracting procedures (100.0% - 102.2% of radioactivity at Day 0), test substance identity and purity at Day 100, and HPLC analysis (recovery of radioactivity within the acceptable range of 90-110%) each met the validity criteria.
Conclusions:
This study showed that aerobic transformation in the aquatic/sediment system is not a major pathway of degradation of the test substance. Instead, the test substance increasingly migrates from the water column to the sediment layer over time. Therefore, the test substance is expected to show persistence in the aerobic aquatic environment.

Description of key information

The experimental study concluded that the half-life of DCDPS in a water/sediment system would exceed 100 days. 

Key value for chemical safety assessment

Half-life in freshwater:
6.2 d
at the temperature of:
20 °C
Half-life in freshwater sediment:
394.3 d
at the temperature of:
20 °C

Additional information

In the study entitled “ [14C] 4,4’-Dichlorodiphenyl Sulphone: Aerobic Trans formation in Aquatic Sediment Systems” (Talken, 2014), the biotransformation of the test substance was studied in two different flooded sediment systems under aerobic conditions. The study showed that the test substance increasingly migrates from the water column to the sediment layer over time and that aerobic transformation is not a major pathway of degradation. Although the values for half-life in water between the two test systems were similar (6.2 d in Goose River, 7.1 d in Tift), the values for half-life in sediment were more divergent (394.3 d in Goose River, 1287.2 d in Tift). The 100-d study concluded that no degradation of the substance (4,4’-DCDPS) was observed in either of the two water/sediment test systems over the course of this study, indicating that the substance would show persistence in aerobic aquatic systems in the environment.