2

Data Gaps

Fate Data

Based on the PPO use pattern as a fumigant and its chemical properties, EFED will not request 

the fate data at this time but will use any available data requested by the Agency’s Health Effects

Division, such as field monitoring data, at the time of registration review risk assessment. 

Ecological Effect Data

The ecological effects database is considered incomplete for risk assessment. EFED 

recommends submission of the following studies. Details of the data gaps are discussed further 

in Section 6.8. 

Avian Acute Inhalation Toxicity Study (A Non-Guideline Study): Propylene oxide 

has fumigant uses that may result in exposure to birds. The acute effects to birds exposed 

to PPO are unknown. This is a non-guideline study under the 40 CFR Part 158 data 

requirements. 

Honeybee Acute Vapor Exposure Toxicity Study (A Non-Guideline Study):

Propylene oxide has fumigant uses that may result in exposure to honeybees. The toxicity 

of PPO to honeybees is unknown. This is a non-guideline study under the 40 CFR Part 

158 data requirements. 

Terrestrial Plants Special Study– Vegetative Vigor Vapor Exposure Toxicity Study 

(A Non-guideline Study): Propylene oxide has fumigant uses that may result in exposure 

to terrestrial plants. Knowledge of the toxicity of PPO to terrestrial plants is limited to 

soybean (MRID 4791701) data that have been submitted to the Agency, which partially 

satisfies the Agency’s data requirements for toxicity testing with terrestrial plants. Data 

on four monocots in two families including corn, six dicots species in four families 

including soybean and a root crop, is needed to completely assess the alkylating effects of 

PPO to terrestrial plants. This is a non-guideline study under the 40 CFR Part 158 data 

requirements. 

Label Uncertainties 

There are uncertainties in the usage of PPO in treatment facilities including the maximum

number of chambers, frequency of treatment and type of emision control device. These factors 

will directly influence emission rates and affect outdoor air concentrations. In addition, there is a 

lack of information related to the design of buildings for the fumigation, including the 

dimensions of buildings, type of buildings, as well as the number and relative locations of stack 

and vents that serve as the release points during PPO aeration operations. These variables all 

impact the magnitude of downwind dispersion from treated structures. EFED recommends label 

amendments to be made to clarify the above uncertainties. 
3

Problem Formulation for the Environmental Fate, 

Ecological Risk, Endangered Species, and Drinking 

Water Exposure Assessments in Support of the 

Registration Review of Propylene Oxide

CAS: 75-56-9

PC Code: 042501

Environmental Fate and Effects Division

Prepared by:

Stephen Carey, Biologist

He Zhong, Ph.D., Biologist

U.S. Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch I

1200 Pennsylvania Ave., NW

Mail Code 7507P

Washington, DC 20460

Reviewed by:

Michael Lowit, Ph.D., Ecologist

Stephen Wente, Ph.D., Fate Scientist
4

Table of Contents

1. Purpose.................................................................................................................................... 5

2. Problem Formulation .............................................................................................................. 5

2.1. Nature of Regulatory Action ........................................................................................ 5

2.2. Previous Assessments................................................................................................... 5

2.2.1. Ecological Risk Assessments................................................................................... 5

2.2.2. Drinking Water Exposure Assessments................................................................... 5

3. Stressor Source and Distribution ............................................................................................ 5

3.1. Mechanism of Action....................................................................................................... 5

3.2. Overview of Pesticide Use and Usage ............................................................................. 6

3.3. Chemical and Physical Properties, and Environmental Fate and Transport .................... 7

3.4. Clean Water Act............................................................................................................. 11

4. Receptors.................................................................................................................................. 11

4.1. Effects to Aquatic Organisms ........................................................................................ 11

4.2. Effects to Terrestrial Organisms .................................................................................... 12

4.3. Incident Databases Review ............................................................................................ 13

5. Exposure Pathways of Concern ............................................................................................... 13

6. Analysis Plan ........................................................................................................................... 14

6.1. Stressors of Concern .......................................................................................................... 15

6.2. Measures of Exposure........................................................................................................ 15

6.3. Measures of Effect ............................................................................................................. 15

6.4. Integration of Exposure and Effects .................................................................................. 16

6.5. Endangered Species Assessments...................................................................................... 16

6.6. Endocrine Disruptor Screening.......................................................................................... 16

6.7. Drinking Water Assessment .............................................................................................. 16

6.8. Preliminary Identification of Data Gaps............................................................................ 16

6.8.1. Environmental Fate Data ............................................................................................ 17

6.8.2. Ecological Effects Data........................................................................................... 17

References..................................................................................................................................... 24

Appendix I .................................................................................................................................... 26

Appendix II................................................................................................................................... 32
5

1. Purpose

The purpose of this problem formulation is to provide an understanding of what is known about 

the environmental fate, ecological effects, and currently registered uses of propylene oxide 

(PPO) (or 1,2-propylene oxide or epoxypropane) as a fumigant. This document provides a plan 

for analyzing data relevant to PPO and for conducting environmental fate, ecological risk, 

endangered species, and drinking water exposure assessments for its registered uses. 

Additionally, this problem formulation identifies data gaps, uncertainties, and potential 

assumptions used to address those uncertainties relative to characterizing the potential ecological 

risk associated with the registered uses of PPO.

2. Problem Formulation

2.1. Nature of Regulatory Action

As part of the implementation of the new Registration Review program1pursuant to Section 3(g) 

of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), the Agency is beginning its 

evaluation of PPO to determine whether it continues to meet the FIFRA standard for registration. 

This problem formulation in support of the registration review of PPO will be posted in the 

initial docket which will open the public phase of the review process.

2.2. Previous Assessments

2.2.1. Ecological Risk Assessments

The Agency’s previous risk assessment for PPO concluded that there are likely no concerns for 

acute lethality or reproduction impairment in terrestrial mammals, reptiles, terrestrial phase 

amphibians, fish and aquatic invertebrates (USEPA 2006). For plants, there was insufficient 

information to preclude the potential concern that PPO may pose risks to terrestrial and aquatic 

plants; thus, the risks could not be precluded. Risk to terrestrial invertebrates is uncertain. 

2.2.2. Drinking Water Exposure Assessments

A drinking water assessment (DWA) has not been conducted for PPO. 

3. Stressor Source and Distribution

As a fumigant, PPO is formulated as a pressurized liquid and/or gas used in chambers for the 

sterilization of packaged food and as a post-harvest treatment for agricultural commodities. Two 

degradates, chloropropanol and 1,2-propanediol, were identified in open literature data.

3.1. Mechanism of Action

PPO is a fumigant used as an insecticide to control insect infestations. It is also used as sterilant 

to prevent bacteria, mold contamination, and microbial spoilage for food and nonfood products 

(USEPA 2006). PPO has been shown to cause central nervous system effects such as ataxia, 

uncoordination, and depression in rats (Propylene Oxide by Dow, accessed 3/18/2013).

 

1

http://www.epa.gov/oppsrrd1/registration_review/
6

(http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_0036/0901b80380036c15.pdf?fi

lepath=propyleneoxide/pdfs/noreg/117-01641.pdf&fromPage=GetDoc). Occupational Safety & 

Health Administration (OSHA) established PPO permissible exposure limit (PEL) as 100 ppm

and the vapor can affect eyes, skin and respiratory system 

https://www.osha.gov/dts/chemicalsampling/data/CH_265000.html (accessed 5/7/2013). PPO is 

a possible carcinogen, mutagen, and teratogen in animals and humans.

3.2. Overview of Pesticide Use and Usage

PPO is registered for both agricultural and non-agricultural use according to the Biological and 

Economic Analysis Division (BEAD) (USEPA 2012). It can be used in sealed chambers

(Propylene Oxide Fumigant with 100% a.i.) or in non-sealed structures including trailers, 

containers, rail cars, tarped materials and tents (Propoxide 892 with 8%, a.i.) for agricultural 

commodities: processed food/feed stored products (raisins, grapes, plums, prunes/figs, cocoa 

beans, cocoa powder, spices, birdseed, processed nuts) and non-agricultural sites: transportation 

vehicles, empty containers (processed feed/food, raw agricultural commodities feed/food), 

airtight chambers, shipping commercial transportation (containers, empty trailers, empty railroad 

boxcars feed/food), pharmaceutical materials, tents, and vaults. PPO is formulated as a 

pressurized gas. The maximum application rate is 150 lb a.i./1000 ft3(or 24 oz a.i./ft3) in a 

sealed chamber (Table 1). In addition, it is also used at a concentration of 8% with an inert gas 

(carbon dioxide, nitrogen) for figs, dried plums (prunes), and raisins (USEPA 2012). PPO is 

only used for processed food/ feed stored products. 

The California Department of Pesticide Regulation (CDPR) reported that in 2010, a total of

300,000 lb of PPO was used for crops in California, the 57th most used pesticide (by pound)

(USEPA 2012). EPA has estimated 64.8 million pounds of commodities were treated with PPO 

annually and the usage is mostly on nutmeats (~ 1.8% treated) and spices (~ 1% treated)

(USEPA 2006).

Table 1. Maximum Rates for Registered uses of Propylene Oxide

Use Method of 

Application

Single Maximum 

Application Rate 

(lb a.i./1,000 ft3)

Allowable Release 

Conditions

EPA Reg No.

Sealed 

Chamber1 Fumigation 150 5 ft stack with emission control

47870-1

47870-3

Sealed 

Chamber2 Fumigation 75 27 ft stack with 20 air changes per hour

47870-1

47870-3

Sealed 

Chamber2 Fumigation 75 40 ft stack with 4 air changes per hour

47870-1

47870-3

Other

Structures

3 Fumigation 2.8 None Specified 47870-3

1 The chamber (>5,000 ft3

and ≤ 10,000 ft3) must be equipped with equipment specifically designed to reduce 

PPO emissions by at least 95%.

2

For chambers <5,000 ft3, 4 air changes per hr for 40 ft stack or 20 air changes per hr for 27 ft stack are 

required. 
7

3Others include: atmospheric chambers, structures, tents, tarped product, rail cars or shipping containers. The 

PPO level in the enclosure is measured to be 10 ppm or less. 

3.3. Chemical and Physical Properties, and Environmental Fate and Transport

PPO is a colorless liquid that is highly volatile and flammable at room temperature and normal 

atmospheric pressure (USEPA 2006). PPO vapor is highly reactive and may form an explosive 

mixture with air. The compound can be removed from the atmosphere by slow oxidation and by 

rain. It evaporates from water and is not expected to bioaccumulate. PPO may polymerize with 

chlorine, ammonia, strong oxidants, and acids. The compound ring opening occurs in reactions 

with nucleophiles, such as water, alcohols, amines, halides, and sulfhydryl compounds. There 

are two reaction products formed during the PPO sterilization process – propylene chlorohydrin 

(PCH) and propylene bromohydrin (PBH). PCH contains two isomers, 1-chloro 2-propanol

(75%) and 2 chloro-1propanol (25%). In addition to PPO, PCH is considered to be a residue of 

concern for dietary risk assessment purposes because residues persist at high levels. PBH 

residues are minimal relative to PCH residues; therefore, PBH is not considered to be a residue 

of concern (USEPA 2006). The physical and chemical properties of PPO are listed in Table 2.
8

Table 2. Physical-chemical Properties of Propylene Oxide

Parameter Value and units Reference Comments

Chemical Propylene Oxide (PPO) USEPA 2006

(RED)

CAS Name 1,2-epoxypropane USEPA 2006

(RED)

Chemical Family Fumigant USEPA 2006

(RED)

Empirical Formula C3 H6 O1 USEPA 2006

(RED)

SMILES CC1CO1 EPI V4.10

CAS Number 75-56-9 USEPA 2006

(RED)

Structure USEPA 2006

(RED)

Molecular Weight 58.08 (g/mole) EPI V4.10

Density 0.83 g/ml, (20 °C) USEPA 2006

Vapor pressure 440 mm Hg (20oC) USEPA 2006

Henry’s law constant 6.96E-05(atm·m3/mol @ 25°C) EPI V4.10

Water Solubility 39.5 g/100mL (20oC) USEPA 2006

Octanol-water partition coefficient

(Kow)

0.03 (25°C) USEPA 2006

Air-water partition coefficient -2.546 (Log Kaw) EPI V4.10

Octanol-air partition coefficient 2.576 (Log Koa) EPI V4.10

Melting point -104(°C) IPCS1

Boiling point 34(°C) IPCS

Flash point <-37(°C) IPCS

Flammable limits 2-37% by volume IPCS

Log Kow 0.13 IPCS

Reaction Products

1,2-propanediol 

CAS No: (57-55-6)

Molecular Formula: C3H8O2

Mass: 76.09 g/mol

SMILES: CC(O)CO

EPI V4.10

&

USEPA 2006

(RED)

(also called propane1,2-diol, or 

Propylene glycol)

Chloropropanol 

CAS No: 96-24-2

Molecular Formula: C3H7ClO2

Mass: 110.539 g/mol

SMILES: ClCC(O)CO

EPI V4.10

&

IPCS

(also called 3-

MCPD, 3-

monochloropropane1,2-diol or 3-

chloropropane-1,2-

diol)
9

Table 2. Physical-chemical Properties of Propylene Oxide

Parameter Value and units Reference Comments

Propylene chlorohydrin (PCH)

1-chloro 2-propanol (75%)

CAS No: 78-89-7

Molecular Formula:C3H7ClO

Mass: 94.54 g/mol

SMILES: CC(O)CCl

EPI V4.10

&

USEPA 2006

(RED)

Propylene chlorohydrin (PCH)

2 chloro-1propanol (25%)

CAS No: 78-89-7

Molecular Formula:C3H7ClO

Mass: 94.54 g/mol

SMILES: CC(Cl)CO

EPI V4.10

&

USEPA 2006

(RED)

1

International Programme on Chemical Safety (IPCS). Environmental Health Criteria Monographs. Available at 

http://www.inchem.org/documents/ehc/ehc/ehc56.htm (Accessed 2/27/2013).

IPCS offered the following formula to convert gas concentration in cubic air (mg/m3) into parts

per million (ppm): 

Conversion Factor: 1 ppm = 2.37 mg/m3air at 25 °C and 101.3 kPa (760 mm Hg)

PPO enters the environment mainly through release of vented gases during/after the application. 

Bogyo et al. (1980) reported that most of the applied PPO fumigant enters the atmosphere. A 

previous estimated total PPO loss to the atmosphere was about 600 tonnes, which is 

approximately 0.07% of total PPO production in the USA (Storck, 1981; US EPA, 1981). 

The entire suite of fate studies described under the 40 CFR 158 data requirements have not been 

submitted to the Agency by the registrant (Table 3). This was the result of assuming indoor 

fumigation did not result in significant concentrations of PPO outside of the fumigated enclosure. 

However, labeled uses associated with the Propoxide 892 product do not entirely fall within the 

indoor uses category. These uses include rail cars, tented areas, tarped materials, and in-field 

treatment chambers. The previous ecological risk assessment addresses risks associated with the 

Propoxide 892 uses and the expected environmental concentrations (EECs) of PPO in terms of 

“air concentration of concern” were established by the Probabilistic Exposure and Risk Model 

for Fumigants model (PERFUM model) as 2.42 g/m3for acute non-listed and listed species

(USEPA 2006). An open literature review suggests that a majority of PPO will be rapidly 

removed from the atmosphere via hydroxyl radical oxidation. On the basis of a theoretical rate 

constant for this reaction, the atmospheric residence time of PPO was calculated to be 8.9 days 

(Cupitt, 1980). Because of its high solubility in water (395 g/L, Table 2), PPO levels in air can 

also be reduced via washout by rain (Bogyo et al., 1980). No data were found concerning the 

rate of volatilization of PPO from water. However, PPO’s half-life was estimated to be >1 hour

(Conway et al., 1983). Chemical degradation in water via ionic reactions appears a slow process 

under environmental conditions. In neutral fresh water and catalyzed by acid at 25 °C, PPO will 

react to form 1,2-propanediol with a half-life of approximately 12 days (Koskikallio & Whalley, 

1959). In neutral marine water, there is a preference for the formation of 1-halopropan-2-ol 
10

(Addy & Parker, 1963). Bogyo et al. (1980) estimated approximately 80% of the PPO present 

will react with chloride to form chloropropanol; the remainder will react with water to form 1,2-

propanediol at 25 °C in neutral sea water of 3% salinity. The overall half-life with respect to 

these reactions is 4 days, but actual retention time in water may only be in few hours due to 

volatilization (Conway et al., 1983).

Microorganisms were found to degrade PPO very slowly. The biological oxygen demand (BOD) 

over 5 days was 8% of the theoretical oxygen demand (Bridié et al., 1979). Bont et al. (1982) 

found the first step in bacterial metabolism is the conversion of propylene oxide to 1,2-

propanediol by epoxide hydrolase, followed by dehydration and oxidation .

Table 3. Environmental Fate of Propylene Oxide

Parameter Value Reference

Hydrolysis (t 1⁄2 @ 25oC, pH 7) 3.6 days Bogyo et al., 1980

Aqueous Photolysis (t 1⁄2 ) No Data

Soil Photolysis (t 1⁄2 ) No Data

Aerobic Soil Metabolism (t 1⁄2 ) No Data

Anaerobic Aquatic Metabolism (t 1⁄2 ) No Data

Aerobic Aquatic Metabolism (t 1⁄2 ) No Data

Bioconcentration / Depuration (t 1⁄2 ) No Data

Mobility

Koc 7.097 (mL/g) EPI V4.10

Field Dissipation

Terrestrial Field Dissipation 

(t 1⁄2 ) No Data

Volatilization (t 1⁄2 from Model River) 7.189 hrs EPI V4.10

Reaction Products

1,2-propanediol 

(in neutral fresh water and catalyzed 

by acid at 25 °C)

50% PPO formed 1,2-propanediol 

in 12 days

Koskikallio & 

Whalley, 1959

Chloropropanol 

(in neutral sea water of 3% salinity at 

25 °C)

80% of the PPO will react with 

chloride to form chloropropanol; 

the remainder will react with water 

to form 1,2-propanediol.

The overall half-life is 4 days.

Bogyo et al. 1980
11

3.4. Clean Water Act

PPO is not identified as a cause of impairment for any water bodies listed as impaired under 

section 303(d) of the Clean Water Act2. In addition, total maximum daily loads (TMDL) have 

not been developed for this fumigant3. The Impaired Waters and TMDL website can be 

consulted for more information4. The Agency invites submission of water quality data for PPO. 

To the extent possible, data should conform to the quality standards in the OPP Standard 

Operating Procedure: Inclusion of Impaired Water Body and Other Water Quality Data in

OPP’s Registration Review Risk Assessment and Management Process5, in order to ensure they 

can be used quantitatively or qualitatively in pesticide risk assessments.

4. Receptors

Tables 4 and 5 provide a summary of the aquatic and terrestrial taxonomic groups, respectively, 

and most sensitive surrogate species tested to characterize the potential acute and chronic 

ecological effects of PPO. In addition, the tables provide a preliminary overview of the potential 

acute toxicity of PPO by providing the acute toxicity classifications. In the absence of effects 

data for PPO, information sources from other alkylene oxides (e.g., ethylene oxide (ETO) which 

is structurally similar to PPO) have been useful in approximating the ecological effects of PPO. 

4.1. Effects to Aquatic Organisms 

Table 4. Summary of the Most Sensitive Endpoints from Aquatic Toxicity Studies for PPO 

Taxonomic 

Group

Study Type Surrogate Species Toxicity Value

(mg a.i./L)

Acute Toxicity 

Classification 

or Adverse 

Effect 

Observed

Source

(Study 

classification)

Freshwater fish1 Acute

Fathead minnow

(Pimephales 

promelas)

LC50 = 84 Slightly toxic Conway et al, 

19832

Chronic No data available. 

Freshwater 

invertebrates

Acute Water Flea 

(Daphnia magna)

EC50 = 137 Practically nontoxic

Conway et al, 

19832

Chronic No data available.

Estuarine/marine 

fish

Acute Striped mullet 

(Mugil cephalus)

LC50 = 89 Slightly toxic Crews et al, 1974

Chronic No data available.

Estuarine/marine 

invertebrates

Acute Brine shrimp 

(Artemia sp.)

EC50 = 490 Practically nontoxic

Conway et al, 

19832

Chronic No data available.

Aquatic plants 

and algae Vascular Duckweed (Lemna gibba)

EC50 >0.87

NOAEC = 0.87 --

a MRID 47921702

(Acceptable)b

 

2

http://iaspub.epa.gov/tmdl_waters10/attains_nation_cy.cause_detail_303d?p_cause_group_id=885

3

http://iaspub.epa.gov/tmdl_waters10/attains_nation.tmdl_pollutant_detail?p_pollutant_group_id=885&p_pollutant_

group_name=PESTICIDES

4

http://www.epa.gov/owow/tmdl/

5

http://www.epa.gov/oppfead1/cb/ppdc/2006/november06/session1-sop.pdf
12

Table 4. Summary of the Most Sensitive Endpoints from Aquatic Toxicity Studies for PPO 

Taxonomic 

Group

Study Type Surrogate Species Toxicity Value

(mg a.i./L)

Acute Toxicity 

Classification 

or Adverse 

Effect 

Observed

Source

(Study 

classification)

Non-vascular

Freshwater green 

alga 

Pseudokirchneriella 

subcapitata

EC50 >0.86

NOAEC= 0.86 --

a MRID 47921703

(Acceptable) b

1 Freshwater fish may be surrogates for aquatic-phase amphibians.

2 ETO data

a Toxicity categories have not been defined.

b The studies were modified to accommodate a volatile substance by using environmental chambers to maintain the 

air concentration of the gas.

4.2. Effects to Terrestrial Organisms

Table 5. Summary of the Most Sensitive Endpoints from Terrestrial Toxicity Studies for PPO

Taxonomic 

Group

Study 

Type

Surrogate 

Species

Toxicity Value Acute Toxicity 

Classification or 

Adverse Effects 

Observed

Source 

(Study 

classification)

Birds1

Acute

Inhalation2 upland game 

bird and 

waterfowl 

LD50 = no data N/A N/A

Chronic NOAEC = no data

LOAEC = no data N/A N/A

Mammals

Acute 

Inhalation

Laboratory 

mice LD50 = 2420 mg a.i./m3 Category IV NTP, 1985

Chronic Laboratory rat 

(Rattus 

norvegicus)

NOAEL = 720 mg a.i./m3

LOAEL >720 mg a.i./m3

Affected Reproduction/Offspring Endpoint: 

None 45292701

(Acceptable) b NOAEL = 240 mg a.i./m3

LOAEL = 720 mg a.i./m3

Affected Parental Endpoint: Decreased body 

weights and weight gain

Terrestrial 

invertebrates Acute

Rust-red flour 

beetle 

(Tribolium 

castaneum)

LD50 = 1000 mg a.i./m3--

a Navarro et al, 2004

Beneficial 

insects

Acute 

Contact

Honey bee 

(Apis mellifera 

L.)

LD50 = no data N/A N/A

Terrestrial 

plants

Seedling 

Emergence

Dicot EC50 = no data

NOAEC = no data --

a

N/A

Monocot EC50 = no data

NOAEC = no data --

a

Vegetative 

Vigor

Dicot 

(soybean)

EC50 > 252 mg a.i./m3

NOAEC = 252 mg a.i./m3 --

a 47921701

(Acceptable) b

Monocot EC50 = no data

NOAEC = no data --

a N/A
13

Table 5. Summary of the Most Sensitive Endpoints from Terrestrial Toxicity Studies for PPO

Taxonomic 

Group

Study 

Type

Surrogate 

Species

Toxicity Value Acute Toxicity 

Classification or 

Adverse Effects 

Observed

Source 

(Study 

classification)

1 Birds represent surrogates for terrestrial-phase amphibians and reptiles. 

2 A non-guideline acute avian inhalation toxicity study.

a Toxicity categories have not been defined.

b The studies were modified to accommodate a volatile substance by using environmental chambers to maintain the air 

concentration of the gas.

4.3. Incident Databases Review

The ecological incident information system (EIIS) is an OPP database that houses ecological 

incidents that have been reported to the Agency. When available, EIIS includes date and 

location of an incident, type and magnitude of effects observed in various species, use(s) of 

pesticides known or suspected of contributing to the incident, and results of any chemical residue 

analysis or other analyses conducted during incident investigation. EIIS incidents are 

categorized according to the certainty that the incident resulted from pesticide exposure. The 

Avian Monitoring System (AIMS) is a database administered by the American Bird Conservancy 

that contains publicly available data on reported avian incidents involving pesticides. Many of 

the incidents listed in this database are also in the EIIS. 

There are no reported incidents for PPO in the EIIS or AIMS databases, as well as no reports of 

aggregate incidents as of April 2013. The absence of reported incidents should not be construed 

as the absence of incidents. Incident reports for non-target organisms typically provide 

information only on mortality events and plant damage. Sublethal effects in organisms such as 

abnormal behavior, reduced growth and/or impaired reproduction are rarely reported, except for 

some phytotoxic effects in terrestrial plants. EPA's changes in the registrant reporting 

requirements for incidents in 1998 may also account for a reduced number of reported incidents. 

5. Exposure Pathways of Concern

For the purposes of this risk assessment, terrestrial non-target organisms are assumed to occupy 

areas immediately adjacent to treatment sites. For a gaseous pesticide released from a treatment 

chamber, tarped material, or rail car, the terrestrial exposure pathway considered most likely to 

occur to terrestrial animals is via inhalation of the gas, and to terrestrial plants is via contact of 

the gas to the external layer of plant tissues. 

AERSCREEN, an air screening model, was used for preliminary estimation of the releasing

fumigant concentration after the sterilization near the treatment facility 

(http://www.epa.gov/scram001/dispersion_screening.htm). The model estimates the "worstcase" 1-hour concentrations for a single source, without the need for hourly meteorological data. 

AERSCREEN is intended to produce concentration estimates that are equal to or greater than the 

estimates produced by other refined air dispersion models with a fully developed set of 

meteorological and terrain data, but the degree of conservatism may vary depending on the 

application. According the current label at 150 lb/1000 ft3 on an estimated treatment facility with 

10,000ft3spaces, the maximum concentration resulting from a one-hour release from one 

fumigation chamber is 16.77 g/m3from scenario 3 (Table 6). If the facility has 95% emission 
14

control, the maximum concentration will be reduced to 840 mg/m

3

. The detailed modeling

information can be found in Appendix I (Modeling Input based on PPO Release Scenarios 

Specified on Labels) and Appendix II (Output Example of AERSCREEN Estimated 

Environmental Concentrations (EECs) for PPO Release Scenario 3). 

Table 6. AERSCREEN Modeling Scenarios and Data Summary

Maximum 1-Hr 

Conc (μ/m3)

Scaled 3-Hr 

Conc (μ/m3)

Scaled 8-Hr 

Conc (μ/m3)

Scaled 24-Hr 

Conc (μ/m3)

Scaled Annual 

Conc (μ/m3)

Scenario 1

Stack Height 40 

ft with 4 air 

exchanges per 

hour

0.2840E+07 0.2840E+07 0.2556E+07 0.1704E+07 0.2840E+06

Scenario 2

Stack Height 27 

ft with 20 air 

exchanges per 

hour

0.1161E+07 0.1161E+07 0.1045E+07 0.6964E+06 0.1161E+06

Scenario 3

Stack Height 5 ft

with 1 air 

exchange per 

hour

0.1677E+08 0.1677E+08 0.1509E+08 0.1006E+08 0.1677E+07

The aquatic exposure pathway to aquatic organisms is by uptake of the gas via gill or integument 

when PPO is introduced to surface water during precipitation events, where the gas dissolves in 

the precipitation. However, PPO’s potential to reach water bodies will be limited by its overall 

atmospheric residence time of 8.9 days. In addition, rapid hydrolysis (t1/2 = 3.16 days) and 

expected rapid volatilization from water is expected to limit PPO exposures once reaching water 

bodies. Therefore, acute and chronic effects to fish and aquatic invertebrates do not appear to be 

of concern (USEPA 2006).

6. Analysis Plan

No environmental fate data consistent with studies outlined in 40 CFR, Part 158 have been submitted 

for PPO. Limited ecological effects data have been submitted for PPO; however, more studies are 

needed to fulfill the 40 CFR Part 158 data requirements for fumigant uses. 

In order to assess potential risks to the non-target organisms when exposed to PPO, the potential 

for adverse effects on the environment will be assessed by estimating air concentrations adjacent 

to the treatment facility through the use of dispersion models (Fig. 1). The quantity of air 

emissions via modeling, submitted ecological effect data and ECOTOX database information 

will be integrated to assess the potential risk. This will be accomplished by determining a risk 

quotient (ratio of exposure concentration to effects concentration) for a given use. Although risk 

is often defined as the likelihood and magnitude of adverse ecological effects, the risk quotientbased approach does not provide a quantitative estimate of likelihood or magnitude of an adverse 

effect. However, as outlined in the Overview Document (USEPA, 2004c), the likelihood of 

effects to individual organisms from particular uses of PPO will be estimated using the probit 

dose-response slope and either the level of concern or actual calculated risk quotient value.
15

Figure 1. Proposed propylene oxide structural fumigant air exposure scenario for the risk 

assessment.

This analysis plan may be revisited and revised depending upon a review of new available data 

and the information submitted by the public in response to the opening of the Registration 

Review docket.

6.1. Stressors of Concern

The stressors of concern will be the parent compound, PPO. There is no evidence that the 

reaction products, PCH, 1,2-propanediol and chloropropanol are formed in substantial amount in 

the air for terrestrial non-target exposure, and in water body for aquatic non-target exposure. 

Because of the PPO’s volatility and short retention time in water, an aquatic risk assessment for 

PPO will not be conducted. 

6.2. Measures of Exposure

PPO concentrations in air will be modeled or monitored using the maximum labeled application 

rates and number of applications, the minimum application intervals, and application methods 

that have the greatest potential for off-site transport. In addition, emission control requirements 

on PPO product labels will be considered.

PPO concentrations in air near the treatment facility will be initially estimated by a Tier-I 

screening model, AERSCREEN (http://www.epa.gov/scram001/dispersion_screening.htm) as 

recommended. The Tier-I model will produce estimates of "worst-case" 1-hour concentrations 

for a single source, without the need for hourly meteorological data. Air EECs may be refined 

by the Tier II Probabilistic Exposure and Risk Model for Fumigants (PERFUM). PERFUM is 

capable of producing a distribution of air EECs from a range of different meteorological 

conditions. 

6.3. Measures of Effect

Toxicity effects data will be used as measures of direct and indirect effects to biological 

receptors (USEPA, 2004c). As discussed previously, data will be obtained from registrantsubmitted studies and from literature studies identified in ECOTOX. 

Quantitative assessment of risks will be based on study endpoints that can be directly linked to 

the Agency’s assessment endpoints of impaired survival, growth, and reproduction. Sub-lethal 

Treated 

Structure

Release Vent or Stack
16

effects (e.g., lethargy and changes in coloration) will be evaluated qualitatively. Available 

incident data will be used to further characterize risk.

6.4. Integration of Exposure and Effects

The exposure and effects data will be integrated in order to evaluate potential adverse ecological 

effects on non-target species. The risk quotient (RQ) method will be used to compare exposure 

and measured toxicity values. EECs will be divided by acute and chronic toxicity values. The 

resulting RQs will be compared to the Agency’s Levels of Concern (LOC) (USEPA, 2004c). 

6.5. Endangered Species Assessments

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), the 

Agency will evaluate risks to Federally-listed threatened and endangered (listed) species from 

registered uses of PPO. This assessment will be conducted in accordance with the Overview 

Document (USEPA, 2004c), provisions of the ESA, and the Services’ Endangered Species 

Consultation Handbook (USFWS and NMFS, 1998).

6.6. Endocrine Disruptor Screening

As required by FIFRA and FFDCA, EPA reviews numerous studies to assess potential adverse 

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

chronic toxicity, including assessments of carcinogenicity, neurotoxicity, developmental, 

reproductive, and general or systemic toxicity. These studies include endpoints which may be 

susceptible to endocrine influence, including effects on endocrine target organ histopathology, 

organ weights, estrus cyclicity, sexual maturation, fertility, pregnancy rates, reproductive loss, 

and sex ratios in offspring. For ecological hazard assessments, EPA evaluates acute tests and 

chronic studies that assess growth, developmental and reproductive effects in different 

taxonomic groups. As part of the most recent registration decision, EPA reviewed these data and 

selected the most sensitive endpoints for relevant risk assessment scenarios from the existing 

hazard database. However, as required by FFDCA section 408(p), PPO is subject to the 

endocrine screening part of the Endocrine Disruptor Screening Program (EDSP). PPO is not in 

the first or second group of pesticide active ingredients to be screened under the EDSP. For 

further information on the status of the EDSP, the policies and procedures, the list of chemicals, 

the test guidelines and the Tier 1 screening battery, please visit our website: 

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

6.7. Drinking Water Assessment

PPO’s labeled use pattern as a fumigant is unlikely to have detectable residues for both parent 

and reaction products in surface water and ground water. Therefore, a DWA will not be 

conducted for PPO. 

6.8. Preliminary Identification of Data Gaps

Available studies submitted to fulfill environmental fate and ecological effects guideline 

requirements, as well as PPO outstanding data gaps are defined in Sections 6.8.1 and 6.8.2, 

respectively. Studies are identified that offer data for each guideline requirement, as well as 
17

study classifications and whether or not further data are needed in order to support risk 

assessment.

Open literature data may not completely comply with the OCSPP guidelines which are 

specifically designed for results to be applied for a wide range of pesticides treatment uses. 

Nevertheless, these studies provide valuable information for risk assessment, and may be 

considered supplemental information for the PPO environmental fate and ecological effects 

profile. 

There are uncertainties in the usage of PPO on treatment facilities, (maximum chambers or 

buildings), frequency of the treatment, aeration methods, air exchange exhaust rates, and the use 

of emission control devices. These factors will directly influence emission rates and affect 

outdoor air concentrations. In addition, there is a lack of information related to the design of 

buildings for the fumigation, including the dimensions of buildings, different sizes of buildings, 

as well as the number, sizes, and relative locations of stacks and vents that serve as the release 

points during PPO aeration operations. These variables all impact the magnitude of downwind 

dispersion from treated structures. 

6.8.1. Environmental Fate Data

No registrant submitted data are available for any of the 40 CFR 158 data requirements for 

environmental fate. Since exposure and resulting risk to terrestrial organisms will be directly 

related to the emissions of propylene oxide mass from aerated structures, environmental fate data 

will not be requested at this time. EFED will use any available data requested by the Agency’s 

Health Effects Division, such as field monitoring data, at the time of the registration review risk 

assessment. 

6.8.2. Ecological Effects Data

Tables 7 and 8 identify ecological effects studies by MRID that offer data for each guideline 

requirement, as well as study classifications and whether or not further data are needed in order 

to support risk assessment. Rationale for the additional data requested is presented below. The 

studies would need to be modified to accommodate a volatile substance.

Avian Acute Inhalation Toxicity Study (A Non-guideline Study): Propylene oxide has 

fumigant uses that may result in exposure to birds. The acute effects to birds exposed to 

PPO are unknown. Avian acute inhalation toxicity data were not submitted for birds 

exposed to PPO; however, the requested study is a non-guideline study under the 40 CFR 

Part 158 data requirements. Typically, the Agency asks for avian acute oral and dietary 

studies with an upland game bird, a passerine bird and a waterfowl to assess the acute 

effects to birds via the oral and dietary routes. However, because PPO is a gas which is 

released to the atmosphere after aeration of the air-tight chambers, the terrestrial animal 

exposure route considered most likely to occur is through inhalation of the gas; therefore 

the Agency is asking for a non-guideline inhalation study with birds instead of the oral 

and dietary studies. Since this inhalation study is a non-guideline study, a study protocol 

must be submitted for review by the Agency prior to test initiation. The preferred bird 

species is the Northern bobwhite quail. Until an acute inhalation endpoint to evaluate 
18

acute risk to birds is available, the acute risk to birds exposed to PPO cannot be precluded 

and will be presumed. 

Honeybee Acute Vapor Exposure Toxicity Study (A Non-guideline Study):

Propylene oxide has fumigant uses that may result in exposure to honeybees. The toxicity 

of PPO to honeybees is unknown. Honeybee acute vapor-phase exposure toxicity data 

were not submitted for beneficial insects exposed to PPO; however, the requested study is 

a non-guideline study under the 40 CFR Part 158 data requirements. PPO is an 

insecticide which is formulated to kill insects, and therefore some effects to insects are 

expected (as observed in other terrestrial invertebrate studies). The Agency is asking for a 

non-guideline vapor-phase exposure study with bees to assess whether the effects seen in 

bees are similar to what was observed in other terrestrial invertebrates. Since this vaporphase exposure study is a non-guideline study, a study protocol that calculates a vaporphase exposure LD50 for adult bees must be submitted for review by the Agency prior to 

initiation of the study. Until an acute vapor-phase exposure endpoint to evaluate the 

toxicity to honeybees is available, the acute risk to bees exposed to PPO cannot be 

precluded and will be presumed.

Terrestrial Plants Special Study– Vegetative Vigor Vapor Exposure Toxicity Study 

(A Non-guideline Study): Propylene oxide has fumigant uses that may result in exposure 

to terrestrial plants. Data on the toxicity of PPO to terrestrial plants is limited to a 

soybean study (MRID 4791701) that has been submitted to the Agency, which partially 

completes the risk assessment for terrestrial plants. Testing with four monocot and six 

dicot species is needed to completely assess the risks to terrestrial plants, including listed 

species. Typically, the Agency asks for seedling emergence and vegetative vigor studies 

to assess the effects to terrestrial plants exposed to a pesticide as a result of surface water 

runoff or/and off-site spray drift, respectively; however, because PPO will be released 

from air-tight chambers as a gas, the terrestrial plant exposure pathway considered most 

likely to occur is through contact of the external layer of plant tissues as a result of spray 

drift. Instead of requesting both seedling emergence and vegetative vigor studies, the 

Agency is only asking for the vegetative vigor study with actively growing plants to 

assess the effects of PPO when the gas penetrates the plants. 

To assess the potential risks to animal and plant species that indirectly rely on terrestrial 

plants as well as the direct risks to terrestrial plants, the study is of importance. Due to the 

lack of data on the range of sensitivity of terrestrial plants, the risks to terrestrial plants,

especially listed species, exposed to PPO cannot be precluded and will be presumed. A 

study protocol must be submitted for review by the Agency prior to test initiation given 

the study needs to be modified to accommodate a volatile substance. The preferred plant 

species are four monocots in two families, including corn, and six dicots in four families,

including soybean and a root crop.
19

Table 7. Submitted Aquatic Ecological Effects Data for PPO

OCSPP

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID or 

Citation)

Study 

Classifications

Are data 

needed to 

conduct risk 

assessment?

Current Additional Data Need

850.1010

Freshwater 

invertebrate

acute toxicity

Conway et 

al, 1983 N/A No --

850.1025

850.1035

Estuarine/Marine 

invertebrate

acute toxicity

Conway et 

al, 1983 N/A No --

850.1075 Freshwater fish 

acute toxicity

Conway et 

al, 1983 N/A No --

850.1075 Estuarine/Marine 

fish acute toxicity

Crews et al, 

1974 N/A No --

850.1300

Freshwater 

invertebrate

life cycle

(None) N/A No

No reproduction data is available 

for freshwater invertebrates; this 

is a data gap. However, EFED is 

not asking for a chronic study 

since significant concentrations 

are not expected to reach the 

receptors due to the rapid decline 

of water concentrations of the gas

by the time it enter water bodies

through runoff/precipitation,

which results in low potential for 

chronic exposure.
20

Table 7. Submitted Aquatic Ecological Effects Data for PPO

OCSPP

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID or 

Citation)

Study 

Classifications

Are data 

needed to 

conduct risk 

assessment?

Current Additional Data Need

850.1350

Estuarine/Marine 

invertebrates

life cycle

(None) N/A No

No reproduction data is available 

for estuarine/marine invertebrates; 

this is a data gap. However, EFED 

is not asking for a chronic study 

since significant concentrations 

are not expected to reach the 

receptors due to the rapid decline 

of water concentrations of the gas 

by the time it enter water bodies 

through runoff/precipitation, 

which results in low potential for 

chronic exposure.

850.1400 Freshwater fish

early-life stage (None) N/A No

No reproduction data is available 

for freshwater fish; this is a data 

gap. However, EFED is not asking 

for a chronic study since 

significant concentrations are not 

expected to reach the receptors 

due to the rapid decline of water 

concentrations of the gas by the 

time it enter water bodies through 

runoff/precipitation, which results 

in low potential for chronic 

exposure.

850.1400

Estuarine/Marine 

fish early-life 

stage

(None) N/A No

No reproduction data is available 

for estuarine/marine fish; this is a 

data gap. However, EFED is not 

asking for a chronic study since 

significant concentrations are not 

expected to reach the receptors 

due to the rapid decline of water 

concentrations of the gas by the 

time it enter water bodies through 

runoff/precipitation, which results 

in low potential for chronic 

exposure.

850.1500 Fish life cycle (None) (N/A) No --

850.4400

Aquatic plant 

growth:

Tier I vascular 

plants

47921702 Acceptable No --

850.4500

Aquatic plant 

growth:

Tier I algae

47921703 Acceptable No

Only one aquatic non-vascular 

species out of three species has 

been submitted for OCSPP 
21

Table 7. Submitted Aquatic Ecological Effects Data for PPO

OCSPP

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID or 

Citation)

Study 

Classifications

Are data 

needed to 

conduct risk 

assessment?

Current Additional Data Need

850.4550

Aquatic plant 

growth: Tier I or 

II cyanobacteria

(None) N/A No

850.4500, while none has been 

submitted for OCSPP 850.4550. 

This is a data gap. However, 

EFED is not asking for these 

aquatic plant studies since 

significant concentrations are not 

expected to reach the receptors via 

the surface water runoff route 

since the exposure pathway most 

likely to occur is via inhalation 

because PPO is a gas.

Table 8. Submitted Terrestrial Ecological Effects Data for PPO

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data 

needed for 

risk 

assessment?

Current Additional Data Need

850.2100 Avian oral 

toxicity

(None) N/A No No acute oral or dietary data is 

available for birds; this is a data 

gap. However, EFED is not asking 

for these acute studies since 

significant concentrations are not 

expected to reach the receptors via 

the oral and dietary routes since 

the exposure pathway most likely 

to occur to birds is via inhalation 

because PPO is a gas.

850.2200 Avian dietary 

toxicity

(None) N/A No

850.2300 Avian 

reproduction

(None) N/A No No avian reproduction data is 

available for birds; this is a data 

gap. However, EFED is not asking 

for a chronic study since 

significant concentrations are not 

expected to reach the receptors 

due to the rapid decline of air 

concentrations of the gas which 

results in low potential for chronic 

exposure.
22

Table 8. Submitted Terrestrial Ecological Effects Data for PPO

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data 

needed for 

risk 

assessment?

Current Additional Data Need

NonguidelineAvian Acute 

inhalation

(None) (N/A) Yes An acute avian inhalation study 

using the Northern bobwhite 

quail is necessary to satisfy the 

toxicity profile for birds exposed 

to a gas. Without data, risk 

would be presumed for birds, 

reptiles, and terrestrial-phase 

amphibians, including listed 

species.

850.3020 Honey bee 

acute contact 

toxicity

(None) (N/A) No A honeybee acute contact study is 

not available for bees; this is a 

data gap. However, EFED is not 

asking for the contact study since 

significant concentrations are not 

expected to reach the receptors via 

the oral and contact routes since 

the greatest exposure pathway to 

honeybees is via inhalation 

because PPO is a gas.

NonguidelineHoneybee 

acute vapor 

exposure 

toxicity

(None) N/A Yes A honeybee acute vapor 

exposure toxicity study is 

necessary to satisfy the toxicity 

profile for bees exposed to a gas. 

Without data, risk would be 

presumed for beneficial insects, 

including listed species.

850.3030 Honey bee 

residue on 

foliage

(None) (N/A) No --

850.3040 Field testing 

for pollinators

(None) (N/A) No --

850.4100 Terrestrial 

plant toxicity:

Tier I or II 

seedling 

emergence

(None) (N/A) No No seedling emergence data is 

available for terrestrial plants; this 

is a data gap. However, EFED is 

not asking for these data since 

significant concentrations of the 

gas are not expected to reach the 

receptors via surface water runoff 

or through precipitation. Also, 

OCSPP guideline 850.4100 is not 

designed for toxicity tests with 

fumigants. 
23

Table 8. Submitted Terrestrial Ecological Effects Data for PPO

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data 

needed for 

risk 

assessment?

Current Additional Data Need

850.4150 Terrestrial 

plant toxicity:

Tier I or II 

vegetative 

vigor

(None) (N/A) No No vegetative vigor data is 

available for terrestrial plants; this 

is a data gap. However, EFED is 

not asking for these data since 

OCSPP guideline 850.4150 is not 

designed for toxicity tests with 

fumigants.

NonguidelineTerrestrial 

plant special 

study: Tier I or 

II vegetative 

vigor vapor 

exposure 

toxicity

47921701 Acceptable Yes Only one dicot species out of 6 

species and none of the four 

monocot species has been 

submitted; this is a data gap.

Additional data are needed to 

completely assess the risks to 

terrestrial plants. Without data, 

risk would be presumed for 

some terrestrial plants, 

including listed species.
24

References

Addy, J.K. & Parker, R. 1963. The mechanism of epoxide reactions. V. The reaction of 1,2-

epoxypropane with chloride ions in water under neutral and acidic conditions. J. Chem. Soc., 

915-921.

Bogyo, D.A., Lande, S.S., Meyland, W.M., Howard, P.H., and Santodonato, J. 1980. 

Investigation of selected potential environmental contaminants: Epoxides, Syracuse, New 

York, Centre for Chemical Hazard Assessment, Syracuse Research Corporation (Prepared for 

US EPA) (US EPA 560/11-80-005, PB 80-183197).

Bont, J.A.M. De, Dijken, J.P. Van, & Ginkel, K.G. Van. 1982. The metabolism of 1,2-

propanediol by the propylene oxide utilizing bacterium Nocardia 60. Biochem. Biophys. 

Acta, 714:465-470.

Bridie, A.L., Wolff, C.J.M., & Winter, M. 1979. BOD and COD of some petrochemicals. Water 

Res., 13: 627-630.

Crews, R.C. 1974. Effects of Propylene Oxide on Selected Species of Fishes. Technical Report

No. AFATL-TR-74-183. Environics Office, Air Force Armament Laboratory, Eglin Air 

Force Base, FL, 13 pp.

Conway, R.A., Waggy, G.T., Spiegel, M.H., and Berglund, R.L. 1983. Environmental fate and 

effects of ethylene oxide. Environ. Sci. Technol., 17: 107-112.

Cupitt, L.T. 1980. Fate of toxic and hazardous materials in the environment, Research Triangle 

Park, North Carolina, USEPA, Environmental Sciences Laboratory, Office of Research and 

Development (US EPA 600/3-80-084, PB 80-221948).

Dow (online publication, accessed 3/18/2013). Propylene Oxide. 

http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_0036/0901b80380036c15.pdf

?filepath=propyleneoxide/pdfs/noreg/117-01641.pdf&fromPage=GetDoc

IARC. 1976. Cadmium, nickel, some epoxides, miscellaneous industrial chemicals and general 

considerations on volatile anaesthetics, Lyons, International Agency for Research on Cancer, 

293 pp (IARC Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Man, 

Vol. 11).

IPCS. (Accessed 2/27/2013). International Programme on Chemical Safety. Environmental 

Health Criteria 56. (http://www.inchem.org/documents/ehc/ehc/ehc56.htm)

Koskikallio, J. & Whalley, E. 1959. Effect of pressure on the spontaneous and the basecatalysed hydrolyses of epoxides. Can. J. Chem., 37: 783-787.

NTP. 1985. Toxicology and Carcinogenesis Studies of Propylene Oxide (CAS No. 75-56-9) in 

F344/N Rats and B6C3F1 Mice (Inhalation Studies). Technical Report Series No. 267. NIH 
25

Publication No. 85-2527. Research Triangle Park, NC: National Toxicology Program. 172 

pp.

S. Navarro, A.A. Iskikber, S. Finkelman, M. Rindner, A. Azrieli, R. Dias. 2004. Effectiveness of 

short exposures of propylene oxide alone and in Combination with low pressure or carbon 

dioxide against Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). Journal of Stored 

Products Research, 40:197-205. 

Storck, W.J. 1981. Output of big-volume chemicals fell in 1980. Chem. Eng. News, 59: 36-39.

USEPA. 1981. Human exposure to atmospheric concentrations of selected chemicals. Research 

Triangle Park, North Carolina, US Environmental Protection Agency, Office of Air Quality 

Planning and Standards (US NTIS PB 84-102540, PB 83-265249).

USEPA. 2006. Reregistration Eligibility Decision for Propylene Oxide, EPA 738-R-06-029. 

192pp. (http://www.epa.gov/oppsrrd1/reregistration/REDs/propylene_oxide_red.pdf), 

(accessed 3/18/2013)

USEPA. 2012. BEAD Chemical Profile for Registration Review: Propylene oxide (042501). 5pp.

WHO. 1978. Environmental health problems associated with the manufacture and uses of 

synthetic organic chemicals, Geneva, World Health Organization (Report No. HCS/78.2).

WHO. 1985. EHC 55: Ethylene oxide, Geneva, World Health Organization, 79 pp.

Submitted Studies

MRID Citation Reference

47921701 Martin, MA. 2009. Propylene Oxide – Vegetative Vigor Test with Soybean Following 

U.S. EPA OPPTS Draft Guideline 850.1450 (Tier I Test). Springborn Smithers 

Laboratories, Wareham, Massachusetts. Study no. 13928.6102. Study sponsored by AgChem Consulting LLC (on behalf of ABERCO), Clifton, Virginia. Study completed on 

November 11, 2009.

47921702 Softcheck, K.A. 2009. Propylene Oxide – 7-Day Static Toxicity Test in a Modified 

Closed System with Duckweed (Lemna gibba). Springborn Smithers Laboratories, 

Wareham, Massachusetts. Study No. 13928.6101. Study sponsored by Ag-Chem 

Consulting LLC (on behalf of ABERCO), Clifton, Virginia. Study completed on 

November 11, 2009.

47921703 Softcheck, K.A. 2009. Propylene Oxide –Static Acute Toxicity Test in a Modified Closed 

System with the Freshwater Alga, Pseudokirchneriella subcapitata. Springborn Smithers 

Laboratories, Wareham, Massachusetts. Study No. 13928.6100. Study sponsored by AgChem Consulting LLC (on behalf of ABERCO), Clifton, Virginia. Study completed on 

November 11, 2009.
26

Appendix I

Modeling Input based on PPO Release Scenarios Specified on Labels

PPO is used to treat food and post-harvested commodities in fumigation chambers. Labels 

specify maximum application rates, or indoor concentrations of PPO, which are maintained over 

periods of time for treatments inside the chambers. Fumigation chambers have a maximum size 

of 10,000 cubic feet6. Labels all require mechanical, or forced, aeration following a treatment of 

the commodities. Mechanical aeration releases the fumigant outdoors from the treated structure 

through a through a stack or vent. In the first set of release scenarios, PPO labels explicitly 

specify the following mechanical release parameters given the following maximum application 

rates and maximum structure sizes:

First Release Scenario

Maximum Application Rate (per chamber) = 75 lbs./1,000 ft.3

Maximum Chamber Size = 5,000 ft.3

Stack Height = 27 ft.

Flow Rate = 20 air exchanges per hour = 1,667 cfm for 5,000 ft.3 chamber

Second Release Scenario

Maximum Application Rate (per chamber) = 75 lbs./1,000 ft.3

Maximum Chamber Size = 5,000 ft.3

Stack Height = 40 ft.

Flow Rate = 4 air exchanges per hour = 333.33 cfm for 5,000 ft.3 chamber

Third Release Scenario

Maximum Application Rate (per chamber) = 75 lbs./1,000 ft.3

Maximum Chamber Size = 10,000 ft.3

Stack Height = 40 ft.

Flow Rate = 4 air exchanges per hour = 666.67 cfm for 10,000 ft.3 chamber

The label also allows other release scenarios where mechanical release parameters are not 

specified. However, for these scenarios, 95 percent of PPO emissions are required to be 

captured. These release scenarios which are also defined by maximum application rates and 

building sizes are described below:

Fourth Release Scenario

Maximum Application Rate (per chamber) = 150 lbs./1,000 ft.3

 

6

Fumigation chambers are assumed to possess similar size to railcars. Citation: 

http://www.csx.com/index.cfm/customers/equipment/railroad-equipment/
27

Maximum Chamber Size = 10,000 ft.3

Fifth Release Scenario

Maximum Application Rate (per chamber) = 75 lbs./1,000 ft.3

Maximum Chamber Size = 5,000 ft.3

Sixth Release Scenario

Maximum Application Rate (per chamber) = 75 lbs./1,000 ft.3

Maximum Chamber Size = 10,000 ft.3

It is important to note that it is possible that more than one simultaneous PPO treatments inside 

fumigation chambers can occur at a time at the same location. The labels do not specify a 

maximum amount of simultaneous fumigation chamber treatments.

AERSCREEN Description

The Agency’s recommended screening dispersion model for the near field, the American 

Meteorological Society/EPA Regulatory Screening Model (AERSCREEN), will be used to 

generate screening EECs for the various release scenarios. The Tier I analysis will consider the 

emission rates and release flow rates and stack parameters for the various mechanical release 

scenarios for PPO. Worst-case meteorological conditions (light winds and stagnant conditions) 

and downwash7parameters are assumed to calculate peak air EECs, representing one-hour 

average concentrations. Documentation on the AERSCREEN model is available at 

http://www.epa.gov/scram001/dispersion_screening.htm. A schematic of release scenarios from 

fumigated structures and the related conceptual model for ground-level exposure is shown in 

Figure A1. For purposes of this screening analysis, all ecological receptors of concern will 

assumed to be present directly downwind from the building at ground level.

 

7 Downwash is defined as the downward flow often observed on the leeward side of buildings induced by wake 

turbulence. Pollutants released from buildings can often become embedded in downwash flows and wake cavities.
28

Figure A1. Schematic illustrating fumigation releases from treated structures and conceptual 

model for ground-level exposure.

AERSCREEN Release Scenarios

The release scenarios on the PPO label, which are described above, can be consolidated to three

scenarios to capture the possibilities for upper-bound air exposure resulting from PPO 

treatments. These scenarios are described below:

Scenario 1

Maximum Application Rate (per chamber) = 75 lbs./1,000 ft.3

Maximum Chamber Size = 10,000 ft.3

Stack Height = 40 ft.

Flow Rate = 4 air exchanges per hour = 666.67 cfm for 10,000 ft.3 chamber

Scenario 2

Maximum Application Rate (per chamber) = 75 lbs./1,000 ft.3

Maximum Chamber Size = 10,000 ft.3

Stack Height = 27 ft.

Flow Rate = 20 air exchanges per hour = 3,333 cfm for 10,000 ft.3 chamber

Scenario 3

Maximum Application Rate (per chamber) = 150 lbs./1,000 ft.3

Maximum Chamber Size = 10,000 ft.3

95 Percent Emissions Capture

Stack Height = 3.33 ft. (Not specified on label, see Table I.1 for explanation of release 

parameter value)

Flow Rate = 1 air exchanges per hour = 166.67 cfm (Not specified on label, see Table I.1

for explanation of release parameter value)
29

The input parameter values used in AERSCREEN for the screening analysis of PPO air exposure 

is shown in Table A1 below. The AERSCREEN modeling captures the upper-bound air 

exposure from release scenarios consolidated above from information on the PPO product label. 

All of the modeled release scenarios conservatively assume that aeration is complete after one 

hour which results in maximized peak (one-hour average) concentrations.

Table A1. AESCREEN input parameter values capturing the upper-bound combination of 

release scenarios identified on the PPO label.

Input Parameter Option/Value Notes

Scenario 1 Scenario 2 Scenario 3

English or Metric 

Units E (English)

Source Type P (Point)

Stack releases required for all 

uses

Emission Rate 

(lbs./hr) 375 375 75

Scenarios 1 and 2

All mass from labeled specified 

application rate inside 10,000 ft.3

chamber released in one-hour 

period1

Scenario 3

5 percent of total mass from 

labeled specified application rate 

inside 10,000 ft.3chamber 

released in one hour period 

corresponding to 95 percent 

emissions capture2

Stack or Release 

Height Above 

Ground (ft.) 

40 27 5

Scenarios 1 and 2: 

Specified on label

Scenario 3: 

Not specified on label

Default for 10,000 ft.3building 

size based on methyl bromide 

HED assessment3

Stack Diameter 

(in.) 39.6

Default for 10,000 ft.3building 

size based on methyl bromide 

HED assessment (1 meter)3

Stack Temperature 

(°F) 0 (Equivalent to Ambient Temperature)

No stack temperatures specified, 

conservative assumption is nonbuoyant source

Option for Flow 

Rate or Flow 

Velocity

3 (Flow Rate ACFM)
30

Table A1. AESCREEN input parameter values capturing the upper-bound combination of 

release scenarios identified on the PPO label.

Input Parameter Option/Value Notes

Scenario 1 Scenario 2 Scenario 3

Stack Exit Stream 

Flow Rate

(f3/min.) 

333 166.7 166.7

Scenario 1: 

Based on 4 air exchanges per 

hour specified on the label4

Scenario 2: 

Based on 20 air exchanges per 

hour specified on the label4

Scenario 3: 

Not specified on label -

Assume one air exchange per 

hour for one-hour release4

Urban or Rural? R (Rural) Conservative default

Minimum 

Distance to 

Ambient Air (ft.) 

3.3 Conservative default

NO2 Chemistry 1 (No chemistry/pollutant is not NO2)

Tracer gas NOx emissions not 

modeled

Include Building 

Downwash? Y (Yes)

Downwash is feasible downward 

transport mechanism for plume 

in release scenarios

Use Pre-Existing 

BPIPPRM File? N (No) Downwash parameters to be input manually

Building Height 

(ft.) 40 27 5 Equivalent to stack height

Maximum 

Horizontal 

Building 

Dimension (ft.)

11.16 13.6 44.72

Square chamber footprint 

consistent with building heights 

specified above

Minimum 

Horizontal 

Building 

Dimension (ft.)

11.16 13.6 44.72

Square chamber footprint 

consistent with building heights 

specified above

Maximum 

Building 

Dimension Angle 

to True North 

(degrees)

0

Conservative parameterization of 

building downwash – stack 

located on the leeward edge of 

the building Direction of Stack 

from Building 

Center (degrees)

0

Distance Between 5.6 6.8 22.3
31

Table A1. AESCREEN input parameter values capturing the upper-bound combination of 

release scenarios identified on the PPO label.

Input Parameter Option/Value Notes

Scenario 1 Scenario 2 Scenario 3

Stack and Building 

Center (ft.)

Terrain Heights? N (No) Only flat terrain considered

Maximum 

Distance to Probe 

(m)

5,000 Default - maximum feasible 

distance for screen

Include Discrete 

Receptors N (No) Automated receptors sufficient

Flagpole 

Receptors N (No) Ground-level concentrationsassumed

Source Elevation 

(ft.) 0

Stack base from ground release 

assumed

Minimum 

Temperature (°F) -10

Default – typical national 

temperature range

Maximum 

Temperature (°F) 100 Default – typical national temperature range

Minimum Wind 

Speed (m/s) 0.5 Minimum in model: conservative default

Anemometer 

Height (ft.) 33 Typical boundary layer reference height (10 meters)

Surface 

Characteristics 

Option

1 (Single User Specified Values)

Albedo 0.6 Bare surface assumed around 

source

5

Bowen Ratio 3.0 Bare surface assumed around 

source5

Surface Roughness 

Length (m) 0.001 Bare surface assumed around source5

1

 Scenario 1 and 2 Emission Rate (lbs./hr) = Application Rate (lbs./ft.3) x Structure Size (ft.3)

Duration of Release (hr.)

2

 Scenario 3 Emission Rate (lbs./hr) = 0.05 x Application Rate (lbs./ft.3) x Structure Size (ft.3)

Duration of Release (hr.)

3

 Methyl bromide HED risk assessment citation: 

Dawson, J. 2008. Second Addenda to the 2006 (DP Barcode 304623) Phase 5 Human Health Risk Assessment 

for Commodity Uses. Office of Pesticide Programs. Washington, DC. (November 26, 2008) (EPA DP Barcode 

304612).

4

 Flow rate (ft.3/min) = Air exchange rate (air exchanges/hr.) x Structure Size (ft.3) x hours

 60 minutes

5

 Default values for bare soil assumed. Please refer to, “User’s Guide for the AERMOD Meteorological 

Preprocessor (AERMET)”, (EPA, 2004) for further details.
32

Appendix II

Output Example of AERSCREEN Estimated Environmental Concentrations (EECs) for 

PPO Release Scenario 3 

AERSCREEN 11126 / AERMOD 1234 04/15/13

 14:34:33

TITLE: PPO-5 

-----------------------------------------------------------------------------

***************************** STACK PARAMETERS ****************************

-----------------------------------------------------------------------------

SOURCE EMISSION RATE: 9.4500 g/s 75.000 lb/hr

STACK HEIGHT: 1.52 meters 5.00 feet

STACK INNER DIAMETER: 1.006 meters 39.60 inches

PLUME EXIT TEMPERATURE: Ambient

PLUME EXIT VELOCITY: 0.099 m/s 0.32 ft/s

STACK AIR FLOW RATE: 167 ACFM

RURAL OR URBAN: RURAL

INITIAL PROBE DISTANCE = 5000. meters 16404. feet

-----------------------------------------------------------------------------

*********************** BUILDING DOWNWASH PARAMETERS **********************

-----------------------------------------------------------------------------

BUILDING HEIGHT: 1.5 meters 5.0 feet

MAX BUILDING DIMENSION: 13.6 meters 44.7 feet

MIN BUILDING DIMENSION: 13.6 meters 44.7 feet

BUILDING ORIENTATION TO NORTH: 0. degrees

STACK DIRECTION FROM CENTER: 0. degrees

STACK DISTANCE FROM CENTER: 6.8 meters 22.3 feet

-----------------------------------------------------------------------------

************************** FLOW SECTOR ANALYSIS *************************** 

 25 meter receptor spacing: 1. meters - 5000. meters

-----------------------------------------------------------------------------

 FLOW BUILD BUILD MAX 1-HR DIST TEMPORAL

 SECTOR WIDTH LENGTH XBADJ YBADJ CONC (m) PERIOD

 -----------------------------------------------------------------------------

 10 15.80 15.79 -14.59 -1.18 0.2280E+07 1.0 ANN

 20 17.48 17.47 -15.12 -2.32 0.2900E+07 1.0 ANN

 30 18.63 18.62 -15.20 -3.40 0.3326E+07 1.0 ANN

 40 19.21 19.21 -14.81 -4.37 0.2848E+07 1.0 ANN
33

 50 19.21 19.21 -13.97 -5.21 0.2162E+07 1.0 ANN

 60 18.62 18.63 -12.71 -5.88 0.1706E+07 1.0 ANN

 70 17.47 17.48 -11.06 -6.39 0.1326E+07 1.0 ANN

 80 15.79 15.80 -9.08 -6.69 0.1016E+07 1.0 ANN

 90 13.63 13.64 -6.82 -6.80 0.8461E+06 25.0 ANN

 100 15.79 15.80 -6.72 -6.69 0.7199E+06 25.0 ANN

 110 17.47 17.48 -6.42 -6.39 0.6613E+06 25.0 ANN

 120 18.62 18.63 -5.92 -5.88 0.6334E+06 25.0 ANN

 130 19.21 19.21 -5.24 -5.21 0.5796E+06 25.0 ANN

 140 19.21 19.21 -4.40 -4.37 0.6181E+06 25.0 ANN

 150 18.63 18.62 -3.43 -3.40 0.6176E+06 25.0 ANN

 160 17.48 17.47 -2.35 -2.32 0.6368E+06 25.0 ANN

 170 15.80 15.79 -1.20 -1.18 0.7031E+06 25.0 ANN

 180 13.64 13.63 -0.02 0.00 0.6304E+06 25.0 ANN

 190 15.80 15.79 -1.20 1.18 0.7031E+06 25.0 ANN

 200 17.48 17.47 -2.35 2.32 0.6368E+06 25.0 ANN

 210 18.63 18.62 -3.43 3.40 0.6176E+06 25.0 ANN

 220 19.21 19.21 -4.40 4.37 0.6181E+06 25.0 ANN

 230 19.21 19.21 -5.24 5.21 0.5796E+06 25.0 ANN

 240 18.62 18.63 -5.92 5.88 0.6334E+06 25.0 ANN

 250 17.47 17.48 -6.42 6.39 0.6613E+06 25.0 ANN

 260 15.79 15.80 -6.72 6.69 0.7199E+06 25.0 ANN

 270 13.63 13.64 -6.82 6.80 0.8461E+06 25.0 ANN

 280 15.79 15.80 -9.08 6.69 0.1016E+07 1.0 ANN

 290 17.47 17.48 -11.06 6.39 0.1326E+07 1.0 ANN

 300 18.62 18.63 -12.71 5.88 0.1706E+07 1.0 ANN

 310 19.21 19.21 -13.97 5.21 0.2162E+07 1.0 ANN

 320 19.21 19.21 -14.81 4.37 0.2848E+07 1.0 ANN

 330 18.63 18.62 -15.20 3.40 0.3326E+07 1.0 ANN

 340 17.48 17.47 -15.12 2.32 0.2900E+07 1.0 ANN

 350 15.80 15.79 -14.59 1.18 0.2280E+07 1.0 ANN

 360* 13.64 13.63 -13.61 0.00 0.1677E+08 1.0 ANN

* = worst case flow sector

-----------------------------------------------------------------------------

********************** MAKEMET METEOROLOGY PARAMETERS *********************

-----------------------------------------------------------------------------

MIN/MAX TEMPERATURE: 249.8 / 310.9 (K)

MINIMUM WIND SPEED: 0.5 m/s

ANEMOMETER HEIGHT: 33.000 meters

SURFACE CHARACTERISTICS INPUT: USER ENTERED

ALBEDO: 0.60

BOWEN RATIO: 3.00

ROUGHNESS LENGTH: 0.001 (meters)

 METEOROLOGY CONDITIONS USED TO PREDICT OVERALL MAXIMUM IMPACT

 -------------------------------------------------------------
34

 YR MO DY JDY HR

 -- -- -- --- --

 10 01 07 7 01

 H0 U* W* DT/DZ ZICNV ZIMCH M-O LEN Z0 BOWEN ALBEDO REF WS

 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

 -0.02 0.010 -9.000 0.020 -999. 2. 3.3 0.001 3.00 0.60 0.50

 HT REF TA HT

- - - - - - - - - - -

 33.0 249.8 2.0

ESTIMATED FINAL PLUME HEIGHT (non-downwash): 1.2 meters

 METEOROLOGY CONDITIONS USED TO PREDICT AMBIENT BOUNDARY IMPACT

 --------------------------------------------------------------

 YR MO DY JDY HR

 -- -- -- --- --

 10 01 07 7 01

 H0 U* W* DT/DZ ZICNV ZIMCH M-O LEN Z0 BOWEN ALBEDO REF WS

 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

 -0.02 0.010 -9.000 0.020 -999. 2. 3.3 0.001 3.00 0.60 0.50

 HT REF TA HT

- - - - - - - - - - -

 33.0 249.8 2.0

ESTIMATED FINAL PLUME HEIGHT (non-downwash): 1.2 meters

-----------------------------------------------------------------------------

************************ AERSCREEN AUTOMATED DISTANCES **********************

 OVERALL MAXIMUM CONCENTRATIONS BY DISTANCE

-----------------------------------------------------------------------------

 MAXIMUM MAXIMUM

 DIST 1-HR CONC DIST 1-HR CONC

 (m) (ug/m3) (m) (ug/m3)

 --------------------- ---------------------

 1.01 0.1677E+08 2525.00 0.1788E+05

 25.00 0.1814E+07 2550.00 0.1762E+05

 50.00 0.9855E+06 2575.00 0.1738E+05

 75.00 0.7962E+06 2600.00 0.1714E+05

 100.00 0.6616E+06 2625.00 0.1690E+05

 125.00 0.6227E+06 2650.00 0.1667E+05

 150.00 0.6382E+06 2675.00 0.1645E+05

 175.00 0.6128E+06 2700.00 0.1623E+05

 200.00 0.5628E+06 2725.00 0.1601E+05

 225.00 0.5038E+06 2750.00 0.1580E+05

 250.00 0.4464E+06 2775.00 0.1560E+05

 275.00 0.3953E+06 2800.00 0.1540E+05
35

 300.00 0.3519E+06 2825.00 0.1520E+05

 325.00 0.3155E+06 2850.00 0.1501E+05

 350.00 0.2849E+06 2875.00 0.1482E+05

 375.00 0.2590E+06 2900.00 0.1463E+05

 400.00 0.2369E+06 2925.00 0.1445E+05

 425.00 0.2178E+06 2950.00 0.1428E+05

 450.00 0.2013E+06 2975.00 0.1410E+05

 475.00 0.1868E+06 3000.00 0.1393E+05

 500.00 0.1739E+06 3025.00 0.1376E+05

 525.00 0.1626E+06 3050.00 0.1360E+05

 550.00 0.1524E+06 3075.00 0.1344E+05

 575.00 0.1433E+06 3100.00 0.1328E+05

 600.00 0.1351E+06 3125.00 0.1313E+05

 625.00 0.1277E+06 3150.00 0.1298E+05

 650.00 0.1209E+06 3175.00 0.1283E+05

 675.00 0.1147E+06 3200.00 0.1268E+05

 700.00 0.1091E+06 3225.00 0.1254E+05

 725.00 0.1039E+06 3250.00 0.1240E+05

 750.00 0.9908E+05 3275.00 0.1226E+05

 775.00 0.9466E+05 3300.00 0.1212E+05

 800.00 0.9057E+05 3325.00 0.1199E+05

 825.00 0.8677E+05 3350.00 0.1186E+05

 850.00 0.8323E+05 3375.00 0.1173E+05

 875.00 0.7994E+05 3400.00 0.1161E+05

 900.00 0.7686E+05 3425.00 0.1148E+05

 925.00 0.7397E+05 3450.00 0.1136E+05

 950.00 0.7127E+05 3475.00 0.1124E+05

 975.00 0.6873E+05 3500.00 0.1112E+05

 1000.00 0.6634E+05 3525.00 0.1101E+05

 1025.00 0.6409E+05 3550.00 0.1089E+05

 1050.00 0.6196E+05 3575.00 0.1078E+05

 1075.00 0.5995E+05 3600.00 0.1067E+05

 1100.00 0.5806E+05 3625.00 0.1056E+05

 1125.00 0.5626E+05 3650.00 0.1046E+05

 1150.00 0.5455E+05 3675.00 0.1035E+05

 1175.00 0.5293E+05 3700.00 0.1025E+05

 1200.00 0.5139E+05 3725.00 0.1015E+05

 1225.00 0.4992E+05 3750.00 0.1005E+05

 1250.00 0.4853E+05 3775.00 9952. 

 1275.00 0.4719E+05 3800.00 9855. 

 1300.00 0.4592E+05 3825.00 9760. 

 1325.00 0.4471E+05 3850.00 9667. 

 1350.00 0.4355E+05 3875.00 9575. 

 1375.00 0.4244E+05 3900.00 9484. 

 1400.00 0.4137E+05 3925.00 9395. 

 1425.00 0.4035E+05 3950.00 9307. 

 1450.00 0.3938E+05 3975.00 9221. 

 1475.00 0.3844E+05 4000.00 9135. 

 1500.00 0.3754E+05 4025.00 9051. 

 1525.00 0.3667E+05 4050.00 8969. 

 1550.00 0.3584E+05 4075.00 8887. 

 1575.00 0.3504E+05 4100.00 8807. 

 1600.00 0.3427E+05 4125.00 8728. 

 1625.00 0.3352E+05 4150.00 8650. 

 1650.00 0.3281E+05 4175.00 8573. 

 1675.00 0.3211E+05 4200.00 8497. 
36

 1700.00 0.3145E+05 4225.00 8423. 

 1725.00 0.3080E+05 4250.00 8349. 

 1750.00 0.3018E+05 4275.00 8276. 

 1775.00 0.2958E+05 4300.00 8205. 

 1800.00 0.2900E+05 4325.00 8134. 

 1825.00 0.2844E+05 4350.00 8065. 

 1850.00 0.2789E+05 4375.00 7996. 

 1875.00 0.2736E+05 4400.00 7928. 

 1900.00 0.2685E+05 4425.00 7861. 

 1925.00 0.2636E+05 4450.00 7796. 

 1950.00 0.2588E+05 4475.00 7731. 

 1975.00 0.2541E+05 4500.00 7666. 

 2000.00 0.2496E+05 4525.00 7603. 

 2025.00 0.2452E+05 4550.00 7541. 

 2050.00 0.2410E+05 4575.00 7479. 

 2075.00 0.2368E+05 4600.00 7418. 

 2100.00 0.2328E+05 4625.00 7358. 

 2125.00 0.2289E+05 4650.00 7299. 

 2150.00 0.2251E+05 4675.00 7241. 

 2175.00 0.2214E+05 4700.00 7183. 

 2200.00 0.2179E+05 4725.00 7126. 

 2225.00 0.2144E+05 4750.00 7070. 

 2250.00 0.2110E+05 4775.00 7014. 

 2275.00 0.2076E+05 4800.00 6959. 

 2300.00 0.2044E+05 4825.00 6905. 

 2325.00 0.2013E+05 4850.00 6852. 

 2350.00 0.1982E+05 4875.00 6799. 

 2375.00 0.1952E+05 4900.00 6747. 

 2400.00 0.1923E+05 4925.00 6695. 

 2425.00 0.1895E+05 4950.00 6644. 

 2450.00 0.1867E+05 4975.00 6594. 

 2475.00 0.1840E+05 5000.00 6544. 

 2500.00 0.1813E+05

-----------------------------------------------------------------------------

********************** AERSCREEN MAXIMUM IMPACT SUMMARY *********************

-----------------------------------------------------------------------------

 MAXIMUM SCALED SCALED SCALED SCALED

 1-HOUR 3-HOUR 8-HOUR 24-HOUR ANNUAL

 CALCULATION CONC CONC CONC CONC CONC

 PROCEDURE (ug/m3) (ug/m3) (ug/m3) (ug/m3) (ug/m3)

--------------- ---------- ---------- ---------- ---------- ----------

FLAT TERRAIN 0.1677E+08 0.1677E+08 0.1509E+08 0.1006E+08 0.1677E+07

DISTANCE FROM SOURCE 1.01 meters directed toward 360 degrees

IMPACT AT THE

AMBIENT BOUNDARY 0.1677E+08 0.1677E+08 0.1509E+08 0.1006E+08 0.1677E+07

DISTANCE FROM SOURCE 1.01 meters directed toward 360 degrees