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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Administrative data

Endpoint:
bioaccumulation in sediment species, other
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
not specified
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Remarks:
The study was not performed according to international guideline nor under GLP. However, the methodology is scientifically acceptable and the report is sufficiently well documented.

Data source

Reference
Reference Type:
publication
Title:
Unnamed
Year:
1998

Materials and methods

Principles of method if other than guideline:
Studies were conducted to assess whether TFA could be metabolized under aerobic conditions by microbial communities in freshwater surface sediments. Sediment samples were collected to a depth of 2 -3 mm from flowing-water mesocosms in which organisms were pre-exposed to 30 µg TFA/L over a 2.5 year period and from control mesocosms that received no TFA. The sediment-associated microbial communities were tested for ability to incorporate of 2 -[14C]TFA (added at 43 µg/L) in time course experiments.
GLP compliance:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): Trifluoroacetate, or TFA (as the sodium salt)
- Analytical purity: no data
- Radiochemical purity (if radiolabelling): 99.6% (determined by high pressure liquid chromatography and absorbance at 205 nm)
- Specific activity (if radiolabelling): 54 mCi/mmol
- Locations of the label (if radiolabelling): [14C]F3COOH
Specific details on test material used for the study:
Aqueous solutions of trifluoroacetic acid have naturally low pH and for testing on organisms either the sodium salt or pH adjustment were required.
Sodium trifluoroacetate (TFANa, CAS RN: 2923-18-4) is appropriate as test material in replacement of trifluoroacetic acid because of the following elements :
Both substances are very soluble in water (water solubility at 25°C of 625 g/L for TFANa and 1520 g/L for TFA) and have a low potential of bioaccumulation (QSAR estimated LogKow values of -3.31 for TFANa and 0.79 for TFA). TFANa is a crystalline solid with a low vapour pressure (Vapour pressure at 25°C of 10E-5 Pa for TFANa estimated by QSAR) whereas TFA is a liquid with a medium vapour pressure (12.4 kPa at 20°C). Despite this different volatility, in the aquatic environment, both substances are ionized into the trifluoroacetate anion. This is justified by the fact that trifluoroacetic acid is a strong organic acid with a pKa of 0.23 meaning that it is under dissociated form in all environmental compartments.
Therefore, the environmental bioavailability of the trifluoroacetate moiety should be the same for both substances. Additionally, as the degradability of the cation Na is not applicable, the degradability of the trifluoroacetate moiety is taken into account to assess the degradability of TFA and TFANa.
Radiolabelling:
yes

Test solutions

Vehicle:
no

Test organisms

Test organisms (species):
other: Freshwater Benthic Microbial Communities

Study design

Route of exposure:
sediment
Test type:
not specified
Water / sediment media type:
natural sediment: freshwater
Total exposure / uptake duration:
130 wk

Test conditions

Nominal and measured concentrations:
TFA concentrations averaged 31.0 +/- 8.9 µg/L ; n=22 samples between September 18. 1992 and June 4. 1993 in one experimental mesocosm and 32.2 +/- 7.3 µg/L ; n=5 spot check samples in the other.
Details on estimation of bioconcentration:
TFA incorporation was evaluated using ANOVA and the Scheffe multiple range test (MRT) to test for a significant increase in radioactivity between sampling times and either the r² and slope of a linear regression of incorporated radioactivity vs time or the r² and expected increasing trend for a quadratic regression of the same data, to test data with appreciable curvilinearity. The r² is an index of the proportion of variance explained by the regression. Data were tested without transformation after preliminary analyses indicated that transformations did not improve the homogeneity of variances.

Results and discussion

Any other information on results incl. tables

The communities pre-exposed to TFA in the mesocosms showed a low, but statistically significant level of radiolabel incorporation. The cell-specific rate of incorporation for communities sampled from the TFA mesocosms increased nearly 20 -fold during the 2.5 year experiment, from 1.15 x 10^-13 to 2.22 x 10^-12 µg/cell/day. Communities from the control mesocosm never showed statistically significant incorporation. Communities pre-exposed to TFA from 1.5 years also incorporated [14C]TFA when exposed to concentrations as low as 2 µg/L.

Applicant's summary and conclusion

Validity criteria fulfilled:
not applicable
Conclusions:
Theses results indicate a low level of incorporation of the xenobiotic TFA by natural microbial communities and thus their potential to serve as a point for TFA to enter into the food web.
Executive summary:

Concentrations of trifluoroacetate (TFA) in the environment are expected to increase because it is an atmospheric degradation product of CFC replacement compounds that will receive widespread use. TFA possesses high water solubility and its movement in the biosphere will be closely linked with the hydrologic cycle. Surface waters and sediment pore waters will receive loadings directly through precipitation and runoff and indirectly via soil-and ground-water inputs. Studies were conducted to assess whether TFA could be metabolized under aerobic conditions by microbial communities in freshwater surface sediments. Sediment samples were collected to a depth of 2 -3 mm from flowing-water mesocosms in which organisms were pre-exposed to 30 µg TFA/L over a 2.5 year period and from control mesocosms that received no TFA. The sediment-associated microbial communities were tested for ability to incorporate of 2 -[14C]TFA (added at 43 µg/L) in time course experiments. The communities pre-exposed to TFA in the mesocosms showed a low, but statistically significant level of radiolabel incorporation. The cell-specific rate of incorporation for communities sampled from the TFA mesocosms increased nearly 20 -fold during the 2.5 year experiment, from 1.15 x 10^-13 to 2.22 x 10^-12 µg/cell/day. Communities from the control mesocosm never showed statistically significant incorporation. Communities pre-exposed to TFA from 1.5 years also incorporated [14C]TFA when exposed to concentrations as low as 2 µg/L. Theses results indicate a low level of incorporation of the xenobiotic TFA by natural microbial communities and thus their potential to serve as a point for TFA to enter into the food web.