Page 2 of 51

Problem Formulation for the 

Environmental Fate, Ecological Risk, Endangered 

Species, and Drinking Water Assessments 

in Support of the Registration Review of Sodium 

Metabisulfite and Sulfur Dioxide

 

Sodium metabisulfite (CAS No. 7681-57-4) Sulfur dioxide (CAS No. 7446-09-5)

Prepared by:

Geoffrey Sinclair Ph.D., Biologist

Larry Liu Ph.D., Chemist U. S. Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch V

1200 Pennsylvania Ave., NW

Mail Code 7507P

Washington, DC 20460

Reviewed by:

Joseph DeCant, Ecologist

Gabe Rothman, Environmental Scientist

Approved by:

Mah T. Shamim, Ph.D., Branch Chief

July 23, 2013
Page 3 of 51

1. Executive summary

The Environmental Fate and Effects Division (EFED) has completed the preliminary problem 

formulation for the ecological risk, environmental fate, endangered species, and drinking water 

assessments to be conducted as part of the registration review of sodium metabisulfite and sulfur 

dioxide. The problem formulation describes the methods planned to be used during the 

completion of drinking water and ecological risk assessments in support of registration review 

and provides an overview of the environmental fate, ecological effects, and potential risks

associated with the use of sodium metabisulfite and sulfur dioxide. This document also 

identifies uncertainties and additional studies that would be beneficial to conduct an ecological 

risk assessment. Major findings include:

Clarification of Labels: Current labels do not have clear application information. In order to 

estimate exposure, this data will be assumed based on a conservative estimate. Adding a 

maximum single application rate, maximum number of applications per year and a minimum 

application interval to labels would significantly reduce uncertainty in exposure estimates. 

Additionally, information on typical number of applications and application intervals in storage 

and shipping would be useful. 

Environmental Fate Data: There are not any identified data needs for the environmental fate 

and transport of sodium metabisulfite and sulfur dioxide.

Ecological Effects Data: Since no significant sodium metabisulfite exposure is expected in the 

environment, ecological studies are not being requested at this time for sodium metabisulfite.

Three ecological studies are required to improve understanding of the ecological impacts of 

sulfur dioxide release into the ecosystem. 

• Avian Acute Inhalation Toxicity Study with Bobwhite Quail (A Non-Guideline 

Study): Sulfur dioxide has fumigant uses that may result in exposure to birds via off-site 

atmospheric transport in the vapor phase. The acute effects to birds exposed to sulfur 

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

requirements. 

• Honeybee Acute Vapor Phase (A Non-Guideline Study): Sulfur dioxide has fumigant 

uses that may result in exposure to listed terrestrial invertebrates via off-site atmospheric 

transport of the vapor phase. The acute effects to listed terrestrial invertebrates exposed to 

sulfur dioxide are unknown. Honeybee acute is a surrogate for endangered species 

assessment for terrestrial invertebrates. This is a non-guideline study under the 40 CFR 

Part 158 data requirements. 

• Vegetative Vigor Vapor phase (A Non-Guideline Study): Sulfur dioxide has fumigant 

uses that may result in exposure to terrestrial plants via off-site atmospheric transport in 

the vapor phase. This is a non-guideline study under the 40 CFR Part 158 data 

requirements.
Page 4 of 51

Current labels suggest that during fumigation of structures such as warehouses and storage 

containers for ships and airplanes, and vehicles such as trucks, vans and rail cars, sulfur dioxide 

is released to the outdoor atmosphere during the aeration phase. Preliminary calculations of 

potential exposure show that sulfur dioxide will be present in environmentally relevant 

concentrations that may affect terrestrial non-target organisms. Sulfur dioxide has a general 

mode of action that indicates the chemical may have toxicity to terrestrial animal and plant 

species. No data are available to assess the toxicity of sulfur dioxide to terrestrial invertebrates, 

birds, or terrestrial vegetation near release points. In the absence of such data, insufficient 

information exists to preclude concerns for direct toxic effect to non-target terrestrial 

invertebrate, bird, and terrestrial plant species.
Page 5 of 51

2. Introduction

Sodium metabisulfite (CAS No. 7681-57-4) and sulfur dioxide (CAS No. 7446-09-5) are 

grouped as inorganic sulfites registered as fungicides (USEPA 2007). End-use inorganic sulfite 

products contain sulfur dioxide at 99.9% to 100% and sodium metabisulfite at 37.5% to 98.5%

respectively and are typically used to treat for Botrytis cinerea, the fungus which causes bunch 

rot, or gray mold disease on grapes.

The sodium metabisulfite products are composed of the anhydrous, solid ingredient contained in 

semi-sealed pads which are added to containers holding grapes prior to shipping. The pads 

absorb moisture, and release low levels of sulfur dioxide in the range of 1-5 ppm. The Agency 

currently has 11 products with sodium metabisulfite (PC Code: 111409) as the active ingredient. 

There are currently 3 products with sulfur dioxide (PC Code: 077601) as the active ingredient.

Sulfur dioxide (SO2) products are formulated as a compressed liquid that converts to a gas upon 

release. These products are used in cold-storage warehouses, trucks, vans and train cars for postharvest grape fumigation. Release of sulfur dioxide after fumigation of structures provides 

routes of exposure that may impact terrestrial non-target organisms that include terrestrial 

invertebrates, mammals, birds and plants.

In addition to the fungicidal use against Botrytis cinerea, sulfur dioxide is also used in 

combination with carbon dioxide to treat for black widow spider on grapes in warehouse 

settings. The black widow spider treatment is not included on any sulfur dioxide product labels 

since it is used in conjunction with carbon dioxide and included in carbon dioxide labels as 

permitted under a FIFRA 24(c) carbon dioxide registration (CA920007). Additional sources of 

sulfur dioxide include the combustion of fossil fuels, smelting of sulfide ores, volcanic 

emissions, and other natural sources. Sulfur dioxide is also used to manufacture hydrosulfites, to 

bleach wood pulp and paper, to process, disinfect, and bleach food, for waste and water 

treatment, in metal and ore refining, and in oil refining (ATSDR-MMG 2004).

Both sodium metabisulfite (21CFR §182.3766) and sulfur dioxide (21CFR §182.3862) are listed 

as GRAS (Generally Recognized as Safe) by the FDA (Food and Drug Administration) as 

preservatives in certain foods. Sodium metabisulfite is also used up to a concentration of 1% as 

an antioxidant in hair care products and as a reducing agent in cosmetic formulations (CIR 

2003). Sulfur dioxide is a criteria air pollutant regulated under the Clean Air Act (40 CFR Part 

50).

EFED evaluated the most recent registration evaluation decision for sodium metabisulfite and 

sulfur dioxide in association with the updated toxicity, exposure, and usage information to 

determine if sufficient data are available and if further updates are needed to support registration 

review. The previous RED (2007) did not identify any risk concerns for terrestrial wildlife and 

aquatic organisms. In addition, sulfur dioxide use is not expected to result in significant exposure 

to drinking water resources. At the time of the RED (2007), environmental fate and ecological 

effects data for sulfur dioxide were not required or received because the pesticide’s uses are 

limited to indoor use and there were not any modeling efforts that demonstrated outdoor 

exposure. 
Page 6 of 51

3. Use Characterization

a. Sodium Metabisulfite

Sodium metabisulfite is an inorganic sulfite which is used as a fungicide. Eleven products are 

currently registered for post-harvest grape fumigation. Sodium metabisulfite is imbedded in the 

paper pad (7 g a.i. per pad). No more than one pad is placed in the packing container for each 18 

lbs of table grapes. When solid sodium metabisulfite is mixed with water or absorbs moisture, it 

produces sulfur dioxide, which is toxic to fungal pathogens. Table 1 includes the use 

information that was summarized from LUIS reports of the eleven registration numbers for 

sodium metabisulfite.

Table 1. Uses Site and Application Information for Sodium Metabisulfite

Use Group Crop/Site

Max 

App 

Rate 

Unit / 

Area

Max 

Application 

#/Year

Max 

Application 

Rate/Year

Minimum 

Retreatment

INDOOR 

FOOD 

(wrap)

GRAPES

depends 

on fruit 

weight

Unspecified Unspecified Unspecified

INDOOR 

NONFOOD 

(stickers)

footwear, 

clothing, luggage,

handbags, 

purses, wallets, 

gloves, hats, 

belts, leather 

goods, sporting 

goods, furniture, 

gift and packing 

boxes, carpets, 

photo albums, 

musical 

instruments, 

toys, bracelets, 

jewelry, dolls, 

lamps

1 

sticker 

per 2 

ft2

Unspecified Unspecified Unspecified

b. Sulfur Dioxide

Sulfur dioxide is a gas with a pungent and irritating smell. Three Section 3 products are currently 

registered (11195-1, 67799-3, and 8996-9). It is formulated as a liquid under pressure which 

turns into gas upon release. It has antifungal and antimicrobial properties and is used for the 
Page 7 of 51

control of mold caused by Botrytis cinerea on grapes during storage and transport. Sulfur 

dioxide is also used for sanitation of corks and barrels in wine industry. Sulfur dioxide use as a 

pesticide has not exceeded 100 tons per year throughout the entire state of California from 2008 

to 2010 (USEPA 2013). This amount represents a minor source as defined by the Clean Air Act 

which defines any individual source which emits sulfur dioxide below 100 tons per year as deminimis (NSR 1990). Table 2 lists the use information for sulfur dioxide that was summarized 

from LUIS reports.

Table 2. Uses Site and Application Information for sulfur dioxide

Use Site (Application 

Method Type Description)

Aerial and/or 

Ground 

Application 

Identified by 

Equipment/ Label 

Restriction

Formulation MaxSingle 

Appl. Rate

Max # 

Appl./Year

Max Yearly 

Appl. Rate

Min Appl. 

Interval

COMMERCIAL 

STORAGES/WAREHOUSE

S PREMISES1 (stored 

commodity fumigation)

Terminology for 

Equipment: 

Ground PRESSURIZED 

GAS

1% (v/v) gas 

conc. in the 

chamber

Unspecified Unspecified 7 days Terminology for 

Restrictions: No 

Restrictions

COMMERCIAL 

TRANSPORTATION 

FACILITIES-FEED/FOODFULL (stored commodity 

fumigation)

Terminology for 

Equipment: 

Ground PRESSURIZED 

GAS

1% (v/v) gas 

conc. in the 

chamber

Unspecified Unspecified Unspecified Terminology for 

Restrictions: No 

Restrictions

FOOD PROCESSING 

PLANT EQUIPMENT 

(FOOD CONTACT) (stored 

commodity fumigation)

Terminology for 

Equipment: 

Ground PRESSURIZED 

GAS

1% (v/v) gas 

conc. in the 

chamber

Unspecified Unspecified Unspecified Terminology for 

Restrictions: No 

Restrictions

GRAPES (stored commodity 

fumigation)

Terminology for 

Equipment: 

Ground PRESSURIZED 

GAS

1% (v/v) gas 

conc. in the 

chamber

Unspecified Unspecified 7 days Terminology for 

Restrictions: No 

Restrictions

GRAPES (stored commodity 

fumigation)

Terminology for 

Equipment: 

Ground PRESSURIZED 

GAS

1% (v/v) gas 

conc. in the 

chamber

Unspecified Unspecified Unspecified Terminology for 

Restrictions: No 

Restrictions

1

Labels specify that all fumigations inside warehouses and food processing plants occur in fumigation chambers within the 

buildings.

Fumigation should occur as soon after harvest as is practical. For fruit to be stored for extended 

periods, initial gassing should occur on the day of harvest and follow on a 7-10 day interval. For 

fruit being shipped to market soon after harvest, fumigation should be done before shipment, or 

in transit, if fruit has been gassed three or fewer times. For fruit gassed in the warehouse more 

than three times, 12 or more hours should be allowed to elapse before shipment. Seeded 

varieties may be fumigated on a 7-10 day interval up to 20 times. Most seedless varieties may be 

fumigated on a 7-10 day interval up to 15 times, but the Thompson Seedless variety should not 
Page 8 of 51

be fumigated more than 12 times. For high frequency - low dosage treatment: sulfur dioxide 

should occur as soon after harvest. For fruit to be stored for extended periods, initial gassing 

should occur on the day of harvest and follow at a three times per week interval (2 days, 2 days, 

and 3 days). Seedless and seeded varieties may be fumigated on this high frequency, low dosage 

basis as long as they are in storage.

c. Additional Sources of Sulfur Dioxide

The largest sources of SO2 emissions are from fossil fuel combustion at power plants (73%) and 

other industrial facilities (20%). Smaller sources of SO2 emissions include industrial processes 

such as extracting metal from ore, and the burning of high sulfur containing fuels by 

locomotives, large ships, and non-road equipment. SO2 is linked with a number of adverse 

effects on the respiratory system. The Clean Air Act requires EPA to set national ambient air 

quality standards for “criteria pollutants.” Currently, sulfur dioxide (SO2) is one of five major 

pollutants that are listed as criteria pollutants.

Sulfur dioxide can cause acid rain that seriously affects ecosystems. Acid rain is a major 

problem in the northern hemisphere, where trees and whole forests have been affected. Sulfur 

dioxide deposition can affect vegetation around industrial discharges and in cities. Lichens are 

good bio-indicators of pollution and do not tend to grow where there is sulfur dioxide in the air

(http://www.epa.gov/airquality/sulfurdioxide). According to Office of Air and Radiation in 

EPA, sulfur dioxide is one of a group of highly reactive gasses known as “oxides of sulfur.”

4. Conclusions from Previous Risk Assessments

As part of the 2007 RED, the Environmental Fate and Effects Division (EFED) reported that the 

only environmental fate data potentially needed for sulfur dioxide would be a hydrolysis study; 

however, the Agency determined that the chemistry of sulfur dioxide is so well documented in 

the open literature that an additional study was not necessary (EPA, 1993b). Sodium 

metabisulfite dissolves in water and forms sodium cations, disulfite anions and sulfur dioxide 

(OECD, 2001). Sodium metabisulfite was not deemed to pose a significant environmental or 

ecological risk due to its applications indoors and lack of exposure routes to non-target 

organisms. Based on the high vapor pressure of sulfur dioxide, the use pattern (indoor food-use) 

and limits established for sulfur dioxide release in this decision document, the Agency had no 

ecological risk concerns resulting from the pesticidal use of sulfur dioxide and sodium 

metabisulfite.

a. Ecological Risk Assessment 

No ecological risk concerns resulting from the indoor use of sulfur dioxide and sodium 

metabisulfite were identified in the 2007 RED (USEPA, 2007).

b. Drinking Water Exposure Assessments
Page 9 of 51

Based on the use pattern and fate characteristics of these chemicals as of the RED 2007, the 

Agency does not have any drinking water concerns for sulfur dioxide and sodium metabisulfite.

c. Clean Water Act Programs

Sodium metabisulfite and sulfur dioxide are not identified as a cause of impairment for any water 

bodies listed as impaired under section 303(d) of the Clean Water Act. No Total Maximum Daily 

Load (TMDL) criteria have been developed for sodium metabisulfite and sulfur dioxide with 

these applications. 

5. Environmental Fate and Transport

Sulfur dioxide is formulated as liquid under pressure which turns into gas upon release. Sodium 

metabisulfite is an inorganic sulfite and is formulated as an anhydrous and solid active 

ingredient. When solid sodium metabisulfite is mixed with water or absorbs moisture, it 

produces sulfur dioxide, which is toxic to fungal pathogens. 

The environmentally relevant parameters including basic physical and chemical properties of 

sodium metabisulfite and sulfur dioxide are presented in Tables 3 and Table 4.
Page 10 of 51

Table 3. Chemical Properties and Environmental Fate Parameters of Sodium 

Metabisulfite.

Common Name Sodium metabisulfite

PC Code 111409

Chemical Names

IUPAC Sodium metabisulfite

CAS Sodium metabisulfite

CAS Number 7681-57-4

Chemical 

Structure

Molecular 

Formula

Na2S2O5

Molecular 

Weight (g/mole)

190.1

SMILES Code [O-]S(=O)S(=O)(=O)[O-].[Na+].[Na+]

Color White

Physical State Free-flowing crystalline

Odor Dry environment: odorless

Moist environment: slight sulfur odor

Boiling Point NA

Melting Point >170 oC

Water Solubility 45% by wt. in water at 20 oC
Page 11 of 51

Table 4. Chemical Properties and Environmental Fate Parameters of Sulfur Dioxide.

Common Name Sulfur dioxide

PC Code 077601

Chemical Names

IUPAC Sulfur dioxide

CAS Sulfur dioxide

CAS Number 7446-09-5

Chemical Structure O=S=O

Molecular Formula SO2

Molecular Weight 

(g/mole)

64.07

SMILES Code O=S=O

Color Colorless

Physical State Gas at standard conditions

Odor Rotten eggs (strong)

Boiling Point -10oC

Melting Point -72 oC

Water Solubility 11.9% by wt. in water at 15 oC and 760 mm Hg

Vapor Pressure 237.2 kPa

a. Transformation Products

Sulfur dioxide is the transformation product of sodium metabisulfite. Sulfur dioxide will take 

water and oxide to transform into sulfuric acid which will result in acid rain in the environment.

SO2 + H2O + 1/2O2 → H2SO4

b. Sulfur Dioxide Concentration in the Environment derived 

from the AERSCREEN Model

In this problem formulation, a Tier 1 model (AERSCREEN) was used to determine whether 

present labeled use patterns of sulfur dioxide would potentially contribute to ambient air 

concentrations of concern to mammalian species. The model estimates the "worst-case" of 1-

hour concentrations for a single source, without the need for hourly meteorological data, and also 

includes conversion factors for the "worst-case" 3-hour, 8-hour, 24-hour, and annual 
Page 12 of 51

concentrations. AERSCREEN is intended to produce concentration estimates that are equal to or 

greater than the estimates produced by other refined air dispersion model with a fully developed 

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

application. The detailed modeling information for mechanical and passive release can be found 

in Appendix 1. The modeling output from mechanical release and passive release can be found in 

Appendix 2 and 3, respectively. According the current labels at 10,000 ppm on an estimated 

treatment facility with 25,000ft3 spaces, the maximum concentrations in the first hour as a result 

of mechanical and passive release are 30.7 and 106.0 mg/m3

, respectively (Table 5). 

Table 5. AERSCREEN hour average air maximum concentration.

Aeration 

Scenario

Maximum 

1-Hour 

Conc.

(ug/m3)

Scaled 3-

Hour Conc.

(ug/m3)

Scaled 8-

Hour Conc.

(ug/m3)

Scaled 24-

Hour Conc.

(ug/m3)

Scaled 

Annual 

Conc.

(ug/m3)

Mechanical 3.07E+04 3.07E+04 2.76E+04 1.84E+04 0.31E+04

Passive 1.06E+05 1.06E+05 1.06E+05 1.06E+05 N/A

6. Receptors 

The receptor is the biological entity that is exposed to the stressor (EPA, 1998). Consistent with 

the process described in the Overview Document (EPA, 2004), a risk assessment uses a surrogate 

species approach in its evaluation of sodium metabisulfite and sulfur dioxide. Toxicological data 

generated from surrogate test species, which are intended to be representative of broad 

taxonomic groups, are used to extrapolate to potential effects on a variety of species (receptors) 

included under these taxonomic groupings. 

Guideline toxicity data are not available for sodium metabisulfite or sulfur dioxide and there 

have not been any studies submitted to EFED. Limited mammalian data is available and was 

outlined in the 2007 RED. Generally acute and chronic toxicity data from studies submitted by 

pesticide registrants along with the available open literature are used to evaluate the potential 

direct effects of sodium metabisulfite and sulfur dioxide to the terrestrial receptors identified in 

this section. This includes toxicity data on the technical grade active ingredient, degradates, and 

when available, formulated products. The open literature studies are identified through EPA’s 

ECOTOX database (http://cfpub.epa.gov/ecotox/), which employs a literature search engine for 

locating chemical toxicity data for aquatic life, terrestrial plants, and wildlife. The evaluation of 

both sources of data can also provide insight into the direct and indirect effects of sodium 

metabisulfite and sulfur dioxide on biotic communities from loss of species that are sensitive to 

the chemical and from changes in structure and functional characteristics of the affected 

communities. 

7. Exposure Pathways of Concern

Sodium metabisulfite and its subsequent transformation into sulfur dioxide will not be assessed 

since it is used in packaging and there are not any anticipated major releases from facilities into 
Page 13 of 51

the environment. The environmental fate properties and use patterns of direct applications of 

sulfur dioxide indicate that aeration of fumigated structures and subsequent atmospheric 

transport of elevated concentrations of sulfur dioxide represent potential exposure mechanisms 

of sulfur dioxide to terrestrial organisms. Due to building downwash, updrafts, and downdrafts, 

the primary exposure pathways are 1) inhalation of sulfur dioxide by non-target mammals, birds

and terrestrial invertebrates, and 2) direct contact of sulfur dioxide on non-target plants. Due to 

lack of direct pathways and minimal contributions to deposition of acid rain, EFED does not 

anticipate any significant aquatic exposure.

 8. Risk Hypothesis

A risk hypothesis describes the predicted relationship among the stressor, exposure, and 

assessment endpoint response along with the rationale for their selection. For sulfur dioxide, the 

following ecological risk hypothesis is being employed for this ecological risk assessment:

Based on the application methods, mode of action, fate and transport, and the sensitivity 

of non-target terrestrial species, sulfur dioxide has the potential to reduce survival, 

reproduction, and/or growth in non-target mammals, birds, reptiles, terrestrial-phase 

amphibians, terrestrial invertebrates and terrestrial plants when used in accordance with 

the current label. Non-target organisms include federally- listed threatened and 

endangered species, as well as non-listed species.

Based on the current application methods and fate and transport of sulfur dioxide, there 

is no expectation of a complete exposure pathway for aquatic organisms and exposure of 

aquatic organisms is expected to be low.

9. Analysis Plan

In order to address the risk hypothesis, the potential for hazardous effects on the environment is 

estimated. The use, environmental fate, and ecological effects of sulfur dioxide are characterized 

and integrated to assess the risks. This is accomplished using a risk quotient (ratio of exposure 

concentration to effects concentration) approach. Although risk is often defined as the likelihood

and magnitude of hazardous ecological effects, the risk quotient-based approach does not 

provide a quantitative estimate of likelihood and/or magnitude of an adverse effect. However, as 

outlined in the Overview Document (USEPA, 2004), the likelihood of effects to individual 

organisms from particular uses of sulfur dioxide is estimated using the probit dose-response 

slope and either the level of concern (discussed below) or the actual calculated risk quotient 

value. 

This analysis plan will be revisited and may be revised at the time of registration risk assessment 

depending upon the data available in the open literature and the information submitted by the 

public in response to the opening of the Registration Review docket.

a. Stressors of Concern
Page 14 of 51

Based on the preliminary screening models in this Problem Formulation that indicate outdoor 

exposure of sulfur dioxide after release from fumigated structures, sulfur dioxide is expected to 

be the dominant stressor present in the environment. Additionally, the RED (2007) indicates that 

both terrestrial plants and animals are sensitive enough that modeled outdoor exposure may 

result in adverse impacts to non-target communities. Uses of sodium metabisulfite are not 

expected to result in outdoor exposures since it is solely used in packaging applications. 

b. Measures of Ecological Exposure

The exposure of the outdoor terrestrial environment to sulfur dioxide will be assessed as passive 

release and as mechanical ventilation through leakage of sulfur dioxide from structures during 

treatment and uncontrolled aeration post-treatment. The largest structures that are fumigated will 

contain the largest mass of sulfur dioxide residues and will require the largest time for ventilation 

and aeration. Therefore, inhalation exposure in the near field outdoor environment will be 

assessed modeling fumigations of different sized structures.

Sulfur dioxide emissions from all treated structures must be quantified in order to determine 

estimated exposure concentrations (EECs) in the air. The temporal emissions profile from each 

outdoor release point will be entered into dispersion models to determine the acute EECs in the 

environment. Given the dispersion due to turbulence and downwind transport, it is not 

anticipated that chronic exposures will be of concern from a single fumigation event. The 

temporal emissions profile will be developed from indoor monitoring data. The emissions from 

each building will be calculated based on the loss of sulfur dioxide mass over time within the 

structure.

Maximum acute inhalation EECs will be determined in the near field area directly adjacent to 

treated structures using the PERFUM model (Tier 2). PERFUM is parameterized by a time 

series of emissions data. PERFUM considers these emission values in tandem with a robust 

statistical sampling of meteorological data from points within rings surrounding a treated field 

(usually 5 years of hourly meteorological data). The current version of PERFUM processes 

estimated air concentrations from EPA’s previously recommended atmospheric dispersion model 

in the near field, the Industrial Source Complex Short-Range Model, Version 3 (ISCST3). The 

framework for PERFUM is illustrated in Figure 1 below. Estimated air concentrations are 

calculated and binned by percentile distributions within each ring and averaging time period. 

First, a peak one-hour averaging period will be used to calculate air EECs. If necessary, a higher 

averaging period equivalent to the exposure duration in toxicity studies will be used to 

characterize the RQs resulting from utilizing the one-hour peak EECs. The highest 90th

percentile estimated air concentration from all averaging periods from the receptor ring closest to 

the edge of the field will be considered as the upper-bound EEC to determine the RQ. The 

PERFUM model is publically available on the web from the follow link:

http://www.exponent.com/projectdetail.aspx?project=450. For the risk assessment, the air 

exposure at ground level outside the treated structure will be evaluated considering 

meteorological conditions most vulnerable to the downward transport of the plume (usually 

associated with light winds and stagnant conditions). 
Page 15 of 51

Figure 1. Illustration of the spatial and temporal aspects of the source to receptor configuration 

in PERFUM. The wind rose (left) illustrates the frequency distribution of variations in wind 

speed and wind direction that PERFUM accounts for in the transport of the vapor plume from the 

treated source to receptors (right).

c. Measures of Ecological Effects

Current data suggest that during fumigation of structures such as warehouses and storage 

containers for ships and airplanes, and vehicles such as trucks, vans and rail cars, sulfur dioxide 

is released to the outdoor atmosphere during the aeration phase. Since sulfur dioxide is highly 

volatile and is a gas at room temperature and standard pressure, inhalation and direct contact 

from vapor following structural fumigation is expected to be the major exposure pathway. 

Preliminary calculations of potential exposure show that sulfur dioxide will be present in 

environmentally relevant concentrations that may affect non-target terrestrial organisms. Sulfur 

dioxide has a general mode of action that indicates the chemical may have toxicity to terrestrial 

invertebrates, mammals, birds, and plant species. No data are available to assess the toxicity of 

sulfur dioxide to terrestrial organisms near release points. In the absence of such data, 

insufficient information exists to preclude concerns for direct toxic effect to non-target terrestrial 

organisms.

a. Effects to Aquatic Organisms

Effects on aquatic organisms from the proposed uses of sodium metabisulfite and sulfur dioxide 

are expected to be minimal due to 1) primarily indoor uses, and 2) the high vapor pressure at 

room temperature of sulfur dioxide resulting in atmospheric transport after release into the 

environment. 

Receptor 

Rings

Treated 

Field
Page 16 of 51

b. Effects to Terrestrial Organisms

Table 6 and Table 7 provide a summary of the terrestrial taxonomic groups, and most sensitive 

surrogate species tested to characterize the potential acute and chronic ecological effects of 

sodium metabisulfite and sulfur dioxide respectively. 

Table 6. Summary of the Most Sensitive Endpoints from Terrestrial Toxicity Studies for Sodium 

metabisulfite 

Taxonomic 

Group

Study 

Type

Surrogate 

Species

Toxicity 

Value

Acute 

Toxicity 

Classification

Source 

(all units 

in terms of 

measured 

active 

ingredient)

Mammals Acute 

Oral

Laboratory 

rat 

LD50 = 

1540 

mg/kg Toxicity 

Category III

TOXNET, 

2005

(Rattus 

norvegicus)

LD50 = 

1131 

mg/kg-bw

OECD, 

2001

A few acute toxicity tests for sodium metabisulfite have been reported though none have been 

submitted to EFED. The 96-hour LC50 was 100 mg/L for fish and the 72-hr EC50 for algae was 

48.1 mg/L. An acute 48-hr EC50 for daphnids has been reported to be 88.76 mg/L and a chronic 

NOEC of >10 mg/L was reported. Due to lack of exposure, EFED is not requesting any data 

effects data on sodium metabisulfite.
Page 17 of 51

Table 7. Summary of the Most Sensitive Endpoints from Terrestrial Toxicity Studies for Suflur 

Dioxide 

Taxonomic 

Group

Study 

Type

Surrogate 

Species

Toxicity 

Value

Acute 

Toxicity 

Classification1

Source 

(all units in 

terms of 

measured 

active 

ingredient)

Mammals

Acute 

Inhalation

Guinea 

Pig

LD50 = 

1000ppm/20 

hr; 130 

ppm/154 hr 

LD50 = 2620 

mg/m3/20hr or 

2.6 mg/L

IV HSDB, 2005

Acute 

Inhalation

Mouse

LD50 = 3000 

ppm / 30 min 

(7.9 mg/ L / 30 

min)

IV NIOSH, 

2004

Acute 

Inhalation

Mouse

LD50 = 150 

ppm / 847 hr; 

1000 ppm / 4 

hr (2.6 mg/L)

IV HSDB, 2005

Acute 

Inhalation

Rat

LD50 = 2520 

ppm/ 1 hr or 

1.65 mg/L; 

2168 mg/m3; 

20mg/m3/5 hr; 

30 mg/m3

III NIOSH, 

2004

Acute 

Inhalation

Guinea 

pig

Lowest 

published LC: 

1039 

ppm/24hr (2.7 

mg/L/24 hr)

IV NIOSH, 

2004

Concentration of sulfur dioxide as low as 1-2 ppm have been reported to cause severe stress to 

green plants (USEPA 2007). The LD50 for a four hour acute exposure of a mouse and 

comparable exposure of a rat to sulfur dioxide has been reported to be 2821 and 2168 mg m-3. 

Current models of both different potential environmental exposures and on the above 
Page 18 of 51

mammalian LD50s, suggest that levels of concern (LOC) may occur at intermediate release 

scenarios (Appendix 4), 

c. Ecological Incidents

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. The National Pesticide Information 

Center, the National Institute of Occupational Safety and Health (NIOSH), National Poison 

Control Centers, the California Department of Pesticide Regulation (CDPR) were also searched. 

As of 17 April, 2013, review of EIIS and AIMS identified no ecological incidents involving 

either sodium metabisulfite or sulfur dioxide. 

d. Additional Ecotoxicity Data

Toxicity data requested in this problem formulation will be used to calculate risk quotients. Any 

additional information submitted by the registrant or found in the open literature prior to conduct 

of the risk assessment will also be considered. The open literature studies are identified using 

EPA’s ECOTOXicology database (ECOTOX) (USEPA, 2007c), which employs a literature 

search engine for locating chemical toxicity data for aquatic life, terrestrial plants, and wildlife. 

The evaluation of both sources of data can also provide insight into the direct and indirect effects 

of pesticides on biotic communities from loss of species that are sensitive to the chemicals and 

from changes in structure and functional characteristics of the affected communities.

e. Drinking Water 

Based on the use pattern (i.e., indoor and packaging) and fate characteristics of these chemicals, 

the Agency does not have any drinking water concerns for sulfur dioxide and sodium 

metabisulfite.

f. Available Monitoring Data

The Agency is not aware of air monitoring conducted by federal and state agencies due to uses as 

a pesticide. If any such data become available, this data will be considered in the assessment to 

the extent that the data on sulfur dioxide is relevant to uses as a pesticide.
Page 19 of 51

10.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/or endangered (listed) species from 

registered uses of pesticides in registration review. The process for evaluating potential risks to 

listed species is further described at 

http://www.epa.gov/oppfead1/endanger/litstatus/riskasses.htm.

11. Endocrine Disruptor Screening Program

Sodium metabisulfite and sulfur dioxide were not included in the first group of 67 chemicals or 

the second group of 134 chemicals issued in order to conduct Tier 1 EDSP testing. For 

additional information the EDSP program, visit http://www.epa.gov/endo/. 

12.Preliminary Identification of Data Gaps 

a. Labels

Current data supplied suggests that labels do not have a maximum application rate, a maximum 

number of applications or a minimum application interval. In order to estimate exposure, this 

data will be assumed based on a conservative estimate. Adding a maximum application rate, a 

maximum number of applications and a minimum application interval to labels would 

significantly reduce uncertainty in exposure estimates. Additionally, information on typical 

number of applications and application intervals would be useful. 

b. Environmental Fate

The fate of sodium metabisulfite and sulfur dioxide in the environment is well documented. 

Therefore there are not any data gaps that necessitate environmental fate studies in support of a 

risk assessment.

c. Effects

There have not been any ecological effects studies submitted to EFED that offer data in support 

of a risk assessment for sodium metabisulfite or sulfur dioxide. Due to the anticipated limited 

exposure of non-target organisms to indoor uses of sodium metabisulfite, EFED is not requesting 

any data for sodium metabisulfite. In contrast, sulfur dioxide is released into the external 

environment. Available toxicity endpoints that have been evaluated for mammals and modeling 

scenarios of sulfur dioxide release in the environment, suggest that exposures from these releases 

may impact non-target organisms in proximity to the treatment facilities. Consequently, three

special studies of terrestrial organisms that may be sensitive to sulfur dioxide have been 

identified as necessary for a risk assessment. These studies include a non-guideline honeybee 

inhalation, a non-guideline avian inhalation study, and a non-guideline terrestrial plant study of 
Page 20 of 51

vegetative vigor and are outlined below (Table 8, 9, 10). Due to lack or exposure routes to 

aquatic ecosystems, EFED is not requesting any data on aquatic organisms at this time. 

Avian Acute Inhalation (Bobwhite Quail)

Because sulfur dioxide is highly volatile and gaseous at room temperature and standard pressure, 

inhalation of vapor following structural fumigation is the major potential exposure pathway for 

non-target mammals and birds. Current data suggest that during sulfur dioxide fumigation of 

structures, the gas is released to the outdoor atmosphere during the aeration phase. No data is 

available to the Agency regarding sulfur dioxide toxicity to avian species via inhalation. This test 

will provide an avian acute inhalation endpoint for assessing risks of off-site movement via 

atmospheric transport of vapors. In the absence of such data, insufficient information exists to 

preclude concerns for direct toxic effects to non-target birds.

Honeybee Acute Toxicity (Vapor Phase) 

Because sulfur dioxide is highly volatile and gaseous at room temperature and standard pressure, 

inhalation of vapor following structural fumigation is the major potential exposure pathway for 

non-target terrestrial invertebrates. Current data suggest that during sulfur dioxide fumigation of 

structures, the gas is released to the outdoor atmosphere during the aeration phase. No data is 

available to the Agency regarding sulfur dioxide toxicity to terrestrial invertebrates exposed to 

fumigant vapors. The honeybee acute study is a surrogate for endangered speces assessment for 

terrestrial invertebrates. In the absence of such data, insufficient information exists to preclude 

concerns for direct toxic effects to non-target invertebrates.

Terrestrial Plant Vegetative Vigor (Vapor Phase)

No quantitative data is available to the Agency regarding sulfur dioxide toxicity to plants. 

Exposure potential exists during the aeration phase following structural fumigation. Sulfur 

dioxide has a general mechanism of action that indicates the chemical may have toxicity to plant 

species upon contact. No data are available to assess the toxicity of sulfur dioxide to vegetation 

near release points. In the absence of such data, insufficient information exists to preclude 

concerns for direct toxic effects to non-target plant species.
Page 21 of 51

Table 8. Ecological Effects Data for Aquatic Animals exposed to Sulfur Dioxide 

Guideline Description MRID Classification Data 

Gap? Comments

850.1075

Acute 

freshwater 

fish toxicity None Not 

applicable No

Limited aquatic 

exposure is 

expected based 

on the labeled 

uses and the 

fate properties 

of sulfur 

dioxide

(cold water 

species)

Acute 

freshwater 

fish toxicity None Not 

applicable No

(warm water 

species)

Acute 

estuarine/

None Not 

applicable No

marine fish 

toxicity

850.101

Acute 

toxicity to 

freshwater 

invertebrates

None Not 

applicable No

850.1025

Acute 

estuarine/

None Not 

applicable marine No

mollusk 

toxicity

850.1035

Acute 

estuarine/

None Not 

applicable marine No

invertebrate 

toxicity

850.13

Freshwater 

invertebrate 

life cycle

None Not 

applicable No

850.14

Freshwater 

fish early life 

stage

None Not 

applicable No
Page 22 of 51

Table 9. Ecological Effects Data for Terrestrial Animals exposed to Sulfur Dioxide 

Guideline Description MRID Classification Data Gap? Comments

850.21

Avian acute oral 

toxicity(upland 

game or 

waterfowl 

species)

None Not 

applicable No1

1 Acute inhalation is 

the primary route of 

exposure; thus, acute 

oral/dietary/contact 

toxicity and 

reproduction studies 

are not 

recommended

2 Birds and insects 

could potentially be 

exposed to sulfur 

dioxide released 

from treated 

structures. Data 

have high value in 

reducing uncertainty 

of risk. A study 

protocol should be 

submitted to the 

Agency prior to 

conducting each 

study.

3 EFED will use a 

weight of evidence 

approach to consider 

possible chronic 

effects to birds since 

practical 

considerations 

prevent requests of 

chronic avian tests.

Avian acute oral 

toxicity 

(passerine 

species)

None Not 

applicable No1

Nonguideline

Avian 

inhalation 

toxicity

None Not 

applicable Yes2,3

850.22

Avian dietary 

toxicity (upland 

game species)

None Not 

applicable No1

Avian dietary 

toxicity 

(waterfowl 

species)

None Not 

applicable No1

850.23

Avian 

reproduction 

(upland game 

species)

None Not 

applicable No1

Avian 

reproduction 

(waterfowl 

species)

None Not 

applicable No1

850.302 Honeybee acute 

contact toxicity None Not 

applicable No1

NonguidelineHoneybee acute 

toxicity None Not applicable Yes2
Page 23 of 51

Table 10. Ecological Effects Data for Plants Exposed to Sulfur Dioxide

Guideline Description MRID Classification Data Gap? Comments

Nonguideline

Terrestrial 

plant 

Vegetative 

Vigor (Vapor 

Phase)

None Not 

applicable Yes2

1 Limited 

exposure is 

anticipated for 

seeds.

850.4100A

Terrestrial plant 

toxicity (Tier 

I&II seedling 

emergence)

None Not 

applicable No1

850.4150B

Terrestrial plant 

toxicity (Tier 

I&II vegetative 

vigor)

None Not 

applicable No1

850.4500C

Aquatic plant 

growth 

(freshwater 

green alga)

None Not 

applicable No3

2 Data on suflur

dioxide toxicity to 

plants have high 

value in reducing 

uncertainty. A 

study protocol 

should be 

submitted to the 

Agency prior to 

conducting the 

study modifying 

exposure route of 

a terrestrial 

vegetative vigor 

study.

Aquatic plant 

growth 

(freshwater 

diatom)

None Not 

applicable No3

Aquatic plant 

growth 

(saltwater 

diatom)

None Not 

applicable No3

3 Limited aquatic 

exposure is 

expected based on 

the labeled uses 

and the fate 

properties of 

sulfur dioxide.

850.45

Aquatic plant 

growth 

(Cyanobacteria)

None Not 

applicable No3

850.44

Aquatic plant 

growth 

(vascular 

plants)

None Not 

applicable No3

A As of July 2012 the Final Guideline 850.4100 contains both Tier I and Tier II test guidance (formerly 850.4100 and 

850.4225, respectively).
Page 24 of 51

B As of July 2012 the Final Guideline 850.4150 contains both Tier I and Tier II test guidance (formerly 850.4150 and 

850.4250, respectively). C

As of July 2012 (formerly 850.4500)
Page 25 of 51

13. References 

Agency for Toxic Substances and Disease Registry (ATSDR). 2004. Medical 

Management Guidelines (MMGs) for Sulfur Dioxide (SO2). 

http://www.atsdr.cdc.gov/MHMI/mmg116.html

Cosmetic Ingredient Review (CIR) 2003. Final report on the safety assessment of sodium

sulfite, potassium sulfite, ammonium sulfite, sodium bisulfite, ammonium bisulfite, 

sodium metabisulfite, and potassium metabisulfite. International Journal of Toxicology, 

22 (Suppl 2): 63-88.

Hazardous Substances Data Bank (HSDB). 2005. Sulfur Dioxide. 

http://toxnet.nlm.nih.gov.

Hazardous Substances Data Bank (HSDB). 2005. Sodium Metabisulfite.

http://toxnet.nlm.nih.gov.

International Agency for Research on Cancer (IARC). 1992, IARC Monographs; Vol 54.

Material Safety Data Sheet for Sulfur Dioxide. Printed 2005; Last updated 1996. BOC 

Gases. http://phyvirtual.nju.edu.cn/material/MSDS/G79.pdf

NIOSH (National Institute for Occupational Safety and Health. 2004. The Registry of 

Toxic Effects of Chemical Substances: Sulfur Dioxide. 

http://www.cdc.gov/niosh/rtecs/ws456d70.html

OECD (Organization for Economic Co-operation and Development) SIDS (Screening

Information Data Set). 2001. Disodium disulphite.

NSR (Office of Air new Source Review Workshop Manual). 1990. 

http://www.epa.gov/NSR/ttnnsr01/gen/wkshpman.pdf

Reiss, R. and Giffin J., 2004. A Probablistic Exposure and Risk Model for Fumigant Bystander 

Exposures using Iodomethane as a Case Study”. Report prepared for the FIFRA Science 

Advisory Panel and sponsored by Arvesta Corporation.

US EPA. 1992. Memo to Bruce Sidwell, PM 53; Accelerated Reregistration Branch, 

Special Review and Reregistration Division from Douglas Urban, Acting Branch 

Chief; Ecological Effects Branch, Environmental Fate and Effects Division. Re: Phase 4 

Review of Reregistration Case #4056 for Sodium Bisulfite (DP Barcode D182472)

USEPA. 1995. Screen3 Model User’s Guide, Washington, D.C. EPA/630/R-95/002F. 

September 1995. http://www.epa.gov/scram001/userg/screen/screen3d.pdf. Accessed 

March 2009.
Page 26 of 51

USEPA. 2004. Overview of the Ecological Risk Assessment Process in the Office of Pesticide 

Programs. U.S. Environmental Protection Agency, Office of Prevention, Pesticides and 

Toxic Substances, Office of Pesticide Programs, Washington DC. January 23, 2004.

USEPA. 2007. Reregistration Eligibility Decision (RED). Inorganic Sulfites. Special Review 

and Reregistration Division. Office of Pesticide Programs. 

USEPA. 2013. Biological and Economic Analysis Division (BEAD) Chemical Profile for 

Registration Review: Sulfur Dioxide (077601). Issued by BEAD (in OPP, OCSPP, EPA) 

on 4/11/2003.
Page 27 of 51

Appendix 1.

Sulfur Dioxide Release Scenarios Specified on Labels

Sulfur dioxide is used to treat food and post-harvested commodities in fumigation chambers, 

trucks, vans, and railcars. Labels specify maximum application rates, or indoor concentrations of 

sulfur dioxide, which are maintained over periods of time for treatments inside the chambers. 

Fumigation chambers, trucks, and railcars have a maximum size of 10,000 cubic feet1. Labels 

all require mechanical, or forced, aeration following a treatment of the commodities in 

fumigation chambers. Mechanical aeration releases the fumigant outdoors from the treated 

structure through a stack or vent. However, this is not necessarily required in truck, vans, or 

railcars as the. Therefore, passive aeration, involving the ventilation of treated structures via 

natural means such as opening of windows and doors to allow air to circulate around the 

building, can occur. Therefore, exposure from passive and mechanical release scenarios will be 

quantified.

Critical parameters for active and passive scenarios are described below. The mechanical 

aeration scenario is a forced release from a stack. The passive aeration scenario is ventilation 

resulting from natural flow through a building. Therefore, the release scenarios for mechanical 

aeration is partially defined by certain specifications for a stack from which the release occurs. 

However, no stack parameters are specified for a passive aeration scenario since release is 

assumed to occur throughout the entire area of the building. 

• Mechanical Aeration Scenario

Table 11. Mechanical Aeration Scenario 

Release Parameter Value Justification

Application Rate (lbs./1,000 ft.3) 1.63 Maximum value from product 

label

Building Size (ft.3) 10,000 CSX website 1

Building Area (ft.2) 400 Consistent with HED Methyl 

Bromide Assessment for 

10,000 ft.3 structure 2

Building Height (ft.) 25 Consistent with HED Methyl 

Bromide Assessment for

10,000 ft.3 structure 2

Stack Diameter (in.) 39.6 Consistent with HED Methyl 

Bromide Assessment for 

10,000 ft.3 structure 2

Stack Height (ft.) 30 Consistent with HED Methyl 

Bromide Assessment for 5 

foot stack atop 25 foot 

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

http://www.csx.com/index.cfm/customers/equipment/railroad-equipment/
Page 28 of 51

Release Parameter Value Justification

building 10,000 ft.3 structure 

2

Emission Rate (lb./hr) 18.3 Full mass release from 10,000 

ft.3 structure from one release 

point over one hour 3

Flow Rate (cfm) 166.67 1 air exchange per hour from 

10,000 ft.3 structure 

(consistent with HED Methyl 

Bromide Assessment for 

10,000 ft.3 structure) 2,4

1

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

2

 Emission Rate (lbs./hr) = Application Rate (lbs./1,000 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

• Table 12. Passive Aeration Scenario

Release Parameter Value Justification

Application Rate (lbs./1,000 ft.3) 1.63 Maximum value from product 

label

Building Size (ft.3) 10,000 CSX website 1

Building Area (ft.2) 400 Consistent with HED Methyl 

Bromide Assessment for 

10,000 ft.3 structure 2

Building Height (ft.) 25 Consistent with HED Methyl 

Bromide Assessment for 

10,000 ft.3 structure 2

Release Height (ft.) 12.5 Half building height for 

10,000 ft.3 structure consistent 

with HED Methyl Bromide 

Assessment 2

Flux Rate (g/m2-s) 6.20 x 10-2 Full mass release from 10,000 

ft.3 structure from 400 ft.2

building over one hour 3

1

 Flux Rate (g/m2-sec) = Application Rate (g/m3) x Structure Size (m3)

 Duration of Release (sec.) x Structure Area (m2)

 where the application rate = 1.63 lbs./1,000 ft3 (26.18 g/m3

), V is the building volume = 

10,000 ft.3 (283.17 m3

), and A is the area = 400 ft.2 (37.2 m2).

2

 Methyl bromide HED risk assessment citation: 
Page 29 of 51

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).

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 sulfur dioxide. Worst-case meteorological conditions (light winds and stagnant 

conditions) and downwash2 parameters 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 2. For purposes of this screening analysis, all ecological receptors of concern will 

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

AERSCREEN Modeling Analyses

The input parameter values used in AERSCREEN for the screening analysis of sulfur dioxide air 

exposure is shown in Tables 13 and 14 below for mechanical and passive release scenarios, 

respectively. 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 13. AESCREEN input parameter values for the mechanical release scenario of sulfur 

dioxide.

Input Parameter Option/Value Notes

 2 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.
Page 30 of 51

Input Parameter Option/Value Notes

English or Metric 

Units E (English)

Source Type P (Point) Mechanical ventilation

Emission Rate 

(lbs./hr) 16.3

Full mass release from 10,000 

ft.3 structure from one release 

point over one hour 1

Stack or Release 

Height Above 

Ground (ft.) 

30

Default for 10,000 ft.3 building 

size based on methyl bromide 

HED assessment 2

Stack Diameter 

(in.) 39.6

Default for 10,000,000 ft.3

building size based on methyl 

bromide HED assessment 2

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)

Stack Exit Stream

Flow Rate

(f

3

/min.)

166.67

Based on 1-hour full exchange of 

volume (air exchange rate = 1.0 

air exchanges per hour) 3

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.) 25

Default for 10,000,000 ft.3

building size based on methyl 

bromide HED assessment 2

Maximum 20 Square building footprint 
Page 31 of 51

Input Parameter Option/Value Notes

Horizontal 

Building 

Dimension (ft.)

consistent with building heights 

specified above

Minimum 

Horizontal 

Building 

Dimension (ft.)

20

Square building 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 

Stack and Building 

Center (ft.)

10

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 concentrations assumed

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

4

Bowen Ratio 3.0 Bare surface assumed around 
Page 32 of 51

Input Parameter Option/Value Notes

source

4

Surface Roughness 

Length (m) 0.001 Bare surface assumed around source

4

1

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

Duration of Release (hr.)

2

 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).

3

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

 60 minutes

4

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

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

Table 14. AESCREEN input parameter values for the passive release scenario of sulfur dioxide.

Input Parameter Option/Value Notes

English or Metric Units M (Metric)

Source Type A (Area)

Emission Rate (g/s) 2.05

Emission rate input is 

based resulting flux rate 

based on one-hour 

complete release (6.20x 

10-2 g/m2

-s) x Area of 

Building Footprint (37.16 

m

2

) 1

Area of building footprint 

for 10,000 ft.3 building 

based on methyl bromide 

HED assessment2

Release Height Above Ground 

(m) 3.81

Release height of half the 

building size assumed 

based on HED assessment2

Height of building for 

10,000 ft.3 based on 

methyl bromide HED 

assessment2

Minimum Horizontal Building 

Dimension (m) 6.1

Square building footprint 

consistent with building 

heights specified above
Page 33 of 51

Input Parameter Option/Value Notes

Maximum Horizontal Building 

Dimension (m) 6.1

Square building footprint 

consistent with building 

heights specified above

Initial Vertical Dimension (m) 3.81 Equivalence to release 

height assumed

Urban or Rural? R (Rural) Conservative default

Minimum Distance to Ambient 

Air (m) 1 Conservative default

NO2 Chemistry 1 (No chemistry/pollutant is 

not NO2)

Tracer gas - NOx emissions 

not modeled

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 

concentrations assumed

Source Elevation (m) 0 Stack base from ground 

release assumed

Minimum Temperature (K) 250 (Default) Default – typical national 

temperature range

Maximum Temperature (K) 310 (Default) Default – typical national 

temperature range

Minimum Wind Speed (m/s) 0.5 Minimum in model: 

conservative default

Anemometer Height (m) 10 Typical boundary layer 

reference height

Surface Characteristics Option 1 (Single User Specified 

Values)

Albedo 0.6 Bare surface assumed 

around source3

Bowen Ratio 3.0 Bare surface assumed 

around source3

Surface Roughness Length (m) 0.001 Bare surface assumed 

around source3

1

 Flux Rate (g/m2-sec) = Application Rate (g/m3) x Structure Size (m3)

 Duration of Release (sec.) x Structure Area (m2)

 where the application rate = 1.63 lbs./1,000 ft3 (26.18 g/m3), V is the building volume = 

10,000 ft.3 (283.17 m3), and A is the area = 400 ft.2 (37.2 m2).

2

 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).
Page 34 of 51

3

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

Meteorological Preprocessor (AERMET)” (EPA, 2004) for further details.
Page 35 of 51

Appendix 2. AERSCREEN output values for the mechanical release 

scenario of sulfur dioxide.

AERSCREEN 11126 / AERMOD 1206 05/06/13

 08:11:36

TITLE: SO2 

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

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

****************************

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

SOURCE EMISSION RATE: 2.0538 g/s 16.300 lb/hr

STACK HEIGHT: 9.14 meters 30.00 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: 7.6 meters 25.0 feet

MAX BUILDING DIMENSION: 6.1 meters 20.0 feet

MIN BUILDING DIMENSION: 6.1 meters 20.0 feet

BUILDING ORIENTATION TO NORTH: 0. degrees

STACK DIRECTION FROM CENTER: 0. degrees

STACK DISTANCE FROM CENTER: 3.0 meters 10.0 feet

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

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

*************************** 
Page 36 of 51

 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 7.07 7.07 -6.54 -0.53 0.2351E+05 50.0 ANN

 20 7.82 7.82 -6.78 -1.04 0.2492E+05 50.0 ANN

 30 8.33 8.33 -6.81 -1.53 0.2472E+05 50.0 ANN

 40 8.59 8.59 -6.63 -1.96 0.2454E+05 50.0 ANN

 50 8.59 8.59 -6.26 -2.34 0.2538E+05 50.0 ANN

 60 8.33 8.33 -5.69 -2.64 0.2544E+05 50.0 ANN

 70* 7.82 7.82 -4.95 -2.87 0.2557E+05 50.0 ANN

 80 7.07 7.07 -4.06 -3.00 0.2518E+05 50.0 ANN

 90 6.10 6.10 -3.05 -3.05 0.2120E+05 50.0 ANN

 100 7.07 7.07 -3.00 -3.00 0.2431E+05 50.0 ANN

 110 7.82 7.82 -2.87 -2.87 0.2377E+05 50.0 ANN

 120 8.33 8.33 -2.64 -2.64 0.2386E+05 50.0 ANN

 130 8.59 8.59 -2.34 -2.34 0.2205E+05 50.0 ANN

 140 8.59 8.59 -1.96 -1.96 0.2227E+05 50.0 ANN

 150 8.33 8.33 -1.52 -1.52 0.2069E+05 50.0 ANN

 160 7.82 7.82 -1.04 -1.04 0.1963E+05 50.0 ANN

 170 7.07 7.07 -0.53 -0.53 0.1664E+05 75.0 ANN

 180 6.10 6.10 0.00 0.00 0.1363E+05 100.0 ANN

 190 7.07 7.07 -0.53 0.53 0.1664E+05 75.0 ANN

 200 7.82 7.82 -1.04 1.04 0.1963E+05 50.0 ANN

 210 8.33 8.33 -1.53 1.53 0.2071E+05 50.0 ANN

 220 8.59 8.59 -1.96 1.96 0.2227E+05 50.0 ANN

 230 8.59 8.59 -2.34 2.34 0.2205E+05 50.0 ANN

 240 8.33 8.33 -2.64 2.64 0.2386E+05 50.0 ANN

 250 7.82 7.82 -2.87 2.87 0.2377E+05 50.0 ANN

 260 7.07 7.07 -3.00 3.00 0.2431E+05 50.0 ANN

 270 6.10 6.10 -3.05 3.05 0.2120E+05 50.0 ANN

 280 7.07 7.07 -4.06 3.00 0.2518E+05 50.0 ANN

 290 7.82 7.82 -4.95 2.87 0.2557E+05 50.0 ANN

 300 8.33 8.33 -5.69 2.64 0.2544E+05 50.0 ANN

 310 8.59 8.59 -6.26 2.34 0.2538E+05 50.0 ANN

 320 8.59 8.59 -6.63 1.96 0.2454E+05 50.0 ANN

 330 8.33 8.33 -6.81 1.52 0.2472E+05 50.0 ANN

 340 7.82 7.82 -6.78 1.04 0.2492E+05 50.0 ANN

 350 7.07 7.07 -6.54 0.53 0.2351E+05 50.0 ANN

 360 6.10 6.10 -6.10 0.00 0.2054E+05 50.0 ANN

* = worst case flow sector
Page 37 of 51

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

********************** 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

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

 YR MO DY JDY HR

 -- -- -- --- --

 10 01 26 26 01

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

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

 -0.01 0.010 -9.000 0.020 -999. 11. 4.6 0.001 3.00 0.60 0.50

 HT REF TA HT

- - - - - - - - - - -

 33.0 249.8 2.0

ESTIMATED FINAL PLUME HEIGHT (non-downwash): 7.3 meters

 METEOROLOGY CONDITIONS USED TO PREDICT AMBIENT BOUNDARY 

IMPACT

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

 YR MO DY JDY HR

 -- -- -- --- --

 10 01 26 26 01
Page 38 of 51

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

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

 -0.01 0.010 -9.000 0.020 -999. 11. 4.6 0.001 3.00 0.60 0.50

 HT REF TA HT

- - - - - - - - - - -

 33.0 249.8 2.0

ESTIMATED FINAL PLUME HEIGHT (non-downwash): 7.3 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 0.2337E+05 2525.00 809.2 

 25.00 0.2148E+05 2550.00 803.9 

 50.00 0.2557E+05 2575.00 799.7 

 75.00 0.2172E+05 2600.00 795.6 

 100.00 0.1833E+05 2625.00 791.4 

 125.00 0.1567E+05 2650.00 787.3 

 150.00 0.1380E+05 2675.00 783.1 

 175.00 0.1239E+05 2700.00 779.0 

 200.00 0.1128E+05 2725.00 774.9 

 225.00 0.1027E+05 2750.00 770.7 

 250.00 9337. 2775.00 766.6 

 275.00 8479. 2800.00 762.6 

 300.00 7642. 2825.00 758.5 

 325.00 6886. 2850.00 754.4 

 350.00 6150. 2875.00 750.4 

 375.00 5442. 2900.00 746.3 

 400.00 4814. 2925.00 742.3 

 425.00 4331. 2950.00 738.3 

 450.00 4060. 2975.00 734.4 

 475.00 3904. 3000.00 730.4 

 500.00 3764. 3025.00 726.5 

 525.00 3626. 3050.00 722.6 

 550.00 3489. 3075.00 718.7 
Page 39 of 51

 575.00 3353. 3100.00 714.8 

 600.00 3218. 3125.00 710.9 

 625.00 3084. 3150.00 707.1 

 650.00 2952. 3175.00 703.3 

 675.00 2827. 3200.00 699.5 

 700.00 2706. 3225.00 695.7 

 725.00 2587. 3250.00 692.0 

 750.00 2469. 3275.00 688.2 

 775.00 2353. 3300.00 684.5 

 800.00 2239. 3325.00 680.8 

 825.00 2128. 3350.00 677.2 

 850.00 2024. 3375.00 673.5 

 875.00 1953. 3400.00 669.9 

 900.00 1885. 3425.00 666.3 

 925.00 1822. 3450.00 662.8 

 950.00 1761. 3475.00 659.2 

 975.00 1704. 3500.00 655.7 

 1000.00 1650. 3525.00 652.2 

 1025.00 1599. 3550.00 648.7 

 1050.00 1551. 3575.00 645.3 

 1075.00 1505. 3600.00 641.9 

 1100.00 1481. 3625.00 638.5 

 1125.00 1462. 3650.00 635.1 

 1150.00 1444. 3675.00 631.7 

 1175.00 1425. 3700.00 628.7 

 1200.00 1407. 3725.00 625.7 

 1225.00 1389. 3750.00 622.7 

 1250.00 1371. 3775.00 619.7 

 1275.00 1353. 3800.00 616.8 

 1300.00 1336. 3825.00 613.8 

 1325.00 1319. 3850.00 610.9 

 1350.00 1302. 3875.00 608.0 

 1375.00 1285. 3900.00 605.1 

 1400.00 1269. 3925.00 602.2 

 1425.00 1253. 3950.00 599.3 

 1450.00 1237. 3975.00 596.5 

 1475.00 1222. 4000.00 593.6 

 1500.00 1206. 4025.00 590.8 

 1525.00 1191. 4050.00 588.0 

 1550.00 1178. 4075.00 585.2 

 1575.00 1166. 4100.00 582.5 

 1600.00 1154. 4125.00 579.7 

 1625.00 1141. 4150.00 577.0 

 1650.00 1129. 4175.00 574.3 

 1675.00 1117. 4200.00 571.8 

 1700.00 1106. 4225.00 569.4 
Page 40 of 51

 1725.00 1094. 4250.00 567.0 

 1750.00 1083. 4275.00 564.7 

 1775.00 1072. 4300.00 562.3 

 1800.00 1061. 4325.00 559.9 

 1825.00 1051. 4350.00 557.6 

 1850.00 1040. 4375.00 555.2 

 1875.00 1030. 4400.00 552.9 

 1900.00 1020. 4425.00 550.6 

 1925.00 1010. 4450.00 548.3 

 1950.00 1001. 4475.00 546.0 

 1975.00 990.9 4500.00 543.7 

 2000.00 981.4 4525.00 541.5 

 2025.00 972.0 4550.00 539.2 

 2050.00 962.8 4575.00 537.0 

 2075.00 953.7 4600.00 534.7 

 2100.00 944.7 4625.00 532.5 

 2125.00 935.8 4650.00 530.3 

 2150.00 927.0 4675.00 528.1 

 2175.00 918.4 4700.00 525.9 

 2200.00 909.9 4725.00 523.8 

 2225.00 901.5 4750.00 521.8 

 2250.00 893.2 4775.00 519.8 

 2275.00 885.0 4800.00 517.7 

 2300.00 876.9 4825.00 515.7 

 2325.00 869.0 4850.00 513.7 

 2350.00 861.1 4875.00 511.7 

 2375.00 853.4 4900.00 509.8 

 2400.00 845.8 4925.00 507.8 

 2425.00 838.3 4950.00 505.8 

 2450.00 830.8 4975.00 503.9 

 2475.00 823.5 5000.00 501.9 

 2500.00 816.3 

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

********************** 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 0.3067E+05 0.3067E+05 0.2760E+05 0.1840E+05 3067. 
Page 41 of 51

DISTANCE FROM SOURCE 3.00 meters directed toward 70 degrees

IMPACT AT THE

AMBIENT BOUNDARY 0.2337E+05 0.2337E+05 0.2104E+05 0.1402E+05 2337. 

DISTANCE FROM SOURCE 1.01 meters directed toward 70 degrees
Page 42 of 51

Appendix 3. AERSCREEN output values for the passive release 

scenario of sulfur dioxide.

AERSCREEN 11126 / AERMOD 1206 05/06/13

 09:05:16

TITLE: so2passive3 

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

****************************** AREA PARAMETERS 

****************************

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

SOURCE EMISSION RATE: 2.0500 g/s 16.270 lb/hr

AREA EMISSION RATE: 0.551E-01 g/(s-m2) 0.437E+00 lb/(hr-m2)

AREA HEIGHT: 3.81 meters 12.50 feet

AREA SOURCE LONG SIDE: 6.10 meters 20.01 feet

AREA SOURCE SHORT SIDE: 6.10 meters 20.01 feet

INITIAL VERTICAL DIMENSION: 3.81 meters 12.50 feet

RURAL OR URBAN: RURAL

INITIAL PROBE DISTANCE = 5000. meters 16404. feet

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

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

**********************

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

 BUILDING DOWNWASH NOT USED FOR NON-POINT SOURCES

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

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

*************************** 

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

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

 MAXIMUM IMPACT RECEPTOR 
Page 43 of 51

 Zo SURFACE 1-HR CONC RADIAL DIST TEMPORAL

 SECTOR ROUGHNESS (ug/m3) (deg) (m) PERIOD

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

 1* 0.001 0.5452E+05 45 1.0 ANN

* = worst case diagonal

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

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

*********************

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

MIN/MAX TEMPERATURE: 250.0 / 310.0 (K)

MINIMUM WIND SPEED: 0.5 m/s

ANEMOMETER HEIGHT: 10.000 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

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

 YR MO DY JDY HR

 -- -- -- --- --

 10 01 17 17 01

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

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

 -0.05 0.011 -9.000 0.020 -999. 13. 2.4 0.001 3.00 0.60 0.50

 HT REF TA HT

- - - - - - - - - - -

 10.0 310.0 2.0

 METEOROLOGY CONDITIONS USED TO PREDICT AMBIENT BOUNDARY 

IMPACT

 --------------------------------------------------------------
Page 44 of 51

 YR MO DY JDY HR

 -- -- -- --- --

 10 01 17 17 01

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

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

 -0.05 0.011 -9.000 0.020 -999. 13. 2.4 0.001 3.00 0.60 0.50

 HT REF TA HT

- - - - - - - - - - -

 10.0 310.0 2.0

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

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

**********************

 OVERALL MAXIMUM CONCENTRATIONS BY DISTANCE

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

 MAXIMUM MAXIMUM

 DIST 1-HR CONC DIST 1-HR CONC

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

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

 1.00 0.5452E+05 2524.99 2062. 

 25.00 0.5432E+05 2550.00 2046. 

 50.00 0.3542E+05 2575.00 2029. 

 75.00 0.2707E+05 2600.00 2012. 

 100.00 0.2226E+05 2625.00 1996. 

 125.00 0.1909E+05 2650.00 1981. 

 150.00 0.1680E+05 2675.00 1965. 

 175.00 0.1520E+05 2700.00 1950. 

 200.00 0.1381E+05 2725.00 1934. 

 225.00 0.1268E+05 2749.99 1920. 

 250.00 0.1175E+05 2775.00 1905. 

 274.99 0.1097E+05 2800.00 1890. 

 300.00 0.1030E+05 2825.00 1876. 

 325.00 9717. 2850.00 1862. 

 350.00 9206. 2875.00 1848. 

 375.00 8753. 2900.00 1835. 

 400.00 8348. 2925.00 1821. 

 425.00 7983. 2950.00 1808. 

 450.00 7651. 2975.00 1795. 

 475.00 7350. 3000.00 1782. 
Page 45 of 51

 500.00 7085. 3025.00 1770. 

 525.00 6840. 3050.00 1757. 

 549.99 6615. 3075.00 1745. 

 575.00 6406. 3100.00 1733. 

 600.00 6211. 3125.00 1721. 

 625.00 6030. 3150.00 1709. 

 649.99 5860. 3175.00 1697. 

 675.00 5701. 3200.00 1686. 

 699.99 5552. 3225.00 1674. 

 725.00 5411. 3250.00 1663. 

 749.99 5278. 3275.00 1652. 

 775.00 5152. 3300.00 1641. 

 800.00 5034. 3325.00 1630. 

 825.00 4921. 3350.00 1620. 

 850.00 4815. 3375.00 1609. 

 875.00 4713. 3400.00 1599. 

 900.00 4616. 3425.00 1589. 

 924.99 4523. 3450.00 1578. 

 950.00 4435. 3475.00 1568. 

 975.00 4350. 3500.00 1559. 

 1000.00 4269. 3525.00 1549. 

 1024.99 4191. 3550.00 1539. 

 1050.00 4116. 3575.00 1530. 

 1075.00 4044. 3600.00 1520. 

 1100.00 3975. 3625.00 1511. 

 1125.00 3908. 3650.00 1502. 

 1150.00 3844. 3674.99 1493. 

 1175.00 3782. 3700.00 1484. 

 1200.00 3722. 3725.00 1475. 

 1224.99 3664. 3750.00 1466. 

 1250.00 3608. 3775.00 1458. 

 1275.00 3554. 3800.00 1449. 

 1300.00 3502. 3825.00 1441. 

 1325.00 3451. 3850.00 1432. 

 1350.00 3402. 3875.00 1424. 

 1375.00 3354. 3900.00 1416. 

 1400.00 3308. 3925.00 1408. 

 1425.00 3263. 3950.00 1400. 

 1450.00 3220. 3975.00 1392. 

 1475.00 3177. 4000.00 1384. 

 1500.00 3136. 4025.00 1376. 

 1525.00 3096. 4050.00 1368. 

 1550.00 3057. 4075.00 1361. 

 1574.99 3019. 4100.00 1353. 

 1600.00 2982. 4125.00 1346. 

 1625.00 2946. 4150.00 1339. 
Page 46 of 51

 1650.00 2911. 4175.00 1331. 

 1675.00 2877. 4200.00 1324. 

 1700.00 2843. 4225.00 1317. 

 1725.00 2811. 4250.00 1310. 

 1750.00 2779. 4275.00 1303. 

 1774.99 2748. 4300.00 1296. 

 1800.00 2718. 4325.00 1289. 

 1825.00 2688. 4350.00 1283. 

 1850.00 2659. 4375.00 1276. 

 1875.00 2630. 4400.00 1269. 

 1900.00 2603. 4425.00 1263. 

 1924.99 2576. 4450.00 1256. 

 1950.00 2549. 4475.00 1250. 

 1975.00 2523. 4500.00 1243. 

 2000.00 2498. 4525.00 1237. 

 2025.00 2473. 4550.00 1231. 

 2050.00 2448. 4575.00 1225. 

 2075.00 2424. 4600.00 1218. 

 2100.00 2401. 4625.00 1212. 

 2125.00 2378. 4650.00 1206. 

 2150.00 2355. 4675.00 1200. 

 2175.00 2333. 4700.00 1195. 

 2200.00 2311. 4725.00 1189. 

 2225.00 2290. 4750.00 1183. 

 2250.00 2269. 4775.00 1177. 

 2275.00 2249. 4800.00 1172. 

 2300.00 2229. 4825.00 1166. 

 2325.00 2209. 4850.00 1160. 

 2350.00 2189. 4875.00 1155. 

 2375.00 2170. 4900.00 1149. 

 2400.00 2151. 4925.00 1144. 

 2425.00 2133. 4950.00 1138. 

 2449.99 2115. 4975.00 1133. 

 2475.00 2097. 5000.00 1128. 

 2500.00 2080. 

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

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

*********************

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

3-hour, 8-hour, and 24-hour scaled

concentrations are equal to the 1-hour concentration as referenced in

SCREENING PROCEDURES FOR ESTIMATING THE AIR QUALITY
Page 47 of 51

IMPACT OF STATIONARY SOURCES, REVISED (Section 4.5.4)

Report number EPA-454/R-92-019

http://www.epa.gov/scram001/guidance_permit.htm

under Screening Guidance

 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 0.1062E+06 0.1062E+06 0.1062E+06 0.1062E+06 N/A

DISTANCE FROM SOURCE 5.01 meters

IMPACT AT THE

AMBIENT BOUNDARY 0.5452E+05 0.5452E+05 0.5452E+05 0.5452E+05 N/A

DISTANCE FROM SOURCE 1.00 meters
Page 48 of 51

Appendix 4. Risk Quotients calculated from passive and mechanical release scenarios based 

on scaled 3-Hour concentration AERSCREEN model. The level of concern for listed species is

risk quotient (RQ) of 0.1.

1 RELEASE

Concentration Mouse Rat

LC50 (mg/m3) 2821 2168

Mechanical (mg/m3) 30.70 30.70

Passive (mg/m3) 106.00 106.00

RQ Mechanical 0.01 0.01

RQ Passive 0.04 0.05

3 SIMULTANEOUS 

RELEASES

Concentration Mouse Rat

LC50 (mg/m3) 2821 2168

Mechanical (mg/m3) 92.10 92.10

Passive (mg/m3) 318.00 318.00

RQ Mechanical 0.03 0.04

RQ Passive 0.11 0.15

5 SIMULTANEOUS 

RELEASES

Concentration Mouse Rat

LC50 (mg/m3) 2821 2168

Mechanical (mg/m3) 153.50 153.50

Passive (mg/m3) 530.00 530.00

RQ Mechanical 0.05 0.07

RQ Passive 0.19 0.24
Page 49 of 51

Appendix 5. Data Call-In tables for non-guideline studies of sulfur 

dioxide 

Guideline Number: Non-guideline

Study Title: Terrestrial Plant Vegetative Vigor (Vapor Phase Special Study)

Rationale for Requiring the Data

Current data suggest that during fumigation of structures such as warehouses and 

storage containers for ships and airplanes, and vehicles such as trucks, vans and rail 

cars, sulfur dioxide is released to the outdoor atmosphere during the aeration phase. 

Preliminary calculations of potential exposure show that sulfur dioxide will be present 

in environmental relevant concentrations that may affect non-target organisms. Sulfur 

dioxide has a general mode of action that indicates the chemical may have toxicity to 

plant species. No data are available to assess the toxicity of sulfur dioxide to vegetation 

near release points. In the absence of such data, insufficient information exists to 

preclude concerns for direct toxic effect to non-target plant species. 

Practical Utility of the Data

How will the data be used?

With this study, the Agency will be able to assess risks to endangered and other nontarget plants downwind from release points of sulfur dioxide. If the terrestrial plant 

special study shows that sulfur dioxide exceeds the Agency’s level of concern for 

federally-listed or other terrestrial plant species, the Agency may be able to use this data 

to mitigate risks.

How could the data change the Agency’s decision or impact the Agency’s future 

decision-making? 

If future endangered species risk assessments are performed without these data, the 

Agency would assume that sulfur dioxide may affect endangered terrestrial plant species 

directly and the endangered species that depend on these plants. Use of sulfur dioxide 

may need to be restricted in areas where endangered species could be exposed. The lack 

of these data will limit the flexibility the Agency and registrants have in complying with 

the Endangered Species Act and could result in use restrictions for sulfur dioxide that 

are unnecessarily severe.
Page 50 of 51

Guideline Number: Non-guideline

Study Title: Avian Acute Inhalation (Bobwhite Quail)

Rationale for Requiring the Data

Current data suggest that during fumigation of structures such as warehouses and 

storage containers for ships and airplanes, and vehicles such as trucks, vans and rail 

cars, sulfur dioxide is released to the outdoor atmosphere during the aeration phase. 

Preliminary calculations of potential exposure show that sulfur dioxide will be present 

in environmental relevant concentrations that may affect non-target organisms. Since 

sulfur dioxide is highly volatile and is a gas at room temperature and standard pressure, 

inhalation of vapor following structural fumigation is the major exposure pathway for 

non-target mammals and birds. No data are available to assess the toxicity of sulfur 

dioxide to avian species near release points. In the absence of toxicity data, insufficient 

information exists to preclude concerns for direct toxic effects to non-target birds.

Practical Utility of the Data

How will the data be used?

With this study, the Agency will be able to assess risks to endangered and other nontarget avian species near release points of sulfur dioxide. If the avian inhalation study 

shows that sulfur dioxide exceeds the Agency’s level of concern for federally-listed or 

other terrestrial avian species, the Agency may be able to use this data to mitigate risks.

How could the data change the Agency’s decision or impact the Agency’s future 

decision-making? 

If future endangered species risk assessments are performed without these data, the 

Agency would assume that sulfur dioxide may affect endangered avian species. Use of 

sulfur dioxide may need to be restricted in areas where endangered species could be 

exposed. The lack of these data will limit the flexibility the Agency and registrants 

have in complying with the Endangered Species Act and could result in use restrictions 

for sulfur dioxide that are unnecessarily severe.
Page 51 of 51

Guideline Number: Non-guideline

Study Title: Honeybee Acute Toxicity (Vapor Phase)

Rationale for Requiring the Data

Current data suggest that during fumigation of structures such as warehouses and 

storage containers for ships and airplanes, and vehicles such as trucks, vans and rail 

cars, sulfur dioxide is released to the outdoor atmosphere during the aeration phase. 

Preliminary calculations of potential exposure show that sulfur dioxide will be present 

in environmentally relevant concentrations that may affect non-target organisms. Since 

sulfur dioxide is highly volatile and is a gas at room temperature and standard pressure, 

inhalation of vapor following structural fumigation is the major exposure pathway for 

non-target terrestrial invertebrates that reside above the soil. No data are available to 

assess the toxicity of sulfur dioxide to non-target invertebrates near release points. The 

honeybee acute test is a surrogate for endangered species assessment for terrestrial 

invertebrates. In the absence of toxicity data, insufficient information exists to preclude 

concerns for direct toxic effects to non-target insects.

Practical Utility of the Data

How will the data be used?

With this study, the Agency will be able to assess risks to endangered and other nontarget terrestrial insect species near release points of sulfur dioxide. If the honeybee 

acute vapor phase study shows that sulfur dioxide exceeds the Agency’s level of 

concern for federally-listed or other terrestrial avian species, the Agency may be able to 

use this data to mitigate risks.

How could the data change the Agency’s decision or impact the Agency’s future 

decision-making? 

If future endangered species risk assessments are performed without these data, the 

Agency would assume that sulfur dioxide may affect endangered terrestrial insect 

species. Use of sulfur dioxide may need to be restricted in areas where endangered 

species could be exposed. The lack of these data will limit the flexibility the Agency 

and registrants have in complying with the Endangered Species Act and could result in 

use restrictions for sulfur dioxide that are unnecessarily severe.