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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Reference
Endpoint:
biodegradation in water: simulation testing on ultimate degradation in surface water
Type of information:
experimental study
Adequacy of study:
key study
Study period:
No data
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study carried out according to well described method under GLP, but not according to international guideline.
Reason / purpose for cross-reference:
reference to same study
Qualifier:
no guideline followed
Principles of method if other than guideline:
The river die-away test method involved exposure of the test chemical to Mississippi River water in sealed bottles. The die-away or decrease in
concentration of the test chemical was monitored as a function of time by sacrifice and analysis of selected bottle contents.
GLP compliance:
yes
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
Not relevant
Radiolabelling:
no
Oxygen conditions:
aerobic
Inoculum or test system:
natural water
Details on source and properties of surface water:
Mississippi River water was collected on 10/27/81 at the St. Louis waterfront (Eads Bridge). A portion of the water was settled for two days to remove large particulates and transferred by a syphon to a 5 -gallon glass carboy. Slow aeration of the water was maintained until time for dispensing and spiking of the water. Four hundred milliliter samples of the water were dispensed from the magnetically-stirred carboy using a stopcock-equipped (PTFE-fluorocarbon) siphon and graduated cylinder and transferred to the sample bottles.
- pH at time of collection: 7.4
- Dissolved organic carbon: 3.0 mg/l
Details on source and properties of sediment:
Not relevant
Details on inoculum:
Unamended, settled active river water was used. In the river water the number of microorganisms/ml decreased from 52,000-54,000 on day 0 to 1,230-1,270 on day 10.
Duration of test (contact time):
27 d
Initial conc.:
0.499 mg/L
Based on:
test mat.
Initial conc.:
0.05 mg/L
Based on:
test mat.
Details on study design:
TEST CONDITIONS
- Volume of test solution/treatment: 400 ml
- Composition of medium: settled active river water without additions
- Solubilising agent (type and concentration if used): dimethyl sulfoxide (DMSO)
- Test temperature: 24°C
- pH: 7.4
- pH adjusted: no
- Continuous darkness: yes

TEST SYSTEM
A S-154 stock solution (0.499 g/50 ml) and a 10:100 dilution (0.0999 g/100 ml) in dimethyl sulfoxide were used to prepare the spiked river water samples at the 50 and 500 ppb concentrations. Twenty μl of the appropriate stock was injected with a twenty-five μl fixed-needle Hamilton syringe into the 400 ml water sample. Each sample bottle was sealed with a PTFE-fluorocarbon lined cap and mixed by shaking.
- Number of culture flasks/concentration: 15

SAMPLING
Duplicate active river water samples were sacrificed at three sampling points and single samples at seven points. Autoclaved and membrane-filtered river water controls were sacrificed periodically to monitor non-biological losses. Biological activity was monitored in both unamended controls and S-154 spiked samples.
Sampling times:
* Settled Mississippi river water (active): day 0, 1, 2, 3, 5, 7, 10, 14, 20, 27
* Membrane-filtered Mississippi river water and Autoclaved Mississippi river water with sediment: day 2, 5, 10, 20, 27
* Microbial assay for unamended river water, DMSO-spiked river water, unamended membrane filtered river water and S-154/DMSO-spiked active river water: day 0, 1, 2, 3, 7, 10, 14

CONTROL AND BLANK SYSTEM
* Blank (unamended active river water): A portion of the settled water was sterilized by membrane-filtration (two times) through 0.2 μm filters (Gelman Metrical GA-8, 47 mm). The filters were washed with hot, Milli-Q water prior to use. Four hundred milliliter samples were transferred directly to the sample bottles from the filtering flask using a graduated cylinder. Five bottles were prepared at each concentration with the membrane-filtered water.
* Autoclaved river water with sediment: A quantity of the settled solids were added back to river water to form a water with a high particulate content (1360 mg/l). This mixture was autoclaved three times. readjusted to volume with purified water, and 400 ml portions transferred to sample bottles. Five autoclaved particulate enriched water samples were prepared at the 500 ppb level.
* Controls for assay of microbial population: Single bottles containing unamended river water and DMSO-spiked river water were also prepared to assay the microbial population.

STATISTICAL METHODS:
The time-component concentration data sets obtained for the active and autoclaved river water samples were treated, where possible, with a first order least squares bit and plot program. The composite data for Santicizer 154 at the 500 ppb initial concentration in the autoclaved river water was also treated with the same program. If the transformation processes follow first order or pseudo first order kinetics, a plot of natural log of concentration versus time yields a straight line.
Test performance:
The membrane-filtered samples showed a slower decrease in S-154 component concentration compared to the active samples, but still relatively rapid. The loss of S-154 in these samples is attributed to bacterial contamination. Although the filtration was designed to sterilize the river water, it was not successful. The microbial concentrations as measured by plate counts showed a high microbial population in the membrane-filtered samples. The microbial population in the active samples remain high during the first two days of exposure, but then showed a rather sharp drop followed by a more gradual decline.The work of Paris et al. suggested that microbial transformation in natural waters conforms to second order kinetics with the rate being proportional to chemical and microbial concentrations. In a given natural water, pseudo first order kinetics were observed because the microbial concentration did not change significantly during these experiments. In this study the concentration-time data are in reasonable agreement with a first order kinetic approach suggesting that the microbial concentration was relatively constant during the time frame of S-154 transformation. Further work on the microbial concentration methodology needs to be carried out.
Compartment:
water
DT50:
< 0.5 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: TPP at both 50 and 500 ppb spiking levels
Compartment:
water
DT50:
1.2 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: TBPDPP at 50 ppb spiking level
Compartment:
water
DT50:
0.8 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: TBPDPP at 500 ppb spiking level
Compartment:
water
DT50:
7.3 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: DTBPPP at 500 ppb spiking level
Compartment:
water
DT50:
27 - 39 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Half-lives of the various components in autoclaved river water
Transformation products:
not measured
Details on transformation products:
No information on degradation products.
Details on results:
Tables containing the S-154 and component analyses summarized as a function of time of exposure and initial concentration and containing data for the autoclaved river water and membrane-filtered river water are included below. The data show that the two major S-154 components, TPP and TBPDPP, are rapidly lost or transformed, while a third component, DTBPPP, decreases more slowly. Figures showing the first order statistical analysis of the various data sets are also provided. For TPP at both 50 and 500 ppb S-154 spiking levels, transformation was so rapid that sufficient data points for statistical analysis were not obtained. For DTBPPP at 50 ppb concentrations were at the limit of detection.
Although a calculated half life for TPP could not be determined, the complete loss of this component at both 50 and 500 ppb spiking levels indicates the half life is less than 0.5 day. For TBPDPP the computed half lives were 1.2 and 0.8 days at 50 and 500 ppb spiking levels. The half life for DTBPPP at 500 ppb was 7.3 days, considerably slower than the two major components. Half lives of the various components in autoclaved river water ranged from 27 to 39 days while the value for the S-154 composite was 29 days. These data show that chemical transformation, e.g. hydrolysis or physical processes, such as adsorption or volatilization, were not significant compared to biotransformation.
Results with reference substance:
Not relevant

Santicizer 154 river die-away analyses:

Elapsed time after S-154 addition (days)

Concentration, μg/l in settledwater (active)

Initial S-154 conc. = 50 μg/l

Initial S-154 conc. = 499 μg/l

TPP

TBPDPP

DTBPPP

S-154

TPP

TBPDPP

DTBPPP

S-154

0

22

22

6

50

192

225

90

507

21

21

6

48

192

225

90

507

1

ND*

12

6

18

ND

146

74

221

ND

12

5

17

ND

148

78

228

2

ND

ND

ND

ND

ND

48

68

116

3

 

 

 

ND

ND

22

69

91

 

 

 

ND

ND

21

64

85

5

 

 

 

ND

ND

ND

41

41

7

 

 

 

ND

ND

ND

45

45

10

 

 

 

ND

ND

ND

36

36

14

 

 

 

ND

ND

ND

ND

ND

20

 

 

 

ND

ND

ND

ND

ND

27

 

 

 

ND

ND

ND

ND

ND

* Below validated lower limit of method – 5μg/l

 

Elapsed time after S-154 addition (days)

Concentration, μg/l

Membrane-filteredwater

Autoclavedwater with sediment

Initial S-154 conc. = 50 μg/l

Initial S-154 conc. = 499 μg/l

Initial S-154 conc. = 499 μg/l

TPP

TBPDPP

DTBPPP

S-154

TPP

TBPDPP

DTBPPP

S-154

TPP

TBPDPP

DTBPPP

S-154

2

ND*

16

6

22

ND

146

77

223

176

177

39

392

5

ND

ND

ND

ND

ND

ND

52

52

152

147

38

337

10

 

 

 

ND

ND

ND

20

20

127

139

40

306

20

 

 

 

ND

ND

ND

35

25

116

127

30

273

27

 

 

 

ND

ND

ND

24

24

91

125

35

251

* Below validated lower limit of method – 5μg/l

Validity criteria fulfilled:
not applicable
Remarks:
no guideline followed and therefore no validity criteria applicable. However the report shows that the test was valid as shown by a number of controls.
Conclusions:
Rapid biotransformation rates were observed for the S-154 major components, triphenyl phosphate (TPP) and t-butylphenyldiphenyl phosphate
(TBPDPP), with half lives of <0.5 and 1 day respectively at 50 and 500 ppb levels. A lesser component, di(t-butylphenyl) phenyl phosphate (DTBPPP)
disappeared more slowly with a half life of 7 days. In autoclaved river water, the composite half life for all components was 29 days indicating that chemical transformation was not a significant route.
Executive summary:

River die-away biodegradation testing of S-154 was carried out in Mississippi River water over a 27 day period at initial concentrations of 50 and 500 μg/L (ppb). The test was carried out under GLP. Rapid biotransformation rates were observed for the S-154 major

components, triphenyl phosphate (TPP) and t-butylphenyldiphenyl phosphate (TBPDPP) with half lives of <0.5 and 1 day respectively at 50 and 500 levels. A lesser component, di(t-butylphenyl) phenyl phosphate (DTBPPP) disappeared more slowly with a half life of 7 days in autoclaved river water. The composite half life for all components was 29 days indicating that chemical transformation was not a significant route. Membrane filtered river water controls showed rapid S-154 loss apparently due to bacterial contamination.

These data, while indicating a higher biotransformation rate in environmental waters for the S-154 major components, must be balanced against the tendency of S-154 to partition to the sediment where the biotransformation rate may be lower. Microcosm studies, however, suggest that the biotransformation rate is not drastically affected by sediment partitioning in aerobic aquatic environments.

Description of key information

The half-life of t-butylphenyldiphenyl phosphate (tBuPDPP) in a river die-away test was 1 day at 50 and 500 ppb levels. 

Key value for chemical safety assessment

Half-life in freshwater:
1 d
at the temperature of:
24 °C

Additional information

Information on the read-across Santicizer 154 is available. As the main component is the same for S-154 and the substance of concern (reaction mass of tert-butylphenyl diphenyl phosphate and di-tert-butylphenyl phenyl phosphate) the information on S-154 is relevant for this substance as well. Additionally, as the reaction mass of tert-butylphenyl diphenyl phosphate and di-tert-butylphenyl phenyl phosphate (substance covered in this registration dossier) is readily biodegradable, further simulation testing in water and sediment is not deemed necessary.

A river die-away study involved exposure of Santicizer 154 (S-154) to Mississippi River water in sealed bottles. The die-away or decrease in concentration of the test chemical was monitored as a function of time by sacrifice and analysis of selected bottle contents. Rapid biotransformation rates were observed for the S-154 major components, triphenyl phosphate (TPP) and t-butylphenyldiphenyl phosphate (tBuPDPP), with half lives of <0.5 and 1 day respectively at 50 and 500 ppb levels. A constituent present at lower concentrations in the multi-constituent, di(t-butylphenyl) phenyl phosphate (di-t-BuBPPP) disappeared more slowly with a half life of 7 days. In autoclaved river water, the composite half life for all components was 29 days indicating that chemical transformation was not a significant route.