UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MEMORANDUM 

DATE: March 18,2014 

OFFICE OF CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

SUBJECT: RESPONSE TO COMMENTS. The Health Effects Division's Response to 

Pesticide Action Network North America on the Chloropicrin Registration 

Review Scoping Document for Human Risk Assessment (OPP Docket# EPA-HQOPP-20 13-0 153). 

PC Code: 081501 

Decision No.: 'fi5!9~ 

Petition No.: NJA 

Risk Assessment Type: Single Chemical/Aggregate 

TXR No.: N/A 

MRID No.: N/A 

FROM: Shalu Shelat, Industrial Hygienist 

Risk Assessment Branch VI 

and 

Monique Perron, S.D., Toxicologist 

Risk Assessment Branch I 

Health Effects Division (7509P) 

DP Ba rcode: 0416740 

Registration No.: N/A 

Regulatory Action: Registration Review 

Case No.: 0040 

CAS No.: 76-06-2 

40 CFR: N/A 

THRU: Charles 

Risk Assessment 

Smith, Branch 

Branch 

Chief 

I 

c__f? 

~ 

~ -

Health Effects Division (7509P) 

TO: Carolyn Schroder, Chemical Review Manager 

Risk Management and Implementation Branch IV (7508P) 

Pesticide Re-evaluation Division 

In response to the letter submitted by the Pesticide Action Network North America (PANNA) in 

regards to the use and application of fumigants as part of the chloropicrin Preliminary Work Plan 

(Docket ID No. EPA-HQ-OPP-2013-0153). 

Page 1 of 18 
I) Levels of concern must be reevaluated: US EPA needs to reevaluate the points of 

departure (PODs) and uncertainty factors (UFs) used for the residential and occupational 

exposure assessments. The acute level of concern of73 ppb averaged over 8 hours is not 

sufficiently protective, a point that was clearly made in the California review and by US 

EPA's Human Subjects Review Panel. Since chloropicrin has short-term irritant 

properties, the acute level of concern is also relevant for short-term exposures, as 

recognized by DPR in their Risk Characterization document. 

EPA Response: 

As stated by the Agency in the Health Effects Division 2009 Response to Comments on the 2008 

Reregistration Eligibility Documents (D348636, May 14, 2009), the Agency has relied on three 

key guidance/framework documents for consideration of mode of action and refinement of the 

intraspecies factor for chloropicrin. These guidance and framework documents which focus on 

mode of action and kinetic and mechanistic data to refine inter-species and intra-species 

extrapolation factors have been outlined in a chloropicrin memo (Reaves and Lowit, 0293356, 

TXR 0054860, 06118/08). This memorandum considered toxicokinetics, dynamics and mode of 

action as well as the level at which individuals in the population detect and become irritated to 

chloropicrin. All of this information was considered in the refinement of the intraspecies factor. 

The BMCL10 or NOAEL of73 ppb is protective of all individuals without an inclusion of 

intraspecies factor since it is 2-fold below a level that the most sensitive subpopulation was 

beginning to detect chloropicrin without direct irritation ( 150 ppb ). The point of departure 

(0.073 ppm) is 145-fold lower than the acute rodent inhalation study (1 0.6 ppm), 14-fold lower 

than irritation produced in repeat inhalation rodent studies (1.0 ppm) and 14-fold lower than 

acute eye and respiratory effects observed in incident reports (1.0 ppm). 

The PANNA comments also discuss the differences between the California DPR toxicology 

database conclusions and those of the Agency. The Agency, as discussed in the cited memo, has 

relied on human data for the acute ( 1-24 hour) point of departure with the endpoint based on eye 

irritation. The DPR approach uses a different endpoint of increased nitric oxide (NO) in expired 

nasal air from the same human study for the acute (I hour) point of departure and in addition, 

DPR retained the 1 OX intraspecies uncertainty factor. DPR also selected a separate acute (8 and 

24 hour) point of departure from a developmental rabbit toxicity study which included I OX 

intraspecies and interspecies uncertainty factors. 

The Agency maintains that the chloropicrin risk assessment is sufficiently protective and utilizes 

the most appropriate points of departure and safety factors. 

2) The bystander exposure assessment must be re-done: The Office of Pesticide 

Programs should eliminate any use of the "whole field" method of exposure assessment 

that averages concentrations and results in .substantially underestimated exposure 

predictions. The "maximum direction" method used by CDPR should be utilized instead 

because it provides a more realistic estimate of worst-case (but very common) bystander 

exposures downwindjrom a.fumigation application. In addition, the ISCST3 model on 

which P ERFUM is based is out of date, and US EPA 's Office of Air and Radiation 

Page 2 of 18 
Page 3 of 18

indicates that the current preferred models for atmospheric exposure assessments are

either AERMOD or CALPUFF. These models will better handle calm wind conditions.

EPA Response:

In the 2009 amended REDs for the soil fumigants, the Agency used a weight of evidence 

approach to develop the buffer zone distances which included consideration of the hazard profile 

of the fumigants, information from incident reports, monitoring data, stakeholder comments 

along with comprehensive analysis of results from PERFUM modeling and consideration of 

results using other models. The analysis of PERFUM results considered distances at various 

percentiles of the whole field and maximum distance distributions, and Margins of Exposure 

(MOEs) for various distances. EPA’s goal for risk management was to achieve a buffer distance 

where associated risks were at or below target concentration levels at high percentiles of 

exposure. In other words, at the outer edge of the buffer zone surrounding an application site, the 

probability of exposure is extremely low.

The Office of Pesticide Programs (OPP) recognizes that different parts of the Agency use 

different models for atmospheric exposure assessments. OPP has previously conducted a

preliminary comparative evaluation of the differences in outputs between the current version of 

PERFUM (based on ISCST3) and an evaluation version of PERFUM (based on AERMOD) and 

in most cases the analysis indicates very similar buffer distance predictions. In addition, OPP has 

also previously conducted a preliminary comparative evaluation of the differences in outputs 

between the current version of PERFUM (based on ISCST3) and the FEMS model (based on 

CALPUFF) and in most cases the analysis indicates very similar buffer distance predictions. For 

most of the instances were small differences in buffer distance predictions were seen, use of 

AERMOD or CALPUFF as the base model resulted in slightly smaller buffer distance 

predictions. This indicates that the use of PERFUM (based on ISCST3) in the chloropicrin risk 

assessment should be considered health protective. 

3) The carcinogenicity of chloropicrin must be reevaluated: Significant concerns were

raised by the DPR toxicologists, OEHHA toxicologists, and the SRP members regarding

the carcinogenicity of chloropicrin. DPR management’s classification of chloropicrin

carcinogenicity as “equivocal” is in contradiction to the conclusions reached by DPR and

OEHHA scientists and the SRP, a point we discuss at greater length below. For the

chloropicrin reregistration, US EPA did not conduct an assessment of the carcinogenicity

of chloropicrin stating that:

“ . . . chloropicrin is currently not considered a carcinogen by the inhalation route of

exposure since there is no evidence of increased tumorigenesis after chronic inhalation

exposure.”

This is incorrect. There is substantial evidence of carcinogenicity from less-than-lifetime

mouse and rat inhalation studies. Less-than-lifetime studies are well known to have

reduced sensitivity for determining the statistical significance of observed effects. In

consideration of the fact that mutagenicity studies and a number of oral-dose animal

studies provide data indicating that chloropicrin is a potent carcinogen, US EPA must

reevaluate its carcinogenicity. Because the existing studies were so poorly conducted, it

may be necessary for US EPA to call in an additional lifetime inhalation cancer study.
Page 4 of 18

EPA Response:

The Agency has reviewed the data submitted in regards to the carcinogenicity of chloropicrin. In 

a letter (see Attachment 1) submitted to the Department of Pesticide Regulation (E. Reaves; 

11/9/09), the Agency provided an analysis of the data that DPR relied on for the mutagenic and 

carcinogenic classification of chloropicrin. In this analysis, the Agency has stated that both 

agencies are using the same cancer data; however, there are key differences in the approaches 

used to determine the classification of chloropicrin. In regards to the mutagenicity 

determination, in vitro mutagenicity assays for chloropicrin have mixed positive and negative 

results; however, in vivo data for chloropicrin are negative.

The Agency determined the chronic mouse inhalation study (MRID 43632201) is adequate for 

use in risk assessment and was analyzed consistent with procedures under the Cancer Review 

Committee (CARC) (Brunsman, 2009; TXR 0055260). Although DPR and OEHHA have 

provided conclusions that chloropicrin is carcinogenic through the inhalation route, the Agency 

believes that there is no concern for the carcinogenic potential for chloropicrin based on a 

number of considerations: 1) no lung tumors were seen in male or female rats exposed to the 

same exposure concentrations for a longer period of time (104 weeks) in the same laboratory; 2) 

no increase in lung tumors was seen in male mice; and 3) the weak response in female mice (i.e., 

the presence of a single common tumor that lacked biological or statistical significance with no 

increase in the proportion of malignant tumors nor decrease in the time to tumor occurrence). In 

addition, in the event that long-term or chronic exposure is expected, the long-term Human 

Equivalent Concentration (HEC) of 0.004 ppm would be used. The HEC is 250 fold lower than 

the concentration that induced biologically insignificant lung tumors and would be protective of 

any potential carcinogenicity from inhalation exposure to chloropicrin.

As a model of cancer risks assessed on an age-adjusted basis, PANNA submitted the report on 

chloropicrin air monitoring conducted in Sisquoc, California. The Agency has previously 

provided comments on the monitoring study and analysis results as part of the 2009 Response to 

Comments on the 2008 Reregistration Eligibility Documents (D348636, May 14, 2009). Any 

conclusions that PANNA has drawn in regards to air concentrations have limitations based on the 

comments provided in 2009. These limitations include the lack of availability of the raw study 

data, variations in the sampler flow rates, and lack of valid methods for quantifying chloropicrin 

air concentrations (i.e., use of the highest sample volume as the basis for air concentrations 

calculations). In addition, the Agency has not determined chloropicrin to have mutagenic effects 

in the in vitro system; therefore, an age-adjusted cancer risk approach would not be appropriate. 

EPA guidance requires age-dependent adjustment factors to be applied to children's cancer 

exposure only for carcinogenic pesticides that have been shown to have a mutagenic mode of 

action. The Agency's policies on conducting cancer risk assessments are contained in Guidelines 

for Carcinogen Risk Assessment1and Supplemental Guidance for Assessing Susceptibility from 

Early-Life Exposure to Carcinogens2. 

 

1 Available at: http://www.epa.gov/raf/publications/pdfs/CANCER_GUIDELINES_FINAL_3-25-05.PDF

2 Available at: http://www.epa.gov/ttn/atw/childrens_supplement_final.pdf
Page 5 of 18

4) Chloropicrin cannot be used safely—it should not be re-registered. However, if EPA

allows its continued use, buffer zones will need to be reevaluated: Based on changes

in 1), 2) and potentially 3) above, buffer zones will need to be recalculated, and

mitigations to protect handlers will need to be reassessed to be protective of human

health. However, we think it is likely that mitigations that would prevent unreasonable

adverse effects on human health or the environment will not prove possible, let alone

practical, so chloropicrin re-registration will not be supportable.

EPA Response:

The Agency reviews the use of pesticides in accordance with labels and best practices 

information. The Agency also takes into consideration incidents that may result in the 

modification of label allowances or restrictions. If information is provided that indicates certain 

label restrictions or application practices are not being met due to the nature of the application, 

the Agency will consider the modifications to the labels that may be necessary to ensure the 

health and safety of the individuals affected. In general, buffers will be reevaluated at the time of 

registration review and will take into consideration any changes in the exposure modeling or 

toxicological database at that time. 

The waiting time between fumigation and tarp cutting activities has been measured in one study 

that was provided to the Agency by DPR. The Agency agreed with DPR that exposure 

concentrations were greater than previously assessed at the time of tarp cutting. The Agency has 

requested additional information from DPR and is awaiting their analysis in order to provide a 

comprehensive assessment of the tarp cutting issue.

The modeling programs used to predicted buffers after the application of fumigants, takes into 

consideration the varying wind patterns and stagnation that may occur in the days following an 

application. The good agricultural practices that are required during all applications are intended 

to reduce exposure but also provide the best conditions to make an efficient application of a 

fumigant. 

5) Fumigant use is costly in many ways, and promising alternatives are available:

Fumigations are expensive, with many of the costs externalized to neighbors and farm

workers. California is aggressively pursuing alternatives to fumigants, with encouraging

results. US EPA BEAD should evaluate these methods when they do their economic

risk/benefit assessment for the use of chloropicrin.

EPA Response:

The soil fumigants have been among the most widely used pesticides in the US, and its use 

provides benefits to both food consumers and growers. In determining the reregistration 

eligibility for chloropicrin, the Biological and Economic Analysis Division (BEAD) conducted a 

number of benefits assessments for the fumigants by crop, and these are located in the 

chloropicrin RED docket at EPA-HQ-OPP-2007-0350. In the Summary of Benefits of Soil 

Fumigation with Chloropicrin (EPA-HQ-OPP-2007-0350-0017), the Agency acknowledged there 
Page 6 of 18

may be registered pesticide alternatives to chloropicrin available depending on the crop, but the 

alternatives may not control the full suite of pests. In addition, alternatives frequently cited for 

chloropicrin are other fumigants. 

However, PANNA is correct that non-chemical alternatives are being explored and developed as 

has been noted in the critical use exemption responses to the methyl bromide phase-out. 

Anaerobic soil disinfestation (ASD), soil substrate amendments, steam treatment, and others 

have potential for replacing some portion of currently fumigated land. If PANNA is aware of 

additional data on fumigant alternatives, please consider submitting this information to the 

Agency for consideration. Through the registration review process, the Agency will revisit the 

mitigation measures from the REDs and update any benefits and alternatives assessments as 

needed. 

6) The risk assessment results need to be more clearly communicated: The 2009 US

EPA Reregistration Eligibility Decision (RED) document for chloropicrin is poorly

written, with important terms and abbreviations left undefined, and substantial

inaccuracies in the summaries of the toxicology studies. In particular, US EPA does not

even provide a term for concentrations of concern. It is important to include such a term

to provide language for discussing the risk assessment. In the past, EPA has called these

regulatory endpoints Reference Concentrations (RfCs), and in 2002, EPA Office of

Research and Development (ORD) suggested new language for use in labeling endpoints

and regulatory target concentrations that more clearly defines exposure route and

duration. We urge EPA to adopt ORD’s suggested language and clean up the risk

assessment in order to clearly communicate the science.

EPA Response:

The Agency will take into consideration the comment provided in regards to clarity of the 

document in any future correspondences.
Page 7 of 18

Attachment 1: U.S. EPA Memo with Comments on CDPR 

Chloropicrin Cancer Assessment
Page 8 of 18

ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460 

OFFICE OF PREVENTION, PESTICIDES 

AND TOXIC SUBSTANCES

November 9, 2009

Carolyn Lewis

California Department of Pesticide Regulation

1001 I Street, P.O. Box 4015

Sacramento, CA 95812-4015

Re: U.S. EPA Comments On CDPR Chloropicrin Cancer Assessment

Dear Carolyn Lewis,

The attached/enclosed document is in response to your request to review the draft cancer assessment 

that CDPR provided to the Agency. The document and section we reviewed can be identified by the 

following information:

 Evaluation of Chloropicrin As A Toxic Air Contaminant. Part B. Human Health Assessment. 

June 1, 2009. Section III.A.4. Carcinogenicity- Weight of Evidence.

Our review specifically addresses the cancer aspects of the assessment for chloropicrin (Attachment A 

and B). It should be noted that lack of comments by the Agency on the other sections of the CDPR’s 

human health assessment is not an endorsement by the Agency.

Our findings indicate that our agencies are essentially using the same cancer data as the basis for our 

individual cancer assessments but the use of the information differs between agencies. These 

different approaches have resulted in different predictions of cancer risk. The key differences 

between the approaches identified include: differences in the uncertainties regarding the mutagenicity 

data and determination of a mutagenic mode of action, differences in the statistical analyses used to 

determine the significance of female mouse lung tumor data; differences in the determination of the 

biological significance of the tumor data; and differences in the use of a quantitative assessment for 

cancer via the inhalation route. It is noted that a formal Cancer Review Committee (CARC) will be 

scheduled for chloropicrin during the Agency’s Registration Review process.

We understand that the chloropicrin human health document by the Department is still considered 

draft. It is our hope that the cancer review document which we have prepared will be utilized in the 

consideration of the final cancer assessment. Please let me know if you have comments, questions or 

require further clarifications on this submission.

Sincerely,

Elissa Reaves, Ph.D.

Toxicologist, USEPA/OPP/HED
Page 9 of 18

Attachment A

The Health Effects Division (HED) was asked to comment on the cancer assessment performed 

by the California Department of Pesticide Regulation (CDPR) for chloropicrin. HED has 

reviewed the draft CDPR document dated June 1, 2009.

Below is HEDs detailed response to CDPRs cancer assessment.

A. HED’s comments on Genotoxicity for Chloropicrin

HED agrees with CDPR that the results of the genotoxicity studies are mixed. Chloropicrin was 

tested in a battery of standard genotoxicity and mutagenicity tests in vitro. The battery included 

acceptable FIFRA guideline studies for the Ames assay in Salmonella typhimurium, gene 

mutation in cultured mouse lymphoma cells, chromosomal aberration assay in Chinese hamster 

ovary (CHO) cells and unscheduled DNA synthesis (UDS) in rat hepatocytes. There is 

convincing evidence from the submitted bacterial reverse mutation assay (San and Wagner 1990, 

MRID 41960801) and the open literature (Haworth et al., 1983; Giller et al., 1995) that 

chloropicrin is mutagenic in Salmonella typhimurium TA 98 and TA100. The response is 

enhanced when the test agent was subjected to the pre-incubation modification to the standard 

“Ames” test. Evidence provided by Schneider et al. (1999) also shows that chloropicrin is 

converted to active dechlorinated metabolites (possibly CHCl2NO2 and/or CH2ClNO2) in the 

presence of glutathione (GSH) alone or complete S9 cofactor mix but not when washed 

microsomes from the S9 liver homogenate are used as the sole source of P450 enzymes. It, 

therefore, appears that GSH is more important than P450 in the initial metabolism of 

chloropicrin. However, the evidence of mutagenicity is limited to the microbial test system as 

indicated by the lack of a mutagenic or clastogenic effect in mammalian cells (San and Sigler 

1990, MRID 41960803; Putnam and Morris 1990, MRID 41960802; Curren 1990, MRID 

41060804). The positive results from the in vitro chromosome assay (Putman and Morris 1990, 

MRID 41960802) using CHO cells as the target organism was revisited and found to occur only 

at concentrations causing severe cytotoxicity (≤50% ↓ in mitotic indices). It is likely, therefore, 

that the increase in chromatid breaks (also suggestive of a cytotoxic effect) is secondary to 

cytotoxicity, and not indicative of a clastogenic response. No in vivo genetic toxicology assays 

were available on chloropicrin; this deficiency in the database represents a data gap. 

Overall, the human health relevance of the reproducible positive Ames test can not be ascertained 

at this time since the mutation response appears to be restricted to bacterial systems and no in 

vivo genetic toxicology studies (e.g. transgenic mouse assay would be ideal, mouse micronucleus 

assay to satisfy FIFRA guideline requirements) were performed.

B. HEDs Response to the CDPR cancer assessment for Chloropicrin

1) Rationale for lack of concern for carcinogenic potential via the inhalation route.

HED has performed a statistical analysis of the lung tumors observed in female mice 

in the chronic mouse inhalation study (43632201) consistent with procedures under 

the Cancer Review Committee (CARC) (Brunsman, 2009; TXR 0055260).
Page 10 of 18

Table1. Results of the Fisher’s Exact Test for Lung Tumors Seen in Female CD-1 Mice+.

Tumor Type 0 ppm 0.1 ppm 0.5 ppm 1.0 ppm

Adenomas

(%)

p =

13/47

(28)

0.02470*

9/47

(19)

0.88860

17/47

(36)

0.25360

19a/48

(40)

0.15571

Carcinomas

(%)

p =

0/47

(0)

0.1275

4/47

(9)

0.05849

3/47

(6)

0.12097

4

b

/48

(8)

0.06112

Combined

(%)

p =

13/47

(28)

0.009535**

12c/47

(26)

0.67943

20/47

(43)

0.09722

22d/48

(46)

0.05192

+Number of tumor bearing animals/Number of animals examined, excluding those that died before 

week 40.

a

First adenoma observed at week 40, dose 1.0 ppm.; 

b

First carcinoma observed at week 76, dose 1.0 

ppm.; 

cOne animal in the 0.1 ppm dose group had both an adenoma and a carcinoma.

dOne animal in the 1.0 ppm dose group had both an adenoma and a carcinoma.

There is no evidence of carcinogenicity in male mice. The incidences of lung tumors in 

female mice are shown in Table 1. There is a slight increase in adenomas at the high dose 

(19/48; 40%) compared to the controls (13/47; 28%). The incidences for carcinomas 

showed a flat dose response (i.e, 0, 4, 3, and 4). There is an increase in the incidences of 

adenomas and carcinomas combined, driven by adenomas, at the high dose (22/48; 46%) 

when compared to controls (13/47; 28%).

The statistical analyses of the tumor incidences consisted of two-tailed Fischer’s exact 

test for pairwise comparisons. A Fisher’s exact test is employed when there are no 

significant disparities in survival between the treated and control groups. The analyses 

showed no pairwise significance for any of the tumor type (i.e., adenomas, carcinomas or 

combined adenomas /carcinomas). 

The statistical significance for the positive trends for adenomas (p=0.0247) and combined 

adenomas and carcinomas (p= 0.05192) are not considered to be biologically significant 

for a common tumor type (i.e., lung tumors in mice) since a statistical significance of 

p<0.05 is required. Similarly, the p=0.05192 obtained in the pairwise comparison of the 

combined adenomas/carcinomas is not considered to be biologically significant for this 

tumor type since a statistical significance of p<0.01 is required (Lin and Rahman, 1998, 

Lin, 2000, Haseman, 1983, 1984). It is also noted that the adjusted denominator numbers 

of female mice (combined adenomas and carcinomas for lungs) in the last row of Table 8
Page 11 of 18

(page 31) by CDPR is inappropriate for statistical analysis. The result of the statistical 

analysis performed on these adjusted numbers is therefore an artifact and not appropriate 

for use in risk assessment.

HED determined the female mouse lung tumors to be of no concern because: lung 

adenomas are tumors of relatively common occurrence in mice, they did not show 

progression to carcinomas, there was a flat dose response for the carcinomas, they did not 

occur with a reduced latency (average time to tumor was 543 day in the high dose group

vs.554 days in the controls), with only an 11 day reduction in average time to lung tumor; 

and there was no evidence of carcinogenicity in male mice or male and female rats.

HED concluded that there is no concern for the carcinogenic potential of chloropicrin 

based on the following weight of evidence considerations: 1) no lung tumors were seen in 

male or female rats exposed to the same exposure concentrations for a longer period of 

time (104 weeks) in the same laboratory; 2) no increase in lung tumors was seen in male 

mice; and 3) the weak response in female mice (i.e., the presence of a single common 

tumor that lacked biological or statistical significance with no increase in the proportion 

of malignant tumors nor decrease in the time to tumor occurrence). The latest risk 

assessment for chloropicrin demonstrates that chronic exposure is unlikely but included a 

long-term Human Equivalent Concentration (HEC) of 0.004 ppm. The HEC of 0.004 

ppb is 250-fold lower than the concentration (1.0 ppm) that induced biologically 

insignificant lung tumors and would be protective of all chronic effects, including, any 

potential carcinogenicity from inhalation exposure to chloropicrin. 

C. HEDs Comments to the CDPR Document Dated June 1, 2009

CDPR The CDPR report (Page 29; Line 31) stated that there was a trend for the combined 

adenomas/carcinomas but no pairwise significance by Fisher’s exact test although the p value 

was 0.053. 

HED Response: Results of the Fischer’s exact test by HED also yielded a comparable pairwise 

p value of 0.0519 for the combined adenomas/carcinomas.

CDPR: The CDPR report (Page 28; Line 33) states that the combined incidence of 

adenomas/carcinomas was further analyzed using the Poly-3 trend test. The Poly-3 test resulted 

in yielding statistical significances for both the trend and pair wise (p=0.021) for the combined 

adenomas/carcinomas.

HED Response: There are no issues related to survival in female mice. Survival was comparable 

among groups (i.e., 29%, 31%, 34%, and 33% at 0, 0.1, 0.5, or 1.0 ppm groups, respectively). 

The Poly 3 test is used only when survival is a confounding factor. The Poly 3 test adjusts for 

differences in mortality among treatment groups by modifying the number of animals at risk in 

the denominators in the calculations of overall tumor rates. 
Page 12 of 18

In this chronic inhalation mouse study, there is no concern for time-to-tumor appearance since 

there are no tumor-related early deaths which affect survival. Consequently, it is unclear why 

CDPR elected to employ the Poly 3 test which is used only when survival time is the 

confounding factor. The National Toxicology Program (NTP) uses the Poly 3 test to adjust for 

intercurrent mortality in their animal bioassays. The Poly 3 test was developed based on the 

results of extensive time-to-tumor appearance data for a variety of tumors in NTP’s 

carcinogenicity bioassays using studies conducted with Fischer 344 rats and B6C3F1 (Bailer and 

Portier, 1988). The chloropicrin study, however, used CD-1 mice and therefore, it is not 

appropriate to “extrapolate” the BC3F1 mice model to a different strain (CD-1) which has a 

different life span. Consequently, it is HED’s position that since survival was not a confounding 

factor in this study there is no need to use the Poly 3 test and that the Fischer’s exact test is the 

appropriate test for tumor analyses. 

CDPR: The CDPR report (Page 29, 30; line 41) states that the average time to tumor was shorter 

in the high dose females (543 days) compared to controls (554 days) primarily due to two deaths 

that occurred within the first year, unrelated to treatment.

HED Response: The reduction of 11 days (554 vs 543) in average time to lung tumor is not 

biologically significant, especially since (as noted by CDPR), the reduction was primarily due to 

two animals that died early of unrelated causes.

CDPR: The CDPR report (Page 30; line 32-38) states that no historical control data were 

available for the testing laboratory and therefore, historical control data published by Charles 

River for this strain for studies conducted between 1987 and 1996 were used instead. These data 

showed an average incidence of 14% (0-28%, range) and 8.7% (0-27% range) for adenomas in 

males and females, respectively (Giknis and Clifford, 2000). The incidence of these tumors was 

above the average for historical control data for all groups and outside historical control range for 

most groups including the control group of males. 

HED Response: The concurrent control group is always the one that is most appropriate and 

important in testing treatment-related increase in tumor rates in carcinogenicity studies Due to 

the large study-to-study variations caused by differences in nomenclatures, laboratory, time 

period, and pathologists it is extremely important that the historical control data chosen should be 

comparable with the current study. CDPR used the historical control data from Charles River 

Laboratories which is not appropriate since all of the studies cited were oral (gavage or dietary) 

studies (i.e., none were inhalation studies). The lung tumor incidences in the current study should 

be compared to the historical control data of inhalation studies since such a study would require a 

closer examination of the lung than oral or dietary studies which would result in the diagnosis of 

more lung tumors.) Even if the Charles River studies are considered, the fact that the concurrent 

control lung tumor rates falls outside the historical control range essentially makes the historical 

control data useless in rendering a meaningful comparison.

In summary, HED does not concur with the conclusions reached by CPDR and reiterates its 

conclusion that there is no evidence of carcinogenic potential in chloropicrin inhalation studies 

and that quantification of cancer risk is not required.
Page 13 of 18

Bailer, J.A and Portier, J. (1988). Effects of treatment-induced mortality and tumor-induced 

mortality on tests for carcinogenicity in small samples. Biometrics 44, 417-431.

Giknis, M.L.A and Clifford, C.B. (2000). Spontaneous neoplastic lesions in the Crl:CD-1 (ICR) 

BR Mouse. Charles River Laboratories. March, 2000.

Giller S., Le Curieux F, Gauthier L, Erb F, Marzin D. (1995). Genotoxicity assay of chloral 

hydrate and chorlopicrine. Mutat Res. 348(4): 147-152.

Haseman J.K (1983) A reexamination of false-positive rates for carcinogenesis studes. 

Fundamental and Applied Toxicology 3: 334-339

Haseman J.K. (1984) Statistical isssues in the design, analysis and interpretation of animal 

carcinogenicity studie. Environ. Hlth. Prespective 58: 385-393

Haworth S, Lawlor T, Mortelmans K, Speck W, Zeiger E. (1983). Salmonella mutagenicity test 

results for 250 chemicals. Environ Mutagen. 1983;5 Suppl 1:1-142.

Lin K.K and Rahman, M. A (1998). Overall false positive rates in tests for linear trend in tumor 

incidence in animal carcinogencity studies of new drugs. J. Biopharm. Stat. 8(1): 1-15.

Lin K. K. (2000) Carcinogenicity studies in pharmaceuticals. In Encyclopedia of 

Biopharmaceutical Statistics, edited by S.C.Chow, Marcel Dekker, New York, 88-103

Schneider, M, Quistad, GB, Casida, JE. (1999). Glutathione activation of chloropicrin in the 

Salmonella mutagenicity test. Mutat Res. 439: 233-238.

USEPA 2005. Guideline for Cancer Risk Assessment. March. EPA/630/P-03/001F.
Page 14 of 18

Attachment B

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460 

OFFICE OF PREVENTION, PESTICIDE

AND TOXIC SUBSTANCES

MEMORANDUM

Date: September 10, 2009

SUBJECT: Chloropicrin Qualitative Risk Assessment Based on CD-1 Mouse Dietary Study

 PC Code: 081501 DP Barcode: D215526

 MRID No.: 43632201 

 

Registration No.: NA

 Petition No.: NA Regulatory Action: NA

 Assessment Type: NA 

 

Reregistration Case No.: NA

 TXR No.: 0055260 CAS No.: 76-06-2

 

FROM: Lori L. Brunsman, Statistician

Science Information Management Branch

Health Effects Division (7509P)

THROUGH: Jessica Kidwell, EPS

and

Brenda May, Acting Branch Chief

Science Information Management Branch

Health Effects Division (7509P)

TO: Elissa Reaves, Toxicologist

Risk Assessment Branch VI

Health Effects Division (7509P)

I. CONCLUSIONS

Female mice had statistically significant trends for lung adenomas (p < 0.05) and 

combined lung adenomas and carcinomas (p < 0.01). There were no significant pair-wise 

comparisons of the dosed groups with the controls.
Page 15 of 18

There was no evidence of survival disparities among dose groups in female mice.

There was no evidence of carcinogenicity in male mice.

II. ACTION REQUESTED

Prepare a qualitative risk assessment of the female mouse lung tumors.

III. BACKGROUND

An inhalation oncogencity study in CD-1 mice was conducted by Bushy Run Research 

Center, Export, Pennsylvania, for The Chloropicrin Manufacturers Task Force c/o Nicklor Chemical 

Company, Long Beach, California, and completed April 25, 1995 (Laboratory Project No. 92N1105).

The study design allocated groups of 50 mice to target exposure concentrations (in air) of 0, 

0.1, 0.5 or 1.0 ppm of Chloropicrin vapor for 6 hours/day, 5 consecutive days/week for 78 weeks. 

Doses were equivalent to analyzed mean concentrations of 0, 100, 498 or 988 ppb.

IV. RESULTS/DISCUSSION

Survival Analyses

There was no evidence of significant differences in mortality with increasing doses of 

Chloropicrin in female mice (Table 1).

Tumor Analyses

Female mice had statistically significant trends for lung adenomas (p < 0.05) and combined 

lung adenomas and carcinomas (p < 0.01). There were no significant pair-wise comparisons of the 

dosed groups with the controls. The statistical analyses of the tumors in the female mice were based 

upon Fisher’s Exact Test for pair-wise comparisons and the Exact Test for trend (Table 2).
Page 16 of 18

Table 1. Chloropicrin – CD-1 Mouse Study (MRID 43632201)

Female Mortality Rates+and Cox or Generalized K/W Test Results

Weeks

Dose (ppm) 1-26 27-52 53-82fTotal

0 1/49a2/47a11/45 14/48

(29)

0.1 1/49b2/48 12/46 15/49

(31)

0.5 0/49c1/47c15/46 16/47

(34)

1.0 0/49d6/48d10/42 16/48

(33)

+Number of animals that died during interval/Number of animals alive at the beginning of the 

interval.

f

Final sacrifice at weeks 81-82.

a

Two accidental deaths in the control group, one each at weeks 3 and 50.

bOne accidental death at week 8, dose 0.1 ppm.

c

Three accidental deaths in the 0.5 ppm dose group, one each at weeks 5, 31 and 32.

d

Two accidental deaths in the 1.0 ppm dose group, one each at weeks 25 and 42.

( )Percent.

Note: Time intervals were selected for display purposes only.

Significance of trend denoted at control.

Significance of pair-wise comparison with control denoted at dose level.

If *, then p < 0.05. If **, then p < 0.01.
Page 17 of 18

Table 2. Chloropicrin – CD-1 Mouse Study (MRID 43632201)

Female Lung Tumor Rates+

and Fisher’s Exact Test and Exact Test for Trend Results

Dose (ppm)

0 0.1 0.5 1.0

Adenomas

(%)

p =

13/47

(28)

0.02470*

9/47

(19)

0.88860

17/47

(36)

0.25360

19a/48

(40)

0.15571

Carcinomas

(%)

p =

0/47

(0)

0.1275

4/47

(9)

0.05849

3/47

(6)

0.12097

4

b

/48

(8)

0.06112

Combined

(%)

p =

13/47

(28)

0.009535**

12c/47

(26)

0.67943

20/47

(43)

0.09722

22d/48

(46)

0.05192

+Number of tumor bearing animals/Number of animals examined, excluding those that died before 

week 40.

a

First adenoma observed at week 40, dose 1.0 ppm.

b

First carcinoma observed at week 76, dose 1.0 ppm.

cOne animal in the 0.1 ppm dose group had both an adenoma and a carcinoma.

dOne animal in the 1.0 ppm dose group had both an adenoma and a carcinoma.

Note: Significance of trend denoted at control.

Significance of pair-wise comparison with control denoted at dose level.

If *, then p < 0.05. If **, then p < 0.01.
Page 18 of 18

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Peto, R., M. Pike, N. Day, R. Gray, P. Lee, S. Parish, J. Peto, S. Richard, and J. Wahrendorf (1980) 

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