Registration Dossier

Administrative data

Endpoint:
phototransformation in water
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1991-08-27 to 1991-11-16
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline study (GLP)

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1992
Report Date:
1992

Materials and methods

Study type:
indirect photolysis
Test guideline
Qualifier:
according to
Guideline:
EPA OTS 795.70 (Indirect Photolysis Screening Test: Sunlight Photolysis in Waters Containing Dissolved Humic Substances)
Deviations:
yes
Remarks:
HPLC with UV detection instead of RAM used, different filtration method used, different preaging method used, concentration of pyridine set by different method, tubes for Phase II initiation placed in light one hour later than protocol stated
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): 14C-2,6-DTBP
- Physical state: a yellow-green solid
- Locations of the label (if radiolabelling): ring labelled
- Specific activity: 0.89 mCi/mmole

- Storage conditions: in freezer until used
- Stability under test conditions: analysis when manufactured (1988) and before the study (1991) showed no degradation

- Name of test material (as cited in study report): 2,6-DTBP (unlabelled)
- Physical state: a yellow-green solid
- Storage conditions: in freezer until used

Study design

Radiolabelling:
yes
Analytical method:
high-performance liquid chromatography
Details on sampling:
- Sampling intervals for the parent/transformation products:
Phase II: sampling on days 0, 1, and 2. Samples in duplicate for each water type (synthetic humic water (SHW) and pure water (PW)), two controls for each water type and three quality control samples.
Phase III: tubes containing either actinometer (PNAP) solution, 2,6 DTBP test solution in pH7 SHW buffer, 2,6 DTBP test solution in pH7 PW buffer, or pH7 buffer solution with SHW, sampled along with appropriate dark control at intervals of 0,1,2,4,8, 25 and 29 consecutive hours (approximately 0, 1, 2, 4, 8, 11, and 15 light hours). Three quality control samples analyzed for 2,6 DTBP or PNAP conditions daily.

- Other observation, if any: Light intensity, and temperature measured at each sampling interval, as well as observation of cloud cover

- Other: calculations
1. Photolysis described by following equation:
Ln C/Co = -kt
where: k = rate constant/hr (slope of line from plotting C/Co versus t)
C = 2,6 DTBP concentration at time t
T = time (hours)
Co = initial 2,6 DTBP concentration

2. Half-life (t ½) = (ln 2)/k

3. Rate Constants for water types Synthetic Humic Water (SHW) and Pure Water (PW):
(kp)shw = (1/t) x ln (Co/Ct)shw

(kp)pw = (1/t) x ln (Co/Ct)pw
where: t = time in hours
Co = initial concentration
Ct = concentration at time t

4. Ratio (R) = (kp)shw/ (kp)pw

If R ranges from 0 to 1, the photoreaction is inhibited by SHW
If R ranges from 1 to 2, the material is marginally susceptible to indirect photolysis
If R > 2, further testing to determine photoreaction rate in sunlight (kPE) and first-order reaction rate for indirect pathway (kIE) of this photoreaction.

5. Photoreaction rate in sunlight in a natural body of water under favorable conditions will yield a net value that is the sum of the two first order reaction rate constants for the direct and indirect pathways expressed as:
kPE = kDE + kIE
The constants kPE and kDE can also be obtained from the equations:
kPE = 0.455(kPE)shw and kDE = 0.455 (kPE)pw where 0.455 is a geometric concentration factor for scattered light in cylindrical tubes versus horizontal surfaces (natural waterways)

6. The initial indirect photoreaction rate constant (kIO) was determined:
(kIO) = (S1) (kA)(S2)

7. The slopes (S1,2 and 3) were obtained by least squares regression S1 = (kIO/k), S2 = (k/kA) and S3 = (kD/kA) in the following equations:

ln (Co/C)shw - ln (Co/C)pw = (kIO/k)[1 – (A370/Ao370)]

ln (Ao370/ A370) = (k/kA) ln(Co/C)PNAP

ln (Co/C)pw = (kD/kA) ln(Co/C)PNAP

where: Ao370 = absorbance of synthetic humic water at 370 nm at test initiation
A370 = absorbance of synthetic humic water at time t
Co = concentration at test initation
C = concentration at time t

Since there was significant loss of 2,6 DTBP in the dark controls, data were corrected by subtracting ln (Co/C)dark from ln (Co/C) observed to obtain ln (Co/C)corr for the SHW and PW samples.

8. Value of ka: Given by TSCA Guideline for latitude 42 degrees north and fall season is 245.
kA = 0.0372 [PYR] ka
where [PYR] is the pyridine concentration in moles per liter

9. Direct photoreaction rate: kDE = (S3)(kA)

10. Rate Constant (kPE) shw = kIO + kDE

11. Net photoreaction rate constant (kPE) and corresponding half life(t1/2E) were calculated by:
(kPE) = 0.455(kPE) shw

(t1/2E) = 0.693/ (kPE)

12. For Phase III testing, the molar concentration of pyridine needed for the actinometer was calculated by using the formula:
[PYR] - 26.9 x (kP) shw / ka

V = 80.6 [PYR]

where: ka = 431 for spring, 532 for summer, 245 for fall, and 139 for
winter at the latitude for Wareham, Massachusetts
[PYR] = pyridine concentration in moles per liter
(Note: [PYR] was set at 0.2 M because at pyridine concentrations
greater, first order kinetics do not hold)
V = volume in mL
Buffers:
- pH:
- Type and final molarity of buffer:
pH7, 0.01 M sodium phosphate buffer solution
- Composition of buffer:
50 mL of 0.2 M sodium phosphate monobasic was diluted to 1 liter with NANOpure water producing a 0.01 M concentration
38 mL of sodium phosphate dibasic 0.378 M was diluted to 1 liter with NANOpure water producing a 0.01M concentration
To produce the final buffer, 445 mL of sodium phosphate monobasic 0.01 M was added to 305 mL sodium phosphate dibasic 0.01 M and the resulting mixture brought to a volume of 1 L with NANOpure water. The pH was adjusted to 7 with 0.01 M sodium phosphate monobasic.

Light source:
sunlight
Details on light source:
- Location:
- Latitude: 42 degrees North (Wareham, Massachusetts)
- Time of year/month: Fall
- Light intensity:
Phase 1: 476 to 693 footcandles
Phase 2: 34 to 156 footcandles
Phase 3: 67.6 to 110 footcandles
- Other: Weather observations
Phase 1: sunny
Phase 2: cloudy
Phase 3: mostly sunny day 1, rain day 2
Details on test conditions:
TEST SYSTEM
- Type, material and volume of test apparatus/vessels: 12 x 1000 mm quartz tubes fitted with rubber sleeve stoppers
- Sterilisation method: autoclaved
- If no traps were used, type of test system: closed, no headspace in tubes, sampling through rubber sleeve stoppers
- Indication of test material adsorbing to the walls of test apparatus: yes. Tubes silanized to prevent adsorption

TEST MEDIUM
- Volume used/treatment: tubes filled to top to minimize headspace
- Kind and purity of water: NANOpure water for dilutions (filtered sterilized water meeting ASTM Type II A standards, typically with greater than 16.6 Mohm-cm resistivity and less than 1 mg/L total organic carbon)
- Preparation of test medium: Test solutions were prepared by diluting the synthetic humic water (SHW) solution ten fold with 0.01 M sodium phosphate buffer solution at pH 7. One solution contained 90% 0.01 M sodium phosphate buffer (pH 7) to 10% NANOpure water. The other solution contained 90% 0.01 M sodium phosphate buffer (pH 7) to 10% SHW solution. The absorbance of the 90:10 SHW solution was measured to be 0.048 at 370 nm. These were the working solutions for exposures. All working solutions were autoclaved and sterilized by aeration through 0.45 um and 0.2 um filters for 20 minutes before use. Solutions were fortified by volumetric addition of these solutions and the 2,6 DTBP stock solutions. ie: 1 mL of acetonitrile 2,6 DTBP stock solution into a 250 ml volumetric flask. This solution was 0.4% acetonitrile by volume.
- Identity and concentration of co-solvent: acetonitrile

PREPARATION OF SYNTHETIC HUMIC WATER
- A stock solution of synthetic humic acid was prepared by adding 20.0 grams of humic acid to 2 liters of 0.02 NaOH solution. This solution was mixed on a stir plate for 1 hour at room temperature and filtered through coarse paper. pH was adjusted stepwise to 7.0 with H2SO4. The 1% solution of humic acid was diluted 100 fold with NANOpure water. Filtration was accomplished through coarse paper, 0.4 um PC-membranes and 0.22 um filters for filter sterilization. The absorbances at 313 and 370 nm were measured to be 1.870 and 0.858. The SHW solution was transferred to a clean 1-liter flask with a Teflon lined screw cap. This solution was pre-aged by placing it in direct sunlight for 4 days. After the solution was removed from direct sunlight, a dilution factor was determined in order to decrease the absorbance of the SHW solution to about 0.50 in a 1 cm path length cell. A dilution of 51% humic acid and 49% NANOpure water was made, which had an absorbance of 0.507 at 370 nm. This solution was labeled the SHW stock solution and was stored capped and refrigerated in the dark until use.

ACTINOMETER SOLUTION PREPARATION
- A para-nitroacetophenone (PNAP) solution was prepared by diluting 0.165 g of PNAP to 100 ml with acetonitrile, producing a 0.01 M solution. A pyridine stock solution was prepared to produce a 15.8 mg/mL (0.2 M) solution. An actinometer solution was prepared by adding 1.00 mL of 0.01 M PNAP stock solution in acetonitrile and 16.1 mL of 0.2 M pyridine to a 1 liter flask, and filled to volume with NANOpure water, wrapped in aluminium foil and stored in the dark.

REPLICATION
- No. of replicates (dark):
Phase II: twelve tubes of each water type (pure water or in synthetic humic water) wrapped in aluminium foil, and placed behind the exposure rack
Phase III: 4 tubes of each type (PNAP actinometer solution, 2,6 DTBP in pure water, 2,6 DTBP in pH 7 buffer solution with pure water, or 2,6 DTBP in pH 7 buffer solution with SHW) wrapped in aluminium foil and placed underneath the exposure rack

- No. of replicates (irradiated):
Phase II: twelve tubes of test material in each water type (pure water or in synthetic humic water)
Phase III: 4 tubes of each type (PNAP actinometer solution, 2,6 DTBP in pure water, 2,6 DTBP in pH 7 buffer solution with pure water, or 2,6 DTBP in pH 7 buffer solution with SHW)

OTHER:
- Exposure details: Sample tubes were placed outdoors exposed to direct sunlight on a non-reflective black board inclined to 30 degrees and facing geographic north on the roof of the building. Phase II tubes were placed on the rack (dark controls behind the rack) at approximately 7:30 am (except on day one when they were placed at 1:00 pm) and removed at 5:30 pm to avoid chance of samples freezing during the night. When removed, and prior to analysis, samples were stored at room temperatures and in the dark. For Phase III, tubes were placed on the rack at about 9 am on day zero.
Dark controls:
yes

Results and discussion

Preliminary study:
Preliminary testing showed significant sorption of 2,6 DTBP onto glass and was evidenced by the decrease in solution concentrations seen in the dark controls. Several glass treatments were evaluated to reduce sorption (silanization, teflon-coating, and acid washing). Silanization of the glassware (quartz) gave the least amount of adsorption).
Dissipation half-life of parent compound
DT50:
2.41 h
Test condition:
Based on corrected data
Predicted environmental photolytic half-life:
Photolytic half-life (t1.2E) for environmental conditions resulted in a value of 2.41 hours, based on corrected data.

Any other information on results incl. tables

Phase II: 2,6 DTBP indirect photolysis data in synthetic water and pure water

Phase II: Light exposed samples

Sampling interval

Replicate

Water Type

Nominal concentration

(mg/L; (M x 10-6))

2,6 DTBP concentration

(mg/L; (M x 10-6)

% Nominal

Hour 0

(Day 0)

1

2

SHW

1.25 (6.06)

1.25 (6.06)

1.24 (5.96)

1.25 (6.06)

99.1

100

1

2

PW

1.25 (6.06)

1.25 (6.06)

1.32 (6.40)

1.32 (6.40)

106

106

Hour 24 (Day 1)

1

2

SHW

1.25 (6.06)

1.25 (6.06)

0.435 (2.11)

0.442 (2.14)

34.8

35.4

1

2

PW

1.25 (6.06)

1.25 (6.06)

0.542 (2.63)

0.615 (2.98)

43.3

49.2

Phase II: Dark Control Samples

Sampling interval

Replicate

Water Type

Nominal concentration

(mg/L; (M x 10-6))

2,6 DTBP concentration

(mg/L; (M x 10-6)

% Nominal

Hour 24 (Day 1)

1

2

SHW

1.25 (6.06)

1.25 (6.06)

0.833 (4.04)

0.822 (3.98)

66.6

65.8

1

2

PW

1.25 (6.06)

1.25 (6.06)

0.664 (3.22)

0.700 (3.39)

53.1

56.0

Calculations for Phase II:

Light Exposed Samples:

           (kp)pw   = 2.163 day ^-1         t1/2 = 0.320 day

           (kp)shw = 2.943 day^-1 t1/2 = 0.236 day

Dark Control Samples:

(kp)pw   = 1.855 day ^-1         t1/2 = 0.5465 day

           (kp)shw = 1.134 day^-1 t1/2 = 0.5513 day

Phase III: 2,6 DTBP indirect photolysis data in synthetic humic water and pure water

Phase III: Light exposed samples

Sampling interval

Water Type

Nominal concentration

(mg/L; (M x 10-6)

2,6 DTBP concentration

(mg/L; (M x 10-6)

% Nominal

Hour 0

(Day 0)

SHW

1.25 (6.06)

1.25 (6.06)

1.41 (6.83)

1.40 (6.79)

113

112

PW

1.25 (6.06)

1.25 (6.06)

1.32 (6.40)

1.32 (6.40)

114

116

Hour 1.08

(Day 0.45)

SHW

1.25 (6.06)

0.804 (3.90)

64.3

PW

1.25 (6.06)

0.762 (3.69)

61.0

Hour 2.08

(Day 0.087)

SHW

1.25 (6.06)

1.25 (6.06)

0.718 (3.48)

57.4

PW

1.25 (6.06)

1.25 (6.06)

0.778 (3.77)

62.2

Hour 4.08 (Day 0.170)

SHW

1.25 (6.06)

1.25 (6.06)

0.488 (2.37)

39.0

PW

1.25 (6.06)

1.25 (6.06)

0.643 (3.12)

51.4

Hour 7.58

(Day 0.316)

SHW

1.25 (6.06)

1.25 (6.06)

0.266 (1.29)

21.2

PW

1.25 (6.06)

1.25 (6.06)

0.358 (1.74)

28.7

Hour 10.92 (Day 0.455

SHW

1.25 (6.06)

1.25 (6.06)

0.366 (1.77)

29.3

PW

1.25 (6.06)

1.25 (6.06)

0.310 (1.50)

24.8

Hour 14.92 (Day 0.622)

SHW

1.25 (6.06)

1.25 (6.06)

0.334 (1.62)

26.7

PW

1.25 (6.06)

1.25 (6.06)

0.293 (1.42)

23.4

Phase III: Dark control samples

Sampling interval

Water Type

Nominal concentration

(mg/L; (M x 10-6)

2,6 DTBP concentration

(mg/L; (M x 10-6)

% Nominal

Hour 1.08

(Day 0.45)

SHW

1.25 (6.06)

0.706 (3.42)

56.5

PW

1.25 (6.06)

0.720 (3.49)

57.6

Hour 2.08

(Day 0.087)

SHW

1.25 (6.06)

0.736 (3.59)

58.8

PW

1.25 (6.06)

0.721 (3.49)

57.6

Hour 4.08 (Day 0.170)

SHW

1.25 (6.06)

0.816 (3.96)

65.3

PW

1.25 (6.06)

0.802 (3.89)

64.2

Hour 7.58

(Day 0.316)

SHW

1.25 (6.06)

0.701 (3.40)

56.1

PW

1.25 (6.06)

0.729 (3.53)

58.3

Hour 10.92 (Day 0.455)

SHW

1.25 (6.06)

0.490 (2.37)

39.2

PW

1.25 (6.06)

0.529 (2.56)

42.3

Hour 14.92 (Day 0.622)

SHW

1.25 (6.06)

0.561 (2.72)

44.9

PW

1.25 (6.06)

0.525 (2.54)

42.0

Phase III: para-nitroacetophenone (PNAP) indirect photolysis data

Sampling interval

Light/

Dark

Nominal concentration

(mg/L; (M x 10-6)

PNAP concentration

(mg/L; (M x 10-6)

% Nominal

Hour 0

(Day 0)

Light

Dark

1.65 (9.99)

1.65 (9.99)

1.60 (9.69)

1.61 (9.75)

97.2

97.3

Hour 1.08

(Day 0.45)

Light

Dark

1.65 (9.99)

1.65 (9.99)

1.58 (9.57)

1.58 (9.57)

95.7

95.4

Hour 2.08

(Day 0.087)

Light

Dark

1.65 (9.99)

1.65 (9.99)

1.57 (9.51)

1.56 (9.45)

95.3

94.7

Hour 4.08 (Day 0.170)

Light

Dark

1.65 (9.99)

1.65 (9.99)

1.54 (9.32)

1.56 (9.45)

93.3

94.7

Hour 7.58

(Day 0.316)

Light

Dark

1.65 (9.99)

1.65 (9.99)

1.53 (9.26)

1.58 (9.57)

93.0

95.9

Hour 10.92 (Day 0.455)

Hour 25.332a

(Day 1.06)

Light

Dark

1.65 (9.99)

1.65 (9.99)

1.51 (9.14)

1.63 (9.87)

91.2

98.5

Hour 14.92 (Day 0.622)

Hour 29.33 a

(Day 1.22)

Light

Dark

1.65 (9.99)

1.65 (9.99)

1.49 (9.02)

1.56 (9.45)

90.2

94.4

a These represent total hours for dark

Phase III: Linear regression data used during 29 hour exposure period not corrected for loss in dark controls

Time

Ln[Co/C]shw

Ln[Co/C]pw

1-[A/Ao]

Ln[A/Ao]

Ln[Co/C]PNAP

Hour 0

(Day 0)

0

0

0

0

0

Hour 1.08

(Day 0.45)

0.555

0.635

0.128

0.137

0.0157

Hour 2.08

(Day 0.087)

0.668

0.614

0.116

0.124

0.0195

Hour 4.08 (Day 0.170)

1.05

0.805

0.337

0.411

0.0414

Hour 7.58

(Day 0.316)

1.66

1.39

0.0814

0.0849

0.0446

Hour 10.92 (Day 0.455)

1.34

1.53

-0.314

-0.273

0.0637

Hour 14.92 (Day 0.622)

1.43

1.59

-0.116

-0.110

0.0744

Calculated S1 = 0.402, R^2 = 0.285

Calculated S2 = -0.00071, R^2 = -2.23

Calculated S3 = 23.9, R^2 = 0.874

Calculated kIO = -0.000520 days^-1

Calculated kD = 43.6 days^-1

Calculated (kPE)shw = 43.6 days^-1

Calculated kPE = 19.9 days^-1

Calculated t1/2E = 0.0349 days = 0.837 hours

Phase III: Linear regression data used during 29 hour exposure period corrected for loss in dark controls

Time

Ln[Co/C]

shw, light

Ln[Co/C]

shw, dark

Ln[Co/C]

shw, corr

Ln[Co/C]

pw, light

Ln[Co/C]

pw, dark

Ln[Co/C]

pw, corr

Hour 0

(Day 0)

0

0

0

0

0

0

Hour 1.08

(Day 0.45)

0.555

0.685

-0.130

0.635

0.691

-0.0564

Hour 2.08

(Day 0.087)

0.668

0.644

0.0244

0.614

0.691

-0.0767

Hour 4.08 (Day 0.170)

1.05

0.540

0.514

0.805

0.584

0.222

Hour 7.58

(Day 0.316)

1.66

0.692

0.971

1.39

0.679

0.710

Hour 10.92 (Day 0.455)

1.34

1.05

0.292

1.53

1.00

0.533

Hour 14.92 (Day 0.622)

1.43

0.915

0.517

1.59

1.01

0.585

Calculated S1 = 0.784, R^2 = 0.678

Calculated S2 = -0.00071, R^2 = -2.23

Calculated S3 = 8.33, R^2 = 0.612

Calculated kIO = -0.00101 days^-1

Calculated kD = 15.2 days^-1

Calculated (kPE)shw = 15.17 days^-1

Calculated kPE = 6.90 days^-1

Calculated t1/2E = 0.1004 days = 2.41 hours

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Executive summary:

The effects of sunlight on the degradation of aqueous solutions of 2,6 DTBP in synthetic humic water (SHW) and pure water (PW) (pH 7.0 buffer) were investigated. The ratio of (kP)shw / (kP)pw was 1.36 and suggests that 2,6 DTBP is marginally susceptible to indirect photolysis.

In preliminary tests, significant sorption of 2,6 DTBP to glass was observed as evidenced by the decrease in solution concentration seen in the dark controls. Silanization of the glassware (quartz) gave the least amount of adsorption. In the phase II study, 2,6 DTBP analysis of individual replicate test solutions using synthetic humic water or pure water in the media was conducted. The values for (kP)shw and (kP)pw were 2.94 day^-1 and 2.16 day^-1 respectively. The ration (R) of these values was 1.36 indicating marginal susceptibility for indirect photolysis and indicating the need for further testing. Phase III was conducted over a 29 hour period. A geometric correction factor for scattered light in tubes versus horizontal surfaces of 0.455 was applied to measured rate constants. The net photolysis rate constant (kPE) is thus 0.455 multiplied by (kP)shw resulting in 6.90 days^-1. The direct photolysis rate constant (kDE) is 8.33 multiplied by (kA) resulting in 15.18 days^-1. The photolytic halflife for environmental conditions resulted in a value of 2.41 hours based on corrected data.