UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MEMORANDUM 

Date: 02-FEB-2016 

OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

SUBJECT: d-Limonene. Revised Human Health Risk Assessment in Support of 

Registration Review. 

PC Codes: 07970 I, 87970 I DP Barcode: 0429982 

Decision No.: 510766 Registration Nos.: NA 

Petition No.: NA Regulatory Action: Registration Review Risk Assessment 

Risk Assessment Type: Single Chemical Case No.: 3083 

TXR No.: NA CAS No.: 5989-27-5 

MRID No.: NA 40 CFR: § 180.539, § 180.910, § 180.930 

FROM: George F. Kramer, Ph.D., Senior Chemis~ ~ ~ -

Monique M. Perron, Sc.D., Toxicologist ~ ~ Risk Assessment Branch 1 (RABI) 

Health Effects Division (HED, 7509P) 

THROUGH: Charles W. Smith III, Branch Chic - ---

RAB 1/HED (7509P) 

TO: Caitlin Newcamp, Chemical Review Manager 

Risk Management and Implementation Branch I 

Pesticide Re-Evaluation Division (PRD/7508P) 

NOTE: This document supersedes "d-Limonene. Human Health Risk Assessment in Support of 

Registration Review," G. Kramer and M. Perron, D411403, dated 04-DEC-2014. This 

assessment has been revised to add a tolerance exemption for agricultural uses of d-limonene 

when used as an active ingredient. 

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d-Limonene Registration Review Human Health Risk Assessment 0429982 

Table of Contents 

1.0 Executive Swnmary .................................................................................................................................... 3 

2.0 HED Recommendations ............................................................................................................................ 3 

2.1 Data Deficiencies ............................................................................................................. 3 

2.2 Tolerance Considerations ................................................................................................. 3 

2.3 Label Recommendations .................................................................................................. 4 

3.0 lntroduction .................................................................................................................................................. .4 

3.1 Chemical Identity ............................................................................................................. 4 

3.2 Physical/Chemical Characteristics ................................................................................... 5 

3.3 Pesticide Use Panern ........................................................................................................ 5 

4.0 Hazard Characterization and Dose-Response Assessment... ........................................................... 6 

4.1 Toxicology Analysis ........................................................................................................ 6 

4.2 Safety Factor for infants and Children (FQP A SF) .......................................................... 6 

4.2.1 Completeness of the Toxicology Database ............................................................... 7 

4.2.2 Evidence ofNeurotoxicity ........................................................................................ 7 

4.2.3 Evidence of Sensitivity/Susceptibility in the Developing or Young Animal ........... 7 

4.2.4 Residual Uncertainty in the Exposure Database ....................................................... 7 

5.0 Dietary Exposure and Risk Assessment ............................................................................................... 8 

6.0 Residential (No_n-Qccupational) Exposure/Risk Characterization ................................................ 8 

6.1 Spray Drift.: ......... : ............................................................................................................ 8 

6.2 Residential Bystander Post-Application Inhalation Exposure ......................................... 8 

7.0 Aggregate Exposure/Risk Characterization ......................................................................................... 8 

8.0 Cumulative Exposure/Risk Characterization ...................................................................................... 8 

9.0 Public Health and Pesticide Epidemiology Data ................................................................................ 9 

10.0 Occupational Exposure/Risk Characterization ................................................................................... 9 

11.0 References ..................................................................................................................................................... 9 

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d-Limonene Registration Review Human Health Risk Assessment 0429982 

1.0 Executive Summary 

HED has prepared a qualitative human-health risk assessment to support registration review for 

the use of d-limonene [(4R)- 1-methyl-4-(1-methylethenyl)cyclohexene]. When writing this risk 

assessment, HED primarily considered the following two documents: (i) d-Limonene. Human 

Health Assessment Scoping Document in Support of Registration Review (G. Kramer et al., 13-

AUG-20 10; 0 374492); and (ii) HED's Hazard and Science Policy Council (HASPOC) 

recommendations (J. Yan Alstine; 05-NOY-2013 ; TXR# 0056807). 

d-Limonene has a lemon-like flavor and smell, and occurs naturally in citrus and certain fruits, 

vegetables, meats, and spices. d-Limonene is used as both an active and inert ingredient in 

pesticide products, and as an ingredient in food products, soaps, and perfumes. As an active 

ingredient, it is used as an insecticide, herbicide, insect repellent, and animal (dog and cat) 

repellent. As a pesticide inert ingredient, it is used as a solvent or fragrance. FDA considers dlimonene to be Generally Recognized as Safe (GRAS) as a food additive when used as a 

synthetic flavoring substance and adjuvant (2 1 CFR § 182.60). d-Limonene is also registered for 

terrestrial food or feed crop uses as an active ingredient (herbicide), and can be used in insectrepellent tablecloths and in insect-repellent strips used in food or feed-handling establishments. 

No data deficiencies were identified for the toxicology, residue chemistry, or occupational/ 

residential exposure databases. No toxicological points of departure have been established fordlimonene. As a result, quantitative risk assessments are not necessary to conclude with 

reasonable certainty that exposures from the currently registered uses of d-limonene do not pose 

a significant human health risk. 

2.0 HED Recommendations 

HED has no objection for continued registration of the current d-limonene pesticide products. 

2.1 Data Deficiencies 

No data deficiencies were identified for the toxicology, residue chemistry, or occupational/ 

residential exposure databases. 

2.2 Tolerance Considerations 

As no toxicological points of departure have been established for d-limonene, tolerances are not 

required for residues in/on food/feed commodities. In addition, there are currently no established 

Codex or Mexican maximum residue limits (MRLs) for d-limonene. However, to support both 

the herbicidal and insecticidal uses of d-limonene, HED recommends that the following 

modifications to 40 CFR 180 Subpart C and Subpart D: 

• The following tolerance exemption be established under 40 CFR 180 Subpart DExemptions From Tolerances: 

(a) An exemption from the requirement of a tolerance is established for residues of dlimonene, (4R)-l-methyl-4-(1-methylethenyl)cyclohexene, in or on all food 

commodities when applied as an herbicide used in accordance with its label and 

labeling registered by the U.S. Environmental Protection Agency. 

(b) An exemption from the requirement of a tolerance is established for residues of dlimonene, ( 4R)-1-methyl-4-( 1-methyletheny l)cyclohexene, in or on all food 

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d-Limonene Registration Review Human Health Risk Assessment 0 429982 

commodities when applied in insect-repellent tablecloths and in insect repellent strips 

used in food- or feed-handling establishments. 

• The removal of subpart 180.539 under 40 CFR 180 Subpart C- Specific Tolerances 

2.3 Label Recommendations 

HED has no label recommendations at this time. 

3.0 Introduction 

d-Limonene has a lemon-like flavor and smell, and occurs naturally in citrus and certain fruits, 

vegetables, meats, and spices. d-Limonene is used as both an active and inert ingredient in 

pesticide products, and as an ingredient in food products, soaps, and perfumes. As an active 

ingredient, it is used as an insecticide, herbicide, insect repellent, and animal (dog and cat) 

repellent. As a pesticide inert ingredient, it is used as a solvent or fragrance. FDA considers d1 imonene to be GRAS as a food additive when used as a synthetic flavoring substance and 

adj uvant (21 CFR § 182.60). The established tolerances and exemptions, with the respective 

CFR citation, and the use patterns as an active and inert ingredient are listed in Table 3.0. 

Table 3.0. Established Tolerances and Exemptions for d-Limonene. 

Tolerance PC List Exemption CASNo. 40 CFR § Code Use Pattern Classification Expression 

Active Ine redient 

Used in insect-repellent 

180.539 07970 1 tablecloths and in insect- NA 

d-Limonene 5989-27-5 repellent strips used in food- or 

feed-handling establishments 

Inert In2redient 

180.910 and 180.930 (formerly 879701 ··Solvent. fragrance·· 4Bc 180. IOOl(c) and (e))o.b .. • Residues listed m 40 CFR § 180.910 arc exempt from a tolerance when u;ed as men ingredients m pcs11c1dc fomrnlatJons applied to growing 

crops or to raw agricultural commodities after harvest and those listed in 40 CFR § 180.930 arc exempt from a tolerance when used as inen 

ingredients in pesticide fonnulations applied to animals. 

b In both sections, the inen ingredient is listed as "d-Limonenc (CAS Reg No. 5989-27-5).'" 

' lnen ingredients are categorized into four lists as described in the 1987 and 1989 Policy Statements. List 4B incn ingredients are those inens 

for which EPA has sufficient information to reasonably conclude drnt the current use pattern in pesticide products will not adversely affect public 

health or the environment. 

3.1 Chemical Identity 

Table 3. 1. Test Compound Nomenclature. 

Compound Chemical Structure 

'9'' 

CH1 

Common name d-Limonene 

IUPAC name (R)-4-isopropcnyl-1-mcthylcyclohexene 

CAS name (4R)- l-methyl-4-( 1-mcthylethenyl)cyclohexene 

CAS# 5989-27-5 

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Table 3.1. Test Compound Nomenclature. 

PC Codes 079701,879701 

3.2 Physical/Chemical Characteristics 

Ta ble 3.2. Physicochemical Properties of d-Limoncnc. 

Parameter Value Reference 

Melting point -75 °°C 

Boiling point 176 °C NIOSH, 2001; WHO, 

Solubility in water 13.8 mg!L at 25°C 1998 

pH Not aoolicable 

Density/Specific Gravity 0.84 .e./mL 

Vapor Density Relative vapor density= 4.7 (air= I) 

Vapor Pressure 0.4 kPa at 14.4°C; 2 mm Hg at 20°C 

Estimated Octanol/Water Coeffi cient log Kow: 4.2 

3.3 Pesticide Use Pattern 

d-Limonene can be used as both an active and an inert ingredient in products registered for use in 

residential environments. It is registered for use on many residential sites, including pets (as a 

shampoo or dip), outdoor premises (spot treatment), indoor treatments (crack and crevice and 

cleaning uses), impregnated materials (repellant clothing, bracelets, strips), roads and sidewalks 

(spot treatment), and professional applications to wooden structures (applied as a wood 

injection). It is also registered for agricultural use as an herbicide. Additional exposure may 

occur naturally through different foods, soaps, and perfumes. These uses are FDA-approved and 

generally regarded as safe. 

3.4 Consideration of Environmental Justice 

Potential areas of environmental justice concerns, to the extent possible, will be considered in 

future human health risk assessments for d-limonene, in accordance with U.S. Executive Order 

12898, "Federal Actions to Address Environmental Justice in Minority Populations and LowJ ncome Populations," http://www.arch iv es. gov/federal-register/executive-orders/pdf/ 12898. pdf. 

As a part of every pesticide risk assessment, OPP considers a large variety of consumer 

subgroups according to well-established procedures. In line with OPP policy, HED estimates 

risks to population subgroups from pesticide exposures that are based on patterns of that 

subgroup's food and water consumption, and activities in and around the home that involve 

pesticide use in a residential setting. Extensive data on food consumption patterns are compiled 

by the United States Department of Agriculture (USDA) National Health and Nutrition 

Examination Survey, What We Eat in America (NHANES/WWEIA; 2003-2008) and are used in 

pesticide risk assessments for all registered food uses of a pesticide. These data are analyzed and 

categorized by subgroups based on age, season of the year, ethnic group, and region of the 

country. Additionally, OPP is able to assess dietary exposure to smaller, specialized subgroups 

and exposure assessments are performed when conditions or circumstances warrant. Whenever 

appropriate, non-dietary exposures based on home use of pesticide products and associated risks 

for adult applicators and for toddlers, youths, and adults entering or playing on treated areas 

post-application are evaluated. Further considerations are currently in development as OPP has 

committed resources and expertise to the development of specialized software and models that 

consider exposure to bystanders and farm workers as well as lifestyle and traditional dietary 

patterns among specific subgroups. 

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d-Limonene Registration Review Human Health Risk Assessment 0 429982 

4.0 Hazard Characterization and Dose-Response Assessment 

4.1 Toxicology Analysis 

d-Limonene has been evaluated extensively in a number of short- and long-term toxicity assays 

since the 1950s 1

• Overall, high doses of d-limonene (2:500 mg/kg/day) are needed to induce any 

form ofrelevant toxicity in laboratory animals. Due to its low toxicity, a reduced set of generic 

data requirements were considered appropriate for d-limonene as discussed in the 1994 

Reregistration Eligibility Document (RED) (EPA-738-R-94-034). In recent years, the 40 CFR 

Toxicology Data Requirements have been revised and require pesticides to have acute 

neurotoxicity, subchronic neurotoxicity, and immunotoxicity studies. The Hazard and Science 

Policy Council (HASPOC) concluded using a weight-of-evidence approach that these studies are 

not required at this time for d-limonene (J. Van Alstine; 5-NOV-2013; TXR# 0056807). 

Therefore, the available toxicological database is considered complete to support existing 

registrations and registration review. 

d-Limonene is a skin and eye irritant, as well as a dermal sensitizer. It has been found to have 

low acute toxicity via the oral and dermal routes. ln numerous studies, d-limonene resulted in 

liver effects that are considered adaptive. Male rats also exhibited kidney effects (hyaline 

droplet nephropathy and renal tumors) that are indicative of a2μ-g lobulin nephropathy, which is 

a sex- and species-dependent syndrome. Therefore, these effects were not considered predictive 

of kidney toxicity in humans since a2μ-globulin is not synthesized by humans. 

There is no evidence of developmental toxicity with d-limonene except at very high doses (>500 

mg/kg/day) and in the presence of maternal toxicity. d-Limonene was negative in several 

mutagenicity and clastogenicity assays. A published 9-week imrnunotoxicity study in mice 

yielded no clear evidence of immunotoxicity from d-limonene. 

There is no evidence of neurotoxicity from exposure to d-limonene. Although decreased motor 

activity was observed in a 13-week oral toxicity study in mice at 1000 mg/kg/day, the effect is 

attributed to general systemic toxicity from exposure to such a high dose. 

Previously, endpoints were selected using a 30-day oral rat toxicity study with liver effects 

(marginal increases in liver weights and liver enzymes) and a 103-week gavage rat toxicity study 

with no effects observed. According to current policies, the liver effects would be considered 

adaptive and a study with no effects cannot be used for endpoint selection. Given the low 

toxicity throughout the database, no toxicity endpoints were selected for d-limonene. Therefore, 

quantitative exposure assessment is not necessary. 

4.2 Safety Factor for Infants and Children (FQPA SF) 

The RAB 1 risk assessment team for d-limonene determined that the Food Quality Protection Act 

(FQP A) SF should be reduced to 1 X for all exposure scenarios. There is a complete toxicology 

database, no evidence of neurotoxicity, and no evidence of offspring susceptibility. 

Additionally, since no endpoints were selected for d-limonene given its low toxicity, a 

quantitative exposure assessment is not necessary. 

1 Summarized in the 1994 EPA Reregistration Eligibility Decision (EPA-738-R-94-034), 2004 EPA Tolerance 

Reassessment Eligibility Decision (EPA-HQ-OPP-2004-0335-0003), published reviews by the World Health 

Organization (1993, 1998), and a technical report by the National Toxicology Program (1990). 

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4.2.1 Completeness of the Toxicology Database 

Limonene was previously classified as a lower-risk pesticide for which a reduced set of generic 

data requirements are appropriate for registration. Accordingly, the toxicology database is 

considered complete and includes developmental studies in the rat, mouse, and rabbit. 

4.2.2 Evidence of Neurotoxicity 

There is no evidence of neurotoxicity from exposure to d-limonene across the available 

toxicological studies. Although decreased motor activity was observed in a 13-week oral 

toxicity study in mice at 1000 mg/kg/day, the effect is attributed to general systemic toxicity 

from exposure to such a high dose. 

4.2.3 Evidence of Sensitivity/Susceptibility in the Developing or Young Animal 

There is no evidence of quantitative or qualitative susceptibility to offspring from d-limonene 

exposure. Developmental toxicity with d-limonene was not observed except at very high doses 

(>500 mg/kg/day) and in the presence of maternal toxicity. 

4.2.4 Residual Uncertainty in the Exposure Database 

Given its low toxicity, no endpoints were selected for d-limonene. Therefore, a quantitative 

exposure assessment is not necessary and no residual uncertainty exists in the exposure database. 

4.3 Endocrine Disruptor Screening Program 

As required by the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and the Federal 

Food, Drug, and Cosmetic Act (FFDCA), EPA reviews numerous studies to assess potential 

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

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

developmental, reproductive, and general or systemic toxicity. These studies include endpoints 

that may be susceptible to endocrine influence, including effects on endocrine target organ 

histopathology, organ weights, estrus cyclicity, sexual maturation, fertility, pregnancy rates, 

reproductive loss, and sex ratios in offspring. For ecological haz.ard assessments, EPA evaluates 

acute tests and chronic studies that assess growth, developmental and reproductive effects in 

different taxonomic groups. As part of its reregistration decision for d-limonene, EPA reviewed 

these data and selected the most sensitive endpoints for relevant risk assessment scenarios from 

the existing haz.ard database. However, as required by FFDCA section 408(p), d-limonene is 

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

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

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

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

may designate." The EDSP employs a two-tiered approach to making the statutorily required 

determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a 

chemical substance to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal 

systems. Chemicals that go through Tier l screening and are found to have the potential to 

interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP where EPA 

will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 

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testing is designed to identify any adverse endocrine-related effects caused by the substance, and 

establish a dose-response relationship between the dose and the E, A, or T effect. 

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

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

chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. A second list 

of chemicals identified for EDSP screening was published on June 14, 20132 and includes some 

pesticides scheduled for registration review and chemicals found in water. Neither of these lists 

should be construed as a list of known or likely endocrine disruptors. 

For further information on the status of the EDSP, the policies and procedures, the lists of 

chemicals, future lists, the test guidelines and the Tier 1 screening battery, please visit our 

website.3 

5.0 Dietary Exposure and Risk Assessment 

Quantitative dietary exposure and risk assessments are not required for d-limonene since no 

toxicological points of departure have been established. ln addition, FDA considers d-lirnonene 

to be GRAS as a food additive when used as a synthetic flavoring substance and adjuvant (21 

CFR § 182.60). 

6.0 Residential (Non-Occupational) Exposure/Risk Characterization 

Quantitative residential exposure and risk assessments are not required for d-limonene since no 

toxicological points of departure have been established. 

6.1 Spray Drift 

Quantitative spray drift exposure and risk assessments are not required for d-limonene since no 

toxicological points of departure have been established. 

6.2 Residential Bystander Post-Application Inhalation Exposure 

Quantitative residential bystander post-application exposure and risk assessments are not 

required for d-limonene since no toxicological points of departure have been established. 

7.0 Aggregate Exposure/Risk Characterization 

As quantitative dietary and residential exposure assessments are not required, a quantitative 

aggregate assessment is not required either to conclude with reasonable certainty that aggregate 

exposures to the currently registered uses of d-limonene do not pose a significant human health 

risk. 

8.0 Cumulative Exposure/Risk Characterization 

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

2 See http://www.epa.gov/endocrine-disruption/overview-second-I ist-chemicals-tier- 1-screen ing-under-endocrinedisruptor for the final second list of chemicals. 

3 http://www.epa.gov/endo/ 

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d-Limonene Registration Review Human Health Risk Assessment 0429982 

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

to d-limonene and any other substances and d-limonene does not appear to produce a toxic 

metabolite produced by other substances. For the purposes of this action, therefore, EPA has 

assumed that d-limonene does not have a common mechanism of toxicity with other substances. 

For information regarding EPA's efforts to determine which chemicals have a common 

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

statements rel eased 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/pesticide-science-and-assessing-pesticiderisks/cumulative-assessment-risk-pesticides. 

9.0 Public Health and Pesticide Epidemiology Data 

A summary report listing incidents for d-limonene reported to the OPP Incident Data System 

(IDS) has been previously conducted (Winfield, S., et al.; D374493, 20-MA Y-20 10). The report 

represents incidents occurring in the U.S. from 2002 to 2009. Based on the low frequency and 

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

further investigation. Although there are incidents reported that resulted in moderate outcomes, 

the symptoms and settings were varied and do not indicate a trend or pattern that would trigger 

follow-up analyses. 

10.0 Occupational Exposure/Risk Characterization 

Quantitative occupational handler and post-application exposure and risk assessments are not 

required for d-limonene since no toxicological points of departure have been established. 

11.0 References 

Memo, S. Winfield el al., D374493; 20-MA Y-20 I 0 

Memo, J. Van Alstine, TXR# 0056807; 05-NOY-2013 

Attachment: Summary of U.S. Tolerances and Jntemational MRLs. 

cc: G. Kramer(RABI) 

RDI: RABI ( 11 /5/14) 

G.F. Kramer:Sl078 I :PY-S:(703)305-5079:7509P:RAB I 

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d-Limonene Registration Review Human Health Risk Assessment 0429982 

Summary of U.S. Tolerances and International MRLs. 

U.S. Canada Mexico• Codex 

Residue Definition: 

§ 180.539 d-Limonene; tolerances for None - None 

residues. 

(a) General. (I) The insecticide d-limonene 

may be safely used in insect-repellent 

tablecloths and in insect-repellent strips 

used in food- or feed-handling 

establishments. 

(2) To assure safe use of the insect 

repellent, its label and labeling shall 

conform to that registered by the U.S. 

Environmental Protection Agency, and it 

shall be used in accordance with such label 

and labeling. 

Commodity Tolerance (oom)/Maximum Residue Limit (mg/ke) 

Commodity U.S. Canada Mexico Codex 

None - None 

Completed by: M. Negussie; 10/21 / 14 

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

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