UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

OFFICE OF CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

MEMORANDUM 

DATE: September 12, 2014 

SUBJECT: Ethoxyquin. Human Health Assessment Scoping Document to Support 

Registration Review. 

PC Code: 055501 

Decision No.: 491210 

DP Barcode: 420308 

Registration No.: N/A 

Petition No.: Not Applicable (N/A) 

Assessment Type: N/ A 

Regulatory Action: Registration Review 

Reregistration Case No.: 0003 

TXRNo.: N/A CAS No.: 91-53-2 

MRIDNo.: None 40 CFR: §180.178 

FROM: 

THROUGH: 

TO: 

Bonnie Cropp-Kohlligian, Risk Assessor-.::t:S~ ~ • ~\~ Abdallah 

Susan 

Kelly O'Rourke, 

V. Hummel

Khasawinah, 

ORE 

, Senior 

Assessor 

Ph.D., 

Chemist 

Toxicologi t / 

. 

~ 

A.-or-

. . 

V 

1 

~ 

Risk Assessment Branch (RAB) IV '7), () 2~ 

Health Effects Division (HED) (7509P) . ---;;? ,..__~ 

Elissa Reaves, Ph.D., Branch Chief ~ -

RAB IV, HED (7509P) 

Khue Nguyen/Thomas Moriarty RM 51 

Risk Management and Implementation Branch 1 

Pesticide Re-Evaluation Division (7508P) 

Executive Summary 

The Health Effects Division (HED) has evaluated the human health risk assessments for 

ethoxyquin and its toxicity, exposure and usage databases, as well as the most current 

Agency science and assessment policies to determine the scope of work necessary to 

support the Ethoxyquin Registration Review. The primary sources of information for this 

evaluation were the 2004 Ethoxyquin Revised Human Health Risk Assessment for the 

Reregistration Eligibility Decision (D31 0459; hereafter referred to as the 2004 RED), the 

subsequent 2008 occupational and residential exposure (ORE) risk assessment conducted 

to evaluate a thermal fogging use on pears (D342695), and updated occupational 

Page 1 of28 
Ethoxyquin Registration Review Human Health Assessment Scoping Document 

exposure estimates reflecting current methodology generated for the HED Hazard and 

Science Policy Council (HASPOC) evaluation (TXR# 0053945). 

Ethoxyquin (1,2-dihydro-6-ethoxy-2,2,4-trimethylquinolene) is an antioxidant currently 

registered for use as a deterrent of scald in pears through post-harvest (indoor) 

application via a drench/in-line spray treatment, thermal fogging and/or impregnated 

wraps. Ethoxyquin is also used for preservation of color in the production of chili 

powder, paprika, and ground chili and as a preservative in animal feed with food additive 

tolerances established by the Food and Drug Administration (FDA) in/on the specified 

spices, as well as, meat, poultry and eggs (21 CFR § 172.140). 

Based on the currently registered pesticidal uses, exposures to ethoxyquin can be 

expected to occur via the dietary (food only) and occupational (dermal and inhalation) 

routes. With adequate label restrictions regarding wash-water recycling practices, it is 

not likely to occur in drinking water and there are no registered residential uses of 

ethoxyquin. 

The residue chemistry and occupational exposure databases for ethoxyquin are adequate 

for Registration Review. The toxicology database for ethoxyquin is adequate with the 

exception of dermal penetration and inhalation toxicity studies. The HED HASPOC 

(TXR# 0053945) determined that dermal penetration and 28-day inhalation studies are 

required due to updated occupational exposure estimates reflecting current methodology 

that identified risks of concern using oral point of departures for assessing risk by the 

dermal and inhalation routes. As part of Registration Review, toxicological endpoints, 

points of departure and uncertainty/safety factors used in the most recent human health 

risk assessments may be re-evaluated according to current HED policy. Updated 

exposure and risk assessments may need to be conducted using current policy and 

procedures if there are any significant changes to ethoxyquin endpoints, points of 

departure, uncertainty/safety factors, and/or exposure estimates/assumptions. The current 

tolerance expression will need to be updated to reflect the HED Interim Guidance on 

Tolerance Expressions (5/27/09, S. Knizner). 

The primary target organs for ethoxyquin in experimental animals were the liver and 

kidney. Dogs were the most sensitive species tested. The major effects in liver, as seen 

in the 90-day dog study, were elevated enzymes and microscopic fmdings (cytoplasmic 

vacuolation and minimal hepatocellular necrosis). The major effects in kidney, as seen in 

the 90-day rat study, were microscopic lesions (renal papillary necrosis, hyalin droplets in 

the cortical tubular epithelial cells and nephropathy). There is no evidence of increased 

susceptibility following pre-natal exposure to rats. The available data does not indicate a 

neurotoxic concern for ethoxyquin. Ethoxyquin has been the subject of numerous studies 

because of its wide use as an antioxidant and its role as a microsomal oxidase system 

inducer. Published studies in rats and dogs indicate that reproductive/offspring toxicity 

occurs at higher doses than maternal toxicity doses. In mutagenicity testing, ethoxyquin 

is negative in Salmonella, negative in the micronucleus assay, negative for chromosomal 

aberrations and positive for in vitro sister chromatid exchanges in Chinese hamster ovary 

cells. There are no guideline studies assessing ethoxyquin carcinogenicity in animals. 

However, it is structurally similar to Flectol H which showed evidence of carcinogenicity 

(kidney tumors) in male rats. Ethoxyquin is also a nephrotoxin in male rats. A 

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Ethoxyquin Registration Review Human Health Assessment Scoping Document

Page 3 of 28

theoretical upper bound oral slope factor (Q1

*

) for ethoxyquin was calculated to be 0.04 

(mg/kg/day)-1, based on a model that correlates cancer slope factor with maximum 

tolerated dose. 

Acute, chronic and cancer dietary risk assessments for food only were previously 

conducted for ethoxyquin and included exposures from its uses on pears as well as from 

its uses as a preservative in foods and feeds. No dietary risks of concern were identified. 

At the 95th percentile, 14% of the acute Population Adjusted Dose (aPAD) was used for 

females 13-49 (the only population subgroup identified as relevant for the acute dietary 

endpoint) and 14% or less of the chronic Population Adjusted Dose (cPAD) was used for 

the general U.S. population and all other population subgroups. The cancer dietary risk 

for ethoxyquin was estimated at 2 x 10-6and assumed additional refinements to the 

exposure; the most notable being an adjustment factor for the fraction of fresh pears that 

were not of the Bartlett variety since ethoxyquin use on pears was limited to the Bosc and 

Anjou varieties. Updated dietary exposure and risk assessments may be necessary if 

exposure assumptions used in the previous assessments change and/or if there are any 

significant changes to ethoxyquin endpoints, points of departure and uncertainty/safety 

factors.

Although no occupational risks of concern were identified in previous risk assessments, 

updated occupational exposure and risk assessments are likely to be necessary given the 

required dermal penetration and inhalation toxicity studies and current occupational 

exposure assessment evaluation methodology for post-harvest treatments.

While there are currently no registered residential uses of ethoxyquin, residential 

bystander exposures resulting from off-site transport (i.e., volatilization) may occur as a 

result of occupational applications. The need for a bystander risk assessment for 

ethoxyquin will be considered during Registration Review.

Introduction

Ethoxyquin (1,2-dihydro-6-ethoxy-2,2,4-trimethylquinolene) is an antioxidant currently 

registered for use as a deterrent of scald in pears through post-harvest (indoor) 

application via a drench/in-line spray treatment, thermal fogging and/or impregnated 

wraps. Currently eight products are registered; two emulsifiable concentrates, one 

soluble concentrate and five impregnated materials. There are four ethoxyquin 

registrants: Wrap Pack Inc., Pace International, Seaman Paper Company and Burrows 

Paper Corporation. The maximum application rates vary by treatment method; 2,700 

parts per million (ppm) for drench/in-line spray treatment (i.e., 0.022 pounds active 

ingredient [ai] per gallon solution), 1.07 x 10-5pounds ai/pound of fruit for thermal 

fogging, and 1,000 ppm per piece for impregnated paper wraps.

The primary sources of information for this evaluation were the 2004 RED (D310459), 

the subsequent 2008 ORE risk assessment conducted to evaluate a thermal fogging use 

on pears (D342695), and updated occupational exposure estimates reflecting current 

methodology generated for the HED HASPOC (TXR# 0053945) evaluation. The 

nomenclature and physiochemical properties of ethoxyquin are presented in 

Attachment 1.
Ethoxyquin Registration Review Human Health Assessment Scoping Document

Page 4 of 28

Hazard Identification/Toxicology

The toxicology database for ethoxyquin is adequate to support existing registrations with 

the exception of dermal penetration and inhalation studies. The HED HASPOC (TXR# 

0053945) granted waivers for the requirements for immunotoxicity, neurotoxicity battery 

and developmental neurotoxicity studies but determined that dermal penetration and 28-

day inhalation studies are required for Registration Review. The HED HASPOC 

decision to require additional dermal penetration and inhalation studies was based on 

updated occupational exposure estimates reflecting current evaluation methodology 

which identified risks of concern using oral points of departure (PODs) for assessing risk 

via dermal and inhalation routes of exposure. 

The published toxicology database on ethoxyquin is very extensive; however, guideline 

toxicology studies are very limited. Ethoxyquin has been the subject of numerous studies 

because of its wide use as an antioxidant and its role as a microsomal oxidase system 

inducer. It has been extensively investigated along with other antioxidants for the 

modification of the carcinogenic properties of known carcinogens. It was nominated by 

the FDA in 1990 for National Toxicology Program (NTP) testing due to “uncertainty 

concerning its toxicological effects stemming from reports of purported toxicity in dogs, 

the need for adequate toxicity data to re-evaluate the currently approved levels in animal 

feed and human feed and being used as an antioxidant in animal feed”. The current status 

of the NTP testing can be found at: http://ntp.niehs.nih.gov/testing/status/agents/tsm88005.html.

Ethoxyquin has low to moderate acute toxicity by the oral (Category III), dermal 

(Category III) and inhalation (Category III) exposure routes. It is not an eye irritant 

(Category IV), and produces minimal irritation to the skin (Category IV). Tests in 

animals show it to have a weak sensitizing potential; however, extensive human 

experience from the use of this chemical showed strong association with contact 

dermatitis that ceased upon discontinuation of working in an ethoxyquin environment.

The primary target organs for ethoxyquin in experimental animals are the liver and 

kidney. Dogs are more susceptible to ethoxyquin toxicity than rats with effects occurring 

at doses as low as 4 mg/kg/day over a 90 day feeding period. The major effects in liver, 

as seen in the 90-day dog study, were elevated enzymes and microscopic findings 

(cytoplasmic vacuolation and minimal hepatocellular necrosis). The major effects in 

kidney, as seen in the 90-day rat study, were microscopic lesions (renal papillary 

necrosis, hyalin droplets in the cortical tubular epithelial cells and nephropathy). 

Ethoxyquin did not cause developmental effects in rats tested at doses of 350 mg/kg/day 

during the gestation period or in rats at doses as high as 500 mg/kg/day of a 67% 

ethoxyquin formulation. Published studies in rats and dogs indicate that

reproductive/offspring toxicity occurs at higher doses than maternal toxicity doses for 

ethoxyquin. Published studies do not indicate a neurotoxic concern for ethoxyquin.

There is low concern (and no residual uncertainty) for pre- and/or postnatal toxicity 

resulting from exposure to ethoxyquin. The available data provided no indication of 

increased susceptibility (quantitative or qualitative) to rats or rabbits to in utero exposure. 
Ethoxyquin Registration Review Human Health Assessment Scoping Document

Page 5 of 28

Therefore, the special FQPA safety factor was reduced to 1X in risk assessments for this 

chemical.

The only suggestion of a potential carcinogenic effect for ethoxyquin came from Manson 

et al (1987, Ethoxyquin alone induces preneoplastic changes in rat kidney while 

preventing induction of such lesions in liver by aflatoxin b-1. Carcinogenesis (London); 8 

(5):723-728) study where feeding of male Fisher 344 rats of ethoxyquin at 0.5% in the 

diet (5000 ppm, equivalent to 250 mg/kg/day) for 23 weeks caused severe damage to the 

kidneys and produced many hyperplastic and putative preneoplastic tubules. However, 

guideline studies in rats and mice have not been submitted. In mutagenicity testing, 

ethoxyquin is negative in Salmonella, negative in the micronucleus assay, negative for 

chromosomal aberrations and positive for in vitro sister chromatid exchanges in Chinese 

hamster ovary cells. Ethoxyquin is structurally similar to Flectol H (1,2-dihydro-2,2,4-

trimethylquinoline) which showed evidence of carcinogenicity (kidney tumors) in male 

rats. Flectol carcinogenicity studies were conducted by the dermal route in F344/N rats 

and B6C3F1 mice in the National Toxicology Program (NTP 1997. Toxicology and 

Carcinogenesis Studies of 1,2-Dihydro-2,2,4-trimethylquinoline (CAS No. 147-47-7) in 

F344/N Rats and B6C3F1 Mice and the Initiation/Promotion (Dermal Study) in Female 

Sencar Mice. NTP Technical Report Series No. 456). Ethoxyquin is also a nephrotoxin 

in male rats. Hence, based on Flectol H data, a theoretical upper bound oral slope factor 

(Q1

*

) for ethoxyquin was calculated to be 0.04 (mg/kg/day)-1for cancer risk (2004 RED 

(D310459)).

The ethoxyquin risk assessment for the 2004 RED (D310459) relied on the published 

literature and the few available guideline studies, the limited use patterns and potential 

exposures in selecting the relevant toxicity endpoints for risk assessment. Subsequently 

an inhalation point of departure was selected for the 2008 ORE risk assessment 

conducted to evaluate the thermal fogging use on pears (D342695). Toxicity profile and

relevant toxicological endpoints are provided in Attachments 2 and 3, respectively.

Conclusions. The toxicology database for ethoxyquin is adequate to support existing 

registrations with the exception of dermal penetration and inhalation studies. The HED 

HASPOC (TXR# 0053945) determined that dermal penetration and 28-day inhalation 

studies are required for Registration Review due to updated occupational exposure 

estimates reflecting current evaluation methodology that identified risks of concern using 

oral points of departure for assessing risk via the dermal and inhalation routes of 

exposure. Until the inhalation study is submitted and found acceptable (or alternative 

information is provided to reduce the uncertainty), a 10X database uncertainty factor will 

be applied for the inhalation route. Once these studies have been received and reviewed, 

the toxicological endpoint selections and uncertainty/safety factors may be re-evaluated.

Dietary Exposure 

The qualitative nature of the residue of ethoxyquin for post-harvest uses on pears is 

adequately understood. The HED Metabolism Committee (meeting held 12/20/1994) 

determined that ethoxyquin is the residue of concern in/on pears for tolerance 

enforcement and risk assessment. There is no reasonable expectation of finite residues of 

ethoxyquin in livestock commodities from the registered pesticidal uses on pears. 
Ethoxyquin Registration Review Human Health Assessment Scoping Document

Page 6 of 28

Adequate analytical enforcement methods are available. No additional residue chemistry 

data are required.

Acute, chronic and cancer dietary risk assessments for food only were conducted for 

ethoxyquin to support the 2004 RED (D310459) using Lifeline Model Version 2.0 and 

Dietary Exposure Evaluation Model (DEEM-FCID, Version 2.03) which uses food 

consumption data from the USDA’s Continuing Surveys of Food Intakes by Individuals 

(CSFII) from 1994-1996 and 1998. These assessments included food from all sources of 

potential exposure to ethoxyquin including its uses as a preservative in food and feeds. 

The conclusions of the assessments were based on Lifeline analyses. 

The acute and chronic (non-cancer) dietary exposure and risk assessments (D297740) 

assumed tolerance level residues and 100 % crop/feed treated. Ethoxyquin-treated pears 

were assumed to be for fresh market only. Available meat/poultry cooking study data 

were used to reduce estimated residues in cooked livestock tissues by 96%. At the 95th

percentile, 14% of the acute Population Adjusted Dose (aPAD) was used for females 13-

49 (the only population subgroup identified as relevant for the acute dietary endpoint) 

and 14% or less of the chronic Population Adjusted Dose (cPAD) was used for the 

general U.S. population and all other population subgroups. 

The cancer dietary exposure and risk assessment (2004 RED; D310459) incorporated the

following additional refinements: (1) assumed the highest average field trial value for 

fresh pears instead of the tolerance, (2) used an adjustment factor for the fraction of fresh 

pears that were not of the Bartlett variety (45% according to USDA Agricultural 

Statistics for 2003) since ethoxyquin use on pears was limited to the Bosc and Anjou 

varieties, and (3) assumed that only dried spices would have incurred residues of 

ethoxyquin since ethoxyquin is not applied to fresh herbs and spices. The cancer dietary 

risk for ethoxyquin was estimated at 2 x 10-6.

Conclusions. The residue chemistry database for ethoxyquin is adequate for Registration

Review. An updated dietary exposure and risk assessment may be conducted if there are

significant changes to ethoxyquin endpoints, points of departure, uncertainty/safety

factors, and/or exposure estimates/assumptions. The assessment, if conducted, will use

the newest version of DEEM and reflect updated consumption information.

Residential Exposure and Risk Assessment

Residential bystander exposures resulting from off-site transport (e.g., spray drift or 

volatilization) may occur as a result of applications of ethoxyquin. The potential for 

spray drift will be quantitatively evaluated for each pesticide during the Registration 

Review process which ensures that all uses for that pesticide will be considered 

concurrently. The approach is outlined in the revised (2012) Standard Operating 

Procedures for Residential Risk Assessment (SOPs) – Residential Exposure Assessment 

Standard Operating Procedures Addenda 1: Consideration of Spray Drift. This 

document outlines the quantification of indirect non-occupational exposure to drift. In 

terms of volatilization, the Agency has developed a Volatilization Screening Tool and a 

subsequent Volatilization Screening Analysis 

(http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OPP-2014-0219). 
Ethoxyquin Registration Review Human Health Assessment Scoping Document

Page 7 of 28

During Registration Review, the Agency will utilize this analysis to determine if data 

(i.e., flux studies, route-specific inhalation toxicological studies) or further analysis is 

required for ethoxyquin. While spray drift is not expected due to the nature of the 

application methods, volatilization potential may be addressed with more information 

regarding filtering practices associated with the ventilation of thermal fogging 

applications.

Conclusions. There are no currently registered residential uses for ethoxyquin; therefore, 

a quantitative residential exposure and risk assessment is not necessary during 

Registration Review. The need for spray drift and volatilization risk assessment for 

ethoxyquin will be examined during Registration Review.

Aggregate Exposure and Risk Assessment

In accordance with the Food Quality Protection Act (FQPA), HED must consider and 

aggregate pesticide exposures and risks from three major sources: food, drinking water, 

and residential exposures. The aggregate risk assessment evaluates the combined risk 

from dietary exposure (food and water) and any non-occupational (residential) uses. 

With adequate label restrictions regarding wash-water recycling practices, ethoxyquin is 

not likely to occur in drinking water and it is not currently registered for residential uses. 

Therefore, an aggregate risk assessment from these exposures to ethoxyquin is not 

expected under Registration Review.

Occupational Exposure 

Occupational handler and post-application exposures are expected based on the registered 

agricultural uses of ethoxyquin. The most recent occupational and residential exposure 

(ORE) risk assessment was conducted in 2008 to evaluate the thermal fogging use on 

pears (D342695); prior to that, the ORE risk assessment for drench/in-line spray 

treatments and impregnated wraps was conducted for the 2004 RED (D310459). The 

level of concern (LOC) is for dermal margins of exposure (MOEs) less than 100. Until 

the required inhalation study is submitted and found acceptable (or alternative 

information is provided to reduce the uncertainty), a 10X database uncertainty factor will 

be applied for the inhalation route (TXR# 0053945); hence, in the absence of inhalation 

data, the LOC would be for inhalation MOEs less than 1000.

Occupational Handlers

There is the potential for dermal and inhalation exposure to occupational handlers from 

the currently registered use pattern of ethoxyquin. Because no chemical-specific data are 

available, occupational handler exposure is based on surrogate unit exposures from the 

Pesticide Handlers Exposure Database (PHED). Previous risk calculations were based on 

the maximum application rates and assumed maximum amount treated per day. Handler 

exposure and risk were calculated at baseline (long pants, a long-sleeved shirt, no 

chemical-resistant gloves, and no respirator) and with personal protective equipment 

(PPE) when necessary (e.g., chemical-resistant gloves, respirators, and engineering 

controls). 
Ethoxyquin Registration Review Human Health Assessment Scoping Document

Page 8 of 28

The previous exposure and risk calculations were updated for the HED HASPOC (TXR# 

0053945) evaluation to reflect current methodology. Short-and intermediate-term 

exposure durations resulted in MOEs for dermal exposure with chemical-resistant gloves 

ranging from 5.6 (direct spraying with hand-held equipment) to 590 (mixing/loading for 

thermal fogging). Inhalation MOEs without a respirator ranged from 1,900 (direct 

spraying with hand-held equipment) to 100,000 (mixing/loading for thermal fogging). 

Cancer estimates range from 5.6 x 10-6(mixing/loading for thermal fogging) to 5.9 x 10-4

(direct spraying with hand-held equipment). 

Occupational Post-Application

There are potentially significant short and intermediate-term post-application exposures 

to workers who sort, cull and pack treated fruit. Because no chemical-specific data are 

available, post-application exposure calculations were updated for the HED HASPOC 

(TXR# 0053945) based on current evaluation methodology and standard assumptions for 

assessing post-harvest commodities. The current assessment methodology for this use 

pattern does not utilize dislodgeable foliar residue (DFR) data; therefore, the requirement 

for DFR data is not applicable. The dermal MOE with chemical-resistant gloves was 56, 

and the inhalation MOE without a respirator was 88. The post-application cancer 

estimate was 9.6 x 10

-5

.

Conclusions. The occupational exposure database is adequate to support the Registration 

Review process for ethoxyquin. Updated occupational handler and post-application 

exposure assessments conducted for the HED HASPOC (TXR# 0053945) evaluation 

using current methodology did identify risks of concern. Registration Review is likely to 

include updated occupational exposure and risk assessments which will be based on 

current policies and the required toxicity studies (i.e., dermal penetration and inhalation). 

Public Health and Pesticide Epidemiology Data 

Both the OPP Incident Data System (IDS) and the Centers for Disease Control and 

Prevention/National Institute for Occupational Safety and Health (CDC/NIOSH) Sentinel 

Event Notification System for Occupational Risk-Pesticides (SENSOR) databases were 

consulted for pesticide incident data on the active ingredient ethoxyquin (D420779). 

Ethoxyquin is not included in the Agricultural Health Study (AHS). The purpose of the 

database search was to identify potential patterns in the frequency and severity of the 

health effects attributed to ethoxyquin exposure. 

Conclusions. The Agency has reviewed the available incident data and concludes that

there does not appear to be a concern that would warrant further investigation, since there

were no incidents involving ethoxyquin reported to either IDS or SENSOR-Pesticides. 

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

A tolerance is established for residues of ethoxyquin from post-harvest use in/on pears at 

3 ppm under 40 CFR §180.178. There is also an exemption from the requirement of a 

tolerance for ethoxyquin (1,2-dihydro-6-ethoxy-2,2,4-trimethylquinolene) as an inert (PC 
Ethoxyquin Registration Review Human Health Assessment Scoping Document

Page 9 of 28

Code 855501) when used as an antioxidant in insecticides under 40 CFR §180.910. FDA 

has established additional food additive tolerances under 21 CFR §172.140(a) at 100 ppm 

in/on chili powder, paprika and ground chili as an antioxidant for preservation of color in 

their production. FDA has also established food additive tolerances in livestock 

commodities under 21 CFR §172.140(b) at 5 ppm in/on the uncooked fat of meat from 

animals except poultry, 3 ppm in/on the uncooked liver and fat of poultry, 0.5 ppm in/on 

the uncooked muscle meat of animals and in poultry eggs in order to provide for the safe 

use of the additive in feed prepared in accordance with 21 CFR §573.380 and 21 CFR 

§573.400. 

The U.S. tolerance is harmonized with the established Codex and Canadian maximum 

residue limits (MRLs) for residues of ethoxyquin in/on pear. Mexico adopts U.S. 

tolerances and/or Codex MRLs for its export purposes. The U.S. tolerance expression 

will need to be updated to reflect the HED Interim Guidance on Tolerance Expressions 

(5/27/09, S. Knizner).

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 ethoxyquin and any other substances and ethoxyquin does not appear to 

produce a toxic metabolite produced by 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/.

Human Studies

The previous ethoxyquin risk assessments relied in part on data from studies in which

adult human subjects were intentionally exposed to a pesticide or other chemical. These

data, which include studies from Pesticide Handler Exposure Database (PHED) 1.1; the

Agricultural Handler Exposure Task Force (AHETF) database; the Agricultural Reentry

Exposure Task Force (ARTF) database; and, are (1) subject to ethics review pursuant to

40 CFR 26, (2) have received that review, and (3) are compliant with applicable ethics

requirements. For certain studies, the ethics review may have included review by the

Human Studies Review Board. Descriptions of data sources, as well as guidance on their

use, can be found at the Agency website1. 

Data Requirements

The following additional toxicology data are required to refine the occupational risk 

assessment.

 GLN 870.7600 Dermal penetration

 GLN 870.3465 28-Day inhalation toxicity study (rat)

 

1 http://www.epa.gov/pesticides/science/handler-exposure-data.html and 

http://www.epa.gov/pesticides/science/post-app-exposure-data.html
Ethoxyquin Registration Review Human Health Assessment Scoping Document

Page 10 of 28

References

Table 1. Memoranda Relevant to Registration Review.

Author Barcode/TXR No. Date Title

Clock, M. D342695 4/1/2008 Ethoxyquin. Occupational Risk Assessment for

Proposed Uses on Stored Pears. ORE Thermal Fogging

Review.

Funk, S. None 1/26/1995 The HED Metabolism Committee Meeting Held on

December 20, 1994: Ethoxyquin.

Hrdy, D., et al. D310495 7/20/2004 Ethoxyquin. Health Effects Division (HED) Revised

Risk Assessment for the Reregistration Eligibility

Decision.

Hrdy, D. D297740 7/2/2004 Ethoxyquin Acute, Chronic, and Cancer Dietary 

Aggregate Exposure Assessments for the Reregistration 

Eligibility Decision.

Knizner, S. None 5/27/2009 HED Interim Guidance on Tolerance Expressions

Leshin, J. 0053945 8/21/2014 Ethoxyquin: Summary of Hazard and Science Policy 

Council (HASPOC) Meeting of June 5, 2014: 

Recommendation on Multiple Toxicology Studies.

Recore, S. D420779 7/16/2014 Ethoxyquin: Tier I Review of Human Incidents

Attachments:

Attachment 1: Ethoxyquin Identity and Physicochemical Properties

Attachment 2: Ethoxyquin Toxicity Profile Tables

Attachment 3: Ethoxyquin Toxicological Doses and Endpoints for Risk Assessment

Attachment 4: Ethoxyquin International Residue Limits
Ethoxyquin Registration Review Human Health Assessment Scoping Document

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Attachment 1. Ethoxyquin Identity and Physicochemical Properties

Table A1.1. Test Compound Nomenclature

Chemical Structure

Empirical Formula C14H19NO

Common name Ethoxyquin

IUPAC name 1,2-dihydro-2,2,4-trimethylquinolin-6-yl ethyl ether

CAS name 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline

CAS Registry Number 91-53-2

Chemical Class Quinoline

Table A1.2. Physicochemical Properties

Parameter Value Reference

Molecular Weight 217.34

Melting point/range Approximately 0 C Sax and Lewis, 1987

pH No information found.

Density No information found.

Water solubility (20 C) Insoluble Monsanto, 1959

Solvent solubility (temperature not 

specified)

Miscible with animal and vegetable 

fat and oils

Monsanto, 1959

Vapor pressure (25 C) 1.82 x 10-5 mm Hg @ 0 C (purified 

material); 2.56 x10-4 mm Hg @ 25

C

Monsanto, 1987

Dissociation constant, pKa No information found.

Octanol/water partition coefficient, 

logPOW (25 C)

No information found.

UV/visible absorption spectrum 1.569-1.572 @ 25 C Sax and Lewis, 1987
Ethoxyquin Registration Review Human Health Assessment Scoping Document

Page 12 of 28

Attachment 2. Ethoxyquin Toxicity Profile Tables

Table A2.1. Acute Toxicity Profile: Ethoxyquin

Guideline

No. Study Type MRID #(s) Results Toxicity 

Category

870.1100 Acute Oral - Rats 43885901 (1995) LD50 = 1726 mg/kg III

870.1200 Acute Dermal- Rats 43885902 (1995) LD50 = > 2000 mg/kg III

870.1300 Acute Inhalation 43894101 (1996) LC50 = > 1.97 mg/L III

870.2400 Primary Eye Irritation 43885903 (1995) not an eye irritant IV

870.2500 Primary Skin Irritation 43885904 (1995) slight irritant IV

870.2600 Dermal Sensitization 43885905 (1995) weak sensitizer NA

Table A2.2. Ethoxyquin Subchronic, Chronic and Other Toxicity Profile

GL # MRID Study Type Results and Classification

Ethoxyquin: Chronic Studies

Nonguideline

Hard & Neal, 

1992

Fund. Appl. 

Tox. 18: 185-

189

Chronic (dietary) toxicity 

study at 0 or 0.5% of 90% 

ethoxyquin (65.5/70.6 

mg/kg/day for 

males/females) in arachis 

oil. Fisher 344 rats (6-

20/sex/dose/sacrifice at 4, 

12-14, 24, 58 weeks or 18 

months.

Body weight gains in treated rats: 80%/ 90% of 

controls for males/females, feed consumption not 

affected. Interstitial degeneration of the extremity of 

the renal papilla was seen in male rats after 4 weeks 

which progressed to necrosis and pyelonephritis with 

loss of part of the papilla and foci of mineralization in 

the abscission layer by week 24. Degeneration in 

female rats paralleled that of males at the 4 or 12 to 

14 week points; neither pyelonephritis nor urothelial 

hyperplasia was seen. At 18 months, all treated 

males had complete papillary necrosis with tissue loss 

and severe end stage chronic progressive 

nephropathy. All treated females had interstitial 

degeneration of the papillary tip, but the lesion had 

not progressed beyond the earlier stage. No evidence 

of recovery of the lesions was seen. Ethoxyquin is a 

potent inducer of renal papillary necrosis in male rats 

and that female rats are far less susceptible to its 

effects. A proposed LOAEL is <65 mg/kg/day and a 

NOAEL would be much less.

Nonguideline

Neal et al, 

2003

Food Chem. 

Tox. 41: 193-

200

Chronic (diet) tox study 

Fisher 344 rats ethoxyquin 

90% in the diet at 0, 0.01, 

0.05, 0.01, 0.25 or 0.5% 

(5, 25, 50, 125, or 250 

mg/kg/day) for 3 or 6 

months (5 males /group for 

3 months feeding; 

8/sex/group in the 6 month 

feeding except in the 0.05, 

0.1, and 0.25% 5 

females/group were used). 

Proposed LOAEL = 5000 ppm (250 mg/kg/day) 

based on a sharp threshold in male rats with either 

interstitial degeneration of the papilla or frank 

papillary necrosis being evident after 3 and 6 months 

but not at 2500 ppm or lower dose. In the female rats, 

6 months of feeding produced early minimal 

interstitial degeneration in one individual only at the 

0.5% exposure level. When C-14 ethoxyquin was 

administered ip or orally by gavage (10 mg/kg), the 

radiolabel was associated with urinary albumin. The 

ratio of the excreted radioactivity in the urine to feces 

was 7.3-8.2. Autoradiographic sections of the 

kidneys did not show differences among the sexes in 
Ethoxyquin Registration Review Human Health Assessment Scoping Document

Page 13 of 28

Table A2.2. Ethoxyquin Subchronic, Chronic and Other Toxicity Profile

GL # MRID Study Type Results and Classification

the distribution of the radioactivity or retention of 

ethoxyquin. Fecal and urinary metabolites’ profiles 

were similar in the two sexes. No unmetabolised 

ethoxyquin was detected in any sample. Treatment of 

the urine and fecal extracts with β-glucuronidase 

failed to produce any detectable level of non-polar 

labeled compounds.

Nonguideline

Hernández et 

al, 1993

Food Chem. 

Tox. 31:

363-367

Renal cortical slices 

prepared from Wistar male 

rats that had consumed a 

diet containing ethoxyquin 

94% (0.01, 0.05, 0.1, 0.2, 

0.5, 1.0 or 2.0 mM 

equivalent to 0.3, 1.5, 3, 6, 

15, 30, 60 mg/rat/day), 

from weanling to adult age

Ethoxyquin inhibited the specific uptake of C14-

labeled p-aminohippurate ([14C]PAH) and 

tetraethylammonium ([14C]TEA), markers of organic 

anion and cation tubular secretion, respectively, in a 

concentration dependent manner. The specific uptake 

of [14C]TEA was five-fold more sensitive to 

ethoxyquin than [14C]PAH uptake (IC50 = 0.33 and 

1.51 mM, respectively). Ethoxyquin (1 mM) 

decreased Na+/K(+)-ATPase activity from 1.58 to 1.0 

mumol inorganic phosphate/mg protein/min in renal 

microsomes. The activity of this enzyme provides the 

energy for the function of both secretory systems. 

Nonguideline Imazawa et 

al, 1989

Bull Natl Hyg 

Sci 107: 68-

72

Male Wistar rats were 

treated with 100 ppm 

N-methyl-N'-nitro-N-nitro

soguanidine (MNNG) in 

the drinking water for 8 

weeks, followed by a 

dietary supplement of 

0.1% ethoxyquin for 32 

weeks. An additional 

group received the 

ethoxyquin treatment 

alone.

Calcification and stones were observed from the renal 

papilla to the pelvis region in all ethoxyquin treated 

groups. The incidence and grade of the lesion in the 

combined treated groups were much greater than in 

the group treated with ethoxyquin alone. 

Ultrastructurally, microvilli on the surface of the renal 

papilla cells appeared degenerated or disappeared 

completely in the treated groups. Chemical element 

analysis of the renal stones revealed P and Ca to be 

the primary constituents. 

Nonguideline

Rudra et al., 

1974

MRID 

5000419

Chronic dietary, Wistar 

male rats (5/group) for 500 

days; 0.0, 0.5% ETX in 

arachis oil (estimated 250 

mg/kg/day)

The ETX rats ate less than controls and experienced a 

decreased growth rate. After 280 days, 4 animals 

died from severe kidney failure.

Nonguideline

Hazelton 

Labs, 1955; 

Monsanto, 

1985;

NTP, 1990

Chronic, capsule, dog, 0 

(I), 10 (II), 50 (III) or 100 

(IV) mg ETX/kg (2-3 dogs 

mixed sex/group; dosed 5 

days/week except group III 

daily for 1st 6 weeks then 

twice/day afterwards. 

Group IV discontinued 

after 6 weeks due to 

toxicity, sacrificed at week 

9, replaced with two dogs 

at 3 mg/kg (V)

Abdominal tenderness, anorexia, depression, soft 

feces, dark brown livers, discolored urine, irritation of 

the large and small intestine, enlarged liver seen in 

some or all dogs at some or at all treatment levels. 

Kidney swelling with fatty accumulation was seen in 

groups I, III, and V. Granulation of cells in collecting 

tubules was also seen in groups 2 and 3. Liver 

degeneration and fatty metamorphosis of the liver was 

seen in groups 2, 3, and 5. Groups 3 and 4 exhibited 

marked retention of exogenous pigment in the liver. 

One dog in group 3 had massive fibrosis. These 

histological changes were thought to be temporary 

and may be reversible. The NOAEL in this study for 

microscopic pathological changes was 28 mg/kg/day 

at day 84.

Nonguideline

Western URB 

1955; 

Monsanto, 

1985;

Chronic, dietary in alfalfa, 

rats. Trial I. (10 

rats/sex/group) at 0, 0.2%, 

In trial I males and females weighed significantly less 

(p<0.05-0.01) than controls. In trial II, a small 

indication of kidney lesions was seen in the 0.1 and 

0.2% ETX groups. Liver weights among females in 
Ethoxyquin Registration Review Human Health Assessment Scoping Document

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Table A2.2. Ethoxyquin Subchronic, Chronic and Other Toxicity Profile

GL # MRID Study Type Results and Classification

(NTP, 1990) 0.4%, ETX (0, 100 or 200 

mg/kg/day) for 155 days.

Trial II. (10 males/group) 

at 0, 0.0062%, 0.0125%, 

0.05%, 0.1%, 0.2% (3, 6, 

25, 50, or 100 mg/kg/day) 

and (10 females/group) at 

0, 0.05%, 0.1%, 0.2% ETX 

for 225 days.

the 0.2% ETX group and males in the 0.1% group as 

well as liver weights in all higher dose groups were 

significantly greater (p<0.01) than controls. Kidneys 

weights were significantly greater (p<0.01) in the 

0.2% (trials 1 and 2) and 0.4% (trial 1) dose groups 

versus controls. Kidneys of 2 male rats in the 0.4% 

ETX group, had stones in the renal pelvis. 

Microscopic examination revealed well-developed 

chronic pyelonephritis among males in the high dose 

groups. Two kidneys had areas of calcification. The 

thyroid glands of male rats exposed to higher doses of 

ETX had evidence of hyperplasia. All male rats in 

the 0.2% ETX group, 3/4 in the 0.1% group, and 2/5 

in the 0.05% group had small kidney scars. Proposed 

LOAEL is 25 mg/kg/day based on kidney lesions, 

proposed NOAEL is 6 mg/kg/day.

Nonguideline

Davies et al, 

1993

Carcinogenes

is 

14(1):47-52

Chronic, albino rats. ETX 

in the diet (0.5%) fed to 21 

days old or 6 weeks old 

until 9 months of age. 

A marked body weight gain reduction (15-20%) 

reported. The conversion of 2N nuclei to 4N and 8N 

nuclei as measured by flow cytometry was slowed 

down. Ethoxyquin is a very potent inducer of gammaglutamyltranspeptidase (GGT), but expression 

depended on the age of the animals, the length of 

treatment time and the ploidy status of the liver.

Nonguideline

Manson et al, 

1992

Arch Toxicol 

66(1):51-56

Chronic (dietary) toxicity 

study at 0 or 0.5% ETX 

(250 mg/kg/day) in 

weanling or adult rats at 

the beginning of the 

experiment for 26 weeks

Female rats were much less susceptible to the toxic 

effects of ethoxyquin than males of the same age. In 

males damage to the cortex, mainly as an acceleration 

of the normal ageing process, was similar in both age 

groups, but rats exposed to ethoxyquin as weanlings 

also suffered from extensive papillary necrosis. Male 

rats were more prone than females to proteinuria.

Ethoxyquin: Sub-chronic Studies

82-1

870.3100

44123801 & 

44222501

28-Day oral gavage – Rat

Acceptable/NonGuideline

5/sex at 0, 50, 250, 500, 

1000 mg/kg/day in corn oil 

(5 mL/kg)

LOAEL = 250 mg/kg/day, based on decreased 

hematology parameters (RBC count, hemoglobin, 

hematocrit), increased serum chemistry values 

(globulin, total protein, Ca, P, K, cholesterol), 

increased liver weights, and histopathological 

findings in the kidneys. At the 1000 mg/kg/day all 

animals died within 2-3 days.

NOAEL = 50 mg/kg/day. 

870.3100 44123901 90-Day oral gavage – Rat

Acceptable/Guideline

10/sex at 0, 20, 40, 200 or 

400 mg/kg/day in corn oil 

(5 mL/kg)

LOAEL = 40 mg/kg/day based on decreased mean 

body weight gain (-14%) in males. At 200 and 400 

mg/kg/day these effects were noted: decreased RBC, 

hematocrit and hemoglobin, increased mean 

reticulocyte counts, decreased mean WBC counts, 

increased serum albumin, and globulin, total protein, 

total bilirubin, GGT, cholesterol, decreased Serum T4 

level and increased TSH level. Reddened and/or 

enlarged thyroid glands, increased liver and kidney 

weights. Microscopic lesions on kidneys: renal 

papillary necrosis, hyalin droplets in the cortical 

tubular epithelial cells and nephropathy.

NOAEL = 20 mg/kg/day. 
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Table A2.2. Ethoxyquin Subchronic, Chronic and Other Toxicity Profile

GL # MRID Study Type Results and Classification

870.3150 44149001 28-Day oral, capsule –

Dog

Acceptable/NonGuideline

2/sex at 0, 25, 50, 100 or 

200 mg/kg/day

LOAEL(estimated) = 25 mg/kg/day based on 

decreased body weight gain (-17%) in females , 

elevated AP, ALT, AST and GGT enzyme levels and 

necropsy findings (dark liver, dilated vessel in the 

heart, GI changes, moderate to severe endogenous 

pigment on the liver). The 100 and 200 mg/kg 

animals were sacrificed in extremis at 5-17 days with 

the following effects: hypoactivity, ataxia, 

hypothermia, emaciation, pale gums, dermal atonis, 

green ocular discharge, decreased defecation, brown 

urine, severe body weight losses, and reduction in 

food consumption. 

NOAEL not established (<25 mg/kg/day). 

870.3150 44148901 90-Day oral, capsule –

Dog

Acceptable/Guideline

2/sex at 0, 2, 4, 20 or 40 

mg/kg/day

LOAEL = 4 mg/kg based on elevated liver enzymes 

and microscopic findings in the liver (cytoplasmic 

vacuolation and minimal hepatocellular necrosis). 

Effects at 20 and 40 mg/kg: brown areas of skin on 

the urogenital and ventral abdominal areas, brown 

sclera, discolored urine (brown or amber), decreased 

and/or black mucoid feces and/or emesis, one 40 

mg/kg female sacrificed in extremis on day 13, 

clinical chemistry findings, bile duct hyperplasia in 

90% of the dogs.

NOAEL = 2 mg/kg/day. 

Nonguideline

Neal et al, 

2003

Food Chem. 

Tox. 41: 193-

200

Sub-chronic (diet) tox 

study Fisher 344 rats 

ethoxyquin 90% in the diet 

at 0, 0.01, 0.05, 0.01, 0.25 

or 0.5% (5, 25, 50, 125, or 

250 mg/kg/day) for 3 or 6 

months (5 males /group for 

3 months feeding; 

8/sex/group in the 6 month 

feeding except in the 0.05, 

0.1, and 0.25% 5 

females/group were used). 

Proposed LOAEL = 5000 ppm (250 mg/kg/day) 

based on a sharp threshold in male rats with either 

interstitial degeneration of the papilla or frank 

papillary necrosis being evident after 3 and 6 months 

but not at 2500 ppm or lower dose. In the female rats, 

6 months of feeding produced early minimal 

interstitial degeneration in one individual only at the 

0.5% exposure level. When C-14 ethoxyquin was 

administered ip or orally by gavage (10 mg/kg), the 

radiolabel was associated with urinary albumin. The 

ratio of the excreted radioactivity in the urine to feces 

was 7.3-8.2. Autoradiographic sections of the 

kidneys did not show differences among the sexes in 

the distribution of the radioactivity or retention of 

ethoxyquin. Fecal and urinary metabolites’ profiles 

were similar in the two sexes. No un-metabolized 

ethoxyquin was detected in any sample. Treatment of 

the urine and fecal extracts with β-glucuronidase 

failed to produce any detectable level of non-polar 

labeled compounds.

Nonguideline

Shibata et al, 

1989 Tox 

Appl 

Pharmaco 99: 

37-49

0.8% ethoxyquin (640 

mg/kg/day) in drinking 

water to Fisher rats for 4 or 

8 weeks.

Significant body weight and food consumption 

reduction. Leafy or ropy microridges and or short 

microvilli observed on the bladder epithelial surface. 

Increased urinary bladder DNA synthesis.

Nonguideline

Kim, 1985

J Tox Env. 

Health,

15: 663-671

0, 0.25 or 0.5% ethoxyquin 

or ethoxyquin-HCl, dietary 

to mice (5/dose) for 20 

days.

Dose-dependent weight loss. Dose-dependent hepatic 

hypertrophy (p<0.0001) compared to controls. Liver 

weights in the high dose group (0.5%) were greater in 

the ethoxyquin group than those in the 

ethoxyquin-hydrochloride group. Tissue thiol levels 
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Table A2.2. Ethoxyquin Subchronic, Chronic and Other Toxicity Profile

GL # MRID Study Type Results and Classification

increased in both ethoxyquin and 

ethoxyquin-hydrochloride groups, especially in the 

small intestine (p=0.007). Liver tissue thiol levels 

also increased significantly (p=0.116). Thiol levels in 

the stomach of ethoxyquin treated rats were 

significantly higher (p=0.024) than levels observed in 

the ethoxyquin-hydrochloride and control groups.

Nonguideline

Ward et al, 

1989

Fund. Appld 

Toxicology, 

12: 163-171

5000 ppm, dietary to male 

F344/DuCrj rats for 6 

weeks

Induced toxic proliferative biliary lesions.

Ethoxyquin: Contact Dermatitis

Nonguideline

Mehlhorn & 

Beetz, 1971

Berufsdermat

osen; 19 

(2):84-91

Animal feed

First case reported of occupational contact eczema 

attributed to ethoxyquin in an animal feeder.

Burrows, 

1975

BR J 

DERMAT.; 

92: 167-170

Animal feed mill, 

ethoxyquin added as 

vitamin E antioxidant

Contact dermatitis in a 30-yr old male and 48 yr old 

foreman.

O’Malley, 

1997

Occup. 

Medicine:, 

12:327-345

Apple and pear packing 

processing

Skin irritation in 20 workers from handling paper 

impregnated with ethoxyquin

Savini et al, 

1989

Contact 

Dermatitis, 

21: 342-343

Poultry feed in a poultry 

farm

Puritic erythematous vesciualr dermatitis in a 21-yr 

old female.

Nishioka et 

al, 1996

Contact 

Dermatitis; 

35:241-245

Rice farmers wearing 

rubber boots - ethoxyquin

Contact dermatitis: itch erythema, papules, scales and 

erosion on the legs, and erythema, vesicles, 

hyperkeratosis, scales and fissures on the soles, 

leading occasionally to generalization of eczema 

(autosensitization dermatitis)

Zachariae, 

1978

Contact 

Dermatitis 

4:117-118

MRID 5000444

Animal feed containing 

ethoxyquin

Three cases of dermatitis reported

Alankoa, 

1997

J European 

Acad Derm 

Venereology 

9(S1): S167

Multivitamin powder 

preparation with 

ethoxyquin

Extensive eczemztous rash in a 43-yr old man 

exposed for 17 years. Potential skin sensitizer.

Rubel and 

Freeman, 

1998

Australas J. 

Dermatol. 

39(2):89-91

Chicken feed with 

ethoxyquin as vitamin 

antioxidant

A case of allergic contact dermatitis reported

Vaneckova & 

Ettler, 1994

Rubber surgical gloves 

confining ethoxyquin

Dermatitis of hands in health care personnel.
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Table A2.2. Ethoxyquin Subchronic, Chronic and Other Toxicity Profile

GL # MRID Study Type Results and Classification

Contact 

Dermatitis, 

31: 266-268

Hecke, 1977

Contact 

Dermatitis, 3: 

341-352

Animal feed farmer and 

animal feed factory 

production workers

Scaly dermatitis on face, hands, arms and legs.

Schubert et 

al, 1973

Dermatolozif

che 

Monatffchrif 

159:791-796

Animal feed mill Acute contact dermatitis in workers attributed to 

ethoxyquin in the feed. 

Brandao, 

1983

Contact 

Dermatitis

Volume 9, 

Issue 3, page 

240

Animal feed mill Contact dermatitis in animal feed workers.

Ethoxyquin: Developmental and Reproduction Studies

870.3700 MRID 

44098901

Developmental Tox studyrat. 

Acceptable/Guideline

25/group at 0, 50, 150, or 

350 mg/kg/day on GD 6-

19

Maternal toxicity LOAEL = 150 mg/kg/day based 

on clinical signs of toxicity (wet yellow staining in 

the urogenital area, wet clear matting on the mouth, 

dried brown staining around the mouth) and reduced 

body weight gains and food consumption. Maternal 

toxicity NOAEL = 50 mg/kg/day.

Developmental toxicity NOAEL = 350 mg/kg/day 

Developmental toxicity LOAEL was not identified.

Nonguideline

Khera et al, 

1979

J Env Sci 

Hlth B 14: 

563-577

Developmental tox study 

in rats. 20/group t 0, 125, 

250 or 500 mg/kg 

Santoquin (67% 

ethoxyquin)

No maternal toxicity reported. It was concluded by 

the study authors that the overall effect of ethoxyquin 

formulation was not teratogenic to rats.

Nonguideline

Telford et al,

1962

MRID 

05000428

Developmental tox study 

in rats. 57 mg/kg/day from 

GD 1-22

Lower fetal absorption rate than in the control.

Nonguideline

King, 1964

J NUTR 

83:123-132

Developmental tox study 

in rats. Examined the 

effect of ethoxyquin on the 

outcome of pregnancy in 

vitamin E deficient rats

Ethoxyquin reduced the incidence of resorptions and 

decreased the occurrence of gross congenital 

malformations.

Nonguideline

DeSesso & 

Goeringer, 

1990

Repro Tox 

4(4): 267-275

Developmental tox study 

in rabbits. 7-10 / group, 

subcutaneous injection on 

GD 12 with 0, 950 

mg/kg/day ethoxyquin 

alone or followed with 650 

mg/kg hydroxyurea (HU) 

or 650 mg/kg of 

hydroxyurea injection 

alone (positive control)

Maternal treatment with HU caused severe 

developmental toxicity in term fetuses: reduced mean 

fetal weight (p<0.01) and 100% malformations (cleft 

lip, cleft palate, limb and tail deformities) vs to 0% 

malformations in controls. Treatment with the ETX 

prior to HU resulted in significant reduction of HUinduced fetal malformations (p<0.001) and an 

increase in the mean fetal body weight compared to 

the HU treatment only. Microscopic analysis of limb 

buds from HU-treated embryos revealed severe 

mesenchymal cell necrosis in the limb buds within 4 

hours of maternal injection. Pre-treatment with 
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Table A2.2. Ethoxyquin Subchronic, Chronic and Other Toxicity Profile

GL # MRID Study Type Results and Classification

ethoxyquin reduced the cell necrosis to less than 20% 

during the first 4 hours, but by 12 hours it was 

comparable to the HU treatment. 

Nonguideline

Isenstein, 

1970

AM J VET 

RES 

31:907-909

Developmental tox study 

in rabbits. 16-20 group, 

dietary at 0, 0.0025% or 

0.005% ethoxyquin 10 day 

prior to breeding to 2 

weeks after parturition. 

Study repeated 4 months 

later at 0, 0.0025% or 

0.01% ethoxyquin

Results were inconsistent, but do suggest that 

ethoxyquin had no effect on newborn mortality or 

abortions in pregnant rabbits at these dietary doses.

Nonguideline

Delaney et al, 

1995

Toxicologist 

Mar;15(1):16

5 

Reproduction study in rats. 

Ethoxyquin in corn oil at 

0, 75, 150, or 300 

mg/kg/day (20/sex/group) 

using the continuous 

breeding protocol.

Proposed LOAEL for reproductive toxicity is 300 

mg/kg/day, based on decreased litters/pair (22%), live 

pups/ litter (22%), and increased cumulative days to 

litter (8%-17%), decreased pup weight (20%) in pups 

born to treated females and decreased body weights in 

F0 and F1 males(7-20%). Proposed NOAELfor 

reproductive toxicity is 150 mg/kg/day.

Proposed parental toxicity LOAEL is 75 mg/kg/day 

based on increased liver and kidney weights (13% to 

56% with increasing dose) in F0 and F1 animals.

Proposed parental toxicity NOAEL is <75 

mg/kg/day

Nonguideline

Gilman & 

Voss, 1995 in 

JMPR 1998

Reproduction study in 

dogs 0, 100, 225 ppm of 

ethoxyquin (Santoquin®) 

dietary (0, 2.5, 6 

mg/kg/day) for two 

generations

Proposed LOAEL for reproductive toxicity is >6 

mg/kg/day. Proposed NOAEL for reproductive 

toxicity is 6 mg/kg/day.

Proposed parental toxicity LOAEL is 2.5 

mg/kg/day based on increased incidences of clinical 

signs such as excess lachrymation and dehydration, 

clinical chemical changes and pigment deposition in 

the liver.

Ethoxyquin: Metabolism and Absorption Studies

Nonguideline

Skaare & 

Nafstad, 1979

Acta 

Pharmacologi

ca et 

Toxicologica 

44:303-307

Metabolism Study -

Distribution & Whole 

body autoradiography -

Male Rat. 2 rats/sacrifice 

time of 0.5, 1, 2, 4, 8, 10, 

12, 16, 20, 24, 48 & 144 

hours given single oral 

dose of 14C-ETX.

0.5 hr autoradiograms showed that radioactivity was 

distributed throughout most tissues, highest in GI 

tract, liver and kidneys. By 24 hours no radioactivity 

detected in the stomach but still persisted in the 

intestines. At 48 hours, radioactivity declined with 

exception of the GI tract, the medulla of the kidney, 

and the blood. At 144 hours, high radioactivity 

persisted in the renal cortex and moderate to weak 

radioactivity in the liver, the intestines, the lungs, and 

heart blood. 

Nonguideline

Skaare & 

Solheim, 

1979

Xenobiotica 9 

(11): 649-657

Metabolism StudyMetabolite Identificationmale rats. 14C-ETX, 100 

mg/kg oral dose

The major metabolic pathway was deethylation and 

hydroxylation. An average of 28 & 36% of dose of 

radioactivity was recovered in bile in 12 & 24 hr 

respectively following intragastric admin of C14-ETX 

to bile duct cannulated rats. Biliary metabolites were 

identified. A 95% of the AD was accounted for 

within 6 days. Less than 1% of the AD was detected 

in 24 hour respired air samples.

Nonguideline

Kim et al, 

1992

Metabolism - Sheep and 

rats. Sheep given 

ETX.HCl as 0.5% of diet. 

ETX was identified in all sheep urine samples 

collected during the first 24 h of feeding, and ETX 

and hydroxylated ETX were identified in all urine 
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Table A2.2. Ethoxyquin Subchronic, Chronic and Other Toxicity Profile

GL # MRID Study Type Results and Classification

Tox Environ 

Health; 37 

(2): 341-347

Rats given ETX in corn oil 

0.08 g/day/rat orally for 7 

days

samples collected after 12 days of feeding. In 

contrast, ETX, hydroxylated ETX, and 

dihydroxylated ETX were identified in urine from rats 

fed ETX for 7 days.

Nonguideline

Sanders et al, 

1996

Xenobiotica; 

26 (6):583-

595

NTP metabolism study, 

rats and mice. 14C-ETX 

per oral or intravenous. 

Excretion studies

The disposition of single doses up to 25 mg/kg was 

similar in the rat and mouse. About 90% of AD was 

excreted in urine and feces within 24 h. In contrast, 

no more than 60% of a 250 mg/kg dose was excreted 

within 24 h following p.o. administration. Urinary 

excretion is the predominant route. Its metabolism 

was rapid in both the rat and mouse following either 

p.o. or i.v. administration. Little or no parent 

compound was detected in cumulative 24-h excreta. 

ETX-derived radioactivity bioaccumulated in some 

tissues (liver, kidney and adipose tissue) following 

repeated exposure to rat of either 25 or 250 mg/kg by 

gavage. 

Nonguideline

Burka et al, 

1996 

Xenobiotica; 

26 (6):597-

611

NTP metabolism study, 

rats and mice. 14C-ETX 

po or iv. Metabolite 

identification

ETX is extensively metabolized by oxidation, 

deethylation and conjugation to endogenous 

substances prior to urinary elimination. Rat urine 

sulphate conjugates: 

1,2-dihydro-6-hydroxy-2,2,4- trimethylquinoline 

sulphate, and 

1,2,3,4-tetrahydro-3,6-dihydroxy-4-methylene-2,2-di

methylquinoline sulphate. Mouse urine had a sulfate 

conjugate and a glucuronide conjugate. ETX-derived 

radioactivity was excreted in rat bile, mainly as GSH 

conjugates, with little unchanged ETX present. 

Nonguideline

Wilson et al, 

1981

Xenobiotica 9 

(6): 343-51

Metabolism study - rats, 

repeated feeding (0.005% 

ETX in diet) for 10 days 

followed by a single oral 

dose 1.5 mg of 14C-ETX 

and sacrificed 1, 2, 7 days 

for males and 7, 14, 28 

days for females. 

Liver and kidney contained the highest concentrations 

(0.3 ppm - 0.4 ppm) of radioactivity after one week. 

The heart, skeletal muscle, and brain contained lower 

levels while the spleen, blood, and abdominal fat 

contained intermediate levels of radioactivity. The 

estimated ETX turnover rate in rats was 10 days. 

ETX is rapidly excreted within one or two days. 

Oxidation of ETX to carbon dioxide was negligible. 

Placental transfer of 14C-ETX or its metabolites was 

demonstrated.

Nonguideline

Meulen et al, 

1980

Journal of 

Animal 

Physiology 

and Animal 

Nutrition) 43: 

164-170

Metabolism studyExcretion and metabolite 

identification, male rats. 

Single oral dose of 40 mg 

of 14C-ETX and sacrificed 

after 6, 12, 24, 48, 72 hrs.

The highest values of the AD observed in the liver, 

kidney, and stomach were 8.0%, 0.3%, and 56.5%, 

respectively, after 6 hours. Levels of radioactivity 

found in the small intestine, large intestine, caecum 

and blood were 11.3%, 0.9%, 6.9% and 0.9% of the 

AD, respectively. 14C-ETX concentration in urine 

exceeded that in feces by two-fold. After 72 hours, 

84.8% of the total labeled dose was found to be 

eliminated in the urine and feces. Unchanged ETX, 

one unknown metabolite and five known metabolites 

were detected in urine.

Ethoxyquin: Special Studies

Nonguideline

Cabral & 

Neal, 1983

Cancer 

Letters, 19: 

125-132

Inhibitory Effects Of 

Ethoxyquin On The 

Carcinogenic Action Of 

Aflatoxin B1 In Rats. Rats 

fed diets containing 0 or 4 

Ethoxyquin produced an inhibition of liver 

carcinogenicity that was dose related. There was a 

high incidence of altered foci, neoplastic nodules, and 

liver cell tumors in rats fed aflatoxin only. Addition 

of ethoxyquin to a diet containing aflatoxin 
Ethoxyquin Registration Review Human Health Assessment Scoping Document

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Table A2.2. Ethoxyquin Subchronic, Chronic and Other Toxicity Profile

GL # MRID Study Type Results and Classification

ppm aflatoxin or 

ethoxyquin 0.05 or 0.5% 

with ethoxyquin 

administered alone or after 

aflatoxin or before 

aflatoxin or together.

completely inhibited liver tumors. When ethoxyquin 

was administered after aflatoxin, there was 

considerable reduction in the incidence of altered foci 

and neoplastic nodules of the liver. No liver tumors 

were found in rats fed ethoxyquin alone or in 

untreated controls. No metastases were found from 

any liver tumor. 

Nonguideline

Wischi, 1981

Toxicology; 

21: 95-104

Inhibitory effects When male mice were injected i.p. with a single dose 

of urethanE and fed 0.75% ETX in the diet and killed 

4 months after urethane, exposure to ETX did not 

enhance formation of lung tumors.

Nonguideline

Wattenberg, 

1972

J Natl Cancer 

Inst; 48: 

1425-1430

Inhibitory effects ETX inhibited the carcinogenicity of benzo(a)pyrene 

or 7,12-dimethylbenz(a)anthracene (DMBA) on the 

forestomach of the mouse. It also inhibited mammary 

tumor formation produced by oral administration of 

DMBA to female Sprague-Dawley rats. ETX given 

to female rats 1 hr before oral administration of 30 

mg DMBA prevented the adrenal necrosis occurring 

in animals not given the antioxidant

Nonguideline

Tsuda et al, 

1984

Carcinogenes

is, 5: 525-531

Tumor promotion & 

inhibition

ETX inhibited the development of liver foci induced 

(initiated) by N-ethyl-N-hydroxyethylnitrosamine 

(EHEN) but enhanced the appearance of

preneoplastic and neoplastic induced lesions in the 

kidney of rats

Nonguideline

Thamavit et 

al, 1985

Cancer 

Letters 27: 

295-304

Inhibitory Effect of ETX. Preneoplastic lesions (foci) in rat liver initiated by 

diethylnitrosamine (DEN, single oral dose 200 mg/kg 

body wt) and partial hepatotectemy were decreased 

(number and area of foci) by subsequent ETX diet 

(0.5%, 0.25% and 0.125%) in a dose dependent 

fashion.

Nonguideline

Takahashi et 

al, 1986

Cancer 

Letters, 30: 

161-168

Tumor promotion, male 

rats received 100 mg of 

N-methyl-N'-nitro-N-nitro

soguanidine (MNNG)/L of 

drinking water for 8 wks 

followed by 1% ETX diet 

for 32 wks or 0, or 1% 

ETX only for 40 weeks.

No rats given ETX alone developed tumors in the 

glandular stomach. The incidence of gastric tumors 

was significantly increased in animals given ETX 

after MNNG treatment compared to the group given 

MNNG alone. Changes were observed in the kidneys 

of animals given ETX and were especially marked for 

animals receiving ETX after MNNG administration. 

Nonguideline

Masui et al, 

1986

Japanese 

Journal of 

Cancer 

Research, 77: 

231-237

Inhibitory Effect of ETX. 

Male rats injected 200 

mg/kg diethylnitrosamine 

(DEN), followed by 0.02% 

of 2-acetylaminofluorene 

(AAF) in the diet for 2 to 8 

weeks. Partial 

hepatectomy 3rd week. 

Week 10 were fed 0.8% 

ETX diet for 26 weeks, 

killed at week 40 and 

necropsied.

Hepatocellular carcinomas were observed in 88.2% of 

the animals initially treated with DEN and AAF. Rats 

treated subsequently with ETX showed incidences of 

hepatocellular carcinoma of 57.1%, significantly 

lower than that of the positive controls. Rats treated 

with ethoxyquin showed significant decreases in the 

number of hepatocellular carcinomas per unit liver, 

compared with the positive controls. Only the 

ethoxyquin treated animals showed significant 

decreases in tumor size. No metastases to other 

organs or primary tumors in other organs were seen.

Nonguideline

Manson et al, 

1987

Carcinogenes

is ; 8:723-728

Inhibitory Effect of ETX. 

Rats pretreated with 0.5% 

ETX diet followed by 

aflatoxin B1

ETX completely prevented the formation of AFB1-

induced preneoplastic liver lesions. However, ETX 

alone caused severe damage to the kidney. In 

addition, many hyperplastic and putative 
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Table A2.2. Ethoxyquin Subchronic, Chronic and Other Toxicity Profile

GL # MRID Study Type Results and Classification

preneoplastic tubules were visible, suggesting that 

ETX may be exerting a carcinogenic effect in the 

kidney.

Nonguideline

Kensler et al, 

1986

Cancer Res 

46: 3924-31

Inhibitory Effect of ETX. 

Rats fed 0.4 % ETX diet 

for 1 wk, gavaged 250 ug 

aflatoxin B1/kg, 5x/wk for 

2wks, then normal diet for 

4 months.

ETX reduced > 95% both area and volume of liver 

gamma-glutamyl transpeptidase-positive foci. ETX 

produced a dramatic reduction in the binding of 

aflatoxin B1 to hepatic DNA: 18-fold initially and 

3-fold at the end of the dosing period. Apparently, 

related to induction of detoxication enzymes. Rats 

fed 0.4% ETX for 7 days showed a 5-fold increase 

ETX in hepatic cytosolic glutathione S-transferase 

(GST)-specific activities. Correspondingly, biliary 

elimination of aflatoxin B1-glutathione conjugate was 

increased 4.5-fold in animals on the ETX diet.

Nonguideline

Hirose et 

al,1986

Cancer 

Letters, 

30:169-174.

Promotion study, male rats 

treated with 0.25% ETX 

diet for 2 wks, and during 

wk 2, 1% 

butylated- hydroxyanisole 

(BHA). 

Pronounced epithelial damage: hyperkeratosis and 

ulcer formation was seen in the forestomach in the 

animals treated with ETX and BHA. Mild 

hyperplasia induced by BHA was increased by ETX . 

Nonguideline

Ito, 1986, 

NTP, 1990

Food and 

Chemical 

Toxicology. 

24:1071-1082

Cancer promotion study in 

male rats. 

N-ethyl-N- hydroxyethyl 

nitrosamine (EHEN), 0.1% 

in drinking water for 2 wk, 

then 0.8% ETX diet for 29 

weeks

The incidence of renal-cell adenomas was 

significantly increased in ETX groups (p<0.01) 

compared to controls. The author concluded that ETX 

promoted induction of EHEN-initiated kidney 

adenomas

Nonguideline

Ito et al, 

1986,

Toxicologic 

Pathology, 

14: 315-323

Cancer promotion study in 

male rats. 

N-butyl-N- (4-hydroxybut

yl)nitrosamine (BBN), 

0.05% in drinking water 

for 4 weeks, then 0.8% 

ETX diet for 32 wk

Administration of ETX significantly increased 

(p<0.001) the incidence of papillary or nodular 

hyperplasia.

Nonguideline

Fukishima et 

al, 1984

Cancer 

Letters, 

23(1): 29-37

Cancer promotion study in 

male rats. 0.05% 

N-butyl-N- (4-hydroxybut

yl)nitrosamine (BBN), in 

drinking water for 4 

weeks, then an 0.8% ETX 

diet for 32 weeks

ETX rats weighed less than the controls at the end of 

36 weeks. Lesions of the urinary bladder were 

significantly higher in the ETX group pretreated with 

BBN (p<0.001). Incidence and number of cancers 

were slightly increased in this group compared to 

controls, but not significantly. The authors concluded 

that ETX promotes urinary bladder carcinogenesis. 

Nonguideline

Fukushima et

al., 1986;

Japan 

Journal 

Cancer 

Research. 77: 

1074-1082

Cancer promotion study in 

male rats. Groups fed a 

basal diet containing a 

tumor promoter, one group 

was fed basal diet with 

0.8% ethoxyquin plus a 

control group 

At week 4, body weight was less in the group 

receiving ETX compared to controls. In ETX treated 

rats, the lumina surface of the urinary bladder had 

irregular- shaped foci with a slight elevation of cells, 

giving the mucosa a cobblestone appearance. 

Scanning electron microscopy revealed pleomorphic 

microvilli, short uniform microvilli and ropy or leafy 

microridges.

Nonguideline

Fukushima et 

al., 1987; 

Cancer Lett; 

34 (1): 83-90

Cancer promotion study in 

male rats. 

N-butyl-N- (4-hydroxybut

yl)nitrosamine (BBN), 

0.05% in drinking water 

Mean body weights of ETX rats were lower than 

controls after week 2, with a slight reduction in food 

intake compared to controls. Incidence of esophageal 

papillomas was significantly higher (p<0.05) in ETX 

rats versus controls. The authors concluded that ETX 
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Table A2.2. Ethoxyquin Subchronic, Chronic and Other Toxicity Profile

GL # MRID Study Type Results and Classification

for 4 weeks, followed by a 

diet of 0, or 0.8% ETX for 

36 weeks.

significantly enhanced the induction of esophageal 

papillomas by DBN

Nonguideline

Fukushima et 

al., 1987; 

Cancer 

Research, 47: 

2113-2116

Cancer promotion study in 

male rats. 

N-butyl-N- (4-hydroxybut

yl)nitrosamine (BBN), 

0.05% in drinking water 

for 2 wk, followed by a 

diet of ETX for 22 wk

A dose-dependent decrease in pre-neoplastic lesions 

in the bladder of BBN treated rats was seen in 

ETX-exposed animals. The authors report that "no 

promoting activity or induction of pre-neoplastic 

lesions in the urinary bladder occurred even at the 

highest ethoxyquin dose (0.5%). 

Nonguideline

Miyata et al, 

1985

Jpn J Cancer 

Res); 76: 

828-834

Cancer promotion study in 

male rats. BBN, 0.05% in 

drinking water for 2 

weeks, followed by a diet 

of 0, or 0.8% ETX for 22 

wk.

Incidences and quantitative values of hyperplasia 

significantly higher in ETX group (p<0.05) indicating 

significant promoting activities in the induction of 

pre-neoplastic lesions of the urinary bladder. 

Nonguideline

Manson et al, 

1997; 

Carcinogenes

is 18: 1729-

1738

Kelly et al,

2000

Cancer Res. 

60:957-969

Enzyme Induction ETX is a phase II enzyme inducer

Nonguideline

Yamano & 

Morita, 1993

Arch. of Env 

Contam and 

Tox. 25: 

271-278

Enzyme Induction ETX at 10-7 - 10-3 M was a potent inhibitor of 

NADPH/Fe+2 lipid peroxidation in isolated rat liver 

microsomes. It also significantly reduced 

hepatocellualr glutathione concentrations at 10-4M

Nonguideline

Hayes et al, 

1991 & 1998

Biochem J; 

279: 385-398

Chemico-Biol

ogical 

Interactions, 

111-112: 

51-67

Enzyme induction ETX induces glutathione S-transferase (GST) 

isoenzymes in rat liver that contribute to 

ethoxyquin-induced chemoprotection against AFB1. 

Nonguideline

Ellis et al, 

1993

Proc Natl 

Acad Sci 90: 

10350-10354

Enzyme induction Dietary ETX induces an aldehyde reductase (AFB1-

AR). The mRNA encoding this enzyme is markedly 

elevated in rat liver fed ETX diet.

Nonguideline

Bock et al, 

1980

Arch 

Pharmacol 

310: 249-52

Enzyme induction 0.5% ETX in diet enhanced rat hepatic 

UDP-glucuronosyltransferase activities and 

3-Methylcholanthrene- and phenobarbital-inducible 

glucuronidation reactions

Nonguideline

Buetler et al, 

1995

Toxicology 

and Applied 

Pharmacol. 

135: 45-57

Enzyme induction Phase I and Phase II enzymes are induced by ETX

Nonguideline

Wilson et al, 

1979

Enzyme induction A single oral dose of ETX 200 mg/kg to rats inhibited 

the hepatic microsomal hydroxylation of 
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Table A2.2. Ethoxyquin Subchronic, Chronic and Other Toxicity Profile

GL # MRID Study Type Results and Classification

Xenobiotica 

9: 343-51

thiabendazole (TBD) (65%), aniline (40%) and 

biphenyl (40%) in vitro at 1 h after dosing; inhibition 

was less at 5 h. TBD 100 mg/kg administered orally 

30 min after oral ETX (400 mg/kg) or TBD 200 

mg/kg administered orally 30 min after oral 

desmethylimipramine (DMP) (80 mg/kg) delayed 

absorption of the TBD and resulted in markedly 

decreased plasma concentration of the anthelmintic. 

Simultaneous administration of ETX (300 mg/kg) 

potentiated the anthelmintic effect of TBD (750 

mg/kg) on the helminth parasite, Nematospiroides 

dubius, in the mouse. DMP showed no similar 

potentiation

Nonguideline

Kahl, 1980

Cancer 

Letters, 

8: 323-328

Enzyme induction ETX feeding to rats increases epoxide hydratse 

activity in liver microsomes. I.p treatment of mice 

with ETX also increases it.

Nonguideline

Mandel et al, 

1987

Cancer Res 

47:5218-5223

.

Enzyme induction ETX increased microsomal cytochrome P-450s, 

phenobarbital inducible, and the in vitro rate of 

metabolism of AFB1. ETX increased the glutathione 

S-transferase activity of the liver cytosol fractions. 

gamma-Glutamyl transpeptidase was induced in the 

periportal areas of the liver lobule. Reduced in vivo 

binding of [3H]AFB1 to DNA of liver and kidney 

was found to result from ETX treatment.

Nonguideline

Zenser & 

Davis, 1978

Metabolism, 

27: 227-233

In vitro Study, renal 

function. Rat inner 

medula slices incubated 

with ETX and assayed for 

prostoglandins E2 (PGE2), 

prostoglandin F2 (PGF2) 

and cyclic AMP levels.

ETX (0.01 and 0.001 mM) caused a 50% significant 

(p<0.05) reduction in PGE2. Also, ETX decreased 

(p<0.05) PGE2 production in the presence of 

arachidonic acid. ETX also inhibited PGF2 synthesis 

significantly (p<0.05) at concentrations of 0.01, and 

0.1 mM. Prostoglandins within the kidney play an 

important role in increased rate of urine flow and 

sodium excretion and thus this inhibition may be 

significant to the renal function.

Nonguideline

Derbel et al, 

1993

Biochimica 

biophysica 

acta; 1158 

(2): 175-180

Enzyme induction

ETX induces various subunits of renal and hepatic 

glutathione S- trnasferase.

Ethoxyquin - Immune Effects

Nonguideline

Travis et al, 

1989

Immunol Cell 

Biol; 67 (1): 

83-84

Subchronic Study - Female 

mice (10/group) were 

given diets containing 

0.005 ppm Se or 1 ppm Se 

or 1 ppm Se and 0.02% 

ETX or 1 ppm Se and 

0.25% ETX for 60 days. 

The 0.005 ppm Se diet is 

selenium deficient and the 

1.0 ppm Se diet is 

selenium sufficient for 

immunosuppression or 

maintenance of normal 

immune function in mice. 

Immunosupression was 

As measured by the plaque-forming cell assay (PFC) 

the Se deficient diet led to immunosuppression 

(p<0.05) compared to the Se sufficient diet. The 

addition of 0.02% ETX to the Se sufficient diet had 

no significant effect on the immune response while 

the addition of 0.25% ETX reduced (p<0.05) the 

immune response to the level of animals receiving the 

Se deficient diet. Food consumption and body 

weights were comparable among all groups. GSH-Px 

levels, generally regarded as indicating the ‘Se status’ 

were statistically equal in the three groups receiving 

the 1.0 ppm of SE and significantly elevated (p<0.01) 

over the Se deficient group. The serum Se levels 

(~30 ug/100 ml) were equal in the 1 ppm Se groups 

with or without the 0.25% ETX. The liver DNA, 
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Table A2.2. Ethoxyquin Subchronic, Chronic and Other Toxicity Profile

GL # MRID Study Type Results and Classification

measured by the plaqueforming cell assay (PFC). RNA and protein values were similar among all the 

dietary groups.

Ethoxyquin: Mutagenicity Studies

870.5100 MRID 

05000385

bacterial reverse mutation Not mutagenic up to 1000 ug/plate in Salmonella 

typhimurium strains in ± microsomal S9 activating 

system.

870.5100 Hedenstedt11

982

MUTAT RES 

97:191

bacterial reverse mutation Mutagenic in Salmonella typhimurium strains TA98, 

100 & 1538 with S9 activating system (concentration 

not specified).

870.5100 Rannung et 

al, 1984

Industrial 

Hazards of 

Plastics and 

Synthetic 

Elastomers 

(1984), pp.

407-419

bacterial reverse mutation Weak mutagen at or above 50 mg/plate in Salmonella 

typhimurium strains with S9 activating system

870.5100 Ohta et al, 

1980

Mut. Res. 77: 

21-30

bacterial reverse mutation Ethoxyquin was negative in the rec-assay. 

Non-mutagenic to E. coli and all strains of S. 

typhimurium tested at concentrations up to 5 mg/plate

Nonguideline

Gille et al,

1991

Mutagenesis 

6(4):313-8

Clastogenic effects ETX potentiates the clastogenic effects of hyperoxia 

(80-90% O2-induced chromosomal aberrations in 

Chinese hamster ovary cells)

Nonguideline

Renner, 1984

Mutation 

Res./Genetic 

Toxicology 

135:125-129

Bone morrow 

chromosomal test:

To test a possible antimutagenic activity of 

ethoxyquin (EQ) in bone-marrow cells, 3 cytogenetic 

tests with distinct genetic end-points were applied 

(SCE, micronucleus test, or chromosome aberration 

test). Cyclophosphamide (CPA), as test mutagen, and 

EQ were administered immediately following each 

other to Chinese hamster by stomach tube. The CPA 

dose was constant, the EQ doses were increased up to 

ratio of CPA/EQ = 1 :50. The formation of SCEs 

induced by CPA was not influenced by EQ- even at 

the highest dose. In the micronucleus test, however, 

EQ drastically reduced the micronucleus rate even at 

the lowest dose applied (20 mg/kg) and abolished the 

CPA effects at a dose of 100 mg/kg. This action of 

EQ against CPA was also found in the rat and mouse 

in the micronucleus test system. Two inbred strains of 

mouse showed similar reactions. In the chromosome 

aberration test, EQ also showed a distinct 

anticlastogenic response. The anticlastogenic effect of 

EQ was quantitatively similar in the micronucleus and 

chromosome aberration tests. It was concluded that 

ETX is antimutagen per se (a factor interfering with 

spontaneous or induced mutagenesis at a cellular 

level) in contrast to desmutagen (inactivator or 

destroyer of mutagen) or a metabolism inhibitor

Nonguideline

Katz and Raj, 

1985

Chromosomal Breakage The ability of ETX to inhibit chromosome breakage 

by genotoxic agents was studied in female mice 

pretreated with ETX 24 hours to 1 week before being 

injected ip with 7, 12-dimethylbenz(a)anthracene 
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Table A2.2. Ethoxyquin Subchronic, Chronic and Other Toxicity Profile

GL # MRID Study Type Results and Classification

(DMBA), benz(a)pyrene (BaP), cyclophosphamide 

(CP) or mitomycin-C (MMC). The mice were killed 

at various times up to 96 hours after treatment, and 

bone marrow samples were taken and scored for 

polychromatic erythrocytes (PCEs) and 

micronucleated polychromatic erythrocytes 

(MNPCEs). ETX inhibited PCE and MNPCE 

induction by all agents except BaP.
Ethoxyquin Registration Review Human Health Assessment Scoping Document

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Attachment 3. Ethoxyquin Toxicological Endpoints and Doses for Risk Assessment

Table A3.1. Summary of Toxicological Doses and Endpoints for Ethoxyquin Human Health Risk 

Assessments (D310495 and D342695).

Exposure/

Scenario

Point of 

Departure

(mg/kg/day)

Uncertainty/

FQPA 

Safety 

Factors

RfD, PAD, Level of 

Concern for Risk 

Assessment

Study and Toxicological 

Effects

Dietary Risk Assessments

Acute Dietary

(Females 13–49 

years old)

NOAEL = >3 

mg/kg/day

UFA = 10

UFH = 10

FQPA SF = 1

Acute RfD = 0.03 

mg/kg/day

aPAD= acute RfD

 FQPA SF

= 0.03 mg/kg/day

Developmental study in rabbits 

where the maximum dose 

tested of 3 mg/kg/day had no 

developmental effects. 

Isenstein RS. 1970. 

Ethoxyquin in rabbit feed: 

study of relationship to 

abortion and early neonatal 

death Am J Vet Res 

31:907-909

Chronic 

Dietary

(All 

Populations)

NOAEL = 2 

mg/kg/day

UFA = 10

UFH = 10

FQPA SF = 1

Chronic RfD = 0.02 

mg/kg/day

cPAD= chronic RfD

 FQPA SF

= 0.02 mg/kg/day

90-day subchronic study in 

dogs, MRID 44148901*

LOAEL = 4 mg/kg/day based 

on elevated liver enzymes and 

microscopic findings in the 

liver (cytoplasmic vacuolation 

and minimal hepatocellular 

necrosis). The dog is highly 

sensitive compared to rats

Non-Dietary Risk Assessments

Incidental Oral Short-Term (1 - 30 Days): Not Applicable

Dermal

(All durations)

NOAEL = 2 

mg/kg/day 

(Oral)

100% 

absorption is 

assumed

UFA = 10

UFH = 10

FQPA SF = 1

Occupational

LOC for MOE = 

100

90-day subchronic study in 

dogs, MRID 44148901*

LOAEL = 4 mg/kg/day based 

on elevated liver enzymes and 

microscopic findings in the 

liver (cytoplasmic vacuolation 

and minimal hepatocellular 

necrosis). The dog is highly 

sensitive compared to rats

Inhalation

(All durations)

NOAEL = 2 

mg/kg/day 

(Oral)

UFA = 10

UFH = 10

UFDB = 10**

FQPA SF = 1

Occupational

LOC for MOE = 

1000

90-day subchronic study in 

dogs, MRID 44148901*

LOAEL = 4 mg/kg/day based 

on elevated liver enzymes and 

microscopic findings in the 

liver (cytoplasmic vacuolation 

and minimal hepatocellular 

necrosis). The dog is highly 

sensitive compared to rats

Cancer There are no guideline studies assessing this effect in animals. It is structurally similar to 

Flectol H which showed evidence of carcinogenicity (kidney tumors) in male rats. 
Ethoxyquin Registration Review Human Health Assessment Scoping Document

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Table A3.1. Summary of Toxicological Doses and Endpoints for Ethoxyquin Human Health Risk 

Assessments (D310495 and D342695).

Exposure/

Scenario

Point of 

Departure

(mg/kg/day)

Uncertainty/

FQPA 

Safety 

Factors

RfD, PAD, Level of 

Concern for Risk 

Assessment

Study and Toxicological 

Effects

Ethoxyquin is also a nephrotoxin in male rats. A theoretical upper bound Q1

*

for 

ethoxyquin was calculated to be 0.04 (mg/kg/day)-1

* The JMPR established an ADI for ethoxyquin of 0-0.005 mg/kg body weight/day on the basis of the 

minimal effect level of 2.5 mg/kg/day in the multigeneration study in dogs and a 500-fold safety factor to 

account for the lack of a NOAEL in this study and for the incompleteness of the database. However, we find 

the subchronic study in dogs better conducted and reported, and is more reliable in deriving an endpoint for 

human risk assessment. Ethoxyquin was more toxic in dogs compared to rats. (Gilman, M.R. & Voss, W.R 

(1995) Reproduction/chronic toxicology study of ethoxyquin with beagle dogs. Unpublished report HRPMI #203-1.1from HRP Inc for Monsanto, St Louis, Missouri, USA. Submitted to WHO by the Oregon, 

Washington and California Pear Association).

** Until the required inhalation study is submitted and found acceptable (or alternative information is 

provided to reduce the uncertainty), a 10X database uncertainty factor will be applied for the inhalation route 

(TXR# 0053945).

Point of Departure (POD) = A data point or an estimated point that is derived from observed dose-response 

data and used to mark the beginning of extrapolation to determine risk associated with lower 

environmentally relevant human exposures. NOAEL = no observed adverse effect level. LOAEL = lowest 

observed adverse effect level. UF = uncertainty factor. UFA = extrapolation from animal to human 

(interspecies). UFH = potential variation in sensitivity among members of the human population 

(intraspecies). UFL = use of a LOAEL to extrapolate a NOAEL. UFS = use of a short-term study for longterm risk assessment. UFDB = to account for the absence of key data (i.e., lack of a critical study). FQPA SF 

= FQPA Safety Factor. PAD = population adjusted dose (a = acute, c = chronic). RfD = reference dose. 

MOE = margin of exposure. LOC = level of concern. N/A = not applicable.
Ethoxyquin Registration Review Human Health Assessment Scoping Document

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Attachment 4. Ethoxyquin International Residue Limits

Table A4.1. Ethoxyquin (055501; 6/23/14)

Summary of US and International Tolerances and Maximum Residue Limits 

Residue Definition:

US Canada Mexico1 Codex2

40 CFR 180.178:

Plant: ethoxyquin (1,2-dihydro-6-ethoxy2,2,4-trimethylquinoline)

1,2-dihydro-6-ethoxy2,2,4-trimethylquinoline polymerEthoxyquin

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

US Canada Mexico1 Codex2

Pear 3 3 3 Po

Completed: M. Negussie; 06/25/14

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

2 * = absent at the limit of quantitation; Po = post-harvest treatment, such as treatment of stored grains. PoP 

= processed post-harvest treated commodity, such as processing of treated stored wheat. (fat) = to be 

measured on the fat portion of the sample. MRLs indicated as proposed have not been finalized by the 

CCPR and the CAC.