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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 87

[EPA-HQ-OAR-2007-0294; FRL_XXXX-X]

RIN 2060-AP79

Advance Notice of Proposed Rulemaking on Lead Emissions from Piston-Engine Aircraft 

Using Leaded Aviation Gasoline

AGENCY: Environmental Protection Agency (EPA).

ACTION: Advance notice of proposed rulemaking.

SUMMARY: EPA is issuing this Advance Notice of Proposed Rulemaking (ANPR) to describe 

information currently available and information being collected that will be used by the 

Administrator to issue a subsequent proposal regarding whether, in the Administrator’s 

judgment, aircraft lead emissions from aircraft using leaded aviation gasoline (avgas) cause or 

contribute to air pollution which may reasonably be anticipated to endanger public health or 

welfare. In this ANPR we describe and request comment on the data available for evaluating 

lead emissions, ambient concentrations and potential exposure to lead from the continued use of 

leaded avgas in piston-engine powered aircraft. We also describe and request comment on 

additional information being collected that will inform any future action.

This ANPR is being issued to further respond to a petition submitted by Friends of the 

Earth (FOE) in 2006. Emissions of lead from piston-engine aircraft using leaded avgas comprise 

approximately half of the national inventory of lead emitted to air. There are almost 20,000 

airport facilities in the U.S. at which leaded avgas may be used. EPA has long-standing concerns 
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regarding exposure to lead, particularly during childhood. The most recent review and revision 

of the National Ambient Air Quality Standard (NAAQS) for lead, promulgated in 2008, found 

that serious health effects occur at much lower levels of lead in blood than previously identified 

and did not identify a safe level of lead exposure. 

DATES: Comments must be received on or before [Insert date 60 days after publication in the 

Federal Register].

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-OAR-2007-

0294, by one of the following methods:

 www.regulations.gov: Follow the on-line instructions for submitting comments.

 Email: a-and-r-docket@epa.gov

 Fax: (202) 566-9744

 Mail: Environmental Protection Agency, Mail Code: 6102T, 1200 Pennsylvania Ave., 

NW, Washington, DC, 20460. Please include two copies.

 Hand Delivery: EPA Docket Center (Air Docket), U.S. Environmental Protection 

Agency, EPA West Building, 1301 Constitution Avenue, NW, Room: 3334 Mail Code: 

2822T, Washington, DC. Such deliveries are only accepted during the Docket’s normal 

hours of operation, and special arrangements should be made for deliveries of boxed 

information.

Instructions: Direct your comments to Docket ID No. EPA-HQ-OAR-2007-0294. EPA's policy

is that all comments received will be included in the public docket without change and may be 

made available online at www.regulations.gov, including any personal information provided, 

unless the comment includes information claimed to be Confidential Business Information (CBI) 
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or other information whose disclosure is restricted by statute. Do not submit information that you 

consider to be CBI or otherwise protected through www.regulations.gov or e-mail. The 

www.regulations.gov website is an “anonymous access” system, which means EPA will not 

know your identity or contact information unless you provide it in the body of your comment. If 

you send an e-mail comment directly to EPA without going through www.regulations.gov your 

e-mail address will be automatically captured and included as part of the comment that is placed 

in the public docket and made available on the Internet. If you submit an electronic comment, 

EPA recommends that you include your name and other contact information in the body of your 

comment and with any disk or CD-ROM you submit. If EPA cannot read your comment due to 

technical difficulties and cannot contact you for clarification, EPA may not be able to consider 

your comment. Electronic files should avoid the use of special characters, any form of 

encryption, and be free of any defects or viruses. For additional information about EPA’s public 

docket visit the EPA Docket Center homepage at http://www.epa.gov/epahome/dockets.htm.

Docket: All documents in the docket are listed in the www.regulations.gov index. Although 

listed in the index, some information is not publicly available, e.g., CBI or other information 

whose disclosure is restricted by statute. Certain other material, such as copyrighted material, 

will be publicly available only in hard copy. Publicly available docket materials are available 

either electronically in www.regulations.gov or in hard copy at the EPA Docket Center, 

EPA/DC, EPA West, Room 3334, 1301 Constitution Avenue, NW, Washington, DC. The Public 

Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal 

holidays. The telephone number for the Public Reading Room is (202) 566-1744, and the 

telephone number for the Air Docket is (202) 566-1742.
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FOR FURTHER INFORMATION CONTACT: Marion Hoyer, Assessment and Standards 

Division, Office of Transportation and Air Quality, 2000 Traverwood Drive, Ann Arbor, MI, 

48105; telephone number: (734) 214-4513; fax number: (734) 214-4939; email address: 

hoyer.marion@epa.gov.

SUPPLEMENTARY INFORMATION: 

I. General Information

A. What Should I Consider as I Prepare My Comments for EPA?

1. Submitting CBI. Do not submit this information to EPA through www.regulations.gov 

or e-mail. Clearly mark the part or all of the information that you claim to be CBI. For CBI 

information in a disk or CD ROM that you mail to EPA, mark the outside of the disk or CD 

ROM as CBI and then identify electronically within the disk or CD ROM the specific 

information that is claimed as CBI. In addition to one complete version of the comment that 

includes information claimed as CBI, a copy of the comment that does not contain the 

information claimed as CBI must be submitted for inclusion in the public docket. Information so 

marked will not be disclosed except in accordance with procedures set forth in 40 CFR Part 2.

2. Tips for Preparing Your Comments. When submitting comments, remember to:

• Identify the rulemaking by docket number and other identifying information 

(subject heading, Federal Register date and page number).
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• Follow directions - The agency may ask you to respond to specific questions or 

organize comments by referencing a Code of Federal Regulations (CFR) part or 

section number.

• Explain why you agree or disagree, suggest alternatives, and substitute language 

for your requested changes.

• Describe any assumptions and provide any technical information and/or data that 

you used.

• If you estimate potential costs or burdens, explain how you arrived at your 

estimate in sufficient detail to allow for it to be reproduced.

• Provide specific examples to illustrate your concerns, and suggest alternatives.

• Explain your views as clearly as possible, avoiding the use of profanity or 

personal threats.

• Make sure to submit your comments by the comment period deadline identified.
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Table of Contents

I. Overview 

A. Background on Leaded Aviation Gasoline

B. Background Information Regarding General Aviation and Use of Piston-Engine 

Aircraft

C. Background on the Petition and EPA’s Response

D. Statutory Authority

1. Background

2. Regulatory Authority for Emission Standards

3. Regulatory Authority for Fuel Standards

E. Federal Actions to Reduce Lead Exposure

II. Health and Welfare Effects of Lead

A. Multimedia and Multi-Pathway Exposure Considerations

B. Health Effects Information

1. Blood Lead 

2. Health Effects

3. At-Risk Populations and Life Stages

C. Welfare Effects

1. Terrestrial Ecosystems

2. Aquatic Ecosystems

III. Lead Emissions from Piston-Engine Aircraft 

A. Inventory of Lead from Piston-Engine Powered Aircraft
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1. National Emissions of Lead from Piston-Engine Aircraft

2. Airport-Specific Emissions of Lead from Piston-Engine Aircraft

B. Projections for Future Growth

IV. Lead Concentrations in the Vicinity of Airports

A. Chemical and Physical Properties of Lead Emitted by Piston-Engine Aircraft

B. Summary of Airport Lead Monitoring and Modeling Studies

1. Summary of Airport Lead Monitoring Studies

2. Summary of Airport Lead Modeling Studies

V. Exposure to Lead from Piston-Engine Aircraft and Potential for Impacts

A. Exposure to Lead Emissions from Piston-Engine Aircraft

1. Population Residing Near Airports

2. Children Attending School Near Airports

3. Agricultural Activities 

4. Pilots, Student-Trainees, Passengers 

5. Bioaccumulation of Lead in Aquatic Organisms

B. Related Exposures of Concern 

1. Lead Contribution to Ambient Particulate Matter

2. Ethylene Dibromide

3. Non-Exhaust Exposure to Tetraethyl Lead

VI. Additional Information Available for the NPRM to Evaluate the Potential for Public Health 

and Welfare Impacts and Considerations Regarding Engine Emission Standards
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A. The Lead NAAQS and Lead Emissions from Piston-Engine Aircraft

1. Monitoring Lead at Airports to Evaluate Ambient Concentrations to Which 

Lead Emissions from Piston-Engine Aircraft Contribute

2. Evaluating the Contribution of Lead Emissions from Piston-Engine Aircraft to 

Areas Approaching or Exceeding the Lead NAAQS

B. Additional Information EPA is Collecting to Evaluate Ambient Lead Concentrations 

Attributable to Emissions from Piston-Engine Aircraft

C. Considerations Regarding Engine Emission Standards

VII. Statutory and Executive Order Reviews

I. Overview

EPA is publishing this ANPR in further response to a petition submitted by Friends of the 

Earth (FOE) entitled “Petition for Rulemaking Seeking the Regulation of Lead Emissions From 

General Aviation Aircraft Under § 231 of the Clean Air Act.”1 In the petition, FOE requests that 

the Administrator of EPA: 1) make a finding that lead emissions from general aviation aircraft 

endanger public health and welfare and issue a proposed emission standard for lead from general 

aviation aircraft under the Clean Air Act (CAA) or, alternatively, 2) if the Administrator of EPA 

believes that insufficient information exists to make such a finding, commence a study and 

investigation of the health and environmental impacts of lead emissions from general aviation 

aircraft, including impacts to humans, animals and ecosystems under the CAA and issue a public 

 

1

See docket item EPA-HQ-OAR-2007-0294-0003. 
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report on the findings of the study and investigation. Section I.C of this notice discusses the 

background on the petition and EPA’s response to date and Section I.D discusses EPA’s 

statutory authority under section 231(a) of the CAA. Under the CAA, if, in the Administrator’s 

judgment, lead emissions from the use of leaded avgas cause or contribute to air pollution which 

may reasonably be anticipated to endanger public health or welfare, then EPA would be required 

under our statutory authority to prescribe standards to control the emissions of lead from pistonengine aircraft. In promulgating such standards, the EPA would be required to consult with the 

Federal Aviation Administration (FAA), and could not change standards if doing so would 

significantly increase noise and adversely affect safety. FAA would then be required, after 

consultation with EPA, to prescribe regulations to insure compliance with any standards to 

control the emissions of lead from piston-engine aircraft. Under 49 USC 44714, FAA would 

also be required to prescribe standards for the composition or chemical or physical properties of 

piston-engine fuel or fuel additives to control or eliminate aircraft lead emissions.

In this notice, we discuss our analysis of the relevant information and issues to date, and 

we seek further public input regarding FOE’s petition. For the purposes of this notice, we will 

refer to the positive or negative exercise of judgment as to whether lead emissions from aircraft 

engines resulting from the use of aviation gasoline (avgas) cause or contribute to air pollution 

which may reasonably be anticipated to endanger public health or welfare as the “endangerment 

finding” and the “cause or contribute finding.” This short-hand use of “endangerment finding” 

and “cause or contribute finding” is strictly for purposes of simplifying the discussion, and 

should not be read as implying that EPA considers the exercise of the Administrator’s judgment 

to require a formal “finding” or “determination.” 
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In 2006, EPA completed the Air Quality Criteria Document (AQCD) for Lead, which 

critically assesses and integrates relevant scientific information regarding the health effects of 

lead.2 EPA concluded that the latest evidence indicates adverse health effects, most notably

among children, are occurring at much lower levels than previously considered. In 2008, EPA 

decreased the level of the primary National Ambient Air Quality Standard (NAAQS) for lead 

from 1.5 micrograms per cubic meter (g/m3) to 0.15 g/m3in order to provide increased 

protection for children and other at-risk populations against an array of adverse health effects, 

most notably neurological effects in children, including neurocognitive and neurobehavioral 

effects.3 Neurotoxic effects in children and cardiovascular effects in adults are among those best 

substantiated as occurring at blood lead concentrations as low as 5 to 10 μg/dL (or possibly

lower); and these categories are currently clearly of greatest public health concern (AQCD for 

Lead, p. 8-60). The U.S. Centers for Disease Control and Prevention (CDC) concluded in 2005 

that no “safe” threshold for blood lead has been identified, and emphasized the importance of 

preventative measures.4, 5 To provide increased protection against lead-related welfare effects, in 

2008 EPA revised the secondary standard to be identical in all respects to the revised primary

standard. Section II of this ANPR provides more detail regarding health and welfare effects of 

lead.

 

2 U.S. Environmental Protection Agency (2006) Air Quality Criteria for Lead. Washington, DC, EPA/600/R5/144aF. Available online at: www.epa.gov/ncea/

3

 National Ambient Air Quality Standards for Lead 73 FR 66964 (Nov. 12, 2008).

4 Centers for Disease Control and Prevention (2005) Preventing lead poisoning in young children: a statement by the 

Centers for Disease Control and Prevention. Atlanta, GA: U.S. Department of Health and Human Services, Public 

Health Service. August.

5 Advisory Committee on Childhood Lead Poisoning Prevention (ACCLPP) (2007) Interpreting and managing blood 

lead levels <10 ug/dL in children and reducing childhood exposures to lead: Recommendations of CDC’s Advisory 

Committee on Childhood Lead Poisoning Prevention. Morbidity and Mortality Weekly Report. 56(RR-8). 

November 2, 2007.
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Given the recent findings of the science summarized by EPA in the AQCD for Lead as 

well as the findings of the CDC, the Agency is concerned about the potential for health and 

welfare effects from exposure to lead emissions from aircraft engines using leaded avgas. On a 

national basis, emissions of lead from aircraft engines using leaded avgas are the largest single 

source category for emissions of lead to air, comprising approximately half of the national 

inventory.

6

 There are almost 20,000 airport facilities in the U.S. at which leaded avgas may be 

used, and in some areas of the country there are densely populated residential developments 

immediately adjacent to these airport facilities. As described in Section V, we estimate that up to 

16 million people reside and three million children attend school in close proximity to airport 

facilities servicing piston-engine aircraft that are operating on leaded avgas. 

Exposure to lead occurs through multiple routes (e.g., inhalation, ingestion and dermal 

adsorption), and lead emitted to the atmosphere can contribute to lead levels in multiple media 

(e.g., air, soil and water). The lead monitoring studies conducted at or near airports, described in 

Section IV of this ANPR, indicate that lead levels in ambient air on and near airports servicing 

piston-engine aircraft are higher than lead levels in areas not directly influenced by a lead source. 

In addition, the emissions of lead from these engines are also expected to distribute widely

through the environment. This is in part due to the emission of lead at various altitudes during 

aircraft operations as well as the fine particle size of lead emitted by piston engines. Continued 

use of leaded avgas provides an ongoing source of new lead that is deposited in various 

environmental media and participates in long term cycling mechanisms in the environment, thus 

adding to the pool of lead available for uptake by humans and biota. We expect the lead from 

 

6 U.S. Environmental Protection Agency Electronic Report on the Environment. Available at: 

http://cfpub.epa.gov/eroe. Updated in December 2009 using the 2005 National Emissions Inventory. 
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avgas to be bioavailable in the same way as the lead emitted by motor vehicles in the past, which 

was well documented to contribute to blood levels through both ingestion and inhalation. 

As noted in Section II of this ANPR, once deposited to surfaces, lead can subsequently be 

resuspended into the ambient air and, because of the persistence of lead, emissions of this metal 

contribute to environmental media concentrations for many years into the future. Lead that is a 

soil or dust contaminant today may have been airborne yesterday or many years ago. Therefore 

lead emissions from piston-engine aircraft could contribute to increased lead exposure and risk 

currently or at some time in the future.

Section VI of this ANPR provides an overview of additional information that will be 

available for the NPRM to evaluate the potential for public health and welfare impacts from lead 

emitted by piston-engine aircraft. These additional data will come from lead monitoring being 

planned to satisfy requirements of the Lead NAAQS, air quality modeling planned at EPA and 

any information submitted to EPA during the comment period for this ANPR.

The remainder of this section provides background on leaded avgas, FOE’s petition and 

EPA’s response to the petition to date, and statutory authority over emissions, fuel for aircraft 

and federal actions to reduce lead exposure. Section II provides a discussion of the health and 

welfare effects of lead. Sections III, IV and V describe the emissions of lead from avgas, 

ambient lead concentration in the vicinity of airports and potential exposure to lead from leaded 

avgas, respectively. In Section VI, we describe the additional information EPA is collecting and

considerations regarding engine emission standards. Section VII contains information on 

statutory and executive order reviews covering this action. 
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A. Background on Leaded Aviation Gasoline 

In 1996, EPA promulgated regulations that banned the use of leaded gasoline in highway

vehicles.7 The addition of lead to fuel used in piston-engine powered aircraft was not banned in 

this action, and the use of leaded avgas is the largest remaining source category of lead 

emissions. Lead is not added to jet fuel that is used in commercial aircraft, most military aircraft, 

or other turbine-engine powered aircraft. Most piston-engine aircraft fall into the categories of 

either general aviation (GA) or air taxi (AT). GA and AT aircraft include a diverse set of aircraft 

types and engine models and are used in a wide variety of applications.8 

Lead is added to fuel for piston-engine aircraft in the form of tetraethyl lead (TEL). This 

lead additive helps boost fuel octane, prevents knock, and prevents valve seat recession and 

subsequent loss of compression for engines without hardened valves. There are two main types 

of leaded avgas: 100 Octane, which can contain up to 4.24 grams of lead per gallon; and 100 

Octane Low Lead (100 LL), which can contain up to 2.12 grams of lead per gallon. Currently, 

100LL is the most commonly available and most commonly used type of avgas.9, 10 TEL was 

first used in piston-engine aircraft in 1927.11 Into the 1950s commercial and military aircraft in 

 

7

See “Prohibition on Gasoline Containing Lead or Lead Additives for Highway Use” 61 FR 3832 (Feb. 2, 1996). 

8 Commercial aircraft include those used for scheduled service transporting passengers, freight, or both. Air taxis 

fly scheduled and for-hire service carrying passengers, freight or both, but they usually are smaller aircraft than 

those operated by commercial air carriers. General aviation includes most other aircraft (fixed and rotary wing) 

used for recreational flying, business, and personal transportation.

9 ChevronTexaco (2006) Aviation Fuels Technical Review. FTR-3. Available online at: 

http://www.chevronglobalaviation.com/docs/aviation_tech_review.pdf

10 ASTM International (2005) Annual Book of ASTM Standards Section 5: Petroleum Products, Lubricants, and 

Fossil Fuels Volume 05.01 Petroleum Products and Lubricants (I): D 56 – D 3230.

11 Ogston, A.R. (1981) A Short History of Aviation Gasoline Development, 1903-1980. Society of Automotive 

Engineers. Paper number 810848.
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the U.S. operated on 100 Octane leaded avgas, but in subsequent years, the commercial and 

military aircraft fleet largely converted to jet turbine-engine propelled aircraft. However, the use 

of avgas containing 4 grams of lead per gallon continued in piston-engine aircraft until the early 

1970s when 100LL became the dominant leaded fuel in use. Currently, very little 100 Octane is 

supplied in the U.S. and we use the lead content of 100LL (2.12 grams per gallon) to characterize 

the lead available from avgas. 

Since lead is a persistent pollutant, it is important to characterize the historical use of this 

fuel. Approximately 14.6 billion gallons of leaded avgas have been consumed in the U.S. 

between 1970 and 2007. If this fuel was all 100LL, it would account for approximately 34,000 

tons12 of lead emitted to the air.13 In terms of the potential impacts from long-term use of leaded 

avgas at and near airports, older facilities would be expected to have a legacy of lead, 

particularly those that supported military and commercial aircraft operating on 100 Octane. Over 

3,000 of the 20,000 airport facilities in the U.S. are at least 50 years old and some airports have 

been in operation since the early 1900s. 

The Department of Energy’s (DOE’s) Energy Information Administration (EIA) provides 

information on the volume of leaded avgas supplied in the U.S.16 The Department of 

Transportation’s (DOT’s) FAA provides information on the volume of leaded avgas consumed in 

the U.S.17 EPA has historically used the DOE EIA avgas fuel volumes supplied to calculate 

national lead inventories from the consumption of leaded avgas. We are currently evaluating 

 

12 In this ANPR and in EPA’s National Emissions Inventory, the use of the unit tons refers to short tons. 

13 Oak Ridge National Laboratory (2009) Transportation Energy Data Book: Edition 28. Available at: 

http://cta.ornl.gov/data. Table A.7.

16 Department of Energy Information Administration. Fuel production volume data obtained from 

http://tonto.eia.doe.gov/dnav/pet/hist/mgaupus1A.htm accessed June 2009.

17 U.S. Department of Transportation Federal Aviation Administration Aviation Policy and Plans. FAA Aerospace 

Forecast Fiscal Years 2009-2025. p.81. Available at: 

http://www.faa.gov/data_research/aviation/aerospace_forecasts/2009-2025/media/2009%20Forecast%20Doc.pdf 

This document provides historical data for 2000-2008 as well as forecast data.
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methods used by DOE and DOT to calculate annual avgas supply and consumption volumes. In 

this document, we provide avgas fuel volume data supplied by DOE and DOT and we note the 

source of the data for clarity. Over the past ten years, DOE estimates of the volume of leaded 

avgas supplied has ranged from 326 million gallons in 1999 to 235 million gallons in 2008

(Figure 1). Applying the concentration of lead in 100LL (2.12 grams of lead per gallon), the 

total quantity of lead supplied in avgas in the nation has ranged from 762 tons in 1999 to 550 

tons in 2008 (a 28% decrease over that time period). The decrease in fuel consumption is 

attributed to the decrease in piston-engine aircraft activity over that time period and not due to a 

shift to unleaded fuel. There are currently over 200,000 piston-engine aircraft in the U.S. that 

continue to consume leaded avgas and approximately 2,000 new piston-engine aircraft requiring 

leaded avgas are manufactured annually.

18

 As described in Section III.B of this ANPR, there is a 

slight growth in the activity of general aviation aircraft projected to 2025. 

 

18 General Aviation Manufacturers Association (2008) General Aviation Statistical Databook & Industry Outlook. 

Available online at: 

http://www.gama.aero/files/2008_general_aviation_statistical_databook__indust_499b0dc37b.pdf
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Avgas Pb, 1999-2008

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Year

Thousand Barrels of Avgas 

Supplied

0

98

196

294

393

491

589

687

785

883

Tons of Pb from Avgas

Figure 1. Tons of Lead Supplied in Aviation Gasoline Annually from 1999 – 2008.

Source: DOE Energy Information Administration

B. Background Information Regarding General Aviation and Use of PistonEngine Aircraft

In the U.S., general aviation aircraft fly over 27 million hours and carry 166 million 

passengers annually.

19

 Approximately 66 percent of hours flown by general aviation are 

conducted by piston-engine aircraft.20 Aircraft in the general aviation fleet are used for personal 

 

19 General Aviation Manufacturers Association (2008) General Aviation Statistical Databook and Industry Outlook, 

p.30. Retrieved on August 17, 2009 from: 

http://www.gama.aero/files/2008_general_aviation_statistical_databook__indust_499b0dc37b.pdf

20 General Aviation Manufacturers Association (2008) General Aviation Statistical Databook and Industry Outlook, 

p.30. Retrieved on August 17, 2009 from: 

http://www.gama.aero/files/2008_general_aviation_statistical_databook__indust_499b0dc37b.pdf
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transportation (36 percent), instructional flying (19 percent), corporate uses (11 percent), 

business (11 percent), air taxi and air tours (eight percent) and the remainder include hours spent

in other applications such as aerial observation and aerial application.21 According to the 2008 

General Aviation Statistical Databook & Industry Outlook report by the General Aviation 

Manufacturers Association (GAMA) there were 578,541 pilots in the United States in 2008.

22

 

According to GAMA, in 2008, the number of active single-engine piston-powered aircraft was 

144,220 and the number of active twin-engine piston-powered aircraft was 18,385. In 2008, 

1,791 new piston-engine aircraft were manufactured in the U.S.

FAA’s Office of Air Traffic provides a complete listing of operational airport facilities in 

the National Airspace System Resources (NASR) database.23 In 2008, there were 19,896 airport 

facilities in the U.S., the vast majority of which are expected to have activity by piston-engine 

aircraft that operate on leaded avgas. FAA’s National Plan of Integrated Airport Systems 

identifies approximately 3,400 airports that are significant to national air transportation. 

C. Background on the Petition and EPA’s Response

In a 2003 letter to the EPA, FOE initially raised the issue of the potential for 

endangerment caused or contributed to by lead emissions from the use of leaded avgas.24 In 

2006, FOE filed a petition with EPA requesting that the Administrator find endangerment or, if 

there was insufficient information to find endangerment, commence a study of lead emissions 

from piston-engine aircraft. In 2007, the EPA issued a Federal Register notice on the petition 

 

21 General Accounting Office Report to Congressional Requesters (2001) General Aviation Status of the Industry, 

Related Infrastructure, and Safety Issues. GAO-01-916.

22 General Aviation Manufacturers Association (2008) General Aviation Statistical Databook and Industry Outlook, 

pp.51-55. Retrieved on August 17, 2009 from: 

http://www.gama.aero/files/2008_general_aviation_statistical_databook__indust_499b0dc37b.pdf

23 An electronic report can be generated from the NASR database and is available for download from the internet at 

the following website. .http://www.faa.gov/airports_airtraffic/airports/airport_safety/airportdata_5010/ This 

database is updated every 56 days.

24 FOE letter dated December 12, 2003 submitted to EPA Docket EPA-HQ-OAR-2002-0030.
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requesting comments and information related to a wide range of issues regarding the use of

leaded avgas and potential public health and welfare exposure issues.25 We sought comments 

regarding exposure to lead from avgas combustion, emissions of lead, fuel options, and pistonengine technology. The comments received to date are publicly available in the docket (EPAHQ-OAR-2007-0294). The majority of comments received concerned the nature of the industry

and fuel supply issues. The commenters did not supply information regarding health or exposure 

issues. In 2008, the EPA initiated a lead study which will improve the manner in which EPA 

models emissions from piston-engine aircraft. This study is described in further detail in Section 

VI of this document. At the time we received FOE’s petition, the EPA was in the process of a 

full re-evaluation of the science supporting the lead NAAQS. Information from that reevaluation and the relationship between the new lead standard and the emissions of lead from 

piston-engine aircraft are discussed in this ANPR. 

D. Statutory Authority

1. Background

Section 231 of the CAA sets forth EPA’s authority to regulate aircraft emissions of air 

pollution. As described further in Section I.D.2 of this ANPR, Section 231(a)(2)(A) requires 

EPA to, from time to time, issue proposed emission standards applicable to the emission of any

air pollutant from any class or classes of aircraft engines which, in the Administrator’s judgment, 

cause or contribute to air pollution which may reasonably be anticipated to endanger public 

 

25 See “Petition Requesting Rulemaking To Limit Lead Emissions from General Aviation Aircraft; Request for 

Comments” 72 FR 64570 (Nov. 16, 2007).
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health or welfare. EPA has broad authority in exercising its judgment regarding whether 

emissions from certain sources cause or contribute to air pollution which may reasonably be 

anticipated to endanger public health or welfare.26 EPA has discussed its “endangerment 

finding” authority at length in recent notices for greenhouse gases published in the Federal 

Register, and we refer readers to those notices for detailed discussions of the analytical and legal 

framework.27 

In 1976, EPA listed lead under CAA section 108, making it what is called a “criteria 

pollutant.” As part of the listing decision, EPA determined that lead was an air pollutant which, 

in the Administrator’s judgment, has an adverse effect on public health or welfare under then 

section 108(a). Once lead was listed, EPA issued primary and secondary NAAQS that the 

Administrator determined were requisite to protect public health with an adequate margin of 

safety and to protect public welfare from any known or anticipated adverse effects. Section 

109(b)(1) and (2). As discussed elsewhere in this notice, EPA issued the first NAAQS for lead 

in 1978, and recently revised the lead NAAQS by reducing the level of the standard from 1.5 

g/m3to 0.15 g/m3, measured over a 3-month averaging period. These actions are part of the 

context for the issues before EPA under section 231(a).

The first part of the endangerment test concerns identification of air pollution which may

reasonably be anticipated to endanger public health or welfare. The CAA defines both “air 

 

26

 See, e.g., Ethyl Corp. v. EPA, 541 F.2d 1, 6 (D.C. Cir.), cert. denied 426 U.S. 941 (1976); see also Massachusetts 

v. EPA, 549 U.S. 497, 506, n.7 (2007).

27

 See, “Endangerment and Cause or Contribute Findings for Greenhouse Gases under Section 202(a) of the Clean 

Air Act; Final Rule,” 74 FR 66496, 66505 (Dec. 15, 2009); see also, “Proposed Endangerment and Cause or 

Contribute Findings for Greenhouse Gases Under Section 202(a) of the Clean Air Act,” 74 FR 18886, 18890-94 

(April 24, 2009); see also “Regulating Greenhouse Gas Emissions Under the Clean Air Act; Advance Notice of 

Proposed Rulemaking,” 73 FR 44354, 44421-23 (July 30, 2008).
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pollutant” and “welfare.” Air pollutant is defined in CAA section 302(g) as: “Any air pollution 

agent or combination of such agents, including any physical, chemical, biological, radioactive 

(including source material, special nuclear material, and byproduct material) substance or matter 

which is emitted into or otherwise enters the ambient air. Such term includes any precursors to 

the formation of any air pollutant, to the extent the Administrator has identified such precursor or 

precursors for the particular purpose for which the term ‘air pollutant’ is used.” Lead fits within 

this capacious definition, and has long been regulated as an air pollutant by EPA under the CAA 

(see Section I.E. of this ANPR). 

There is no definition of public health in the CAA. The U.S. Supreme Court has 

discussed the concept in the context of whether costs can be considered when setting NAAQS. 

Whitman v. American Trucking Ass’n, 531 U.S. 457 (2001). In Whitman, the Court imbued the 

term with its most natural meaning: “the health of the public.” Id., at 466. When considering 

public health, EPA has looked at morbidity, including acute and chronic health effects, as well as 

mortality. EPA has long regulated emissions of lead air pollution due to their adverse impacts on 

public health (see section I.E. of this ANPR). Exposure to lead causes “a broad array of 

deleterious effects on multiple organ systems,” among children and adults (AQCD for Lead, p.8-

24 and Section 8.4.1). Of particular concern are the neurotoxic effects of lead in young 

children.28 See Section II of this ANPR for a more complete overview of the public health 

effects of lead.

Regarding “welfare,” CAA section 302(h) states that “[a]ll language referring to effects 

on welfare includes, but is not limited to, effects on soils, water, crops, vegetation, man-made 

 

28 See “National Ambient Air Quality Standards for Lead” 73 FR 66970-67007 (Nov. 12, 2008)
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materials, animals, wildlife, weather, visibility, and climate, damage to and deterioration of 

property, and hazards to transportation, as well as effects on economic values and on personal 

comfort and well-being, whether caused by transformation, conversion, or combination with 

other air pollutants.” This definition is quite broad, and may include effects other than those 

listed here as effects on welfare. Welfare effects caused by lead have been evaluated by EPA 

and were the basis for establishing the secondary lead standard.29

By instructing the Administrator to consider whether emissions of an air pollutant cause 

or contribute to air pollution, the statute is clear that she need not find that emissions from any

one sector or group of sources are the sole or even the major part of an air pollution problem. 

Moreover, section 231(a) does not contain a modifier on its use of the term contribute. Unlike 

some other CAA provisions, it does not require “significant” contribution.30 Congress made it 

clear that the Administrator is to exercise her judgment in determining contribution, and 

authorized regulatory controls to address air pollution even if the air pollution problem results 

from a wide variety of sources. The cause or contribute test is designed to authorize EPA to 

identify and then address what may well be many different sectors or groups of sources that are 

each part of an air pollution problem.

Section 231(a)(2) refers to contribution and does not specify that the contribution must be 

significant before an affirmative finding can be made. Any finding of a “contribution” requires 

some threshold to be met; a truly trivial or de minimis “contribution” might not count as such. In 

the past, the Administrator has evaluated the emissions of the source or sources in different 

ways, based on the particular circumstances involved. In some mobile source rulemakings, the 

 

29 See “National Ambient Air Quality Standards for Lead” 73 FR 67007-67012 (Nov. 12, 2008).

30 See, e.g., CAA sections 111(b); 213(a)(2), (4). 
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22

Administrator has used the percent of emissions from the regulated mobile source category

compared to the total mobile source inventory for that air pollutant as the best way to evaluate 

contribution.31 In other instances the Administrator has looked at the percent of emissions 

compared to the total nonattainment area inventory of the air pollution at issue.32 EPA has found 

that air pollutant emissions that amount to 1.2 percent of the total inventory met the statutory test 

for contribution, triggering EPA’s regulatory authority.

33

2. Regulatory Authority for Emission Standards

Section 231 of the CAA sets forth EPA’s authority to regulate aircraft emissions of air 

pollution. Section 231(a)(2)(A) requires EPA to, from time to time, issue proposed emission 

standards applicable to the emission of any air pollutant from any class or classes of aircraft 

engines which, in the Administrator’s judgment, cause or contribute to air pollution which may

reasonably be anticipated to endanger public health or welfare. Section 231(a)(2)(B)(i) directs 

EPA to consult with FAA on aircraft engine emission standards, and section 231(a)(2)(B)(ii) 

provides that EPA shall not change the aircraft engine emission standards if such change would 

significantly increase noise and adversely affect safety. Section 231(a)(3) directs EPA to issue 

final regulations with such modifications as the Administrator “deems appropriate.” 

In setting or revising standards, section 231(b) provides that EPA shall have them take 

effect after such period as EPA finds necessary (after consultation with the Secretary of 

 

31 See, e.g., 66 FR 5001 (January 18, 2001) (heavy duty engine and diesel sulfur rule).

32 See, e.g., 67 FR 68242 (November 8, 2002) (snowmobile rule).

33 Bluewater Network v. EPA, 370 F.3d 1, 15 (D.C. Cir. 2004) (For Fairbanks, this contribution was equivalent to 

1.2 percent of the total daily CO inventory for 2001).
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23

Transportation) to permit the development and application of the requisite technology, giving 

appropriate consideration to the cost of compliance within such period. Section 231(c) then 

states that EPA’s regulations regarding aircraft shall not apply if disapproved by the President, 

after notice and opportunity for public hearing, on the basis of a finding by DOT that such 

regulations would create a hazard to aircraft safety. Section 232 directs DOT to issue and 

implement regulations to insure compliance with EPA’s standards, while section 233 pre-empts 

states and local governments from adopting or enforcing any aircraft emission standards that are 

not identical to EPA’s standards.

In recently reviewing this statutory scheme, the U.S. Court of Appeals for the District of 

Columbia Circuit ruled that it constitutes a “both explicit and extraordinarily broad” delegation 

of “expansive authority to EPA to enact appropriate regulations applicable to the emissions of air 

pollutants from aircraft engines.”34 

3. Regulatory Authority for Fuel Standards

Section 211(c) of the CAA allows EPA to regulate fuels used in motor vehicles and 

nonroad vehicles or engines where emission products of the fuel either: (1) cause or contribute to 

air pollution that reasonably may be anticipated to endanger public health or welfare, or (2) will 

impair to a significant degree the performance of any emission control device or system which is 

in general use, or which the Administrator finds has been developed to a point where in a 

reasonable time it will be in general use were such a regulation to be promulgated. This section 

of the CAA was used to eliminate lead from fuel used in motor vehicles. EPA’s authority to 

 

34

 NACAA v. EPA, 489 F.3d 1221, 1229-30 (D.C. Cir. 2007).
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regulate fuels is limited to those fuels used in motor vehicles, motor vehicle engines, or nonroad 

engines or vehicles, under CAA section 211(c)(1). The CAA defines “motor vehicle,” “nonroad 

engine,” and “nonroad vehicle” in section 216 for purposes of part A of title II of the CAA. Part 

A is also where the authority to regulate fuels under section 211 resides. However, EPA’s 

authority to regulate aircraft resides in part B of title II, and therefore the definitions of section 

216 do not apply to aircraft. This means that aircraft are not “nonroad vehicles,” and aircraft 

engines are not “nonroad engines.” Consequently, EPA’s authority to regulate fuels under 

section 211 does not extend to fuels used exclusively in aircraft, such as leaded avgas, that are 

not also used in motor vehicles or nonroad vehicles or engines (excluding fuel used in vehicles 

exclusively).

Instead, fuels used exclusively in aircraft engines are to be regulated by the FAA. Title 

49 (49 U.S.C. 44714) requires that “the Administrator of the Federal Aviation Administration 

shall prescribe (1) standards for the composition or chemical or physical properties of an aircraft 

fuel or fuel additive to control or eliminate aircraft emissions the Administrator of the 

Environmental Protection Agency decides under section 231 of the Clean Air Act (42 U.S.C. 

7571) endanger the public health or welfare; and (2) regulations providing for carrying out and 

enforcing those standards.”

E. Federal Actions to Reduce Lead Exposure

The U.S. has made tremendous progress in reducing lead concentrations in the outdoor 

air. Nationwide, average concentrations of lead in the air have dropped 91 percent between 1980 
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25

and 2008.35 Much of this dramatic improvement occurred as a result of the permanent phase-out 

of lead in motor vehicle gasoline discussed in this section of the ANPR. However, lead 

continues to be emitted into the air from many different types of stationary sources and pistonengine aircraft as well as certain high performance engines such as race cars.

Federal programs provide for nationwide reductions in emissions of lead and other air 

pollutants through several provisions in the CAA. In the early 1970s, EPA issued regulations 

regarding lead in gasoline in order to accomplish two purposes.36 First, EPA issued regulations 

designed to ensure the availability of unleaded gasoline for use in motor vehicles equipped with 

emission control systems such as catalytic converters. EPA had determined that lead additives 

would impair to a significant degree the performance of emission control systems. Second, EPA 

issued regulations designed to gradually reduce the content of lead in leaded gasoline, because 

EPA found that lead emissions from motor vehicles presented a significant risk of harm to the 

health of urban population groups, especially children. Children are at a sensitive life stage with 

regard to the adverse health effects of lead. In 1985, EPA, noting the significant reduction in 

adverse health effects, mainly among pre-school age children, that would result from reductions 

in lead content in gasoline, promulgated additional regulations to decrease the allowable 

concentration of lead in gasoline for motor vehicles to 0.10 grams per gallon.37 In 1990 

Congress added section 211(n) to the CAA which provides that after December 31, 1995, it shall 

be unlawful to sell any gasoline for use in any motor vehicle which contains lead or lead 

additives. In 1996, EPA incorporated the CAA statutory ban on gasoline containing lead or lead 

additives for highway use into the Agency’s existing regulations on the lead content of 

 

35

 See http://www.epa.gov/airtrends/lead.html

36 “Regulation of Fuels and Fuel Additives” 38 FR 1254 (Dec. 4, 1973)

37 “Regulation of Fuels and Fuel Additives; Gasoline Lead Content” 50 FR 9386 (March 7, 1985)
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gasoline.38 In this regulation, it was noted that the petroleum industry may continue to make and 

market gasoline produced with lead additives for all remaining uses, including use as fuel in 

aircraft, racing cars, and nonroad engines such as farm equipment engines and marine engines, to 

the extent otherwise allowed by law.39

In fact, there have been no regulatory limits placed on the production and consumption of 

leaded avgas, and, as noted in Section I.A of this ANPR, emissions of lead from piston-engine 

aircraft account for an increasing fraction of the lead emissions to air (e.g., accounting for 

approximately half the national inventory of lead emission in 2005). This is in spite of the 

decrease in the supply of leaded avgas nationally from 374 million gallons (875 tons of lead) in 

1990 to 235 million gallons (550 tons of lead) in 2008.40 The decrease in fuel consumption is 

attributed to the decrease in piston-engine aircraft activity over that time period and not due to a 

shift to unleaded fuel. There are over 200,000 piston-engine aircraft in the U.S. that continue to 

consume leaded avgas and approximately 2,000 new piston-engine aircraft requiring leaded 

avgas are manufactured annually. Projected growth for this industry is discussed in Section 

III.B. 

Significant reductions in emission of lead from stationary sources have been achieved 

between 1985 and 2002, totaling almost 2,000 tons of lead.41 Regulations promulgated in 1995, 

1997 and 1999 controlled emissions of lead from primary and secondary lead smelters, 

 

38 “Prohibition on Gasoline Containing Lead or Lead Additives for Highway Use” 61 FR 3832 (Feb. 2, 1996)

39 “Prohibition on Gasoline Containing Lead or Lead Additives for Highway Use” 61 FR 3834 (Feb. 2, 1996)

40 These fuel volume estimates are from the Department of Energy Information Administration. 

http://tonto.eia.doe.gov/dnav/pet/hist/mgaupus1A.htm

41 U.S. Environmental Protection Agency (2008) EPA’s Report on the Environment EPA/600/R-07/045F. Available 

at: http://www.epa.gov/roe/
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contributing to these reductions.42, 43, 44 Currently, metal industry emissions of lead comprise 

23% of the national inventory (298 tons). Additional reductions in the emission of lead have 

been accomplished through controls on waste incineration and other stationary sources.45 , 46, 47 

These standards have been set at “maximum achievable control technology” (MACT) levels, and 

under CAA sections 112 and 129 EPA must revisit these standards in the future to determine 

whether they are sufficiently stringent to provide an ample margin of safety to protect public 

health and prevent an adverse environmental effect.

As lead is a multimedia pollutant, a broad range of Federal programs beyond those that 

focus on air pollution control provide for nationwide reductions in environmental releases and 

human exposures. In addition, the U.S. Centers for Disease Control and Prevention (CDC) 

programs provide for the tracking of children’s blood lead levels nationally and provide guidance 

on levels at which medical and environmental case management activities should be 

implemented.48,49 In 1991, the Secretary of the U.S. Department of Health and Human Services 

(HHS) characterized lead poisoning as the “number one environmental threat to the health of 

 

42 “National Emission Standards for Hazardous Air Pollutants From Secondary Lead Smelting” 60 FR 32587 (June 

23, 1995)

43 “National Emission Standards for Hazardous Air Pollutants From Secondary Lead Smelting” 62 FR 32209 (June 

13, 1997)

44 “National Emission Standards for Hazardous Air Pollutants for Primary Lead Smelting” 64 FR 30194 (June 4, 

1999)

45 “Standards of Performance for New Stationary Sources and Emission Guidelines for Existing Sources: Municipal 

Waste Combustors” 60 FR 65387 (Dec. 19, 1995)

46

 “Emission Guidelines for Existing Sources and Standards of Performance for New Stationary Sources” 62 FR 

45124 (Aug. 25, 1997)

47 “Standards of Performance for New Stationary Sources and Emission Guidelines for Existing Sources: Large 

Municipal Waste Combustors” 71 FR 27324-27348 (May 10, 2006)

48 Centers for Disease Control and Prevention (2005) Preventing lead poisoning in young children: a statement by 

the Centers for Disease Control and Prevention. Atlanta, GA: U.S. Department of Health and Human Services, 

Public Health Service. August.

49 Advisory Committee on Childhood Lead Poisoning Prevention (2007) Interpreting and managing blood lead 

levels <10 μg/dL in children and reducing childhood exposures to lead: Recommendations of CDC’s Advisory 

Committee on Childhood Lead Poisoning Prevention. Morbidity and Mortality Weekly Report. 56(RR-8). 

November 2, 2007.
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children in the United States.”50 In 1997, President Clinton created, by Executive Order 13045, 

the President’s Task Force on Environmental Health Risks and Safety Risks to Children in 

response to increased awareness that children face disproportionate risks from environmental 

health and safety hazards (62 FR 19885).51 By Executive Orders issued in October 2001 and 

April 2003, President Bush extended the work for the Task Force for an additional three and a 

half years beyond its original charter (66 FR 52013 and 68 FR 19931). The Task Force set a 

Federal goal of eliminating childhood lead poisoning by the year 2010, and reducing lead 

poisoning in children was identified as the Task Force’s top priority. 

Federal abatement programs provide for the reduction in human exposures and 

environmental releases from in-place materials containing lead (e.g., lead-based paint, urban soil 

and dust, and contaminated waste sites). Federal regulations on disposal of lead-based paint 

waste help facilitate the removal of lead-based paint from residences (68 FR 36487). Further, in 

1991, EPA lowered the maximum levels of lead permitted in public water systems from 50 parts 

per billion (ppb) to 15 ppb measured at the consumer’s tap (56 FR 26460).

Federal programs to reduce exposure to lead in paint, dust, and soil are specified under 

the comprehensive federal regulatory framework developed under the Residential Lead-Based 

Paint Hazard Reduction Act (Title X). Under Title X and Title IV of the Toxic Substances 

Control Act (TSCA), EPA has established regulations and associated programs with the goal of 

reducing exposure to lead via lead-based paint. For example, under Title IV of TSCA, EPA 

established standards identifying hazardous levels of lead in residential paint, dust, and soil in 

 

50 Alliance to End Childhood Lead Poisoning (1991) The First Comprehensive National Conference; Final Report. 

October 6, 7, 8, 1991

51 Co-chaired by the Secretary of the HHS and the Administrator of the EPA, the Task Force consisted of 

representatives from 16 Federal departments and agencies.
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29

2001. On March 31, 2008, the Agency issued a new rule (73 FR 21692) to further protect 

children from lead-based paint hazards resulting from renovation and repair work occurring in 

housing in which they live. 

Programs associated with the Comprehensive Environmental Response, Compensation, 

and Liability Act (CERCLA or Superfund) and Resource Conservation Recovery Act (RCRA) 

also implement abatement programs, reducing exposures to lead and other pollutants. For 

example, EPA determines and implements protective levels for lead in soil at Superfund sites 

and RCRA corrective action facilities. Federal programs, including those implementing RCRA, 

provide for management of hazardous substances in hazardous and municipal solid waste.52 

Federal regulations concerning batteries in municipal solid waste control the collection and 

recycling or proper disposal of batteries containing lead.53 Similarly, Federal programs provide 

for the reduction in environmental releases of hazardous substances such as lead in the 

management of wastewater.54

A variety of federal nonregulatory programs also provide for reduced environmental 

release of lead-containing materials through voluntary measures and more general 

encouragement of pollution prevention, promotion of reuse and recycling, reduction of priority 

and toxic chemicals in products and waste, and conservation of energy and materials. These 

include the voluntary partnership between EPA and the National Association for Stock Car Auto 

Racing (NASCAR) which has achieved the goal of removing alkyl lead (organic forms of lead) 

 

52 See, e.g., 66 FR 58258.

53 See, e.g., “Implementation of the Mercury-Containing and Rechargeable Battery Management Act” 

http://www.epa.gov/epaoswer/hazwaste/recycle/battery.pdf and “Municipal Solid Waste Generation, Recycling, and 

Disposal in the United States: Facts and Figures for 2005” 

http://www.epa.gov/epaoswer/osw/conserve/resources/msw-2005.pdf.

54 http://www.epa.gov/owm/
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from racing fuels used in the Nextel Cup, Busch and Craftsman Truck Series.55 Other programs 

include the Resource Conservation Challenge,56 the National Waste Minimization Program,57

“Plug in to eCycling” (a partnership between EPA and consumer electronics manufacturers and 

retailers),58 and activities to reduce the practice of backyard trash burning.59

In addition to the lead control programs summarized above, EPA’s research program, 

with other Federal agencies, identifies, encourages and conducts research needed to locate and 

assess serious risks and to develop methods and tools to characterize and help reduce risks. For 

example, EPA’s Integrated Exposure Uptake Biokinetic Model for Lead in Children (IEUBK 

model) and the Adult Lead Methodology are widely used and accepted as tools that provide 

guidance in evaluating site specific data. More recently, in recognition of the need for a single 

model that predicts lead concentrations in tissues for children and adults, EPA is developing the 

All Ages Lead Model (AALM) to provide researchers and risk assessors with a pharmacokinetic 

model capable of estimating blood, tissue, and bone concentrations of lead based on estimates of 

exposure over the lifetime of the individual. EPA research activities on substances including 

lead focus on better characterizing aspects of health and environmental effects, exposure, and 

control or management of environmental releases.60

 

55 U.S. Environmental Protection Agency Persistent, Bioaccumulative, and Toxic Pollutants (PBT) Program (2002) 

PBT national action plan for alkyl-Pb. Washington, DC. Available online at: 

http://www.epa.gov/pbt/pubs/Alkyl_lead_action_plan_final.pdf

56 http://www.epa.gov/epawaste/rcc/index.htm 

57 http://www.epa.gov/epawaste/hazard/wastemin/ 

58 http://www.epa.gov/epawaste/partnerships/plugin/index.htm 

59 http://www.epa.gov/epawaste/nonhaz/municipal/backyard/index.htm 

60 http://www.epa.gov/ord/
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II. Health and Welfare Effects of Lead 

A. Multimedia and Multi-Pathway Exposure Considerations

This section briefly summarizes the information presented in the 2008 NAAQS for 

Lead,61 the 2007 Lead Staff Paper62 and the 2006 Air Quality Criteria Document for Lead 

(AQCD for Lead).63 Lead is an unusual pollutant in that the distribution of lead to different 

environmental media (e.g., air, soil, water) is important for evaluating public health and welfare 

effects. Lead emitted to the air can result in exposure via multiple pathways (e.g., inhalation, 

ingestion, dermal absorption). Some key multimedia and multi-pathway considerations for lead 

include the following:

(1) Lead is emitted into the air from many sources encompassing a wide variety of 

stationary and mobile source types. Lead emitted to the air is predominantly in particulate form, 

with the particles occurring in various sizes. Once emitted, the particles can be transported long 

or short distances depending on their size, which influences the amount of time spent in the 

aerosol phase. In general, larger particles tend to deposit more quickly, within shorter distances 

from emissions points (e.g., kilometers), while smaller particles will remain in the aerosol phase 

and travel longer distances before depositing (e.g., hundreds to thousands of kilometers).

64

 As 

 

61 National Ambient Air Quality Standards for Lead 73 FR 66970-67007 (Nov. 12, 2008) Section II.A.

62 U.S. Environmental Protection Agency Review of the National Ambient Air Quality Standards for Lead: Policy 

Assessment of Scientific and Technical Information OAQPS Staff Paper (2007) Chapter 2. EPA-452/R-07-013 

November. 

63 U.S. Environmental Protection Agency Air Quality Criteria for Lead (2006) Volume I: Chapters 2 & 3. 

EPA/600/R-5/144aF. October. 

64 U.S. Environmental Protection Agency (2004) Air quality criteria for particulate matter. Research Triangle Park, 

NC: Office of Research and Development, National Center for Environmental Assessment; EPA report no. EPA600/P-99/0028aF.
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summarized in the AQCD for Lead, airborne concentrations of lead at sites near sources are 

much higher than at sites not known to be directly influenced by sources. 

(2) Once deposited to surfaces, lead can subsequently be resuspended into the ambient air 

and, because of the persistence of lead, emissions of this metal contribute to environmental 

media concentrations for many years into the future as it is cycled within and between 

environmental media such as soil, air and water. Lead that is a soil or dust contaminant today

may have been airborne yesterday or many years ago.65

(3) Exposure to lead emitted into the ambient air can occur directly by inhalation, or 

indirectly by ingestion of lead-contaminated food, water or other materials including dust and 

soil. This occurs due to the environmental cycling of this persistent metal which, once emitted 

into the ambient air is distributed to other environmental media and can contribute to human 

exposures via indoor and outdoor dusts, outdoor soil, food and drinking water, as well as 

inhalation of air. Atmospheric deposition is estimated to comprise a significant proportion of 

lead in food (AQCD for Lead, p. 3–48). For example, livestock may be exposed to lead in 

vegetation (e.g., grasses and silage) and in surface soils via incidental ingestion of soil while 

grazing (USEPA 1986, Section 7.2.2.2.2).66 And dietary intake may be a predominant source of 

lead exposure among adults, greater than consumption of water and beverages or inhalation (73 

FR 66971). These exposure pathways are described more fully in Section 8.2.2 of the AQCD for 

Lead.

 

65 National Ambient Air Quality Standards for Lead 73 FR 66971 (Nov. 12, 2008), AQC for Lead, Section 2.5.

66 U.S. Environmental Protection Agency (1986) Air quality criteria for lead. Research Triangle Park, NC: Office of 

Health and Environmental Assessment, Environmental Criteria and Assessment Office; EPA report no. EPA-600/8-

83/028aF-dF. 4v. Available from: NTIS, Springfield, VA; PB87-142378.
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(4) Air-related exposure pathways are affected by changes to air quality, including 

changes in concentrations of lead in air and changes in atmospheric deposition of lead. Further, 

because of its persistence in the environment, lead deposited from the air may contribute to 

human and ecological exposures for years into the future as described above. 

Additionally, human exposures to lead include pathways that are not related to ambient 

air concentrations. The pathways of human exposure to lead that are not air-related include 

ingestion of indoor lead paint,67 lead in diet as a result of inadvertent additions during food 

processing, and lead in drinking water attributable to lead in distribution systems, as well as 

other generally less prevalent pathways, as described in the AQCD for Lead (pp. 3-50 to 3-51).

B. Health Effects Information

In 2008, EPA decreased the level of the primary (health-based) NAAQS for Lead from 

1.5 g/m3to 0.15 g/m3in order to provide increased protection for children and other at-risk 

populations against an array of adverse health effects, most notably neurological effects in 

children, including neurocognitive and neurobehavioral effects.68 This section summarizes 

information provided in the numerous recent documents summarizing health and welfare effects 

from exposure to lead, including the AQCD for Lead, CDC documents, the EPA Staff Paper69

and the proposed and final NAAQS for Lead. First, the use of blood lead as a measure of 

exposure to lead is described followed by a brief summary of the broad array of lead-induced 

 

67 Weathering of outdoor lead paint may also contribute to soil lead levels adjacent to the house.

68

 National Ambient Air Quality Standards for Lead 73 FR 66965 (Nov. 12, 2008).

69 U.S. Environmental Protection Agency (2007) Review of the National Ambient Air Quality Standards for Lead: 

Policy Assessment of Scientific and Technical Information, OAQPS Staff Paper. EPA-452/R-07-013. Office of Air 

Quality Planning and Standards, Research Triangle Park.
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health effects. Particular focus is given here to the effects of lead on the developing nervous 

system in children since this is among the most sensitive endpoints identified for this toxic metal. 

The section ends with a description of at-risk populations and life stages. 

1. Blood Lead

Lead enters the body most commonly via the respiratory system and/or gastrointestinal 

tract, from which it is quickly absorbed into the blood stream and distributed throughout the 

body.

70

 Less commonly, lead, particularly organic forms of lead such as akyl lead, can be 

absorbed through the skin (AQCD for Lead, page 4-12). Blood lead levels are extensively used 

as an index or biomarker of exposure by national and international health agencies, as well as in 

epidemiological (AQCD for Lead, Sections 4.3.1.3 and 8.3.2) and toxicological studies of lead 

health effects and dose-response relationships (AQCD for Lead, Chapter 5). The U.S. CDC, and 

its predecessor agencies, has for many years used blood lead level as a metric for identifying 

children at risk of adverse health effects and for specifying particular public health 

recommendations.71 Most recently, in 2005, with consideration of a review of the evidence by

their advisory committee, CDC revised their statement on Preventing Lead Poisoning in Young 

Children.72 CDC specifically recognized the evidence of adverse health effects in children with 

 

70 Additionally, lead freely crosses the placenta resulting in continued fetal exposure throughout pregnancy, with 

that exposure increasing during the latter half of pregnancy (AQC for Lead, Section 6.6.2).

71 Centers for Disease Control (1991) Preventing lead poisoning in young children: a statement by the Centers for 

Disease Control. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service; October 1. 

Available online at: http://wonder.cdc.gov/wonder/prevguid/p0000029/p0000029.asp

72 Centers for Disease Control and Prevention (2005) Preventing lead poisoning in young children: a statement by 

the Centers for Disease Control and Prevention. Atlanta, GA: U.S. Department of Health and Human Services, 

Public Health Service. August.
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blood lead levels below 10 μg/dL,73 the data demonstrating that no “safe” threshold for blood 

lead had been identified, and emphasized the importance of preventative measures.74 

Since 1976, the CDC has been monitoring blood lead levels in multiple age 

groups nationally through the National Health and Nutrition Examination Survey

(NHANES).75 The NHANES information has documented the dramatic decline in mean 

blood lead levels in the U.S. population that has occurred since the 1970s and that 

coincides with regulations regarding leaded motor vehicle fuels, leaded paint, and leadcontaining plumbing materials that have reduced lead exposure among the general 

population (AQCD for Lead, Sections 4.3.1.3 and 8.3.3). 

While blood lead levels in the U.S. general population, including geometric mean levels 

in children aged 1-5 have declined significantly, levels have been found to vary among children 

of different socioeconomic status (SES) and other demographic characteristics (AQCD for Lead, 

p. 4-21), as well as by age.76 Racial/ethnic and income disparities in blood lead levels in children 

persist. For example, blood lead levels for lower income and African American children are 

higher than those for the general population. 

 

73 As described by the Advisory Committee on Childhood Lead Poisoning Prevention, “In 1991, CDC defined the 

blood lead level (BLL) that should prompt public health actions as 10 μg/dL. Concurrently, CDC also recognized 

that a BLL of 10 μg/dL did not define a threshold for the harmful effects of lead. Research conducted since 1991 

has strengthened the evidence that children’s physical and mental development can be affected at BLLS <10 μg/dL” 

(ACCLPP, 2007).

74 Advisory Committee on Childhood Lead Poisoning Prevention (2007) Interpreting and managing blood lead 

levels <10 μg/dL in children and reducing childhood exposures to lead: Recommendations of CDC’s Advisory 

Committee on Childhood Lead Poisoning Prevention. Morbidity and Mortality Weekly Report. 56(RR-8). 

November 2, 2007.

75 This information documents a variation in mean blood lead levels across the various age groups monitored. For 

example, mean blood lead levels in 2001-2002 for ages 1-5, 6-11, 12-19 and greater than or equal to 20 years of age, 

are 1.70, 1.25, 0.94, and 1.56 μg/dL, respectively (AQC for Lead, p. 4-22).

76 Axelrad, D., U.S. EPA (November 4, 2009) E-mail message to Marion Hoyer, U.S. EPA. Available in docket 

number EPA-HQ-OAR-2007-0294.
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The spectrum of health effects discussed in the following section is relevant for all forms 

of lead that enter the blood stream. Once in the blood stream, lead bioaccumulates in the body, 

with the bone serving as a large, long-term storage compartment. Soft tissues (e.g., kidney, liver, 

brain, etc.) serve as smaller compartments, in which lead may be more mobile (AQCD for Lead, 

Sections 4.3.1.4 and 8.3.1). During childhood development, bone represents approximately 70% 

of a child’s body burden of lead, and this accumulation continues through adulthood, when more 

than 90% of the total lead body burden is stored in the bone (AQCD for Lead, Section 4.2.2). 

Lead in bone can be mobilized during critical periods including pregnancy and lactation (AQCD 

for Lead, Section 5.8.6).

2. Health Effects 

Lead, as with mercury and arsenic, has no known biological function.77 Lead has been 

demonstrated to exert “a broad array of deleterious effects on multiple organ systems via widely 

diverse mechanisms of action” (AQCD for Lead, p. 8-24 and Section 8.4.1). This array of health 

effects includes effects on heme biosynthesis and related functions; neurological development 

and function; reproduction and physical development; kidney function; cardiovascular function; 

and immune function. The weight of evidence varies across this array of effects and is 

comprehensively described in the AQCD for Lead. There is also some evidence of lead 

carcinogenicity, primarily from animal studies, together with limited human evidence of 

suggestive associations (AQCD for Lead, Sections 5.6.2, 6.7, and 8.4.10). The U.S. EPA has 

listed lead under current EPA guidelines as a probable human carcinogen based on the available 

 

77 U.S. Environmental Protection Agency (2007) Framework for Metals Risk Assessment. Office of the Science 

Advisor. EPA 120/R-07/001. 
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animal data (AQCD for Lead, p. 6-195).78 Inorganic lead has been classified as a probable 

human carcinogen by the International Agency for Research on Cancer (inorganic lead 

compounds), based mainly on sufficient animal evidence,79 and classified as reasonably 

anticipated to be a human carcinogen by the U.S. National Toxicology Program (lead and lead 

compounds) (AQCD for Lead, Section 6.7.2).80,81

As described in the AQCD for Lead, the key effects associated with individual blood lead 

levels in children and adults in the range of 10 μg/dL and lower include neurological, 

hematological and immune82 effects for children, and hematological, cardiovascular and renal 

effects for adults (AQCD for Lead, Tables 8-5 and 8-6, pp. 8-60 to 8-62). As evident from the 

discussions in Chapters 5, 6 and 8 of the AQCD for Lead, “neurotoxic effects in children and 

cardiovascular effects in adults are among those best substantiated as occurring at blood lead 

concentrations as low as 5 to 10 μg/dL (or possibly lower); and these categories are currently

clearly of greatest public health concern” (AQCD for Lead, p. 8-60).83, 84 The AQCD for Lead 

 

78 U.S. Environmental Protection Agency, Integrated Risk Information System (IRIS) (1993) IRIS Summary for 

Lead and compounds (CASRN 7439-92-1), Available online at: http://www.epa.gov/ncea/iris/subst/0277.htm.

79 International Agency for Research on Cancer (IARC) (2006) Inorganic and organic lead compounds. Lyon, 

France: International Agency for Research on Cancer. IARC monographs on the evaluation of the carcinogenic

risk of chemicals to humans: volume 87. Available online at: 

http://monographs.iarc.fr/ENG/Monographs/vol87/index.php.

80 National Toxicology Program (2003) Report on carcinogens background document for lead and lead compounds.

Research Triangle Park, NC: U.S. Department of Health and Human Services. Available online at:

http://ntp.niehs.nih.gov/ntp/newhomeroc/roc11/Lead-Public.pdf 

81 National Toxicology Program. (2004) Lead (CAS no. 7439-92-1) and lead compounds. In: Report on carcinogens,

eleventh edition. Research Triangle Park, NC: U.S. Department of Health and Human Services. Available online at:

http://ntp.niehs.nih.gov/ntp/roc/eleventh/profiles/s101lead.pdf.

82 At mean blood lead levels, in children, on the order of 10 μg/dL, and somewhat lower, associations have been 

found with effects to the immune system, including altered macrophage activation, increased IgE levels and 

associated increased risk for autoimmunity and asthma (AQC for Lead, Sections 5.9, 6.8, and 8.4.6).

83 With regard to blood lead levels in individual children associated with particular neurological effects, the AQC for 

Lead states “Collectively, the prospective cohort and cross-sectional studies offer evidence that exposure to lead 

affects the intellectual attainment of preschool and school age children at blood lead levels <10 μg/dL (most clearly 

in the 5 to 10 μg/dL range, but, less definitively, possibly lower).” (p. 6-269)

84 Epidemiological studies have consistently demonstrated associations between lead exposure and enhanced risk of 

deleterious cardiovascular outcomes, including increased blood pressure and incidence of hypertension. A metaanalysis of numerous studies estimates that a doubling of blood-lead level (e.g., from 5 to 10 μg/dL) is associated 
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states, “There is no level of lead exposure that can yet be identified, with confidence, as clearly 

not being associated with some risk of deleterious health effects” (AQCD for Lead, p. 8-63). 

While adults are susceptible to lead effects at lower blood lead levels than previously

understood (e.g., AQCD for Lead, p. 8-25), among the wide variety of health endpoints 

associated with lead exposures, there is general consensus that the developing nervous system in 

children is among the, if not the, most sensitive. Blood lead levels in U.S. children have 

decreased notably since the late 1970s. Studies evaluating current blood lead levels in children 

have reported associations with neurodevelopment effects (AQCD for Lead, Chapter 6). 

Functional manifestations of lead neurotoxicity during childhood include sensory, motor, 

cognitive and behavioral impacts. Numerous epidemiological studies have reported 

neurocognitive, neurobehavioral, sensory, and motor function effects in children with blood lead 

levels below 10 μg/dL (AQCD Lead, Sections 6.2 and 8.4). 

Cognitive effects associated with lead exposures that have been observed in 

epidemiological studies have included decrements in intelligence test results, such as the widely 

used IQ score, and in academic achievement as assessed by various standardized tests as well as 

by class ranking and graduation rates (AQCD for Lead, Section 6.2.16 and pp 8-29 to 8-30). As 

noted in the AQCD for Lead with regard to the latter, “Associations between lead exposure and 

academic achievement observed in the above-noted studies were significant even after adjusting 

for IQ, suggesting that lead-sensitive neuropsychological processing and learning factors not 

reflected by global intelligence indices might contribute to reduced performance on academic 

tasks” (AQCD for Lead, pp 8-29 to 8-30). 

 

with ~1.0 mm Hg increase in systolic blood pressure and ~0.6 mm Hg increase in diastolic pressure (AQC for Lead, 

p. E-10). 
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With regard to potential implications of lead effects on IQ, the AQCD for Lead 

recognizes the “critical” distinction between population and individual risk, identifying issues 

regarding declines in IQ for an individual and for the population. The AQCD for Lead further 

states that a “point estimate indicating a modest mean change on a health index at the individual 

level can have substantial implications at the population level” (AQCD for Lead, p. 8-77).85 A 

downward shift in the mean IQ value is associated with both substantial decreases in percentages 

achieving very high scores and substantial increases in the percentage of individuals achieving 

very low scores (AQCD for Lead, p. 8-81).86 For an individual functioning in the low IQ range 

due to the influence of developmental risk factors other than lead, a lead-associated IQ decline of 

several points might be sufficient to drop that individual into the range associated with increased 

risk of educational, vocational, and social failure (AQCD for Lead, p. 8-77).

Other cognitive effects observed in studies of children have included decrements in

attention, executive functions, language, memory, learning and visuospatial processing (AQCD 

for Lead, Sections 5.3.5, 6.2.5 and 8.4.2.1), with attention and executive function effects 

associated with lead exposures indexed by blood lead levels below 10 μg/dL (AQCD for Lead, 

Section 6.2.5 and pp. 8-30 to 8-31). The evidence for the role of lead in this suite of effects 

includes experimental animal findings (discussed in the AQCD for Lead, Section 8.4.2.1; p. 8-

 

85 As an example, the AQC for Lead states “although an increase of a few mmHg in blood pressure might not be of 

concern for an individual’s well-being, the same increase in the population mean might be associated with 

substantial increases in the percentages of individuals with values that are sufficiently extreme that they exceed the 

criteria used to diagnose hypertension” (AQC for Lead, p. 8-77).

86 For example, for a population mean IQ of 100 (and standard deviation of 15), 2.3% of the population would score 

above 130, but a shift of the population to a mean of 95 results in only 0.99% of the population scoring above 130 

(AQC for Lead, pp. 8-81 to 8-82).
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31), which provide strong biological plausibility of lead effects on learning ability, memory and 

attention (AQCD for Lead, Section 5.3.5), as well as associated mechanistic findings. 

The persistence of such lead-induced effects is described in the AQCD for Lead (e.g., 

AQCD for Lead Sections 5.3.5, 6.2.11, and 8.5.2). The persistence or irreversibility of such 

effects can be the result of damage occurring without adequate repair offsets or of the persistence 

of lead in the body (AQCD for Lead, Section 8.5.2). It is additionally important to note that 

there may be long-term consequences of such deficits over a lifetime. Poor academic skills and 

achievement can have “enduring and important effects on objective parameters of success in real 

life,” as well as increased risk of antisocial and delinquent behavior (AQCD for Lead, Section 

6.2.16). 

The current evidence reviewed in the AQCD for Lead with regard to the quantitative 

relationship between neurocognitive decrement, such as IQ, and blood lead levels indicates that 

the slope for lead effects on IQ is nonlinear and is steeper at lower blood lead levels, such that 

each μg/dL increase in blood lead may have a greater effect on IQ at lower blood lead levels 

(e.g., below 10 μg/dL) than at higher levels (AQCD for Lead, Section 6.2.13; pp. 8-63 to 8-64; 

Figure 8-7). As noted in the AQCD for Lead, a number of examples of non- or supralinear doseresponse relationships exist in toxicology (AQCD for Lead, pp. 6-76 and 8-38 to 8-39). With 

regard to the effects of lead on neurodevelopmental outcomes such as IQ, the AQCD for Lead 

suggests that initial neurodevelopmental effects at lower lead levels may be disrupting very

different biological mechanisms (e.g., early developmental processes in the central nervous 

system) than more severe effects of high exposures that result in symptomatic lead poisoning and 

frank mental retardation (AQCD for Lead, p. 6-76). The AQCD for Lead describes this issue in 
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detail with regard to lead (summarized in AQCD for Lead at p. 8-39). Various findings within 

the toxicological evidence, presented in the AQCD for Lead, provide biologic plausibility for a 

steeper IQ loss at low blood lead levels, with a potential explanation being that the predominant 

mechanism at very low blood lead levels is rapidly saturated and that a different, less-rapidlysaturated process becomes predominant at blood lead levels greater than 10 μg/dL.

3. At-Risk Populations and Life Stages

Individuals potentially at risk from exposure to environmental pollutants include those 

with increased susceptibility and vulnerability. The terms "susceptibility" and "vulnerability" 

have been used to characterize those with a greater likelihood of an adverse outcome given a 

specific exposure in comparison with the general population. This increased likelihood of 

response to a pollutant can result from a multitude of factors, including genetic or developmental 

factors, life stages (i.e., childhood or old age), gender differences, or preexisting disease states. 

In addition, new attention has been paid to the concept of some population groups having 

increased responses to pollution-related effects due to factors including socioeconomic status 

(SES) (e.g., reduced access to health care, poor nutritional status) or particularly elevated 

exposure levels. 

EPA uses the term "life stage" to refer to a distinguishable time frame in an individual's 

life characterized by unique and relatively stable behavioral and/or physiological characteristics 

that are associated with development and growth. To recognize the rapid changes that occur 

during childhood related to physiology, metabolism, anatomy and behavior that can impact 

exposure and risk to environmental hazards, EPA now views childhood as a sequence of life 
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stages, from conception through fetal development, infancy, and adolescence. EPA published 

several exposure and risk assessment guidance documents beginning in 2005,87 88 89 in which we 

emphasized the importance of considering the potential for increased sensitivity of different life 

stages or age groups in addition to that of groups that form a fixed portion of the population 

based on characteristics such as pre-existing disease, gender, socioeconomic status, geographical 

location, culture/ethnicity, or genetic make-up.

Physiological, behavioral and demographic factors contribute to increased risk of leadrelated health effects. Children are at increased risk of lead-related health effects due to various 

factors that enhance their exposures (e.g., via the hand-to-mouth activity that is prevalent in very

young children, AQCD for Lead, Section 4.4.3) and susceptibility. While children are 

considered to be at a period of maximum exposure around 18-27 months, the current evidence 

has found even stronger associations between blood lead levels at school age and IQ at school 

age. The evidence “supports the idea that lead exposure continues to be toxic to children as they

reach school age, and [does] not lend support to the interpretation that all the damage is done by 

the time the child reaches 2 to 3 years of age” (AQCD for Lead, Section 6.2.12). Physiological 

factors that can affect risk of lead-related effects in children include genetic polymorphisms and 

nutritional status. Children with particular genetic polymorphisms (e.g., presence of the δaminolevulinic acid dehydratase-2 [ALAD-2] allele) have increased sensitivity to lead toxicity, 

which may be due to increased susceptibility to the same internal dose and/or to increased 

internal dose associated with the same exposure (AQCD for Lead, p. 8-71, Sections 6.3.5, 6.4.7.3 

 

87 US EPA (2005) Guidance on Selecting Age Groups for Monitoring and Assessing Childhood Exposure to 

Environmental Contaminants. EPA/630/P-03/003F.

88 US EPA (2006) A Framework for Assessing Health Risks of Environmental Exposures to Children. EPA/600/R05/093A.

89 US EPA (2008) Child-Specific Exposure Factors Handbook. EPA/600/R-06/096F.
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and 6.3.6). Some children may have blood lead levels higher than those otherwise associated 

with a given lead exposure (AQCD for Lead, Section 8.5.3) as a result of nutritional status (e.g., 

iron deficiency, calcium intake), as well as genetic and other factors (AQCD for Lead, Chapter 4 

and Sections 3.4, 5.3.7 and 8.5.3). 

Demographic factors that can affect risk of lead-related effects in children include 

residential location, poverty, and race. As noted in previous EPA actions on lead, situations of 

elevated exposure, such as residing near sources of ambient lead, as well as socioeconomic 

factors, such as reduced access to health care or low socioeconomic status can also contribute to 

increased blood lead levels and increased risk of associated health effects from air-related lead.90 

Additionally, as described in the NAAQS for Lead, children in poverty and black, non-Hispanic 

children have notably higher blood lead levels than do economically well-off children and white 

children, in general.91 

C. Welfare Effects

Lead is persistent in the environment and accumulates in soils, aquatic systems (including 

sediments), and some biological tissues of plants, animals and other organisms, thereby 

providing long-term, multi-pathway exposures to organisms and ecosystems. In 2008, EPA 

established a secondary lead standard of 0.15 ug/m3. This standard is intended to protect the 

public welfare from known or anticipated adverse effects associated with the presence of lead in 

 

90 U.S. Environmental Protection Agency (2007) Review of the National Ambient Air Quality Standards for Lead: 

Policy Assessment of Scientific and Technical Information, OAQPS Staff Paper. EPA-452/R-07-013. Office of Air 

Quality Planning and Standards, Research Triangle Park.

91 See 73 FR 66973 (November 12, 2008).
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the ambient air. This section provides a summary of information regarding welfare effects of 

lead, focusing on terrestrial and aquatic ecosystems. This information is largely drawn from the 

2006 AQCD for Lead, Chapter 6 of the Office of Air Quality Planning and Standards Staff Paper 

on Lead (SP)92 and the Lead NAAQS. 

1. Terrestrial Ecosystems 

Lead is removed from the atmosphere and deposited on soil and other surfaces via wet or 

dry deposition. In soils, most lead is retained via the formation of stable solid phase compounds, 

precipitates, or complexes with organic matter. Thus, terrestrial ecosystems remain primarily 

sinks for lead but amounts retained in various soil layers vary based on forest type, climate, and 

litter cycling (AQCD for Lead, Section 7.1). Once in the soil, the migration and distribution of 

lead is controlled by a multitude of factors including pH, precipitation, litter composition and 

other factors, which in turn, govern the rate at which lead is bound to organic materials in the soil 

(AQCD for Lead, Section 2.3.5, and Section AX 7.1.4.1). 

Lead exists in the environment in different forms which vary widely in their ability to 

cause adverse effects on ecosystems and organisms. Many forms of lead in the ambient air are 

quite insoluble and thus not easily leached to underground water once deposited to surfaces. 

However, leaching may occur under acidic conditions, where lead concentrations are extremely 

high, or in the presence of substances (e.g., soluble organic matter, high concentrations of 

 

92 U.S. Environmental Protection Agency (2007) Review of the National Ambient Air Quality Standards for Lead: 

Policy Assessment of Scientific and Technical Information, OAQPS Staff Paper. EPA-452/R-07-013. Office of Air 

Quality Planning and Standards, Research Triangle Park.
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chlorides or sulfates) that form relatively soluble complexes with lead (AQCD for Lead, Section 

2.3.5).

Plants take up lead via their foliage and through their root systems. The rate of plant 

uptake from soil varies by plant species, soil conditions, and lead species. Most lead in plants is 

stored in roots, and very little is stored in fruits. Metals that are applied to soil as salts (usually

as sulfate, chloride, or nitrate salt) are accumulated more readily than the same quantity of metal 

added via sewage sludge, flue dust, or fly ash (AQCD for Lead, Section 2.3.7). 

Surface deposition of lead onto plants may represent a significant contribution to the total 

lead in and on the plant, as has been observed for plants near smelters and along roadsides 

(AQCD for Lead, page E-19). Atmospheric deposition of lead also contributes to lead in 

vegetation as a result of contact with above-ground portions of the plant (AQCD for Lead, pp. 7–

9 and AXZ7–39; USEPA, 1986, Sections 6.5.3 and 7.2.2.2.1). Wildlife may subsequently be 

exposed to lead in vegetation (e.g., grasses and silage) and in surface soils via incidental 

ingestion of soil while grazing (USEPA 1986, Section 7.2.2.2.2).93

By far, the majority of air-related lead found in natural terrestrial ecosystems was 

deposited in the past during the use of lead additives in motor vehicle gasoline. Many sites 

receiving lead predominantly through long-range transport of gasoline-derived small particles 

have accumulated large amounts of lead in soils (AQCD for Lead, p. AX7-98). There is little 

evidence that terrestrial sites exposed as a result of this long range transport of lead have 

 

93 U.S. Environmental Protection Agency (1986) Air quality Criteria for Lead. Research Triangle Park, NC: Office 

of Health and Environmental Assessment, Environmental Criteria and Assessment Office; EPA report no. EPA600/8-83/028aF-dF. 4v. Available from: NTIS, Springfield, VA; PB87-142378.
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experienced significant effects on ecosystem structure or function (AQCD for Lead, Section 

AX7.1.4.2 and p. AX7-98). Strong complexation of lead by organic matter in soil may explain 

why few ecological effects have been observed (AQCD for Lead, p. AX7-98). Studies have 

shown decreasing levels of lead in vegetation, which appears to correlate with decreases in 

atmospheric deposition of lead resulting from the removal of lead additives to motor vehicle 

gasoline (AQCD for Lead, Section AX 7.1.4.2).

The deposition of gasoline-derived lead into forest soils has produced a legacy of slow 

moving lead that remains bound to organic materials despite dramatic reductions in the use of 

leaded additives to motor vehicle fuels. Current levels of lead in soil vary widely depending on 

the source of lead but in all ecosystems lead concentrations exceed natural background levels. 

For areas influenced by point sources of air lead, concentrations of lead in soil may exceed by 

many orders of magnitude the concentrations which are considered harmful to laboratory

organisms. Adverse effects in terrestrial organisms associated with lead include neurological, 

physiological and behavioral effects which may influence ecosystem structure and functioning 

(73 FR 67008).

2. Aquatic Ecosystems

Atmospheric lead enters aquatic ecosystems primarily through deposition (wet and dry) 

and the erosion and runoff of soils containing lead. While overall deposition rates of 

atmospheric lead have decreased dramatically since the removal of lead additives from motor 

vehicle gasoline, lead continues to accumulate and may be re-exposed in sediments and water 

bodies throughout the United States (AQCD for Lead, Section 2.3.6).
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Several physical and chemical factors govern the fate and bioavailability of lead in 

aquatic systems. A significant portion of lead remains bound to suspended particulate matter in 

the water column and eventually settles into the substrate. Species, pH, salinity, temperature, 

turbulence and other factors govern the bioavailability of lead in surface waters (AQCD for 

Lead, Section 7.2.2). Lead can bioaccumulate in the tissues of aquatic organisms through 

ingestion of food and water, and adsorption from water, and can subsequently lead to adverse 

effects if tissue levels are sufficiently high.94 The accumulation of lead is influenced by pH and 

decreasing pH favors bioavailability and bioaccumulation. Organisms that bioaccumulate lead 

with little excretion must partition the metal such that it has limited bioavailability, otherwise 

toxicity will occur if a sufficiently high concentration is reached.95 The general symptoms of 

lead toxicity in fish include production of excess mucus, lordosis, anemia, darkening of the 

dorsal tail region, degeneration of the caudal fin, destruction of spinal neurons, aminolevulinic 

acid dehydratase (ALAD) inhibition, growth inhibition, renal pathology, reproductive effects, 

growth inhibition, and mortality.

96

 Toxicity in fish has been closely correlated with duration of 

lead exposure and uptake.97

Lead exists in the aquatic environment in various forms and under various chemical and 

physical parameters which determine the ability of lead to cause adverse effects either from 

dissolved lead in the water column or lead in sediment. Current levels of lead in water and 

sediment vary widely depending on the source of lead. Conditions exist in which adverse effects 

to organisms and thereby ecosystems may be anticipated given experimental results. It is 

 

94 AQC for Lead I. 7-24: (Vink, 2002; Rainbow, 1996).

95 AQC for Lead AX7.2.3.1

96 AQC for Lead page 232, Annex 7

97 AQC for Lead page 232, Annex 7
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unlikely that dissolved lead in surface water constitutes a threat to ecosystems that are not 

directly influenced by point sources. For lead in sediment, the evidence regarding the effects is 

less clear. It is likely that some areas with long-term historical deposition of lead to sediment 

from a variety of sources as well as areas influenced by point sources have the potential for 

adverse effects to aquatic communities. The long residence time of lead in sediment and its 

ability to be resuspended by turbulence make lead likely to be a factor for consideration 

regarding potential risk to aquatic systems for the foreseeable future (73 FR 67008). 

III. Lead Emissions from Piston-Engine Aircraft

Currently, lead emitted by piston-engine aircraft operating on leaded avgas is the largest 

source of lead to the air, contributing about 50% of the National Emission Inventory in 2005. 

This section describes the draft 2008 avgas lead inventory which is currently undergoing review 

by state, local and tribal air agencies. We describe and request comment on input data used to 

derive airport-specific lead inventories. This section ends with a summary of data forecasting 

the potential growth of the industry using leaded avgas.

A. Inventory of Lead from Piston-Engine Powered Aircraft 

Every three years, the EPA prepares a National Emissions Inventory (NEI) of air 

emissions of criteria pollutants and hazardous air pollutants with input from numerous state, 

local, and tribal air agencies and from industry.

98

 For the purposes of this ANPR, EPA is 

 

98 http://www.epa.gov/air/data/neidb.html
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describing piston-engine aircraft lead information provided in the draft 2008 NEI as well as 

information from the final 2005 NEI. We have chosen to describe the draft 2008 NEI for the 

following reasons: 1) this is the first version of the NEI that will include airport-specific lead 

inventories that use our most recently developed methods for estimating lead (described below); 

2) this inventory is the first NEI to include approximately 20,000 airport facilities in the U.S.; 

and 3) to increase awareness of the opportunity for state, local, and tribal governments and 

industry to review this draft NEI and provide information that could improve airport lead 

inventories. Comments and data can be supplied to EPA for the 2008 NEI until mid-2010. 

While we are describing the draft 2008 NEI for piston-engine aircraft emissions of lead, we do 

not have draft inventory estimates for 2008 for all sources of lead. The 2008 NEI will be final in 

2010. 

1. National Emissions of Lead from Piston-Engine Aircraft

To calculate the national avgas lead inventory, the volume of leaded avgas produced in a 

given year is multiplied by the concentration of lead in the avgas and by the fraction of lead 

emitted from a combustion system operating on leaded fuel (to account for the lead that is 

retained in the engine, engine oil and/or exhaust system). For example, the volume of avgas 

produced in the U.S. in 2008 according to DOE was 235,326,000 gallons.99 The concentration of 

lead in avgas ([Pb] in the equation below) can be one of four levels (ranging from 0.14 to 1.12 

grams of lead per liter or 0.53 to 4.24 grams of lead per gallon) as specified by the American 

Society for Testing and Materials (ASTM). By far the most common avgas supplied is “100 

Low Lead” or 100LL which has a maximum lead concentration specified by ASTM of 0.56 

 

99 DOE Energy Information Administration. Fuel production volume data obtained from 

http://tonto.eia.doe.gov/dnav/pet/hist/mgaupus1A.htm accessed November 2006.
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grams per liter or 2.12 grams per gallon.100, 101 A fraction of lead is retained in the engine, 

engine oil and/or exhaust system which we currently estimate at 5%.102 

For 2008, using DOE fuel volume estimates, the national estimate of lead emissions from 

the consumption of avgas is 522 tons as calculated according to the following equation: 

(235,326,000 gal)(2.12 g Pb/gal)(0.95) = 522 short tons Pb

 907,185 g/short ton

As described in the Overview section of this ANPR, DOT’s FAA also provides estimates 

of annual avgas fuel consumption. For 2008, DOT estimates 351,000,000 gallons of avgas were 

consumed. Consumption of this volume of avgas equates to a national lead emissions estimate 

for this source of 779 short tons. DOT fuel volume data are derived from FAA estimates of 

piston-engine activity annually.

103

 We are working to identify the source(s) of the information 

used to derive DOE fuel volume estimates. In the draft 2008 NEI, we are using DOT fuel 

volume estimates. 

We currently cannot estimate the fraction of total lead emissions these estimates comprise 

since the inventories for all other sources of lead to air are not yet in the draft 2008 NEI. In 

 

100 ChevronTexaco (2006) Aviation Fuels Technical Review. FTR-3. Available online at: 

http://www.chevronglobalaviation.com/docs/aviation_tech_review.pdf

101 ASTM International (2005) Annual Book of ASTM Standards Section 5: Petroleum Products, Lubricants, and 

Fossil Fuels Volume 05.01 Petroleum Products and Lubricants (I): D 56 – D 3230.

102 U.S. Environmental Protection Agency (2008) Lead Emissions from the Use of Leaded Aviation Gasoline in the 

United States, Technical Support Document. EPA420-R-08-020. Available online at: 

www.epa.gov/otaq/aviation.htm.

103 U.S. Department of Transportation Federal Aviation Administration Aviation Policy and Plans. FAA Aerospace 

Forecast Fiscal Years 2009-2025. p.81. Available at: 

http://www.faa.gov/data_research/aviation/aerospace_forecasts/2009-2025/media/2009%20Forecast%20Doc.pdf 

This document provides historical data for 2000-2008 as well as forecast data.
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2005, lead from avgas comprised about 50% of the national lead inventory for emissions to air. 

As point source emissions of lead have decreased, lead emissions from piston-engine aircraft 

have become the largest single source of lead to air (Figure 2). These lead emissions estimates 

do not include evaporative losses of lead and minimal military aircraft data. Few military

aircraft are piston-engine powered and consume leaded avgas.104 Military aircraft data are 

supplied by states, and data provided to EPA during the 2008 NEI review will be included in the 

final 2008 inventory.

0

100

200

300

400

500

600

700

800

1999 2002 2005 2008

Year

Tons of Lead from Avgas

0%

10%

20%

30%

40%

50%

60%

% Contribution of Avgas to 

Total Lead

Tons of Lead from Avgas % C ontribution of Avgas to Total Lead

Figure 2. The Increasing Contribution of Lead from Aviation Gasoline to the Total Inventory of 

Lead Emissions to Air Annually (the total lead inventory for 2008 will be available in 2010).

 

104 ChevronTexaco (2006) Aviation Fuels Technical Review p. 44. Available online at: 

http://www.chevronglobalaviation.com/docs/aviation_tech_review.pdf. 
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Fuel volume data is from DOE’s Energy Information Administration.

2. Airport-Specific Emissions of Lead from Piston-Engine Aircraft

Aircraft gaseous and particulate matter (PM) emissions are calculated through the FAA’s 

Emissions and Dispersion Modeling System (EDMS).105 This modeling system was designed to 

develop emission inventories for the purpose of assessing potential air quality impacts of airport 

operations and proposed airport development projects. Lead emissions from piston-engine 

aircraft are not included in EDMS. To estimate airport-specific lead inventories we use engine 

data and other attributes of general aviation (GA) and air taxi (AT) that are used in EDMS for 

GA and AT and we use methods similar to those in EDMS that are described in an EPA 

Technical Support Document (TSD) and briefly summarized here.106 The data required to 

estimate airport-specific lead inventories includes the landing and take-off (LTO) activity of 

piston-engine aircraft at a facility; fuel consumption rates by these aircraft during the various 

modes of the landing and take-off cycle; the time spent in each mode of the LTO (taxi/idle-out, 

takeoff, climb-out, approach, and taxi/idle-in); the concentration of lead in the fuel; and the 

retention of lead in the engine and oil. The equation used to calculate airport-specific lead 

emissions during the LTO cycle is below, followed by a description of each of the input 

parameters.

LTO Pb (tons) = (piston-engine LTO)(avgas gal/LTO)([Pb])(1-Pb retention)

 

105 EDMS is available online at: 

http://www.faa.gov/about/office_org/headquarters_offices/aep/models/edms_model/

106 U.S. Environmental Protection Agency (2008) Lead Emissions from the Use of Leaded Aviation Gasoline in the 

United States, Technical Support Document. EPA420-R-08-020. Available online at: 

www.epa.gov/otaq/aviation.htm.
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907,185 g/short ton

Piston-engine LTO: Most piston-engine aircraft fall into the categories of either GA or 

AT. Some GA and AT activity is conducted by turboprop and turbojet aircraft which do not use 

leaded avgas. There are no national databases that provide airport-specific LTO activity data for 

piston-engine aircraft separately from turbojet and turboprop aircraft. The fraction of GA and

AT aircraft that use piston engines will vary by airport. However, in the absence of airportspecific data, EPA calculated a national default estimate using FAA’s GA and AT Activity

(GAATA) Survey.

107

 The 2005 GAATA Survey reports that approximately 72% of all GA and 

AT LTOs are from piston-engine aircraft which use avgas, and about 28% are turboprop and 

turbojet powered which use jet fuel, such as Jet A.108 Lead is not added to jet fuel. Therefore, to 

calculate piston-engine aircraft LTO as input for this equation, the total GA plus AT LTOs are 

multiplied by 0.72.

Avgas use (gal/LTO): Piston-engine aircraft can have either one or two engines. EDMS 

version 5.0.2 contains information on the amount of avgas used per LTO for some single and 

twin-engine aircraft. The proportion of piston-engine LTOs conducted by single- versus twinengine aircraft was taken from the FAA’s GAATA Survey for 2005 (90% of LTOs are 

conducted by aircraft having one engine and 10% of LTOs by aircraft having two engines). 

Since twin-engine aircraft have higher fuel consumption rates than those with single engines, a 

weighted average LTO fuel usage rate was established to apply to the population of piston-

 

107 The FAA GAATA is a database collected from surveys of pilots flying aircraft used for general aviation and air 

taxi activity. For more information on the GAATA, see Appendix A, online at:

http://www.faa.gov/data_statistics/aviation_data_statistics/general_aviation/

108 There are about 194,000 piston-engine aircraft in the U.S. general aviation and air taxi fleet (175,000 singleengine and 19,000 twin-engine aircraft) according to FAA’s 2005 GAATA Survey.
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engine aircraft as a whole. For the single-engine aircraft, the average amount of fuel consumed 

per LTO was determined from the six types of single piston-engine aircraft within EDMS.109 

This was accomplished by averaging the single-engine EDMS outputs for fuel consumed per 

LTO using the EDMS scenario property of ICAO/USEPA Default - Times in Mode (TIM), with 

a 16 minute taxi-in/taxi-out time according to EPA’s Procedures for Emission Inventory 

Preparation, Volume IV: Mobile Sources, 1992.110 This gives a value of 16.96 pounds of fuel 

per LTO (lbs/LTO). Next, the average single-engine consumption rate was divided by the 

average density of 100LL avgas, 6 pounds per gallon (lbs/gal), producing an average fuel usage 

for single-engine piston aircraft of 2.83 gallons per LTO (gal/LTO). This same calculation was 

performed for the two twin-engine piston aircraft within EDMS, producing an average LTO fuel 

usage rate for twin-engine piston aircraft of 9.12 gal/LTO. 

Using these single- and twin-engine piston aircraft fuel consumption rates, a weighted 

average fuel usage rate per LTO was computed by multiplying the average fuel usage rate for 

single-engine aircraft (2.83 gal/LTO) by the fleet percentage of single-engine aircraft LTOs 

(90%). Next, the twin-engine piston aircraft average fuel usage rate (9.12 gal/LTO) was 

multiplied by the fleet percentage of twin-engine aircraft LTOs (10%). By summing the results 

of the single- and twin-engine aircraft usage rates, the overall weighted average fuel usage rate 

per LTO of 3.46 gal/LTO is obtained.

Concentration of lead in fuel, [Pb]: The maximum lead concentration specified by 

ASTM for 100LL is 0.56 grams per liter or 2.12 grams per gallon. This amount of lead is 

 

109 EPA understands that EDMS 5.0.2 has a limited list of piston engines, but these are currently the best data 

available.

110 U.S. Environmental Protection Agency (1992) Procedures for Emission Inventory Preparation, Volume IV: 

Mobile Sources, EPA-450/4-81-026d (Revised).
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normally added to assure that the required lean and rich mixture knock values are achieved. As 

noted above, 100 Octane (containing 1.12 grams of lead per liter or 4.24 grams of lead per 

gallon) is used by a small number of piston-engine aircraft. We currently do not include 

estimates of lead emissions using 100 Octane and we are requesting comment on the airport 

facilities where 100 Octane is used and the LTO activity associated with the use of this fuel.

Retention of lead in engine and oil (1-Pb Retention): Recent data collected from aircraft 

piston engines operating on leaded avgas suggests that about 5% of the lead from the fuel is 

retained in the engine and engine oil.111 Thus the emitted fraction is 0.95. 

Multiplying the lead concentration in 100LL avgas by the weighted average fuel usage 

rate produces an overall average value of 7.34 grams of lead per LTO (g Pb/LTO) for piston 

engines: 3.46 gal/LTO x 2.12 g Pb/gal = 7.34 g Pb/LTO. The denominator is a unit conversion 

factor used to express the lead inventory in units of short tons.

Applying these parameters in the equation above yields the following equation:

Pb (tons) =(piston-engine LTO)(7.34 g Pb/LTO) (0.95)

907,185 g/short ton

which simplifies to: Pb = (piston-engine LTO) (7.7 X 10-6short tons) or 7 grams of lead per 

 

111 The information used to develop this estimate is from the following references: (a) Todd L. Petersen, Petersen 

Aviation, Inc, Aviation Oil Lead Content Analysis, Report Number EPA 1-2008, January 2, 2008, available at 

William J. Hughes Technical Center Technical Reference and Research Library at http://actlibrary.tc.faa.gov/ and 

(b) E-mail from Theo Rindlisbacher of Switzerland Federal Office of Civil Aviation to Bryan Manning of U.S. EPA, 

regarding lead retained in engine, September 28, 2007.
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LTO where piston-engine LTO = (GA LTO + AT LTO)(0.72). EPA used similar methods to 

estimate lead emissions from piston-engine powered helicopters which are described 

separately.

112

 We currently estimate there are 6 grams of lead emitted by piston-engine 

helicopters per LTO. 

Lead emitted during the LTO cycle is assigned to the airport facility where the aircraft 

operations occur.113 FAA’s Office of Air Traffic provides a complete listing of operational 

airport facilities in the National Airspace System Resources (NASR) database.114 In 2008, there 

were 19,896 airport facilities in the U.S., the vast majority of which are expected to have activity

by piston-engine aircraft that operate on leaded avgas. There are seven types of airport facilities: 

airports, balloonports, seaplane bases, gliderports, heliports, stolports,115 and ultralight facilities. 

Among these, balloonports are the only facilities not expected to have piston-engine aircraft 

activity. 

Preparing airport-specific lead inventories requires information regarding LTO activity. 

These activity data are reported to the FAA for only a small subset of the approximately 20,000 

facilities in the U.S. EPA obtains LTO information for approximately 3,400 facilities from 

FAA’s Terminal Area Forecast (TAF) database that is prepared by FAA’s Office of Aviation 

 

112 U.S. EPA (March 2010) Memorandum from Meredith Pedde to docket EPA-HQ-OAR-2007-0294, titled, 

“Calculating Aviation Gasoline Lead Emissions in the 2008 NEI.” pp.8-9.

113 An aircraft operation is defined as any landing or take-off event, therefore, to calculate LTOs, operations are 

divided by two. Most data sources from FAA report aircraft activity in numbers of operations which, for the 

purposes of calculating lead emissions using the method described in the TSD, need to be converted to LTO events.

114 An electronic report can be generated from the NASR database and is available for download from the internet at 

the following website. .http://www.faa.gov/airports_airtraffic/airports/airport_safety/airportdata_5010/ This 

database is updated every 56 days.

115 Stolport is an airport designed with STOL (Short Take-Off and Landing) operations in mind, normally having a 

short single runway.
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Policy and Plans.116 The TAF database currently includes information for airports in FAA’s 

National Plan of Integrated Airport Systems (NPIAS), which identifies airports that are 

significant to national air transportation. For airports not listed in the TAF, operations data are 

obtained from the NASR database, where available. Operations data provided by the NASR 

database may be self-reported by airport operators through data collection accomplished by

airport inspectors who work for the State Aviation Agency, or operations data can be obtained 

through other means.117 

We are using the January 15, 2009 version of the NASR database to evaluate airport lead 

emissions inventories for 2008. Using the TAF database as the primary source of LTO 

information and the NASR as a secondary source, we have LTO activity data for approximately

5,600 airport facilities. There are approximately 14,000 facilities in the NASR database for 

which there are no LTO activity data.118 We developed methods based on previous work 

conducted by the FAA to estimate LTO activity at the remaining airport and heliport facilities. 

We are requesting comment on these methods which are described here briefly. The details 

regarding the method described here are available in the docket.119 

The FAA has used regression models to estimate operations at facilities where operations 

data are not available.120, 121 In this work and other work, FAA identified characteristics of small 

 

116 http://aspm.faa.gov/main/taf.asp

117 In the absence of updated information from States, local authorities or Tribes, we are using the LTO data 

provided in the FAA database.

118 No Commuter, GA Itinerant, GA Local, or Air Taxi operations data.

119 U.S. EPA (March 2010) Memorandum from Meredith Pedde to docket EPA-HQ-OAR-2007-0294, titled, 

“Calculating Aviation Gasoline Lead Emissions in the 2008 NEI.”. 

120 Federal Aviation Administration, Office of Aviation Policy and Plans, Statistics and Forecast Branch. (July 

2001) Model for Estimating General Aviation Operations at Non-towered Airports Using Towered and Nontowered Airport Data. Prepared by GRA, Inc.
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towered airports for which there were statistically significant relationships with operations at 

these airports.122 Regression models based on the airport characteristics were then used to 

estimate general aviation operations for a set of non-towered airports. The airport characteristics 

identified by the FAA and used to estimate general aviation operations at small airports include: 

the number and type of aircraft based at the facility (i.e., ‘based aircraft’), population in the 

vicinity of the airport, airport regional prominence, per capita income, region of the country, and 

the presence of certificated flight schools. We were able to obtain data from the NASR and the 

U.S. Census Bureau to evaluate relationships between several airport characteristics and LTO 

activity. LTO estimates were derived using different models depending on data availability. 

The number of based aircraft and county population in which the airport is located were 

the most highly significant and positive regressors to LTO activity that our analysis provided.123 

The regression equation for based aircraft and county population is: LTOs = 1248 + 

203.04*Aircraft + 0.0019*County Population with an R2= 0.64. For approximately 7,800 

facilities that do not report LTO activity to FAA, we used based aircraft and county population to 

estimate activity. We request comment on the method we are using to estimate LTO activity at 

these airport facilities. 

To estimate LTO activity at the airport facilities that do not report based aircraft, we used 

a regression equation based on county population and region of the country. The regression 

equation using county population and regression of the country is: LTOs = 6200.2 + 

 

121 Hoekstra, M. (April, 2000) Model for Estimating General Aviation Operations at Non-Towered Airports.

Prepared for FAA Office of Aviation Policy and Plans.

122 GRA, Inc. “Review of TAF Methods,” Final Report, prepared for FAA Office of Aviation Policy and Plans under 

Work Order 45, Contract No. DTFA01-93-C-00066, February 25, 1998.

123 U.S. EPA (March 2010) Memorandum from Meredith Pedde to docket EPA-HQ-OAR-2007-0294, titled, 

“Calculating Aviation Gasoline Lead Emissions in the 2008 NEI.” .
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0.0087*county population – 175.07*West State – 5567.3*Alaska + 854.83*Northeast with an R2

= 0.15. This equation has a low correlation coefficient and we are exploring additional options 

for estimating LTO activity at these facilities for which very little information is reported to the 

FAA. We request comment on applying the regression equation above and alternative methods 

to estimate LTO activity at these facilities.

For heliports, which comprise approximately 5,500 facilities in the NASR database, we 

had insufficient information on which to develop a regression equation and are currently using 

the median of activity (141 LTOs/year) at heliports for which we have LTO activity data. 

Nationally, 25% of helicopters are piston-engine powered and therefore use leaded avgas. The 

FAA and EPA have limited information regarding the specific heliports that have activity by

piston-engine helicopters. We are requesting information regarding heliport facilities at which 

piston-engine powered aircraft operate and the activity of these aircraft.

The draft 2008 NEI is the first inventory for which we are implementing the use of LTObased lead estimates at almost 20,000 airport facilities and we are expecting state, local and tribal 

air agency review of these data to improve our current estimates. The specific information on 

which we are requesting data include: 1) the fraction of GA and AT LTO activity reported to 

FAA that is conducted by piston-engine versus jet-engine powered aircraft, 2) airport-specific 

LTO activity for single- versus twin-engine piston-powered aircraft, 3) fuel consumption rates 

for the piston-engine aircraft operating at each airport, 4) the time spent in each mode of 

operation including run-up checks conducted by piston-engine aircraft prior to take-off, and 5) 

the concentration of lead in fuel delivered to individual airports. Methods for providing 

information to EPA as part of the review process involved in finalizing the 2008 NEI are 
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available.124 

The discussion above pertains only to lead emissions during the LTO cycle. Lead 

emitted outside the LTO cycle occurs during aircraft cruise mode and portions of the climb-out 

and approach modes. This part of an aircraft operation emits lead at various altitudes as well as 

close to and away from airports. We are developing methods to estimate lead emissions outside 

the LTO cycle which we anticipate will be available in 2010. 

B. Projections for Future Growth

The FAA publishes an annual forecast of the number of piston-engine powered aircraft, 

hours flown, the consumption of avgas, the numbers of pilots and student pilots.125 The most 

recent forecast is for the years 2009 through 2025. The General Aviation Manufacturers 

Association (GAMA) reproduces the FAA forecast in their annual statistical databook.126 

According to the GAMA summary, the number of active single-engine piston-powered aircraft is 

projected to increase annually at a 0.5% growth rate, with the aircraft population increasing from 

144,220 in 2008 to 157,400 in 2025. The number of active twin-engine piston-powered aircraft 

is projected to decrease 0.9% annually, with aircraft population decreasing from 18,385 in 2008 

to 15,650 in 2025. The piston-powered helicopter population is expected to grow 4.7% annually

from a population of 3,970 in 2008 to 8,295 in 2025.

 

124 All documentation for use in preparing 2008 emission inventories can by found on the NEI/EIS Implementation

website: http://www.epa.gov/ttn/chief/net/neip/index.html.

125 FAA Aerospace Forecast Fiscal Years 2009–2025. Available online at:

http://www.faa.gov/data_research/aviation

126 General Aviation Manufacturers Association (2008) General Aviation Statistical Databook and Industry Outlook, 

pp.51-55. Available online at: 

http://www.gama.aero/files/2008_general_aviation_statistical_databook__indust_499b0dc37b.pdf
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The FAA forecast predicts the number of hours flown in single-engine piston-powered 

aircraft is projected to increase 0.5% yearly from 2008 to 2025); the number of hours flown in 

twin-engine piston-powered aircraft is projected to decrease 1.5% annually and the number of 

hours flown in piston-powered rotocraft is projected to increase 3.9% annually. The changes in 

numbers of piston aircraft and hours flown is generally reflected in the consumption of leaded 

avgas. For the years 2008 through 2025, DOT’s FAA estimates no change in the volume of 

leaded avgas consumed by single-engine aircraft in the U.S. (204 million gallons in 2008 and 

2025), a 1.9% decrease in leaded avgas consumed by multi-engine aircraft (from a baseline of 

108 million gallons in 2008 to 78 million gallons in 2025), and a 3.8% annual increase in the 

volume of leaded avgas consumed by piston-powered helicopters (from a baseline of 13 million 

gallons in 2008 to 24 million gallons in 2025). For 2025, the forecast volume of leaded avgas is 

348 million gallons. Consumption of this volume of fuel would release 773 tons of lead to the 

air in 2025.

The number of active pilots flying general aviation aircraft (excluding air transport pilots) 

is projected to be slightly over half a million in 2025, representing a yearly increase of 0.7% over 

the forecast period.127 The student pilot population is forecast to increase at a slightly higher rate 

of 1.0% yearly for a 2025 total slightly over 100,000. Private pilots and sport pilots are also 

projected to increase yearly (0.2% yearly increase in the number of private pilots). EPA is 

requesting comments on the forecast information presented in this section and on the uncertainty

in these projections.

 

127 Except for sport pilots, an active pilot is a person with a pilot certificate with a valid medical certificate. Source: 

FAA 2008-2025 Aerospace Forecast.
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IV. Lead Concentrations in the Vicinity of Airports 

This section summarizes information regarding the chemical and physical properties of 

lead emitted by piston-engine aircraft and monitoring and modeling studies regarding ambient 

and soil lead concentrations in the vicinity of airports where piston-engine aircraft operate. 

A. Chemical and Physical Properties of Lead Emitted by Piston-Engine Aircraft 

Information regarding lead emissions from engines operating on leaded fuel is

summarized in prior AQCDs for Lead.128, 129 The chemical form of lead added to avgas (i.e., 

tetraethyl lead) and the lead scavenger, ethylene dibromide, are the same compounds used in 

leaded gasoline for motor vehicles in the past. Therefore, the summary of the science regarding 

emissions of lead from motor vehicles presented in the 1997 and 1986 AQCD for Lead are 

relevant to understanding some of the properties of lead emitted from piston-engine aircraft. In 

addition, the Swiss Federal Office of Civil Aviation (FOCA) published a study of piston-engine 

aircraft emissions including measurements of lead.130 

When leaded avgas is combusted, the lead is oxidized to form lead oxide. In the absence 

of a lead scavenger in the fuel, lead oxide can collect on the valves and spark plugs and if the 

 

128 U.S. Environmental Protection Agency (1977) Air Quality Criteria for Lead. Research Triangle Park, NC: Office 

of Health and Environmental Assessment, Environmental Criteria and Assessment Office; EPA report no. EPA600/8-77-017. Available at: http://www.epa.gov/ttn/naaqs/standards/pb/s_pb_pr.html.

129 U.S. Environmental Protection Agency (1986) Air Quality Criteria for Lead. Research Triangle Park, NC: Office 

of Health and Environmental Assessment, Environmental Criteria and Assessment Office; EPA report no. EPA600/8-83/028aF-dF. 4v. Available at: http://www.epa.gov/ttn/naaqs/standards/pb/s_pb_pr.html.

130 Federal Office of Civil Aviation Environmental Affairs (2007) Aircraft Piston Engine Emissions Summary 

Report. 33-05-003 Piston Engine Emissions_Swiss FOCA_Summary. Report_070612_rit. Available online at: 

http://www.bazl.admin.ch.
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deposits become thick enough, the engine can be damaged. Ethylene dibromide reacts with the 

lead oxide, converting it to brominated lead and lead oxybromides. These halogenated forms of 

lead are volatile at the high temperatures experienced under combustion conditions and are 

therefore exhausted from the engine along with the other combustion by-products.131 Upon 

cooling to ambient temperatures these brominated lead compounds are converted to particulate 

matter. In addition to lead halides, ammonium salts of lead halides were also emitted by motor 

vehicles.132 Lead halides undergo compositional changes upon cooling and mixing with the 

ambient air as well as during transport; the water-solubility of these lead-bearing particles 

increases with a shift toward smaller mean particle size (USEPA 1977, Section 6.2.2.1). Lead 

halides from automobile exhaust break down rapidly in the atmosphere, via redox reactions in 

the presence of atmospheric acids (AQCD for Lead, page E-17).

A small fraction of uncombusted alkyl lead was measured in the exhaust of motor 

vehicles operating with leaded gasoline and is therefore likely to be present in the exhaust from 

piston-engine aircraft.133 Alkyl lead is the general term for organic lead compounds and includes 

the lead additives tetramethyl lead and tetraethyl lead. Tetraethyl lead is a highly volatile 

compound and therefore, a portion of tetraethyl lead in fuel exposed to air will partition into the 

vapor phase. Tetraethyl lead can enter the atmosphere from avgas distribution systems, refueling 

 

131 ChevronTexaco (2006) Aviation Fuels Technical Review pp. 64-65. Available online at: 

http://www.chevronglobalaviation.com/docs/aviation_tech_review.pdf

132 U.S. Environmental Protection Agency (1986) Air Quality Criteria for Lead. Volume 2 Section Chapters 5 & 6. 

Research Triangle Park, NC: Office of Health and Environmental Assessment, Environmental Criteria and 

Assessment Office; EPA report no. EPA-600/8-83/028aF-dF. 4v. Available from: NTIS, Springfield, VA; PB87-

142378.

133 U.S. Environmental Protection Agency Persistent, Bioaccumulative, and Toxic Pollutants (PBT) Program (2002) 

PBT national action plan for alkyl-Pb. Washington, DC. Available online at: 

http://www.epa.gov/pbt/pubs/Alkyl_lead_action_plan_final.pdf
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operations, fuel check pre-flight procedures and evaporative losses from the aircraft.134 

Tetraethyl lead has an atmospheric residence time ranging from a few hours to a few days. 

Tetraethyl lead reacts with the hydroxyl radical in the gas-phase to form a variety of products 

that include ionic trialkyl lead, dialkyl lead and metallic lead. Trialkyl lead is slow to react with 

the hydroxyl radical and is quite persistent in the atmosphere (AQCD for Lead, page 2-5). 

Particles emitted by piston-engine aircraft are in the submicron size range (less than one 

micron in diameter). The Swiss FOCA reported the mean particle diameter of particulate matter 

emitted by one single-engine piston-powered aircraft ranged from 0.049 to 0.108 microns under 

different power conditions. The particle number concentration ranged from 5.7x106to 8.6x106

particles per cm3and using a specific density for soot of 1.2, the authors estimated the mass 

concentration of particulate emissions as approximately 10,000 g/m3. The authors noted that 

these particle emission rates are comparable to those from a typical diesel passenger car engine 

without a particle filter (FOCA, Section 2.2.3.a). 

A significant fraction of particles in the submicron size range are deposited and retained 

in the lower respiratory system of humans and animals (AQCD for PM, page 6-108).135 The 

1986 AQCD for Lead concludes that lead deposited in the lower respiratory tract is totally

absorbed (USEPA 1986, page 10-2). 

 

134 U.S. Environmental Protection Agency Persistent, Bioaccumulative, and Toxic Pollutants (PBT) Program (2002) 

PBT national action plan for alkyl-Pb. Washington, DC. p. 12. Available online at: 

http://www.epa.gov/pbt/pubs/Alkyl_lead_action_plan_final.pdf

135 U.S. Environmental Protection Agency (2004) Air Quality Criteria for Particulate Matter (AQCD). Volume II 

Document No. EPA600/P-99/002bF. Washington, DC: U.S. Environmental Protection Agency. Available online at:

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=87903
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Due to their small size (i.e., typically less than one micron in diameter), lead-bearing 

particles emitted by piston engines may disperse widely in the environment. However, lead 

emitted during LTO, particularly during ground-based operations such as start-up, idle, preflight 

run-up checks, taxi and take-off may deposit to the local environment. Meteorological factors 

(e.g., wind speed, convection, rain, humidity) will influence local deposition rates. As discussed 

in the overview section of this ANPR, many airports in the country have been home to pistonengine operations for decades, including years when lead concentrations in avgas were twice as 

high as current levels. We seek comment on the chemical and physical form of lead emissions 

from piston-engine aircraft as well as dispersion and deposition patterns that may influence the 

risk for local-scale impacts.

B. Summary of Airport Lead Monitoring and Modeling Studies 

Lead concentrations in ambient air have been reported for samples collected on or near 

five airports: the Santa Monica municipal airport in Santa Monica, CA, the Van Nuys airport in 

Van Nuys, CA, the Chicago O’Hare airport in IL, the Toronto Buttonville municipal airport in 

Ontario, Canada, and the Destin airport in Destin, FL.136, 137, 138, 139, 140 Air quality modeling of 

lead emissions from piston-engine aircraft has been conducted as part of EPA’s National Air 

 

136 South Coast Air Quality Management District (2007) Community-Scale Air Toxics Monitoring – Sun Valley 

Neighborhood and General Aviation Airports. Presented by Dr. Philip Fine at the U.S. EPA Air Toxics Data 

Analysis Workshop - Chicago, IL. October 2 - 4, 2007.

137 Illinois Environmental Protection Agency Bureau of Air (2002) Chicago O’Hare Airport Air Toxic Monitoring 

Program June – December, 2000.

138 Environment Canada (2000) Airborne Particulate Matter, Lead and Manganese at Buttonville Airport. Toronto, 

Ontario, Canada:Conor Pacific Environmental Technologies for Environmental Protection Service, Ontario Region.

139 Tetra Tech, Inc. (2007) Destin Airport Air Sampling Project Executive Summary. Prepared for City of Destin, 

Florida.

140 Tetra Tech, Inc. (2008) Destin, Florida Airport Sampling Report. October 2008. Prepared for City of Destin, 

Florida.
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Toxics Assessment and in one study.

141, 142

 As discussed in Section VI.A of this ANPR, state 

and local agencies are initiating lead monitoring at four airports in 2010 that will provide 

additional information regarding the air quality impact of lead emissions from piston-engine 

aircraft.

1. Summary of Airport Lead Monitoring Studies

The ambient air monitoring studies reporting lead concentrations on and near airport 

property served many purposes and therefore used different criteria for determining sample 

locations, sample durations, sample collection methods, and collection of important metadata 

(e.g., activity of piston-engine aircraft and aircraft engine type). This section summarizes results 

from these studies. 

Ambient monitoring studies at and near airports indicate that lead levels in ambient air at 

or near airports with piston-engine activity are higher than lead levels in areas not directly

influenced by a lead source. The study at the Santa Monica Airport143 is the only study to date in 

which a lead monitor was sited at an area of anticipated maximum concentration for a period of 

time that provides ambient concentrations relevant for comparison to the Lead NAAQS.144 In 

 

141 Piazza, B for the Los Angeles Unified School District Environmental Health and Safety Branch (1999) Santa 

Monica Municipal Airport: A Report on the Generation and Downwind Extent of Emissions Generated from 

Aircraft and Ground Support Operations. Report Prepared for The Santa Monica Airport Working Group. 

Available online at: 

http://yosemite.epa.gov/oar/CommunityAssessment.nsf/6ce396ab3fa98ee485256db0004acd94/$FILE/Santa_Monica

.pdf

142 U.S. Environmental Protection Agency (2009) 2002 National-Scale Air Toxics Assessment (NATA). Available 

online at: http://www.epa.gov/ttn/atw/nata2002/index.html

143 South Coast Air Quality Management District (2007) Community-Scale Air Toxics Monitoring – Sun Valley 

Neighborhood and General Aviation Airports. Presented by Dr. Philip Fine at the U.S. EPA Air Toxics Data 

Analysis Workshop - Chicago, IL. October 2 - 4, 2007. This presentation includes lead monitoring data collected at 

and near the Santa Monica Airport and the Van Nuys Airport.

144

 As with other lead sources, source-oriented monitors for airports should be sited in ambient air at the
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this study where monitors were placed in locations to identify the gradient in lead concentrations 

with distance from piston-engine activity, ambient lead increased with increasing proximity to 

the airport. Lead monitors were located at seven sites around the Santa Monica Airport for two 

three-month periods, in Spring 2006 and Winter 2006-2007. At the monitor placed near the 

runway blast fence (i.e., the maximum impact site) on the Santa Monica Airport property, the 

quarterly average concentrations of lead in total suspended particulate matter (TSP) were 0.08 

(winter) and 0.10 (spring) g/m3.

145

 The maximum quarterly average concentration of lead in 

total suspended particulate matter (TSP) was 0.10 g/m3, 67% of the 2008 Lead NAAQS of 0.15 

g/m3. This suggests that ambient air lead concentrations at similar airports with more pistonengine activity than the Santa Monica Airport may be higher, and could further approach or 

exceed 0.15 g/m3. At a neighborhood site, 70 meters in the prevailing downwind direction 

from the maximum impact site, quarterly average concentrations of lead in TSP were 0.02 g/m3

(winter) and 0.03 g/m3(spring).146 At a distance of one kilometer in the prevailing downwind 

direction from the maximum impact site, lead concentrations were 0.004 g/m3and 0.008 g/m3

in winter and spring, respectively (these concentrations are considered the background lead 

concentration). The study conducted at the Santa Monica Airport reported concentrations of 

ambient lead that were highest at on- and near airport areas downwind from the emissions of 

piston-engine aircraft. These data suggest that piston-engine activity can increase ambient lead 

concentrations in downwind neighborhood sites, resulting in levels that are four to five times 

 

location of predicted maximum lead concentration. Typically, the location of maximum lead concentration will be 

downwind of the take off strip near the “blast fence.” 

http://www.epa.gov/ttnamti1/files/ambient/pb/NetworkDesignQA.pdf

145 A low-volume sampler was used at this site which EPA expects would yield comparable results to a high-volume 

sampler, the later of which is the current method used to collect samples for comparison with the Lead NAAQS.

146 These distances were measured using Google Earth Pro software.
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higher than background levels and maximum impact site concentrations that are up to 25 times 

higher than background lead levels.147

As with other emissions from internal combustion engines, lead emitted by piston-engine 

aircraft are largely in the submicron and even ultrafine size fraction; therefore, analogies to 

gradients in ultrafine PM are relevant. As summarized in EPA’s 2009 Integrated Science 

Assessment for Particulate Matter, ultrafine particulate number counts decrease exponentially 

with distance from roadways.148 A recent study at the Santa Monica Airport reported increased 

ultrafine PM in a neighborhood downwind from aircraft operations that were conducted by jet 

and piston-engine aircraft.149 The EPA is conducting modeling and monitoring studies to 

further evaluate the gradient in lead concentrations with distance from airports (see Section VI.B 

of this ANPR).

At the Van Nuys Airport, lead monitoring in ambient air was conducted at six sites for 

two three-month periods. Lead monitoring for this study included locations of ambient air on 

airport property. However, monitors were not sited in the area anticipated to experience the 

maximum impact from piston-engine aircraft emissions. The monitoring site that was in closest 

proximity to the maximum impact area was more than one kilometer downwind from the 

maximum impact site. 150 The highest quarterly concentration of lead observed at the Van Nuys

Airport was at the monitor located over one kilometer away from the maximum impact site and 

 

147 EPA notes that additional information regarding this study at the Santa Monica Airport may become available. If 

additional information does become available, EPA will take this information into account in the NPRM.

148 U.S. Environmental Protection Agency (2009) Integrated Science Assessment for Particulate Matter. Second 

External Review Draft. EPA/600/R-08/139B. p. 3-110. Available online at: 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=210586

149 Hu, S., Fruin, S., Kozawa, K., Mara, S., Winer, A.M., Paulson, S.E. (2009) Aircraft Emission Impacts in a 

Neighborhood Adjacent to a General Aviation Airport in Southern California. Environ. Sci. Technol. 43:8039-8045.

150 These distances were measured using Google Earth Pro software. Prevailing wind direction, which determines 

the direction in which the majority of aircraft depart, is provided in the SCAQMD presentation of these data. 
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the lead concentration at this site was 0.03 g/m3 which was four-fold higher than the regional 

background level of 0.008 g/m3 measured during the same time period at a site over 2.5 

kilometers from the north end of the Van Nuys Airport. 

At the Toronto Buttonville Municipal Airport, ten 24-hour PM10 samples were collected 

at four sites at the airport (as close as 15 meters from the runway) and one urban background site 

in downtown Toronto (located about 10 kilometers west, southwest of the airport). PM10 is 

particulate matter less than ten microns in aerodynamic diameter. The average lead 

concentration among the airport monitors (which includes three samples that were taken for less 

than a 12-hour period), was 0.03 g/m3and the maximum 24-hour lead concentration was 0.13 

g/m3. One sample, collected for 11 hours, measured 0.30 g/m3. The maximum concentration 

observed over a 24-hour period at the airport during this study (0.13 g/m3) was 11 times higher 

than the lead concentration reported for the downtown Toronto, Canada background site during 

the same time period (0.012 g/m3).

151

 The average lead concentration reported for the 

downtown Toronto site was 0.007 g/m3. The total particulate matter mass in PM10 was also 

measured in this study, and at the airport, the average mass of lead in PM10 was 0.15% of the 

total PM10 mass. At the downtown Toronto site, the average mass of lead in PM10 was 0.04% of 

the total PM10 mass. The study reported that the use of leaded avgas at the airport was evident in 

enhanced airborne lead levels.

Lead and other hazardous air pollutants were measured at sites upwind and downwind of 

the Chicago O’Hare Airport on sixteen days during the period from June through December, 

 

151 Average concentrations reported in this study include three days of short-duration sampling so the average is not 

used for comparison here. 
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2000. In order to assess the potential impact of airport operations on ambient concentrations of 

lead and other pollutants in areas adjacent to airport property, two monitoring sites were 

deployed on different sides of the airport: one in Bensenville, IL and the other in Schiller Park, 

IL. For five days during the sampling campaign, the prevailing wind direction provided samples 

that were collected simultaneously upwind and downwind of the airport. Lead concentrations 

measured at the downwind site on these five days were, on average, 88% higher than lead 

concentrations measured at the upwind site. Lead concentrations at the upwind site over the five 

days averaged 0.016 g/m3and downwind concentrations averaged 0.030 g/m3. This study

demonstrates the potential for operations on airport property to impact ambient lead 

concentrations downwind.

Lead TSP samples were collected for four days in April 2007 and for three days in July

2008 near the Destin Airport in Destin, FL. Twelve-hour TSP samples (AM and PM) were 

collected at four residential locations ranging from 200 meters to 400 meters from the runway at 

the Destin Airport and at two urban background locations which were 1.4 kilometers and 2.7 

kilometers from the airport.152 The average lead concentration among the four residential 

locations was 0.004 g/m

3

and 0.005 g/m3in April and July, respectively, and the average 

urban background lead concentration was 0.003 and 0.004 g/m3in April and July, respectively. 

In addition to these airport-specific studies, authors evaluating ambient lead 

concentrations collected as part of the Interagency Monitoring of Protected Visual Environments 

(IMPROVE) network and the National Oceanic and Atmospheric Administration (NOAA) 

monitoring sites reported a weekend increase in ambient lead that the authors attributed to 

 

152 These distances were measured using Google Earth Pro software. 
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weekend increases in piston-engine powered general aviation activity.

153

 At some airports, 

piston-engine aircraft activity conducted for recreational purposes can increase greatly on 

weekends and can also change seasonally with weather conditions. These peaks in activity are 

important to capture because they may have a strong influence on long-term average 

concentrations in an area. However, the current database for ambient lead concentrations at 

maximum impact sites at airports is severely limited and does not allow us to quantitatively

evaluate the influence of this variability in activity on ambient lead concentrations. 

We have identified no studies evaluating the potential contribution of piston-engine 

aircraft emissions on vegetation. We have identified only one study that reports soil 

concentrations on airport property where piston-engine aircraft are active. The air monitoring 

study conducted at the Toronto Buttonville airport in Ontario, Canada reported lead 

concentrations in soil samples collected at eight locations at the airport and two locations at the 

urban background site. Soil samples that were collected at the Toronto Buttonville airport had 

lead concentrations ranging from 22 – 46 g/g which was not substantially higher than the lead 

concentrations in soil samples at the two urban background sites (29 and 31 g/g). We are 

seeking comments on the potential for piston-engine aircraft emissions to impact local soil lead 

concentrations. 

2. Summary of Airport Lead Modeling Studies

Lead emissions from piston-engine aircraft at 3,410 airports were included in the recently

 

153 Murphy, D.M., Capps, S.L., Daniel, J.S., Frost, G.J., and White, W.H. (2008) Weekly patterns of aerosol in the 

United States. Atmos. Chem. Phys., 8, 2729–2739.
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released 2002 National Air Toxics Assessment (NATA) as nonroad sources of lead.154 Ambient 

lead concentrations and exposures to lead are modeled for area, point and nonroad sources. 

Nonroad sources include only lead emissions from piston-engine aircraft. Lead emission rates 

are based on the lead concentration in fuel and not direct emission measurements. For the 

NPRM we will summarize modeling results from the 2005 NATA which will incorporate all 

20,000 airport facilities discussed in Section III of this ANPR.

As discussed in Section VI of this ANPR, the EPA has conducted a study to develop a

modeling approach to evaluate the local-scale variability in ambient lead concentrations 

attributable to piston-engine activity at a case study airport. This project includes collection of 

air monitoring data for use in evaluating model performance. In the NPRM, we will describe the 

results of the modeling study with NATA results for this airport and previous modeling work.156

We are requesting comment on the availability of additional monitoring or modeling 

studies that evaluate the air quality impact of lead emissions from piston-engine aircraft as well 

as potential impacts on soil, house dust, surface water or other environmental media. We also 

request comment on the availability of studies that assess the potential public health and welfare 

impacts of lead emissions from piston-engine aircraft. 

 

154 U.S. Environmental Protection Agency (2009) 2002 National-Scale Air Toxics Assessment (NATA). Available 

online at: http://www.epa.gov/ttn/atw/nata2002/tables.html.

156 Piazza, B for the Los Angeles Unified School District Environmental Health and Safety Branch (1999) Santa 

Monica Municipal Airport: A Report on the Generation and Downwind Extent of Emissions Generated from 

Aircraft and Ground Support Operations. Report Prepared for The Santa Monica Airport Working Group. Available 

online at: 

http://yosemite.epa.gov/oar/CommunityAssessment.nsf/6ce396ab3fa98ee485256db0004acd94/$FILE/Santa_Monica

.pdf
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V. Exposure to Lead from Piston-Engine Aircraft and Potential for

Impacts

The continued use of lead in avgas by piston-engine aircraft is a significant source of 

current lead emissions to the environment. Piston-engine aircraft emissions of lead occur at 

ground level as well as at flying altitude. Lead from this source is thus concentrated near airports 

and is also deposited over a large geographic area potentially contributing to higher ambient 

concentrations in many communities. Numerous groups within the population may be at risk of 

exposure to lead in fresh emissions from piston-engine aircraft, resuspended dust or other routes. 

Further, lead accumulates in the environment posing a potential risk to future generations

In this section we discuss a variety of exposure pathways and scenarios by which the 

general population and environment may experience an increase in lead exposure from emissions 

of lead by piston-engine aircraft. This section also describes the potential for public health and 

welfare effects from exposure to compounds associated with the continued use of tetraethyl lead 

in fuel, such as the contribution of lead to ambient particulate matter, emissions of ethylene 

dibromide and non-exhaust exposure to tetraethyl lead. We are seeking comments and 

information on these exposure scenarios as well as additional exposure pathways and scenarios.

A. Exposure to Lead Emissions from Piston-Engine Aircraft

Piston-engine aircraft emissions of lead occur at ground level as well as at altitudes, 

resulting in areas of more concentrated ambient air exposure, as discussed in Section IV, and can 
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also be distributed over large geographic areas due to in-flight emissions. Lead particles can 

deposit to soil, water, vegetation and other surfaces or remain airborne for some time following 

emissions. In this section we discuss potentially exposed populations which include people 

living or attending schools near airports and pilots. Additional pathways by which people and 

animals could be exposed to lead emissions from piston-engine aircraft are those associated with 

agricultural applications of these aircraft and piston-engine activity at seaport and inland 

waterways.

Lead from aviation gasoline has been identified as a potential source of contamination for 

local communities.157 As described below, many general aviation airports are located in densely 

populated areas. GA airport facilities were typically built in sparsely populated areas, many of 

which are now heavily populated or are experiencing increased residential development. This 

development includes dense residential neighborhoods, schools, businesses, and recreational 

facilities. 

Airports can function as a center of many forms of activity in a community. In EPA’s 

initial research, EPA has found that airports are often surrounded by a variety of land uses 

including recreational sport facilities (e.g., baseball diamonds, soccer fields, golf courses, and 

swimming pools) and residential communities that take advantage of the ease of transport and 

pilot training/recreation offered by quick access to an airport. Many airports offer on-site tours 

to the general public, educational classes, and recreational opportunities that can present nearsource exposure scenarios. Airports are especially attractive to young children, and programs at 

some airports are focused on this population and provide outdoor observation facilities and 

 

157Levin, R.; Brown, MJ; Kashtock, ME; Jacobs, DE; Whelan, EA; Rodman, J; Schock, MR; Padilla, A; Sinks, T. 

(2008) US Children’s Lead Exposures, 2008: Implications for Prevention. Environ. Health Perspec. 116:1285-1293.
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picnic facilities for families to observe aircraft operations. Many general aviation airports offer 

instructional flying and/or clubs where children 14 years of age and older as well as adults can 

learn to fly in rental aircraft. Airport facilities also host community-friendly activities such as 

antique sales, fireworks displays, air shows and community meals. Many airport facilities 

provide activities which bring people from the general public in close proximity to lead 

emissions from piston-engine aircraft and piston-engine helicopters. EPA is requesting 

information regarding national databases that provide information regarding recreational fields 

and community gardens in close proximity to airports. 

1. Population Residing Near Airports

To evaluate the number of people who might be exposed to elevated lead levels due to 

emissions from piston-engine aircraft, EPA calculated the number of people that live within one 

kilometer of the centroid of an airport.158 The centroid of the airport is defined here as the 

latitude and longitude coordinate provided by airports to FAA.159 These coordinates typically

identify a location in the center of the runway or runway area. For some airports, nearby 

residences are outside the one kilometer distance from the airport centroid. This is the case for 

residences near airports that have runways that are longer than two kilometers and for residences 

near large airports such as those servicing primarily commercial aircraft activity. For airport 

facilities with one runway that is approximately one kilometer in length, this method will 

generally include people residing within approximately 500 meters from the ends of the runway 

and may include residences up to approximately 900 meters from the sides of the runway. The 

 

158 U.S. EPA (March 2010) Memorandum from Meredith Pedde to docket EPA-HQ-OAR-2007-0294, titled,

“Evaluation of People Living Within 1 km of U.S Airport Facilities.”

159 Federal Aviation Administration. Airport Data (5010) & Contact Information, Airport Facilities Data. Retrieved 

on August 13, 2009 from: http://www.faa.gov/airports/airport_safety/airportdata_5010/menu/index.cfm 
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limited ambient lead monitoring data near airports presented in Section IV of this ANPR 

suggests that for some airports this analysis will underestimate the actual number of people 

potentially exposed to elevated levels of ambient lead from piston-engine powered aircraft. This 

is because the analysis will include very little of the nearby population for airports that have a 

large footprint. We plan to revise this analysis for the NPRM using a graphical interface system 

that will allow us to evaluate the number of people living within uniform distances of aircraft 

activity.

Using 2000 U.S. Census Data160 at the block level, EPA estimates that 16 million people 

live within one kilometer of the centroid of the 19,896 airport facilities which includes airports, 

seaplane bases, heliports, stolports, ultralight facilities and glider ports. There are currently 

5,567 heliports in this analysis, which can be in densely populated areas. Fourteen of the 16 

million people living within one kilometer of the centroid of an airport facility live within one 

kilometer of a heliport. We currently have limited information regarding which heliport facilities 

have piston-engine activity and we are seeking comment on piston-engine activity at heliports.

There are several pathways by which people may be exposed to lead associated with the 

use of piston-engine aircraft. These include inhalation of ambient airborne lead as well as 

incidental ingestion of ambient lead through contact with indoor or outdoor surfaces to which 

ambient lead has deposited. Additionally, ambient lead deposited to outdoor soil can be tracked 

into interior spaces. There is also the potential for ingestion of lead emitted by piston engine 

aircraft emissions to deposit on edible plants and produce being cultivated in locations near 

airports. Consequently, there is the potential for exposure to lead emitted by piston-engine 

 

160 Obtained from: http://www.epa.gov/ttn/fera/human_hem_censusandmet.html
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aircraft via ingestion for those consuming vegetables grown near airports that service pistonengine aircraft. In addition to personal gardens, community gardens are sometimes sited near 

airports as these areas can have undeveloped available land. We do not have information on the 

potential significance of this exposure pathway and we are seeking comment on information and 

analyses that could inform this issue.

In some cases, pilots and their families choose to live in close proximity to an airstrip. 

These communities intentionally placed near airports are known as airport communities, fly-in 

communities or residential airparks. Some residential airparks are private while others have 

public services and facilities. Some residential airparks are specifically designed as airport 

communities with driveways leading from aircraft hangars or tie-downs onto the airstrip, while 

other residential airparks allow apartments to be built in the airplane hangar. Other residential 

airparks are developed by the addition of a neighborhood immediately adjacent to a commercial 

airport. FAA terms this a “through-the-fence” operation.161 Homes are required to be at least 45 

meters from the runway centerline and can be built along one or both sides of the runway.162 

Some residential airparks provide taxiways for access to the runway, some provide streets 

separate from taxiways, and some share automobile and aircraft traffic on the same 

thoroughfares. A variety of resources list the location and services offered by residential 

airparks in the U.S. and estimates of the number of residential airparks range from 300 to 600.163,

 

161 FAA officially defines “through-the-fence” as those activities permitted by an airport sponsor through an 

agreement that permits access to the public landing area by independent entities or operations offering an 

aeronautical activity or to owners of aircraft based on land adjacent to, but not part of, the airport property. The 

obligation to make an airport available for the use and benefit of the public does not impose any requirement for the 

airport sponsor to permit ground access by aircraft from adjacent property.

(http://www.aopa.org/whatsnew/region/airportOps0712.pdf)

162 ASTM International (2005) ASTM F2507 – 05 Standard Specification for Recreational Airpark Design

163 www.airparks.com maintains a list of airparks that have five or more homes/lots. The list can be updated by the 

public and as of July 31, 2009, lists 326 residential airparks.
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164

 In some cases, records are maintained only for those residential parks that have five or more 

homes or lots. 

Exposure modeling at the EPA indicates that, for the 20 highest air emission sources, 

local emissions are significantly related to local blood lead levels.165 We are aware of no studies 

evaluating blood lead levels among people who live in close proximity to airports with pistonengine activity or those for whom lead emissions from piston engines may elevate their exposure 

via other exposure pathways. As noted in Section II.B.2, the current evidence indicates that the 

slope for lead effects on IQ is nonlinear and is steeper at lower blood lead levels, such that each 

μg/dL increase in blood lead may have a greater effect on IQ at lower blood lead levels (e.g., 

below 10 μg/dL) than at higher levels (AQCD for Lead, Section 6.2.13; pp. 8-63 to 8-64; Figure 

8-7). We are therefore seeking comment and information regarding blood lead concentrations in 

children living near airports and the extent to which these emissions cause or contribute to any 

increases in blood lead levels.

2. Children Attending School Near Airports

As noted in Section II.B.2 of this ANPR, while adults are susceptible to lead effects at 

lower blood lead levels than previously understood (e.g., AQCD for Lead, p. 8-25), there is 

general consensus that the developing nervous system in children is among the, if not the, most 

sensitive health endpoints. Also, as noted in Section II.B.3, while children are considered to be 

at a period of maximum exposure around 18-27 months, the current evidence has found even 

stronger associations between blood lead levels at school age and IQ at school age. The 

 

164 http://livingwithyourplane.com/about/ has a directory of over 600 residential airparks.

165

 U.S. Environmental Protection Agency (2007) Pilot Study of Targeting Elevated Blood Lead Levels in Children 

(Draft Final Report). Washington DC:U.S. EPA Office of Pollution Prevention and Toxics. 

http://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=195303.
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evidence “supports the idea that lead exposure continues to be toxic to children as they reach 

school age, and [does] not lend support to the interpretation that all the damage is done by the 

time the child reaches 2 to 3 years of age” (AQCD for Lead, Section 6.2.12). Accordingly, 

school-age children are an at-risk population for lead exposures. This section discusses potential 

exposures of children at school to lead associated with piston-engine aircraft. 

During the school year, students spend many hours a day at school, which usually

includes time on school playgrounds and on school athletic fields. Those children attending 

schools in close proximity to piston-engine activity may have increased exposure to lead. Using 

data from the U.S. Department of Education’s National Center for Education Statistics, EPA 

calculated that there are 8,637 schools located within one kilometer of the centroid of an airport 

in the U.S., at which over 3 million children are in attendance (Table 1).166, 167 These children 

represent 6% of the total U.S. student population.

Table 1. Numbers of Public and Private Schools and School Children Attending Schools 

Located within One Kilometer of the Centroid of an Airport Servicing Piston-engine Aircraft.

Number of 

Schools within 1 

km of an airport

Number of students who 

attend schools within 1 

km of an airport

Private Schools 2,185 420,824

 

166 U.S. EPA (March 2010) Memorandum from Meredith Pedde to docket EPA-HQ-OAR-2007-0294, titled, 

“Identification of Schools Within 1 km of U.S Airport Facilities.”

167 Public School Data available for 2006-2007: http://nces.ed.gov/ccd/bat/ ; Private School Data available for 2007-

2008: http://nces.ed.gov/surveys/pss/pssdata.asp
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Public Schools 6,452 2,869,939

All Schools 8,637 3,290,763

 

Section II.B.1 notes that children in poverty and black, non-Hispanic children have 

notably higher blood lead levels than do economically well-off children and white children, in 

general. To evaluate potential ethnic and economic disparities among children attending schools 

close to airports compared with the general population, we used data from the Department of 

Education that provides this information. These data indicate that minorities are overrepresented 

at schools that are located within one kilometer from the centroid of an airport. For example,

Hispanic students represent 23% of students at schools located within one kilometer of an 

airport, whereas Hispanic students represent 19% of students in all U.S. schools (Table 2). Black 

students represent 18% of students at schools located within one kilometer of an airport, whereas 

black students represent 16% of the student population in the U.S. (Table 2).

Table 2. Racial Distribution at Schools within One Kilometer of the Centroid of an 

Airport and the Racial Distribution at all U.S. Schools.

American 

Indian / 

Alaskan 

Indian

Asian / 

Pacific 

Islander

Black, 

NonHispanic Hispanic

White, 

NonHispanicTotal 

Students*

All Number 46,861 154,408 597,223 764,704 1,646,882 3,290,763
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Schools 

within 1 

km of an 

airport

Percent 1% 5% 18% 23% 50%

All U.S. 

Schools

Number 632,237 2,581,822 8,696,565 10,525,763 30,664,231 54,271,986

Percent 1% 5% 16% 19% 57%

*This table includes only those children that identify as one of the five races/ethnicities. A small fraction of students 

identify as mixed race or ‘other’ and they are not included here, therefore the percent of students does not total 

100%.

In general, housing and income data suggest that people living in close proximity to 

major transportation sources (i.e., major roadways, airports, ports, railyards) are likely to have 

lower income than the general population.168 To evaluate the socioeconomic status of students 

who attend schools near airports, EPA evaluated the number of students who are eligible for the 

U.S. Department of Agriculture’s free or reduced school lunch program. Children from families 

with incomes at or below 130 percent of the poverty level are eligible for free meals. Those with 

incomes between 130 percent and 185 percent of the poverty level are eligible for reduced-price 

meals.169 Free and reduced lunch eligibility is only tracked by the U.S. Department of 

Education’s National Center for Education Statistics for students who attend public schools. At 

public schools that are located within one kilometer of the centroid of an airport, 47% of students 

are eligible for either free or reduced lunches, whereas nationally, 41% of students at public 

 

168 U.S. Environmental Protection Agency (2007) Regulatory Impact Analysis for the Regulation to Control 

Hazardous Air Pollutant Emissions from Mobile Sources. Chapter 3, p. 3-122. 

169 United States Department of Agriculture: Food and Nutrition Service, National School Lunch Program Fact 

Sheet. Obtained from: http://www.fns.usda.gov/cnd/Lunch/AboutLunch/NSLPFactSheet.pdf, August 3, 2009. For 

the period July 1, 2008, through June 30, 2009, 130 percent of the poverty level is $27,560 for a family of four; 185 

percent is $39,220.
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schools are eligible for either free or reduced lunches. As this analysis demonstrates, those 

living in the vicinity of airports are more likely to be low-income households and minority

residents. 

We are aware of no studies evaluating blood lead levels among children attending school 

in close proximity to airports with piston-engine activity. We are seeking comment and 

information regarding blood lead concentrations in children who attend schools in close 

proximity to airports and the extent to which these emissions cause or contribute to any increases 

in blood lead levels. 

3. Agricultural Activities

Piston-engine aircraft are used in a variety of agricultural activities that may introduce 

lead into the human diet as well as contribute to lead in the environment. The FAA conducts the 

General Aviation and Air Taxi Activity (GAATA) Survey annually to obtain information on the 

general aviation and air taxi fleet, the number of hours flown, and the reasons people use general 

aviation and air taxi aircraft.

170, 171

 According to the results of the 2007 GAATA Survey (the 

most recent), aerial application in agriculture and forestry represented 5% of all hours flown by 

general aviation aircraft in 2007. Of the total aerial application hours flown in 2007 (1.41 

million hours), 60% of the hours were flown by piston-engine aircraft. Aerial application 

activity includes crop and timber production, which involve fertilizer and pesticide application 

 

170 The FAA GAATA is a database collected from surveys of pilots flying aircraft used for general aviation and air 

taxi activity. For more information on the GAATA, see Appendix A at 

http://www.faa.gov/data_statistics/aviation_data_statistics/general_aviation/

171 National Agricultural Aviation Association: “Help the Aerial Application Industry by completing the 2008 

General Aviation Activity Survey”. Retrieved from: http://www.agaviation.org/2008%20GenAvnSurvey.htm on 

August 13, 2009
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and seeding cropland. The National Agricultural Aviation Association estimates that there are 

approximately 3,200 aerial application professional operators and pilots in the United States.172

As discussed in Section II.C.1, surface deposition of lead onto plants may represent a 

significant contribution to the total lead in and on the plant. Lead halides, the primary form of 

lead emitted by engines operating on leaded fuel, are slightly water soluble. They therefore may

be more readily absorbed by plants than other forms of inorganic lead. Atmospheric deposition 

of lead also contributes to lead in vegetation as a result of contact with above-ground portions of 

the plant (AQCD for Lead, pp. 7–9 and AXZ7–39; USEPA, 1986, Sections 6.5.3 and 7.2.2.2.1). 

Livestock may subsequently be exposed to lead in vegetation (e.g., grasses and silage) and in 

surface soils via incidental ingestion of soil while grazing (USEPA 1986, Section 7.2.2.2.2).173 

The lead concentration of plants ingested by animals is primarily a result of atmospheric 

deposition of lead particles onto plant surfaces rather than the uptake of soil lead through plant 

roots. Some of the highest levels of lead exposure among livestock have been attributed to 

grazing near major sources such as smelters (AQCD for Lead, Section 2.3.8). Atmospheric 

deposition is estimated to comprise a significant proportion of lead in food (AQCD for Lead, p. 

3–48) and dietary intake may be a predominant source of lead exposure among adults (greater 

than consumption of water and beverages or inhalation (73 FR 66971)).

 

172 National Agricultural Aviation Association: “History”. Retrieved from: http://www.agaviation.org/history.htm 

on August 13, 2009.

173 U.S. Environmental Protection Agency (1986) Air Quality Criteria for Lead. Research Triangle Park, NC: Office 

of Health and Environmental Assessment, Environmental Criteria and Assessment Office; EPA report no. EPA600/8-83/028aF-dF. 4v. Available from: NTIS, Springfield, VA; PB87-142378.
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Depending on wind conditions, an aircraft involved in aerial application may fly only 4 

inches to 12 feet above the crops.174, 175, 176 The low flying height is needed to minimize the drift 

of the fertilizer and pesticide particles away from their intended target. An unintended 

consequence of this practice is that exhaust emissions of lead have a substantially increased 

potential for directly depositing on vegetation and surrounding soil. We have not identified any 

data or analyses regarding the contribution of piston-engine aircraft lead emissions to lead 

concentrations in or on plant tissues, in livestock or the dose that this might deliver to the human 

population. We are seeking comments on the potential significance of this exposure pathway.

4. Pilots, Student-Trainees, Passengers

Pilots, student-trainees, and passengers are all potentially exposed to lead emissions from 

piston-engine aircraft that use leaded avgas. General aviation passengers and pilots access their 

aircraft in areas that are typically in close proximity to runways. Therefore, these individuals 

walk near and breathe the air near locations where aircraft are idling, conducting run-up checks, 

taxiing, taking off, and landing.

In the U.S., general aviation aircraft fly over 27 million hours and carry 166 million 

passengers annually.

177

 Approximately 36 percent of the hours flown by general aviation are for 

personal transportation, 19 percent are instructional flight hours, 11 percent are corporate flight 

 

174 Xiong, Chao. (9-23-2007) “Future for Crop Dusters is up in the Air”. The Star Tribune. Retrieved on August 12, 

2009 from: http://www.startribune.com/local/11606661.html

175 Harpole, T. (3-1-2007) “That Old-Time Profession” Air & Space Magazine. Retrieved on August 12, 2009 

from: http://www.airspacemag.com/history-of-flight/old_time_profession.html

176 Petersen, R. “So you want to be a spray pilot”. AgAir Update. Retrieved on October 9, 2009 from: 

http://www.agairupdate.com/aau/wannabe/pilot.html

177 General Aviation Manufacturers Association (2008) General Aviation Statistical Databook and Industry Outlook. 

Available at: http://www.gama.aero/files/2008_general_aviation_statistical_databook__indust_499b0dc37b.pdf
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hours, 11 percent are for business, eight percent are air taxi and air tours and the remainder 

include hours spent in other applications such as aerial observation and aerial application.178 

According to the 2008 General Aviation Statistical Databook & Industry Outlook report by the 

General Aviation Manufacturers Association (GAMA) there were 578,541 pilots in the United 

States in 2008.179 Among the pilot population, 75,382 were student pilots, comprising 13% of 

the total pilot population. The majority of initial pilot training is conducted in piston-engine 

aircraft.180 There is no age minimum for pilots to begin taking flying lessons.181 The minimum 

age for conducting a solo flight is 16 years and a pilot certificate cannot be issued until 17 years 

of age. According to the 2008 General Aviation Statistical Databook & Industry Outlook report 

by the GAMA, there are 190 student pilots in the 14-15 year old age group and 11,562 student 

pilots in the 16-19 years old age group. GAMA reports that in 2008 there are 3,846 private pilots 

in the 16-19 years old age group. According to the FAA there are more than 500 flight training 

schools. 182, 183 The requirement for a private pilot certificate is 40 hours in a non-approved 

school, and 35 hours in an approved school. However, most people obtain 60 to 75 hours of 

training before earning their pilot certificate.

The general public for whom flying is a recreational activity may be the most highly

exposed population to lead emissions from piston-engine activity. In addition to their inhalation 

 

178 General Accounting Office Report to Congressional Requesters (2001) General Aviation Status of the Industry, 

Related Infrastructure, and Safety Issues. GAO-01-916.

179 GAMA 2008 General Aviation Statistical Databook & Industry Outlook report. Retrieved on August 17, 2009 

from: http://www.gama.aero/files/2008_general_aviation_statistical_databook__indust_499b0dc37b.pdf 

180 See http://flighttraining.aopa.org/learntofly/aircraft/

181 Federal Aviation Administration (FAA). “Become a Pilot — Student Pilot's Certificate Requirements.” 

Retrieved on August 17, 2009 from: http://www.faa.gov/pilots/become/student_cert/ 

182 Federal Aviation Administration (FAA). “Types of Pilot Schools & Choosing a Pilot School”. Retrieved on 

August 17, 2009 from: http://www.faa.gov/training_testing/training/pilot_schools/ 

183 Federal Aviation Administration (FAA). “Pilot Schools - Search”. Retrieved on August 17, 2009 from: http://avinfo.faa.gov/PilotSchool.asp
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exposure to engine exhaust emissions, pilots can be exposed to evaporative emissions of TEL

during aircraft fueling, and fuel sump checks during preflight inspections. 

5. Bioaccumulation of Lead in Aquatic Organisms

As discussed in Section II.C.2 of this ANPR, lead bioaccumulates in the tissues of 

aquatic organisms through ingestion of food and water. Because of the potential for significant 

deposition of lead compounds to water bodies, EPA researches and reports on the atmospheric 

deposition of lead compounds to the Great Waters (the Great Waters include the Great Lakes,

Lake Champlain, Chesapeake Bay and many U.S. coastal estuaries).184 Alkyl lead, in particular, 

has been identified by EPA as a Level I Persistent, Bioaccumulative, and Toxic (PBT) pollutant. 

Level I substances are targeted for virtual elimination through pollution prevention and other 

incentive-based actions that phase out their use, generation or release in a cost-effective manner 

within the most expedient time-frame. In 2002, EPA issued the PBT National Action Plan for 

Alkyl-lead to promote further voluntary reductions of use and exposure to alkyl lead compounds, 

including leaded avgas.185

We are interested in the potential for lead emissions from piston-engine aircraft to be a 

source of lead pollution to aquatic organisms. Among the approximately 20,000 airport facilities 

in the United States there are 448 seaplane facilities. Landing and take-off activity by aircraft at 

these facilities provides a direct pathway for emission of organic and inorganic lead to the air 

 

184 U.S. Environmental Protection Agency, “The Great Waters Program.” Retrieved on August 17, 2009 from: 

http://www.epa.gov/air/oaqps/gr8water/

185 U.S. Environmental Protection Agency Persistent, Bioaccumulative, and Toxic Pollutants (PBT) Program (2002) 

PBT national action plan for alkyl-Pb. Washington, DC. Available online at: 

http://www.epa.gov/pbt/pubs/Alkyl_lead_action_plan_final.pdf
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near/above inland waters and ocean seaports where these aircraft operate. In addition to seaplane 

facilities, many airports and heliports are located very close to rivers, lakes and streams, which 

can provide a direct pathway for emission of organic and inorganic lead to the air near/above 

inland waters. Lead emissions from seaplane facilities as well as airports and heliports near 

water bodies can enter the aquatic ecosystem by either deposition from ambient air or runoff of 

lead deposited to surface soils. As noted in Section IV.A, lead halides (the primary form of lead 

emitted by engines operating on leaded fuel) are slightly water-soluble and may be more readily 

dissolved into water than other inorganic forms of lead. 

The EPA Office of Water maintains a database of the National Listing of Fish Advisories 

(NLFA) which is made available on the Internet to provide information regarding locally-issued 

fish advisories and safe eating guidelines.186 States, territories, and tribes (collectively referred 

to here as "states") provide this information to EPA every year. The most recent year for which 

data are available is 2008. States provide information regarding contaminant levels of 

bioaccumulative toxins measured in fish including lead, mercury, polychlorinated biphenyls 

(PCBs) and dioxin. Based on these data states issue fish consumption advisories that provide 

information regarding water bodies for which fish tissue concentrations of these pollutants are 

found by the state criteria to be safe or unsafe for consumption. The EPA recommends that if 

fish are detected as having any measureable level of accumulated lead in their tissues that this is 

cause for concern for all consumers, but especially for children and pregnant or nursing women, 

and that issuing an advisory is prudent. 

The 2008 NLFA database includes data on lead concentrations in over 23,000 fish from 

over 1,000 lakes and streams. Among these fish, lead concentrations were above the analytical 

 

186 U.S. Environmental Protection Agency, “The National Listing of Fish Advisories”. Retrieved on August 17, 

2009 from: http://www.epa.gov/waterscience/fish/advisories/
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detection limit in 1,000 fish samples187 and among the fish in which measureable lead 

concentrations were reported, the concentrations of lead ranged from 5 ppb to 60,400 ppb.188 

States do not provide information regarding the source of contamination in water bodies where 

fish tissue concentrations of lead are above detection limits. Lead concentrations in fish tissue 

samples declined from mean concentrations of 0.28 ppm in 1976 to 0.11ppm in 1984. 189 The 

decrease in mean lead concentrations was attributed primarily to reductions in the lead content of 

motor vehicle gasoline. Sources of contamination of lead to waterways frequently noted include 

lead gunshot, lead sinkers, and Superfund sites.190 Lead emissions from piston-engine aircraft 

may contribute to fish tissue lead concentrations in water bodies that are in close proximity to 

piston-engine aircraft activity. In one case, a state reported lead contaminated fish in a lake on 

airport property. Piston-engine aircraft emissions of lead also have the potential to contribute to 

fish tissue lead concentrations at water bodies throughout the U.S. due to the emission of lead inflight. These in-flight emissions are greatly dispersed in the environment and have been 

providing a source of lead to the environment for over 80 years.

The Fond du Lac Band of Lake Superior Chippewa, the Leech Lake Band of Ojibwe and 

the Mille Lacs Band of Ojibwe submitted comments to the Lead NAAQS docket noting the 

importance of fish consumption in their diet.191 The Fond du Lac Band of Lake Superior 

Chippewa also noted in their comments, “As a reservation with municipal airport within its 

 

187 In some instances states supply individual fish tissue sample results and in some instances states supply averages 

of multiple fish tissue sample results

188 State-specific fish advisories for lead can be downloaded from: 

http://oaspub.epa.gov/nlfwa/nlfwa.bld_qry?p_type=advrpt&p_loc=on

189 U.S. Environmental Protection Agency (2000) Guidance for Assessing Chemical Contaminant Data for Use in 

Fish Advisories. Volume 1: Fish Sampling and Analysis. EPA 823-B-00-007. p.4-59. Available online at: 

www.epa.gov/waterscience/fish/advice/volume1/index.html

190 U.S. Environmental Protection Agency, “Lead Fishing”. Retrieved on August 17, 2009 from: 

http://www.epa.gov/owow/fish/animals.html

191 See Docket ID Number EPA-HQ-OAR-2006-0735. The tribes that submitted comments were: The Bad River 

Band of Lake Superior Tribe of Chippewa Indians, The Quapaw Tribe of Oklahoma, The Leech Lake Band of 

Ojibwe, The Lone Pine Paiute-Shoshone Reservation, The Fond du Lac Band of Lake Superior Chippewa, and The 

Mille Lacs Band of Ojibwe. 
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exterior boundaries with two schools and tribal housing in close proximity to the airport (one 

half mile), leaded aircraft fuel is a concern.” The Leech Lake Band of Ojibwe noted in their 

comments, “Along with the concerns over the emission inventory, the Tribes have great concern 

regarding the amount of lead from “small” prop engine airports. On or very near the Leech Lake 

Reservation there are seven prop plane airports with many private air strips scattered throughout the 

area.” EPA is requesting comment on any information regarding the potential impact of lead 

emissions from piston-engine aircraft on aquatic environments.

B. Related Exposures of Concern

While the subject of this ANPR is focused on the emissions of lead from piston-engine 

aircraft, the use of tetraethyl lead in fuel contributes to additional public health and welfare 

issues that are also of concern to the Agency. Among these issues are 1) the contribution of lead 

emissions to ambient PM, especially in areas in nonattainment with the PM2.5 NAAQS, 2) the 

emissions of ethylene dibromide to the environment and 3) the evaporative emissions of 

tetraethyl lead. 

1. Lead Contribution to Ambient Particulate Matter 

As discussed in Section IV.A of this ANPR, lead emitted by piston engines is expected to 

be predominantly in the particle phase and will contribute to ambient PM. There are two U.S. 

National Ambient Air Quality Standards (NAAQS) for PM2.5: an annual standard (15 μg/m3) and 

a 24-hour standard (35 μg/m3). As of March 4, 2009 there are 39 1997 PM2.5 nonattainment 

areas. Area designations for the 2006 24-hour PM2.5 NAAQS were promulgated in 2009 for 31 
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areas.192 All of these nonattainment areas have at least one airport servicing aircraft using leaded 

avgas and most nonattainment areas have several airport facilities. The Los Angeles-South 

Coast Air Basin has 343 airport facilities which have a cumulative lead inventory of 15.0 tons. 

The contribution of PM-lead to these nonattainment areas ranges from 0.001 to 0.7% of the 

mobile source PM2.5 inventory in these areas. In each of four areas designated as nonattainment 

with the PM2.5 annual standard, there is at least one lead monitor at which design values for 

2006-2008 are greater than the 2008 Lead NAAQS and two of these counties have PM2.5

concentrations exceeding the 24-hour PM2.5 NAAQS. Reductions in lead emissions in these 

counties would help bring the area into attainment.

2. Ethylene Dibromide

As noted in Section IV.A, ethylene dibromide (1,2-dibromoethane) is added to leaded 

avgas to scavenge lead in order to prevent the deposition of lead oxide to valves and spark plugs. 

Emissions of ethylene dibromide are a concern to the EPA. Ethylene dibromide is classified in 

EPA’s Integrated Risk Information System database as likely to be carcinogenic to humans, and 

a number of chronic noncancer effects have been observed in animals and humans exposed to 

ethylene dibromide by inhalation and ingestion.193 EPA developed an inhalation reference 

concentration, ingestion dose and cancer unit risk estimates for inhalation and ingestion of 

ethylene dibromide.194 Evidence of nasal tumors, hemangiosarcomas and mesotheliomas in 

rodents was used by EPA to develop inhalation unit risk estimates (central tendency estimates 

 

192 http://www.epa.gov/pmdesignations/

193 U.S. Environmental Protection Agency (2004) Integrated Risk Information System (IRIS), IRIS Summary for 

1,2-dibromoethane CASRN 106-93-4. Available online at: http://www.epa.gov/ncea/iris/subst/0361.htm.

194 U.S. Environmental Protection Agency (2004) Integrated Risk Information System (IRIS), Toxicological Review 

of 1,2-dibromoethane in support of summary information on the Integrated Risk Information System. Available 

online at: http://www.epa.gov/ncea/iris/toxreviews/0361-tr.pdf
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and 95% upper bound estimates) of 3x10-4to 6x10-4per μg/m3. Evidence of forestomach 

tumors, hemangiosarcomas, thyroid follicular cell adenomas or carcinomas was used by EPA to 

develop drinking water unit risk estimates (central tendency estimates and 95% upper bound 

estimates) of 3x10-5to 6x10-5per μg/L assuming consumption of 2 L of water per day by a 70 kg 

human. EPA developed a reference concentration for chronic inhalation of 9 μg/m3based on the 

critical effect of nasal inflammation and a reference dose for chronic ingestion of 9 μg per kg per 

day based on the critical effects of testicular atrophy, liver peliosis, and adrenal cortical 

degeneration. The National Toxicology Program listed ethylene dibromide as "reasonably

anticipated to be a human carcinogen" in the Eleventh Report on Carcinogens in 2005.195 The 

International Agency for Research on Cancer (IARC) has classified ethylene dibromide as a 

Group 2A carcinogen: probably carcinogenic to humans. 

In the additive package used to dose fuel with lead, ethylene dibromide is added to 

achieve a lead-to-bromine atom ratio of 1:2 and a bromine-to-lead weight ratio of 1:2.196 The 

concentration of ethylene dibromide in leaded avgas is listed as less than 4 milliliters per gallon 

(<9 grams per gallon).197 Since ethylene dibromide was measured in the exhaust and evaporative 

emissions from light-duty vehicles in the U.S. when they were operated on leaded fuel 

containing ethylene dibromide we anticipate piston-engine aircraft are currently a source of 

ethylene dibromide to air.198 Measurements of ethylene dibromide have not been made that 

 

195 National Toxicology Program (NTP) (2005). 11th Report on Carcinogens. Public Health Service, U.S. 

Department of Health and Human Services, Research Triangle Park, NC. Available from: http://ntpserver.niehs.nih.gov.

196 Thomas VM; Bedford JA; Cicerone RJ. (1997) Bromine emissions from leaded gasoline. Geophys Res Letters 

24(11):1371-1374.

197 Chevron Material Safety Data Sheet for aviation gasoline. Available online at: 

http://www.chevronglobalaviation.com/docs/aviation_gas.doc

198 Sigsby, J.E.; Dropkin, D.L.; Bradow, R.L.; Lang, J.M. (1982) Automotive Emissions of Ethylene Dibromide. 

SAE Technical Paper Series 820786.
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would allow estimation of the exhaust and evaporative emissions from piston-engine aircraft as 

well as the emissions associated with refueling and pre-flight fuel checks. 

In addition to contributing to ambient concentrations, ethylene dibromide may also enter 

underground aquifers via leaking underground storage tanks or fuel spills. Studies demonstrate 

that ethylene dibromide may persist for long periods of time in certain groundwater 

environments.199 The EPA established a Maximum Concentration Level (MCL) of 0.05 g/L for 

ethylene dibromide, which is 100-fold lower than the MCL for benzene and 300-fold lower than 

the MCL for lead. The MCL is the highest level of a contaminant that is allowed in drinking 

water and is an enforceable drinking water standard.200 

The EPA Office of Underground Storage Tanks (OUST) and Office of Research and 

Development’s National Risk Management Research Laboratory (NRMRL) in association with 

the Association of State and Territorial Solid Waste Management Officials (ATSWMO) have 

formed a team to evaluate the potential for public health and welfare effects attributable to 

ethylene dibromide from past or present fuel leaks and spills.201 Among the goals of the 

EPA/ATSWMO team is to develop information on the distribution of ethylene dibromide in 

groundwater at leaking underground storage tank sites in states that do not routinely monitor this 

contaminant. Water samples for this study were provided by state agencies to EPA between 

October 2005 and July 2007. Of the 802 groundwater samples provided from 102 sites, ethylene 

 

199 U.S. Environmental Protection Agency Office of Research and Development (2008) Natural Attenuation of the 

Lead Scavengers 1,2-Dibromoethan (EDB) and 1,2-Dichloroethane (1,2-DCA) at Motor Fuel Release Sites and 

Implications for Risk Management, Chapter 2. EPA 600/R-08/107. Available online at: www.epa.gov/ada. 

200 U.S. Environmental Protection Agency, “Drinking Water Contaminants” Available online at: 

http://www.epa.gov/safewater/contaminants/index.html

201 U.S. Environmental Protection Agency Office of Research and Development (2008) Natural Attenuation of the 

Lead Scavengers 1,2-Dibromoethan (EDB) and 1,2-Dichloroethane (1,2-DCA) at Motor Fuel Release Sites and 

Implications for Risk Management. p.3. EPA 600/R-08/107. Available online at: www.epa.gov/ada. 
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dibromide was detected in 54 samples, 43 of which had ethylene dibromide concentrations above 

the MCL.

202

 These sites did not include analysis of groundwater at airports. 

While not the focus of this ANPR, ethylene dibromide exposure from inhalation or 

ingestion pathways is an ongoing concern for EPA, and reduction in the use of leaded gasoline 

containing ethylene dibromide may reduce exposure and risk to public health and welfare from 

ethylene dibromide.

3. Non-Exhaust Exposure to Tetraethyl Lead

Tetraethyl lead is a volatile component of leaded avgas. The largest source of tetraethyl

lead exposure is expected to originate from evaporative emissions associated with fuel 

production, fuel distribution, aircraft refueling, pre-flight fuel checks, accidental spills, and fuel 

tank venting. Pilots check fuel for contaminants by draining a small amount of fuel from each 

tank sump before flight and after refueling. This fuel is frequently deposited onto the tarmac 

after the fuel check. EPA is interested in data regarding this practice and any estimates of lead 

emitted to the air by evaporation of the alkyl lead in the fuel deposited on the tarmac. Alkyl lead 

becomes oxidized in the atmosphere by direct photolysis, reaction with ozone, and by reaction 

with hydroxyl compounds. Therefore, depending on ambient conditions, alkyl lead may exist in 

the atmosphere for hours to days.

Pilots, aviation fuel attendants and mechanics are likely to be among the most highly

exposed population to alkyl lead. These populations are at risk due to both inhalation and 

 

202 U.S. Environmental Protection Agency Office of Research and Development (2008) Natural Attenuation of the 

Lead Scavengers 1,2-Dibromoethan (EDB) and 1,2-Dichloroethane (1,2-DCA) at Motor Fuel Release Sites and 

Implications for Risk Management. p.4. EPA 600/R-08/107. Available online at: www.epa.gov/ada. 
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possible dermal exposure. Absorption of inhaled alkyl lead into the bloodstream is higher than 

that for inorganic lead compounds which are generally in particulate form (AQCD for Lead, 

Section 4.2.1). In addition to exposure to lead in the exhaust emissions from piston-engine 

aircraft, the PBT National Action Plan for Alkyl-lead203 noted that aviation fuel attendants and 

mechanics are potentially exposed to alkyl lead emissions due to inhalation of alkyl lead 

compounds released to the air during fueling, via evaporative emissions from spills, or via 

evaporative emissions from unused gasoline remaining in the engine or fuel tanks. Further, these 

populations are also at risk because of possible dermal absorption of gasoline containing alkyl

lead compounds. Due to the lipophilic nature of alkyl lead and its ability to permeate biological 

membranes, alkyl lead is absorbed rapidly and extensively through the skin (AQCD for Lead, 

page 4-12). In addition to direct human exposure, runoff and deposition of alkyl lead to 

waterways would increase the amount of lead available for uptake by aquatic plants and animals 

(see Section V.A.7 of this ANPR for more information). 

VI. Additional Information Available for the NPRM to Evaluate the 

Potential for Public Health and Welfare Impacts and Considerations 

Regarding Engine Emission Standards

As noted in the Overview section of this ANPR, in this action we are describing 

information currently available and information being collected that will be used by the 

 

203 U.S. Environmental Protection Agency Persistent, Bioaccumulative, and Toxic Pollutants (PBT) Program (2002) 

PBT national action plan for alkyl-Pb. Washington, DC. Page 14. Available online at: 

http://www.epa.gov/pbt/pubs/Alkyl_lead_action_plan_final.pdf
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Administrator to subsequently exercise her judgment regarding whether aircraft lead emissions 

from avgas use cause or contribute to air pollution which may reasonably be anticipated to 

endanger public health or welfare. These additional data will come from lead monitoring being 

planned to satisfy requirements of the Lead NAAQS, air quality modeling planned at EPA that is 

described below and any information submitted to EPA during the comment period for this 

ANPR.

A. The Lead NAAQS and Lead Emissions from Piston-Engine Aircraft

On November 12, 2008, when EPA promulgated revisions to the Lead NAAQS, EPA 

also adopted revisions to ambient air monitoring requirements for lead, described the approach 

for implementing the revised standards, and provided an implementation timeline. We describe 

each of these activities as well as more recent activities below. This section also discusses the 

most current information available regarding how implementation of the Lead NAAQS may

provide additional data on the potential for lead emissions from piston-engine aircraft to cause or 

contribute to ambient air concentrations that exceed the 2008 Lead NAAQS. 

Acknowledging that the existing monitoring network for lead is not sufficient to 

determine whether many areas of the country would meet the 2008 Lead NAAQS, the EPA redesigned the nation’s lead monitoring network to allow assessment of compliance with the 

revised lead standard. Lead monitoring requirements promulgated in 2008 stipulate that, at a 

minimum, monitoring agencies must place monitors at maximum impact areas where lead 

emissions are greater than or equal to one ton or more per year. We refer to these monitors as 
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source-oriented monitors. EPA Regional Administrators may waive the source-oriented 

monitoring requirements if the monitoring agency can demonstrate that emissions from the 

source will not contribute to maximum air lead concentrations greater than 50 percent of the 

revised standard, or 0.075 ug/m3. EPA estimated that approximately 135 facilities emit lead at 

levels over the one ton emission threshold, making them subject to the lead monitoring 

requirements. Lead monitors are operating at a small number of these sources (described in 

Section VI.A.2 below). For the remainder, source-oriented monitors are to be operational by 

January 1, 2010.

EPA also required monitors to be operated in each of the 101 urban areas with 

populations greater than 500,000 in order to gather information on the general population’s 

exposure to lead in air. We refer to these monitors as population-oriented monitors. 

Following promulgation of the 2008 Lead NAAQS and monitoring requirements, the 

Natural Resources Defense Council, the Missouri Coalition for the Environment Foundation, 

Physicians for Social Responsibility, and the Coalition to End Childhood Lead Poisoning 

(Petitioners) petitioned EPA for reconsideration of the lead emission rate at which we required 

monitoring (the “emission threshold,” currently 1.0 tpy).204 EPA granted the petition to 

reconsider aspects of the monitoring requirements and proposed revisions to lead ambient air 

monitoring requirements in December 2009 (74 FR 69050).

Also as part of promulgating the 2008 Lead NAAQS, EPA described the approach for 

implementing the revised standards and provided an implementation timeline. EPA will use 

 

204 The petition is available at: http://www.epa.gov/air/lead/pdfs/OAR.09.000.7687.pdf
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county boundaries as the presumptive boundaries for nonattainment areas, and adjustments to 

boundaries will be made on case-by-case bases. States in which there is sufficient monitoring 

data made recommendations for areas to be designated attainment, nonattainment, or 

unclassifiable in October 2009. States update their recommendations to EPA in October 2010 

using any additional monitoring data available from the increased source-oriented monitoring 

network described above. Final designations of all attainment, nonattainment and unclassifiable 

areas will be effective no later than January 2012. Where data are sufficient from the currently

existing lead monitoring network, we expect that initial designations will be effective January

2011. States are directed to submit State Implementation Plans (SIPs) no later than eighteen 

months after designation, outlining how they will reduce pollution to meet the lead standards. 

States are required to attain the standards no later than five years after designation. Additional 

information regarding the lead standard implementation is available at 

www.epa.gov/air/lead/actions.html and in the 2008 Lead NAAQS (73 FR 67030-67043).

1. Monitoring Lead at Airports to Evaluate Ambient Concentrations to Which Lead 

Emissions from Piston-Engine Aircraft Contribute

Among the estimated 135 source-oriented lead monitoring sites, there are four airports 

where we expect lead monitoring to begin in January 2010. These airports are the Van Nuys 

Airport in Van Nuys, CA; the Phoenix Deer Valley Airport in Phoenix, AZ; the Centennial 

Airport in Englewood, CO; and the Daytona Beach International Airport in Daytona Beach, FL. 

In each of these areas, we will, as data becomes available, evaluate the impact of lead emissions 

from piston-engine aircraft on air quality.
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2. Evaluating the Contribution of Lead Emissions from Piston-Engine Aircraft to 

Areas Approaching or Exceeding the Lead NAAQS

In this section we discuss available information and information that will become 

available in 2010 that can be used to evaluate the potential for lead emissions from piston-engine 

aircraft to contribute to ambient concentrations in areas exceeding the Lead NAAQS. This 

evaluation may include the following: 1) areas currently out of attainment or designated as 

maintenance with the 1978 Lead NAAQS; 2) areas with current lead monitors that are out of 

attainment with the 2008 Lead NAAQS; and 3) locations that will have new lead monitors to 

meet the 2008 Lead NAAQS source-oriented monitoring requirements. In each of these areas, 

we will, as data become available, evaluate the contribution of lead emissions from piston-engine 

aircraft to lead inventories and air quality. 

The EPA is retaining the 1978 Lead NAAQS until one year after designations for the 

2008 Lead NAAQS, except in current nonattainment areas. In those areas, EPA will retain the 

1978 standard until the area submits, and EPA approves, attainment and/or maintenance 

demonstrations for the new standards. Only two areas, East Helena, MT (including Lewis and 

Clark counties), and part of Jefferson County in Herculaneum, MO, are designated 

nonattainment with the 1978 Lead NAAQS. The industrial facility causing nonattainment with 

the Lead NAAQS in the East Helena area closed in 2001. Eleven areas are designated as 

maintenance areas, only three of which currently have lead monitors. These three locations (Iron 

County, MO, Dakota County MN, and Collin County, TX) have lead monitors with design value 
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concentrations exceeding the 2008 Lead NAAQS. The design value is the highest “rolling” three 

month average over a three-year period that is relevant for comparison to the level of the 2008 

Lead NAAQS. 

Implementation of the 2008 Lead NAAQS is underway, and we have not yet designated 

areas under it. When EPA promulgated the 2008 Lead NAAQS, EPA provided a list of 18 

counties with design values exceeding the 2008 lead standard of 0.15 μg/m3. Using more recent 

data from EPA’s Air Quality System, there are 14 sites at which design values exceed the 2008 

Lead NAAQS (Table 3). Over 4.6 million people live in the counties where design values are 

greater than the 2008 Lead NAAQS. After EPA designates areas that currently have sufficient 

lead monitoring data, no later than October 15, 2010, we will evaluate the contribution of lead 

emissions from piston-engine aircraft to lead inventories in nonattainment, maintenance and in 

some cases, unclassifiable areas, depending on the presence of point sources of lead and the 

status of ambient lead monitoring in those areas. 

Table 3. Counties with Maximum Rolling Quarterly Average Lead Concentrations Exceeding 

the 2008 Lead NAAQS. 

County, State EPA Region County Population 

(2000 Census)

Design Value, 2006-

2008 (g/m3)

Jefferson, MO 7 198,099 2.89

Iron, MO 7 10,697 2.46

Delaware, IN 5 118,769 2.16
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Hillsborough, FL 4 998,948 1.77

Collin, TX 6 491,675 1.26

Pike, AL 4 29,605 1.21

Dakota, MN 5 355,904 0.70

Fulton, OH 5 42,084 0.69

Berks, PA 3 373,638 0.36

Madison, IL 5 258,941 0.28

Logan, OH 5 46,005 0.27

Sullivan, TN 4 153,048 0.26

Beaver, PA 3 181,412 0.20

Cuyahoga, OH 5 1,393,978 0.17

Lead emissions from piston-engine aircraft operating at airports outside nonattainment 

areas can also contribute to lead measured in the nonattainment area. In addition, other sources 

of lead that do not, by themselves, exceed the lead emission monitoring threshold may be located 

near airports. For example, at some airports in the U.S., race track venues are located 

immediately adjacent to runways where piston-engine aircraft operate. We are seeking 

information regarding ambient concentrations of lead that can result from the combined 

emissions of leaded fuel used in some race vehicles, lead emissions from piston-engine aircraft 

and other sources of ambient lead.

The EPA intends to conduct modeling analyses to evaluate the contribution of these lead 

emissions to nonattainment areas and areas that may be approaching nonattainment 

concentrations. Lead emitted by piston-engine aircraft flying through nonattainment areas may
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also contribute to lead measured in the nonattainment area. These emissions would be 

potentially challenging to quantify, although a series of scoping analyses could be conducted. 

We seek comment on characterizing the contribution of lead emissions from piston-engine 

aircraft flying through areas that are not attaining the 2008 Lead NAAQS and the potential 

contribution of piston-engine lead emissions that may be transported into lead nonattainment 

areas.

As noted above, approximately 135 new lead monitors will begin collecting ambient lead 

samples starting in January 2010 in order to satisfy the source-oriented monitoring requirements 

of the 2008 Lead NAAQS. In the NPRM we will discuss the potential contribution of lead from 

piston-engine aircraft to these areas where the ambient data suggest lead concentrations are close 

to or exceeding the 2008 Lead NAAQS of 0.15 g/m3. 

B. Additional Information EPA is Collecting to Evaluate Ambient Lead 

Concentrations Attributable to Emissions from Piston-Engine Aircraft

In 2008 EPA initiated a study to provide information regarding the local-scale gradient in 

lead concentrations on- and near airport facilities with piston-engine powered aircraft activity.

205

 

This study focused mainly on developing an approach for modeling lead emissions from pistonengine aircraft using the Meteorological Society (AMS)/EPA Regulatory Model (AERMOD), 

and evaluating it using air quality measurements. For purposes of local-scale dispersion 

 

205 U.S. EPA (March 2010) Memorandum from Marion Hoyer to the docket EPA-HQ-OAR-2007-0294, titled, 

“Work Plan for Air Quality Modeling and Monitoring of Lead.”

Emissions from Piston-Engine Powered Aircraft.” Docket number EPA-HQ-OAR-2007-0294. 
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modeling, AERMOD is EPA’s preferred model.206 The approach developed includes 

apportioning lead emitted during landing and take-off to different altitudes in order to 

characterize emissions during these modes of operation in a realistic manner. In addition, this 

modeling study includes analysis of the spatial and temporal emissions from piston-engine 

aircraft during the other modes of aircraft operation (e.g., taxi, run-up check, take-off, landing). 

The modeling results include an evaluation of the relative contributions of all known sources of 

lead to the local ambient air, including piston-engine aircraft, local traffic, resuspended road 

dust, and industrial sources within 20 km of the airport selected for our case study. The EPA 

study at the Santa Monica Airport was recently completed.207

As part of this work, we collected air, soil and house dust samples for lead analysis in 

order to conduct a model-to-monitor evaluation, and to evaluate the potential for lead emissions 

from piston-engine aircraft to create a gradient in air, soil and house dust concentrations of lead 

in proximity to the airport activities. 

We selected the Santa Monica municipal airport for this study because of the data 

available from the monitoring study conducted by the SCAQMD in 2005-2007 discussed in 

Section IV.B of this ANPR. In addition, there are no major point sources of lead in close 

proximity to the airport, simplifying the model development and interpretation of monitoring 

results. 

EPA intends to use this modeling approach to evaluate potential for exceedance of the 

 

206 The EPA provides modeling guidance for AERMOD at www.epa.gov/ttn/scram/guidanceindex.htm and 

www.epa.gov/scram001/dispersion_prefree.htm#aermod. A post-processor for AERMOD that reads model output 

and calculates rolling 3-month averages for the period modeled to provide lead concentrations that can be compared 

with the Lead NAAQS is available online at: http://www.epa.gov/ttn/amtic/files/ambient/pb/leadpost.zip.

207 The report from this study is posted at www.epa.gov/otaq/aviation.htm.
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Lead NAAQS on airport property and surrounding areas, as well as providing an approach to 

characterize the contribution of lead emissions from piston-engine aircraft to areas with ambient 

lead concentrations currently exceeding the 2008 Lead NAAQS. This modeling approach will 

also allow us to quantify the changes in ambient lead concentrations following the 

implementation of different piston-engine control strategies. The application of this modeling 

approach to a case-study airport could also be used as input to conduct a risk assessment 

evaluating the potential contribution of lead from piston-engine emissions on blood lead levels 

and IQ deficits for those living near or attending school near general aviation activity.

We request comment on all information EPA is collecting to evaluate ambient lead 

concentrations attributable to emissions from piston-engine aircraft and risk posed by emissions 

of lead from piston-engine aircraft. 

C. Considerations Regarding Engine Emission Standards 

A positive endangerment and cause or contribute finding with respect to the emissions of 

lead from general aviation aircraft would trigger EPA’s duty to set emission standards. In 

considering emission standards, EPA would consider controlling emissions from piston engines 

using aviation gasoline in aircraft. In cooperation with FAA, EPA would evaluate the technical 

feasibility of a possible phase-down or elimination of leaded aviation gasoline. One option to 

consider, for example, could be an emissions standard (established under 40 CFR 87) that would 

require all newly-manufactured general aviation piston engines to be able to operate with 

appropriate reliability and durability on unleaded aviation gasoline by some future date. Such a 
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standard might require that new engines used in aircraft would have to receive an FAA type 

certificate that reflects achievement of these requirements under FAA regulations set forth at 14 

CFR parts 33/34. 

Beyond this, EPA recognizes that there is a big challenge in dealing with the in-use fleet. 

Converting in-use aircraft/engines to operate on unleaded aviation gasoline would be a 

significant logistical challenge, and in some cases a technical challenge as well. In many cases, 

the implementation of this concept might depend upon efforts and actions of aircraft and engine 

manufacturers in identifying the necessary modifications and developing hardware as necessary. 

Depending on timing, these engines might need to be able to operate on either leaded or 

unleaded aviation gasoline, or a blend thereof. EPA recognizes that in many cases these 

modifications could trigger the need for FAA regulatory approval of the modifications for both 

the engines and airframes. Given the potentially large number of affected aircraft and the 

potential complexities involved, a program affecting in-use aircraft engines would need careful 

consideration by both EPA and FAA and the two agencies would need to work together in 

considering any potential program affecting the in-use fleet. 

EPA requests comment on this outline of approaches for transitioning the fleet to 

unleaded aviation gasoline, as well as potential implementation dates, if EPA were to trigger the 

duty to set emission standards. Comment is also requested on how a program could be best 

structured to assure that conversions conducted by engine manufacturers (OEMs), independent 

shops, and in the field by certified power plant mechanics are performed to fully meet the intent 

of a possible program without compromising the safety of those aircraft and engines. EPA also 

asks for comment on potential problems with this approach including suggested modifications, 
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improvements, or other approaches. EPA requests comment on how market incentives might be 

developed to encourage modification to run on unleaded aviation gasoline as part of a regulatory

requirement. 

As part of the responses to the Federal Register notice EPA published in November 2007 

entitled “Petition Requesting Rulemaking to Limit Lead Emissions from General Aviation 

Aircraft,” EPA received a number of comments addressing both technology and fuel-based 

options as potential measures to reduce or eliminate lead in avgas.209 In addition to these 

comments, EPA is aware of completed and ongoing work done under the auspices of the 

Coordinating Research Council and more recent viewpoints and efforts put forth by industry

trade associations, airframe/engine manufacturers, specialty vendors, aviation user groups, and 

other innovators. The work and perspectives of these groups on technology and avgas fuel 

quality options are important, and EPA asks for further comment reflecting any new data on 

technology developments, fuel formulation approaches, or other technical viewpoints.

According to Department of Energy data, annual demand for aviation gasoline is very

small in comparison to motor gasoline yet its use is as geographically widespread. This of 

course creates challenges for supply, distribution, and storage. EPA asks for comment on the 

avgas refining locations and practices, supply (including imports and exports, if any), details on 

distribution to terminals and airports, and storage practices for avgas at terminals and airports 

across the country. EPA is also interested in comments on progress and timeframes for 

developing alternatives to current leaded avgas and how these might be integrated into the fuel 

supply and distribution system.

 

209 72 FR 64570 (Nov. 16, 2007); EPA Docket EPA-HQ-OAR-2007-0294.
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VII. Statutory and Executive Order Reviews

Under Executive Order 12866, entitled Regulatory Planning and Review (58 FR 51735, 

October 4, 1993), this is a “significant regulatory action” because of the cross-agency nature of 

this issue. Accordingly, EPA submitted this action to the Office of Management and Budget 

(OMB) for review under Executive Order 12866 and any changes made in response to OMB 

recommendations have been documented in the docket for this action. Because this action does 

not propose or impose any requirements, other statutory and Executive Order reviews that apply 

to rulemaking do not apply. Should EPA subsequently determine to pursue a rulemaking, EPA 

will address the statues and Executive Orders as applicable to that rulemaking.

Nevertheless, the Agency welcomes comments and/or information that would help the 

Agency to assess any of the following: tribal implications pursuant to Executive Order 13175, 

entitled Consultation and Coordination with Indian Tribal Governments (65 FR 67249, 

November 6, 2000); environmental health or safety effects on children pursuant to Executive 

Order 13045, entitled Protection of Children from Environmental Health Risks and Safety Risks 

(62 FR 19885, April 23, 1997) and human health or environmental effects on minority or lowincome populations pursuant to Executive Order 12898, entitled Federal Actions to Address 

Environmental Justice in Minority Populations and Low-Income Populations (59 FR 7629, 

February 16, 1994). The Agency will consider such comments during the development of any

subsequent rulemaking.

Dated_____________

___________________________________
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Lisa P. Jackson,

Administrator

Advance Notice of Proposed Endangerment Finding for Lead Emissions from PistonEngine Aircraft Using Leaded Aviation Gasoline page 103 of 103