Registration Dossier

Administrative data

Endpoint:
distribution modelling
Type of information:
calculation (if not (Q)SAR)
Remarks:
Migrated phrase: estimated by calculation
Adequacy of study:
key study
Study period:
24 Feb - 14 Dec 2014
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Commonly-accepted level 3 fugacity model, use justified in scientific literature

Data source

Reference
Reference Type:
other company data
Title:
Unnamed
Year:
2015
Report Date:
2015

Materials and methods

Model:
calculation according to Mackay, Level III
Calculation programme:
NewEQC v.1.01, Centre for Environmental Modelling and Chemistry, Trent University, Peterborough, Ontario, Canada
Release year:
2 012
Media:
air - biota - sediment(s) - soil - water

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): FC-770

Study design

Test substance input data:
- Molar mass: 399.057
- Data temperature: 23 °C
- Water solubility: 0.0662 g/m³
- Vapour pressure: 6750 Pa
- log Pow: 5.7
- Mineral matter - water partition coefficient: N/A
- Melting point: -127 °C
- Reaction half-life estimates for
- Air: 3.50E+07 hours
- Water: 1E+15 hours
- Soil: 1E+15 hours
- Sediment: 1E+15 hours

Since the uses described in this dossier direct 100% of releases to the air, a total emission rate of 250 tonnes/year entirely to the air compartment was modeled.

Results and discussion

Percent distribution in media

Air (%):
99.996
Water (%):
0
Soil (%):
0.004
Sediment (%):
0
Susp. sediment (%):
0
Biota (%):
0
Aerosol (%):
0
Other distribution results:
Soil distribution: 0.0041% in bulk soil, 0.0036% in gas-filled pore paces, 0.00052% on solids, and 1e-07% in pore water. Shortest intermedia transport half-time: soil to air, 1.59 hours. Half-times from air to soil or to water are >24,000 times longer.

Any other information on results incl. tables

FC-770 distribution was examined using the NewEQC v.1.01a Level III Mackay model.  This model incorporates advances in the science of chemical partitioning and reactivity as compared to the original EQC fugacity model (note: EQC is currently adapted for use in EpiSuite/Epiweb v 4.1). The NewEQC model specifically includes improved treatment of input partitioning and reactivity data, temperature dependence, and sensitivity /uncertainty analysis. In addition to the variables which EpiSuite's adaptation of EQC allows to be entered (Henry's Law constant, melting point, boiling point, water solubility, vapor pressure, and Log Kow), New EQC allows the user to enter Log Kaw, Log Koc, BCF, the aerosol-air partition coefficient, the soil/water partition coefficient, and the benthic- and suspended-sediment/water partition coefficients.  Where these values have not been directly measured, specific default calculations are applied. Use of this model is most appropriate when applied to chemicals of unusual properties such as FC-770.  The most useful results provided by the model are the percentage distribution of chemical mass between media or phases, and the residence times for reaction, advection and overall removal.  The result, for FC-770< is a marked decrease in the dependence on release patterns for NewEQC as compared to EpiSuite's adaptation. The NewEQC model is commonly accepted and has been validated in the literature (Hughes, L., Mackay, D., Powell, D. E., and Kim, J. 2012. An updated state of the science EQC model for evaluating chemical fate in the environment: Application to D5 (decamethylcyclopentasiloxane). Chemosphere 87(2): 118-124).

In keeping with the uses defined for FC-770, the entire volume is modeled as being released exclusively to the atmospheric compartment, at a rate of 250 tonnes per year (i.e., 2.5-times larger than the maximum annual volume for this volume band).  The model environment has an area of 10,000,000 hectares, which is 2.5-times larger than the 4,000,000-hectare Standard Region normally considered during exposure assessment modeling with EUSES software.  The atmospheric residence time of the model environment is 100 hours.  When compared to EpiSuite, use of the NewEQC Level III Mackay fugacity model results in significant changes in the distribution pattern upon release to air (the only release of FC-770). EpiSuite modeling gives 90.3% to air, 0.2% to water, 8.9% to soil, and 0.6% to sediment.  In contrast, New EQC gives 99.996 % to air, 5.1 x 10-6 % to water, 3.8 x 10-3 % to soil, and 1.8 x 10-5 % to sediment.  It should be noted that the volume fraction and default densities of these compartments, as well as default mass transfer coefficients, were not modified between EpiSuite's adaptation of EQC and NewEQC.  Expressed in terms of absolute loadings, all compartments showed predicted concentrations in the part-per-trillion range or less.  The model showed that the overwhelming majority of FC-770 remains in the atmospheric compartment on a mass basis (Table 2).

Table 2, predicted distribution of FC-770 in the modeled environment

Compartment

Amount in compartment (kg)

Concentration in compartment (g/L except as indicated)

Percent of total in compartment

Air: Bulk

7.14E+03

2.85E-11

99.996

      Gas Phase

7.14E+03

2.85E-11

99.996

      Aerosol

1.27E-04

1.27E-05 µg/g

1.78E-06

Water: Bulk

3.60E-04

7.18E-16

5.04E-06

      Liquid

3.26E-04

6.51E-16

4.57E-06

      Suspended Sediment

2.52E-05

6.71E-09 µg/g

3.53E-07

      Fish (wet weight)

8.16E-06

1.68E-08 µg/g

1.14E-07

Soil: Bulk

2.95E-01

6.53E-12

4.12E-03

      Pore Air

2.57E-01

2.85E-11

3.60E-03

      Pore Water

9.10E-06

6.72E-16

1.27E-07

      Solids

3.75E-02

6.92E-10 µg/g

5.25E-04

Sediment: Bulk

3.04E-03

2.42E-12

4.25E-05

      Water

2.47E-06

2.46E-15

3.46E-08

      Solids

3.04E-03

5.05E-09 µg/g

4.25E-05

It is important to note in Table 2 that most (87%) FC-770 in the soil compartment is in air-filled pore spaces, rather than sorbed to solids or dissolved in pore water.

Essentially no net transport from air to soil or from air to water occurs based on relative intermedia transportation rates. The driving factor in the distribution model is advective transport out of the model area’s atmospheric compartment. Removal by this mechanism is essentially equal to the release rate into the atmospheric compartment. The residence time of 100 hours leads to far faster rates of removal by transport than either reaction or transfer between compartments (Table 3).

Table 3, Details on loss and distribution processes

Process

Loss Rate (kg/h)

Advection

 

Air

28.5

Water

1.44E-07

Soil

N/A

Sediment

2.42E-08

Reaction

 

Air

5.64E-05

Water

9.95E-20

Soil

8.15E-17

Sediment

8.40E-19

Intermedia Transport

 

Air to Water

4.89E-07

Air to Soil

5.11E-02

Water to Air

3.26E-07

Water to Sediment

5.09E-08

Soil to Air

5.11E-02

Soil to Water

4.52E-09

Sediment to Water

2.67E-08

 

The intermedia transport rates depend on concentration in the relevant compartments. The model also generates a more general set of intermedia transport half times (Table 4), which depend on chemical and compartment characteristics but not concentration. It is evident from the half-times that only extreme concentration gradients favoring the atmospheric compartment allow transfer of meaningful amounts of FC-770 to soil or water.

Table 4, Intermedia transport half-times

Transfer process

Half-time (days unless otherwise listed)

Air to Water

461,000 years

Air to Soil

1610

Water to Air

12.7

Water to Sediment

81.4

Soil to Air

1.59 hours

Soil to Water

2060 years

Sediment to Water

1310

Transfer time ratio

 

Air : Water

1.32E+07

Air : Soil

2.43E+05

Water : Sediment

0.062

Based on the results of this distribution modeling, which places 250 tonnes per year of FC-770 into an area 2.5 times larger than the Standard Region for exposure assessment modeling, FC-770 will not distribute meaningfully into the terrestrial or aquatic compartments.  The model calculated that 99.996% of FC-72 is distributed to the air.  The air to water half-life was modeled to be 461,000 years while the water to air half-life was 12.7 days; the air to soil half-life was 1610 days while the soil to air half-life was calculated to be 1.59 hours; the water to sediment half-life was 81.4 hours while the sediment to water half-life was calculated to be 1310 days.

Applicant's summary and conclusion

Conclusions:
FC-770 will distribute predominantly (99.996%) to the atmospheric compartment according to a Level III Mackay model
Executive summary:

FC-770 distribution in the environment was modeled using a Level III fugacity model within the New Equilibrium Criterion model (NewEQC) v.1.01 (Trent University, Peterborough, ON, Canada). Substance properties were entered as per data in this dossier. A total emission rate of 250 kg/year of FC-770 was directed entirely (100%) to air based on uses described in this dossier. The predominant fraction (99.996%) was modeled as remaining present in the gas phase of the air compartment. The calculated intermedia distribution half-time from the soil compartment to the air compartment was 1.59 hours while the reverse process had a half-time of 1610 days. The calculated half-time for water to air was 12.7 days while the half-time for air to water was 461,000 years. FC-770 will not distribute meaningfully into the terrestrial or aquatic compartments.

Distribution modeling was done using a well-accepted model. It is considered reliable with restrictions.