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2 

target rate of 2 pints product/acre (0.878 lb ai/A) in approximately 20 GPA of water. A buffer (BU-pHER)1

 was added to the water to reduce the pH of the spray solution from 7.0 to 5.5. The actual application 

rate was reported as 0.877 lb ai/acre. The application was made on September 9, 2011 between 9:10 – 

10:40 am using a ground broadcast method (tractor mounted sprayer). The boom height was 20 inches 

above the crop canopy. The alfalfa was cut 14 days prior to application. The crop height was 10 inches 

at the time of application; the alfalfa field had just dried after irrigation. 

 

Air sampling was conducted for three days during and after the application and was performed using SKC 

226-52 XAD-2 sampling tubes, Tygon tubing, and SKC air sampling pumps set to a flow rate of 1 L/min. 

Air samples were collected from eight off-field monitoring stations placed uniformly around each field 

(30 m from the edge of the treated area) during the first sampling period which included the application 

event. The sampling height of the off-field monitors was 1.5 m. After the application, an on-site profile 

monitoring station was set up in the center of the field which measured concentrations at heights of 0.15, 

0.33, 0.55, 0.90, and 1.5 m. The on-field air samples were taken at approximately 6 hour intervals from 

time 0 (after the application) through 24 hours and at 12 hour intervals from time 24 to 72 hours. The 12 

hour samples coincided approximately with sunrise and sunset and were centered at 07:00 and 19:00 

hours when possible. 

On-site meteorological conditions were monitored continuously at the site. Soil samples were collected 

one day prior to application from four locations across the plot at depths of 0-6”, 6-12”, 12-18”, and 18-

24”. These pre-application soil samples were analyzed for texture, bulk density, CEC, pH, maximum 

water holding capacity, organic matter, and soil moisture by Agvise Laboratories. The soil texture was 

classified as clay loam (no soil series data reported). The organic matter ranged from 0.82-2.1%. The 

soil pH increased as depth increased ranging from 7.7-8.4. 

The samples were analyzed for residues of chlorpyrifos, chlorpyrifos-oxon, and 3,5-6 tricloropyridinol 

(TCP) using Dow AgroScience Analytical Method “Determination of Residues of Chlorpyrifos in Air 

Sampling Tubes by High Performance Liquid Chromatography with Mass Spectrometry Detection.” The 

limit of quantification (LOQ) was 2 ng per tube. Field fortification was conducted during two sampling 

periods, using three different fortification levels. Air concentrations were calculated in terms of μg/m3

.

 

Flux rates for chlorpyrifos and total residues in μg/m2

-s for the first period when the application was in 

progress (Sampling Period 1) were calculated using the Indirect Flux Method. Flux rates for the other 

sampling periods were calculated using both the Integrated Horizontal Flux (IHF) method and the 

Aerodynamic (AD) method. Total toxic residues are defined as the sum of the chlorpyrifos concentration 

and the oxon concentration which has been corrected using the toxicity adjustment factor (TAF) of 12.2

Air samples were initially corrected to account for formation of oxon on the XAD-2 resin (Appendix G). 

The samples were corrected using the average field fortification recoveries. Residues ≤0.275 μg were 

corrected for the average low level field fortification recovery (81.1% for chlorpyrifos and 86.7% for the 

total toxic residues), residues >1.25 μg were corrected for the average high level field fortification 

recovery (82.0% for chlorpyrifos and 84.5% for total toxic residues), and residues between 0.275 and 1.25 

μg were corrected for the average mid-level field fortification recovery (75.3% for chlorpyrifos and 

79.6% for total toxic residues). Values reported as below the LOQ were assigned a value of 1⁄2 LOQ. 

 

1 BU-pH-ER is a spray adjuvant designed to improve the effectiveness of certain agricultural chemicals by reducing 

the pH of higher alkaline water and contains phosphoric acid, propylene glycol, casuistic soda as well as other 

constituents. 

2 Email from Wade Britton (OPP/HED) to Rochelle Bohaty (OPP/EFED) September 10, 2012. 
Air Monitoring (2012)/Page 3 of 44 

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3 

Reviewer-estimated flux rate values using the Indirect Method for Period 1 (application period) were 0.22 

μg/m2

-s(for chlorpyrifos and 0.46 μg/m2-s for total toxic residues (based on parent toxicity equivalent 

units). The r2

 values for all of the regressions were above 0.81. The reviewer-estimated flux rate values 

for chlorpyrifos compare well with the study author’s results even though the study authors did not 

correct for field fortification. 

The chlorpyrifos flux calculated for the first period after application using the AD method was 0.824 

μg/m2

-s. The flux then declined over the next 24 hours, followed by a second smaller peak of 0.081 

μg/m2

-s. Flux generally continued to decrease over the remainder of the study and was 0.002 μg/m2-s by 

the last sampling interval. 

The chlorpyrifos flux calculated for the first period after application using the Indirect Method was 0.591 

μg/m2

-s. The highest flux was observed during the subsequent period (Period 2) at a considerably higher 

level of 0.759 μg/m2

-s. The flux then declined over the next 24 hours, followed by a second smaller peak 

of 0.167 μg/m2

-s. Flux generally continued to decrease over the remainder of the study and was 0.004-

0.005 μg/m2

-s by the last sampling interval. 

The reviewer-estimated flux rates for chlorpyrifos using the AD method were comparable to those 

estimated by the study author. The reviewer-estimated flux rate values for chlorpyrifos using the IHF 

method were much higher than those estimated by the study author. A review of the study author’s 

calculations indicated that Zp (height of plume) was truncated at 150 cm, which in turn yielded lower flux 

rate estimates. The reviewer’s calculations were based on Zp (the height of the plume top in units of 

meters; see equations in the Flux Calculations section of this document). The flux trends exhibited by 

both those estimated by the reviewer and those by the study authors were very similar. 

In this study approximately 29% of the applied chlorpyrifos was observed to volatilize off the field during 

the first 24 hours following application. 

The total toxic residue flux calculated for the first period after application using the AD method was 

1.102 μg/m2

-s. The flux then declined over the next 24 hours, followed by a second smaller peak of 0.186 

μg/m2

-s. Two smaller peaks occurred at 0.034 μg/m2-s and at 0.052 μg/m2-s. Flux was 0.002-0.003 

μg/m2

-s by the last sampling interval. 

The total toxic residue flux calculated for the first period after application using the Indirect Method was 

0.791 μg/m2

-s. The highest flux was observed during the subsequent period (Period 2) at a considerably 

higher level of 1.27 μg/m2

-s. The flux then declined over the next 24 hours, followed by a second smaller 

peak of 0.384 μg/m2

-s. Two smaller peaks occurred at 0.057 μg/m2-s and at 0.038 μg/m2-s. Flux was 

0.007-0.010 μg/m2

-s by the last sampling interval. 

COMPLIANCE: 

Signed and dated GLP, Quality Assurance, and Data Confidentiality statements were provided. The study 

sponsor waived claims of confidentiality within the scope of FIFRA Section 10 (d)1(A), (B), or (C). The 

Study Report indicated that the study was conducted under EPA Good Laboratory Practice Standards (40 

CFR Part 160) and OECD ENV/MC/CHEM (98)17, with the following exceptions: GPS coordinates 

were collected with a non-GLP compliant instrument; the crop history and chlorpyrifos use were obtained 

from the grower; sunrise/sunset and cloud cover information were obtained from the National Climate 

Data Center. None of the noted field phase GLP deviations had any impact on the validity of the study. 

 
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4 

I. MATERIALS AND METHODS

A. MATERIALS:

1. Test Material: 

Formulation: The test substance is Lorsban Advanced Insecticide (Reg. No. 

62719-591), a liquid formulation containing 3.66 lb ai/gal (439 g 

ai/L; 40.2% w/w) chlorpyrifos as the active ingredient. 

Lot/Batch #: A lot number for the test substance was not provided. Lot numbers 

for the reference substances were: MM 930503-17 (chlorpyrifos 

reference substance); YC2-106153-76 (chlorpyrifos-oxon reference 

substance); and 597-F0580-42A (TCP reference substance). 

 Formulation guarantee: The Certificate of Analysis for the test product was not provided. 

Purity: Reference standard of chlorpyrifos was analyzed and found to have a 

purity of 99.8% (expiration date not reported). Reference standard 

of chlorpyrifos-oxon was analyzed and found to have a purity of 

98% (expiration date not reported). Reference standard of TCP was 

analyzed and found to have a purity of 100% (expiration date not 

reported). The stable isotope internal standard of chlorpyrifos was 

analyzed and found to have a purity of 100% (expiration date 

3/17/10). The stable isotope internal standard of chlorpyrifos-oxon 

was analyzed and found to have a purity of 95% (expiration date not 

reported). 

CAS No. (s): 2921-88-2 

Storage conditions: Formulation was stored at ambient temperatures, ranging from 19 to 

34oC. 

2. Relevance of Test Material to Proposed Formulation(s):

The test product used in this study was Lorsban Advanced Insecticide, containing 3.66 lb ai/gal (40.2% 

w/w) chlorpyrifos. A label was not provided with the study report but the reviewer was able to locate a 

label on EPA’s Pesticide Product Label System (PPLS) website. The test product formulation appears to 

be the same as that listed in the label. Discussion of the uncertainties associated with the formulation used 

in this study is provided in the Reviewer’s Comments (RC 1) section of this document. 

B. STUDY DESIGN:

The study protocol was provided in advance and also included in the study report. EPA provided 

comments on the protocol; however, these comments arrived after the study had already started. Many of 

EPA’s comments were addressed in the study and the study authors provided a response to each comment 

in the study report. There were eight amendments and three deviations from the protocol. Protocol 

amendments involved: 1) removing Appendix B, 2) changing the foliage sample size from 1 kg to 0.5 kg, 

3) changing the meteorological monitoring heights for relative humidity, solar radiation, and barometric 

pressure and adding the use of a buffer to lower pH in the spray solution, 4) providing the name and 

address of the principal analyst, 5) providing the details of the laboratory stability study and changing the 

name of the principal investigator, 6) supplying supplemental information to the protocol regarding the 

analytical method, 7) authorization to reactivate the study on the master schedule to allow it to be 

amended to change an incorrect field fortification, and 8) authorization to reactivate the study on the 

master schedule to allow it to be amended to change an incorrect chain of custody date. Protocol 

deviations involved: 1) the front and back sections of the first two air sampling tubes were analyzed 
Air Monitoring (2012)/Page 5 of 44 

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5 

separately instead of the first four tubes as called for in the protocol and analytical set recoveries were not 

calculated for each analytical set, 2) the air temperature was collected at 1.7 m, and 3) the leaf area index 

was not collected according to the protocol (see RC 2). 

The study author stated that none of the deviations had any negative effect on the overall study objectives. 

1. Site Description:

Test location: The study was conducted on a 7.59 acre (575 ft x 575 ft) field in Los 

Banos, California. The plot had established alfalfa that was in its fourth 

year of production. The plot area was flat and was free of obstacles 

around the edges. The location of the field is shown in Figure 1 

(provided at the end of this report). 

Meteorological Data: Meteorological conditions during application and monitoring were 

typical for the region and season that the application was made. The air 

temperature and wind were moderate with daily maximum air 

temperatures that ranged from the high 20’s to the low 30’s (°C). No 

precipitation occurred during the course of the study. 

 Meteorological equipment was established within 4 meters of the treated 

area. The wind monitor orientation was set to true North; the field 

orientation was approximately 15 degrees east of North. Details of the 

sensor heights and the meteorological parameters for which data were 

collected are illustrated in Table 1. The location of the meteorological 

equipment is shown in Figure 2 (provided at the end of this report). 

 Irrigation during the study was not discussed in the study report. Prior to 

application, the alfalfa field was irrigated and dried. 

 
Air Monitoring (2012)/Page 6 of 44 

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6 

Table 1. Summary of Meteorological Parameters Measured in the Field

Parameter Monitoring height (m) Averaging Period 

Wind speed/Wind direction1 0.15, 0.33, 0.55, & 0.9 1 minute, hourly 

Ambient air temperature1 0.15, 0.33, 0.55, & 0.9 1 minute, hourly 

Relative humidity 1.7 hourly 

Solar radiation 1.7 hourly 

Precipitation 1.8 hourly 

Barometric pressure 0.9 hourly 

1. While the protocol and study indicated that wind speed and temperature would be collected at 1.8 m, data were only provided 

for up to 0.9 m in the final report. 

Soil Sampling: Soil samples were collected one day prior to application from four 

locations across the plot at depths of 0-6”, 6-12”, 12-18”, and 18-24”. 

Soil samples were analyzed for texture, bulk density, CEC, pH, 

maximum water holding capacity, organic matter, and soil moisture by 

Agvise Laboratories. Soil properties are provided in Table 2. 

Table 2. Summary of Soil Analysis 

Depth (in) 0 to 6 6 to 12 12 to 18 18 to 24 

USDA Texture Class Clay Loam Clay Loam Clay Loam Clay Loam 

USDA Sand (%) 31 29 31 33 

USDA Silt (%) 34 36 34 28 

USDA Clay (%) 35 35 35 39 

Bulk Density, disturbed (gm/cc) 1.18 1.22 1.20 1.23 

Cation Exchange Capacity (meq/100 g) 23.2 23.7 23.7 25.5 

pH (1:1 soil:water ratio) 7.7 8.1 8.2 8.4 

Maximum Water Holding Capacity (g/100 g) 45.4 38.5 36.8 39.1 

Moisture (% @ 1/3 bar) 26.0 27.7 27.3 28.9 

Moisture (% @ 15 bar) 14.8 16.0 16.2 16.2 

Moisture before monitoring (%) 15.6 19.5 21.7 21.8 

Organic Matter (%) 2.1 1.7 1.2 0.82 

2. Surface Monitored:

Plant Species: Alfalfa: AmeriStand 802 variety. Discussion of the uncertainties 

associated with the crop used in this study is provided in the Reviewer’s 

Comments (RC 3) section of this document 

 

Residential or Public Area: The field site was representative of current commercial practice in the 

California Central Valley. Discussion of the uncertainties associated with 

the site used in this study is provided in the Reviewer’s Comments (RC 

4) section of this document 

 

3. Physical State of Formulation as Applied:

Lorsban Advanced Insecticide (US EPA Reg. No. 62719-591) is a liquid formulation (water 

emulsion/emulsifiable concentrate) containing 3.66 lb ai/gal (439 g ai/L; 40.2% w/w) of the active 

ingredient chlorpyrifos. 

 
Air Monitoring (2012)/Page 7 of 44 

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7 

4. Application Details: 

Application rate(s): The target application rate was 2 pints product/A (0.878 lb ai/A). The 

actual application rate was 0.877 lb ai/A (92.5% of the target rate). The 

maximum label rate for alfalfa is 2 pints ai/A (0.878 lb ai/A). 

Application Regime: One broadcast spray application was made on September 9, 2011 

between 9:10 and 10:40 am. The alfalfa was cut 14 days prior to 

application. The crop height was 10 inches at the time of application; the 

alfalfa field had just dried after irrigation. 

Spray Volume: A spray volume of approximately 20 gallons per acre (GPA) was used 

for the application. A buffer (BU-pH-ER)1

 was added to the water to 

reduce the pH of the spray solution from 7.0 to 5.5. 

Application Equipment: A Massy Ferguson 2405 tractor-mounted boom sprayer equipped with 15 

teejet nozzles spaced 20 inches apart. The boom height was 20 inches 

above the crop. 

Equipment Calibration According to the study protocol, equipment calibration results will be 

Procedures: recorded in the field raw data notebook. No further equipment 

calibration details were provided in the Study Report.

5. Flux Air Sampling Procedures: 

Method and Equipment: For the first flux period (during application), eight off-field monitoring 

stations were placed uniformly around the field in eight directions at 

approximately 30 m from the field edges (Figure 2). The sampling 

height of the off-field monitors was 1.5 m. The on-site profile 

monitoring station (located approximately at the center of each field) 

measured concentrations at heights of 15, 33, 55, 90, and 150 cm. 

Sampling using on-site samplers began less than 2 hours after the center 

of the plot was treated and was continued for the remainder of the study. 

Air sampling was performed using SKC 226-52 XAD-2 resin sampling 

tubes, Tygon tubing, and SKC air sampling pumps using a flow rate of 1 

L/min during the duration of the study. The sorbent tubes were covered 

with a PVC tube to protect them from sunlight. 

Sampling Procedure: The flow rate was measured at the beginning and end of each monitoring 

period and recorded. The tubes were removed, capped, and placed in 

pre-labeled re-sealable bags. Samples were stored frozen (temperature 

not reported) prior to shipment. 

Replicates: Air samples were collected from the eight off-field monitoring stations 

during the application. The air flow was started just prior to application 

and was concluded after the application was complete. Air samples were 

collected from the on-field profile monitoring stations approximately 24 

hours prior to application. Following application, the on-field air 

samples were taken at approximately 6 hour intervals from time 0 (after 

the application) through 24 hours and at 12 hour intervals from time 24 
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8 

to 72 hours. The 12 hour samples coincided approximately with sunrise 

and sunset and were centered at 07:00 and 19:00 hours when possible. 

Single replicates were collected at each sampling station from each 

sampling period. 

6. Sample Handling: 

The samples were maintained frozen (temperature not reported) at the field facilities until they were 

shipped frozen via FedEx to Dow AgroSciences for analysis. Samples were received at the analytical 

facility on September 13, 2011 through September 15, 2011 and were stored at approximately -20 oC until 

extraction. The maximum length of frozen storage for the samples from sample collection to analysis was 

285 days. Sample extracts were stored 0-8 days prior to analysis and storage conditions for the extracts 

were not reported. 

7. Analytical Methodology: 

Extraction method: The contents of each OSHA Versatile Sampler (OVS) tube were divided 

into two separate samples. The front section (polytetrafluoroethylene 

[PTFE] retainer ring, glass fiber filter, 270 mg of XAD-2 sorbent, and 

the foam separator plug) and the back section (140 mg of XAD-2 sorbent 

and a foam retention plug). Front and back section samples were 

initially analyzed separately. Since residue levels of the back sections 

were non-detectable or relatively inconsequential, the remainder of the 

samples were analyzed together to represent one sample. 

Residues of chlorpyrifos, chlorpyrifos-oxon, and 3,5-6 tricloropyridinol 

(TCP) were extracted from the air sampling tubes by sonicating and 

shaking with an acetonitrile/methanol solution (1:1, v:v). Samples were 

either diluted or concentrated prior to being brought to a final volume of 

1.0 mL using an aqueous 0.2% acetic acid solution. 50 μL of a mixed 

internal standard solution containing 0.1 μg/mL of chlorpyrifos-d10 and 

0.1 μg/mL of 3,5,6-trichloropyridin-2-ol-1-15N-2,6-13C was added to 

each sample and calibration standard. The solution was mixed and 

analyzed using LC-MS/MS. 

Detection methods: The air sampling tube extracts were analyzed for chlorpyrifos, 

chlorpyrifos-oxon, and TCP by liquid chromatography with positive-ion 

electrospray tandem mass spectrometry. A summary of the LC-MS/MS 

conditions are shown in Table 3. 

 
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9 

Table 3. Typical HPLC/MS/MS Instrument Parameters 

Instrument: Agilent Model 1200 

Column: Phenomenex Luna C-18, 50 x 2.0 mm, 5 μm 

Injection Volume: 20 μl 

Mobile Phase A: 

Mobile Phase B: 

Water containing 0.1% acetic acid 

Acetonitrile containing 0.1% acetic acid 

Flow Rate: 0.40 mL/min 

Steps Time (min) Flowrate (mL/min) Phase A Phase B 

4:00 0.4 75 25 

0:00 0.4 75 25 

10:00 0.4 0 100 

Expected Retention Times Not reported. 

Ionization Mode: Positive 

Transitions: Chlorpyrifos 

Chlorpyrifos-oxon 

TCP 

Chlorpyrifos-d10 

TCP [M+3] 

350.0→197.8 and 349.9→97.0 

334.1→277.9 and 334.1→197.8 

198.0→134.0 and 198.0→107.0 

359.9→198.9 

202.9→109.1 

Method validation: A separate method validation study was not conducted prior to the start 

of the study. The analytical method was validated concurrently by 

analyzing an appropriate number of air sampling tubes spiked 

individually at the limit of quantification (LOQ), the limit of detection 

(LOD), and concentrations high enough to cover the high-end of the 

expected residues. The LOQ was 2 ng per tube. The LOD was 0.65 ng 

per tube. 

Instrument performance: A series of calibration standards were injected with each set to quantify 

residues in the samples. These calibration standards generated a linear 

plot of chlorpyrifos, chlorpyrifos-oxon, or TCP versus area with 1/x 

weighting. 

Quantification: Quantitation of residues in all samples was achieved by using a 

calibration curve for each of the reference substances at multiple 

concentrations.

8. Quality Control: 

Lab Recovery: Analytical method performance was monitored through concurrent 

analysis of freshly fortified control samples. Control air sampling tube 

samples were fortified with chlorpyrifos at concentrations of 2, 500, 

2000, 3000, and 6500 ng/tube and with chlorpyrifos-oxon and TCP at 

concentrations of 2, 500, and 2000 ng/tube. Individual concurrent 

laboratory recoveries ranged from 58% to 99% with an overall mean 

recovery of 83.7% ± 7.82% (n= 32) for chlorpyrifos, from 61% to 104% 

with an overall mean recovery of 78.5% ± 11.3% (n= 22) for 

chlorpyrifos-oxon, and from 61% to 108% with an overall mean 

recovery of 89.5% ± 12.1% (n= 22) for TCP. 

 
Air Monitoring (2012)/Page 10 of 44 

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Field blanks: During the day before the application, background sampling was 

conducted for approximately 12 hours at two off-field sample locations. 

Background chlorpyrifos and chlorpyrifos-oxon concentrations were not 

detected. 

Triplicate field blanks were weathered with the 6-hr and 12-hr field 

fortification spikes. Residues of chlorpyrifos and chlorpyrifos-oxon 

were not detected. 

Field Fortifications: Fortified samples were prepared in the analytical laboratory and shipped 

to the field prior to the application. Spikes were prepared in triplicate at 

loading levels that approximate the levels anticipated on the air samples. 

The solid sorbent tubes were fortified with chlorpyrifos and chlorpyrifosoxon at 50, 500, and 2,000 ng/tube. Air was drawn through the spiked 

tubes at similar flow rates and sampling durations (6 and 12 hours) as 

used for the collection of the on-field air monitoring samples. Field 

spikes were handled, stored, shipped and analyzed in the same manner as 

all other samples. The field fortification experiments were conducted 

during Periods 5 and 7 for chlorpyrifos and Periods 5 and 9 for 

chlorpyrifos-oxon. 

Table 4 provides a summary of the field fortification recoveries. While 

some individual field fortification samples indicated low recoveries the 

overall averages were between 70 and 120 % (generally acceptable range 

criteria). The overall average recoveries for chlorpyrifos were 81.1%, 

75.3%, and 82.0% at the 0.05, 0.5, and 2.00 g fortification levels, 

respectively. The overall average recoveries for total toxic residues were 

86.7%, 79.6%, and 84.5% at the 0.05, 0.5, and 2.00 g fortification 

levels, respectively. 

The field fortification levels bracketed the expected residues in the field. 

Table 4. Summary of Field Fortification Recoveries 

Analyte

Trapping 

Interval 

(hr)1

Fortification 

Level 

(μg/sample)

n

Range of 

Recoveries1 

(%)

Average 

Recovery ± 

Standard 

Deviation 

(%)

Overall Average Percent Recovery ± 

Standard Deviation (%) 

Low Level Mid Level High Level

Chlorpyrifos

6 

0.05 3 76.5-98.0 87.0 ± 10.8 

81.1 ± 9.84 75.3 ± 13.4 82.0 ± 4.11 

0.50 3 49.1-77.4 66.9 ± 15.5 

2.00 3 74.8-83.9 79.7 ± 4.59 

12 

0.05 3 71.2-80.6 75.3 ± 4.83 

0.50 3 81.6-85.5 83.6 ± 1.95 

2.00 3 82.1-86.8 84.2 ± 2.38 

Total Toxic 

Residues2

6 

0.05 3 82.8-104 92.6 ± 10.9 

86.7 ± 9.98 79.6 ± 12.6 84.5 ± 3.43 

0.50 3 54.5-83.3 72.6 ± 15.8 

2.00 3 78.7-85.3 82.6 ± 3.46 

12 

0.05 3 77.5-86.9 80.9 ± 5.24 

0.50 3 85.0-88.2 86.6 ± 1.60 

2.00 3 84.1-89.2 86.4 ± 2.60 
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11 

1 Presented values represent “with flow” samples. 

2 Total toxic residues = chlorpyrifos + total oxon. The chlorpyrifos and oxon values are from the chlorpyrifos field 

fortification samples. 

Travel Recovery: Travel recovery samples were not used in this study. 

Application Verification: Tank mix samples were not collected for this study. However, the 

application rate was confirmed using monitoring pads. Prior to 

application, at least 12 filter pads, measuring 301.4 cm2

, were placed in 

shallow foil pans that were put on supports immediately above the plant 

canopy. Immediately following application, the pads were collected, 

individually bagged, and stored frozen. The filter pad samples ranged 

from 1,398 to 4,341 g/sample and averaged 2,751 g/sample. This 

corresponds to 0.878 lb ai/A, which is 92.5% of the target application 

rate. 

Storage Stability: Sorbent tubes were prepared and spiked chlorpyrifos, oxon, or TCP at 

50, 500, and 2,000 ng/tube. The samples were aged in a laboratory hood 

at ambient conditions for 6 and 12 hours with airflow at 1 L/min. TCP 

was stable in the sorbent tubes. Oxon was not stable showing substantial 

conversion to TCP. Chlorpyrifos was not stable showing conversion to 

oxon. The petitioner used a simple linear regression of % conversion vs. 

time to correct the chlorpyrifos concentrations. See APPENDIX G for a 

more thorough discussion of the correction factor development. 

 Table 5 provides a summary of the storage stability recoveries. 

Table 5. Summary of Storage Stability Recoveries 

Analyte

Trapping 

Interval 

(hr)1

Fortificatio

n Level 

(μg/sample)

n

Range of 

Recoveries1 

(%)

Average 

Recovery ± 

Standard 

Deviation 

(%)

Overall Average Percent Recovery ± 

Standard Deviation (%) 

Low Level Mid Level High Level

Chlorpyrifos

6 

0.05 3 81.0-91.9 86.6 ± 5.45 

91.6 ± 6.61 97.3 ± 10.1 94.2 ± 3.25 

0.50 3 89.6-92.7 91.3 ± 1.58 

2.00 3 91.3-93.4 92.5 ± 1.10 

12 

0.05 3 95.5-98.6 96.7 ± 1.69 

0.50 3 89.7-112 103 ± 11.9 

2.00 3 91.7-100 95.8 ± 4.15 

Total Toxic 

Residues2

6 

0.05 3 81.0-91.9 86.6 ± 5.45 

91.6 ± 6.61 97.3 ± 10.1 94.2 ± 3.25 

0.50 3 89.6-92.7 91.3 ± 1.58 

2.00 3 91.3-93.4 92.5 ± 1.10 

12 

0.05 3 95.5-98.6 96.7 ± 1.69 

0.50 3 89.7-112 103 ± 11.9 

2.00 3 91.7-100 95.8 ± 4.15 1 Presented values represent “with flow” samples. 

2 Total toxic residues = chlorpyrifos + total oxon. The chlorpyrifos and oxon values are from the chlorpyrifos storage 

stability samples. Note: storage stability recoveries for chlorpyrifos were calculated from total residues because oxon 

contributions were minimal. 
Air Monitoring (2012)/Page 12 of 44 

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12 

Breakthrough: Front and back sections were initially analyzed separately. As residue 

levels in the back sections were nondetectable, breakthrough analysis 

was discontinued. 

C. FLUX CALCULATIONS: 

Flux rates for Sampling Period 1 were calculated using the Indirect Flux Method. Flux rates for the 

remaining sampling periods were calculated using the Integrated Horizontal Flux (IHF) Method and 

the Aerodynamic (AD) Method. A brief description of these methods is given below. 

1. Flux determination using the Indirect Method (IM): 

The indirect method, commonly referred to as the “back calculation” method, was the technique 

employed for estimating flux rates from fields during application. In the indirect method, air 

samples are collected at various locations outside the boundaries of a treated field. Meteorological 

conditions, including air temperature, wind speed, and wind direction, are also collected for the 

duration of the sampling event. The dimensions and orientation of the treated field, the location of 

the samplers, and the meteorological information is used in combination with the ISCST3 

dispersion model (Version 02035) and a unit flux rate of 0.001 μg/m2•s to estimate 

concentrations at the sampler locations. Since there is a linear relationship between flux and the 

concentration at a given location, the results from the ISC model runs are compared to those 

concentrations actually measured and a regression is performed, using the modeled values along 

the x-axis and the measured values along the y-axis. If the linear regression does not result in a 

statistically significant relationship, the regression may be rerun forcing the intercept through the 

origin, or the ratio of averages between the monitored to modeled concentrations may be 

computed, removing the spatial relationship of the concentrations. The indirect method flux back 

calculation procedure is described in detail in Johnson et al., 1999. 

2. Flux determination using the integrated horizontal flux (IHF) method:

The integrated horizontal flux method, also referred to as the “mass balance” method, was the 

technique employed for estimating flux rates from fields following application. In the integrated 

horizontal flux method, a mast is erected in the middle of the treated field and concentration 

samples are typically collected at four or five different heights, ranging from approximately 0.5 to 

5 feet. Likewise, wind speed data are collected at a variety of heights. A log-linear regression is 

performed relating the natural logarithm of the sample height to the air concentration and wind 

speed following the log law relationships for the atmospheric boundary layer. These relationships 

are then incorporated into an equation to estimate flux. The methods to estimate flux and related 

equations are presented in Majewski et al., 1990. The equation for estimating flux using the 

integrated horizontal flux method is the following expression: 

  

Z p

Z

cudz

x

P

0

1

where P is the volatile flux in units of g/m2

·s, c is the average pesticide residue concentration in 

units of g/m3

 at height Z in units of meters, u is the wind speed in units of m/s at height Z, x is 

the fetch of the air trajectory blowing across the field in units of meters, Z0 is the aerodynamic 

surface roughness length in units of meters, Zp is the height of the plume top in units of meters, 
Air Monitoring (2012)/Page 13 of 44 

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13 

and dz is the depth of an incremental layer in units of meters. Following trapezoidal integration, 

the above equation is simplified as follows (Yates, 1996): 

    

ZP

Z

A Ln z B C Ln z D dz

x

P

0

( * ( ) ) *( * ( ) ) 1

where A is the slope of the wind speed regression line by ln(z), B is the intercept of the wind 

speed regression line by ln(z), C is the slope of the concentration regression by ln(z), D is the 

intercept of the concentration regression by ln(z), z is the height above ground level. Zp can be 

determined from the following equation: 

  



 



   C

D Z P

0.1

exp

The minimum fetch requirement of 20 meters for this method to be valid was satisfied at all 

times. The raw wind speed and wind direction data at varying heights were averaged for the 

concentration sampling durations. The wind direction values were used to calculate a fetch at 

every minute, which then was averaged for the concentration sampling periods. Finally, the 

period averaged wind speed values were used along with the natural logarithm of the height 

measurements to calculate regression coefficients (slope, intercept, and r2

) for each period. 

Period averaged meteorological parameters for each field and the meteorological regression 

coefficients are shown in Appendix B. 

3. Flux determination using the Aerodynamic Method (AD): 

The aerodynamic method, also referred to as the “flux-gradient” method, was the technique 

employed for estimating flux rates from fields following application. In the aerodynamic method, 

a mast is erected in the middle of the treated field and concentration samples are typically 

collected at four or five different heights, ranging from 0.5 to 10 feet. Likewise, temperature and 

wind speed data are collected at a variety of heights. A log-linear regression is performed relating 

the natural logarithm of the sample height to the concentration, temperature, and wind speed. 

These relationships are then incorporated into an equation to estimate flux. These methods to 

estimate flux and related equations are presented in Majewski et al., 1990. The equation for 

estimating flux using the aerodynamic method is Thornthwaite-Holzman Equation which is 

shown in the following expression: 

 

2

1

2

2

[ln ]

( )( )

















  

z

z

k c u P

 m p

where P is the flux in units of g/m2

·s, k is the von Karman’s constant (dimensionless ~0.4), Δc

is the vertical gradient pesticide residue concentration in air in units of g/m3

 between heights ztop

and zbottom in units of meters, Δū is the vertical gradient wind speed in units of m/s between 

heights ztop and zbottom, and  m and  p are the momentum and vapor stability correction terms 

respectively. Following the conditions expected in the neutrally stable internal boundary layer 

characterized by an absence of convective (buoyant) mixing but mechanical mixing due to wind 

shear and frictional drag, a log-linear regression is performed relating the natural logarithm of the 
Air Monitoring (2012)/Page 14 of 44 

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14 

sample height to the concentration, temperature, and wind speed. The adjusted values of the 

concentration, temperature, and wind speed from this regression is incorporated into the equation 

above to arrive at the following equation, which is ultimate used to compute the flux. 

2

2

ln

(0.42) ( )( )

















   

bottom

top

m p

ztop zbottom ztop zbottom

z

z

c c u u

Flux

 

where  m and  p are internal boundary layer (IBL) stability correction terms determined 

according to the following conditions based on the calculation of the Richardson number, Ri: 

Equation x3

 2 273.16

2

(9.8)( )( )

ztop zbottom

ztop zbottom

top bottom ztop zbottom

i

u u

T T

z z T T

R

  





























 

  

where Tztop and Tzbottom are the regressed temperatures at the top and bottom of the vertical profile 

in units of °C. 

if Ri >0 (for Stagnant/Stable IBL) 

 0.33  m  116Ri and 0.4 0.885(1 34 )  p   Ri

if Ri <0 (for Convective/Unstable IBL) 

  0.33 1 16   m   Ri and 0.4 0.885(1 22 )

  p   Ri

The minimum fetch requirement that the fetch is 100 times the highest height of the air sampler 

for this method to be valid was not satisfied at all times. The raw wind speed and temperature 

data at varying heights were averaged for the concentration sampling durations. The period 

averaged wind speed and temperature values were used along with the natural logarithm of the 

height measurements to calculate regression coefficients (slope, intercept, and r2

) for each period. 

Meteorological parameters for each averaging period and the regression coefficients are shown in 

Appendix D. The aerodynamic method used to estimate flux and related equations are presented 

in Majewski et al., 1990. 

II. RESULTS AND CALCULATIONS

Chlorpyrifos and Total Toxic Residue Concentrations 

Air samples were initially corrected to account for formation of oxon on the XAD-2 resin (Appendix G). 

Air samples were corrected using the average field fortification recoveries. Residues ≤0.275 μg were 

corrected for the average low level field fortification recovery (81.1% for chlorpyrifos and 86.7% for the 

total toxic residues), residues >1.25 μg were corrected for the average high level field fortification 

recovery (82.0% for chlorpyrifos and 84.5% for total toxic residues), and residues between 0.275 and 1.25 

μg were corrected for the average mid level field fortification recovery (75.3% for chlorpyrifos and 

79.6% for total toxic residues). Values reported as below the LOQ were assigned a value of 1⁄2 LOQ. 

Total toxic residues were estimated by summing the chlorpyrifos concentration and oxon concentration 

which was corrected using the relative potency factor (TAF of 12X)2

. 
Air Monitoring (2012)/Page 15 of 44 

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15 

Flux Rate Estimates 

 

Reviewer-estimated flux rate values using the Indirect Method for Period 1 (application period) were 0.22 

μg/m2

-sfor chlorpyrifos and 0.46 μg/m2-sfor total toxic residues. The r2 values for all of the regressions 

were above 0.81. Calculations are provided in APPENDIX A. 

 Chlorpyrifos 

The reviewer-estimated flux rate values for chlorpyrifos are presented in Table 6 for AD Flux and Table 

7 for IHF along with those estimated by the study author. Regression results for the sampler 

concentrations are provided in APPENDICES C (IHF) and E (AD). 

The chlorpyrifos flux calculated for the first period after application using the AD method was 0.824 

μg/m2

-s. The flux then declined over the next 24 hours, followed by a second smaller peak of 0.081 

μg/m2

-s. Flux generally continued to decrease over the remainder of the study and was 0.002 μg/m2-s by 

the last sampling interval. 

The chlorpyrifos flux calculated for the first period after application using the Indirect Method was 0.591 

μg/m2

-s The highest flux was observed during the subsequent period (Period 2) at a considerably higher 

level of 0.759 μg/m2

-s The flux then declined over the next 24 hours, followed by a second smaller peak 

of 0.167 μg/m2

-s at Sampling Period 6. Flux generally continued to decrease over the remainder of the 

study and was 0.004-0.005 μg/m2

-s by the last sampling interval. 

Table 6. Estimated Flux Rates for Chlorpyrifos Using AD Method 

Period Sample Start 

Times 

Sample End 

Times 

Duration 

(hh:mm) 

Estimated 

Flux FF 

(μg/m2-s) 

Study Author 

Estimated 

Flux (μg/m2-s) 

2 9/9/2011 10:45 9/9/2011 13:00 2.25 0.747 0.657 

3 9/9/2011 13:00 9/9/2011 19:00 6.00 0.236 0.204 

4 9/9/2011 19:00 9/10/2011 1:00 6.00 0.035 0.035 

5 9/10/2011 1:00 9/10/2011 7:00 6.00 0.024 0.022 

6 9/10/2011 7:00 9/10/2011 19:00 12.00 0.073 0.068 

7 9/10/2011 19:00 9/11/2011 7:00 12.00 0.011 0.008 

8 9/11/2011 7:00 9/11/2011 19:00 12.00 0.018 0.015 

9 9/11/2011 19:00 9/12/2011 7:00 12.00 0.006 0.005 

10 9/12/2011 7:00 9/12/2011 19:00 12.00 0.016 0.012 

11 9/12/2011 19:00 9/13/2011 7:00 12.00 0.002 0.002 

Table 7. Estimated Flux Rates for Chlorpyrifos Using IHF Method 

Period Sample Start 

Times 

Sample End 

Times 

Duration 

(hh:mm) 

Estimated 

Flux FF 

(μg/m2-s) 

2 9/9/2011 10:45 9/9/2011 13:00 2.25 0.591 

3 9/9/2011 13:00 9/9/2011 19:00 6.00 0.759 

4 9/9/2011 19:00 9/10/2011 1:00 6.00 0.171 

5 9/10/2011 1:00 9/10/2011 7:00 6.00 0.054 
Air Monitoring (2012)/Page 16 of 44 

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16 

Table 7. Estimated Flux Rates for Chlorpyrifos Using IHF Method 

Period Sample Start 

Times 

Sample End 

Times 

Duration 

(hh:mm) 

Estimated 

Flux FF 

(μg/m2-s) 

6 9/10/2011 7:00 9/10/2011 19:00 12.00 0.167 

7 9/10/2011 19:00 9/11/2011 7:00 12.00 0.021 

8 9/11/2011 7:00 9/11/2011 19:00 12.00 0.033 

9 9/11/2011 19:00 9/12/2011 7:00 12.00 0.006 

10 9/12/2011 7:00 9/12/2011 19:00 12.00 0.012 

11 9/12/2011 19:00 9/13/2011 7:00 12.00 0.005 

The reviewer-estimated flux rates for chlorpyrifos using the AD method were comparable to those 

estimated by the study author. The reviewer-estimated flux rate values for chlorpyrifos using the IHF 

method were much higher than those estimated by the study author. A review of the study author’s 

calculations indicated that Zp (height of plume) was truncated at 150 cm, which in turn yielded lower flux 

rate estimates. The flux trends exhibited by both those estimated by the reviewer and those by the study 

author were very similar. 

Chloropyrifos-oxon 

The reviewer examined the flux rate values for oxon only; however, attempts at conducting a regression 

analysis for the residues generated poor fitting results. The study authors also completed this analysis and 

are consistent with EPA’s analysis. It is unclear if the oxon residues are a result of oxon flux off the field 

or from transformation of chlorpyrifos in the air or on the tube. As a result, the reviewer decided to 

examine total toxic residues together (see section below as well as RC 6). 

 Total Toxic Residues 

The reviewer estimated flux rate values for total toxic residues are presented in Table 8 for both AD and 

IHF methods based on total mass. The flux estimates based on based on parent toxicity equivalent units 

(takes into account the TAF) are provided in Table 9 and Table 10 for the AD and IHF, respectively. 

Regression results for the sampler concentrations are provided in APPENDICES C (IHF) and E (AD). 

Initial attempts at conducting a regression analysis for the total toxic residues generated poor fitting 

results (e.g., r2

<0.2). In general, the oxon concentrations did not follow a decreasing trend with height 

like the chlorpyrifos concentrations, resulting in poor results. In an effort to use the available data, a 

conversion factor was developed for each sampling period, which took the total mass of oxon for all four 

air samplers and divided this total by the total mass of chlorpyrifos for all four air samplers. The mass of 

chlorpyrifos at each height was then multiplied by this conversion factor to estimate the mass of oxon at 

the same height. The mass of the oxon was then multiplied by the TAF (12X)2

 and added to the 

chlorpyrifos mass and divided by the volume of air sampled to estimate the total toxic residues at each 

height. 

An example calculation is provided below for sampling Period 2. The total oxon mass is 0.397 μg and the 

total chlorpyrifos mass is 12.571 μg, resulting in a conversion factor of 0.031581. This conversion factor 

is then applied to each of the chlorpyrifos samples to estimate a revised oxon amount. The revised oxon 

amount is then multiplied by the TAF (12) 2 and added to the chlorpyrifos mass to estimate the total toxic 

residue. This total toxic residue mass was divided by the sampler flowrate and length of sampling time 
Air Monitoring (2012)/Page 17 of 44 

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17 

for each sampler (131-133 minutes) to arrive at the total toxic residue concentration at each sampler 

height. 

Period Sampler 

Sampler 

Flowrate 

(L/min) 

Chlorpyrifos 

(μg) 

Oxon 

(μg) 

Revised 

Oxon 

(μg) 

Total 

Toxic 

Residue 

(μg) 

Total 

Toxic 

Residue 

(μg/m3) 

2 

A1 (15 cm) 1.076 3.630 0.082 0.115 5.01 35.54 

B1 (33 cm) 1.047 2.901 0.082 0.092 4.005 29.20 

C1 (55 cm) 1.029 2.473 0.083 0.078 3.409 25.10 

D1 (90 cm) 1.081 2.097 0.086 0.066 2.889 20.25 

E1 (150 cm) 1.043 1.470 0.064 0.046 2.022 14.58 

These concentrations were then corrected for field fortification or storage stability recoveries and used to 

estimate the regression for total toxic residues to be used in both the AD and IHF methods. The 

calculation of the revised total toxic residues is provided in APPENDIX F. 

The total toxic residue flux calculated for the first period after application using the AD method was 

1.102 μg/m2

-s. The flux then declined over the next 24 hours, followed by a second smaller peak of 

0.186 μg/m2

-s. Two smaller peaks occurred at 0.034 μg/m2-s and at 0.052 μg/m2-s. Flux was 0.002-

0.003 μg/m2

-s by the last sampling interval. 

The total toxic residue flux calculated for the first period after application using the Indirect Method was 

0.791 μg/m2

-s. The highest flux was observed during the subsequent period (Period 2) at a considerably 

higher level of 1.27 μg/m2

-s. The flux then declined over the next 24 hours, followed by a second smaller 

peak of 0.384 μg/m2

-s . Two smaller peaks occurred at 0.057 μg/m2-s and at 0.038 μg/m2-s. Flux was 

0.007-0.010 μg/m2

-s by the last sampling interval. 

Table 8. Estimated Flux Rates for Total Toxic Chlorpyrifos Residues (Chlorpyrifos and 

Chlorpyrifos-oxon) Using AD and IHF Methods for the Alfalfa Study (based on mass) 

Sampling 

Period 

Sample Start 

Times 

Sample End 

Times 

Duration 

(hh:mm) 

Hours Post 

Application 

at Sample 

Collection 

AD 

Method 

IHF 

Method* 

Estimate

d Flux 

FF 

(μg/m2-

s) 

Estimated 

Flux FF 

(μg/m2-s) 

2 9/9/2011 10:45 9/9/2011 13:00 2.25 2.25 0.75 0.59 

3 9/9/2011 13:00 9/9/2011 19:00 6.00 8.25 0.24 0.78 

4 9/9/2011 19:00 9/10/2011 1:00 6.00 14.25 0.034 0.17 

5 9/10/2011 1:00 9/10/2011 7:00 6.00 20.25 0.024 0.051 

6 9/10/2011 7:00 9/10/2011 19:00 12.00 32.25 0.080 0.18 

7 9/10/2011 19:00 9/11/2011 7:00 12.00 42.25 0.010 0.024 

8 9/11/2011 7:00 9/11/2011 19:00 12.00 54.25 0.019 0.033 

9 9/11/2011 19:00 9/12/2011 7:00 12.00 66.25 0.006 0.006 

10 9/12/2011 7:00 9/12/2011 19:00 12.00 78.25 0.018 0.013 

11 9/12/2011 19:00 9/13/2011 7:00 12.00 90.25 0.002 0.004 

Data provided in this table are based on the application rate used in the study (0.877 lb a.i./A). 

Flux profile is based on mass only and does not take into account the difference in toxicity between 

chlorpyrifos and chlorpyrifos-oxon. 
Air Monitoring (2012)/Page 18 of 44 

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18 

Table 9. Estimated Flux Rates for Total Toxic Residue Using AD 

Method*(based on parent toxicity equivalent units)

Period Sample Start 

Times 

Sample End 

Times 

Duration 

(hh:mm) 

Estimated Flux FF 

(μg/m2-s) 

2 9/9/2011 10:45 9/9/2011 13:00 2.25 1.00 

3 9/9/2011 13:00 9/9/2011 19:00 6.00 0.395 

4 9/9/2011 19:00 9/10/2011 1:00 6.00 0.040 

5 9/10/2011 1:00 9/10/2011 7:00 6.00 0.030 

6 9/10/2011 7:00 9/10/2011 19:00 12.00 0.168 

7 9/10/2011 19:00 9/11/2011 7:00 12.00 0.018 

8 9/11/2011 7:00 9/11/2011 19:00 12.00 0.031 

9 9/11/2011 19:00 9/12/2011 7:00 12.00 0.007 

10 9/12/2011 7:00 9/12/2011 19:00 12.00 0.047 

11 9/12/2011 19:00 9/13/2011 7:00 12.00 0.003 

* The study author did not estimate total toxic residue flux rates, instead the study author 

calculated flux rates for the chlorpyrifos-oxon alone. 

Data provided in this table are based on the application rate used in the study (0.877 lb 

a.i./A). 

Flux profile takes into account the difference in toxicity between chlorpyrifos and 

chlorpyrifos-oxon. 

Table 10. Estimated Flux Rates for Total Toxic Residue Using IHF 

Method* (based on parent toxicity equivalent units)

Period Sample Start 

Times 

Sample End 

Times 

Duration 

(hh:mm) 

Estimated Flux FF 

(μg/m2-s) 

2 9/9/2011 10:45 9/9/2011 13:00 2.25 0.791 

3 9/9/2011 13:00 9/9/2011 19:00 6.00 1.270 

4 9/9/2011 19:00 9/10/2011 1:00 6.00 0.197 

5 9/10/2011 1:00 9/10/2011 7:00 6.00 0.064 

6 9/10/2011 7:00 9/10/2011 19:00 12.00 0.384 

7 9/10/2011 19:00 9/11/2011 7:00 12.00 0.047 

8 9/11/2011 7:00 9/11/2011 19:00 12.00 0.057 

9 9/11/2011 19:00 9/12/2011 7:00 12.00 0.007 

10 9/12/2011 7:00 9/12/2011 19:00 12.00 0.038 

11 9/12/2011 19:00 9/13/2011 7:00 12.00 0.007 

* The study author did not estimate total toxic residue flux rates, instead the study 

author calculated flux rates for the chlorpyrifos-oxon alone. 

III DISCUSSION:

Flux rates for chlorpyrifos and total toxic residues started off low, but reached a peak in the second or 

third sampling period, depending on the method used to estimate flux rates, and then generally decreased, 

with other lower subsequent peaks that occurred during daytime hours of Days 2, 3, and 4. 

Log-normal regressions developed for wind speed, temperature, and concentration data versus the lognormal estimates for height usually provided good fits, with most r2

 estimates above 0.9. 
Air Monitoring (2012)/Page 19 of 44 

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19 

IV REVIEWER’S COMMENTS:

1 While Lorsban Advanced may be an end-use emulsifiable concentrate (water emulsion) used on a 

range of crops including alfalfa and is a preferred chlorpyrifos liquid formulation sold by Dow 

AgroSciences it may not represent the preferred formulation by applicators. In addition, Lorsban 

Advance is reported to be a low VOC (a low volatility formulation); therefore, the observed flux 

rates reported in this study may not represent the potential flux for other formulations and the 

results could under predict the potential exposure from other chlorpyrifos formulations. California 

is currently the only state actively working to reduce pesticide VOC; therefore, it is not expected 

the Lorsban Advance and other low VOC formulations dominate the market. Additional 

information on the use of Lorban Advance and other low VOC formulations compared to other 

“regular/non-low VOC” would be helpful to determine the representative nature of the selected 

formulation. 

2 The study protocol indicated that the leaf area index would be reported. Although reporting the 

leaf is not a critical component of this study and does not affect the results and conclusions of this 

study, not having the leaf area index for the studied crop limits the comparative value of this 

study to other crops. 

3 The maximum single application rate for alfalfa (1 lb ai/a; 4 lb ai/a per year) is higher than the 

0.878 lb ai/a used in this study. In addition, these rates are substantially lower than current 

maximum single applications for grapes (33.3 lb ai/a; 33.3 lb ai/a per year) permitted on currently 

labeled chlorpyrifos products. In addition to grapes, several other uses also have maximum single 

application rates substantially higher than alfalfa including citrus (6 lb ai/a; 10.5 lb ai/a per year), 

mint (2.0 ai/a; 6 lb ai/a per season), and turf (4.0 lb ai/a; no yearly application restriction). 

Field volatility studies are typically conducted similar to terrestrial field dissipation studies 

(OCSPP 835.6100); therefore, the maximum single application rate of all uses is normally 

recommended. To address this uncertainty, additional studies may be necessary to evaluate flux 

rates under different cropping conditions and application rates. 

4 In addition to temperature, environmental factors such as humidity and rainfall may influence the 

amount of chlorpyrifos and chlorpyrifos-oxon observed in air samples. While the temperature 

throughout the study may have been high, higher humidity may increase the amount of 

chlorpyrifos and chlorpyrifos-oxon observed in air samples. It is uncertain how the results 

obtained from this study, conducted in the central valley of California, compare to the results that 

may be obtained for other sites in the US. To address this uncertainty, additional studies may be 

necessary to evaluate flux rates under different environmental conditions in different regions of 

the country. 

5 The total oxon chlorpyrifos equivalents for the 12-hour 500 ug sample (pg. 118 of report) were 

not consistent with the other data. Either the corrected concentrations are too high or the raw data 

is reported incorrectly. The reviewer thinks the corrected equivalents should be down around 2% 

based on examination of the molecular weight conversion. This error was confirmed with the 

study authors; however, a corrected report has not been provided. If this is the case, the oxon 

concentration would be slightly less than currently calculated. This is not expected to have a 

substantial impact on the total toxic residue concentrations and the calculated flux rates because 

the oxon concentrations are low and the change in the correction factor is not expected to be great 

(>5%). 
Air Monitoring (2012)/Page 20 of 44 

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20 

6 It is unclear if the oxon residues observed in this study are a result of oxon flux off the field or 

from transformation of chlorpyrifos in the air or on the tube. As a result, the reviewer decided to 

examine total toxic residues (chlorpyrifos and chlorpyrifos-oxon) together. The study authors did 

not complete this analysis. This is thought to be a reasonable approach to account for any toxic 

residues that may end up in air as a result of chlorpyrifos applications independent of the route of 

oxon formation. 

V CONCLUSION:

Despite issues with oxon recoveries during the study, the data and the flux rate estimates derived from the 

data appear to be scientifically sound. This study is classified as acceptable. 

V REFERENCES:

Johnson, B., Barry, T., and Wofford P. 1999. Workbook for Gaussian Modeling Analysis of Air 

Concentrations Measurements. State of California Environmental Protection Agency, Department 

of Pesticide Regulation. Sacramento, CA. 

Majewski, M.S., Glotfelty, D.E., Kyaw Tha Paw U., Seiber, JN. 1990. A field comparison of several 

methods for measuring pesticide evaporation rates from soil. Environmental Science and 

Technology, 24:1490-1497. 

Wilson, J.D., and Shum. W.K.N. 1992. A re-examination of the integrated horizontal flux method for 

estimating volatilisation from circular plots. Agriculture Forest Meteor. Vol 57:281-295. 

Yates, S.R., F.F. Ernst, J. Gan, F. Gao, and Yates, M.V. 1996. Methyl Bromide Emissions from a 

Covered Field: II. Volatilization,” Journal of Environmental Quality, 25: 192-202. 

 
Air Monitoring (2012)/Page 21 of 44 

Chlorpyrifos / 059101/ MRID 48883201 OPPTS 835.8100 / DACO 5.9a 

21 

Figure 1. Location of Field in California 

 
Air Monitoring (2012)/Page 22 of 44 

Chlorpyrifos / 059101/ MRID 48883201 OPPTS 835.8100 / DACO 5.9a 

22 

Figure 2. Air Quality and Meteorological Monitoring Stations 

 

 
Air Monitoring (2012)/Page 23 of 44 

Chlorpyrifos / 059101/ MRID 48883201 OPPTS 835.8100 / DACO 5.9a 

23 

COMPLIANCE CHECKLIST 

Applicable Checklist Items Taken from: 

FIELD VOLATILITY STUDIES 

 Investigators should submit protocols for review purposes prior to the inception of the study. This 

criterion was met. A protocol was provided in the study report and was submitted prior to the 

inception of the study. Comments provided by EPA on the protocol were also addressed in the 

study report. 

 Expected deviations from GLPs should be presented concurrently with any protocol deviations 

and their potential study impacts. This criterion was met. 

 The test substance must be the typical end use product of the active ingredient. This criterion was 

met. 

 The production of metabolites, breakdown products, or the presence of contaminants of potential 

toxicologic concern, should be considered on a case-by-case basis. This criterion was met. 

Samples were analyzed for chlorpyrifos-oxon and TCP. 

 The application rate should be the maximum rate specified on the label. If multiple applications 

are made, the minimum allowable interval between applications should be used. This criterion 

was met. 

 The percentage of active ingredient and formulation type should be reported. Properties of the 

pesticide (i.e., vapor pressure, water solubility, adsorption to soil, and texture) should also be 

addressed. This criterion was met. 

 The study should be conducted domestically (USA). The site should be typical in geography, 

topography, soil type, season, and meteorology of those sites with intended use patterns. The use 

of two or more topographically and meteorologically diverse sites is recommended in order to 

ascertain the effects of these variables on spray drift. These criteria were partially met. The study 

was conducted on a representative field in California. However, only one test site was used. 

 Field data should be documented, including area description, meteorological conditions, 

application data, and equipment information. Volatility (g/ha/day), air concentrations (μg/m3

), 

and vapor pressure (mm Hg or equivalent) should also be reported. These criteria were partially 

met. Volatility and vapor pressure data were not provided. 

 Appropriate air sampling media should be selected. The medium should entrap a high percentage 

of the chemical passing through it, and it should allow the elution of a high percentage of the 

entrapped chemical for analysis. A trapping efficiency test for the monitoring media chosen must 

be documented. These criteria were partially met. An appropriate air sampling media was 

selected. However, a trapping efficiency test was not performed. 

 Air monitoring techniques area (i.e., stationary) should contain sufficient samples to characterize 

the likely range of possible exposure concentrations, and to ensure that the reentry and/or 

bystander scenarios can be adequately addressed. Stationary samples should be collected from 

the center of treated fields and from at least 4 other locations, preferably at the cardinal compass 
Air Monitoring (2012)/Page 24 of 44 

Chlorpyrifos / 059101/ MRID 48883201 OPPTS 835.8100 / DACO 5.9a 

24 

points from the center location and at representative distances to reflect buffer zones. Air 

samplers should be placed at a height that is representative of the breathing zone of potentially 

exposed individual (i.e. 2 to 3 feet for workers removing tarps, 4 to 5 feet for bystanders 

downwind, etc.) At least three downwind collection sites should be used. If homes or structures 

are present, representative samples should be taken within the structure to establish buffer zones. 

These criteria were met. 

 The duration of the sampling interval and air flow rates should be maximized within the 

appropriate flow rate range to increase the potential for capturing enough residues to be 

quantifiable. This criterion was met. The flow rate was maintained at 1 L/min (appropriate range 

for gaseous residue). 

 A sufficient number of replicates should be generated to address the exposure issues associated 

with the population of interest. This criterion was met. 

 Air samples should be monitored for residues at intervals which increase with time after 

application. Sampling should be continued until the nature of the dissipation curve has been 

clearly established. This criterion was met. 

 A monitoring pump capable of producing airflow of at least 2 L/min. should be used and its 

batteries should be capable of sustaining maximum airflow for at least 4 hours without 

recharging. Airflow should be measured at the beginning and end of the exposure period. These 

criteria were met. The pumps were operated at airflow appropriate for the monitoring of gases and 

were sampled for intervals ranging from 6 to 12 hours. Airflow was monitored before and after 

the exposure period to ensure proper operation. 

 Field calibration of air monitors should be performed at the beginning and end of the sampling 

period. This criterion was met. 

 An adequate number of field blanks should be analyzed for contamination. If an appropriate 

analytical method had not been established (i.e by NIOSH or OSHA), field fortification samples 

should be analyzed for correction of residue losses occurring during the sampling period. When 

appropriate, fortified samples and blanks should be fortified at the expected residue level of the 

actual field samples. Fortified blanks should be exposed to the same weather conditions. These 

criteria were met. 

 Retention and breakthrough studies should be performed under conditions similar to those 

anticipated in the field phase of the study to ensure that collected material is not lost from the 

medium during sampling. It is recommended that at least one test be carried out where the initial 

trap contains 10x the highest amount of residue expected in the field. These criteria were not met. 

 Samples should be stored in a manner that will minimize deterioration and loss of analytes 

between collection and analyses. Storage stability samples should be extracted and analyzed 

immediately before and at appropriate periods during storage. The time periods for storage 

should be chosen so that the longest interval corresponds to the longest projected storage period 

for field samples. These criteria were met. 

 If exposed media are to be stored prior to extraction, storage media/containers should be made of 

appropriate material that protects against contamination and that does not interfere with analysis. 

These criteria were met. 
Air Monitoring (2012)/Page 25 of 44 

Chlorpyrifos / 059101/ MRID 48883201 OPPTS 835.8100 / DACO 5.9a 

25 

 Validated analytical methods of sufficient sensitivity are needed. The method must be specific for 

the analyte of interest. Information on method efficiency (residue recovery) and limit of 

quantification (LOQ) should be provided. This criterion was met. 

 Analysis methods should be documented and appropriate. The analytical procedure must be 

capable of measuring exposure to 1μg/hr (or less, if the toxicity of the material under study 

warrants greater sensitivity). Not applicable. 

 Method accuracy should range between 70 and 120 percent. Precision values should be less than 

or equal to 20 percent (coefficient of variation). The extraction efficiency of laboratory fortified 

controls is considered acceptable if the lower limit of the 95% confidence interval is greater than 

75%, unless otherwise specified by the Agency. These criteria were met 

 Information on recovery samples must be included in the study report. A complete set of field 

recoveries should consist of at least one blank control sample and three or more each of a lowlevel and high-level fortification. These fortifications should be in the range of anticipated residue 

levels in the field study. Total recovery from field-fortified samples must be greater than 50% for 

the study. These criteria were met. 

 Raw residue data must be corrected if appropriate recovery values are less than 90 percent. This 

criterion was not met. The study authors did not correct for field recoveries. However, the 

petitioner used a simple linear regression of % conversion vs. time to correct the chlorpyrifos 

concentrations. 

 Residues should be reported as μg pesticide active ingredient per sample and as an airborne 

concentration (μg/m3). Distributional data should be reported, to the extent possible. This 

criterion was met. 

 A sample history sheet must be prepared by the laboratory upon receipt of the samples. This 

criterion was met. 
Air Monitoring (2012)/Page 26 of 44 

Chlorpyrifos / 059101/ MRID 48883201 OPPTS 835.8100 / DACO 5.9a 

26 

APPENDIX A 

Indirect Method Regression Analysis 
Air Monitoring (2012)/Page 27 of 44 

Chlorpyrifos / 059101/ MRID 48883201 OPPTS 835.8100 / DACO 5.9a 

27 

Indirect Regression Analysis for Chlorpyrifos (Adjusted for Field Fortification) 

Location Measured concentration (μg/m3) Modeled concentration (μg/m3) 

OP - 0 0 0.000 

OP - 45 0 0.000 

OP - 90 1.67721 1.381 

OP - 135 7.75345 2.208 

OP - 180 11.41688 2.315 

OP - 225 0.01814 0.019 

OP - 270 0.00008 0.000 

OP - 315 0 0.000 

Linear Regression 

0.219083 0.168975 

0.036237 0.178115 

0.858993 0.427006 

36.55118 6 

Least Squares Regression 

0.237325 0 

0.030495 #N/A 

0.896401 0.423945 

60.56806 7 

Is LR Slope Sig.? Yes 

Is LR Intercept Sig.? No 

Is Intercept < 25 Per. No 

Is LSR Slope Sig.? Yes 

Flux 0.22 

Flux source Linear Regression 
Air Monitoring (2012)/Page 28 of 44 

Chlorpyrifos / 059101/ MRID 48883201 OPPTS 835.8100 / DACO 5.9a 

28 

Indirect Regression Analysis for Total Residues (Adjusted for Field Fortification) 

Location Measured concentration (μg/m3) Modeled concentration (μg/m3) 

OP - 0 0 0 

OP - 45 0 0 

OP - 90 1.67721 3.244886 

OP - 135 7.75345 4.758321 

OP - 180 11.41688 4.799108 

OP - 225 0.01814 0.018528 

OP - 270 0.00008 0 

OP - 315 0 0 

Linear Regression 

0.458671 0.406291 

0.087951 0.432297 

0.819261 1.036372 

27.19712 6 

Least Squares Regression 

0.502534 0 

0.073923 #N/A 

0.868456 1.027697 

46.21409 7 

Is LR Slope Sig.? Yes 

Is LR Intercept Sig.? No 

Is Intercept < 25 Per. No 

Is LSR Slope Sig.? Yes 

Flux 0.459 

Flux source Linear Regression 
Air Monitoring (2012)/Page 29 of 44 

Chlorpyrifos / 059101/ MRID 48883201 OPPTS 835.8100 / DACO 5.9a 

29 

APPENDIX B 

Integrated Horizontal Flux Method Meteorological Calculations
Air Mon

Chlorpyrifos / 059101/ MRID 48883201 OP

30 

IHF Method Meteorological Parameters for Chlorpyrifos and Total Residues 

Period 

Start End 

Duration 

(hours) 

Period Averaged Wind Speed m/s Regre

Date Time Date Time 15 cm 33 cm 55 cm 90 cm Slope 

2 9/9/2011 10:45 9/9/2011 13:00 2.25 0.44 0.56 0.63 0.74 0.16 3 9/9/2011 13:00 9/9/2011 19:00 6.00 0.79 1.11 1.23 1.59 0.42 4 9/9/2011 19:00 9/10/2011 1:00 6.00 0.31 0.44 0.57 0.74 0.23 5 9/10/2011 1:00 9/10/2011 7:00 6.00 0.23 0.36 0.48 0.62 0.22 6 9/10/2011 7:00 9/10/2011 19:00 12.00 0.55 0.76 0.94 1.14 0.33 7 9/10/2011 19:00 9/11/2011 7:00 12.00 0.92 1.18 1.40 1.69 0.43 8 9/11/2011 7:00 9/11/2011 19:00 12.00 0.60 0.83 0.97 1.17 0.31 9 9/11/2011 19:00 9/12/2011 7:00 12.00 0.55 0.77 0.94 1.14 0.33 

10 9/12/2011 7:00 9/12/2011 19:00 12.00 0.65 0.98 1.15 1.40 0.41 11 9/12/2011 19:00 9/13/2011 7:00 12.00 0.31 0.44 0.57 0.75 0.24 
Air Monitoring (2012)/Page 31 of 44 

Chlorpyrifos / 059101/ MRID 48883201 OPPTS 835.8100 / DACO 5.9a

31 

APPENDIX C 

Integrated Horizontal Flux Method Concentration Calculations
 Air Mon

Chlorpyrifos / 059101/ MRID 48883201 O

32 

IHF Method Concentration Parameters for Chlorpyrifos (Field Fortifications) 

Period 

Start End 

Duration 

(hours) 

Period Averaged Concentrations (μg m-3)1 

Date Time Date Time 15 cm 33 cm 55 cm 90 cm 150 cm 

2 9/9/2011 10:45 9/9/2011 13:00 2.25 31.419 25.804 22.213 17.929 12.935 3 9/9/2011 13:00 9/9/2011 19:00 6.00 17.652 15.768 12.746 9.644 7.153 4 9/9/2011 19:00 9/10/2011 1:00 6.00 10.750 10.308 7.459 5.673 2.699 5 9/10/2011 1:00 9/10/2011 7:00 6.00 8.064 6.772 5.340 3.392 1.679 6 9/10/2011 7:00 9/10/2011 19:00 12.00 5.255 4.828 3.714 3.011 2.073 7 9/10/2011 19:00 9/11/2011 7:00 12.00 0.683 0.614 0.446 0.371 0.269 8 9/11/2011 7:00 9/11/2011 19:00 12.00 1.173 1.010 0.793 0.679 0.425 9 9/11/2011 19:00 9/12/2011 7:00 12.00 0.594 0.507 0.385 0.269 0.167 

10 9/12/2011 7:00 9/12/2011 19:00 12.00 0.608 0.498 0.371 0.323 0.196 11 9/12/2011 19:00 9/13/2011 7:00 12.00 0.460 0.408 0.332 0.227 0.109 

1. As wind data were only provided up to 90 cm, only the concentration data up to 90 cm were used in generating the regression coefficients. 
 Air Mon

Chlorpyrifos / 059101/ MRID 48883201 O

33 

IHF Method Concentration Parameters for Total Residue (Field Fortifications) 

Period 

Start End 

Duration 

(hours) 

Period Averaged Concentrations (μg m-3) 1, 2 

Date Time Date Time 15 cm 33 cm 55 cm 90 cm 150 cm 

2 9/9/2011 10:45 9/9/2011 13:00 2.25 42.035 34.523 29.718 23.987 17.305 3 9/9/2011 13:00 9/9/2011 19:00 6.00 29.545 26.392 21.334 16.143 11.973 4 9/9/2011 19:00 9/10/2011 1:00 6.00 12.349 11.841 8.568 6.517 3.020 5 9/10/2011 1:00 9/10/2011 7:00 6.00 10.019 8.414 6.635 4.104 2.032 6 9/10/2011 7:00 9/10/2011 19:00 12.00 12.041 11.064 8.510 6.900 4.361 7 9/10/2011 19:00 9/11/2011 7:00 12.00 1.213 1.089 0.854 0.652 0.472 8 9/11/2011 7:00 9/11/2011 19:00 12.00 1.958 1.686 1.323 1.133 0.703 9 9/11/2011 19:00 9/12/2011 7:00 12.00 0.636 0.542 0.408 0.285 0.177 

10 9/12/2011 7:00 9/12/2011 19:00 12.00 1.754 1.437 1.060 0.923 0.560 11 9/12/2011 19:00 9/13/2011 7:00 12.00 0.752 0.612 0.499 0.341 0.164 

1. As wind data were only provided up to 90 cm, only the concentration data up to 90 cm were used in generating the regression coefficients. 2. This takes into account the toxicity adjustment factor of 12x. 
 Air Monitoring (2012)/Page 34 of 44 

Chlorpyrifos / 059101/ MRID 48883201 OPPTS 835.8100 / DACO 5.9a

34 

APPENDIX D 

Aerodynamic Flux Method Temperature and Wind Speed Calculations 
 Air Monitoring (2012)/Page 35 o

Chlorpyrifos / 059101/ MRID 48883201 OPPT

35 

AD Method Temperature Parameters for Chlorpyrifos and Total Residues 

Period 

Start End 

Duration 

(hours) 

Period Averaged Temperature oC Regression Coefficie

Date Time Date Time 15 cm 33 cm 55 cm 90 cm Slope Intercept 

2 9/9/2011 10:45 9/9/2011 13:00 2.25 29.7 29.4 29.4 29.0 -0.33 30.60 3 9/9/2011 13:00 9/9/2011 19:00 6.00 31.3 31.5 31.6 31.7 0.25 30.59 4 9/9/2011 19:00 9/10/2011 1:00 6.00 22.4 22.7 23.0 23.4 0.57 20.79 5 9/10/2011 1:00 9/10/2011 7:00 6.00 17.0 17.3 17.6 18.1 0.64 15.13 6 9/10/2011 7:00 9/10/2011 19:00 12.00 29.8 29.8 29.8 29.8 0.01 29.75 7 9/10/2011 19:00 9/11/2011 7:00 12.00 20.6 20.7 20.8 21.0 0.18 20.11 8 9/11/2011 7:00 9/11/2011 19:00 12.00 22.8 22.7 22.7 22.7 -0.06 22.94 9 9/11/2011 19:00 9/12/2011 7:00 12.00 17.7 17.8 17.9 18.1 0.26 16.93 

10 9/12/2011 7:00 9/12/2011 19:00 12.00 25.8 25.6 25.6 25.4 -0.20 26.34 11 9/12/2011 19:00 9/13/2011 7:00 12.00 17.4 17.7 17.9 18.2 0.45 16.18 

AD Method Wind Speed Parameters for Chlorpyrifos and Total Residues 

Period 

Start End 

Duration 

(hours) 

Period Averaged Wind Speed m/s Regression Coefficie

Date Time Date Time 15 cm 33 cm 55 cm 90 cm Slope Intercept 

2 9/9/2011 10:45 9/9/2011 13:00 2.25 0.44 0.56 0.63 0.74 0.16 -0.01 3 9/9/2011 13:00 9/9/2011 19:00 6.00 0.79 1.11 1.23 1.59 0.42 -0.37 4 9/9/2011 19:00 9/10/2011 1:00 6.00 0.31 0.44 0.57 0.74 0.23 -0.35 5 9/10/2011 1:00 9/10/2011 7:00 6.00 0.23 0.36 0.48 0.62 0.22 -0.38 6 9/10/2011 7:00 9/10/2011 19:00 12.00 0.55 0.76 0.94 1.14 0.33 -0.36 7 9/10/2011 19:00 9/11/2011 7:00 12.00 0.92 1.18 1.40 1.69 0.43 -0.27 8 9/11/2011 7:00 9/11/2011 19:00 12.00 0.60 0.83 0.97 1.17 0.31 -0.24 9 9/11/2011 19:00 9/12/2011 7:00 12.00 0.55 0.77 0.94 1.14 0.33 -0.35 

10 9/12/2011 7:00 9/12/2011 19:00 12.00 0.65 0.98 1.15 1.40 0.41 -0.47 11 9/12/2011 19:00 9/13/2011 7:00 12.00 0.31 0.44 0.57 0.75 0.24 -0.35 
 Air Monitoring (2012)/Page 36 of 44 

Chlorpyrifos / 059101/ MRID 48883201 OPPTS 835.8100 / DACO 5.9a

36 

APPENDIX E 

Aerodynamic Flux Method Concentration Calculations 
 Air Monitoring (2012)/Page 37 o

Chlorpyrifos / 059101 / MRID 48883201 OPPTS 835.8100 / DACO 5.9a

37 

AD Method Concentration Parameters for Chlorpyrifos (Field Fortifications) 

Period 

Start End 

Duration 

(hours) 

Period Averaged Concentrations (μg m-3)

1 Regression Coeffi

Date Time Date Time 15 cm 33 cm 55 cm 90 cm 150 cm Slope Intercept 

2 9/9/2011 10:45 9/9/2011 13:00 2.25 31.419 25.804 22.213 17.929 12.935 -7.45 51.76 3 9/9/2011 13:00 9/9/2011 19:00 6.00 17.652 15.768 12.746 9.644 7.153 -4.47 30.39 4 9/9/2011 19:00 9/10/2011 1:00 6.00 10.750 10.308 7.459 5.673 2.699 -2.95 19.38 5 9/10/2011 1:00 9/10/2011 7:00 6.00 8.064 6.772 5.340 3.392 1.679 -2.56 15.31 6 9/10/2011 7:00 9/10/2011 19:00 12.00 5.255 4.828 3.714 3.011 2.073 -1.29 8.96 7 9/10/2011 19:00 9/11/2011 7:00 12.00 0.683 0.614 0.446 0.371 0.269 -0.18 1.20 8 9/11/2011 7:00 9/11/2011 19:00 12.00 1.173 1.010 0.793 0.679 0.425 -0.29 1.97 9 9/11/2011 19:00 9/12/2011 7:00 12.00 0.594 0.507 0.385 0.269 0.167 -0.18 1.11 

10 9/12/2011 7:00 9/12/2011 19:00 12.00 0.608 0.498 0.371 0.323 0.196 -0.17 1.06 11 9/12/2011 19:00 9/13/2011 7:00 12.00 0.460 0.408 0.332 0.227 0.109 -0.13 0.82 

1. As wind and temperature data were only provided up to 90 cm, only the concentration data up to 90 cm were used in generating the regression coefficie

AD Method Concentration Parameters for Total Residues (Field Fortifications) 

Period 

Start End 

Duration 

(hours) 

Period Averaged Concentrations (μg m-3) 1,2 Regression Coe

Date Time Date Time 15 cm 33 cm 55 cm 90 cm 150 cm Slope Interce

2 9/9/2011 10:45 9/9/2011 13:00 2.25 42.035 34.523 29.718 23.987 17.305 -9.97 69.24 3 9/9/2011 13:00 9/9/2011 19:00 6.00 29.545 26.392 21.334 16.143 11.973 -7.48 50.87 4 9/9/2011 19:00 9/10/2011 1:00 6.00 12.349 11.841 8.568 6.517 3.020 -3.38 22.26 5 9/10/2011 1:00 9/10/2011 7:00 6.00 10.019 8.414 6.635 4.104 2.032 -3.23 19.19 6 9/10/2011 7:00 9/10/2011 19:00 12.00 12.041 11.064 8.510 6.900 4.361 -2.97 20.53 7 9/10/2011 19:00 9/11/2011 7:00 12.00 1.213 1.089 0.854 0.652 0.472 -0.32 2.12 8 9/11/2011 7:00 9/11/2011 19:00 12.00 1.958 1.686 1.323 1.133 0.703 -0.48 3.28 9 9/11/2011 19:00 9/12/2011 7:00 12.00 0.636 0.542 0.408 0.285 0.177 -0.20 1.19 

10 9/12/2011 7:00 9/12/2011 19:00 12.00 1.754 1.437 1.060 0.923 0.560 -0.49 3.08 11 9/12/2011 19:00 9/13/2011 7:00 12.00 0.752 0.612 0.499 0.341 0.164 -0.22 1.38 

1. As wind and temperature data were only provided up to 90 cm, only the concentration data up to 90 cm were used in generating the regressio

2. This takes into account the toxicity adjustment factor of 12x. 
 Air Monitoring (2012)/Page 38 of 44 

Chlorpyrifos / 059101 / MRID 48883201 OPPTS 835.8100 / DACO 5.9a

38 

APPENDIX F 

Total Residue Estimation 
 Air Mon

Chlorpyrifos / 059101 / MRID 48883201 O

39 

Period Sampler 

Sampler 

Flowrate 

(L/min) 

Chlorpyrifos 

(μg) 

Oxon 

(μg) 

Ratio of Total Oxon to Total 

Chlorpyrifos 

Revised 

Oxon 

(μg) 

Total 

Residue 

Adjusted 

for FF 

(μg)1 

Total 

Residue 

Adjusted 

for FF 

(μg/m3)1 

2 

A1 (15 cm) 1.076 3.630 0.082 

0.031581 

0.115 5.925 42.03 

B1 (33 cm) 1.047 2.901 0.082 0.092 4.735 34.52 C1 (55 cm) 1.029 2.473 0.083 0.078 4.037 29.72 D1 (90 cm) 1.081 2.097 0.086 0.066 3.423 23.99 E1 (150 cm) 1.043 1.470 0.064 0.046 2.399 17.31 

3 

A2 (15 cm) 1.011 5.266 0.21 

0.060431 

0.318 10.753 29.55 

B2 (33 cm) 1.022 4.766 0.169 0.288 9.732 26.39 C2 (55 cm) 1.018 3.827 0.256 0.231 7.815 21.33 D2 (90 cm) 1.026 2.928 0.274 0.177 5.979 16.14 E2 (150 cm) 1.047 2.210 0.239 0.134 4.513 11.97 

4 

A3 (15 cm) 1.014 3.206 0.015 

0.015332 

0.049 4.493 12.35 

B3 (33 cm) 0.993 3.012 0.032 0.046 4.221 11.84 C3 (55 cm) 0.980 2.157 0.035 0.033 3.023 8.57 D3 (90 cm) 0.980 1.636 0.048 0.025 2.293 6.52 E3 (150 cm) 1.027 0.751 0.035 0.012 1.117 3.02 

5 

A4 (15 cm) 0.992 2.367 0.051 

0.023382 

0.055 3.588 10.02 

B4 (33 cm) 1.008 2.020 0.047 0.047 3.062 8.41 C4 (55 cm) 1.004 1.582 0.042 0.037 2.398 6.63 D4 (90 cm) 1.005 0.926 0.022 0.022 1.489 4.10 E4 (150 cm) 1.011 0.461 0.01 0.011 0.741 2.03 

6 

A5 (15 cm) 1.015 3.146 0.258 

0.113496 

0.357 8.795 12.04 

B5 (33 cm) 1.007 2.864 0.273 0.325 8.007 11.06 C5 (55 cm) 1.018 2.230 0.252 0.253 6.235 8.51 D5 (90 cm) 1.016 1.802 0.247 0.205 5.038 6.90 E5 (150 cm) 1.016 1.139 0.239 0.129 3.184 4.36 

7 

A6 (15 cm) 1.018 0.378 0.024 

0.073153 

0.028 0.891 1.21 

B6 (33 cm) 1.023 0.341 0.023 0.025 0.804 1.09 C6 (55 cm) 1.022 0.267 0.021 0.020 0.630 0.85 D6 (90 cm) 1.015 0.221 0.018 0.016 0.478 0.65 E6 (150 cm) 1.017 0.160 0.014 0.012 0.346 0.47 
 Air Mon

Chlorpyrifos / 059101 / MRID 48883201 O

40 

Period Sampler 

Sampler 

Flowrate 

(L/min) 

Chlorpyrifos 

(μg) 

Oxon 

(μg) 

Ratio of Total Oxon to Total 

Chlorpyrifos 

Revised 

Oxon 

(μg) 

Total 

Residue 

Adjusted 

for FF 

(μg)1 

Total 

Residue 

Adjusted 

for FF 

(μg/m3)1 

8 

A7 (15 cm) 1.026 0.652 0.021 

0.063848 

0.042 1.446 1.96 

B7 (33 cm) 1.055 0.577 0.026 0.037 1.280 1.69 C7 (55 cm) 1.039 0.446 0.037 0.028 0.989 1.32 D7 (90 cm) 1.047 0.385 0.027 0.025 0.854 1.13 E7 (150 cm) 1.039 0.258 0.037 0.016 0.525 0.70 

9 

A8 (15 cm) 1.025 0.330 0.001 

0.011029 

0.004 0.469 0.64 

B8 (33 cm) 1.017 0.279 0.000 0.003 0.397 0.54 C8 (55 cm) 1.019 0.229 0.003 0.003 0.299 0.41 D8 (90 cm) 0.975 0.153 0.004 0.002 0.200 0.28 E8 (150 cm) 0.997 0.097 0.004 0.001 0.127 0.18 

10 

A9 (15 cm) 1.072 0.353 0.040 

0.170997 

0.060 1.353 1.75 

B9 (33 cm) 1.048 0.283 0.040 0.048 1.085 1.44 C9 (55 cm) 1.070 0.232 0.048 0.040 0.816 1.06 D9 (90 cm) 1.086 0.205 0.037 0.035 0.721 0.92 E9 (150 cm) 1.048 0.120 0.039 0.021 0.422 0.56 

11 

A10 (15 cm) 1.005 0.270 0.011 

0.050336 

0.014 0.544 0.75 

B10 (33 cm) 1.001 0.238 0.011 0.012 0.440 0.61 C10 (55 cm) 0.987 0.191 0.010 0.010 0.353 0.50 D10 (90 cm) 0.990 0.131 0.007 0.007 0.242 0.34 E10 (150 cm) 1.005 0.064 0.006 0.003 0.118 0.16 

1. This takes into account the toxicity adjustment factor of 12x.
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APPENDIX G 

Stability of Chlorpyrifos and Chlorpyrifos-oxon on Sorbent Tubes 
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The study authors reported that in a recent air monitoring study (Fenske et al., 2009) where chlorpyrifosoxon was analyzed in air samples, it was found that oxon could form on the air sampler sorbent resin. 

Fenske et al. examined the rate of conversion as a function of the starting chlorpyrifos concentration and 

sampler flow rate. However, by correcting for this conversion artifact, Fenske et al. could still not 

account for all of the oxon found and thus concluded that it had formed in the environment. 

To further examine these issues, the study authors spiked separate sets of sorbent tubes at 50, 500, and 

2000 ng chlorpyrifos, oxon and 3,5-6 tricloropyridinol (TCP) per tube. Sets were aged in a laboratory 

hood (ambient conditions, approximately 70°F)) for 6 and 12 hours, with half aged with airflow at 1 

L/min and the other half with no flow (each sample was run in triplicate). Duplicate spiked controls (nonaged) were also included. Tubes spiked with parent chlorpyrifos were analyzed for chlorpyrifos, 

chlorpyrifos-oxon and TCP. Tubes spiked with oxon were analyzed for oxon and TCP, and tubes spiked 

with TCP were analyzed for TCP only. As a result, TCP analyses were determined to be necessary during 

the course of analytical method validation, as chlorpyrifos-oxon was found to significantly convert to 

TCP on the sorbent material. 

Based on the sorbent tube analyses, study authors estimated correction factors of 1.1, 3.4 and 6.8% for 2, 

6 and 12 hour sampling periods, respectively. These correction factors were then applied to the analytical 

results for parent and oxon. For example, a measured chlorpyrifos concentration from a 12-hour sample 

period would be increased by a factor of 1.068 (6.8%) and the corresponding oxon reduced by same 

molar amount. Final oxon values were expressed as the sum of oxon and TCP values (with TCP in oxon 

molar equivalents). 

The raw data are presented below (Table G-1). This raw data was used to develop a regression equation 

to estimate the correction factors (see Figure G-1). 
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Table G-1. Storage Stability Data Used to Develop Correction Factors 

Sample Name Measure 

chlorpyrifos 

(μg/tube) 

Measure oxon 

(μg/tube) 

Total oxon, 

chlorpyrifos 

equivalents1

% oxon in CPF 

equivalents 

No flow 

L-c-sp1-50-nf-1 

L-c-sp1-50-nf-2 

L-c-sp1-50-nf-3 

0.040 

0.046 

0.044 

0 

0 

0 

0 

0 

0 

0 

0 

0 

L-c-sp1-500-nf-1 

L-c-sp1-500-nf-2 

L-c-sp1-500-nf-3 

0.432 

0.467 

0.449 

0 

0 

0 

0 

0 

0 

0 

0 

0 

L-c-sp1-2000-nf-1 

L-c-sp1-2000-nf-2 

L-c-sp1-2000-nf-3 

1.833 

1.910 

1.757 

0 

0 

0 

0 

0 

0 

0 

0 

0 

L-c-sp2-50-nf-1 

L-c-sp2-50-nf-2 

L-c-sp2-50-nf-3 

0.046 

0.047 

0.043 

0 

0 

0 

0 

0 

0 

0 

0 

0 

L-c-sp2-500-nf-1 

L-c-sp2-500-nf-2 

L-c-sp2-500-nf-3 

0.436 

0.539 

0.482 

0 

0 

0 

0 

0 

0 

0 

0 

0 

L-c-sp2-2000-nf-1 

L-c-sp2-2000-nf-2 

L-c-sp2-2000-nf-3 

1.890 

1.940 

1.894 

0 

0 

0 

0 

0 

0 

0 

0 

0 

6-hour flow period 

L-c-sp1-50-1 

L-c-sp1-50-2 

L-c-sp1-50-3 

0.040 

0.043 

0.046 

0 

0 

0 

0 

0 

0 

0 

0 

0 

L-c-sp1-500-1 

L-c-sp1-500-2 

L-c-sp1-500-3 

0.463 

0.458 

0.449 

0 

0 

0 

0 

0 

0 

0 

0 

0 

L-c-sp1-2000-1 

L-c-sp1-2000-2 

L-c-sp1-2000-3 

1.818 

1.824 

1.781 

0.039 

0.043 

0.044 

0.041 

0.045 

0.046 

2.25 

2.46 

2.58 

12-hour flow period 

L-c-sp2-50-1 

L-c-sp2-50-2 

L-c-sp2-50-3 

0.048 

0.048 

0.049 

0 

0 

0 

0 

0 

0 

0 

0 

0 

L-c-sp2-500-1 

L-c-sp2-500-2 

L-c-sp2-500-3 

0.408 

0.513 

0.485 

0.017 

0.020 

0.024 

0.041 

0.048 

0.056 

9.97 

9.33 

11.58 

L-c-sp2-2000-1 

L-c-sp2-2000-2 

L-c-sp2-2000-3 

1.760 

1.936 

1.845 

0.071 

0.061 

0.065 

0.074 

0.064 

0.068 

4.21 

3.28 

3.71 

1. Total oxon (chlorpyrifos equivalents) = total oxon * (350.59/334.52). 

Using the percent oxon (in CPF equivalents) values above as a function of aging time, the plot and regression shown 

below was produced. Although there is some difference in stability at the 12-hr aging period between spiking 

levels, there was not sufficient data to form a complete relationship with measured concentration (oxon was only 
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44 

detected at the highest spiking level at 6 hours), the data were combined to form the regression shown. Using the 

regression, the % correction factors were 1.1, 3.4 and 6.8% for 2, 6 and 12 hour sampling periods, respectively. 

Figure G-1. Regression Analysis for Correction Factors