Interregional Research Project Number 4 (IR-4)

4E8312

EPA has received a pesticide petition (4E8312) from Interregional Research 

Project Number 4 (IR-4), 500 College Road East, Princeton, NJ 08540 requesting, 

pursuant to section 408(d) of the Federal Food, Drug, and Cosmetic Act (FFDCA), 21 

U.S.C. 346a(d), to amend 40 CFR part 180 by establishing tolerances for residues of

clofentezine in or on the raw agricultural commodities avocado at 0.3 parts per million 

(ppm); papaya at 0.3 ppm; fruit, pome, group 11-10 at 0.5 ppm; cherry, subgroup 12-12A

at 1.0 ppm; peach, subgroup 12-12B at 1.0 ppm; and fruit, small, vine climbing, except 

fuzzy kiwifruit, subgroup 13-07F at 1.0 ppm. Upon the approval of the aforementioned 

tolerances, IR-4 proposes that the existing tolerances for apple at 0.5 ppm; pear at 0.5 

ppm; cherry at 1.0 ppm; nectarine at 1.0 ppm; peach at 1.0 ppm; and grape at 1.0 ppm be 

removed as unnecessary.

EPA has determined that the petition contains data or information regarding the 

elements set forth in section 408 (d)(2) of FDDCA; however, EPA has not fully

evaluated the sufficiency of the submitted data at this time or whether the data supports 

granting of the petition. Additional data may be needed before EPA rules on the petition.

A. Residue Chemistry

1. Plant metabolism. The qualitative nature of clofentezine residues in plants is 

adequately understood. The metabolism of clofentezine has been studied in three crops 

representative of the use pattern for APOLLO SC: Apples (pome fruit), peaches (stone 

fruit), and grapes (vines/small fruit). In each case, unchanged clofentezine was the major 

extractable residue present. Non-extractable residues (fiber-bound) were negligible. 

Minor amounts of 2-chlorobenzonitrile, the major photo-degradation product, were 

detected, predominantly on the fruit surface. Dissipation of this component may be a 

significant route in the degradation of clofentezine on the surface of these crops. The 

nature of the residue in grapes, and in all the other registered crops, is therefore 

adequately understood. The residue of concern is the parent, clofentezine.

2. Analytical method. An adequate method for purposes of enforcement of the 

proposed clofentezine tolerance is available. An independent method validation was 

successfully completed, and the method was found acceptable. An extensive database of 

method validation data using this method on various crop commodities is available. The 

Limit of Quantitation (LOQ) and Minimum Detection Limit (MDL) were determined to 

be 0.01 ppm and 0.003 ppm, respectively. The method was forwarded to FDA for 

inclusion in PAM-II

3. Magnitude of residues. Adequate crop field trial data are available for 

clofentezine in/on almonds, peaches, nectarines, persimmons, and grapes following 

application of a SC formulation containing 0.25 lb ai/A. The established tolerances range 

from 0.02 ppm in walnuts to 5.0 ppm in almond hulls (40 CFR §180.446). The magnitude 

of residues for the proposed tolerance is adequately understood. The results demonstrate 

that the maximum residue of clofentezine in or on avocado was 0.0305 ppm, measured 
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133 to 140 days after application (0.25 pounds active ingredient (lb a.i.)/acre).

B. Toxicological Profile

1. Acute toxicity. Clofentezine has a relatively low degree of acute toxicity and 

irritation potential. It is classified as toxicity category III for oral, dermal and inhalation 

toxicity, and toxicity category IV for eye and skin irritation. The acute oral lethal dose 

(LD 50) of clofentezine was determined to be 5,200 milligrams/kilograms (mg/kg) in rats 

and mice, 3,200 mg/kg in hamsters, and 2,000 mg/kg in beagle dogs. The acute rat 

dermal LD 50 was 2,100 mg/kg. Clofentezine is considered to be practically nonirritating to eyes and skin but is considered to be a week skin sensitizer in the guinea pig 

maximization assay.

2. Genotoxicty. No evidence of genotoxicity was noted in a battery of in vitro and 

in vivo studies. Studies submitted included Ames Salmonella and mouse lymphoma gene 

mutation assay, a mouse micronucleus assay, a rat dominant lethal assay, and a gene 

conversion and mitotic recombination assay in yeast. Therefore, the registrant concludes 

that clofentezine has no potential to induce genotoxicity.

3. Reproductive and developmental toxicity. A multigeneration rate reproduction 

study was conducted at dietary concentrations of 0, 4, 40, and 400 ppm. The parental no 

observed adverse effect level (NOAEL) was 40 ppm based on slightly reduced body 

weights, increased liver weights and hepatocellular hypertrophy at 400 ppm. No 

treatment-related reproductive effects were noted at any dose level.

In a rat developmental toxicity study, clofentezine was administered by gavage at dose 

levels of 0, 320, 1, 280 and 3,200 mg/kg/day during gestation days 6 to 20. Evidence of 

maternal toxicity was noted at 3,200 mg/kg/day and consisted of decreased weight gain, 

increased liver weights and centrilobular hepatocellular enlargement. No developmental 

effects were observed at any dose level.

In a rabbit developmental toxicity study, clofentezine was administered by gavage at dose 

levels of 0, 250, 1,000 and 3,000 mg/kg/day during gestation days 7 to 28. Slight 

maternal toxicity (decreased maternal food consumption and weight gain) and a slight 

decrease in fetal weight were noted at 3,000 mg/kg/day. Thus, the NOAEL was 

considered to be 1,000 mg/kg/day for both maternal and developmental effects.

4. Subchronic toxicity. In a preliminary 90-day feeding study designed to select a 

suitable high dose level for a subsequent chronic rate study, clofentezine was 

administered to rats at dietary concentrations of 0, 3,000, 9,000 and 27,000 ppm. A 

significant reduction in weight gain was noted at 9,000 and 27,000 ppm. In addition, a 

marked, dose-related hepatomegaly and centrilobular hepatocyte enlargement was noted 

in all treatment groups.

In a subsequent 90-day feeding study, clofentezine was administered to rats at dietary

concentrations of 0, 40, 400, and 4,000 ppm. Slightly reduced weight gain, alterations in 

several clinical pathology parameters, increased liver, kidney and spleen weights, and 

centrilobular hepatocyte enlargement were noted at 400 and/or 4,000 ppm. Thus, 40 ppm 

(2.8 mg/kg/day) was considered to be the NOAEL for this study.
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Clofentezine was administered to beagle dogs for 90 days at dietary concentrations of 0, 

3,200, 8,000 and 20,000 ppm. Increased liver weights were noted at all dose levels but no 

histopathological changes nor any other treatment-related effects were observed.

5. Chronic toxicity. In a 12-month feeding study, clofentezine was administered to 

beagle dogs at dietary concentrations of 0, 50, 1,000, and 20,000 ppm. An increase in 

adrenal and thyroid weights, as well as moderate hepatotoxicity consisting of minimal 

periportal hepatocyte enlargement with cytoplasmic eosinophilia, hepatomegaly and 

increased plasma cholesterol, triglycerides and alkaline phosphatase levels, were noted at 

20,000 ppm. Evidence of slight hepatotoxicity was also noted at 1,000 ppm. Thus, the 

NOAEL for this study was considered to be 50 ppm (1.25 mg/kg/day).

In a 27-month feeding study, clofentezine was administered to rats at dietary

concentrations of 0, 10, 40, and 400 ppm. Effects noted at 400 ppm were limited to the 

liver and thyroid, primarily of males, and consisted of increased liver weights, a variety 

of microscopic liver lesions (centrilobular hepatocyte hypertrophy and vacuolation, focal 

cystic hepatocellular degeneration and diffuse distribution of fat deposits), increased 

serum thyroxine levels, and a slight but statistically significant increase in the incidence 

of thyroid follicular cell tumors. The NOAEL was considered to be 40 ppm (2 

mg/kg/day).

Clofentezine was not oncogenic to mice when administered for 2 years at dietary

concentrations of 0, 50, 500, and 5,000 ppm. Decreased weight gain, increased liver 

weights, and increased mortality were noted at 5,000 ppm. An increased incidence of 

eosinophilic or basophilic hepatocytes was noted at 5,000 ppm, and possibly 500 

ppm.Show citation box

Numerous studies were conducted to investigate the mechanism for the increased 

incidence of male thyroid follicular tumors that was observed in the chronic rat study. 

These studies suggest that the tumors may have been caused by increased thyroid 

stimulating hormone (TSH) levels, which, in turn, resulted from clofentezine's liver 

toxicity, and were not attributable to a genotoxic mode of action.

6. Animal metabolism. The metabolism, tissue distribution and excretion of 

clofentezine have been evaluated in a number of species. In all species, almost all of the 

administered dose was recovered within 24 to 48 hours after treatment, primarily via the 

feces. The major route of metabolism was found to be ring hydroxylation, sometimes 

preceded by the replacement of a chlorine atom with a methyl-thio group. Blood and 

tissue levels in the fetuses of pregnant rats that had been treated with clofentezine were 

much lower than the levels found in the mother, indicating that clofentezine does not 

readily pass across the placenta. In addition, less than 1% of the administered dose was 

absorbed through the skin of rats following a 10-hour exposure to the end use formulation 

of clofentezine, APOLLO SC.

Following oral dosing of a cow and three goats with 14C-labeled clofentezine, the residue 

in milk was identified as a single metabolite, 4-hydroxyclofentezine. Similarly, 4-

hydroxyclofentezine has been shown to be the only metabolite present in fat, liver, and 

kidney. No unchanged clofentezine or other metabolites were found. Therefore, the 
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nature of the residue in animals is adequately understood. The residues of concern in 

ruminant commodities and milk are the combined residues of the parent, clofentezine, 

and the 4-hydroxyclofentezine metabolite.

7. Metabolite toxicology. There are no metabolites of toxicological concern and 

therefore, no metabolites need to be included in the tolerance expression and require 

regulation.

8. Endocrine disruption. Except for the thyroid mechanistic studies mentioned 

above, no special studies have been conducted to investigate the potential of clofentezine 

to induce estrogenic or other endocrine effects. However, the standard battery of required 

toxicity studies has been completed. These studies include an evaluation of the potential 

effects on reproduction and development, and an evaluation of the pathology of the 

endocrine organs following repeated or long-term exposure. Repeated dose studies are 

generally considered to be of substantial value as a means for detection of any endocrine 

effects. However, with the exception of a slightly increased incidence of thyroid tumors 

in male rats, no such effects were noted in any of the repeated dose toxicity studies with 

clofentezine. The male rat is known to be much more susceptible than humans to the 

carcinogenic effects resulting from thyroid hormone imbalance and/or increased levels of 

TSH. Therefore, the alterations in thyroid hormone and subsequent thyroid pathological 

changes, which have been noted following administration of high doses of clofentezine, 

are considered to be of minimal relevance to human risk assessment, particularly

considering the low levels of clofentezine to which humans are likely to be exposed.

C. Aggregate Exposure

1. Dietary exposure. The chronic dietary exposure estimates from food and 

drinking water do not exceed HED’s level of concern. The cancer dietary exposure 

estimates from food and drinking water result in a cancer risk estimate of 2.8 x 10-7.

Tolerances for bean, snap, succulent, dry, seed; for vegetable, fruiting, group 8; for fruit, 

pome, group 11; for cherry; and for fruit, stone, group 12, except cherry have previously 

been established and the updates to the crop grouping is not likely to influence 

assessment calculations. As avocado is considered minor crops, contribution from these 

sources is not likely to have significant impact on this assessment. 

i. Food. Clofentezine chronic and cancer dietary risk assessments were previously

conducted using the Dietary Exposure Evaluation Model DEEM-FCIDTM, Version 3.16 

which uses food consumption data from the USDA’s NHANES/WWEIA from 2003-

2008. A description can be found the June 6, 2013 Human Health Risk Assessment (PC 

Code: 125501; Decision No.: 464564; DP Barcode: D401611). 

ii. Drinking water. There are no monitoring data currently available for 

clofentezine or its residues of concern in drinking water. Estimated drinking water 

concentrations (EDWCs) were generated by the Environmental Fate and Effects Division 

(EFED) using computer modeling methods. Tier II EDWCs were generated to support 

clofentezine use on almonds, apples, Christmas trees, nectarines, containerized plants, 

peaches, pears, persimmons, pecans, and walnuts (R. Parker; D404287; 08/03/2012). The 

surface water EDWCs are based on the USEPA Pesticide Root Zone Model (PRZM) and 

Exposure Analysis Modeling System (EXAMS) using the EXPRESS shell. Estimated 

groundwater EDWCs were calculated using the screening model SCI-GROW (Screening 

Concentrations in Ground Water, version 2.3, 07/29/03). The highest surface water 
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EDWCs values are 7.59 ppb (1-in-10 year acute) and 0.062 ppb (1-in-10 year annual 

average). The SCI-GROW groundwater concentration is 0.04 ppb. 

2. Non-dietary exposure. There are currently no registered residential uses 

associated with clofentezine; therefore, a residential/non-occupational exposure 

assessment is not required. As a result, the clofentezine aggregate risk assessment 

includes only dietary exposure (food and water).

D. Cumulative Effects 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 clofentezine and any other substances. For the 

purposes of this assessment, therefore, EPA has not assumed that clofentezine has a 

common mechanism of toxicity with other substances.

E. Safety Determination

1. U.S. population. An acute dietary exposure assessment was not performed as 

no appropriate endpoints were identified from the available clofentezine toxicity studies 

for the acute dietary scenario. A somewhat refined chronic dietary exposure assessment 

was previously performed that directly incorporated potential drinking water residues. 

The estimated exposure to the general U.S. population resulted in an estimated risk of 

<1% of the chronic population adjusted dose (cPAD).

2. Infants and children. The estimated exposure to the highest population 

subgroup (children 1 < 2 years old) resulted in an estimated risk of <1% of the chronic 

population adjusted dose (cPAD).

F. International Tolerances At present, no Canadian, Mexican, or CODEX maximum residue 

limits (MRLs) are established for clofentezine on avocado.

Codex maintains a clofentezine MRL of 0.5ppm set on “stone fruit” which could impact 

sweet and tart cherries.

The tolerance for Fruit, small, vine climbing, except fuzzy kiwifruit, subgroup 13-07F, is 

set at 1.0ppm. This does not harmonize with the 2.0ppm Codex tolerance. We would like 

to keep the tolerance at 1.0ppm because several countries including Japan and Korea also 

maintain a 1.0ppm tolerance and it would create export issues were the tolerance

changed.