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d-Limonene Final Work Plan 

Introduction:

This is the Environmental Protection Agency’s (EPA’s) Final Work Plan (FWP) for the 

registration review of d-Limonene (“limonene” unless otherwise specified). The FWP includes 

the expected registration review timeline. The FWP also addresses public comments received 

concerning the Preliminary Work Plan in the Summary Document, which was posted in the 

limonene registration review docket (EPA-HQ-OPP-2010-0673), and any other comments 

concerning the initial docket postings. The Summary Document provided information on what 

EPA knows about the pesticide and what additional risk analyses and data or information the 

Agency believes are needed to make a registration review decision. 

The Agency is implementing the new registration review program and will review each 

registered pesticide every 15 years to determine whether it continues to meet the Federal 

Insecticide, Fungicide, and Rodenticide Act (FIFRA) standard for registration. Changes in 

science, public policy, and pesticide use practices will occur over time. The registration review 

program is intended to make sure that, as the ability to assess risk evolves and as policies and 

practices change, all registered pesticides continue to meet the statutory standard. The public 

phase of registration review begins when the initial docket is opened for each case. Information 

on this program is provided at: http://www.epa.gov/oppsrrd1/registration_review/. 

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

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

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

products containing limonene as an active ingredient are registered for use as insecticides, 

herbicides, insect repellents, and animal (dog and cat) repellents. As a pesticide inert ingredient, 

it is used as a solvent or fragrance in antimicrobial products. The U.S. Food and Drug 

Administration (FDA) considers d-limonene to be Generally Recognized as Safe (GRAS) as a 

food additive when used as a synthetic flavoring substance and adjuvant (21 CFR §182.60). 

Limonene is registered for use in/on terrestrial food, feed crops, non-food crops, for residential 

uses, and as an inert ingredient. Non-pesticidal uses of limonene include use in solvents 

(substitute for chlorinated hydrocarbons, chlorofluorocarbons, and other solvents); use as a metal 

degreaser; use as a cleaning agent in the printing industry and household cleaning products; and, 

as a solvent for paint. Limonene was first registered as an insecticide in 1958 and as an 

antimicrobial in 1971. Currently, the only antimicrobial uses of limonene are as an inert 

ingredient and are not subject for registration review. The reregistration eligibility decision 

(RED) was issued in 1994 and the tolerance reassessment eligibility decision (TRED) was issued 

in 2005. 

Comments Received on Preliminary Work Plan

No comments were received on the limonene Preliminary Work Plan (PWP) during the public 

comment period. The 60-day public comment period on the limonene PWP began on September 

22, 2010 and closed on November 22, 2010. 
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Risk Assessment and Data Needs:

• The most recent ecological risk assessment for limonene was completed in 1994 to 

support the RED. 

• The Agency has not conducted a risk assessment that supports a complete endangered 

species determination for limonene. The ecological risk assessment planned during 

registration review will allow the Agency to determine whether limonene’s use has “no 

effect” or “may affect” federally listed threatened or endangered species (listed species) 

or their designated critical habitats. When an assessment concludes that a pesticide’s use 

“may affect” a listed species or its designated critical habitat, the Agency will consult 

with the U.S. Fish and Wildlife Service and/or National Marine Fisheries Service (the 

Services), as appropriate. 

• Based upon the use pattern and limonene’s current ecotoxicity and environmental fate 

database, the Agency will require the following data in order to conduct a complete 

ecological risk assessment, including an endangered species assessment, for all uses: 

o GLN 850.4100 - Seedling emergence, Tier II (using TEP) 

o GLN 850.4150 - Vegetative vigor, Tier II (using TEP) 

o GLN 850.4400 - Aquatic plant toxicity test using Lemna spp., Tier II (using TEP) 

o GLN 850.5400 - Algal toxicity, Tier II (using TEP) 

• Please refer to the document, Registration Review – Problem Formulation for dLimonene dated June 30, 2010, located in the docket for a detailed discussion of the 

anticipated risk assessment and data needs. 

Human Health Risk:

• The most recent human health risk assessment for limonene was completed in 2004 to 

support the TRED. 

• The RED Data Call-in (DCI) required a developmental toxicity study and a 2-week 

dermal toxicity study. These studies have been received by the Agency and will be 

reviewed during registration review. The toxicity endpoints established in the 2004 risk 

assessment may be updated following Agency review of these studies. 

• The human health toxicity database (including the developmental and dermal study) for 

limonene is adequate to support its current use patterns and the Agency does not 

anticipate requiring new data to support a human health risk assessment for registration 

review. 

• The Agency will conduct a new dietary risk assessment that incorporates potential 

drinking water residues and revised endpoints to support registration review. 

• Limonene is listed in 40 CFR §180.539 without numeric tolerances and is identified as 

being safe for use, as an insecticide, in tablecloths and repellant strips and in food or 
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feed-handling establishments. The Agency does not anticipate the need to re-evaluate 

this tolerance expression during registration review. 

• The residential exposure assessment that was conducted to support the 2004 TRED only 

examined dermal exposure to pesticide products containing limonene as an active 

ingredient. The Agency will update the 2004 residential assessment using the revised 

Agency Standard Operating Procedures (SOPs) for residential exposure to incorporate 

potential changes in dermal and inhalation endpoints, and to include exposure from 

outdoor uses and pet product uses. 

• To support registration review, the Agency will conduct a new and updated aggregate 

risk assessment incorporating new toxicity endpoints as appropriate, the dietary risk 

assessment incorporating drinking water residues and the updated residential assessment. 

• The most recent occupational exposure and risk assessments for limonene were 

conducted in 2008 to support proposed new uses (use on nut, vine, and berry crops, and 

non-crop areas). The Agency will update the occupational exposure and risk assessment 

to include the inhalation route of exposure and potential changes in the hazard endpoints. 

This 2008 occupational exposure and risk assessment may be found in the docket under 

the document titled d-Limonene Occupational Exposure/Risk Assessment for Proposed 

New Uses of d-Limonene on Tree, Nut, Vine, Berry Crops and Non-Crop Areas. 

• Please refer to the document, d-Limonene: Human Health Assessment Scoping 

Document in Support of Registration Review dated August 13, 2010, located in the 

docket for a detailed discussion of the anticipated risk assessment and data needs for 

human health. 

Other Data Needs: 

• GLN 830.7050 UV/Visible Light Absorption – this study is a new data requirement under 

40 CFR part 158 (Product Chemistry Data Requirements) for registration of a pesticide 

(food and non-food uses). The Agency will require this study to obtain basic information 

about the compound’s identity/composition and the wavelengths at which the compound 

may be susceptible to photochemical degradation. 
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Timeline:

EPA has created the following estimated timeline for the completion of the limonene registration 

review. This timeline has been shortened since the PWP to account for a shorter period between 

issuance of the DCI and data submission, since the Agency will not be requiring any studies that 

take more than one year to conduct. 

Registration Review for Limonene – Projected Registration Review Timeline

Activities Estimated Date 

Opening the Docket 

Open Docket and Public Comment Period 2010 – September 

Close Public Comment 2010 – November 

Case Development 

Final Work Plan 2011 – January 

Issue DCI 2011 – Oct – Dec 

Data Submission 2012 – Oct – Dec 

Open Public Comment Period for Preliminary Risk Assessments 2014 – April – June 

Close Public Comment Period 2014 – July – Sept 

Registration Review Decision 

Open Public Comment Period for Proposed Registration Review 

Decision 

 2014 – Oct – Dec. 

Close Public Comment Period 2015 – Jan. – March 

Final Registration Review Decision and Begin Post-Decision Follow-up 2015 

Total (years) 5 

Data Requirements Table

The Agency will issue a DCI for the following studies listed in both the PWP and FWP. 

Data Requirement Guideline Number Listed In PWP Listed In FWP 

Seedling emergence, 

Tier II (using TEP)

850.4100 

The Agency’s anticipated data needs did not 

change and the Agency will issue a DCI for these 

studies. 

Vegetative vigor, Tier 

II (using TEP)

850.4150 

Aquatic plant toxicity 

test using Lemna spp., 

Tier II (using TEP)

850.4400 

Algal toxicity, Tier II 

(using TEP)

850.5400 

UV/Visible Light 

Absorption 

830.7050