2

• Honeybee inhalation toxicity (non-guideline, phosphine)

Additionally, there are uncertainties about the characteristics of the treatment facilities in which 

phosphine is used. Examples include building size (dimensions), aeration methods, air exchange 

exhaust rates, emission control devices (if any), and the number, size, and relative location of 

stacks and vents that serve as the release points during phosphine aeration operations. 

Collectively these factors will directly influence emission rates, the magnitude of downwind 

dispersion from treated structures, and therefore affect outdoor air concentrations. Submission of 

this information will aid the Agency in estimating realistic, high-end exposure scenarios and will 

reduce the potential of the Agency producing overly protective restrictions on the use of this 

pesticide.
3

Problem Formulation for the Environmental Fate, 

Ecological Risk, Endangered Species, and Drinking 

Water Exposure Assessments in Support of the 

Registration Review of Aluminum Phosphide, 

Magnesium Phosphide, and Phosphine

Phosphine (PH3) 1

CAS: 7803-51-2, 20859-73-8, 12057-74-8

PC Code: 066500, 066501, 066504

Environmental Fate and Effects Division

Prepared by:

Michael Lowit, Ph.D., Ecologist

Stephen Wente, 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:

Faruque Khan, Ph.D., Senior Fate Scientist

Robin Sternberg, Ph.D., Wildlife Biologist

 1 Al phosphide (a crystalline solid) and Mg phosphide (an amorphous solid) are difficult to represent structurally; 

therefore, only the active ingredient of all three pesticides, phosphine, is depicted.

P

H

H H
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 Assessments........................................................................................ 6

3. Stressor Source and Distribution ................................................................................................ 6

3.1. Mechanism of Action.......................................................................................................... 6

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

3.3. Environmental Fate and Transport...................................................................................... 9

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

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

4.1. Incident Databases Review............................................................................................... 12

5. Risk Hypotheses....................................................................................................................... 12

6. Analysis Plan ........................................................................................................................... 13

6.1. Stressors of Concern .......................................................................................................... 13

6.2. Measures of Exposure........................................................................................................ 13

6.2.1. Aquatic Exposure........................................................................................................ 14

6.2.2. Terrestrial Exposure.................................................................................................... 14

6.3. Measures of Effect ............................................................................................................. 16

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............................................................................ 17

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

6.8.2. Ecological Effects Data............................................................................................... 18

7. References................................................................................................................................ 21

Appendix A. Atmospheric Modeling........................................................................................... 23

Appendix B. Data Call-In Tables................................................................................................. 27
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 Aluminum (Al) 

phosphide, Magnesium (Mg) phosphide, and phosphine2. This document provides a plan for 

analyzing data relevant to Al phosphide, Mg phosphide, and phosphine and for conducting 

environmental fate, ecological risk, endangered species, and drinking water exposure 

assessments for 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 Al phosphide, 

Mg phosphide, and phosphine.

2. Problem Formulation

2.1. Nature of Regulatory Action

As part of the implementation of the new Registration Review program3 pursuant to Section 3(g) 

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

evaluation of Al phosphide, Mg phosphide, and phosphine to determine whether they continue to 

meet the FIFRA standard for registration. This problem formulation in support of the 

registration review of Al phosphide, Mg phosphide, and phosphine 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

Previous assessments identified a risk concern for non-target species using or inhabiting burrows 

treated with Al phosphide or Mg phosphide. There was no ecological risk concern for indoor 

uses.

• In 2010, EFED conducted an assessment on the risk to several federally threatened and 

endangered species from use of Al phosphide and Mg phosphide (USEPA, 2010). A “no 

effect” determination was made for indoor uses due to an incomplete exposure pathway. 

For outdoor uses (burrow treatment), a “may affect and likely to adversely affect” 

determination was made for all evaluated species: Alameda whipsnake (Masticophis 

lateralis euryxanthus), California Tiger Salamander (Ambystoma californiense) – Central 

California, Sonoma County, and Santa Barbara County distinct population segments, San 

Francisco garter snake (Thamnophis sirtalis), and San Joaquin Kit Fox (Vulpes macrotis 

mutica). Additionally, the assessment concluded that “...there is the potential for 

modification of designated critical habitat for the Alameda whipsnake and the California 

Tiger Salamander by virtue of sealing and rendering toxic treated small mammal 

burrows, and the elimination of small mammals that construct such burrows.”

• EFED completed the Al phosphide and Mg phosphide Reregistration Eligibility 

Document (RED) in 1998 (DP 236730). The RED cited endangered species 

consultations (see below) regarding risk to listed species; risk to non-listed species was 

 2 Zinc phosphide, although similar in many respects to the pesticides assessed in this document, is not used as a 

structural fumigant, and therefore, will be addressed in the future in a separate document.

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

not addressed. The document concluded that “no ecological or fate data have been 

required in the past .... and none are needed at this time.” The potential for exposure was 

summarized as “Al phosphide and Mg phosphide are expected to degrade rapidly in the 

environment to aluminum hydroxide and magnesium hydroxide and phosphine, the 

toxicant of these pesticides. It appears that phosphine will degrade in days and is at low 

risk for contaminating ground or surface waters. Phosphine near the soil surface is 

expected to diffuse into the atmosphere and be removed via photodegradation. 

Phosphine trapped beneath the soil surface will bind to soil, inhibiting movement, and be 

oxidized to phosphates.” 

• In 1981, The United States Department of the Interior’s Fish and Wildlife Service 

completed a Biological Opinion on the use of Mg phosphide for rodent and mole pest 

control (FWS/OES EPA-81-6). The Biological Opinion stated: “Analysis of the chemical 

action of magnesium phosphide, the areas of intended use, the life history and ecological 

data of listed and proposed species indicate that any species using or inhabiting burrow 

systems could be impacted by the use of this pesticide.” The document continues with the 

finding of jeopardy for the following species: black footed ferret (Mustela nigripes), 

eastern indigo snake (Drymarchon corais couperi), San Joaquin kit fox (Vulpes macrotis 

mutica), Utah prairie dog (Cynomys parvidens), blunt-nosed leopard lizard (Gamelia 

silus), and desert tortoise (Gopherus agassizii). A follow-up consultation (FWS/OES 

EPA-81-9) indicated that conclusions from the Biological Opinion on the use of Mg 

phosphide apply to the same uses of Al phosphide. 

2.2.2. Drinking Water Assessments

A drinking water assessment (DWA) has not been conducted on Al phosphide, Mg phosphide, or 

phosphine.

3. Stressor Source and Distribution

Al phosphide, Mg phosphide, and phosphine are considered to be three different pesticides for 

regulatory purposes. However, Al phosphide and Mg phosphide breakdown in the presence of 

moisture to produce phosphine gas, which is the active ingredient (ai) of all three pesticides. 

Indoor uses of Al phosphide, Mg phosphide, and phosphine include treatment of food/feed, 

agricultural commodities, food preparation sites, storage sites, and beehives. Al phosphide and 

Mg phosphide are also labeled for outdoor use in sealed burrows. 

3.1. Mechanism of Action

The mechanism of phosphine toxicity is not completely understood. Phosphine is a strong 

reducing agent that likely inhibits mitochondrial respiration by reacting with enzymes such as 

cytochrome c oxidase.

3.2. Overview of Pesticide Use and Usage

Al phosphide was first registered for use in the US in 1958, followed by Mg phosphide in 1979, 

and phosphine in 2002. Al phosphide and Mg phosphide are registered for use in burrows for 

rodent control. Phosphine is registered for indoor use on numerous food (post-harvest) and nonfood items as an insecticide and rodenticide. In recent years phosphine usage increased sharply 
7

in California (Screening Level Usage Analysis, 8/6/2012) due to new phosphine products and 

reduced availability of methyl-bromide according to the Biological and Economic Analysis 

Division (BEAD).

Uses and application rates are based on the most recent Label Use Information System report 

(LUIS report) provided by BEAD (4/29/2013 – Al phosphide; 3/13/2013 – Mg phosphide; and 

3/5/2013 - phosphine). The maximum application rates and application methods are listed in 

Table 1 and 2. The registration review ecological risk assessment will be based on current label 

information at the time of assessment.

Table 1. Maximum Rates for Registered Outdoor Uses of Al Phosphide and Mg Phosphide1

 

Use Site Method of 

Application

Single Maximum 

Application Rate 

(lb ai/burrow)

Maximum Number 

of Applications per 

Year

Annual Maximum

(lb ai/burrow)

Al Phosphide

Various2 Animal Burrow 

Treatment 0.0158 Not specified Not specified

Mg Phosphide

Various2 Animal Burrow 

Treatment 0.0174 Not specified Not specified

1 There is no registered outdoor use of phosphine. 2 Agricultural crops/soils (unspecified), agricultural fallow/idleland/conservation reserve (Mg phosphide only), 

agricultural rights-of-way/fencerows/hedgerows (Mg phosphide only), airports/landing fields, 

commercial/institutional/industrial premises/equipment (outdoor), golf course turf, nonagricultural rights-ofway/fencerows/hedgerows, nonagricultural uncultivated areas/soils, orchards (unspecified), pastures, rangeland, 

recreational areas, and residential lawns (Al phosphide only)

Table 2. Maximum Rates for Registered Indoor Uses of Al Phosphide, Mg Phosphide, and 

Phosphine

Use Site Method of 

Application

Single Maximum 

Application Rate 

(lb ai/ft3)

Maximum Number 

of Applications per 

Year

Annual Maximum

(lb ai/ft3)

Al Phosphide

Various1 Fumigant 0.0006 Not specified Not specified

Mg Phosphide

Various1 Fumigant 0.00064313 Not specified Not specified

Phosphine

Various1 Fumigant 0.00032 Not specified Not specified

1

See the following text for descriptions of specific indoor uses.

Indoor uses of Al Phosphide include: airtight storage (flat)-empty, airtight storage (flat)-full, 

airtight storage (small)-empty, airtight storage (small)-full, almond, automobiles, taxis, 

limousines, recreational vehicles, & tires, barges (empty), barges (full), barley, beehives/bee 

colony (diseased/nuisance), brazil nut, candy (processed), cashew, cereal flour/bakery mixes 

(processed), cereal foods (pasta/crackers) (processed), cereals (processed), cheese/cheese 

byproducts (processed), chocolate/chocolate products (processed), cocoa, coffee, coffee 

(processed), commercial shipping containers-feed/food-empty, commercial shipping containersfeed/food-full, commercial storages/warehouses premises, commercial transportation facilitiesfeed/food-empty, commercial transportation facilities-feed/food-full, commercial transportation 
8

facilities (non-feed/non-food), corn (processed/ground), corn (unspecified), corn, pop, cotton, 

cotton (unspecified), cottonseed (animal feed) (processed), date, egg yolk solids (dried) 

(processed), feed mills/feed processing plants, feed/food commodities (bagged/temporary 

storage), fig, filbert (hazelnut), fish (unspecified)(meat), food and feed products (processed), 

food processing plant premises (nonfood contact), fruits (dried/dehydrated) (processed), 

furs/feathers/hair (stored processed products), grain/cereal/flour bins-empty, grain/cereal/flour 

bins-full, grasses grown for seed, herbs and spices (processed), human clothing (insect and 

mold/mildew control), leather/leather hides (stored processed products), legume vegetables, 

livestock feed (processed), malt/malt beverage (processed), meat products (cured) (processed), 

meat products (processed), milk (dried)/nondairy creamers (processed), non-feed/non-food 

commodities (temporary storage), non-grass forage/fodder/straw/hay, nut meats (processed), 

oats, oats (processed), ornamental herbaceous plants, paper/paper products, peanuts, pecan, pet 

animal/bird feed (processed), pistachio, plantago ovata (medicinal), proso millet, rice, rice 

(processed/milled/enriched/polished/brewers grits), rice, wild, rye, safflower, seeds 

(unspecified), sesame, ships and boats, silos, sorghum, soybean flour/milled fractions 

(processed), soybeans (unspecified), sugar (processed), sunflower, tea (processed), 

textiles/fabrics/fibers (stored), tobacco, triticale, vegetables (dried/dehydrated) (processed), 

walnut (English/black), wheat, wood pressure treatment to forest products, and yeast (processed).

Indoor uses of Mg Phosphide include: airtight storage (flat)-full, airtight storage (small)-empty, 

airtight storage (small)-full, almond, automobiles, taxis, limousines, recreational vehicles, & 

tires, barges (full), barley, beans, beehives/bee colony (diseased/nuisance), brazil nut, breweries, 

candy (processed), cashew, cereal flour/bakery mixes (processed), cereal foods (pasta/crackers) 

(processed), cereals (processed), cheese/cheese byproducts (processed), chocolate/chocolate 

products (processed), coffee (processed), commercial shipping containers-feed/food-full, 

commercial storages/warehouses premises, commercial transportation facilities-feed/food-full, 

corn (unspecified), corn, pop, cotton (unspecified), cottonseed (animal feed) (processed), dairy 

animal feed (processed), date, egg yolk solids (dried) (processed), empty containers to be used 

for processed feed/food, feed mills/feed processing plants, feed/food commodities 

(bagged/temporary storage), feed/food containers-full, felt/furs/feathers/felt products, fig, filbert 

(hazelnut), fish (unspecified)(meat), food and feed products (processed), food processing plant 

equipment (food contact), food processing plant premises (nonfood contact), fruits 

(dried/dehydrated) (processed), furs/feathers/hair (stored processed products), grain/cereal/flour 

bins-empty, grain/cereal/flour bins-full, grain/cereal/flour elevators-empty, herbs and spices 

(processed), leather/leather hides (stored processed products), legume vegetables, livestock feed 

(processed), malt/malt beverage (processed), meat products (cured) (processed), milk 

(dried)/nondairy creamers (processed), non-feed/non-food commodities (temporary storage), 

non-feed/non-food containers-full, nut meats (processed), oats, oats (processed), paper/paper 

products, peanuts (unspecified), pecan, pet animal/bird feed (processed), pistachio, plantago 

ovata (medicinal), proso millet, rice, rice (processed/milled/enriched/polished/brewers grits), 

rice, wild, rye, seeds (unspecified), ships and boats, silos, sorghum (unspecified), soybean 

flour/milled fractions (processed), soybeans (unspecified), storage areas-full, sugar (processed), 

tea (processed), textiles/fabrics/fibers (stored), tobacco/tobacco products (processed), triticale, 

vegetables (dried/dehydrated) (processed), vegetables (processed), vegetables (unspecified),

walnut (English/black), wheat, yeast (processed)

Indoor uses of phosphine include: airtight storage (flat)-full, alfalfa, almond, automobiles, taxis, 

limousines, recreational vehicles, & tires, avocado, banana, barley, brazil nut, breweries, 
9

cabbage, chinese, candy (processed), cashew, cereal flour/bakery mixes (processed), cereal foods 

(pasta/crackers) (processed), cereals (processed), cheese/cheese byproducts (processed), 

chocolate/chocolate products (processed), citron (citrus), cocoa, coffee, coffee (processed), 

commercial storages/warehouses premises, commercial transportation facilities (all or 

unspecified), commercial transportation facilities (non-feed/non-food), corn (processed/ground), 

corn (unspecified), corn, pop, cottonseed (animal feed) (processed), date, dill, egg yolk solids 

(dried) (processed), eggplant, endive (escarole), feed mills/feed processing plants, feed/food 

treatment-storage/processing/handling equipment, fig, filbert (hazelnut), fish 

(unspecified)(meat), food and feed products (processed), food processing plant equipment (food 

contact), food processing plant premises (nonfood contact), fruits (dried/dehydrated) (processed), 

furs/feathers/hair (stored processed products), grapefruit, grasses grown for seed, herbs and 

spices (processed), human clothing (insect and mold/mildew control), kumquat, leather/leather 

hides (stored processed products), leather/leather products, legume vegetables, lemon, lettuce, 

lime, malt/malt beverage (processed), mango, meat products (cured) (processed), milk 

(dried)/nondairy creamers (processed), millet (proso), non-feed/nonfood commodities 

(temporary storage), non-feed/nonfood commodities temporary storage (tents/tarps), nonfeed/nonfood treatments-storage/processing/handling equip, non-grass animal feeds, non-grass 

forage/fodder/straw/hay, nut meats (processed), oats, oats (processed), okra, orange, ornamental 

herbaceous plants, papaya, paper/paper products, peanuts, pecan, pepper, persimmon, pimento, 

pistachio, plantago ovata (medicinal), plantain, rice, rice 

(processed/milled/enriched/polished/brewers grits), rice, wild, rye, safflower, salsify, seeds 

(unspecified), sesame, ships and boats, silos, sorghum, soybean flour/milled fractions 

(processed), soybeans (unspecified), starch (processed), sugar (processed), sunflower, sweet 

potato, tangelo, tangerines, tea (processed), textiles/fabrics/fibers (stored), tobacco, 

tobacco/tobacco products (processed), tomato, triticale, vegetables (dried/dehydrated) 

(processed), walnut (English/black), wheat, wood protection treatment to forest products 

(unseasoned), and yeast (processed).

There are uncertainties in the usage of phosphine in treatment facilities (maximum chamber or 

building sizes), 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 used 

for fumigation treatments, 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 phosphine aeration operations. These variables all impact the magnitude of 

downwind dispersion from treated structures.

3.3. Environmental Fate and Transport

The physical and chemical properties of Al phosphide, Mg phosphide, and phosphine are 

summarized in Table 3.
10

Table 3. Physical, Chemical, and Environmental Fate Properties of Al Phosphide, Mg 

Phosphide, and Phosphine

Physical Chemical 

Property

Al Phosphide Mg Phosphide Phosphine

Chemical Structure Crystalline solid Amorphous solid

Molecular Formula AlP Mg3P2 PH3

Molecular Weight 57.96 g/mol 134.86 g/mol 34 g/mol

Solubility at 20oC 260 mg/L No data 371 mg/L

Flammability Limit NA NA 18,000 ppm

Melting Point 2530oC Decomposes before 

melting -134oC

Vapor Pressure (mmHg) NA NA 2.93 × 104 (25 ̊C)

The following discussion summarizes the properties and fate assessment of Al phosphide, Mg 

phosphide, and phosphine as described in the 1998 Al phosphide and Mg phosphide RED (DP 

236730).

Phosphine Gas

Under normal environmental conditions, phosphine (PH3) exists as a gas. The solubility of 

phosphine in water at normal atmospheric pressure is approximately 340 ppm (WHO, 1988). 

Because of its high vapor pressure (2.93 × 104 mm Hg at 25  ̊C; Daubert and Danner, 1989) and 

Henry's Law Constant (0.1 atm m3

/mol), phosphine is expected to mainly remain in the 

atmosphere (WHO, 1988).

Phosphine in the atmosphere is rapidly degraded (WHO, 1988). Gas-phase phosphine will be 

degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals; and 

has a reported atmospheric half-life of less than 1 day. Phosphine does not contain chromophores 

that absorb at wavelengths >290 nm and therefore is not expected to be susceptible to direct 

photolysis by sunlight (Lyman et al, 1990). The expected reaction products of phosphine in air 

with photochemically-produced hydroxyl radicals are oxyacids of phosphorus and inorganic 

phosphate.

Al phosphide and Mg Phosphide

Al phosphide (AlP) and Mg phosphide (Mg3P2) appear to be non-persistent under most 

environmental conditions and are non-mobile in soil because of their instability at atmospheric 

moisture conditions. Al phosphide and Mg phosphide react with water or moisture in air to 

generate the gas phosphine which is the active ingredient of these pesticides (Cotton and 

Wilkerson, 1988; Fluck, 1973; Greenwood and Earnshaw, 1984; and WHO, 1988). Other 

products of hydrolysis are aluminum and magnesium hydroxides. The reactions can be written 

as follows:

P

H

H H
11

(1) AlP + 3H20 → Al(OH)3 + PH3 or

(2) Mg3P2 + 6H20 → 3Mg(OH)2 + 2PH3

The aluminum and magnesium hydroxide residues can further react to produce mineral phases 

that are known to occur naturally in the environment (Lindsay, 1979). Inorganic phosphate and 

other phosphorus oxyacids are expected to be products formed from the oxidation of phosphine

in soils (WHO, 1988; Hilton and Robinson, 1972).

Several published laboratory studies suggest that phosphine below the soil surface is quickly 

adsorbed and degraded. Gaseous phosphine added to soil headspace at 1000 mg/kg dry soil in 

closed containers degrades 50% after approximately 5 days with air dried soil and 11 days in 

water saturated soil (Hilton and Robinson, 1972). Smaller quantities of phosphine may be 

removed by soil through a faster mechanism because phosphine added at a lower concentration 

(0.35 μg/kg) was undetectable in 50 minutes (Eiseman et al., 1997). Diffusion through the soil 

environment is expected to be slow as phosphine is sorbed in seconds when pushed through 

several types of soil in a nitrogen carrier (Berck and Gunther, 1970).

It should be noted that the labels for burrow uses of Al phosphide and Mg phosphide require 

insertion of the pellets far enough below the soil surface to prevent smothering of the pellets by 

the seal closing off the burrow. This suggests that release of phosphine gas will not occur at the 

soil surface where it might dissipate to the atmosphere. The combination of heavier than air 

density (vapor density 1.17; WHO, 1988), insertion well below the soil surface, and the 

reactivity and binding of phosphine to soil all suggest that exposures to phosphine gas from 

burrow uses are isolated within the burrow chamber.

3.4. Clean Water Act

Al phosphide, Mg phosphide, and phosphine are not identified as a cause of impairment for any 

water bodies listed as impaired under section 303(d) of the Clean Water Act4

. In addition, no 

Total Maximum Daily Loads (TMDL) related to these chemicals has been developed5. The 

Impaired Waters and Total Maximum Daily Loads website can be consulted for more 

information6. The Agency invites submission of water quality data for Al phosphide, Mg

phosphide, and phosphine, if any such data exist. 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 Process7, in order to ensure they can be used quantitatively or qualitatively in 

pesticide risk assessments.

4. Receptors

Consistent with the process described in the Overview Document (USEPA, 2004), the risk 

assessment will rely on a surrogate species approach. Toxicological data generated from 

surrogate test species, which are intended to be representative of broad taxonomic groups, are 

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

5

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

group_name=PESTICIDES

6 http://www.epa.gov/owow/tmdl/ 7 http://www.epa.gov/oppfead1/cb/ppdc/2006/november06/session1-sop.pdf
12

used to extrapolate the potential effects on a variety of species (receptors) included under these 

taxonomic groupings.

Toxicity data from studies submitted by pesticide registrants along with available open literature 

will be used to evaluate the potential direct and indirect effects of Al phosphide, Mg phosphide, 

and phosphine to terrestrial receptors. This includes toxicity on the technical grade active 

ingredient, degradates, and when available, formulated products (e.g., “Six-Pack” studies). Open 

literature studies will be identified through EPA’s ECOTOXicology (ECOTOX) database8, 

which uses a literature search engine for locating chemical toxicity data.

Guideline toxicity data are not available for Al phosphide, Mg phosphide, or phosphine except 

for limited mammalian data. The phosphine 4-hour inhalation LC50 = 0.117 mg/L for rats 

(MRID 46290604). The ECOTOX database will be searched when the risk assessment is 

prepared. At that time, open literature studies with endpoints more sensitive than those from 

guideline studies will be reviewed.

4.1. Incident Databases Review

Reviews were conducted of the Ecological Incident Information System (EIIS, v 2.1.1), the 

Aggregate Incident Data System, and the Avian Incident Monitoring System (AIMS)9 on 

2/2/2013.

There were four incidents associated with Al phosphide involving birds, two involving 

mammals, and one involving terrestrial plants. No incidents were reported for Mg phosphide. 

Details of these incidents were reported in the last risk assessment (USEPA, 2010). Reported 

vertebrate incidents for Al phosphide were not likely associated with labeled uses of the 

pesticide; reports of phosphine detected in dead animals were probably associated with ingestion 

of Al phosphide or Zn (Zinc) phosphide. The one minor plant incident associated with Al 

phosphide contained too little information to reach a definitive conclusion regarding plant 

effects.

The total number of actual incidents associated with the use of Al phosphide, Mg phosphide, and 

phosphine may be higher than what is reported to the Agency. Incidents may go unreported 

since effects may not be immediately apparent or readily attributed to the use of a chemical. As 

such, the absence of incident reports cannot be construed as the absence of incidents.

5. Risk Hypotheses

Al phosphide and Mg phosphide, when used in sealed burrows in accordance with current 

labels, are expected to quickly degrade to phosphine gas. All three compounds are expected to 

remain in the sealed burrow until degraded. When used in accordance with the labels, use of Al 

phosphide and Mg phosphide will be lethal to all non-target terrestrial animals within the sealed 

burrow and will adversely affect the survival, growth, and reproduction of terrestrial plants 

possessing root systems that penetrate a treated burrow. Non-target organisms include 

federally-listed threatened and endangered species.

 8 http://cfpub.epa.gov/ecotox/

9 http://www.abcbirds.org/abcprograms/policy/toxins/aims/aims/index.cfm
13

Al phosphide, Mg phosphide, and phosphine, when used for indoor treatment in accordance with 

current labels, will result in offsite movement of phosphine via emission to the atmosphere from 

treated structures, leading to exposure of non-target terrestrial organisms (Al phosphide and Mg 

phosphide are expected to quickly and completely degrade to phosphine). There is no 

expectation of a complete exposure pathway for aquatic organisms. Phosphine emissions from 

treated structures may serve as a source of phosphine exposure to terrestrial wildlife. When 

used in accordance with the labels, phosphine will adversely affect the survival, growth, and 

reproduction of non-target terrestrial organisms. Non-target organisms include federally-listed 

threatened and endangered species.

6. Analysis Plan

In order to address the risk hypotheses, the potential for adverse effects on the environment is 

estimated. The use, environmental fate, and ecological effects of Al phosphide, Mg phosphide, 

and phosphine will be characterized and integrated to assess risk. This will be accomplished 

using a risk quotient (ratio of exposure concentration to effects concentration) approach. 

Although risk is often defined as the likelihood and magnitude of adverse ecological effects, the 

risk quotient-based approach does not provide a quantitative estimate of likelihood 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 Al phosphide, Mg 

phosphide, and phosphine will be estimated using the probit dose-response slope and either the 

level of concern (LOC) or actual calculated risk quotient value.

This analysis plan will be revisited and may be revised depending upon a full review of the data 

available in the open literature 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 Al phosphide, Mg phosphide, and phosphine. Phosphine is a 

registered active ingredient and the major degradation product of Al phosphide and Mg

phosphide, which are effectively delivery agents for phosphine. Other degradates are Al 

hydroxide, Mg hydroxide, and phosphate; all of which occur naturally in the environment.

Phosphine released from structures or within burrows are the primary exposure pathways of 

concern for terrestrial organisms. Terrestrial and aquatic exposure to Al phosphide and Mg 

phosphide is not expected. Aquatic exposure to phosphine is assumed minimal (see Section 6.2).

6.2. Measures of Exposure

Exposure from structural fumigant uses will be modeled using high-end exposure scenarios 

based on the maximum labeled-allowed concentrations in the structure to be fumigated and 

release rates designed to produce a realistic, high-end exposure. As stated previously, there are 

uncertainties in the usage of phosphine in treatment facilities (maximum chamber or building

sizes), 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 used for fumigation

treatments, 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 

phosphine aeration operations. These variables all impact the magnitude of downwind 
14

dispersion from treated structures. Submission of information that aids the Agency in designing 

realistic, high-end exposure scenarios will reduce the potential of the Agency producing overly 

protective restrictions to the use of this pesticide. Burrow uses are expected to produce sufficient

exposures to kill organisms within the burrow, but negligible exposure outside the burrow.

6.2.1. Aquatic Exposure 

Limited exposure is expected based on the labeled uses and the fate properties of Al phosphide, 

Mg phosphide, and phosphine. As described previously, burrow applications are expected to 

remain in the burrow and are not considered to have a complete exposure pathway to aquatic 

environments outside of the burrow. Structural releases of phosphine are expected to result in 

minimal aquatic exposure given its rapid atmospheric degradation and that it will not tend to 

partition to water given its high vapor pressure (2.93 × 104 at 25 ̊C) and Henry's Law Constant 

(0.1 atm m3/mol).

If available, monitoring data will be evaluated and used for characterization.

6.2.2. Terrestrial Exposure

No above-ground exposure modeling will be conducted for burrow applications. Al phosphide 

and Mg phosphide are expected to react fully in a sealed burrow, producing lethal concentrations 

of phosphine gas. Exposure will be assumed lethal to all animals within a sealed burrow. 

Phosphine is expected to remain in the sealed burrow until degraded given that it is heavier than 

air, reacts quickly with water, and binds to soil particles. Phosphine exposure within a treated 

burrow will be characterized because plants will be exposed if their root systems penetrate the

burrow.

6.2.2.1. Phosphine, Al Phosphide, and Mg Phosphide Release Scenarios 

Specified on Labels

Phosphine concentrations in air near treated facilities were initially estimated by a Tier-I 

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

Al phosphide, Mg phosphide, and phosphine are used to treat a wide variety of stored food 

products and post-harvested commodities. Treatments are permissible for a wide variety of 

structures including grain mills, grain bins, industrial facilities, warehouses, cargo holds with 

fumigation chambers, and other storage facilities. Labels also allow mechanical and passive 

aeration of treated structures. Mechanical aeration releases the fumigant outdoors from the 

treated structure using a forced airflow through a stack or vent. Passive aeration involves the 

ventilation of treated structures via natural means such as opening of windows and doors to 

allow air to circulate around the building.

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

periods of time for treatments inside the structures. Phosphine gas is applied at a maximum 

application rate of 0.320 lb/1,000 ft3

. The maximum phosphine-equivalent application rates 
15

from Al phosphide and Mg phosphide products are also at 0.320 lb/1,000 ft3. The maximum 

application rates identified from product labels for each formulation for the phosphides are 

specified in Table 4.

Table 4. Maximum Phosphine-Equivalent Indoor Application Rates for Various Al

Phosphide and Mg Phosphide Formulations.

Mg Phosphide Formulation Phosphine Equivalent Application Rate

(lb/1,000 ft3)

Tablets 0.320

Bag 0.146

Fumi Cell 0.317

Fumi Strip 0.316

Pellets 0.220

Granules 0.320

Al Phosphide Formulation Phosphine Equivalent Application Rate

(lb/1,000 ft3)

Tablets 0.320

Pellets 0.320

Bags 0.315

Granules 0.316

Rope 0.316

*Bold values indicate maximum application rate

In this screening-level approach, EFED will develop upper-bound atmospheric release scenarios

for these use patterns. The Health Effects Division (HED) has conducted an air exposure 

assessment with methyl bromide which possesses a similar broad use pattern (USEPA, 2008). 

The HED assessment identified the largest building size for a grain mill or warehouse of up to 

10,000,000 cubic feet. In addition, HED assumed a 12-hour minimum release from these large 

structures. Furthermore, HED assumed that emissions over the 12-hour period declined at an 

exponential rate. This is based on indoor air monitoring shown for passive aeration and 

mechanical aeration of methyl bromide in treated buildings. Therefore, since phosphine releases 

are similar to methyl bromide, EFED’s approach for developing release scenarios will be 

consistent with HED’s approach for methyl bromide.

Based on this parameterization and the mechanical release scenario, AERSCREEN produces a 

maximum 1-hour concentration estimate of 8.4 × 108 μg/m3 (Appendix A). This estimate is 

obviously overly conservative (too high) in that it exceeds the flammability limit of phosphine 

gas (18,000 ppm10) by a factor of ~34:

8.423 × 108 μg/m3 = 8.423 × 105 mg/m3

24.45 L/mol*8.423 × 105 mg/m3 ÷ 34 g/mol = 605,712.8 ppm

11

605,712.8 ppm ÷ 18,000 ppm = 33.6

Where, the molecular volume of one mole of ideal gas is 24.465 L/mol at 25 °C at 1 atm.

 10 http://www.cdc.gov/niosh/ershdb/EmergencyResponseCard_29750035.html 11 http://www.ccohs.ca/oshanswers/chemicals/convert.html
16

Therefore EFED has elected to use the intended application concentration (3,625 ppm) as stated 

on the ECO2FUMETM (Reg. # 68387-7) and VAPORPH3O5TM (Reg. # 68387-8) labels as a 

more reasonable screening level maximum 1-hour air concentration. This would approximate a 

scenario in which a catastrophic release (e.g., structural failure of some sort) occurs rather than a 

controlled release. Again, the Agency welcomes the submission of additional information that 

might help the Agency arrive at a more reasonable maximum screening level.

6.3. Measures of Effect

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

receptors (USEPA, 2004). 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 

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 toxicity values. The resulting RQs will 

be compared to the Agency’s LOCs (USEPA, 2004).

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 Al phosphide, Mg phosphide, and phosphine. This assessment will be 

conducted in accordance with the Overview Document (USEPA, 2004), provisions of the ESA, 

and the Services’ Endangered Species Consultation Handbook (USFWS and NMFS, 1998).

6.6. Endocrine Disruptor Screening

As required by Federal Food, Drug and Cosmetic Act (FFDCA) section 408(p), Al phosphide,

Mg phosphide, and phosphine are subject to the endocrine screening part of the Endocrine 

Disruptor Screening Program (EDSP)12. Al phosphide, Mg phosphide, and phosphine are not in 

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

6.7. Drinking Water Assessment

A drinking water assessment will not be conducted for Al phosphide, Mg phosphide, or 

phosphine because exposure via drinking water is expected to be minimal. Again, limited 

exposure is expected based on the labeled uses and the fate properties of Al phosphide, Mg 

phosphide, and phosphine. As described previously, burrow applications are expected to remain 

in the burrow and are not considered to have a complete exposure pathway to aquatic 

environments outside of the burrow. Structural releases of phosphine are expected to result in 

minimal aquatic exposure given its rapid atmospheric degradation and that it will not tend to 

 12 http://www.epa.gov/endo/
17

partition to water given its high vapor pressure (2.93 × 104 at 25 ̊C) and Henry's Law Constant 

(0.1 atm m3/mol).

6.8. Preliminary Identification of Data Gaps

6.8.1. Environmental Fate Data

No fate data have been submitted for Al phosphide, Mg phosphide, or phosphine (Table 5). 

Table 5. Environmental Fate Data for Al Phosphide, Mg Phosphide, and Phosphine

Guideline Description MRID Classification Data Gap Comments

835.2120 Hydrolysis None Not applicable No Typically, data is not 

required for highly 

reactive solids (Al 

phosphide and Mg 

phosphide) or gases 

(phosphine). 

Furthermore, limited 

aquatic exposure is 

expected based on the 

labeled uses and the 

fate properties of these 

compounds.

835.2240 Photodegradation in Water None Not applicable No

835.2410 Soil Photolysis None Not applicable No

835.2370 Photodegradation in Air None Not applicable No

835.4100 Aerobic Soil Metabolism None Not applicable No

835.4200 Anaerobic Soil Metabolism None Not applicable No

835.4300 Aerobic Aquatic Metabolism None Not applicable No

835.4400 Anaerobic Aquatic Metabolism None Not applicable No

835.1230

835.1240

Leaching

Adsorption/Desorption None Not applicable No

835.1410 Laboratory Volatility None Not applicable No

835.8100 Field Volatility None Not applicable No

835.6100 Terrestrial Field Dissipation None Not applicable No

835.6200 Aquatic Field Dissipation None Not applicable No

850.6100 ECM/ILV (Water) None Not applicable No

850.6100 ECM/ILV (Soil) None Not applicable No

850.1730 Bioaccumulation in Fish None Not applicable No

Exposure to phosphine is expected to occur through air and will be modeled using atmospheric 

transport models. Typically such modeling estimates the air concentration over time (exposure 

duration) assuming gaseous emissions dissipate with time due to dispersion with air movement 

and degradation over time. It is anticipated that dispersion will reduce air concentrations much 

faster than degradation. Therefore at this time, EFED is not requesting additional fate data for Al 

phosphide, Mg phosphide, or phosphine to support its atmospheric transport modeling efforts.

There are uncertainties in the usage of phosphine in treatment facilities (maximum chamber or 

building sizes), 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 

phosphine aeration operations. These variables all impact the magnitude of downwind 
18

dispersion from treated structures. Submission of information that refines these uncertainties is 

expected to have a high potential to add value to the ecological risk assessment.

6.8.2. Ecological Effects Data

No toxicity data have been submitted for Al phosphide, Mg phosphide, or phosphine (Tables 6, 

7, and 8).

Aquatic studies are not requested for Al phosphide, Mg phosphide, or phosphine because 

exposure is expected to be minimal.

Terrestrial studies are not requested for Al phosphide or Mg phosphide because exposure will be 

assumed lethal to all animals within a sealed burrow (via formation of phosphine gas). There is 

not a complete exposure pathway for organisms outside the sealed burrow because Al phosphide 

and Mg phosphide are expected to react fully (inside the burrow) to produce phosphine gas. 

Additionally, there is not a complete exposure pathway for indoor uses of Al phosphide and Mg 

phosphide.

The following studies are requested for phosphine due to potential exposure after release from 

treated structures:

• Terrestrial plant toxicity (non-guideline vegetative vigor) 

• Avian inhalation toxicity (non-guideline)

• Honeybee inhalation toxicity (non-guideline)

Terrestrial Plants - Vegetative Vigor (phosphine)

A non-guideline terrestrial plant study (vegetative vigor, exposure to phosphine gas) is 

recommended to reduce uncertainty in risk conclusions because of potential exposure and 

adverse effects to non-target plants. Phosphine exposure is expected via atmospheric emission 

from treated structures; once released, phosphine is expected to move to ground-level given that 

it is heavier than air. Plants will also be exposed to phosphine in treated burrows if their root 

systems penetrate the burrow. There is some evidence to suggest that plants may be adversely 

affected if exposed to phosphine; according to a WHO report (1998), phosphine produced 

harmful effects on growing lettuce at concentrations between 3 and 8 mg/m3

. Given the potential 

for effects and exposure, risk to plants will be presumed in the absence of data.

Avian acute inhalation toxicity (phosphine)

An avian inhalation study is recommended to reduce uncertainty in risk conclusions because of 

potential exposure and the known inhalation toxicity of phosphine to vertebrates. According to a 

WHO report (1998), 100% mortality was observed in hens and turkeys exposed to 211-224 

mg/m3 for roughly 1 hour, although the study results may have been confounded by the presence 

of compounds other than phosphine (reported in Pepelko et al., 2004). Given the potential for 

effects and exposure, risk to birds will be presumed in the absence of data.
19

Honeybee acute inhalation toxicity (phosphine)

A honeybee inhalation study is recommended to reduce uncertainty in risk conclusions because 

of potential exposure and effects. Adverse effects are expected for insects given that the 

proposed mode-of-action of phosphine is related to the inhibition of mitochondrial respiration. 

Furthermore, phosphine is used to control insects in structures; therefore, there is a reasonable 

expectation that phosphine would pose a direct risk to non-target invertebrates, including insects. 

Given the potential for effects and exposure, risk to terrestrial invertebrates will be presumed in 

the absence of data.

Table 6. Ecological Effects Data for Aquatic Animals Exposed to Al Phosphide, Mg

Phosphide, and Phosphine

Guideline Description MRID Classification Data 

Gap? Comments

850.1075

Acute freshwater fish 

toxicity

(cold water species)

None Not applicable No

Typically, data is not required for 

highly reactive solids (Al

phosphide and Mg phosphide) or 

gases (phosphine). Furthermore, 

limited aquatic exposure is 

expected based on the labeled uses 

and the fate properties of these 

compounds.

Acute freshwater fish 

toxicity

(warm water species)

None Not applicable No

Acute estuarine/

marine fish toxicity None Not applicable No

850.1010

Acute toxicity to 

freshwater 

invertebrates

None Not applicable No

850.1025

Acute estuarine/

marine mollusk 

toxicity

None Not applicable No

850.1035

Acute estuarine/

marine invertebrate 

toxicity

None Not applicable No

850.1300 Freshwater 

invertebrate life cycle None Not applicable No

850.1400 Freshwater fish early 

life stage None Not applicable No
20

Table 7. Ecological Effects Data for Terrestrial Animals Exposed to Al Phosphide, Mg 

Phosphide, and Phosphine

Guideline Description MRID Classification Data 

Gap?

Comments

850.2100

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 studies are not 

recommended.

2 Birds and insects could 

potentially be exposed to 

phosphine 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. 

Bobwhite quail is the 

recommended test species for 

the bird study.

3 Inhalation is the primary 

route of exposure. Continual 

inhalation exposure to 

phosphine is unlikely; 

however, acute inhalation 

exposure could cause 

reproductive effects depending 

on the timing of the exposure. 

Although reproductive risk is 

uncertain without data, data 

are not recommended because 

of logistical constraints on 

study design. It is impractical

to conduct long term 

inhalation exposure 

experiments with phosphine or 

to detect reproductive effects 

from acute exposure because it 

is unknown when exposure 

may elicit and effect. In lieu 

of data, a weight of evidence 

approach will be used to 

characterize risk on a 

qualitative basis.

Avian acute oral toxicity 

(passerine species) None Not applicable No1

NonguidelineAvian acute inhalation 

toxicity None Not applicable Yes2

850.2200

Avian dietary toxicity 

(upland game species) None Not applicable No1

Avian dietary toxicity 

(waterfowl species) None Not applicable No1

850.2300

Avian reproduction 

(upland game species) None Not applicable No1

Avian reproduction 

(waterfowl species) None Not applicable No1

NonguidelineAvian reproduction 

(inhalation toxicity) None Not applicable Yes3

850.3020 Honeybee acute contact 

toxicity None Not applicable No1

NonguidelineHoneybee inhalation 

toxicity None Not applicable Yes2
21

Table 8. Ecological Effects Data for Plants Exposed to Al Phosphide, Mg Phosphide, and 

Phosphine

Guideline Description MRID Classification Data Gap? Comments

850.4100A

Terrestrial plant toxicity 

(Tier I&II seedling 

emergence)

None Not applicable No1

1 Limited exposure is 

anticipated for seeds.

2 Exposure is anticipated in 

the form of phosphine gas

(the exposure regime of 

standard plant testing does 

not apply). Data on 

phosphine toxicity have high 

value in reducing uncertainty. 

A study protocol should be 

submitted to the Agency prior 

to conducting the study. 

3 Limited aquatic exposure is 

expected based on the labeled 

uses and the fate properties of 

these compounds.

850.4150B

Terrestrial plant toxicity 

(Tier I&II vegetative 

vigor)

None Not applicable No2

Nonguideline

Terrestrial plant toxicity 

(Tier I&II vegetative 

vigor)- vapor phase

None Not applicable Yes2

850.4500C

Aquatic plant growth

(freshwater green alga) None Not applicable No3

Aquatic plant growth 

(freshwater diatom) None Not applicable No3

Aquatic plant growth 

(saltwater diatom) None Not applicable No3

850.4550C Aquatic plant growth 

(Cyanobacteria) None Not applicable No3

850.4400 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). 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 850.5400)

7. References

Berck, B. and F.A. Gunther. 1970. Rapid determination of sorption affinity of phosphine by 

fumigation within a gas chromatographic column. J. Agric. Food Chem. 18(1): 148-153.

Cotton, F.A. and G. Wilkerson. 1988. Advanced Inorganic Chemistry. Fifth Edition. John 

Wiley and Sons, New York.

Daubert, T.E. and R.P. Danner. Physical and Thermodynamic Properties of Pure Chemicals Data 

Compilation. Washington, D.C.: Taylor and Francis, 1989, p. 458.

Eiseman, F., Glindemann, D., Bergman, A., and P. Kuschk. 1997. Soils as a source and sink of 

phosphine. Chemosphere 35(3): 523-533.

Fluck, E. The Chemistry of Phosphine. 1973. in Topics in Current Chemistry. 35:1-64.

Greenwood, N.N. and A. Earnshaw. 1984. Chemistry of the Elements. Pergamon Press, Oxford, 

U.K.
22

Hilton, H.W. and W.H. Robinson. 1972. Fate of zinc phosphide and phosphine in the soilwater environment. J. Agric. Food Chem. 20(6): 1209-1213.

Lindsay, W.L. 1979. Chemical Equilibria in soils. John Wiley and Sons, New York.

Lyman WJ et al. 1990. Handbook of Chemical Property Estimation Methods. Washington, DC: 

Amer Chem Soc pp. 8-12.

Pepelko, B., J. Seckar, P.R. Harp, J.H. Kim, D. Gray, and E.L. Anderson. 2004. Worker 

Exposure Standard for Phosphine Gas. Risk Analysis. Vol. 24, No. 5, pg 1201-1213.

USEPA. 2010. Risks of Aluminum and Magnesium Phosphides Uses to the Federally 

Threatened Alameda Whipsnake (Masticophis lateralis euryxanthus) and California Tiger 

Salamander (Ambystoma californiense), Central California Distinct Population Segment 

and Federally Endangered California Tiger Salamander (Ambystoma californiense) 

Sonoma County Distinct Population Segment and Santa Barbara County Distinct 

Population Segment, San Francisco Garter Snake (Thamnophis sirtalis tetrataenia), and 

San Joaquin Kit Fox (Vulpes macrotis mutica). U.S. Environmental Protection Agency, 

Office of Pesticide Programs, Washington DC.

USEPA. 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) (DP 304612).

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.

USFWS and NMFS. 1998. Endangered Species Consultation Handbook: Procedures for 

Conducting Consultation and Conference Activities Under Section 7 of the Endangered 

Species Act. Final Draft. 

WHO (World Health Organization). 1998. Phosphine and Selected Metal Phosphides. WHO, 

Geneva.
23

Appendix A. Atmospheric Modeling

AERSCREEN Description

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

Meteorological Society/EPA Regulatory Screening Model (AERSCREEN)13, will be used to 

generate screening estimated environmental concentrations (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 phosphine. Worst-case 

meteorological conditions (light winds and stagnant conditions) and downwash14 parameters are 

assumed to calculate peak air EECs, representing one-hour average concentrations. 

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-level analysis, all 

ecological receptors of concern will be assumed to be present directly downwind from the 

building at ground level.

Figure A1. Schematic illustrating fumigation releases from treated structures and 

conceptual model for ground-level exposure.

AERSCREEN Release Scenarios

Each release scenario for phosphine will be based on the maximum application rate of 0.320 

lb/1,000 ft3 inside a 10,000,000 ft3 structure. Scenario 1 of the AERSCREEN evaluation 

represents the mechanical release of phosphine. Scenario 2 represents the passive aeration 

release scenario. Each modeled release scenarios assumes that the aeration is complete after 

twelve hours. However, peak air concentrations will only consider the mode of the exponential 

emissions curve which results in maximized peak (one-hour) air concentrations.

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

exposure for Mechanical Scenario (Scenario 1) is shown in Table A1. The AERSCREEN input 

parameter values for Passive Scenario (Scenario 2) is shown in Table A2. The AERSCREEN 

modeling captures the upper-bound air exposure from release scenarios consolidated above from 

information on the phosphine product label.

 13 http://www.epa.gov/scram001/dispersion_screening.htm 14 Downwash is defined as the downward flow often observed on the leeside of buildings induced by wake 

turbulence. Pollutants released from buildings can often become embedded in downwash flows and wake cavities.
24

Table A1. AESCREEN Input Parameter Values for the Mechanical Release Scenario 

(Scenario 1) of Phosphine, Al Phosphide, and Mg Phosphide Labels

Input Parameter Option/Value Notes Scenario 1

English or Metric Units E (English)

Source Type P (Point) Stack releases required for all uses

Emission Rate (lb/hr) 253.97 Mode of exponential emissions trend curve 1

Stack or Release Height Above 

Ground (ft) 100 Default for 10,000,000 ft.3 building size based on methyl bromide HED assessment 2

Stack Diameter (in) 590.55 Default for 10,000,000 ft.3 building size based on 

methyl bromide HED assessment 2

Stack Temperature (°F) Equivalent to Ambient 

Temperature (input = 0)

No stack temperatures specified, conservative 

assumption is non-buoyant source

Option for Flow Rate or Flow 

Velocity 3 (Flow Rate ACFM)

Stack Exit Stream 

Flow Rate (ft

3

/min) 13,889 Based on 12-hour exchange of volume (air exchange rate = 0.083 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) 100 Equivalent to stack height

Maximum Horizontal Building 

Dimension (ft) 316.23 Square building footprint consistent with building heights specified above

Minimum Horizontal Building 

Dimension (ft) 316.23 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) 158.1

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 source4

Bowen Ratio 3.0 Bare surface assumed around source4

Surface Roughness Length (m) 0.001 Bare surface assumed around source4

1

 Emission Rate (lb/hr) = [ ( )]

3,600 sec/ .

0 1 exp

hr

C ×V × − − AXR where Co is the application rate = 0.321 lb/1,000 ft3

, V is the 

building volume = 10,000,000 ft3

, and AXR is the air exchange rate = 0.083 air exchanges per hour.
25

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) (DP 304612). 3

 Flow rate (ft.3/min) = Air exchange rate (air exchanges/hr) x Structure Size (ft3) x hr

 60 min 4

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

Preprocessor (AERMET)” (http://www.epa.gov/scram001/7thconf/aermod/aermetugb.pdf) for further details.

Table A2. AESCREEN Input Parameter Values for the Passive Release Scenario (Scenario 

2) of Al Phosphide, Mg Phosphide, and Phosphine Labels

Input Parameter Option/Value Notes Scenario 2

English or Metric Units M (Metric)

Source Type A (Area)

Emission Rate (g/s) 32.11

Mode of exponential flux rate trend curve 1

Emission rate input is based on resulting flux 

rate (3.456 x 10-3 g/m2

-s) x Area of Building 

Footprint (9,290 m2

)

Area of building footprint for 10,000,000 ft.3

building based on methyl bromide HED 

assessment2

Release Height Above Ground (m) 15.24

Release height of half the building size 

assumed based on HED assessment2

Height of building for 10,000,000 ft.3 based on 

methyl bromide HED assessment2

Minimum Horizontal Building 

Dimension (m) 96.4 Square building footprint consistent with building heights specified above

Maximum Horizontal Building 

Dimension (m) 96.4 Square building footprint consistent with building heights specified above

Initial Vertical Dimension (m) 15.24 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-s) [ ( )]

hr A

C V AXR

×

× × − − = 3,600 sec/ .

0 1 exp where Co is the application rate = 0.321 lbs./1,000 ft3 (5.13 g/ft3

), V 

is the building volume = 10,000,000 ft3 (283,168.5 m3

), A is the area = 100,000 ft2 (9,290 m2), and AXR is the air 

exchange rate = 0.083 air exchanges per hour. 2

 Methyl bromide HED risk assessment citation: 
26

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) (DP 304612). 3

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

Preprocessor (AERMET)” (http://www.epa.gov/scram001/7thconf/aermod/aermetugb.pdf) for further details.
27

Appendix B. Data Call-In Tables

Guideline Number: Non-guideline

Study Title: Acute Honeybee Vapor Exposure Study

Rationale for Requiring the Data

A honeybee inhalation (vapor exposure) study is recommended to reduce uncertainty in risk 

conclusions because of potential exposure and effects. It is expected that honeybees and other 

insect pollinators will be exposed to phosphine primarily in the vapor phase. Adverse effects are 

expected for insects given that the proposed mode-of-action of phosphine is related to the 

inhibition of mitochondrial respiration. Furthermore, phosphine is used to control insects in 

structures; therefore, there is a reasonable expectation that phosphine would pose a direct risk to 

non-target invertebrates once it is vented outside of the structure. Given the potential for effects 

and exposure, risk to terrestrial invertebrates will be presumed in the absence of data. 

Practical Utility of the Data

How will the data be used?

Data from an acute honeybee vapor exposure study will be used to assess risk to non-target 

terrestrial invertebrates exposed to phosphine near release points. 

How could the data impact the Agency’s future decision-making?

If future ecological risk assessments are performed without these data, the Agency would have 

to presume risk to non-target terrestrial invertebrates from exposure to phosphine. Therefore, 

use of phosphine, Al phosphide, and Mg phosphide would be potentially restricted in areas 

where honeybees, other pollinator insects, or listed insects could be exposed. The lack of these 

data will limit the flexibility the Agency and registrants have in mitigating potential risks and 

could result in restrictions for use of phosphine, Al phosphide, and Mg phosphide that are 

unnecessarily severe.

Guideline Number: Non-guideline

Study Title: Avian Inhalation

Rationale for Requiring the Data

An avian inhalation study is recommended to reduce uncertainty in risk conclusions because of 

potential exposure and the known inhalation toxicity of phosphine to vertebrates. According to 

a WHO report (1998), 100% mortality was observed in hens and turkeys exposed to 211-224 

mg/m3 for roughly 1 hour, although the study results may have been confounded by the presence 

of compounds other than phosphine (reported in Pepelko et al., 2004). Given the potential for 

effects and exposure, risk to birds will be presumed in the absence of data.

Practical Utility of the Data

How will the data be used?

Data from an avian inhalation study will be used to assess risk to avian species exposed to 

phosphine near release points. 

How could the data impact the Agency’s future decision-making?

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

would assume risk to birds from exposure to phosphine. Therefore, use of phosphine, Al 

phosphide, and Mg phosphide would be potentially restricted in areas where listed species could 

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

mitigating potential risks and could result in restrictions for use of phosphine, Al phosphide, and 

Mg phosphide that are unnecessarily severe.
28

Guideline Number: Non-guideline

Study Title: Terrestrial Plant Vapor Phase Study

Rationale for Requiring the Data

A non-guideline terrestrial plant study (vegetative vigor, vapor exposure) is recommended to 

reduce uncertainty in risk conclusions because of potential exposure and adverse effects to 

terrestrial plants. Phosphine exposure is expected via atmospheric emission from treated 

structures; once released, phosphine is expected to move to ground-level given that it is heavier 

than air. Plants will also be exposed to phosphine in treated burrows if their root systems 

penetrate the burrow. There is some evidence to suggest that plants may be adversely affected if 

exposed to phosphine; according to a WHO report (1998), phosphine produced harmful effects 

on growing lettuce at concentrations between 3 and 8 mg/m3. Given the potential for effects and 

exposure, risk to plants will be presumed in the absence of data.

Practical Utility of the Data

How will the data be used? 

Data from a terrestrial plant study (vegetative vigor, vapor exposure) will be used to assess risk 

to terrestrial plants exposed to phosphine near release points. 

How could the data impact the Agency’s future decision-making?

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

would assume risk to terrestrial plants from exposure to phosphine. Therefore, use of 

phosphine, Al phosphide, and Mg phosphide would be potentially restricted in areas where listed 

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

registrants have in mitigating potential risks and could result in restrictions for use of phosphine, 

Al phosphide, and Mg phosphide that are unnecessarily severe.