UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

 WASHINGTON, D.C. 20460

 OFFICE OF

PREVENTION, PESTICIDES AND

TOXIC SUBSTANCES

CERTIFIED MAIL

Dear Registrant:

This is to inform you that the Environmental Protection Agency (hereafter referred to as EPA or

the Agency) has completed its “Report of FQPA Tolerance Reassessment Progress and Interim Risk

Management Decision (TRED) for chlorpropham”. A Notice of Availability, allowing public comment

for a 30-day period, will be published in the Federal Register (FR) shortly. This TRED, which was

approved on July 19, 2002, contains the Agency’s decision on chlorpropham.

The Federal Food, Drug and Cosmetic Act (FFDCA), as amended, requires EPA to reassess

all the tolerances for registered chemicals in effect on or before the date of the enactment of the Food

Quality Protection Act (FQPA) in August of 1996 against the new safety standard adopted in the

FQPA. In reassessing these tolerances, the Agency must consider, among other things, aggregate risks

from non-occupational sources of pesticide exposure, whether there is increased susceptibility to infants

and children, and the cumulative effects of pesticides with a common mechanism of toxicity. The

tolerances are considered reassessed once the safety finding has been made or a modification or

revocation occurs. A reregistration eligibility decision (RED) for chlorpropham, was finalized and

signed on August 1, 1996, prior to FQPA enactment. Therefore, it needed to be updated to reassess

the tolerances under the FQPA standard.

The Agency has evaluated the dietary risk associated with chlorpropham and has determined

that provided the Special Local Need registration (SLN) for Easter lily bulb use is amended to reduce

the maximum rate of application from 3.99 lb a.i./A to 2.0 lb a.i./A as agreed upon by stakeholders,

there is a reasonable certainty that no harm to any population subgroup will result from aggregate

exposure to chlorpropham when considering dietary exposure and all other non-occupational sources

of pesticide exposure for which there is reliable information. Therefore, with this mitigation measure in

place, 15 tolerances are now considered reassessed and 9 new tolerances are will be established for

residues of chlorpropham in/on raw agricultural commodities under section 408(q) of the FFDCA. 
FQPA requires that EPA consider “available information” concerning the cumulative effects of a

particular pesticide’s residues and “other substances that have a common mechanism of toxicity.” The

reason for consideration of other substances is due to the possibility that low-level exposures to multiple

chemical substances that cause a common toxic effect by a common mechanism could lead to the same

adverse health effect, as would a higher level of exposure to any of the other substances individually.

EPA did not perform a cumulative risk assessment as part of this reregistration review of chlorpropham,

because the Agency has not determined if there are any other chemical substances that have a

mechanism of toxicity common with that of chlorpropham. If EPA identifies other substances that share

a common mechanism of toxicity with chlorpropham, then a cumulative risk assessment will be

conducted that includes chlorpropham. Further, EPA is in the process of developing criteria for

characterizing and testing endocrine disrupting chemicals and plans to implement an Endocrine

Disruptor Screening Program. Chlorpropham will be reevaluated at that time and additional studies

may be required. 

The Agency’s human health findings for the pesticide chlorpropham, were discussed in a

closure conference call, and are summarized in the enclosed chemical overview of the risk assessments. 

These risk assessments and other documents pertaining to the chlorpropham tolerance reassessment

decision are listed at the end of this document (Attachment 1) and are available on the Internet at

http://www.epa.gov/pesticides/reregistration/status.htm and in the public docket for viewing. 

Tolerances are established for residues of chlorpropham in/on raw agricultural commodities as

defined in 40 CFR §180.181. The current tolerance in or on potatoes is currently expressed in terms

of the combined residues of chlorpropham and its 1-hydroxy-2-propyl-3'-chlorocarbanilate metabolite

and is established at 50 parts per million (ppm). The tolerance for potatoes should be reduced to 30

ppm, and be expressed in terms of chlorpropham alone (chlorpropham per se). Additionally, a

tolerance for residues of chlorpropham on potatoes, wet peel, should be established at 40 ppm. 

Interim tolerances have been established for residues of chlorpropham in/on plant and animal

commodities in 40 CFR §180.319. The Agency will propose to reassess thirteen interim tolerances

including milk, meat, fat, and meat byproducts of cattle, hog, horse, and sheep, based on results of the

ruminant feeding study, and will propose to revoke one interim tolerance (spinach) for failure to

provide additional data required to support reregistration. Tolerances will be raised or established to

express combined residues of chlorpropham and 4-HSA 

(4-hydroxychlorpropham-O-sulfonic acid) for the meat and meat byproducts of cattle, horse, sheep,

goat, and hog at 0.06 ppm (except kidney), 0.30 ppm for kidney and milk, and 0.20 ppm for fat (a

total of 21 tolerances). A total of 24 tolerances will be raised, established, or revoked by the TRED

for chlorpropham when the tolerances for post-harvest and wet peel potato are included, and the

revocation for spinach occurs. 

The Codex Commission has not established or proposed maximum residue limits (MRLs) for

residues of chlorpropham in/on various raw agricultural and processed commodities. Therefore, there

are no inconsistencies with respect to compatibility of U.S. tolerances with Codex MRLs. The

following table summarizes EPA’s tolerance reassessment decision.
Table 1. Tolerance Reassessment Summary for Chlorpropham

Commodity Current

Tolerance

(ppm)

Tolerance

Reassessment

(ppm)

Comment/Correct Commodity Definition

Current and Proposed Tolerances Under 40 CFR § 180.181

for chlorpropham per se

Potato

(Post-Harvest)

50 30 Tolerance lowered based on results of a magnitude of residue

study in potatoes for chlorpropham per se. Currently listed

under 40 CFR § 180.181 as combined residues of chlorpropham

and its 1-hydroxy-2-propyl-3'- chlorocarbanilate metabolite.

Potato, 

wet peel 

none 40 Tolerance to be established based on field trial and commercialscale processed potato waste studies. This tolerance is based on

the Highest Average Field Trial (HAFT), the maximum

expected residue in potato, wet peel, at 36 ppm, and the average

concentration factor (3x) from a commercial-scale processed

potato waste study.

Interim Tolerances Currently Listed Under 40 CFR § 180.319 

for chlorpropham per se and Proposed Reassessed Tolerances

Cattle, meat 0.05 0.06

Tolerance raised (or established) based on results of a ruminant

feeding study and calculated Maximum Theoretical Dietary

Burden (MTDB) estimates. The current tolerance should be

recodified under 40 CFR §180.181(a) (1) to be expressed for

combined residues of chlorpropham and 4-

hydroxychlorpropham-O-sulfonic acid (4-HSA). 

Cattle, fat 0.05 0.20

Cattle, kidney none 0.30

Cattle, meat

byproduct1

0.05 0.06

Hog, meat 0.05 0.06

Hog, fat 0.05 0.20

Hog, Kidney none 0.30

Hog, meat

byproducts1

0.05 0.06

Goat, meat none 0.06

Goat, fat none 0.20

Goat, kidney none 0.30

Goat, meat

byproducts1

none 0.06

Horse, meat 0.05 0.06

Horse, fat 0.05 0.20

Horse, kidney none 0.30

Horse, meat

byproducts1

0.05 0.06

Milk 0.05 0.30
Commodity Current

Tolerance

(ppm)

Tolerance

Reassessment

(ppm)

Comment/Correct Commodity Definition

Sheep, meat 0.05 0.06 Tolerance raised (or established) based on results of a ruminant

feeding study and calculated Maximum Theoretical Dietary

Burden (MTDB) estimates. The current tolerance should be

recodified under 40 CFR §180.181(a) (1) to be expressed for

combined residues of chlorpropham and 4-

hydroxychlorpropham-O-sulfonic acid (4-HSA). 

Sheep, fat 0.05 0.20

Sheep, kidney none 0.30

Sheep, meat

byproducts1

0.05 0.06

Spinach 0.3 Revoke The interim tolerance was based on insufficient data; proposed

revocation is based on failure to provide additional data required

to support tolerance reassessment

1

 Revised Commodity Definition: (except kidney)

Labeling For End-Use Products

In completing this TRED, the Agency has identified certain label amendments which should be

implemented. A tabular summary of label amendments, listed below, describes how label language

should be amended. The implementation of these amendments will ensure that the reassessed

tolerances are adequate for the maximum label rates, and will also ensure consistency among the labels. 

In order to be eligible for reregistration, registrants supporting chlorpropham registrations must

submit label applications for amended registration. This application should include the following items: a

completed EPA application form 8570-1, five copies of the draft label with all label amendments

outlined in Table 2 of this document incorporated, and a description on the application, such as,

“Responding to TRED Document”. All amended labels need to be submitted within 8 months of

signature of this document to the Registration Division (RD). The RD contact is Cynthia Giles-Parker

at (703) 305-7740.
Table 2. Amendments to CIPC Labels based on Formulation Class

Formulation Class Recommended Label Amendments

Aerosol Ready To Use (RTU)

Products

The product labels currently state that “if potatoes are held in storage longer than

originally anticipated, the potatoes may be retreated.” The labels should clearly state a

total seasonal rate of 0.028 lb ai/1000 lbs potatoes, not to exceed 165% of the typical

(0.017lb ai/1000lbs of potatoes) rate. In the case of labels specifying 145% of the

typical rate, the total seasonal rate should not exceed 0.025lbs ai/1000lbs of potatoes. 

For all products heated above 250E F,

including CIPC Briquette Aerosol

(EPA Reg. Number 2749-520), and

Pin Nip 98.6% Aerosol (EPA Reg.

Number 65726-3)

For entry into the enclosed treatment/storage area anytime after application until

ventilation requirements listed on this labeling have been completed, in addition to PPE

(long-sleeved shirt and long pants; shoes plus socks; chemical resistant gloves such as or

made of any waterproof material); handlers must wear a respirator with an organicvapor removing cartridge with a prefilter approved for pesticides (MSHA/NIOSH

approval number prefix TC-23C), or a canister approved for pesticides (MSHA/NIOSH

approval number prefix TC-14G), or a NIOSH-approved respirator with an organic

vapor (OV) cartridge or canister with any R, P prefilter

Emulsifiable Concentrate (EC) Label should be amended to reduce the maximum rate of application from 3.99 lb a.i. to

2.0 lb a.i. per acre for Easter lily use

For potatoes, a maximum seasonal rate (0.0104 lb ai/1000lbs potatoes) should be

specified.

Additional Generic Data Requirements

Additional generic confirmatory data are required concerning UV/Visible Absorption (OPPTS

830.7050) for technical registrants of chlorpropham. 

The Agency is also requesting a special residue study (under crop field trial guideline study,

OPPTS 860.1500) to determine the potential for thermal degradates to form during aerosol application

as a result of thermal degradation to deposit as residues in or on stored potatoes. The study is required

because the Agency cannot determine whether or not the chlorophenyl isocyanate, or other thermal

degradates, are produced during aerosol treatment based on the literature citations and the submitted

plant metabolism study alone. The study should include the range of temperatures typically used by the

aerosol generators, at what temperature the decomposition products are formed during the process and

the presence and amount of any isocyanates; (in particular, chlorophenyl isoncyanate), as well as the

potential intermediary 5-chloro-2-benzoxazolinone. 

Note that Technical registrants will be sent a Federal Insecticide, Fungicide, and Rodenticide

Act (FIFRA) Section 3(c)(2)(B) Data-Call-In (DCI) letter in a separate mailing. If
 you have questions on this document, please contact the Chemical Review Manager, Gary Mullins, at

(703) 308-8044.

Sincerely,

Lois A. Rossi, Director

Special Review and 

 Reregistration Division

2 Enclosures: Chlorpropham Summary and Overview
ATTACHMENT 1

Supporting Documents Considered for the Chlorpropham Tolerance Reassessment Decision

1. Danette Drew (USEPA\OPPTS\OPP\HED).Chlorpropham (CIPC) (018301). HED’s

Revised Human Health Risk Assessment Chapter for the Tolerance Reassessment Eligibility

Decision. July 10, 2002.

2. Danette Drew (USEPA\OPPTS\OPP\HED).Chlorpropham (CIPC) (018301).Revised

Product Chemistry and Residue Chemistry Chapter for the Tolerance Reassessment Eligibility

Decision (TRED). June 10, 2002.

3. Danette Drew (USEPA\OPPTS\OPP\HED). Chlorpropham (CIPC) (018301).Acute, Chronic

and Cancer Anticipated Residues and Dietary Exposure Assessments for the Tolerance

Reassessment Eligibility Decision. February 25, 2002.

4. William B. Greear (USEPA\OPPTS\OPP\HED).Chlorpropham - Reregistration Case No.

0271 - Toxicology Chapter for the Reregistration Eligibility Decision Document on

Chlorpropham. January 13, 1999.

5. Brenda Tarplee (USEPA\OPPTS\OPP\HED).Report of the FQPA Safety Factor Committee. 

December 17, 1998.

6. Dirk F. Young, Ph.D., (USEPA\OPPTS\OPP\EFED). Revised FQPA Drinking Water

Assessment for Chlorpropham. June 3, 2002.

7. Danette Drew, (USEPA\OPPTS\OPP\HED). Response to Registrant’s Letter Regarding

Label Amendments. November 20, 2001.

8. David G. Anderson, Ph.D., (USEPA\OPPTS\OPP\HED). Carcinogenicity Peer Review of

Chlorpropham October 11, 1994.

9. Danette Drew, (USEPA\OPPTS\OPP\HED). Response to CIPC Task Force Comments on

the Human Health Risk Assessment for the TRED. March 27, 2002

10. Danette Drew, (USEPA\OPPTS\OPP\HED). Agency’s Response to Pin Nip April 08, 2002

Comments on the Human Health Risk Assessment for the Tolerance Reassessment Eligibility

Decision (TRED). April 11, 2002

11. Lori L. Brunsman (USEPA\OPPTS\OPP\HED). Para-Chloroaniline Hydrochloride

(Diflubenzuron, Dimilin), (017203), Quantitative Risk Assessment (Q1*) Based on B6C3F1

Mouse Gavage Study With mg/kg Body Weight3/4/Day Unterspecies Scaling Factor. June 14,

2001.
12. William B. Greear (USEPA\OPPTS\OPP\HED). Chlorpropham - Report of the Hazard

Identification Review Committee. October 16, 1998.

These risk assessments and other documents pertaining to the chlorpropham tolerance

reassessment decision are available on the Internet at

http://www.epa.gov/pesticides/reregistration/status.htm, and in the public docket for viewing. 
OVERVIEW OF CHLORPROPHAM

RISK ASSESSMENT

Introduction 

This document summarizes EPA’s human health and drinking water risk findings and

conclusions for the herbicidal carbamate pesticide chlorpropham, as presented fully in the

documents, "Chlorpropham HED Revised Human Health Risk Assessment Chapter for the

Tolerance Reassessment Eligibility Decision, June 7, 2002" and “Revised FQPA Drinking Water

Assessment for Chlorpropham, June 5, 2002”. The purpose of this overview is to assist the reader

by identifying the key features and findings of these risk assessments. This overview was developed

in response to comments and requests from the public, which indicated that the risk assessments

were difficult to understand, that they were too lengthy, and that it was not easy to compare the

assessments for different chemicals due to the use of different formats.

The chlorpropham risk assessment, and additional supporting documents, are posted on

EPA’s Internet website (http://www.epa.gov/pesticides/chlorpropham.html) and are available in the

Pesticide Docket for public viewing. The availability of the Agency’s report on the FQPA

Tolerance Reassessment Decision (TRED) for chlorpropham will be announced in a Federal

Register Notice. Prior to publication of the Notice, the Agency conducted a closure conference call

to describe the regulatory decisions to stakeholders. 

The Federal Food, Drug, and Cosmetic Act (FFDCA), as amended by the Food Quality

Protection Act (FQPA) of 1996, requires EPA to review all the tolerances for registered chemicals

in effect on or before the date of the enactment of FQPA. In reviewing these tolerances, the Agency

must consider, among other things, aggregate risks from non-occupational sources of pesticide

exposure, whether there is increased susceptibility to infants and children, and the cumulative effects

of pesticides with a common mechanism of toxicity. The tolerances are considered reassessed once

the safety finding has been made or a revocation occurs. A reregistration eligibility decision (RED)

for chlorpropham was finalized and signed on August 1, 1996, prior to FQPA enactment; therefore,

tolerances needed to be reassessed to reflect the provisions of FQPA. 

Risks summarized in this document are those that result only from the use of chlorpropham.

The FQPA requires that the Agency consider “available information” concerning the cumulative

effects of a particular pesticide’s residues and “other substances that have a common mechanism of

toxicity”. The reason for consideration of other substances is due to the possibility that low-level

exposures to multiple chemical substances that cause a common toxic effect by a common

mechanism could lead to the same adverse health effect as would a higher level of exposure to any

of the other substances individually. The Agency did not perform a cumulative risk assessment as

part of this tolerance reassessment of chlorpropham because the Agency has determined that

chlorpropham does not share a common mechanism of toxicity with other cholinesterase-inhibiting

methyl-carbamates. 
2

Use Profile

Herbicide: registered for use on the following crops/sites: sprout control on post-harvest stored

potatoes. There are four Special Local Needs [24(c)] registrations. They are for use on Easter lilies

(on approximately 150 acres annually in Oregon and California), on gingko trees in Washington,

DC, and on post-harvest stored potatoes growing in high humidity conditions in the state of Maine

which requires a higher application rate. 

Formulations: registered formulations include a technical grade (from 98%, to 99% active

ingredient (a.i.)), aerosol ready-to-use (RTU) (from 46.5 to 98.7% a.i.), and liquid emulsifiable

concentrate (EC), (from 23.8 to 36% a.i.). The registrant of an additional RTU product (formulated

at 49.65% a.i.) has requested a voluntary cancellation of this product. 

Methods of Application: may be applied by direct spray, low volume direct spray (concentrate),

high pressure spray (dilute), stored commodity fumigation, and stored commodity non-fumigation

(aerosol). 

Application Rate: chlorpropham application rates to post-harvest potatoes vary, and depend on

method of application, length of storage, and storage temperature. Rates of application to postharvest potatoes destined for processing range from a maximum total application rate of 1.65 lb

a.i./600 hundred weight (cwt) to 1.65 lb a.i./400 cwt. Post-harvest stored potatoes destined for fresh

markets may receive a maximum total application rate of 1.45 lb a.i./600 cwt. Current labels do not

restrict or limit the number of applications to stored potatoes, as long as the maximum application

rate is not exceeded. A total of approximately 300 lbs of chlorpropham a.i is used annually on

gingko trees in Washington, DC, at an application rate of 0.02 lbs a.i./gallon. The maximum total

application rate for the Easter lily bulb use is 3.99 lb a.i./A. 

Application Timing: chlorpropham may be applied pre-bloom (for Easter lilies and gingko trees),

and as a dormant application to post-harvest potatoes in storage. Post-harvest potatoes are the only

food/feed use.

Annual Poundage: the best available data for total annual amount of chlorpropham active

ingredient (a.i.) used is from a USDA National Agricultural Statistics Service (NASS) publication

for 1996. Total annual chlorpropham used was approximately 445,600 pounds. 

Registrants: Aceto Agriculture Chemicals Corporation, Cerexagri, Inc., and Pin/Nip Inc. 
3

Human Health Risk Assessment

Acute Dietary (Food) Risk

Acute dietary risk from food is calculated by considering what is eaten in one day. A risk

estimate that is less than 100% of the acute Population Adjusted Dose (aPAD) (the dose at which

an individual could be exposed on any given day and no adverse health effects would be expected)

is not of concern to the Agency. The aPAD is the reference dose (RfD) adjusted for the FQPA

Safety Factor. 

The Agency performed a conservative deterministic (Tier 1) analysis (which assumed

tolerance level residues based on existing and/or reassessed tolerances and 100 % crop treated (CT).

The acute dietary exposure analysis is based on the Dietary Exposure Evaluation Model (DEEMTM).

One day consumption data from USDA’s Continuing Surveys of Food Intake by Individuals (CSFII

1989-92) are used on an individual-by-individual basis for acute exposure assessment. 

• Acute dietary (food) risk is not of concern (4.0% of the aPAD) at the 95th exposure percentile

for females 13-50 years old (the only subgroup requiring an acute assessment). 

• An acute endpoint for the general population, including infants and children, was not

available from the toxicity studies, including the developmental toxicity studies. The

maternal toxicity in these studies was not attributable to a single exposure. Therefore, no

toxicity endpoint or dose was selected for the general population including infants and

children. 

• The toxicity endpoint for the acute dietary assessment is increased resorption and postimplantation loss based on a developmental toxicity study in rabbits (NOAEL = 250

mg/kg/day). These effects were observed at 500 mg/kg/day (LOAEL).

• The uncertainty factor is 100x, 10x for intraspecies variability and 10x for interspecies

extrapolation. 

• The FQPA Safety Factor was reduced to 1X for acute and chronic exposures because: 1) the

toxicology data base is complete; 2) there is no indication of increased susceptibility of rats

or rabbit fetuses to in utero and/or postnatal exposure in the developmental and reproductive

toxicity studies; 3) a developmental neurotoxicity study is not required; 4) dietary (food)

exposure estimates are partially refined resulting in a more realistic estimate of dietary

exposure; 5) quantifiable contamination of surface or ground water is not likely to result

from this use; and 6) there are currently no registered residential uses of chlorpropham,

therefore, this type of exposure to infants and children is not expected.

• The acute RfD (aRfD) is 2.5 mg/kg/day. Because the FQPA Safety Factor was reduced to
4

1X, the aPAD is equal to the aRfD.

• There is no evidence of endocrine disruption from exposure to chlorpropham. 

Chronic Dietary (Food) Risk

Chronic dietary risk from food is calculated by using the average consumption values for

food and average residue values for those foods over a lifetime. Chronic dietary exposure that is less

than 100% of the chronic Population Adjusted Dose (cPAD) does not exceed the Agency’s level of

concern. The cPAD is the chronic reference dose (cRfD) adjusted for the FQPA Safety Factor. 

Residues of chlorpropham per se from USDA Pesticide Data Program (PDP) monitoring

data, calculated as point estimates, were used for potatoes in the chronic dietary assessment.

Anticipated residues of parent chlorpropham and the 4-HSA metabolite in livestock tissues were

derived from the ruminant feeding studies and were used as point estimates in the assessment. Total

residues of chlorpropham and the metabolite 4-HSA in milk were calculated by determining the ratio

of residues of parent to metabolite in milk from the feeding study and applied to the amount of

parent reported in milk in the PDP monitoring data.

• Chronic dietary risk estimates for food are below the Agency’s level of concern (<100%

cPAD) for the general U.S. population (4% of the cPAD) and all population subgroups. The

chronic dietary exposure estimate for highest exposed population subgroup, children 1-6

years old, is 10% of the cPAD. 

• The toxicity endpoint for the chronic dietary risk assessment is thyroid toxicity, based on the

results of a 2-year feeding study in dogs, where increased thyroid weights and

histopathological changes in the thyroid were observed (NOAEL=5 mg/kg/day). These

effects were observed at 50 mg/kg/day (LOAEL).

• The uncertainty factor is 100x; 10x for intraspecies variability and 10x for interspecies

extrapolation. 

• The chronic RfD (cRfD) is 0.05 mg/kg/day. As noted in the Acute Dietary Risk section, the

FQPA Safety Factor was reduced to 1x.

Cancer Dietary (food) Risk

The Agency has classified parent chlorpropham as a “Group E” human carcinogen (no

evidence of carcinogenicity). However, some chlorpropham is metabolized to 3-chloroaniline (3-

CA) in potatoes and some anilines are known carcinogens. The Agency does not have data on 3-CA

necessary to conduct a carcinogenicity risk assessment. However, data are available for 

4-chloroaniline (4-CA) which is structurally similar to 3-CA and has a cancer potency factor (Q1*)

of 1.12 x 10-1 (mg/kg/day)-1. This Q1* was used as a surrogate to assess the potential cancer risk

from 3-CA. However, the use of the 4-CA carcinogenic potency is expected to overestimate risk.
5

• In livestock metabolism studies, 3-CA was not detected in milk, meat, kidney or fat. 3-CA

was detected in liver. Although no 3-CA was detected in milk, a cancer dietary exposure

assessment was performed using 1⁄2 LOD (limit of detection) for milk as well as the 3-CA

residue found in liver and potatoes. This exposure scenario reflects a conservative

assumption that finite residues may be expected in milk and liver consumed by individuals

living in a “local milkshed” where cattle may be fed processed potato waste from nearby

potato processing plants. The cancer dietary risk estimate for the general population is 

3.4 x 10-6, based on this conservative “local milkshed” scenario. 

• A second cancer dietary exposure assessment was performed using estimated potato residues

only and omitting milk and cattle liver. This assessment reflects an exposure scenario that

assumes no potato waste containing chlorpropham is fed to livestock. This typical scenario

is more realistic than the local milkshed scenario since residues of 3-CA are not expected

in milk and only a small amount of the population can be assumed to live in an area where

local potato waste may be fed to livestock. The cancer dietary risk estimate for the typical

scenario is 2.2 x 10-6. 

The Agency’s level of concern for lifetime cancer risk is generally 1.0 x 10-6. However, for

chlorpropham, several factors are expected to contribute to overestimating risk including use of the

surrogate Q1*, the 10-fold range between the NOAEL and LOAEL derived from the 2 year dog

feeding study, and the conservatism associated with the use of anticipated residues. Therefore, the

Agency does not consider the dietary cancer risk estimate from chlorpropham use to be of concern.

Drinking Water Dietary Risk

Drinking water exposure to pesticides can occur through surface and/or ground water

contamination. EPA considers acute (one day) and chronic (lifetime) drinking water risks and uses

either modeling or actual monitoring data, if available, to estimate those risks. To determine the

maximum allowable contribution from water allowed in the diet, EPA looks at how much of the

overall allowable risk is contributed by food, then calculates a “drinking water level of comparison”

(DWLOC) to determine whether modeled or monitoring levels exceed this level. 

The Agency uses a DWLOC as a surrogate to capture risk associated with exposure from

pesticides in drinking water. The DWLOCs represent the maximum contribution to the human diet

that may be attributed to residues of a pesticide in drinking water after dietary exposure is

considered. Risks from drinking water are assessed by comparing the DWLOCs to the estimated

environmental concentrations (EECs) in surface and/or ground water. When the EECs are less than

the DWLOCs, the Agency is not concerned with drinking water risks. 

As previously noted, annual outdoor use of chlorpropham is limited to 300 lbs a.i. each on

Easter lilies and gingko trees. However, accurate assessment of the drinking water contamination

potential posed by these limited outdoor uses of chlorpropham and its 3-chloroaniline metabolite,

is hampered by the near complete lack of environmental fate data for both compounds. Therefore,

the Agency is relying on modeling to estimate drinking water dietary risks and on monitoring data

for other pesticides used in the lily bulb growing region along with fate parameters from surrogate
6

chemicals to characterize exposures. 

Gingko Tree Use – Surface and Ground Water

Chlorpropham is applied to gingko trees in Washington, DC by mist blower to “near dripping

point” at an application rate of 0.02 lbs a.i./gallon. There are no drinking water intakes on the

Potomac River downstream of Washington, DC, so there is no potential for exposure to

chlorpropham through drinking water. Therefore, neither surface water or ground water sources of

drinking water are of concern as a result of the gingko tree use.

Easter Lilies – Surface Water

The only chlorpropham use that may result in exposure through drinking water is application

to Easter lilies. The Agency assessed potential exposure to water based on the Easter lily use which

is limited to Curry County, Oregon and Del Norte County, California. Approximately 150 acres (1/4

square mile) receives treatment with chlorpropham annually. Any potential exposure would be

limited to these two counties. Surface water intakes are not located near lily bulb cultivating areas,

therefore, the potential for exposure to CIPC/3-CA in surface water sources of drinking water is

negligible. The Agency concludes that no population group is exposed to chlorpropham residues

in surface water sources of drinking water at a level that poses an acute or chronic risk concern. 

Easter Lilies – Ground Water

Estimated drinking water concentrations for ground water are based on the SCI-GROW

model. The model is a conservative, Tier I assessment that provides a reasonable estimate of

exposure in hydrologic environments similar to those in which lily bulbs are grown. However, the

modeled EEC is a conservative estimate of lifetime exposure and does have considerable uncertainty

because of the lack of environmental fate data. 

• For acute risk, potential exposure to chlorpropham from drinking water is not of concern.

 The acute ground water EEC for chlorpropham of 100 ppb does not exceed the DWLOC

(72,000 ppb).

 

• For chronic risk, the Easter lily use is not of concern. The modeled EEC is 100 ppb which

does not exceed the 450 ppb DWLOC for kids 1-6 years (the most sensitive subpopulation).

• For carcinogenic risk, potential chronic exposure to chlorpropham from ground water

sources of drinking water associated with the Easter lily bulb use is estimated to range from

2.0 ppb to 8.0 ppb. This range is based on varying modeling parameters including

degradation half life and assuming 100% of the parent chlorpropham is degraded to 3-

chloroanaline. As such, these estimates may not be suitable for a cancer assessment and will

overestimate cancer risk. 

Residential Risk
7

There are currently no registered residential uses of chlorpropham. Therefore, there is no

expected exposure of homeowners to chlorpropham and aggregation with dietary sources of

exposure is not necessary. 

Aggregate Risk

The aggregate risk assessment considers exposure through food, drinking water, and nonoccupational uses (i.e., residential use). Since there are no chlorpropham residential uses, the

aggregate assessment examines the combined exposure through food and drinking water only. 

• Acute aggregate risk estimates from exposure to chlorpropham in food and water do not

exceed the Agency’s level of concern. The modeled groundwater EEC does not exceed the

acute DWLOC for females 13-50 years old nor is there potential acute exposure to

chlorpropham from surface water sources that exceed the Agency’s level of concern. 

• Chronic aggregate risk estimates from exposure to chlorpropham in food and water do not

exceed the Agency’s level of concern. The modeled groundwater EEC does not exceed the

chronic DWLOC for the US population and all population subgroups nor is there potential

chronic exposure to chlorpropham from surface water sources that exceed the Agency’s level

of concern. 

Aggregate Cancer Risk

The carcinogenic risk estimate (2.2x10-6) for dietary (food) exposure based on the typical use

scenario fills the “risk cup”. The only potential drinking water concern is for ground water

associated with the use on Easter lilies in Oregon and California (surface water is not of concern for

any use). However, the cancer risk assessment is based on a surrogate Q1* which is likely to

overestimate cancer risk. Similarly, the modeled ground water EEC reflects a bounding analysis

which would not appreciately contribute to aggregate risks at the low end but would represent a risk

concern based on worse case assumptions. These uncertainties which likely overestimate exposure

and risk, combined with the limited use area and reduction in the maximum application rate (50%),

give the Agency reasonable assurance that aggregate cancer risks are not of concern.

Occupational Risk

Chlorpropham is currently under review for tolerance reassessment only. Occupational risk

management decisions were made as part of the 1996 Chlorpropham RED, and no new data has been

received to warrant reconsideration of these risks. Therefore, no occupational risk assessment was

conducted.

Ecological Risk
8

Chlorpropham is currently under review for tolerance reassessment only. Ecological risk

management decisions were made as part of the 1996 Chlorpropham RED, and no new data has been

received to warrant reconsideration of these risks. Therefore, an ecological risk assessment was not

conducted.

Summary of Pending Data 

• All product chemistry data requirements have been fulfilled for 1. Aceto 98% T (EPA Reg.

No. 2749-102, 2. Cerexagri 99% T (EPA Reg. No. 2792-67), and 3.Pin Nip 98% T (EPA

Reg. No. 65726-2) except data are required concerning UV/Visible Absorption (OPPTS

830.7050).

• The requirements for Analytical Methodology (OPPTS 860.1340) will remain unfulfilled

until receipt of the revised version of the proposed GC/NPD method for tolerance

enforcement in stored potato commodities. 

• Method validation for HPLC/UV method for tolerance enforcement in stored potato

commodities will remain unfulfilled for the registrant (Pin Nip, Inc) until successful

radiovalidation, confirmatory method, and independent laboratory validation have been

submitted and reviewed. 

• Separate enforcement methods (GC/MSD for chlorpropham and HPLC for 4-HSA) have

been submitted for determination of chlorpropham and its 4-HSA metabolite in meat and

milk. Method validation for tolerance enforcement will remain unfulfilled until successful

ILVs are submitted. 

Additional Generic Data Requirements

• A special residue study (under crop field trial guideline study number OPPTS 860.1500) is

required to determine the potential for chlorpropham degradates to form and possibly deposit

as residues in or on stored potatoes during application as a result of thermal degradation.

The study is required because the Agency cannot determine whether or not the chlorophenyl

isocyanate, or other thermal degradates, are produced during aerosol treatment (based on the

literature citations and the submitted metabolism study alone). The study should include the

range of temperatures typically used by the generators, at what temperature the

decomposition products are formed during the process, and the presence and amount of any

isocyanates (in particular, chlorophenyl isoncyanate, and 5-chloro-2-benzoxazolinone). 

• The protocol for this study must be submitted to the Agency prior to initiating the study. 

A residue analytical method may need to be developed, should existing methodology be

insufficient. Technical registrants will be sent a Federal Insecticide, Fungicide, Rodenticide

Act (FIFRA) Section 3(c)(2)(B) Data-Call-In (DCI) letter in a separate mailing. 
Chlorpropham Summary

Use

• Chlorpropham is a plant growth regulator used for sprout control on post-harvest stored

potatoes. 

• There is a Special Local Need (SLN) registration for use on post-harvest potatoes grown in

high humidity areas in the state of Maine. 

• There are two SLN registrations for use on Easter lilies for floral bud removal and to decrease

botrytis infection in limited acreage (about 150 acres annually), in two counties of Oregon and

California. 

• There is also a SLN registration for flower bud/immature fruit removal on gingko trees in

Washington, DC. 

• Annual usage of chlorpropham is approximately 445,600 pounds of active ingredient (a.i.).

There are 3 technical grade formulations and 12 active end-use products. 

• Chlorpropham can be applied by: spray, low volume spray (concentrate), high pressure spray

(dilute), stored commodity fumigation (aerosol), and stored commodity non-fumigation

(aerosol). 

Risks

• Acute and chronic dietary (food) risk is not of concern. 

• Cancer dietary (food) risk for the general U.S. population is estimated to be 2.2 x 10-6 which

slightly exceeds the Agency’s level of concern for lifetime cancer risk of 1.0 x 10-6. However,

because conservative surrogate data were used to estimate the cancer potency (Q1*), the

Agency does not consider the chlorpropham dietary cancer risk to be of concern. 

• Drinking water dietary risk is not of concern for surface water sources. The Easter lily

ground water drinking water assessment suggests a potential cancer risk of concern for that

very limited use. However mitigation measures provide sufficient assurance that cancer risks

are not of concern for the limited Easter lily use. For ginko trees, the Agency is not concerned

with potential acute or chronic exposure to chlorpropham from surface or ground water sources

of drinking water.

• Residential risk was not assessed. There are no registered residential uses for chlorpropham.

• Acute and chronic aggregate (food and water) risks are not of concern. 

• Aggregate cancer risks for ground water suggest a risk concern. However mitigation measures

combined with the conservatism in the assessment provide sufficient assurance that cancer

risks are not of concern for the limited Easter lily use, the only area of potential concern.

• Occupational and ecological risk have not been assessed. Occupational and ecological risk

management decisions were made as part of the 1996 chlorpropham reregistration eligibility

decision (RED). No new data has been received to warrant reconsideration of these risks.