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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF

CHEMICAL SAFETY AND

POLLUTION PREVENTION

MEMORANDUM

Date: May 27, 2011

SUBJECT: DCPA. (Chlorthal Dimethyl). Human Health Assessment Scoping Document in 

Support of Registration Review.

PC Code: 078701 DP Barcode: 386637

Decision No.: 444895 Registration No.: Not Applicable

Petition No.: Not Applicable Regulatory Action: Registration Review Scoping

Risk Assessment Type: Not Applicable Case No.: 0270

TXR No.: Not Applicable CAS No.: 1861-32-1

MRID No.: None 40 CFR: 180.185

FROM: Christine L. Olinger, Risk Assessor

Kit Farwell, D.V.M., Toxicologist

Jeffrey L. Dawson, Chemist

Risk Assessment Branch VII

Health Effects Division (7509P)

Office of Pesticide Programs

THRU: Michael S. Metzger, Chief,

Risk Assessment Branch VII

Health Effects Division (7509P)

Office of Pesticide Programs

TO: Jill Bloom

Risk Management and Implementation Branch III 

Pesticide Re-evaluation Division (7508P)

Office of Pesticide Programs

Executive Summary

The Health Effects Division (HED) DCPA (dimethyl tetrachlorophthalate) Registration Review

Team has evaluated the most recent human health assessments and database for the herbicide 

DCPA to determine the scope of work necessary to support the established tolerances and 

existing registrations. The risk assessment used to support the 1998 Reregistration Eligibility

Decision (RED) and a risk assessment to support new tolerances of DCPA (Dole, 2004) were the 

primary sources for this evaluation. DCPA is registered for use on several vegetable crops and 

some ornamental plants. Most residential uses have been cancelled and are no longer supported 

by the primary registrant.
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Liver and thyroid effects are observed in many DCPA toxicity studies. The acute toxicity of 

DCPA is low. Toxicity in longer term studies with DCPA included thyroid toxicity as shown by 

decreased levels of thyroid hormone, microscopic thyroid changes, and increased thyroid weight. 

Liver toxicity included increased liver weight, elevated liver enzyme activity, increased 

cholesterol, and liver hypertrophy. It is believed that the liver effects are precursor events to the 

thyroid effects, with increased metabolism of thyroid hormone by the liver resulting in a 

compensatory stimulation of the thyroid. Effects on the kidney have also been observed. There 

were no mutagenicity concerns for DCPA, but thyroid follicular cell adenomas/carcinomas, 

hepatocellular adenomas/carcinomas, and hepatocholangiocarcinomas were found in rats;

hepatic adenomas were found in mice. DCPA is classified a Group C, possible human 

carcinogen with a cancer potency factor based on the three combined liver tumors in female rats. 

DCPA has not been identified as a member of a common mechanism group for cumulative risk 

assessment.

The previous risk assessment identified a 28-day inhalation toxicity study and a comparative 

thyroid toxicity study as data gaps. These studies are still required. The test guidelines have 

been updated since the 2002 assessment and additional studies are now required, including 

immunotoxicity and acute and subchronic neurotoxicity studies. The endpoints and the FQPA 

safety factor will be re-evaluated after these studies have been completed and reviewed. 

The most recent dietary, residential, aggregate, and occupational risk assessments did not 

identify risk estimates of concern. It is noted that DCPA and its environmental degradates are 

often found in groundwater monitoring studies. Additional residue chemistry studies are needed 

to support the registration review of DCPA including rotational crop field trials, sample storage 

information from prior crop field trials, a ruminant feeding study, a poultry metabolism study, 

and a livestock method validation. These studies had been previously requested in the RED and 

in response to new tolerances established in 2004. A new poultry feeding study is reserved 

pending results of the metabolism study. Once these studies have been received and reviewed, a 

new dietary assessment will be conducted to support the registration review of DCPA. Since the 

residential uses are no longer supported a new residential assessment will not be needed. 

However several studies have been identified in the literature that describe off-target movement 

of DCPA into residential settings, particularly in agricultural areas. The Agency will evaluate 

these studies during registration review to determine if a quantitative assessment of risk to 

residents in agricultural areas is needed. Should new points of departure for dermal and 

inhalation routes of exposure be identified once the new toxicity studies are received, a revised 

occupational assessment may be required.

There are impurities of toxicity concern in DCPA formulations. Prior assessments have 

estimated risks from exposure to these contaminants, and have determined them to be negligible. 

During registration review the registrants should certify that the impurities in current 

formulations are at similar levels or below the levels previously assessed. If not, then a new 

assessment may be required.
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Introduction

DCPA (dimethyl tetrachlorophthalate) is also commonly referred to as dacthal, chlorthal 

dimethyl or chlorthal methyl. DCPA is a chlorinated benzoic acid herbicide which inhibits cell 

division of root tips in target plants. It controls many annual grasses and broadleaf weeds in a 

variety of agricultural crops and ornamental varieties (e.g., broccoli, onions, tomatoes, cabbage, 

cauliflower, dogwood, azalea). Annual agricultural use from 1998 through 2008 averaged 

approximately 500,000 pounds over 100,000 acres with broccoli and onions accounting for 79 

percent of that use (Ratnayake, 2011). Information also suggests that on average 50 percent of 

broccoli is treated and 15 percent of onions (SLUA). It was also reported that use for ornamental

crops in nurseries is low at around 2,600 pounds in 2006. California usage data exhibit similar 

trends for the years 2006-2008 (CA Usage reference). Most uses in residential settings have 

been cancelled and the remaining residential uses are not supported, so will eventually be 

removed (personal communication, J. Bloom, 3/3/11).

Tolerances are established in 40 CFR § 180.185 for residues of DCPA, which address direct 

treatment of crops as well as inadvertent residues of DCPA from off-target movement and carryover of residues to rotational crops. The metabolites monomethyltetrachloroterephthalate (MTP) 

and tetrachloroterephthalic acid (TCP or TPA) are included in the tolerance expression for 

DCPA. Codex has not established maximum residue limits (MRLs) but MRLs are established in 

Canada for several commodities.

The HED DCPA Registration Review Team evaluated the most recent human health assessments 

and database for DCPA to determine the scope of work necessary to support Registration 

Review. In addition, HED has conducted a screening literature search for studies that could 

contribute to the assessment. The Reregistration Eligibility Decision (RED) and associated 

chapters as well as a risk assessment to support new tolerances were the primary sources for this 

document. It should also be noted that previous assessments assessed risks from trace 

contaminant materials in DCPA products.

Hazard Identification/Toxicology

Toxicity of DCPA: The database for DCPA is extensive. Previous risk assessments considered

subchronic and chronic oral studies in rats, subchronic and chronic oral studies in mice, 

developmental studies in rats and rabbits, a 2-generation reproduction study in rats, a dermal 

toxicity study in rats, metabolism studies, a dermal absorption study, and a battery of 

mutagenicity studies with DCPA. Since the previous risk assessment, the registrant has 

conducted subchronic rat and dog studies and a chronic dog study with DCPA. These studies 

have been reviewed and will not result in changes to previously selected endpoints for DCPA. 

The previous risk assessment identified an inhalation toxicity study and a comparative thyroid 

study as data gaps. These studies are still required. The test guidelines have been updated since 

the 2002 assessment and additional studies are now required, including immunotoxicity and 

acute and subchronic neurotoxicity studies. 
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The acute toxicity of DCPA is low. DCPA is in acute toxicity category III for the oral route of 

exposure and is in toxicity category IV for dermal and inhalation routes of exposure. It is a mild 

irritant to the eyes and skin and it is not a skin sensitizer. 

Toxicity in longer term studies with DCPA included thyroid toxicity as shown by decreased 

levels of thyroid hormone, microscopic thyroid changes, and increased thyroid weight. Liver 

toxicity included increased liver weight, elevated liver enzyme activity, increased cholesterol, 

and liver hypertrophy. It is believed that the liver effects are precursor events to the thyroid 

effects, with increased metabolism of thyroid hormone by the liver resulting in a compensatory

stimulation of the thyroid. Other toxicity included anemia, pneumonitis, and kidney toxicity

(increased kidney weight, increased incidences of chronic nephropathy, and changes in clinical 

pathology). A PubMed search was conducted and no new toxicity information which would 

result in changes to the previous risk assessment was found. 

There were no mutagenicity concerns for DCPA. Thyroid follicular cell adenomas/carcinomas, 

hepatocellular adenomas/carcinomas, and hepatocholangiocarcinomas were found in rats;

hepatic adenomas were found in mice. DCPA was classified a Group C, possible human 

carcinogen, with a cancer potency factor based on the three combined liver tumors in female rats

of 1.5 x 10-3(mg/kg/day)-1.

FQPA Assessment: There were acceptable rat and rabbit developmental toxicity studies and an 

acceptable 2-generation reproduction study. No quantitative or qualitative susceptibility

occurred in these studies and no neurotoxicity was noted in any of the studies. The 

FQPA safety factor for DCPA was reduced to 1X in the most recent risk assessment. 

Considering current policy for FQPA database uncertainty factors, the FQPA factor would likely

be retained at 10x for the lack of a comparative thyroid study. The most recent risk assessment 

showed very low risk estimates, so retaining the 10x factor would not likely result in these 

estimates exceeding the level of concern.

Toxicity Endpoints: The chronic dietary endpoint for DCPA was thyroid toxicity with a NOAEL 

of 1 mg/kg/day and a LOAEL of 10 mg/kg/day from a chronic rat study. The endpoint for 

incidental oral exposure and for inhalation exposure was hepatocellular hypertrophy with a 

NOAEL of 50 mg/kg/day and a LOAEL of 100 mg/kg/day from a subchronic rat study. No 

appropriate endpoint for acute dietary exposure was identified in any of the toxicity studies. 

Quantitation of dermal exposure was not required because no systemic toxicity occurred in the 

dermal toxicity study at the high dose of 1000 mg/kg/day. There were no concerns for 

developmental or reproductive toxicity by the dermal route of exposure because no 

developmental toxicity occurred in the developmental studies and parental and offspring effects 

in the reproduction study (decreased body weight) occurred at the same dose. Although the 

thyroid was not evaluated in this study, no liver effects were noted and liver hypertrophy is 

believed to be a precursor event for thyroid changes. The endpoints and the FQPA safety factor 

will be re-evaluated after completion of the inhalation, neurotoxicity, comparative thyroid 

toxicity, and immunotoxicity studies. 

Toxicity of Metabolites and Degradates: Also evaluated in previous risk assessments were 

subchronic oral studies, a developmental rat study, and mutagenicity studies with TPA, a 
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degradate found in water. The only effects occurring in these studies were irritation from the 

acid moiety on this compound. Since the previous risk assessment, the registrant has conducted 

a mutagenicity study with MTP, which is a rat metabolite and environmental degradate. This 

study has been reviewed and will not result in changes to conclusions in the previous risk 

assessment. 

Conclusions: Additional toxicity data are required, including a comparative thyroid toxicity

study, an immunotoxicity study, and acute and subchronic neurotoxicity studies. Once these 

studies have been received and reviewed the Agency will evaluate the need for modifying 

endpoints for risk assessment and associated safety factors.

Dietary Exposure

DCPA is registered for use on several vegetable crops; according to the use profile prepared by 

BEAD the predominant uses are on broccoli and onions. The residue chemistry data was most 

recently reviewed in association with tolerances in/on several herbs (Hazel, 2002). Adequate 

plant metabolism, analytical method, crop field trial, and processing studies are available to 

support the existing uses. However, the following residue data gaps were identified in the most 

recent discussion of the residue database: (i) rotational crop field trials and labeling proposals, 

including crops to be rotated and plant-back intervals (PBIs); (ii) sample storage temperature and 

duration to confirm the stability of residues in samples collected and analyzed as part of certain 

field trials conducted prior to 1995; (iii) a ruminant feeding study; (iv) a poultry metabolism 

study; and (v) livestock method validation. Rotational crop field trials and storage stability data 

remain outstanding; the specific studies requiring stability data are listed in the W. Hazel memo 

of 2002. The acceptability of the existing poultry feeding study will be addressed once the 

poultry metabolism study has been submitted and evaluated.

It is noted that the previous technical registrant attempted to address some of these deficiencies 

in 2002 in MRIDs 43340401, 42713501, and 43938901. However, these studies were 

resubmissions of existing data and did not fully address the requirements.

There is some concern for inadvertent residues of DCPA due to off-site movement that appears 

to be largely due to wind-blown soil particles to which DCPA residues have adsorbed.

HED has updated the maximum reasonable dietary burden for livestock in accordance with the 

guidance published in 2008. The maximum reasonable dietary burden (MRDB) for dairy cattle 

is 8 ppm; residues in edible livestock commodities are likely, so the requirement for the ruminant 

feeding study remains outstanding. An adequate poultry metabolism study is not available, and 

the existing feeding study for poultry has numerous deficiencies. Therefore, the previously 

required poultry metabolism study is still needed to assess potential exposure to DCPA residues 

in poultry commodities. A method validation for the livestock residue analytical method remains 

outstanding. An updated summary of the MRDB may be found in Table 3 of this document.

PDP data are available for residues of DCPA on numerous commodities. Over the last several 

years, quantifiable residues were found in/on broccoli, cantaloupe, cauliflower, green beans, 

green onions, collards, kale, lettuce, onion, potatoes, summer squash, and bell peppers. In 
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addition, residues have been detected occasionally on commodities where no tolerances have 

been established. For example, during 2007 and 2008 5% of celery samples analyzed had 

detectable residues of DCPA per se at an average residue of 2.5 ppb, with residues ranging from 

1.2 to 12 ppb (lowest LOD is 0.7 ppb). In addition in the years 2003, 2006, and 2008 2% of 

spinach samples have detectable residues of DCPA per se at average residue of 5.5 ppb, with 

residues ranging from 1.2 to 43 ppb (lowest LOD is 0.7 ppb). No tolerances have been 

established on celery and spinach.

There are a large number of studies and data available on DCPA and degradate residues in air, 

surface water, drinking water, ground water, rain, and snow. The most recent review of 

monitoring data was completed in May 2008 by the Office of Water (EPA, 2008), and reported 

in detail in the 2009 California Red-legged Frog risk assessment of DCPA. Monitoring data 

indicate widespread occurrence of DCPA in surface water, ground water, drinking water, and air. 

DCPA and TPA are among the most commonly found pesticides/degradates found in water 

samples (U.S. EPA, 2008). DCPA is typically detected at low concentrations in remote areas 

where it is not used and at higher concentrations near where it is used. DCPA's degradates, TPA 

and MTP are more commonly detected in ground water samples than DCPA. TPA is typically

found at higher concentrations. TPA was the most commonly detected pesticide-derived 

compound in the National Survey of Pesticides in Drinking Water Wells Survey (U.S. EPA, 

1998).

The estimated chronic risk from residues of DCPA in food was well below the level of concern 

in the most recent risk assessment, with the highest population estimated at 1% of the cPAD. 

Cancer risk estimates were in the range of 10-7. Prior assessments did not directly include 

drinking water, but estimated environmental concentrations were well below the drinking water 

level of comparison indicating that no human health risk estimates of concern exist.

HED has also assessed dietary risks for the impurities of concern. Further discussion may be 

found in the appendix to this document.

Conclusions. The following studies remain outstanding: (i) rotational crop field trials and 

labeling proposals (crops to be rotated and PBIs); (ii) sample storage temperature and duration to 

confirm the stability of residues in samples collected and analyzed as part of certain field trials 

conducted prior to 1995; (iii) a ruminant feeding study; (iv) a poultry metabolism study; and (v) 

livestock method validation. The rationale for requiring these studies is attached to this 

document. Once these studies have been received and reviewed a new dietary risk assessment 

should be conducted. In addition, the registrants should certify that the impurity levels 

previously assessed in dietary risk assessment have remained the same or decreased. 

Residential Exposure

Residential risks from DCPA use were considered in the previous assessments and the risk

estimates that were calculated were not of concern for the uses at the time and given the policies 

used to define them. A turf transferable residue study for DCPA and its impurities was used in 

this assessment. Since the existing assessments were completed, most residential uses have been 
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deleted from most DCPA labels and the remaining residential uses are not supported, so will 

eventually be removed (personal communication, J. Bloom, 3/3/11).

It should be noted, however, that the Agency is considering how to evaluate risks associated with 

exposures that can occur from the off-target movement of pesticide residues in agricultural areas. 

During the screening literature search EPA identified a few studies that quantify residues of

DCPA in homes in agricultural areas (Bradman, Gunier, Harnley, etc.) so any future changes in 

risk assessment policies regarding these exposures may require updated DCPA risk assessments.

Conclusions: No residential data gaps were identified during the Registration Review scoping 

process for DCPA. At this time residential uses of DCPA are not supported, so assessments are 

not needed in registration review. However, an assessment may be needed to address changes in 

other risk assessment policies related to spray drift, and volatilization of pesticides. This is 

especially germane since data exist that quantify some level of off-target movement from treated 

areas into residential settings.

Aggregate Risk Assessment

The most recent risk assessment included aggregate assessments that considered exposure from 

food, drinking water, and residential uses. All risk estimates were below the level of concern. 

Risk estimates from the impurities were also considered, and were below the level of concern. A 

new assessment will likely be needed that considers the required new toxicity and residue data as 

well as changes in residential uses. In addition, the new assessment may need to consider 

changes that consider off-target movement of pesticides into residential settings.

Cumulative Risk Assessment

Unlike other pesticides for which EPA has followed a cumulative risk approach based on a 

common mechanism of toxicity, EPA has not made a common mechanism of toxicity finding as 

to DCPA and any other substances. For the purposes of this registration review assessment of 

data needs EPA has not assumed that DCPA has a common mechanism of toxicity with other 

substances. For information regarding EPA’s efforts to determine which chemicals have a 

common mechanism of toxicity and to evaluate the cumulative effects of such chemicals, see the 

policy statements released by EPA’s Office of Pesticide Programs concerning common 

mechanism determinations and procedures for cumulating effects from substances found to have 

a common mechanism on EPA’s website at http://www.epa.gov/pesticides/cumulative/.

Occupational Exposure

DCPA controls many annual grasses and broadleaf weeds in a variety of agricultural crops and 

ornamental varieties (e.g., broccoli, onions, tomatoes, cabbage, cauliflower, dogwood, azalea). 

DCPA formulations include flowable concentrates and wettable powders. In agriculture, 

groundboom and aerial applications would be typical but DCPA can also be applied via 

chemigation and using handheld equipment, especially associated with the production of 

ornamental and nursery crops. Application rates can be as high as 10.5 pounds DCPA per acre. 

DCPA is marketed in typical containers that would allow open mixing activities (e.g., bottle). 
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Applications can be made prior to planting, as a pre-emergent, and as a layby treatment over 

existing crops. Concurrent cultivation practices are also recommended by labels to ensure 

efficacy of DCPA and reduce the potential for off-site movement (e.g., soil incorporation, 

banding applications, and proper irrigation timing). 

Occupational risk estimates from DCPA use were considered in the previous assessments. 

Current labels require the use of normal work clothing for handlers with gloves and dust/mist 

respirators. The current Restricted-Entry Interval is 12 hours. Prior assessments were based on 

chemical-specific dislodgeable foliar residue studies. For all scenarios assessed, occupational 

risks were not of concern if these required label risk management elements were followed.

A revised occupational risk assessment will be required because updated monitoring data are 

being developed for pertinent occupational handler exposures and additional handler exposure 

scenarios also need to be addressed that were not included in previous assessments. These 

include aerial application and handheld methods used for the production of nursery and 

ornamental crops. Additionally, a revised risk assessment may be needed to address possible 

exposure to workers doing activities in previously treated areas (i.e., post-application exposure). 

The existing policy on farmworker activities was recently revised and includes either updated 

values for quantitatively evaluating these exposures or it will provide a more definitive 

qualitative rationale for not conducting a quantitative assessment. 

In the existing assessments a dermal noncancer endpoint was not identified for risk assessment 

purposes but cancer risks from dermal exposures were quantitatively assessed. Additionally, 

noncancer and cancer risks were quantified for occupational handler inhalation exposures. 

Finally, post-application cancer risks from dermal exposures were quantified. Any changes in 

risk assessment endpoints for DCPA would necessitate appropriate revisions to the risk 

assessment.

It should also be noted that there are trace contaminant materials in DCPA products which were 

addressed in existing risk assessments, but they may require further review and analysis as part 

of the registration review process. 

Conclusions: No occupational data gaps were identified during the Registration Review scoping 

process for DCPA. Adequate data, including studies currently in progress by various task forces, 

are available to assess all of the occupational exposure scenarios for the registered uses of 

DCPA. It is noted that the primary registrants are members of the Agricultural Reentry Task 

Force (ARTF), the Agricultural Handlers Exposure Task Force (AHETF), and the Outdoor 

Residential Exposure Task Force (ORETF). It should also be noted that likely upcoming policy

revisions such as anticipated modifications in the Agency policies for completing occupational 

exposures could cause elements of the current exposure assessments to be revised (e.g., possible 

changes in transfer coefficients for field workers and unit exposures for handlers). These 

changes could specifically occur based on the results of the ARTF, AHETF and ORETF. Also, 

additional scenarios may be needed to address changes in other risk assessment policies related 

to spray drift, worker protection and volatilization of pesticides.
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Public Health and Pesticide Epidemiology Data

HED has reviewed the OPP Incident Data System (IDS) to determine if there were significant 

incidents related to DCPA and human health (Winfield, 2011). Based on the low frequency and 

severity of incident cases, there does not appear to be a concern at this time that would warrant 

further investigation of incidents involving DCPA. The Agency will continue to monitor the 

incident information and if a concern is triggered, additional analysis will be included in the risk 

assessment.

Tolerance Assessment and International Harmonization

The US has established tolerances crops with registered uses of DCPA as well as inadvertent 

residue tolerances resulting from indirect exposure to crops via carry-over in the soil and

transport of residues through drift. A summary of US tolerances may be found in Table 2 

attached to this document, along with a summary of Canadian Maximum Residue Limits (MRL). 

Codex has not established MRLs in/on any commodity, and Mexico generally adopts US

tolerances and/or Codex MRLs for export purposes. Note that the MRL regulations for Canada 

do not include a separate entry for inadvertent residues. The US and Canada are not harmonized 

with respect to residue definition: the US includes two metabolites (MPA and TPA) in the 

residue definition, while the Canadian MRL includes only the parent. With respect to residue 

levels, for almost all commodities where both US and Canadian limits have been established, the 

values are the same, with the exception of the Brassica vegetables. Whereas the US has 

established a crop group tolerance at a level of 5 ppm, Canada has established limits for the 

individual commodities, ranging from 1 to 5 ppm.

Some of the entries for the section on inadvertent tolerances include crops with registered uses. 

The registrants should clearly indicate in their response to the Registration Review Preliminary 

Work Plan (PWP) those crops where direct applications will be supported, and those tolerances 

that will be supported as inadvertent tolerances. During registration review HED will re-evaluate 

the data supporting the tolerances, correct the entries in the tolerance regulation, and will attempt 

to harmonize with international MRLs to the extent possible. In addition the residue definition 

should be modified in accordance with current policy on tolerance definitions (S. Knizner, 

5/27/09) as describe below:

Tolerances are established for residues of the herbicide dimethyl 

tetrachloroterephthalate (DCPA), 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 the sum of DCPA and its 

metabolites monomethyltetrachloroterephthalate (MTP) and 

tetrachloroterephthalic acid (TCP), calculated as the stoichiometric equivalent of 

DCPA, in or on the commodity.

Environmental Justice

Potential areas of environmental justice concerns, to the extent possible, were considered in this 

human health risk assessment, in accordance with U.S. Executive Order 12898, "Federal Actions 

to Address Environmental Justice in Minority Populations and Low-Income Populations," 
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http://www.epa.gov/environmentaljustice/resources/policy/exec_order_12898.pdf. The Office of 

Pesticide Programs (OPP) typically considers the highest potential exposures from the legal use 

of a pesticide when conducting human health risk assessments, including, but not limited to, 

people who obtain drinking water from sources near agricultural areas, the variability of diets 

within the U.S. (including different ages, regions, and ethnicities), and people who may be 

exposed when harvesting crops. Should these highest exposures indicate potential risks of 

concern, OPP further refines the risk assessments to ensure that the risk estimates are based on 

the best available information.

Human Studies

Past DCPA risk assessments relied in part on data in generic databases from studies in which 

adult human subjects were intentionally exposed to a pesticide to determine their dermal and 

inhalation exposure or similar studies from the literature. Many such studies, involving exposure 

to many different pesticides including DCPA, are included in generic pesticide exposure 

databases such as the Pesticide Handler Exposure Database (PHED), the Agricultural Reentry

Task Force (ARTF), and the Outdoor Residential Exposure Task Force (ORETF). Also, there 

will be a reliance on the work of the Agricultural Handlers Exposure Task Force (AHETF) for 

revisions to the occupational handler risk assessments possibly needed in the future. These 

studies have been determined to require a review of their ethical conduct and have received the 

appropriate review.

Endocrine Disruption

As required by FIFRA and FFDCA, EPA reviews numerous studies to assess potential adverse 

outcomes from exposure to chemicals. Collectively, these studies include acute, subchronic 

and chronic toxicity, including assessments of carcinogenicity, neurotoxicity, developmental, 

reproductive, and general or systemic toxicity. These studies include endpoints which may be 

susceptible to endocrine influence, including effects on endocrine target organ histopathology, 

organ weights, estrus cyclicity, sexual maturation, fertility, pregnancy rates, reproductive loss, 

and sex ratios in offspring. For ecological hazard assessments, EPA evaluates acute tests and 

chronic studies that assess growth, developmental and reproductive effects in different 

taxonomic groups. As part of its reregistration decision, EPA reviewed these data and selected 

the most sensitive endpoints for relevant risk assessment scenarios from the existing hazard 

database. However, as required by FFDCA section 408(p), DCPA is subject to the endocrine 

screening part of the Endocrine Disruptor Screening Program (EDSP). 

EPA has developed the EDSP to determine whether certain substances (including pesticide 

active and other ingredients) may have an effect in humans or wildlife similar to an effect 

produced by a “naturally occurring estrogen, or other such endocrine effects as the 

Administrator may designate”. The EDSP employs a two-tiered approach to making the 

statutorily required determinations. Tier 1 consists of a battery of 11 screening assays to 

identify the potential of a chemical substance to interact with the estrogen, androgen, or thyroid 

(E, A, or T) hormonal systems. Chemicals that go through Tier 1 screening and are found to 

have the potential to interact with E, A, or T hormonal systems will proceed to the next stage of 

the EDSP where EPA will determine which, if any, of the Tier 2 tests are necessary based on 
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the available data. Tier 2 testing is designed to identify any adverse endocrine-related effects 

caused by the substance, and establish a dose-response relationship between the dose and the E, 

A, or T effect. 

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. Between 

October 2009 and February 2010, EPA issued test orders/data call-ins for the first group of 67 

chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. DCPA was 

included on that list and has been issued an order to conduct the Tier 1 testing. Once all 

required Tier 1 and Tier 2 data have been received and reviewed, the endpoints and safety 

factors used for risk assessment purposes will be examined and a new risk assessment 

performed if necessary. For further information on the status of the EDSP, the policies and 

procedures, the list of 67 chemicals, future lists, the test guidelines and the Tier 1 screening 

battery, please visit our website: http://www.epa.gov/endo/.

Data Requirements

The following studies are required to support the registration review of DCPA:

Toxicity studies

 870.7800: Immunotoxicity

 870.3700SS (Special Study): Comparative Thyroid Study

 870.3465: Subchronic Inhalation Toxicity Study – 28 day

 870.6200: Neurotoxicity Battery (Acute and Subchronic Studies)

Residue Chemistry Studies

 860.1300: Nature of the Residue: Poultry

 860.1340: Residue Analytical Method: Livestock Commodities

 860.1380: Storage Stability

 860:1480: Meat/Milk/Poultry/Eggs: Ruminants

 860.1900: Field Accumulation in Rotational Crops

Tables describing the rationale for requiring these studies are attached to this document. In 

addition, once the rotational crop studies have been completed product labels should be modified 

to include appropriate plant-back intervals. The registrants should also certify that the levels of 

the impurities of concern have not changed since the most recent risk assessment that considered 

the cancer risk to these toxic impurities.
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References

Bradman A, et al. 2007. Pesticides and their metabolites in the homes and urine of farmworker 

children living in the Salinas Valley, CA. J Expo Sci Environ Epidemiol 17:331-349.

FR Vol. 70 No. 143 (07/27/05) pp 43408-43410, DCPA; Order to Amend to Terminate Uses.

Gray, Jr. LE, et al. Perinatal Exposure to the Phthalates DEHP, BBP, and DINP, but Not DEP, 

DMP, or DOTP, Alters Sexual Differentiation of the Male Rat. Toxicol. Sci. (2000) 58(2): 350-

365 doi:10.1093/toxsci/58.2.350

Gunier RB, et al. 2011. Determinants of Agricultural Pesticide Concentrations in Carpet Dust. 

Environ Health Perspect doi:10.1289/ehp.1002532 (accessed March 3, 2011)

Harnly ME, et al. 2009. Pesticides in dust from homes in an agricultural area. Environ Sci 

Technol 43:8767-8774.

Nuckols JR, et al. 2007. Linkage of the California Pesticide Use Reporting Database with spatial 

land use data for exposure assessment. Environ Health Perspect 115:684-689.

Nuckols JR, Riggs PD, Gunier RB, Ward MH 2008. Geographic-based prediction of agricultural 

pesticides in household carpet dust in the central valley of California. Epidemiology 19:S320.

U.S. EPA. 1998b. Reregistration Eligibility Decision (RED): DCPA. EPA 738-R-98-005. 

November 1998. Special Review and Reregistration Division, Office of Pesticide Programs. 

Washington, D.C. U.S.A. Available at: http://www.epa.gov/oppsrrd1/REDs/0270red.pdf

(accessed January 28, 2011)

U.S. EPA. 2008a. Health Effects Support Document for Dacthal Degradates: 

Tetrachloroterephthalic Acid (TPA) and Monomethyl Tetrachloroterephthalic Acid (MTP). 

EPA-822-R-08-005. May, 2008. Health and Ecological Criteria Division. Office of Water. 

Washington, D.C. U.S.A. Available at: 

http://www.epa.gov/safewater/ccl/pdfs/reg_determine2/healtheffects_ccl2-

reg2_dacthaldegradates.pdf (accessed February 28, 2011)

OPP Memoranda Citations

Author DP Barcode/ 

Record No. Date Title

Winfield, S. D386640 3/1/11 DCPA: Review of Human Incidents

Ratnayake, 

S., et al. N/A 1/20/11 BEAD Chemical Profile for Registration Review: DCPA (07870I)

N/A N/A 8/18/10 EPA Screening Level Estimate of Agricultural Uses (SLUA) 

(8/18/10)

N/A N/A 8/10/10 EPA Analysis of California DPR Pesticide Usage Data (
Page 13 of 22

Author DP Barcode/ 

Record No. Date Title

Dole, T. D303994 6/9/04

2nd Revised Drinking Water and Aggregate Human Health Risk 

Assessment for Chlorthal dimethyl (DCPA) and the metabolite 

tetrachloroterephthalic acid (TPA) 

Farwell, K. D303156 5/25/04 TPA (tetrachloroterephthalic acid) - metabolite of DCPA 

(Dacthal). Evaluation of Potential for Carcinogenicity. 

Farwell, K. 

and AbdelSaheb, I.

TXR No.

0052585 5/25/04

TPA (tetrachloroterephthalic acid) - metabolite of DCPA 

(Dacthal). Report of the Metabolism Assessment Review 

Committee

Dole, T., et. 

al. D281320 7/8/02

HED Human Health Risk Assessment For DCPA to Support New

Uses on California Parsley and Other Minor Crops (D281320, 

7/8/02)

Hazel, W. D280398 6/14/02 PP#0E3883 and PP#2E6442. IR-4 Petitions for Tolerances and 

Proposals. Review of Analytical Chemistry and Residue Data.

Dole, T. D283509 6/10/02

Occupational and Residential Risk Assessment to Support Request

for Establishment of Tolerance for Chlorthal-Dimethyl (DCPA) on 

Minor Crops.

Taylor, L., 

and Rinde, 

E.

TXR No.

0050123 2/10/95

Carcinogenicity Peer Review of DCPA (Dimethyl 

tetrachloroterephthalate or Dacthal)for meetings on June 29 and 

Nov. 16, 1994. Linda Taylor and Esther Rinde. 
Page 14 of 22

Attachments

Chemical Identity

Table 1. Chemical Identity 

Common Name DCPA

Other Names Chlorthal dimethyl; CAS Name: dimethyl 2,3,5,6-tetrachloro-1,4-

benzenedicarboxylate; IUPAC Name: dimethyl tetrachloroterephthalate

PC Code 078701

1861-32-1

Case No. 0720

Chemical Structure 

Metabolites/Degradates of Concern

Name monomethyltetrachloroterephthalate (MTP)

CAS registry number 887-54-7

Chemical Structure

Name tetrachloroterephthalic acid (TCP or TPA)

CAS registry number 2136-79-0

Chemical Structure

Table 2. Summary of US and International Residue Limits

Commodity1

Tolerance (ppm) /Maximum Residue Limit (mg/kg)

US Canada Mexico2 Codex

180.185(a)

Cantaloupe 1.0 1.0 None None

Garlic 1.0 1.0 None None

Ginseng 2.0 None None None

Horseradish 2.0 None None None
Page 15 of 22

Table 2. Summary of US and International Residue Limits

Commodity1

Tolerance (ppm) /Maximum Residue Limit (mg/kg)

US Canada Mexico2 Codex

Muskmelon 1.0 Honeydew melon: 

1.0 None None

Onion, bulb 1.0 1.0 None None

Onion, green 1.0 None None None

Strawberry 2.0 2.0 None None

Tomato 1.0 1.0 None None

Vegetable, brassica, leafy, group 5

5.0

Broccoli, Brussels 

Sprouts, Cabbages, 

Cauliflower: 1.0 

Collards, Kale: 2

Mustard Greens: 5

None None

Watermelon 1.0 1.0 None None

180.185(c) (tolerances with regional registration)

Radish, roots 2.0 None None None

Radish, tops 15.0 None None None

180.185(d) (inadvertent tolerances) 3

Basil, dried leaves 20.0 None None None

Basil, fresh leaves 5.0 None None None

Bean, dry 2.0 None None None

Bean, mung, seed 2.0 None None None

Bean, snap, succulent 2.0 2.0 None None

Celeriac 2.0 None None None

Chicory, roots 2.0 None None None

Chicory, tops 5.0 None None None

Chive 5.0 None None None

Coriander, leaves 5.0 None None None

Corn, field, forage 0.4 None None None

Corn, field, grain 0.05 None None None

Corn, field, stover 0.4 None None None

Corn, pop, forage 0.4 None None None

Corn, pop, grain 0.05 None None None

Corn, pop, stover 0.4 None None None

Corn, sweet, forage 0.4 None None None

Corn, sweet, kernel plus cob with 

husks removed 0.05 None None None

Corn, sweet, stover 0.4 None None None

Cotton, undelinted seed 0.2 None None None

Cucumber 1.0 1.0 None None

Dill 5.0 None None None

Eggplant 1.0 1.0 None None

Lettuce 2.0 2.0 None None

Marjoram 5.0 None None None

Parsley, dried leaves 20.0 None None None

Parsley, leaves 5.0 None None None

Pea, blackeyed, seed 2.0 2.0 None None

Pepper 2.0 2.0 None None

Pimento 2.0 2.0 None None

Potato 2.0 2.0 None None

Radicchio 5.0 None None None

Radish, oriental, roots 2.0 None None None
Page 16 of 22

Table 2. Summary of US and International Residue Limits

Commodity1

Tolerance (ppm) /Maximum Residue Limit (mg/kg)

US Canada Mexico2 Codex

Radish, oriental, tops 2.0 None None None

Rutabaga 2.0 None None None

Soybean 2.0 None None None

Squash, summer 1.0 1.0 None None

Squash, winter 1.0 None None None

Sweet potato 2.0 2.0 None None

Turnip, roots 2.0 2 None None

Turnip, tops 5.0 5 None None

Yam, true, tuber 2.0 2 None None

1

Includes only commodities of interest for this action. Tolerance values should be the HED recommendations and 

not those proposed by the applicant.

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

3Canada does not distinguish maximum residue limits in their maximum residue limit regulations. Therefore the 

Canadian limits included in this section do not specifically refer to inadvertent residues.

Table 3. Summary of Revised Maximum Reasonable Dietary Burden for DCPA

Feed Commodity Feedstuff 

Type

% Dry 

Matter

Percent in 

Diet

Tolerance 

Level

Max 

Contribution

Beef Cattle (R=15%; CC=80%; PC=5%)

Corn Forage R 40 15 0.4 0.15

Corn Grain CC 88 50 0.05 0.028

Processed Potato Waste CC 15 30 2 4

Soybean Seed PC 89 5 2 0.11

Total NA NA 100 NA 4.29

Dairy Cattle (R=45%; CC=45%; PC10%)

Corn Forage R 40 15 0.4 0.15

Turnip Tops R 30 30 5 5

Turnip Roots CC 15 10 2 1.33

Processed Potato Waste CC 15 10 2 1.33

Corn Grain CC 88 25 0.05 0.014

Soybean Seed PC 89 10 2 0.22

Total NA NA 100 NA 8.06

Poultry (CC=75-80%; PC=20-25%)

Corn Grain CC NA 0 80 0.05 0.04

Soybean Seed PC 20 2 0.4

Total 0.44

Hogs (CC=80-85%; PC=15-20%)

Corn Grain CC 0 80 0.05 0.04

Soybean Seed PC 20 2 0.4

Total NA NA 100 NA 0.44
Page 17 of 22

Rationale for Requiring a Poultry Nature of the Residue Study

Guideline Number: 860.1300

Study Title: Nature of the Residue, Livestock (Poultry)

Rationale for Requiring the Data

This study provides essential information on the potential transfer and bioconcentration of residues in

poultry meat and eggs for pesticides applied to feed items. Many pesticides undergo change during or 

after livestock consume treated feed. The composition of the terminal residue must be determined 

before complete residue detection methodology and residue quantification data can be developed. The 

study may help to validate the poultry magnitude of residue data previously submitted if no new 

residues of concern are identified. The requested poultry nature of the residue study will need 

supporting storage stability data for all DCPA residues of concern, unless the samples from the feeding 

study are analyzed within six months of collection.

Practical Utility of the Data

How did the Agency make its re-registration decision without these data? 

In order to make its reregistration decision, the Agency assumed poultry would have similar types of 

residues as cattle and goats. 

How will the data be used? 

The data will be used to provide a full characterization of the DCPA residue profile. The submission 

will provide the necessary data to set tolerances for livestock commodities. These data may also result 

in a change in how dietary risks are quantified. 

Rationale for Requiring an Independent Laboratory Validation for a Livestock Residue 

Analytical Method

Guideline Number: 860.1340

Study Title: Residue Analytical Methods (enforcement analytical method for livestock) 

Rationale for Requiring the Data

One of the analytical methods submitted by the registrant must be suitable for use by various Federal 

and State enforcement agencies. The Food and Drug Administration (FDA) collects these methods and 

then publishes them to be used for tolerance enforcement purposes. The registrant has submitted a 

method for determining residues of DCPA and its metabolites that may be suitable but must be tested 

by an independent laboratory to ensure that it is useful. 

Practical Utility of the Data

How will the data be used?

EPA would review the independent laboratory validation of the submitted method and determine its 

suitability as an enforcement method. If suitable, EPA would forward the method to FDA. The 

enforcement analytical methods are published by FDA and are available to all regulatory laboratories 

for use in monitoring the specific pesticide concentrations in foods and feeds. They are a necessary 

tool for tolerance enforcement and residue monitoring and, as such are essential in the efforts to ensure 

a safe food supply for the consumer. 
Page 18 of 22

Rationale for Requiring Cattle Magnitude of Residue Study 

Guideline Number: 860.1480

Study Title: Magnitude of the Residue (Cattle Feeding Study)

Rationale for Requiring the Data

A new ruminant feeding study is required to determine whether tolerances are needed (and if so the 

appropriate tolerance levels) for milk and meat. The requested ruminant feeding study will need 

supporting storage stability data for all DCPA residues of concern, unless the samples from the feeding 

study are analyzed within 30 days of collection.

Practical Utility of the Data

How did the Agency make its re-registration decision without these data?

The Agency has made conservative assumptions within the dietary assessment to account for the lack 

of magnitude of the residue (MOR) data from the cattle feeding studies. Residue estimates based on the 

metabolism studies were included to account for potential exposure to DCPA and it metabolites in meat 

and milk from ruminants. However, these data are needed to ensure that the correct assumptions were 

made.

How will the data be used?

The data will be used to provide a full characterization of the DCPA residue profile. The submission of 

livestock MOR data would provide the necessary data to determine if tolerances are needed for 

livestock commodities and if necessary, to set the appropriate tolerance levels.

How could the data impact the Agency’s future decision-making?

The submission of MOR data would provide the necessary data to set tolerances for livestock 

commodities. These data may also result in a change in how dietary risks are quantified.
Page 19 of 22

Rationale for Requiring Field Accumulation in Rotational Crops Study 

Guideline Number: 860.1900

Study Title: Field Accumulation in Rotational Crops 

Rationale for Requiring the Data

A rotational crop use is any field-vegetable crop use or any other site use on which it is reasonably 

foreseeable that any food or feed crop may be planted after harvest of a treated crop. The purpose of 

field accumulation in rotational crop studies is to determine the amount of pesticide residue uptake into 

rotational crops. The study uses a typical end-use product applied to a field plot. Results of these 

studies are used to determine whether residues occur in rotational crops grown under actual field 

conditions. Based on these data, appropriate crop rotation restrictions (time from application to 

planting of rotational crop) may be established and the need for tolerances on the rotated crops 

determined.

Carrot roots and tops, corn fodder and silage, oat forage, and turnip tops from plants sowed at a 1-year 

plantback interval in soil treated at half the maximum application rate bore quantifiable residues in one 

or more samples. These data indicate that tolerances are needed for residues of DCPA and metabolites 

in some crops if they are rotated to fields that have been treated at even half the maximum seasonal 

label rate. The petitioner/registrant has not proposed any restrictions that obviate the need for 

rotational crop tolerances.

Large-scale rotational crop field trials are required to determine the appropriate tolerance levels for 

rotated crop commodities. The scope of the required tests is dependent upon the 

petitioner’s/registrant's intent with respect to the crops to be allowed in rotation and the desired 

plantback interval(s) for these crops. Any crop without a registered use, for which the 

petitioner/registrant wishes to allow rotation, requires field trial data to determine a suitable tolerance 

level. A crop group approach, requiring data on representative commodities, may be appropriate if 

several crops within a group are to be rotated. For individual crops, the standard number of trials 

needed to support direct crop treatment tolerances are required, e.g., 20 trials for wheat.

Practical Utility of the Data

How did the Agency make its re-registration decision without these data? 

Since the data were lacking, the Agency was not able to evaluate risks for rotational crops. 

How will the data be used? 

The data will be used to provide a full characterization of the DCPA residue profile. The submission of 

these data would provide the necessary information to determine if tolerances are needed for rotated 

crops and if so, to set the appropriate tolerance levels. These data may also result in a change in how 

dietary risks are quantified. 

How could the data impact the Agency’s future decision-making?

The submission of these data would allow the Agency determine if tolerances are necessary for 

rotational crops and if so, to set the appropriate tolerances. The previously submitted confined and 

limited field rotational crop studies have shown potential residue uptake into rotated crops. If residues 

are detected in crops without established tolerances, these crops may be seized by the Food and Drug 

Administration (FDA). Accurate rotational crop tolerances protect farmers from inappropriate crop 

seizures. 
Page 20 of 22

Rationale for Requiring a 28-day Subchronic Toxicity Study

Guideline Number: 870.3465

Study Title: Subchronic Inhalation Toxicity Study

Rationale for Requiring the Data

This data requirement is conditionally required under 40 CFR Part 158 as a part of the data 

requirements for registration of a pesticide (food and non-food uses). This study is required for DCPA 

because workers can potentially be exposed to DCPA via the inhalation route of exposure. DCPA is in 

toxicity category IV for inhalation exposure and is a mild irritant to the eyes and skin and is not a skin 

sensitizer. 

Practical Utility of the Data

How will the data be used?

This study can be used to select endpoints and doses for use in exposure assessment for workers by the 

inhalation route of exposure. 

How could the data impact the Agency's future decision-making?

This study will be used in a worker occupational exposure assessment. This study was requested in the 

previous risk assessment. 

Rationale for Requiring a Comparative Thyroid Study

Guideline Number: 870.3700SS (Special Study)

Study Title: Comparative Thyroid Study

Rationale for Requiring the Data

Thyroid toxicity with treatment with DCPA has been observed in studies with adult animals, but no 

such data exist for developmental effects of DCPA on the thyroid and thyroid hormones of young 

animals. 

Practical Utility of the Data

How will the data be used?

The thyroid and thyroid hormones are adversely affected by treatment with DCPA, but data are lacking 

with which to estimate developmental risks associated with this toxicity. The data may provide a dose 

and endpoint for use in the assessment of risks for children and will play a role in the registration 

review decision.

How could the data impact the Agency’s future decision-making?

If the study indicates there is a special vulnerability to children from DCPA, a new toxicity endpoint 

will be incorporated into the risk assessment for children. 
Page 21 of 22

Rationale for Requiring The Neurotoxicity Battery

Guideline Number: 870.6200

Study Title: Neurotoxicity Battery (Acute and Subchronic Studies)

Rationale for Requiring the Data

The Neurotoxicity Screening Battery (OPPTS 870.6200) is designed to evaluate the potential adverse 

effects on the nervous system from exposure to pesticide chemicals. The Agency believes that the 

guideline studies are inadequate in their assessment of behavioral effects and do not use optimal 

methods to evaluate the potential toxicity to the nervous tissue structure and function. To detect and 

characterize these potential effects more fully, a battery of more sensitive testing is required. The 

objective of this neurotoxicity battery testing is to evaluate the incidence and severity of the functional 

and/or behavioral effects, the level of motor activity, and the histopathology of the nervous system. The 

acute neurotoxicity study is required to detect possible effects resulting from a single exposure. The 

subchronic neurotoxicity study is intended to detect possible effects resulting from repeated or longterm exposures. 

Neurotoxicity was not detected in the toxicity studies with DCPA. 

Practical Utility of the Data

How will the data be used?

The acute and subchronic neurotoxicity studies provide critical scientific information needed to 

characterize potential hazard to the human population on the nervous system from pesticide exposure. 

These studies can provide data on a wide range of functional tests for evaluating neurotoxicity 

including sensory effects, neuromuscular effects, learning and memory and histopathology of the 

nervous system and can be used to select endpoints and doses for use in risk assessment of all exposure 

scenarios and are considered a primary data source for reliable reference dose calculation. 

How could the data impact the Agency's future decision-making?

If the acute or subchronic neurotoxicity studies show that DCPA poses either a greater or a diminished 

risk than that given in the previous risk assessment, the risk assessment may need to be revised to 

reflect the magnitude of potential risk derived from the new data. 

If the Agency does not have these data, a 10X database uncertainty factor may be applied when 

conducting a risk assessment using the currently available studies.
Page 22 of 22

Rationale for Requiring an Immunotoxicity Study

Guideline Number: 870.7800

Study Title: Immunotoxicity

Rationale for Requiring the Data

This is a new data requirement under 40 CFR Part 158 as a part of the data requirements for 

registration of a pesticide (food and non-food uses). 

The Immunotoxicity Test Guideline (OPPTS 870.7800) prescribes functional immunotoxicity testing 

and is designed to evaluate the potential of a repeated chemical exposure to produce adverse effects 

(i.e., suppression) on the immune system. Immunosuppression is a deficit in the ability of the immune 

system to respond to a challenge of bacterial or viral infections such as tuberculosis (TB), Severe 

Acquired Respiratory Syndrome (SARS), or neoplasia. Because the immune system is highly complex, 

studies assessing functional immunotoxic endpoints are helpful in fully characterizing a pesticide’s 

potential immunotoxicity. These data will be used in combination with data from hematology, 

lymphoid organ weights, and histopathology in routine chronic or subchronic toxicity studies to 

characterize potential immunotoxic effects. 

Practical Utility of the Data

How will the data be used?

These animal studies can be used to select endpoints and doses for use in risk assessment of all 

exposure scenarios and are considered a primary data source for reliable reference dose calculation. For 

example, animal studies have demonstrated that immunotoxicity in rodents is one of the more sensitive 

manifestations of TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) among developmental, reproductive, 

and endocrinologic toxicities. Additionally, the EPA has established an oral reference dose (RfD) for 

tributyltin oxide (TBTO) based on observed immunotoxicity in animal studies (IRIS, 1997).

How could the data impact the Agency's future decision-making?

If the immunotoxicity study shows that the test material poses either a greater or a diminished risk than 

that given in the interim decision’s conclusion, the risk assessments for the test material may need to be 

revised to reflect the magnitude of potential risk derived from the new data.

If the Agency does not have these data, a 10X database uncertainty factor may be applied for 

conducting a risk assessment from the available studies.
APPENDIX TO DCPA SCOPING DOCUMENT

Page 1 of 1

Discussion on Toxic Impurities

The manufacturing process of DCPA produces several contaminants known to be of significant 

toxicological concern, including hexachlorobenzene (HCB) and congeners (structurally related 

chemicals) of polyhalogenated dibenzo-p-dioxins/dibenzofurans (dioxins/furans). Carcinogenic 

risk was assessed for dietary exposure to HCB and dioxin/furans using cancer potency factors of 

1.02 (mg/kg/day)

-1

and 1 x 105, respectively. Estimated dietary risks were negligible and below 

the level of concern. In addition, cancer risk from these contaminants was assessed for 

occupational exposure and was below the level of concern.