Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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Executive Summary

Chlorpyrifos is an organophosphate class insecticide that is currently used for insect control on a 

variety of fruit, vegetable and field crops. The qualitative nature of the residue in plants and 

livestock is adequately understood mainly based on acceptable metabolism studies with cereal 

grain (corn), root and tuber vegetable (sugar beets), poultry and ruminant. The terminal residue 

of concern in/on plants and livestock is chlorpyrifos per se. Tolerances for residues of the 

insecticide chlorpyrifos per se, O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate, are 

established under the 40 CFR §180.342. 

The 2009 scoping document for chlorpyrifos registration review summarizes the status of the 

residue chemistry database based on the Reregistration Eligibility Decision (RED) and the 

mitigation measures addressed in the 2002 Interim Reregistration Eligibility Decision (IRED). 

Since the 2000 assessment new crop field trial studies have been submitted for cotton gin 

byproducts, tart cherries, aspirated grain fractions for soybean, sorghum and wheat, and grass 

forage and hay as part of a data call in related to the RED. These studies were reviewed 

previously and a discussion is included in this document for all the commodities with the 

exception of grass forage and hay (original petition withdrawn). In addition, petitions for a PHI 

reduction for sweet potato and the registration of a microencapsulated formulation were 

submitted but the requests were cancelled and denied, respectively. 

Currently, no petitions for the establishment of new tolerances for chlorpyrifos are pending. 

Moreover, the petitions 7F7248 (alfalfa, alfalfa mixed stands, grass grown for hay or pasture), 

3F4188 (barley grain and forage), and 3H5662 (barley, milling fractions) identified in the 2009 

scoping document were withdrawn in 07/May/2009. Studies for clover were not received as part 

of a Special Local Need action identified in the 2000 RED; therefore, tolerances for clover were 

not established in the CFR. 

Label restrictions prohibiting feeding of corn forage and stover to meat or dairy animals are not 

considered practical (D266564, S. Knizner, 20/June/2000). A revision to Section 3 labels of corn 

was performed and HED recommended removing pre-foraging and pre-grazing intervals from 

the labels (D338439, C. Swartz, 28/March/2007). Based on this the SLN label DE930004 may 

be revised to eliminate feeding restrictions. 

Adequate enforcement and multiresidue analytical methods are available for analysis of 

chlorpyrifos in crops, feed and animal commodities. Two data collections methods, a GC/MS 

and a HPLC/MS method, were used and adequately validated in conjunction with the analysis of 

samples for the field trials with cotton and tart cherries and for the processing study with cereal 

grains. For these methods, residues of chlorpyrifos are extracted with acetone/water and cleaned 

up using a C18 solid-phase extraction (SPE) column, and 13C2

15N-chlorpyrifos is added as an 

internal standard prior to analysis. Recoveries were within the acceptable range of 70-120%. 

The crop field trial data requested in the RED and submitted by the petitioner is considered 

adequate to establish a tolerance of 15 ppm for cotton gin byproducts and 22 ppm for aspirated 

grain fractions, and to keep the current tolerance for tart cherries under the condition that only 
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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dormant/delayed dormant and trunk spray applications remain on the label of the 75% WDG end 

use product. 

Studies submitted to support the registration of a new formulation of chlorpyrifos showed over 

tolerance residues after a foliar application of Lorsban 4E end use product to lemon with a rate of 

6 lb ai/A. The maximum residue observed in that study was at a concentration of 1.41 ppm 

which is over the current tolerance for citrus fruit (CG 10), 1.0 ppm. The label of the Lorsban 4E 

end use product (44.9% chlorpyrifos) allows a maximum application rate of 6.4 lb ai/A and 

addition of oil to the spray mixture. Under these conditions residues over tolerance may occur; 

therefore, HED recommends a reassessment of the tolerance for citrus fruit using lemon as the 

representative commodity. 

The dietary burden to livestock was recalculated to consider residues at tolerance level in the 

feedstock commodities (aspirated grain fractions and cotton gin by-products) included in this 

assessment and to use the most current version of Table 1 (OPPTS Test Guidelines 860.1000) 

released on June 2008. Based on the residues observed in the feeding study of cattle beef, dairy 

cow, swine and poultry at the 1x and/or 3x level, HED concludes that the possible residues 

observed on livestock commodities (from animals fed with feedstock that may contain residues 

resulting from legal applications) are covered by the current tolerances established in the 40 CFR 

§ 180.342. 

According OPPTS 860.1000 guideline several processing studies are required to establish a 

tolerance for food/feed items that correspond to RACs treated with chlorpyrifos. Processing 

studies are required for: cotton meal, hulls and refined oil; soybean meal, hulls and refined oil; 

and wheat hay. Moreover, the following tolerances can be reestablished to cover the processing 

studies required: corn milled byproducts as 0.1 ppm; and wheat milled byproducts as 1.5 ppm.

Regulatory Recommendations and Residue Chemistry Deficiencies

HED has the following regulatory recommendations:

1. Revise the corn and cotton use restrictions in the chlorpyrifos labels to eliminate feeding 

restrictions in treated areas. 

2. Tolerances for cotton gin byproducts and aspirated grain fractions are recommended. 

Cotton, gin byproducts ................................................. 15 ppm

Aspirated grain fractions ...............................................22 ppm

3. Maintain only dormant/delay dormant and trunk spray applications for tart cherries in the 

label of the 75% WDG end use product.

4. Revocation of the tolerance for lettuce is in process as uses of chlorpyrifos in this crop 

are not included in the label for the registered products.
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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5. Magnitude of the residue studies with lemon after application of Lorsban 4E and 75% 

WDG formulations separately to reassess the tolerance for the citrus fruit crop group.

6. Processing studies for:

a. Cotton meal, hulls and refined oil

b. Soybean meal, hulls and refined oil

7. Field trials to establish a tolerance for wheat hay.

8. Reestablish the tolerance for:

a. Corn milled by products as 0.1 ppm

b. Wheat milled by products as 1.5 ppm

9. EPA should inform the FDA about these illegal residues of chlorpyrifos detected in crops 

and catfish for them to take the appropriate action. 

10. Modification of the tolerance expression for chlorpyrifos in the 40 CFR § 180.342 to 

comply with the Interim Guidance for Writing Tolerance Expressions.

A revised human health risk assessment is being prepared as a separate document.
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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Background

Chlorpyrifos is an organophosphate class insecticide that is currently used for insect control on a 

variety of fruit, vegetable and field crops. Tolerances for residues for residues of the insecticide 

chlorpyrifos per se, O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate, are established 

under the 40 CFR §180.342. As stated in the scoping document, 3,5,6-trichloro-2-pyridinol 

(TCP) is no longer a residue of concern. On the other hand, the chlorpyrifos oxon was identified 

as a residue of concern in drinking water but not for plants or livestock.

Table 1. Chlorpyrifos Nomenclature.

Compound

O

P

S

N

Cl Cl

Cl OC2H5

OC2H5

Common name Chlorpyrifos

Company experimental name NA

IUPAC name O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate

CAS name O,O-diethyl O-(3,5,6-trichloro-2-pyridinyl) phosphorothioate

CAS registry number 2921-88-2

End-use product (EP) Lorsban 4E, Lorsban 75% WDG and Lorsban 50% WP (EPs used in the new 

studies submitted and included in this chapter)

Metabolite

Common Name TCP

IUPAC Name 3,5,6-trichloro-2-pyridinol

Metabolite

(Residue of Concern for 

Canada)

Common Name Chlorpyrifos Oxon

IUPAC Name O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphate

N OH

Cl Cl

Cl
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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Table 2. Physicochemical Properties of Chlorpyrifos.

Parameter Value Reference

Melting point/range 41.5-42.5 oC Chlorpyrifos IRED

pH NR

Density (21oC) 1.51 g/mL 

Water solubility (25°C) 1.05 mg/L

Solvent solubility (20°C) Acetone >400 g/L Dichloromethane >400 g/L

Methanol 250 g/L Ethyl acetate >400 g/L

Toluene >400 g/L n-hexane >400 g/L

Vapor pressure, mPa at 25oC 3.35

Dissociation constant, pKa NR

Octanol/water partition coefficient, 

Log(KOW)

4.7 

UV/visible absorption spectrum NR

NR – not reported.

860.1200 Directions for Use

Since the chlorpyrifos IRED, studies were submitted to establish tolerances in cotton gin 

byproducts and aspirated grain fractions after application of the 75% WG (EPA Reg. No. 62719-

301) and/or Lorsban 4E (EPA Reg. No. 62719-220) end use products. Moreover, a bridging 

study was submitted to compare residues in tart cherries after application of the 50% WP (EPA 

Reg. No. 62719-221) and 75% WG end use products. The use directions described in the label 

of the formulations used in these studies are described in Table 3.

Table 3. Summary of Directions for Use of Chlorpyrifos.

Applic. 

Timing, Type, 

and Equip.

Formulation

[EPA Reg. 

No.]

Applic. 

Rate 

(lb ai/A)

Max. No. 

Applic. 

per Season

Max. 

Seasonal 

Applic. Rate

(lb ai/A)

PHI

(days)

Use Directions and 

Limitations

Tart Cherries

Foliar Spray 50% WP 2 3 6 14

Dormant/Delay

ed Dormant 

Foliar Spray

75% WG 2 1 2 NA

Trunk Spray 

and/or Preplant 

Dip

75% WG 3 1 3 21

Cotton

Broadcast 

Foliar Spray

75% WG 1 3 3 14

Do not allow meat or 

dairy animals to graze in 

treated areas. Do not 

feed gin trash or treated 

forage to meat or diary 

animals.1

Lorsban 4E 1 3 3 14
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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Table 3. Summary of Directions for Use of Chlorpyrifos.

Applic. 

Timing, Type, 

and Equip.

Formulation

[EPA Reg. 

No.]

Applic. 

Rate 

(lb ai/A)

Max. No. 

Applic. 

per Season

Max. 

Seasonal 

Applic. Rate

(lb ai/A)

PHI

(days)

Use Directions and 

Limitations

Cereal Grains (For Aspirated Grain Fractions)

Sorghum

Postemergence 

broadcast 

foliar spray

75% WG 1 3 1.5 30 or 60 PHI is either 30-day or 

60-day if application 

rate is below or above 

0.5 lb ai/A, respectively. Lorsban 4E 1 3 1.5 30 or 60

Soybean

Postemergence 

broadcast 

foliar spray

75% WG 1 3 3 28

Do not allow meat or 

dairy animals to graze in 

treated areas or 

otherwise feed treated 

soybean forage, hay, and 

straw to these.

Lorsban 4E 1 3 3 28

Wheat

Foliar Spray Lorsban 4E 0.5 2 1

14 (forage 

and hay) 

or 28

(grain and 

straw)

Do not allow meat or 

dairy animals to graze or 

otherwise feed on 

treated forage within 14 

days of application.

1

Feeding restrictions to livestock can be eliminated from the corresponding labels.

Cherries - Chlorpyrifos formulated as either a 75% WDG (water dispersible granule) or 50% WP 

(wettable powder) was applied five times as broadcast foliar applications at 1.5-1.6 lb 

ai/A/application at RTIs of 10-14 days, for a total of 7.4-7.6 lb ai/A/season and a 14-day PHI. 

Applications were made using ground equipment and did not include any spray adjuvant. This 

use pattern differs from that included in the label of the 75% WDG and 50% WP end-use 

products, see Table 3. Only postemergence foliar applications are included in the label of the 

50% WP end-use product. Moreover, the maximum single and seasonal application rates 

included in the label are below those used in the crop field trials.

Cotton - Chlorpyrifos formulated as a 75% WDG and a 4 lb/gal EC was applied to cotton as 

broadcast foliar applications at ~1.0 lb ai/A/application, at RTIs of 10-14 days, for a total of 3.0-

3.1 lb ai/A/season, and a 14-day PHI. All applications were made using ground equipment and 

no adjuvants were added to the spray mixture. This corresponds to the use pattern described in 

the label of the 75% WDG and 4 lb/gal EC end-use products.

Cereal Grains – Chlorpyrifos was applied as 4 lb/gal EC and 75 % WDG formulations to 

soybean and sorghum, and only the EC formulation to wheat. Broadcast foliar applications were 

performed to the three crops. For soybean, 3 applications at rates totaling 3.0 lb ai/A/season (1x 

rate); for sorghum 2 applications at rates totaling 1.5 lb ai/A/season (1x rate); and for wheat 2 

applications at rates totaling 1.0 lb ai/A/season (1x rate) were used. The samples were harvested 

at 27-29 days after the last treatment (DAT). These use patterns correspond to those described in 

the label of the 75% WDG and 4 lb/gal EC end-use products with the exception that wheat 
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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forage and hay can be harvested 14 days after treatment.

Conclusions. For tart cherries, the label of the 50% WP end use product contains instructions for 

foliar application with a maximum seasonal rate of 6 lb ai/A and 14-day PHI. On the other hand, 

the current label for the 75% WDG end use product contain instructions for dormant/delay 

dormant and trunk spray applications to tart cherries with a maximum seasonal rate of 2 lb ai/A 

and 3 lb ai/A, respectively. These use patterns correspond to a lower maximum seasonal 

application rate than that used in the study submitted for tart cherries. For cotton, sorghum, 

soybean and wheat, the use pattern in the study submitted is equivalent to that described in the 

label of the 75% WDG and/or 4 lb/gal EC formulation. 

860.1300 Nature of the Residue – Plants and Livestock

D266564, S. Knizner, 20/June/2000

Plants - The qualitative nature of the residue in plants is adequately understood based on 

acceptable metabolism studies with cereal grain (corn) and root and tuber vegetable (sugar 

beets). The terminal residue of concern in/on plants is chlorpyrifos. The requirement of the 

metabolism study in a third crop (legume vegetable) was waived. Earlier metabolism studies 

with apples, dry beans, and soybeans, although not completely acceptable, provide supplemental 

data to elucidate the metabolism of chlorpyrifos in plants.

Livestock - The qualitative nature of residue in animals is adequately understood based on 

acceptable poultry and ruminant metabolism studies. The residue of concern in animals is 

chlorpyrifos. 

1 NA = Not Applicable

The database for determining residues of concern for chlorpyrifos is considered adequate and 

new studies haven’t been requested or submitted. However, the chlorpyrifos oxon has been 

characterized as having higher toxicity than chlorpyrifos. It is considered a residue of concern in 

drinking water based on it toxicity and because the oxon has been detected in environmental 

samples including surface water, precipitation, and air.

The chlorpyrifos oxon has not been identified as a residue of concern in plants. Previous 

metabolism studies in corn and sugar beet commodities (with PHIs longer than 38 days)

Table 4. Summary of Metabolites and Degradates to be included in the Risk Assessment and Tolerance 

Expression

Matrix Residues included in Risk 

Assessment

Residues included in 

Tolerance Expression

Plants

Primary Crop Chlorpyrifos parent only Chlorpyrifos parent only

Rotational Crop NA1 NA

Livestock

Ruminant Chlorpyrifos parent only Chlorpyrifos parent only

Poultry Chlorpyrifos parent only Chlorpyrifos parent only
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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characterize TCP as the major metabolite (D198040, S. Knizner, 15/Sep/1994). Other minor 

metabolites, hydrolyzable to TCP, were also identified. However, detection of the oxon is not 

reported. Two peer-reviewed articles report formation of the oxon in plants. A study of 

dislodgeable residues on citrus leaf report presence of the oxon after treatment with Lorsban

(Iwata et. al., J. Agric. Food Chem.). The chlorpyrifos oxon was not sought in the fruit, 

however, no residues from parent chlorpyrifos were reported above the limit of detection (0.03 

ppm) in the edible portion of the citrus fruit. Another study reports the presence of the 

chlorpyrifos oxon in tomatoes and green beans grown in greenhouses treated with Dursban at a 

rate of 1.5 lb ai/A (Martinez et. al., J. Agric. Food Chem.). The reported LOD was 0.012 ppm. 

The oxon appears in both crops only during the first 5 days after application with a maximum 

concentration of 0.21 ppm in green beans and 0.19 ppm in tomatoes at the 3rd day. In terms of 

the registered uses of chlorpyrifos, with the exception of asparagus (1-day PHI) and alfalfa (4-

day PHI in one of the 10 registered products), the shortest PHI established in the labels is 6 days.

However, most crops have PHIs longer than 14-days. Based on the short life of the chlorpyrifos 

oxon is unlikely that it may be present at significant concentration in the edible portions of the 

crops. Indeed, during 2008 and 2009 the United States Department of Agriculture monitoring 

program searched for the chlorpyrifos oxon in 17 commodities (including asparagus) for a total 

of 11041 samples being analyzed. Only one sample of potato showed presence of the oxon at 

trace levels, 0.003 ppm (the LOD was 0.002). However, there are no registered uses of 

chlorpyrifos on potato in the U.S.

In terms of exposure of livestock to feed commodities containing the oxon, toxicity studies show 

that the oxon is unstable and is rapidly deactivated through hydrolytic cleavage by a process 

called dearylation releasing TCP. Therefore, it may be expected that low levels of the oxon are 

metabolized before human consumption of livestock commodities. Indeed, it presence in was 

assessed in cattle and dairy cow feeding studies with unradiolabled material to preclude its 

presence (MRID 00095179). These studies showed absence of the oxon at all feeding levels. 

Conclusions. Based on the absence of evidence indicating that the chlorpyrifos oxon would be 

present in edible portions of the crops at periods longer than the registered PHIs, HED considers 

that it is not a residue of concern at this time. However, HED may reconsider this decision if 

monitoring data or new studies raise concern about the presence of the oxon at significant levels 

in plant or livestock commodities. 

860.1340 Residue Analytical Methods

Data Collection Methods

46640901.der, 46651201.der and 46651202.der

Tart Cherries

Cherry samples were analyzed for chlorpyrifos only, using two methods, a GC/MS method 

(GRM 02.03) using negative-ion chemical ionization and a newer HPLC/MS/MS method (GRM 

04.15) using electrospray as the interfase. All samples were analyzed using Method GRM 02.03 
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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and a subset of samples was also analyzed using GRM 04.15 in order to demonstrate the validity 

of the newer HPLC/MS/MS method. Both methods were adequately validated in conjunction 

with the analysis of field trial samples. In both methods, resides of chlorpyrifos are extracted 

with acetone/water (80:20) and centrifuged. For the GRM 02.03 method, the sample is

transferred to a C18 solid-phase extraction (SPE) column, eluted with acetonitrile/0.1 N HCl, 

diluted with 0.1 N HCl and extracted with isooctane containing 13C2

15N-chlorpyrifos as the 

internal standard. For the GRM 04.15 method, the internal standard is added first and then the 

sample is cleaned up using an on-line SPE column, methanol/water (60:40) is used to wash the 

column and then the sample is eluted with the mobile phase.

The above methods were validated in conjunction with the analysis of field trial samples using 

control samples of cherries fortified with chlorpyrifos at 0.01 to 1.0 ppm. Concurrent recoveries 

of chlorpyrifos were 73-93% (87 ± 3%), from fortified cherries analyzed using method GRM 

02.03, and recoveries of chlorpyrifos were 81-93% (87 ± 3%) from fortified cherries analyzed 

using Method GRM 04.15. The validated limit of quantitation (LOQ) is 0.01 ppm for both 

methods and the limit of detection (LOD) is 0.003 ppm. Comparison of samples analyzed for 

chlorpyrifos using the GC/MS and HPLC/MS methods indicated the two methods yielded similar 

residue values, with an r2of 0.9891. Adequate sample calculations and example chromatograms 

were provided.

Aspirated Grain Fractions

The HPLC/MS/MS method (GRM 04.15) described above was used to determine chlorpyrifos 

residues in/on grain and AGF are adequate for data collection. In conjunction with the analysis 

of treated samples, the above method was validated using control samples of grain and AGF 

fortified with chlorpyrifos at 0.01 and 1.0 ppm. Concurrent recoveries of chlorpyrifos averaged 

83-92% with standard deviations of 1-6%. No values were outside the acceptable 70-120% 

range. Apparent residues were <LOQ in all control samples. The validated method LOQ for 

chlorpyrifos is 0.01 ppm, and the LOD is 0.003 ppm. Adequate sample calculations and 

example chromatograms were provided.

Cotton gin by-products

Residues of chlorpyrifos were determined in gin trash using a HPLC/MS/MS method (GRM 

04.15). The method was adequately validated in conjunction with the field sample analyses. 

Concurrent recoveries of chlorpyrifos were 91±5% from gin trash fortified at 0.01-200 ppm. 

Apparent residues of chlorpyrifos were <LOQ in/on 3 controls and 0.02-0.12 ppm in/on 3 other 

controls. The method limit of quantitation (LOQ) is 0.01 ppm, and the limit of detection (LOD) 

is 0.003 ppm. Adequate samples calculations and example chromatograms were provided.

Conclusions. The residue analytical methods used for the analysis of samples in the studies 

under consideration are adequate based on the method recoveries, precision and the range of 

levels tested which included the LOQ, the current tolerance for tart cherries, the tolerance level

recommended for cotton gin byproducts and the residues observed in the samples used to 

calculate the tolerance recommended for AGF. 
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Enforcement Methods

D266564, S. Knizner, 20/June/2000

The Pesticide Analytical Manual (PAM) Volume II lists three methods (designated as Methods I, 

II and VI) for the enforcement of tolerances of chlorpyrifos in plant commodities. These are 

based on analysis of chlorpyrifos by Gas Liquid Chromatography (GLC) with flame photometric 

detection and a detection limit of 0.01 ppm. Three confirmatory procedures are listed as Method 

A. For the enforcement of tolerances in livestock commodities, PAM Vol. II lists Method IV 

which is based on the quantitation of chlorpyrifos by GLC with electron capture detection. The 

detection limit is 0.01 ppm. 

Conclusions. The methods in the PAM Volume II are adequate to analyze the residue of concern 

for tolerance enforcement purposes, chlorpyrifos only. The limit of detection of these methods is 

adequate to cover the lowest tolerance level included in the 40 CFR § 180.342 for detection of 

chlorpyrifos only, 0.01 ppm.

860.1360 Multiresidue Methods

D266564, S. Knizner, 20/June/2000

The FDA PESTDATA database dated 8/93 (PAM Vol. I, Appendix II) indicates that 

chlorpyrifos is completely recovered (>80%) using FDA multiresidue method protocols D 

(Section 232.4) and E (Section 212.1/232.1, nonfatty matrices) and partially (50-80%) recovered 

using multiresidue method protocol E (Section 211.1/232.1, fatty matrices).

Conclusions. The multiresidue methods in the PAM Volume I under protocol D and E are 

adequate to analyze the residue of concern for enforcement purposes, chlorpyrifos only. 

860.1380 Storage Stability

D266564, S. Knizner, 20/June/2000

46640901.der, 46651201.der and 46651202.der

Storage stability studies in a variety of crops, processed commodities and livestock commodities 

have been submitted and considered adequate as established in the RED. A summary of these 

studies is presented in Table 5.
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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TABLE 5. Summary of Storage Conditions for Chlorpyrifos.

Matrix 

(RAC)

Storage 

Temperature

(°C)

Longest Storage 

Duration from 

Sampling to 

Extraction

Interval of Demonstrated Storage Stability (months)

Cherry Field: Ambient

Processor: Frozen

Analytical 

Facility: -17±5

215 days 

(7.2 months) Oil seeds: Residues of chlorpyrifos are stable in/on 

almonds and almond hulls stored at -18 °C for 9 

months and in/on walnuts stored at -18°C for 4 years.

Non-oily grains: Residues of chlorpyrifos are stable 

in/on corn grain, forage, and fodder stored at -18 °C for 

27 months, in/on sweet corn fodder stored at -18 ° C 

for almost 3 years, and in/on sorghum grain, forage, 

and fodder stored at -18 °C for 3 months.

Root and bulb crops: Residues of chlorpyrifos are 

stable in/on sweet potatoes stored at -18 °C for 4 

months in/on sugar beet roots stored at -18 ° C for 

almost 4 years. and in/on onions stored at -23 °C for 15 

months.

Fruits and fruiting vegetables: Residues of chlorpyrifos 

are stable in/on apples, apricots, cherries, peaches, 

pears, and plums stored at -18 °C for 9 months, in/on 

whole bananas and banana pulp and peel stored under 

frozen storage conditions (temperature unspecified) for 

3 months, in/on tomatoes stored at -18 °C up to 29 

months, and in/on cherries stored at -23 °C for 15.6 

months, and in/on whole oranges stored at -18 C for 6 

months.

Low moisture content forage/hay: Residues of 

chlorpyrifos are stable in/on fresh and spent mint hay 

stored under frozen storage conditions (temperature 

unspecified) for 10 months and in/on alfalfa forage and 

hay stored at -18 °C for 12 months.

Processed commodities: Residues of chlorpyrifos are 

stable in orange peel and pulp stored at -18 ° C for 5-6 

months and in mint oil stored under frozen storage 

conditions (temperature unspecified) for 10 months.

Animal commodities: Residues of chlorpyrifos are 

stable in cattle tissues stored at -18 ° C for up to 41 

months and in milk stored at -18 °C for 49 months.

Cotton gin 

by-products

198 days

(6.6 months)

Grain and 

AGF

244 days 

(8.1 months)

The storage conditions and intervals of commodity samples used for tolerance establishment 

(cotton gin by-products and aspirated grain fractions) and reassessment (tart cherries) are 

supported by adequate storage stability data as follows: 
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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- Cherry samples were stored frozen for up to 215 days prior to extraction for analysis. 

Adequate storage stability data are available on cherries indicating that chlorpyrifos is 

stable at ≤-20 °C in cherries for at least 15.6 months. These data will support the frozen 

storage durations in the current cherry field trials.

- Gin trash samples were stored frozen for up to 198 days prior to extraction for analysis. 

Adequate storage stability data are available indicating that chlorpyrifos is stable at ≤-18 

°C in/on alfalfa forage and hay for at least 12 months. These data will support the 

frozen storage duration in the current cotton field trials.

- Grain and AGF were stored frozen for up to 244 days prior to extraction for analysis. 

Adequate storage stability data are available that indicate that residues of chlorpyrifos 

are stable in corn grain for up to 27 months. These data will support the frozen storage 

duration in the current field trials.

Conclusions. There are adequate storage stability data available in a wide variety of crops which 

can be applied or translated to validate sample storage conditions and durations of samples of tart 

cherries, cotton and aspirated grain fractions used in the studies being considered. In addition, as 

described in Table 5 and discussed in the RED, acceptable storage stability studies have been

conducted on representative oil seeds, non-oily grains, root crops, fruits and fruiting vegetables, 

low moisture content forage and hay, selected processed food/feed commodities, and in animal 

tissues and milk.

 

860.1400 Water, Fish, and Irrigated Crops

D326647, D. Drew, 07/Dec/2009

A petition to establish a tolerance in catfish was received based on the detection of chlorpyrifos 

in farm-raised Mississippi catfish as part of the Food and Drug Administration (FDA) 

aquaculture monitoring program. After considering the residue and usage data, HED contended 

that the likely source of residues in catfish may not be from catfish feed but from off-target drift 

from a nearby crop; therefore, a tolerance was not recommended. In 1994, the Mississippi 

Department of Agriculture and Commerce took action to reduce off-target drift by prohibiting 

the use of chlorpyrifos on cotton and limiting its use to ground applications only for many other 

crops. No detections of chlorpyrifos were reported between 2002 and 2005 by the Mississippi 

State Chemical Laboratory monitoring program. Currently, the USDA PDP data for 2008 and 

2009 shows 0.5% to 0.7% of detects in the USA ranging from 1 ppb to 2.8 ppb while the data for 

imported catfish shows 0% to 50% of detects ranging from ND to 38.2 ppb. 

Conclusions. EPA should inform the FDA about these illegal residues of chlorpyrifos detected 

in several crops and catfish for them to take the appropriate action. 
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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860.1460 Food Handling

D266564, S. Knizner, 20/June/2000

The RED established that reregistration requirements for magnitude of the residue of 

chlorpyrifos in food-handling establishments (FHE) are fulfilled. Results of submitted studies in 

FHE indicate that no detectable residues (<0.01 to <0.025 ppm) are likely to occur in food items. 

Currently, the 40 CFR 180.342 limits FHE uses of chlorpyrifos to spot and/or crack and crevice 

treatment. In addition, a tolerance of 0.1 ppm is established for residues of chlorpyrifos only, in 

or on food commodities in FHE with the exception of those commodities covered by a higher 

tolerance as a result of use on growing crops. At this time it appears that we have two 

chlorpyrifos containing products labeled for FHE use. However, BEAD reviewed more recent 

proprietary data (2008) for pesticide use in food handling establishments and found that chlorpyrifos 

use was not reported. However, they report a 2% use to provide an upper bound estimate of 

chlorpyrifos use in FHEs.

Conclusions. The requirements for chlorpyrifos formulations for use in FHE were previously 

assessed and considered fulfilled according to the current guidelines, OPPTS 860.1460. Since 

then new end use products for use in FHE haven’t been registered.

860.1480 Meat, Milk, Poultry, and Eggs

D266564, S. Knizner, 20/June/2000

MRID 00095179

There are presently no registered direct application uses of chlorpyrifos on livestock animals 

except for ear tag treatment of cattle. As established in the 2000 RED, residues in whole milk 

and fat resulting from ear tag use should not be a significant fraction of the residues resulting 

from intake of animal feeds containing chlorpyrifos. Uses of chlorpyrifos may result in residues 

in several feed commodities. Cattle, swine, dairy cow and poultry feeding studies were 

previously evaluated and found adequate to satisfy feeding study requirements (D266564, S. 

Knizner, 20/June/2000; and MRID 00095179). A conservative reassessment of the dietary 

burden was performed to consider residues at tolerance level in feedstock commodities (aspirated 

grain fractions and cotton gin by-products) included in this assessment and to use the most 

current version of Table 1 (OPPTS Test Guidelines 860.1000) released on June 2008. The

dietary burden estimated is considered a worst case scenario as the percent of crop treated is not 

included in the calculations.

For beef, a dietary burden of 6.56 ppm was calculated, see Table 6. In the cattle feeding study 

chlorpyrifos was administered daily to groups of three animals for 30 days at dry weight basis

levels of 0, 3 ppm (0.5x), 10 ppm (1.5x), 30 ppm (4.6x) or 100 ppm (15x). The dosing levels in 

the feeding study are appropriate to cover the beef dietary burden estimated based on current 

feeding practices. This study is also appropriate in terms of the tolerances established for cattle 

fat (0.3 ppm), cattle meat (0.05 ppm) and cattle meat byproducts (0.05 ppm) since residues of 
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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chlorpyrifos observed after dosing at the 10 ppm (1.5x) level were not detected (ND) in kidney, 

ND-0.03 ppm in liver, ND-0.02 ppm in muscle, and 0.07-0.16 ppm in fat. Therefore, the 

tolerances previously established cover possible residues in beef commodities. 

For dairy cattle, a dietary burden of 15.27 ppm was calculated. To assess residues in milk 

samples groups of three dairy cows were dosed on a daily basis for a period of two weeks with 

chlorpyrifos at levels of 0.3 ppm (0.02x), 1 ppm (0.7x), 3 ppm (0.2x), 10 ppm (0.7x) or 30 ppm

(2x). The dosing levels in the feeding study are appropriate to cover the dairy cattle dietary 

burden estimated based on current feeding practices. This study is also appropriate in terms of 

the tolerances established for milk fat (0.25 ppm) since residues of chlorpyrifos observed after 

dosing at the 30 ppm (2x) level were < 0.02 ppm in whole milk and < 0.15 ppm in cream. The 

tolerance for milk fat covers residues in whole milk which previously had a tolerance of 0.01 

ppm. Therefore, the current tolerance for milk fat covers possible residues in milk commodities. 

For swine, a dietary burden of 1.16 ppm was calculated. In the swine feeding study chlorpyrifos 

was administered to groups of 3 animals on a daily basis for a period of 30 days at levels of 0

ppm, 1 ppm (0.9x), 3 ppm (2.6x) or 10 ppm (8.6x). The dosing levels in the feeding study are 

appropriate to cover the swine dietary burden estimated based on current feeding practices. This 

study is also appropriate in terms of the tolerances established for hog fat (0.2 ppm), hog meat 

(0.05 ppm), hog meat byproducts (0.05 ppm) since residues of chlorpyrifos were not detected in 

swine muscle, liver and kidney at levels up to 3 ppm (2.6x) and were < 0.04 ppm in swine fat at a 

dose of 3 ppm (2.6x). Therefore, the tolerances previously established cover possible residues in 

hog commodities. 

For poultry, a dietary burden of 1.09 ppm was calculated. The poultry feeding study was 

performed by dosing groups of 36 birds for 30 days at levels of 0 ppm, 0.3 ppm (0.3x), 1 ppm

(0.9x), 3 ppm (2.8x) or 10 ppm (9.2x) of chlorpyrifos. Twenty four birds from each group were 

slaughtered and their muscle, liver, kidney and peritoneal fat analyzed for residues of 

chlorpyrifos while the remaining twelve birds were dosed for additional 15 days and their whole 

eggs analyzed. The dosing levels in the feeding study are appropriate to cover the poultry 

dietary burden estimated based on current feeding practices. This study is also appropriate in 

terms of the tolerances established for poultry fat (0.1 ppm), poultry meat (0.1 ppm), poultry 

meat byproducts (0.1 ppm), and eggs (0.01 ppm) since residues were not detected in whole eggs, 

poultry muscle, poultry liver, and poultry kidney at all dose levels and were <0.02 ppm in fat at a 

dose of 3 ppm (2.8x). Therefore, the tolerances previously established cover possible residues in 

poultry commodities. 

Based on concerns with the higher toxicity of chlorpyrifos oxon it’s important to mention that it 

was assessed in the cattle (limit of sensitivity of 0.05 ppm) and dairy cow (limit of sensitivity of 

0.01 ppm) feeding studies to preclude its presence. These studies showed absence of the oxon at 

all feeding levels.
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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Table 6. Calculation of maximum dietary burden for Chlorpyrifos.

Feed Commodity 

(Classification) Tolerance (ppm) % Dry Matter 1 % of Diet Burden (ppm)2

Beef Cattle

Aspirated Grain Fractions (CC) 22 85 5 1.29

Field Corn Grain (CC) 0.05 88 25 0.02

Beet Sugar Molasses (CC) 15 75 10 2.00

Sorghum, grain, grain (CC) 0.5 86 40 0.23

Field Corn Forage (R) 8 40 15 3.00

Soybean Meal (PC) 0.3 92 5 0.02

TOTAL 100 6.56

Dairy Cattle

Beet Sugar Molasses (CC) 15 75 10 2.00

Sorghum, grain, grain (CC) 0.5 86 25 0.15

Sweet Corn, cannery waste (CC) 8 30 10 2.67

Field Corn Forage (R) 8 40 45 9.00

Alfalfa, meal (PC) 13 89 10 1.46

TOTAL 100 15.27

Poultry

Wheat Grain (CC) 0.5 NA 75 0.375

Soybean Seed (PC) 0.3 NA 20 0.060

Alfalfa Meal (PC) 13 NA 5 0.650

TOTAL 100 1.09

Swine

Sorghum, grain, grain (CC) 0.5 NA 80 0.400

Wheat, milled by products (CC)3

1.5 NA 5 0.075

Alfalfa Meal (PC) 13 NA 5 0.650

Soybean Seed (PC) 0.3 NA 10 0.030

TOTAL 100 1.16

1

 As per Revised Table 1 (OPPTS Guideline 860.1000).

2

 Burden = [anticipated residue % DM] X % diet.

3

 Tolerance recommended for milling fractions excluding flour (pg 75, 2000 RED)

4 Tolerances in bold correspond to estimated residue based on translation of tolerances from similar commodities; 

from alfalfa hay to alfalfa meal, from soybean seed to soybean meal, and from sweet corn forage to sweet corn 

cannery waste.

5 

 Aspirated grain fractions provided a higher dietary burden to beef cattle but based on availability of feedstock it 

can’t be considered simultaneously with cotton gin byproducts, see Table 1 of 860.1000.

Conclusions. The calculated dietary burdens are covered by the dosing levels used in the feeding 

studies at a 1x level and two exaggerated levels 3x and about 10x for beef cattle, poultry and 

swine while for dairy cattle it covers the dosing levels up to 2x. Based on the residues observed 

in the feeding study of cattle beef, dairy cow, swine and poultry at the 1x level or higher, HED 

concludes that the possible residues observed on livestock commodities (feed with feedstock that 

may contain residues resulting from legal applications) are covered by the current tolerances 

established in the 40 CFR 180.342. 
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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860.1500 Crop Field Trials

D326647, D. Drew, 7/Dec/2009

D266564, S. Knizner, 20/Jun/2000

46651201.der and 46651202.der

The 2009 scoping document presents a summary of the status of the residue chemistry database 

after the 2000 RED and the mitigation measures addressed in the 2002 Interim Reregistration 

Eligibility Decision (IRED). Additional magnitude of the residue data were required in the RED 

for corn fodder and forage, cotton gin byproducts, clover and grasses grown for seed, aspirated 

grain fractions of sorghum, soybean and wheat, and cherries. Since the 2000 assessment some 

new crop field trial studies have been submitted for cotton gin byproducts, tart cherries, aspirated 

grain fractions for soybean, sorghum and wheat, and grass forage and hay as part of a data call in 

related to the RED. There has also been new petitions/label amendments submitted for Group 17 

alfalfa, alfalfa mixed stands and grass grown for hay or pasture, and barley. In addition, the 

IRED issued in February 2002 included mitigation measures addressing additional risks not 

included in the RED. Risk mitigation measures related to current uses included restricting use on 

apples to pre-bloom and dormant application resulting in a reduced tolerance, and the tolerance 

for grape was reduced to reflect domestic dormant application only. The following is a 

discussion of the status of the residue chemistry deficiencies and actions related to mitigation 

measures. 

Apart from deficiencies listed in the scoping document, new studies were submitted by the 

petitioner for label amendments related to sweet potato uses and a bridging study for a 

microencapsulated formulation. The studies for sweet potato (47122001 and 46995201) follow a 

request to reduce the labeled PHI (125 days) in the Lorsban 4E end use product. The petition for 

the review of these studies was cancelled in 29/June/2009. In addition, a bridging study to 

support the registration of a microencapsulated formulation was submitted but found inadequate 

(D373650, I. Negron, 23/Nov/2010); therefore, the registration of the new formulation was not 

granted. However, during this study Lorsban 4E end use product was applied as a foliar spray to 

lemon with a single application at a rate of 6 lb ai/A and the crop was harvested at a 35-day PHI. 

No adjuvant was added to the spray mixture. The maximum residue observed in that study was 

at a concentration of 1.41 ppm which is over the current tolerance for citrus fruit (CG 10), 1.0 

ppm. The label of the Lorsban 4E (44.9% chlorpyrifos) end use products allows a maximum 

application rate of 6.4 lb ai/A, addition of petroleum oil or citrus oil to the spray mixture and a 

PHI of 35-days (when the application rate is above 3.75 lb ai/A). Under these conditions 

residues over tolerance may occur; therefore, HED recommends a reassessment of the tolerance 

for citrus fruit using lemon (it’s the citrus that shows higher residues in the bridging study) as the 

representative commodity. Indeed, the studies used to establish the tolerance for citrus fruit were 

performed with oranges and grapefruit only. Moreover, these previous studies showed that 

higher residues are observed after using low application volumes; therefore, the formulation shall 

be applied with the lowest volume recommended in the label. Since this reassessment is for 
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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postemergence foliar applications its necessary to include the 75% WDG as a side-by-side trial

with Lorsban 4E. Three plots are recommended per field trial: (1) one application of Lorsban 4E

at the maximum single rate and 35-day PHI, (2) one application of 75% WDG at the maximum 

single rate and 35-day PHI, and (3) control. This would not reflect the maximum seasonal rate of 

7.5 lb ai/A but may yield higher residues than two applications at a lower rate since a RTI of 30 

days is established in the label.

As part of the mitigation efforts the tolerance for apple was reduced to 0.01 ppm to reflect prebloom and dormant applications only. In September 2007 a petition from IR-4 was received to 

amend the label of Lorsban 4E to include trunk treatment on apple trees (D310433 and D336586, 

M. Doherty, 18/Sep/2007). The residue data showed residues below 0.01 ppm in all control and 

treated samples; therefore, HED supported the label revision and tree trunk applications are 

currently allowed.

Currently, no petitions for the establishment of new tolerances for chlorpyrifos are pending. 

Moreover, the petitions 7F7248 (alfalfa, alfalfa mixed stands, grass grown for hay or pasture), 

3F4188 (barley grain and forage), and 3H5662 (barley, milling fractions) identified in the 2009 

scoping document were withdrawn in 07/May/2009. A magnitude of the residue study to 

establish a tolerance for wheat hay was required in the RED and has not been received. Studies 

for clover were not received as part of a Special Local Need action identified in the RED; 

therefore, tolerances for clover were not established in the CFR. 

For corn, label restrictions prohibiting feeding of forage and stover to meat or dairy animals are

not considered practical. Two SLN labels were identified in the RED as containing these 

restrictions, SLN DE930004 and FL 940003; however, the latter was cancelled. A revision to

Section 3 labels for corn was performed by HED to specify PHIs and resolve other discrepancies 

(D338439, C. Swartz, 28/March/2007). Label amendments were recommended to reflect the 

crop field trial use pattern. Moreover, pre-foraging intervals and pre-grazing intervals may be 

removed from the labels since tolerances for residues in corn forage and stover are included in 

the CFR. Based on this the SLN label DE930004 and all the labels for chlorpyrifos products 

may be revised to eliminate feeding restrictions.

The new crop field trial data submitted include magnitude of the residue or processing studies for 

sweet potatoes, grass forage and hay, cotton gin byproducts, tart cherries, and aspirated grain 

fractions (AGF) of soybean, sorghum and wheat. The studies for grass forage and hay were 

withdrawn with petition 7F7248 and no tolerances for these commodities are currently included 

in the CFR. Studies for cotton gin byproducts and tart cherries were reviewed and a summary is 

included in this section. Residue studies for cotton gin by products were requested in the RED 

since feeding restrictions established in the label are not considered practical. For tart cherries, 

the registrant committed to perform residue studies to show similarity between a water 

dissolvable granule (WDG) and the EC formulation. Chlorpyrifos and TCP residues were 

determined in the magnitude of residue studies for tart cherries, cotton gin by-products and 

aspirated grain fractions. However, since TCP was excluded as a residue of concern the 

following discussion will be limited to chlorpyrifos.

Tart Cherries
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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The number and geographic location of the tart cherry field trials are adequate. A total of 8 field 

trials conducted on tart cherries in 2004, with each field site consisting of a control plot and four 

treated plots using chlorpyrifos formulated as either a 75% WDG or 50% WP and applied as 

either concentrated sprays (43-54 gal/A) or dilute sprays (192-219 gal/A). In each test, 

chlorpyrifos was applied five times as broadcast foliar applications at 1.5-1.6 lb ai/A/application 

at RTIs of 10-14 days, for a total of 7.4-7.6 lb ai/A/season. Applications were made using 

ground equipment and did not include any spray adjuvant. A single control and duplicate treated 

samples of cherries were harvested from each site at 14 DAT, and at 0, 7, 14 and 21 DAT from 

the two concentrated spray tests at one location.

At 14 DAT, residues of chlorpyrifos in/on cherries treated with the 75% WDG were 0.14-1.70 

ppm for the concentrated sprays and 0.01-1.12 ppm for the dilute sprays. Residues of 

chlorpyrifos in/on tart cherries treated with the 50% WP were <0.01-0.41 ppm for the 

concentrated sprays and <0.01-0.25 ppm for the dilute sprays. Average chlorpyrifos residues 

were 0.48 and 0.39 ppm, respectively, from the concentrate and dilute sprays of the 75% WDG, 

and 0.12 and 0.11 ppm, respectively, from the concentrate and dilute sprays of the 50% WP. 

When data are pooled for the two application volumes, average chlorpyrifos residues are 0.43 

ppm for the 75% WDG and 0.11 ppm for the 50% WP, see Table 7. Residue decline data 

indicate residues of chlorpyrifos declined in the 21 days following application for concentrated 

applications of both the 75% WDG and 50% WP formulations.

The data show an insignificant difference in residue levels between the two application volumes. 

Residues were notably higher in the tests using the 75% WDG compared to the 50% WP. A 

tolerance of 2.0 ppm may be recommended based on the analysis of the 75%WDG formulation 

by using the OECD calculator. However, the current label for the 75% WDG end use product 

contains instructions for dormant/delay dormant and trunk spray applications with a maximum 

seasonal rate of 2 lb ai/A and 3 lb ai/A, respectively. These use patterns are not expected to 

result in residues at the levels observed in the current study after foliar application with a 

maximum rate of 7.5 lb ai/A. The label of the 50% WP end use product contains instructions for 

foliar application with a maximum seasonal rate of 6 lb ai/A and a 14-day PHI. This use pattern 

is covered by the current study which shows a maximum residue of 0.41 ppm which is covered 

by the current tolerance for tart cherries, 1.0 ppm. Since the data for tart cherries treated with a 

foliar spray of the 75% WDG formulation showed residues above tolerance, HED recommends 

to maintain only the dormant/delay dormant and trunk spray applications on the label of the 75% 

WDG end use product. The use pattern in the label of the 50% WP formulation is considered 

adequate.

Table 7. Summary of Residue Data from the Crop Field Trials with Chlorpyrifos (WDG or WP).

Commodity Total Applic. 

Rate

(lb ai/A)

PHI 

(days)

End-use 

Product

Residue Levels (ppm)1

n Mean Std. Dev. HAFT2 Min. Max.

Tart Cherry (proposed use = 6 lb ai/A total application rate, 14-day PHI)

Tart Cherry 7.4-7.6 14 75% WDG 32 0.43 0.38 1.56 0.01 1.70

50% WP 32 0.11 0.10 0.36 <0.01 0.41

1 The LOQ for Chlorpyrifos residues in/on cherry is 0.01 ppm. The LOD is 0.003 ppm. For calculation of the median, mean, 

and standard deviation, 1⁄2LOQ was used for samples with residues <LOQ.

2 HAFT = Highest Average Field Trial. 
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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Cotton gin by-products

The number and geographic location of the cotton field trials are adequate since for cotton gin 

byproducts three trials per each harvest method are required. The field trials were conducted in 

four locations during 2004 in Regions 6, 8, and 10. Side-by-side tests were conducted at each 

field site using chlorpyrifos formulated as a 75% WDG and a 4 lb/gal EC. Each formulation was 

applied to cotton at each site as three broadcast foliar applications at ~1.0 lb ai/A/application, at 

RTIs of 10-14 days, for a total of 3.0-3.1 lb ai/A/season. All applications were made using 

ground equipment at 11-17 gal/A, and no adjuvants were added to the spray mixture. A single 

control and duplicate treated samples of cotton were machine harvested from each test at 14 

DAT. The cotton was harvested using either a mechanical picker or stripper at two sites, and 

using both pickers and strippers at the remaining two sites, for a total of 3 tests each being 

harvested by mechanical pickers and strippers for each formulation. The cotton was then ginned 

to yield samples of gin trash.

Following broadcast applications of chlorpyrifos (WDG or EC) at rates totaling 3.0-3.1 lb 

ai/A/season, residue levels in gin trash were similar for the two types of formulations, but were 

substantially higher in gin trash from cotton harvested with a picker than cotton harvested with a 

stripper. At 14 DAT, residues of chlorpyrifos were 9.2-76.5 ppm in/on 12 samples of gin trash 

from picker-harvested cotton and 0.9-6.9 ppm in/on 12 samples of gin trash from stripperharvested cotton (Table 8). Average residues were 33.4 and 2.9 ppm, respectively, for gin trash 

from picker and stripper harvested cotton. A residue decline study was not conducted.

The use pattern in the study submitted is consider adequate as it is equivalent to that described in 

the label of the 75% WDG and 4 lb/gal EC formulation. The data obtained with the stripper is 

considered to set the tolerance for cotton gin byproducts since the cotton harvested with the 

stripper is the one used as a feed item. A tolerance estimate of 15 ppm is recommended by the 

OECD calculator, see appendix 1. 

Table 8. Summary of Residues from the Crop Field Trials with Chlorpyrifos (WDG or EC).

Commodity Total Applic. 

Rate

(lb ai/A)

Harvest 

Method 

PHI 

(days)

Residue Levels (ppm)1

n Mean Std. Dev. HAFT2 Min. Max.

Cotton (proposed use = 3 lb ai/A total application rate, 14-day PHI)

Gin Trash 3.0-3.1 Picker 14 12 33.4 25.5 66.7 9.2 76.5

Stripper 14 12 2.9 2.0 5.9 0.9 6.9

1 The LOQ for Chlorpyrifos is 0.01 ppm; and the LOD is 0.003 ppm. 

2 HAFT = Highest Average Field Trial. 

Conclusions. Based on the residues over tolerance observed after application of Lorsban 4E to 

lemon, HED recommends a reassessment of the tolerance for citrus fruit using lemon as the 

representative commodity. Magnitude of residue studies to establish a tolerance for wheat hay 

are required.
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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The number and location of field trials for tart cherries and cotton comply with the requirements 

of OPPTS 860.1500 guideline. The data are adequate to establish a tolerance of 15 ppm for 

cotton gin byproducts and to keep the current tolerance for tart cherries under the condition that 

only dormant/delayed dormant and trunk spray applications remain in the label of the 75% WDG 

end use product. The studies with tart cherries showed that residues decline with increase in 

DAT; therefore, at intervals longer than the PHI residues are not expected to be higher than the 

tolerance level established for tart cherries. 

860.1520 Processed Food and Feed

D266564, S. Knizner, 20/June/2000

46640901.der

As established in the 2000 RED, acceptable processing studies have been submitted and 

evaluated for apples, citrus, corn, cottonseed, fig, grapes, mint, peanuts, plums, soybeans, sugar 

beets, sugarcane, sunflowers, tomatoes, and wheat. The requirements for processing data on 

alfalfa meal were waived because residue data indicated that levels of chlorpyrifos per se were 

not likely to exceed the established tolerance in alfalfa hay following tests conducted according 

to registered uses. 

According to the revised version of Table 1 OPPTS 860.1000 several processing studies are 

required to establish a tolerance for feed items that correspond to RACs treated with 

chlorpyrifos. In addition, other processing studies are required for processed food commodities 

based on the same guideline. Tolerances are required for wheat milled byproducts and wheat 

hay. A tolerance was previously established for wheat milling fractions excluding flour as 1.5 

ppm. This tolerance should be reestablished as the tolerance for wheat milled byproducts. For 

corn milled byproducts a tolerance of 0.1 ppm was previously recommended based on 

concentration factors from 1.25x in grits to 2x in flour (D188151, S. Knizner, 20/Aug/1993). 

This tolerance should be established based on the importance of corn milled byproducts as a feed 

commodity based on the revised version of Table 1. For cotton, processing studies are required 

to establish tolerances in cotton meal, cotton hulls and refined oil. Similarly, for soybean, 

processing studies are required to establish tolerances in soybean meal, hulls and refined oil. 

Two processing studies were received as part of the current action. A non-guideline cooking 

study has been submitted to calculate processing factors for use in the dietary assessment (MRID 

45619801). Further discussion of this study is included in the dietary assessment supporting the 

current risk assessment (D388166, D. Soderberg, in process). The other “processing study” is

for the establishment of a tolerance for aspirated grain fractions (AGF) of soybean, sorghum and 

wheat. (Note: Although this study does provide a concentration factor for AGF, it is technically 

not processing studies since AGF are considered to be a RAC.) This study was requested in the 

RED since feeding restrictions established in the label are not considered practical. 

Aspirated Grain Fractions

Three field trials were conducted during 2004 to generate samples of chlorpyrifos-treated 

soybean seed, sorghum grain, and wheat grain for use in generating samples of aspirated grain 

fractions (AGF). In the soybean and sorghum trials, chlorpyrifos was applied in side-by-side 

tests using the 4 lb/gal EC and 75 % WDG formulations, and only the EC formulation was used 
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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in the wheat field trial. Chlorpyrifos was applied to soybeans as three broadcast foliar 

applications at rates totaling 3.0 lb ai/A/season (1x rate), to sorghum as two broadcast foliar 

application at rates totaling 1.5 lb ai/A/season (1x rate), and to wheat as two broadcast foliar 

applications at rates totaling 1.0 lb ai/A/season (1x rate). Single bulk samples of control and 

treated seeds/grain were harvested from each test at commercial maturity, 27-29 days after the 

last treatment (DAT). Following harvest, seeds and grain were processed into cleaned 

grain/seed and AGF using simulated handling procedures. 

Following three broadcast foliar applications of chlorpyrifos (4 lb/gal EC or 75% WDG) to 

soybeans at rates totaling 3.0 lb ai/A/season (1x rate), residues of chlorpyrifos were 0.015 and 

0.012 ppm from seeds harvested 29 DAT from plants treated with the WDG and EC 

formulations, respectively. Residues in the respective AGF samples were 0.74 and 1.029 ppm, 

for processing factors of 49x and 86x (average 68x). For sorghum, following two broadcast 

foliar applications of chlorpyrifos (4 lb/gal EC or 75% WDG) at rates totaling 1.5 lb ai/A/season 

(1x rate), residue of chlorpyrifos were 0.029 and 0.025 ppm in/on grain harvested 29 DAT from 

plants treated with the WDG and EC formulations, respectively. Residues in the respective AGF 

samples were 0.124 and 0.140 ppm, for processing factors of 4.3x and 5.6x (average 5x). For 

wheat, following two broadcast foliar applications of chlorpyrifos (4 lb/gal EC) at rates totaling 

1.0 lb ai/A/season (1x rate), residue of chlorpyrifos were 0.136 ppm in/on grain harvested 29 

DAT, and 1.616 ppm in/on wheat AGF, for a processing factor of 11.9x. The use patterns in the 

study submitted are considered adequate as they are equivalent to those described on the labels 

of the 75% WDG and 4 lb/gal EC formulations for foliar applications to soybean, sorghum and 

wheat. A tolerance can be established as 22 ppm for chlorpyrifos residues in/on aspirated grain 

fraction. This tolerance corresponds to the residue level estimated for soybean AGF which was 

the highest in comparison to 2 ppm for sorghum AGF and 3 ppm for wheat AGF. These residue 

levels were estimated by multiplying the maximum residue for the cereal grain (obtained from 

the magnitude of residue studies used to set the tolerance) with the highest concentration factor 

(obtained from the current study). 

Table 9. Residue Data from Grain and AGF Processing Study with Chlorpyrifos.

Crop End-Use 

Product

Commodity Total 

Rate

(lb ai/A) 

PHI 

(days)

Residues (ppm) 1 Processing 

Factor 

Soybean 75 % WDG RAC Grain

3.01 29

0.015, 0.015

[0.015] 2 NA

Grain 

(processor)3

0.037, 0.022

[0.029] NA

Clean Grain 0.014, 0.014

[0.014] 0.93x

AGF 0.740 49x

4 lb/gal EC RAC Grain

3.00 29

0.011, 0.012

[0.012] NA

Grain 

(processor)

0.011, 0.013

[0.012] NA

Clean Grain 0.010, (0.008)

[0.009] 0.75x

AGF 1.029 86x

Sorghum 75 % WDG RAC Grain 1.48 29 0.022, 0.035

[0.029] NA
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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Table 9. Residue Data from Grain and AGF Processing Study with Chlorpyrifos.

Crop End-Use 

Product

Commodity Total 

Rate

(lb ai/A) 

PHI 

(days)

Residues (ppm) 1 Processing 

Factor 

Clean Grain 0.014, 0.011

[0.013] 0.45x

AGF 0.124 4.3x

4 lb/gal EC RAC Grain

1.48 29

0.028, 0.022

[0.025] NA

Clean Grain 0.018, ND

[0.14] 0.56x

AGF 0.140 5.6x

Wheat 4 lb/gal EC RAC Grain

1.00 27

0.138, 0.134

[0.136] NA

Clean Grain 0.127, 0.139

[0.133] 0.98x

AGF 1.616 11.9x

1 The LOQ for each analyte is 0.01 ppm. The LOD is 0.003 ppm.

2 Average residues used to calculate processing factors are in brackets.

3

Samples of soybean seeds were also collected at the processor.

4 ND = not detectable, NA = not applicable

Conclusions. According to OPPTS 860.1000 several processing studies are required to establish 

a tolerance for food/feed items that correspond to RACs treated with chlorpyrifos. Processing 

studies are required for: cotton meal, hulls and refined oil; soybean meal, hulls and refined oil. 

Moreover, the following tolerances can be reestablished to cover the processing studies required: 

corn milled by products as 0.1 ppm; and wheat milled by products as 1.5 ppm.

Studies required under the OPPTS 860.1500 guidelines for the aspirated grain fractions of 

soybean, sorghum and wheat were performed. These studies are considered acceptable. A 

single tolerance of 22 ppm is recommended for aspirated grain fractions which cover residues on 

soybean, sorghum and wheat. 

860.1650 Submittal of Analytical Reference Standards

Analytical standards for the insecticide chlorpyrifos are to be kept available in the EPA National 

Pesticide Standards Repository. These analytical reference standards must be replenished as 

requested by the Repository. If requested, reference standards should be sent to the Analytical 

Chemistry Laboratory located in Fort Meade to the attention of Theresa Cole at the following 

address:

U.S. EPA

National Pesticide Standards Repository/ Analytical Chemistry Branch/OPP

701 Mapes Road

Fort George G. Meade, MD 20755-5350

Please note that mail will be returned if the entire extended zip code is not used when addressing 

correspondence to the Repository. 

860.1850 Confined Accumulation in Rotational Crops
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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D266564, S. Knizner, 20/June/2000

Confined rotational crops studies with chlorpyrifos haven’t been required or submitted since the 

RED. The studies discussed in the RED were based on the uptake of residues by lettuce, wheat 

and carrot after application of radio labeled chlorpyrifos to the soil at a rate of 4.8 lb ai/A and a 

plant back interval of 30 days. The TRR was above 0.01 ppm in all the rotational crops but the 

highest concentration of chlorpyrifos was 0.009 ppm.

860.1900 Field Accumulation in Rotational Crops

D266564, S. Knizner, 20/June/2000

Field trial studies with rotational crops haven’t been submitted. Based on the RED, a 30-day 

plant back interval for rotational crops is appropriate provided that all labels for chlorpyrifos 

containing products limit application to 5 lb ai/A on those crops where rotation to another crops 

could occur. Therefore, HED doesn’t require field rotational crop studies. 

860.1550 Proposed Tolerances

Previously, the Agency concluded that the TCP metabolite of chlorpyrifos is not of toxicological 

concern and no longer needs to be regulated, and therefore, it was excluded from the tolerance 

expression (D266564, S. Knizner, 20/June/2000). Currently, the tolerance levels included under

the 40 CFR §180.342 are amended to reflect residues of chlorpyrifos per se. However, as stated 

in the RED, for some crops the field trial used to establish tolerances for some of these 

commodities is based on combined residues of chlorpyrifos and TCP. In the absence of adequate 

data depicting residues of chlorpyrifos per se the established tolerances were maintained at the 

existing levels. The registrant may submit additional data depicting residues of chlorpyrifos per 

se if tolerance-level reductions are desired. 

The established or proposed tolerances for chlorpyrifos are included in Table 10. Chlorpyrifos 

tolerances are established under 40 CFR §180.342. On 27/May/2009 HED established interim 

guidance on writing tolerance expressions for enforcement purposes. In order to add clarity to 

the language used to establish the coverage of the tolerance expression and measurement of the 

level of the residue in the RACs the text in the 40 CFR § 180.342 should read: “(a) General. (1) 

Tolerances are established for residues of chlorpyrifos, including its metabolites and degradates, 

in or on the commodities in the table below. Compliance with the tolerance levels specified 

below is to be determined by measuring only chlorpyrifos (O,O-diethyl O-(3,5,6-trichloro-2-

pyridyl) phosphorothioate).”

Table 10. Tolerance Summary for Chlorpyrifos

Commodity Established/Proposed 

Tolerance (ppm)

Recommended 

Tolerance (ppm)

Comments

Correct Commodity Definition

Alfalfa, forage 3.0 3.0

Alfalfa, hay 13 13

Almond 0.2 0.2
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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Table 10. Tolerance Summary for Chlorpyrifos

Commodity Established/Proposed 

Tolerance (ppm)

Recommended 

Tolerance (ppm)

Comments

Correct Commodity Definition

Almond, hulls 12 12

Apple 0.01 0.01

Apple, wet pomace 0.02 0.02

Aspirated grain fractions NA 22

Banana 0.1 0.1

Beet, sugar, dried pulp 5.0 5.0

Beet, sugar, molasses 15 15

Beet, sugar, roots 1.0 1.0

Beet, sugar, tops 8.0 8.0

Cattle, fat 0.3 0.3

Cattle, meat 0.05 0.05

Cattle, meat byproducts 0.05 0.05

Cherry, sweet 1.0 1.0

Cherry, tart 1.0 1.0

Citrus, dried pulp 5.0 5.0

Citrus, oil 20 20

Corn, field, forage 8.0 8.0

Corn, field, grain 0.05 0.05

Corn, field, refined oil 0.25 0.25

Corn, field, stover 8.0 8.0

Corn, sweet, forage 8.0 8.0

Corn, sweet, kernel plus cob 

with husk removed

0.05 0.05

Corn, sweet, stover 8.0 8.0

Cotton, undelinted seed 0.2 0.2

Cotton, gin by-products NA 15

Cranberry 1.0 1.0

Cucumber 0.05 0.05

Egg 0.01 0.01

Fig 0.01 0.01

Fruit, citrus, group 10 1.0 1.0

Goat, fat 0.2 0.2

Goat, meat 0.05 0.05

Goat, meat byproducts 0.05 0.05

Hazelnut 0.2 0.2

Hog, fat 0.2 0.2

Hog, meat 0.05 0.05

Hog, meat byproducts 0.05 0.05

Horse, fat 0.25 0.25

Horse, meat 0.25 0.25

Horse, meat byproducts 0.25 0.25

Kiwifruit 2.0 2.0

Lettuce 1.0 Revoke1

Milk, fat (Reflecting 0.01 

ppm in whole milk)

0.25 0.25

Nectarine 0.05 0.05
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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Table 10. Tolerance Summary for Chlorpyrifos

Commodity Established/Proposed 

Tolerance (ppm)

Recommended 

Tolerance (ppm)

Comments

Correct Commodity Definition

Onion, bulb 0.5 0.5

Peach 0.05 0.05

Peanut 0.2 0.2

Peanut, refined oil 0.2 0.2

Pear 0.05 0.05

Pecan 0.2 0.2

Pepper 1.0 1.0

Peppermint, tops 0.8 0.8

Peppermint, oil 8.0 8.0

Plum, prune, fresh 0.05 0.05

Poultry, fat 0.1 0.1

Poultry, meat 0.1 0.1

Poultry, meat byproducts 0.1 0.1

Pumpkin 0.05 0.05

Radish 2.0 2.0

Rutabaga 0.5 0.5

Sheep, fat 0.2 0.2

Sheep, meat 0.05 0.05

Sheep, meat byproducts 0.05 0.05

Spearmint, tops 0.8 0.8

Spearmint, oil 8.0 8.0

Sorghum, grain, forage 0.5 0.5

Sorghum, grain, grain 0.5 0.5

Sorghum, grain, stover 2.0 2.0

Soybean, seed 0.3 0.3

Strawberry 0.2 0.2

Sunflower, seed 0.1 0.1

Sweet potato, roots 0.05 0.05

Turnip, roots 1.0 1.0

Turnip, tops 0.3 0.3

Vegetable, brassica, leafy, 

group 5

1.0 1.0

Vegetable, legume, group 6 

except soybean

0.05 0.05

Walnut 0.2 0.2

Wheat, forage 3.0 3.0

Wheat, grain 0.5 0.5

Wheat, straw 6.0 6.0

Tolerances with regional registrations

Asparagus 5.0 5.0

Grapes 0.01 0.01 Grape

1 The tolerance for lettuce will be revoked since no uses of chlorpyrifos on lettuce are included in the current labels.

Current US permanent tolerances for chlorpyrifos are listed in 40 CFR 180.342 are summarized 

and compared to international Maximum Residue Limits (MRLs) in Table 11. The CFR was 
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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updated to revoke/modify tolerances and to change the tolerance definition as chlorpyrifos per 

se. The Codex Alimentarius Commission and Canada have established MRLs for chlorpyrifos. 

Mexico adopts US tolerances and/or Codex MRLs for its export purposes. US tolerances and 

Codex MRLs are for residues of chlorpyrifos. Canada MRLs are based on the analysis of 

chlorpyrifos for some commodities and on both parent chlorpyrifos and its metabolite TCP 

(3,5,6-trichloro-2-pyridinol) for other commodities.

With the exception of apple commodities, harmonization with the Canada MRLs is not possible 

as the residue definition is for the combined residues of chlorpyrifos and TCP. Harmonization 

between the USA tolerances and Codex MRLs is only possible for corn, field, grain; cranberry; 

egg; sorghum, grain, grain; sorghum, grain, stover; and wheat, grain. In addition, two

commodities of the Leafy Vegetable (CG 5) can be harmonized with the Codex, head cabbage, 

and Chinese cabbage (type petsai). A summary of the US and international tolerances and MRLs 

is included in Table 11.

Table 11. Summary of US and International Tolerances and Maximum Residue Limits 

Residue Definition:

US Canada Mexico2 Codex3

40CFR180.342

chlorpyrifos per se ( O,O -

diethyl O -(3,5,6-trichloro-2-

pyridyl) phosphorothioate

O,O-diethyl-O-(3,5,6-trichloro-2-

pyridyl) phosphorothioate

(apples, grapes, tomatoes)

O,O-diethyl-O-(3,5,6- trichloro2-pyridyl) phosphorothioate, 

including the metabolite 3,5,6-

trichloro-2-pyridinol

(citrus fruits; fat, kidney, and

liver of cattle; kiwifruit; peppers; 

rutabagas; meat and meat 

byproducts of cattle (calculated 

on the fat content)

Chlorpyrifos. The 

residue is fat 

soluble. 

Commodity1, 4 Tolerance (ppm) /Maximum Residue Limit (mg/kg)

US Canada Mexico2 Codex3

Alfalfa, forage 3.0

Alfalfa, hay 13 5 alfalfa fodder

Almond 0.2 0.05

Almond, hulls 12

Apple 0.01 0.01 1 pome fruits

Apple, wet pomace 0.02

Aspirated grain fractions 22

Banana 0.1 2

Beet, sugar, dried pulp 5.0

Beet, sugar, molasses 15

Beet, sugar, roots 1.0 0.05

Beet, sugar, tops 8.0

Cattle, fat 0.3 1.0

Cattle, meat 0.05 1.0 1 (fat)
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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Table 11. Summary of US and International Tolerances and Maximum Residue Limits 

Cattle, meat byproducts 0.05 1.0 0.01 cattle, 

kidney and liver

Cherry, sweet 1.0

Cherry, tart 1.0

Citrus, dried pulp 5.0

Citrus, oil 20

Corn, field, forage 8.0

Corn, field, grain 0.05 0.05 0.05 maize

Corn, field, refined oil 0.25 0.2 maize oil, 

edible

Corn, field, stover 8.0 10 maize fodder 

(dry)

Corn, sweet, forage 8.0

Corn, sweet, kernel plus cob 

with husk removed

0.05 0.05 0.01 sweet corn 

(corn-on-the-cob)

Corn, sweet, stover 8.0

Cotton, undelinted seed 0.2 0.3 cotton seed

Cotton, gin by-products 15

Cranberry 1.0 1

Cucumber 0.05 0.05

Egg 0.01 0.01 (*)

Fig 0.01

Fruit, citrus, group 10 1.0 1.0 1

Goat, fat 0.2

Goat, meat 0.05

Goat, meat byproducts 0.05

Hazelnut 0.2

Hog, fat 0.2

Hog, meat 0.05 0.02 (fat)

Hog, meat byproducts 0.05 0.01 (*) pig, 

edible offal 

Horse, fat 0.25

Horse, meat 0.25

Horse, meat byproducts 0.25

Kiwifruit 2.0 2.0

Lettuce 1.0

Milk, fat (Reflecting 0.01 

ppm in whole milk)

0.25 0.02 milk

Nectarine 0.05 0.05

Onion, bulb 0.5 0.2

Peach 0.05 0.05 0.5

Peanut 0.2

Peanut, refined oil 0.2

Pear 0.05 1 pome fruits

Pecan 0.2 0.05 (*)
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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Table 11. Summary of US and International Tolerances and Maximum Residue Limits 

Pepper 1.0 1.0 2 peppers sweet 

including pimento 

or pimiento); 20 

peppers chili, 

dried

Peppermint, tops 0.8

Peppermint, oil 8.0

Plum, prune, fresh 0.05 0.5 plums 

(including prunes)

Poultry, fat 0.1

Poultry, meat 0.1 0.01 (fat) 

Poultry, meat byproducts 0.1 0.01 (*) poultry, 

edible offal

Pumpkin 0.05

Radish 2.0

Rutabaga 0.5 0.5

Sheep, fat 0.2

Sheep, meat 0.05 1 (fat)

Sheep, meat byproducts 0.05 0.01 sheep, edible 

offal

Spearmint, tops 0.8

Spearmint, oil 8.0

Sorghum, grain, forage 0.5

Sorghum, grain, grain 0.5 0.5

Sorghum, grain, stover 2.0 2 sorghum straw 

and fodder, dry

Soybean, seed 0.3 0.1 soya bean 

(dry)

Strawberry 0.2 0.3

Sunflower, seed 0.1 0.1

Sweet potato, roots 0.05

Turnip, roots 1.0

Turnip, tops 0.3

Vegetable, brassica, leafy, 

group 5

1.0 2 Broccoli 

1 Cabbages, head 

0.05 Cauliflower 

1 Chinese 

cabbage (type petsai)

Vegetable, legume, group 6 

except soybean

0.05 0.05 lentils 0.01 common 

bean (pods and/or 

immature seeds); 

peas (pods and 

succulent=immat

ure seeds)

Walnut 0.2 0.05 (*)

Wheat, forage 3.0
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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Table 11. Summary of US and International Tolerances and Maximum Residue Limits 

Wheat, grain 0.5 0.5

Wheat, straw 6.0 5 wheat straw and 

fodder, dry

MRLs with No US Equivalents

Grapes 0.01 0.5

Tomatoes 0.01

Carrot 0.1

Coffee beans 0.05

Cotton seed oil, crude 0.05 (*)

Cotton seed oil, edible 0.05 (*)

Dried grapes (=currants, 

raisins and sultanas) 0.1

Potato 2

Rice 0.5

Soya bean oil, refined 0.03

Tea, green, black (black, 

fermented and dried) 2

Wheat flour 0.1

Completed: M. Negussie; 04/12/2011

1

Includes commodities listed in the CFR as of today. 

2 Mexico adopts US tolerances and/or Codex MRLs for its export purposes.

3 * = absent at the limit of quantitation; Po = postharvest treatment, such as treatment of stored grains. PoP = 

processed postharvest treated commodity, such as processing of treated stored wheat. (fat) = to be measured on the 

fat portion of the sample. MRLs indicated as proposed have not been finalized by the CCPR and the CAC.

4 Commodities with new or reassessed tolerances being proposed are in bold.

(c) Tolerances with regional registrations. Tolerances with regional registration, as defined in 180.1(m), are 

established for residues of the pesticide chlorpyrifos per se ( O,O -diethyl- O -(3,5,6-trichloro-2-pyridyl) 

phosphorothioate) in or on the following food commodities:

A list of the guideline requirements is included in Table 12. Studies submitted after the RED and 

Commodity Parts per million Canada Codex

Asparagus 5.0

Grape 0.01 0.01 0.5
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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those corresponding to dietary burden calculations were assessed against the current guidelines 

for this registration review action. The remaining data was reassessed in the RED according to 

the corresponding OPPTS guideline. Therefore, a reassessment is not needed at this time since 

the OPPTS guidelines are applicable. 

Table 12. Residue Chemistry Science Assessment for the Registration Review of Chlorpyrifos.

GLN Data Requirements Current 

Tolerances 

(ppm)

[40 CFR]

Additional 

Data 

Needed?

References (list all MRIDs 

associated with each GLN)

860.1200: Directions for use NA Yes1

860.1300: Plant Metabolism NA No2

860.1300: Animal Metabolism NA No3

860.1340: Residue Analytical Methods NA No3

860.1380: Storage Stability NA No3

860.1500: Magnitude of the Residue in 

Plants

Almond 0.2 No3

Apple 0.01 No3

Banana 0.1 No3

Beet, sugar, roots 1.0 No3

Beet, sugar, tops 8.0 No3

Cherry, sweet 1.0 No3

Cherry, tart 1.0 No3

Citrus, oil 20 No3

Cotton, refined oil TBD Yes7

Corn, field, grain 0.05 No3

Corn, field, refined oil 0.25 No3

Corn, sweet, kernel plus cob with husk 

removed

0.05

No3

Cranberry 1.0 No3

Cucumber 0.05 No3

Fig 0.01 No3

Fruit, citrus, group 10 1.0 Yes4

Hazelnut 0.2 No3

Kiwifruit 2.0 No3

Lettuce 1.0 No8

Nectarine 0.05 No3

Onion, bulb 0.5 No3
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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Table 12. Residue Chemistry Science Assessment for the Registration Review of Chlorpyrifos.

GLN Data Requirements Current 

Tolerances 

(ppm)

[40 CFR]

Additional 

Data 

Needed?

References (list all MRIDs 

associated with each GLN)

Peach 0.05 No3

Peanut 0.2 No3

Peanut, refined oil 0.2 No3

Pear 0.05 No3

Pecan 0.2 No3

Pepper 1.0 No3

Peppermint, tops 0.8 No3

Peppermint, oil 8.0 No3

Plum, prune, fresh 0.05 No3

Pumpkin 0.05 No3

Radish 2.0 No3

Rutabaga 0.5 No3

Spearmint, tops 0.8 No3

Spearmint, oil 8.0 No3

Sorghum, grain, grain 0.5 No3

Soybean, refined oil TBD Yes7

Soybean, seed 0.3 No3

Strawberry 0.2 No3

Sunflower, seed 0.1 No3

Sweet potato, roots 0.05 No3

Turnip, roots 1.0 No3

Turnip, tops 0.3 No3

Vegetable, brassica, leafy, group 5 1.0 No3

Vegetable, legume, group 6 except 

soybean

0.05

No3

Walnut 0.2 No3

Wheat, grain 0.5 No3

860.1520: Magnitude of the Residues in 

Processed Food/Feed

Alfalfa, forage 3.0 No3

Alfalfa, hay 13 No3

Almond, hulls 12 No3

Apple, wet pomace 0.02 No3

Aspirated grain fractions NA No546640901

Beet, sugar, dried pulp 5.0 No3

Beet, sugar, molasses 15 No3

Citrus, dried pulp 5.0 No3

Corn, field, forage 8.0 No3

Corn, field, stover 8.0 No3

Corn, milled byproducts NA No6

Corn, sweet, forage 8.0 No3

Corn, sweet, stover 8.0 No

3

Cotton, undelinted seed 0.2 No3

Cotton, gin by-products NA No546651202
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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Table 12. Residue Chemistry Science Assessment for the Registration Review of Chlorpyrifos.

GLN Data Requirements Current 

Tolerances 

(ppm)

[40 CFR]

Additional 

Data 

Needed?

References (list all MRIDs 

associated with each GLN)

Cotton, meal TBD Yes7

Cotton, hulls TBD Yes7

Sorghum, grain, stover 2.0 No3

Sorghum, grain, forage 0.5 No3

Soybean, meal TBD Yes7

Soybean, hulls TBD Yes7

Wheat, hay TBD Yes7

Wheat, forage 3.0 No3

Wheat, milled byproducts NA No6

Wheat, straw 6.0 No3

860.1480: Magnitude of the Residue in 

Meat, Milk, Poultry, and Eggs (Revised 

version of Table 1approved in 2008)

Cattle, fat 0.3 No3

Cattle, meat 0.05 No3

Cattle, meat byproducts 0.05 No3

Egg 0.01 No3

Goat, fat 0.2 No3

Goat, meat 0.05 No3

Goat, meat byproducts 0.05 No3

Hog, fat 0.2 No3

Hog, meat 0.05 No3

Hog, meat byproducts 0.05 No3

Horse, fat 0.25 No3

Horse, meat 0.25 No3

Horse, meat byproducts 0.25 No3

Milk, fat (Reflecting 0.01 ppm in whole 

milk)

0.25

No3

Poultry, fat 0.1 No3

Poultry, meat 0.1 No3

Poultry, meat byproducts 0.1 No3

Sheep, fat 0.2 No3

Sheep, meat 0.05 No3

Sheep, meat byproducts 0.05 No3

860.1460: Magnitude of the Residue in

Food-Handling Establishments No3

860.1850: Rotational Crops (Confined) No3

860.1900: Rotational Crops (Field) No3
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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1 Label revisions are required for some crops and are noted in appropriate crop section.

2 NA = Not Applies, TBD = To be determined.

3 Was reassessed in the RED according to the current version of the OPPTS guidelines, refer to the RED 

for more information.

4 Crop field trials are needed to reassess the tolerance for citrus fruits due to residues over tolerance 

observed during the bridging study for the microencapsulated formulation. 

5 New crop field trials to support this tolerance were submitted as DCIs from the RED and reviewed in 

this chapter against the current OPPTS guidelines. A tolerance of 22 ppm is recommended for AGF and 

15 ppm for cotton gin byproducts.

6 A tolerance of 0.1 ppm for corn milled byproducts and 1.5 ppm for wheat milled by products should be 

reestablished based on processing studies requirements. Refer to the RED to find a reference to the value 

recommended.

7

Processing studies are required for these commodities based on OPPTS 180.1000 guideline.

8 Tolerance to be revoked based on the absence of chlorpyrifos end use products registered to uses on 

lettuce.
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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References

S. Knizner, Chlorpyrifos. Revised Product and Residue Chemistry Chapters of the HED Chapter 

of the RED. Chemical Number 059101., D266564, 20/June/2000.

D. Drew, W. Britton, J. Doherty, Chlorpyrifos. Revised Human Health Assessment Scoping 

Document in Support of Registration Review, D361144, 09/Feb/2009.

D. Soderberg, Chlorpyrifos. Acute Dietary Risk Assessment for Chlorpyrifos. Revised after 

Public Comments., D263890, 22/June/2000

J. Ellenberger, Chlorpyrifos in or on Wheat. Evaluation of analytical method and residue data., 

20/Jan/1984

S. Knizner, Magnitude of the Residue in Onions and Corn Processed Commodities, D188151, 

18/Aug/1993.

J. Morales, Chlorpyrifos. Magnitude of the Residue of Chlorpyrifos and 3,5,6-Trichloro-2-

pyridinol (TCP) in Tart Cherries., D322077, 23/Aug/2006.

J. Morales, Chlorpyrifos. Magnitude of the Residue of Chlorpyrifos and 3,5,6-Trichloro-2-

pyridinol (TCP) in in Aspirated Grain Fractions of Soybean, Sorghum, and Wheat., D322077, 

23/Aug/2006.

J. Morales, Chlorpyrifos. Magnitude of the Residue of Chlorpyrifos and 3,5,6-Trichloro-2-

pyridinol (TCP) in Cotton Gin By-Products., D322077, 23/Aug/2006.

J.L. Martínez Vidal, F.J. Egea Gonzalez, M. Martínez Galera, M. L. Castro Cano, Diminution of 

Chlorpyrifos and Chlorpyrifos Oxon in tomatoes and Green Beans Grown in Greenhouses, J. 

Agric. Food Chem., 1998, v. 46, 1440.

Y. Iwata, J.R. O’Neal, J. H. Barkley, R. M. Dinoff, M. E. Düsch, Chlorpyrifos Applied to 

California Citrus: Residue Levels on Foliage and on and in Fruit, J. Agric. Food Chem., 1983, v. 

31, 603. 

S. Knizner, Chlorpyrifos. Product Chemistry Chapter and Residue Chemistry Chapter for the

Reregistration Eligibility Document, D198040, 15/Sep/1994.

C. Swartz, Chlorpyrifos: Revisions to Section 3 Labels for Corn., D338439, 28/March/2007.

M. A. Doherty, Chlorpyrifos – Use as a Spray on Apple Tree Trunks. Residue Chemistry 

Considerations., D310433 and D336586, 18/Sept/2007.

D. Drew, Chlorpyrifos. Proposed Tolerance for Residues in Catfish, D326647, 07/Dec/2009.
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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MRID 00095179, Section D.4.0.0, Residues of Chlorpyrifos, its Oxygen Analog and 3,5,6-

Trichloro-2-pyridinol in Plant Tissues and in Tissues of Animals and Poultry Fed Chlorpyrifos in 

Their Diet, 28/May/1982.

MRID 00095270, Residues of Chlorpyrifos and 3,5,6-Trichloro-2-pyridinol in or on Soybean 

Receiving Multiple Applications of Lorsban Insecticide, P.W. Miller, 31/July/1979.

S. Knizner, Chlorpyrifos. Sunflower Seed Processing Study and Sorghum Grain Magnitude of 

the Residue Study., D201562, 23/May/1994.

M. T. Flood, Chlorpyrifos in/on Wheat and Wheat Processed Products. Anticipated Residues., 

D176971, 11/Aug/1992.
Chlorpyrifos Summary of Analytical Chemistry and Residue Data D388164

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Appendix 1: MRL Estimate by the OECD Calculator: Chlorpyrifos in/on Cotton Gin 

ByProducts 

Chemical: Chlorpyrifos

Crop: Cotton, Gin ByProducts

Region/Country: TX and CA / USA

GAP: 7.6 lb ai/A

Total number of data (n) 6

Percentage of censored data 0%

Number of non-censored data 6

Lowest residue 0.945

Highest residue 5.850

Median residue 2.250

Mean 2.908

Standard deviation (SD) 2.053

Correction factor for censoring (CF) 1.000

Proposed MRL estimate

- Highest residue 5.850

- Mean + 4 SD 11.119

- CF x 3 Mean 8.723

Unrounded MRL 11.119

Rounded MRL 15

High uncertainty of MRL estimate.

[Small dataset]

Template Version November 2003