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Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Guideline study under ISO certification with acceptable restriction.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2013
Report Date:
2013

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
other: OPPTS 835.1410 “Laboratory Volatility” from soils.
Type of study:
volatility
Media:
soil - air

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): FC-3284
- Substance type: single-constituent substance
- Physical state: Clear and colorless liquid
- Analytical purity: 96.67%
- Storage condition of test material: room temperature

Results and discussion

Any other information on results incl. tables

The measured concentration of FC-3284 in the headspace at each time points were fitted to a pseudo first order kinetic equation Ln (Ct) = kT+b, where k is the rate of volatilization. Half lives for each concentration were calculated by the equation of T1/2 = Ln (2)/k. The calculated rate constant and half life are in Table 2 and Fig 1.

Atmospheric deposition followed by volatilization would ordinarily require at least a 3rd order kinetic equation to fit the data. However, a 3rd order kinetic fit to the data requires knowledge of the initial concentration of the target chemical on the soil. When the mode of transport into the soil is deposition from the atmosphere, the initial concentration is not known. Yet this scenario is the one most often studied as it describes the transport, deposition and subsequent volatilization of most volatile and semi-volatile organic compounds.

Mathematically, use of a first order rate equation fit to third order rate data often yields poor to moderate correlation, as the correction coefficients were 0.348, 0.712 and 0.271 for the 0.5, 5.0 and 50 ppm concentrations, respectively (Fig 1).

Effectively, this mathematical treatment artificially weights the slowest kinetic parameter and represents the slowest kinetics for the system. Alternatively, use of a pseudo first order kinetic treatment gives an upper bound to the desorption kinetics, which is the most conservative estimation of the soil volatilization of the chemical.

Data (not shown) from the additional experiment: the first set of three vials that had the second transfer followed by 600 second holding time controls did not significantly alter the quantity of FC-3284 in the headspace when compared to those samples were only one transfer had taken place. This argues favorably that transfer was from the soil to the headspace not from pore space as the mixing necessary for a second transfer would have disrupted gas trapped in pores. Data from second set of three vials that had post transfer holding times of 20 hours showed levels slightly higher than those of any other experimental condition. This argues favorably that equilibrium had not been achieved in the kinetic study and that measurements were made in the kinetically valid region of the data. Measurements made for the third set of three vials that were open for 20 minutes followed by 20 minutes sitting showed levels far below the limit of quantitation indicating that the half-life in the real world would be much shorter than measured by this study and therefore the kinetics measured using the first-order approximation do indeed represent the upper bound for the rate of volatilization.

Table2. Volatilization kinetics of FC-3284 from Soil 

Post transfer Time

0.5 ppm

5 ppm

50 ppm

Measured ng/cc in headspace

Ln(C)

Measured ng/cc in headspace

Ln(C)

Measured ng/cc in headspace

Ln(C)

3

0.813

-0.208

8.77

2.17

73.3

4.29

10

0.929

-0.0740

8.92

2.19

81.4

4.40

20

1.04

0.0420

9.00

2.20

85.6

4.45

30

1.01

0.0130

9.20

2.22

96.0

4.57

40

1.01

0.0120

9.41

2.24

80.2

4.39

50

1.00

0.000

9.05

2.20

76.0

4.33

70

0.936

-0.0660

8.77

2.17

103

4.63

90

1.03

0.0300

10.2

2.32

90.7

4.51

120

1.35

0.299

9.62

2.26

80.8

4.39

180

1.33

0.282

9.02

2.20

89.2

4.49

300

1.31

0.270

9.87

2.29

94.4

4.55

600

1.16

0.145

11.0

2.40

104

4.64

1200

1.31

0.267

11.6

2.45

101

4.62

1200

1.28

0.249

10.6

2.36

92.8

4.53

K

2.26E-04

1.80E-04

1.39E-04

t1/2 (min)

51.1

64.1

83.0

Average t1/2 = 66.1 (min)

Stdev = 16 min

Applicant's summary and conclusion

Conclusions:
The average half-life of FC-3284 volatilization to the vapor phase was 66.1 ± 16 minutes under the test condition.
Executive summary:

The kinetics of volatilization from soil of FC-3284 was determined by direct measurement of FC-3284 in the vapor phase over time in a closed system where release from dosed soil was the sole source of the test material. Soils were equilibrated in vials containing 0.5, 5 or 50 ppmv of FC-3284 for 30 minutes with tumbling. Once equilibrated, the soils were transferred to clean vials and allowed to off-gas into the headspace for selected periods of time.

The measured concentration of FC-3284 in the headspace at each time points were fitted to a pseudo first order kinetic equation Ln (Ct) = kT+b, where k is the rate of volatilization. Half lives for each concentration were calculated by the equation of T1/2 = Ln (2)/k. It is expected that use of a first order rate equation fit to third order rate data would yields poor to moderate correlation. However, this mathematical treatment artificially weights the slowest kinetic parameter and represents the slowest kinetics for the system. Ultimately, use of a pseudo first order kinetic treatment gives an upper bound to the desorption kinetics, which is the most conservative estimation of the soil volatilization of the chemical.

The calculated half lives were 51.1, 64.1 and 83 minutes for the 0.5, 5.0 and 50 ppm concentrations, respectively. The average half-life of FC-3284 volatilization to the vapor phase was 66.1 ± 16 minutes under the test condition.

This is a guideline study conducted under ISO certification. The results give the most conservative estimations of the soil volatilization of the chemical. Therefore, it is considered reliable with restriction.