UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

PC Code: 077702

DP Barcode: 344574

MEMORANDUM

Subject: Registration Review – Preliminary problem formulation for the Ecological Risk 

Assessment of Propionic Acid

To: Wilhelmena Livingston

Reregistration Branch 7508P

Special Review and Reregistration Division

From: William Shaughnessy, Ph.D., Environmental Scientist

Carolyn Hammer, Environmental Scientist

Through: Dana Spatz, Acting Chief

Environmental Risk Branch 2

Environmental Fate and Effects Division

Office of Pesticide Programs

Attached is the preliminary problem formulation for the ecological risk assessment to be 

conducted as part of the Registration Review of the fungicide and bactericide propionic 

acid.
Registration Review

Ecological Risk Assessment

Problem Formulation For

Propionic Acid and Salts

Synonyms: Methylacetic acid; ethylformic acid; propanoic acid; 

carboxyethane PC Code: 077702

Chemical Formula: CH3CH2COOH

Prepared By:

Carolyn Hammer, Environmental Scientist

Wm. J. Shaughnessy, Ph.D., Environmental Scientist

Environmental Risk Branch 2

Environmental Fate and Effects Division

Office of Pesticide Programs

Approved By:

Dana Spatz, Chief

Environmental Risk Branch 2

Environmental Fate and Effects Division

Office of Pesticide Programs
1

Stressor Source and Distribution

Propionic acid is a fungicide and bactericide that is registered to control fungi and 

bacteria in stored hay and grains. It is formulated as a liquid and sprayed onto hay and 

grain at the time of baling. Currently, two manufacturing-use pesticide products are 

registered, as are 12 end-use products, each containing propionic acid as its sole active 

ingredient.

The pesticide is a colorless, oily, pungent liquid that is soluble in water and occurs 

naturally in animals and dairy products. It also is a normal component of metabolism in 

the human body. Humans consume naturally-occurring propionic acid in common foods 

such as butter and cheese (Swiss cheese may contain as much as one percent propionic

acid), and as an added ingredient in other foods. In its more concentrated form it is 

corrosive and flammable, thus requiring special handling. 

The active ingredient propionic acid is a fungicide/bactericide used to: (1) preserve 

stored grains for animal and human consumption, (2) inhibit bacterial growth in drinking 

water for livestock and poultry, (3) control mold and fungi in poultry litter and animal 

feed, and (4) sanitize pre-cleaned food contact surfaces. Propionic acid is formulated as 

soluble concentrate (10%, 70.5- 70.6% a.i.), solution (70.5% a.i.), and granular (15% 

a.i.). Application rates to grains are dependent on the moisture content of the grain at the 

time it is placed in storage, up to 31 pounds per ton. Propionic acid is also used as an 

inert ingredient in pesticide formulations. EFED was not provided with the name(s) of 

chemicals that are formulated with this inert ingredient.

Propionic acid and its salts, sodium and calcium propionates, are approved in the 

United States as Generally Recognized As Safe (GRAS) (21 CFR 184.1081) for use in 

food. Their antimicrobial action is directed to molds and rope bacteria, with almost no 

effect on yeast, thus making them an ideal choice for products that use commercial yeast 

as an ingredient.

Propionic acid is applied undiluted to grain and hay with a calibrated liquid metering 

applicator that provides the desired coverage to grain as it is moved into storage, or to 

hay just prior to bailing and stacking. In general, the rate of application is a function of 

the moisture content of the grain or hay and occurs within the bailing equipment. It has 

also been approved for outdoor use as an additive to poultry and live stock drinking 

water.1The application rate of active ingredient ranges significantly per ton of hay and 

grain, depending on the moisture content (see Table 1). The following parameters are not 

specified on the label and therefore not included in the table below: the maximum 

number of applications per crop cycle or year, maximum application rate, and minimum 

application interval (days).

1 USEPA 1991. Reregistration Eligibility Document – Propionic Acid, and Salts. Office of Pesticide 

Programs, Special Review and Reregistration Division. September 1991.
2

Table 1. Listing of the label uses, application rates, form and equipment for propionic

acid as an active ingredient.

Use Site Max. Rate

per App

Max. Rate

Unit/Area

*UG 

Form Application Equipment

//Type

(Reg # Code)

NON-FOOD/NON-FEED USES

silos .2981 lb 1K sq.ft

*M1 

SC/L Not on label 

//Indoor general surface treatment (a)

FOOD/FEED USES

alfalfa 15 lb ton (L)

*B1 

RTU Sprayer 

//Spray/ Stored commodity non-fumigation (a)

animal drinking water 8824 W ppm

*L1 

SC/L Not on label 

//Water treatment (a)

barley 1.528 lb cwt

*L1 

RTU Sprayer 

//Spray (a)

barley 31 lb ton (L)

*B1 

RTU Sprayer 

//Stored commodity non-fumigation (b)

cereal grains 29 lb ton (L)

*A2 

RTU Low pressure 

//Grain treatment (a)

corn (silage) 3 lb ton (L)

*B1 

RTU

SC/L

Low pressure/ Low pressure ground sprayer/ 

Sprayer 

//Spray (a)

corn (unspecified) .8458 lb cwt

*A2 

RTU Sprayer 

//Spray (a)

corn (unspecified) 6 lb A (L)

*A2 

SC/L Low pressure 

//Spray (b)

corn (unspecified) 23 lb ton (L)

*B1 

RTU Sprayer 

//Stored commodity non-fumigation (c)

corn, field 1.156 lb cwt

*A2 

RTU Sprayer 

//Spray (a)

cowpeas 31 lb ton (L)

*B1 

RTU Low pressure ground sprayer 

//Stored commodity non-fumigation (a)

dairies/cheese processing plant 

equipment (food contact) 

158 W ppm

*L1 

SC/L Not on label 

//Circulation treatment (a)

feed/food commodities 

(bagged/temporary storage) 

4 lb ton (L)

*L1 

RTU

SC/L

Sprayer 

//Spray (a)

food processing plant equipment 

(food contact) 

158 W ppm

*L1 

SC/L Not on label 

//Circulation treatment (a)

grain/cereal/flour 

(bagged/temporary storage) 

1 lb ton (L)

*L1 

RTU Low pressure 

//Spray (a)

grain/cereal/flour storage areasempty .2981 lb 1K sq.ft

*L1 

SC/L Not on label 

//Indoor general surface treatment (a)

grass forage/fodder/hay 20 lb ton (L)

*B1 

RTU

SC/L

Low pressure/ Low pressure ground sprayer/ 

Metering pump 
3

Use Site Max. Rate

per App

Max. Rate

Unit/Area

*UG 

Form Application Equipment

//Type

(Reg # Code)

//Spray (a)

hay (silage) 4 lb ton (L)

*B1 

RTU

SC/L

Low pressure/ Sprayer 

//Spray (a)

livestock feed (processed) 1.428 lb ton

*L1 

SC/L Not on label 

//Stored commodity non-fumigation (a)

nongrass forage/fodder/straw/hay 31 lb ton (L)

*B1 

RTU Low pressure 

//Grain treatment (a)

oats 1.528 lb cwt

*L1 

RTU Sprayer 

//Spray (a)

oats 31 lb ton (L)

*B1 

RTU Sprayer 

//Stored commodity non-fumigation (b)

peanuts 31 lb ton (L)

*B1 

RTU Low pressure ground sprayer 

//Stored commodity non-fumigation (a)

peas (including vines) 31 lb ton 

(L)*B1 

RTU Low pressure ground sprayer 

//Stored commodity non-fumigation (a)

poultry drinking water 8824 W ppm

*L1 

SC/L Not on label 

//Water treatment (a)

poultry feed (processed) 1.428 lb ton

*L1 

SC/L Not on label 

//Stored commodity 

non-fumigation (a)

poultry litter .2981 lb 1K sq.ft

*L1 

SC/L Not on label 

//Animal bedding/litter treatment (a)

small grains 4 lb ton (L)

*B1 

RTU

SC/L

Low pressure/ Sprayer 

//Spray (a)

sorghum 1.528 lb cwt

*L1 

RTU Sprayer 

//Spray (a)

sorghum 31 lb ton (L)

*B1 

RTU Sprayer 

//Stored commodity non-fumigation (b)

sorghum (unspecified) .8458 lb cwt

*A2 

RTU Sprayer 

//Spray (a)

soybeans 31 lb ton (L)

*B1 

RTU Low pressure ground sprayer 

//Stored commodity non-fumigation (a)

wheat 1.528 lb cwt

*L1 

RTU Sprayer 

//Spray (a)

wheat 31 lb ton (L)

*B1 

RTU Sprayer 

//Stored commodity non-fumigation (b)

LEGEND

HEADER 

ABBREVIATIONS 

Use Site : The use site refers to the entity (crop, building, surface or article) where a 

pesticide is applied and/or which is being protected. 

Max.Rate per App : Maximum dose for a single application to a single site. System calculated. 

Max.Rate Unit/Area : Units and Area associated with the maximum dose. 

*UG : Use Group codes. 
4

Form : The physical form of the end use product found in the container. 

Max. # Apps cc & yr : The maximum number of applications. 

Max. App Rate/cc & yr : The maximum amount of pesticide product that can be applied to a site in one 

growing season (/cc) or during the span of one year (/yr). 

Min. App Interval (days): The minimum retreatment interval between applications in days (aggregated). 

Application Equipment : The equipment used to apply pesticide (aggregated). 

Application Type : The type of pesticide application (aggregated). 

Current as of - : The label data for the listed products in this report is current as of this date. 

ABBREVIATIONS 

AN - As Needed. 

NA - Not Applicable. 

NS - Not Specified (on label). 

(L) - The dosage information provided is from the label in terms of product (e.g., ounces, gallons, or 

pounds of the product) because there was insufficient information (e.g., missing density, area, or 

active ingredient percentages) to provide converted dosage information. 

~ - The tilde in "Max. Rate per App" indicates a dosage that includes information from a SLN label. 

UC - Unconverted due to lack of data (on label). 

APPLICATION RATE 

W : PPM calculated by weight 

V : PPM calculated by volume 

U : Unknown whether PPM is given by weight or by volume 

cwt : Hundred Weight. 

nnE-xx : nn times (10 power -xx), for instance, "1.234E-4" is equivalent to ".0001234". 

-- : No description available in LUIS unit conversion vocabulary. 

~ : The dosage information includes a contribution from one or more (TQ, CL, BR, I) 

active ingredients. 

FORMULATION CODES 

RTU : Liquid-ready To Use 

SC/L : Soluble Concentrate/liquid 

USE GROUP CODES 

A2 : TERRESTRIAL FOOD+FEED CROP 

B1 : TERRESTRIAL FEED CROP 

L1 : INDOOR FOOD 

M1 : INDOOR NON-FOOD 

Integration of Available Information

Propionic acid was first registered as a pesticide in the early 1970's. In 1975, EPA 

first exempted propionic acid from tolerances for residues following post-harvest 

application in grains or hays (40 CFR 180.1023). In September 1991, EPA completed a 

Reregistration Eligibility Document (RED) for propionic acid and salts. In this document 

the EPA noted that data available at that time was sufficient to support the conclusion 

that the registered uses of propionic acid would not result in unreasonable adverse effects 

to human health and the environment. The RED also noted that propionic acid is exempt 

from the requirement of a tolerance when applied (as an inert ingredient) to growing 

crops or to raw agricultural commodities after harvest as described in 40 CFR 180.1001c. 

The current assessment considers the risks from propionic acid as an active ingredient 

applied post-harvest. When the RED was published in 1991, EPA waived all 
5

environmental fate and ecological effects data requirements because the use profile did 

not lead the Agency to foresee the potential for significant environmental risks associated 

with the registered uses of propionic acid.

Ecological Effects

Propionic acid has limited outdoor use and low toxicity, therefore its hazard to nontarget organisms is expected to be minimal. Previous assessments have determined that

all ecological effects data requirements were waived but this conclusion will be 

reconsidered in the current reregistration assessment. 

The existing toxicity dataset includes acute studies on freshwater fish and 

invertebrates, birds, and mammals. Propionic acid is classified as slightly toxic to aquatic 

organisms on an acute basis. Toxicity data are not available to assess the effects of 

chronic exposure to freshwater organisms or acute and chronic effects to estuarine/marine 

organisms. Propionic acid is classified as practically non-toxic to birds and mammals on 

an acute basis. There are no available data on reproductive effects to birds and mammals. 

Aquatic Effects

An acute toxicity study with freshwater fish, Rainbow trout, resulted in a 96-hr LC50= 

51 ppm

2

. For the freshwater invertebrate Daphnia magna, acute toxicity testing resulted 

in a 48-hour EC50=22.7 ppm (MRID # 00068178). Each study was a static test where 

propionic acid was assumed to be 100% a.i. It was not measured for verification.

Terrestrial Effects

Mammalian acute toxicity tests resulted in a rat LD50=2,600 mg/kg (Accession 

no.091042). Although death was not an obvious endpoint resulting from exposure to 

propionic acid, ocular and dermal irritation was reported (MRID # 41456306, 46125010). 

An avian acute oral toxicity test with mallard duck resulted in an LD50 1467 mg/kg

(MRID #: 00079594). Sub-acute, 8-day dietary exposure of mallard duck and bobwhite 

quail to the salts of propionic acid resulted in LC50 values greater than 10,000 (MRID #: 

00085932, 00079595). These studies need to be reevaluated to verify the rates/units of 

exposure as well as the exposure media. The use of propionic salts data may not be 

relevant and therefore would not qualify as a measurement endpoint with which to assess 

effects to birds, amphibians, and reptiles. Dermal effects tests were not conducted with 

birds. However, based on mammalian testing described above and label warnings of 

danger to wildlife, it can be assumed that exposure to propionic acid will have a severely

irritating and corrosive effect on birds, amphibians and reptiles. The impacts of such an 

2 Acute Toxicity to Freshwater Fish. Animal Biol. Lab., EPA-TSD, Test No. 604, June 

1973; Test No. 609, September 1973. 
6

effect may vary by species. Amphibians, which respire through their skin, may

experience severe effects from this type of exposure. 

Although plant toxicity data are not available, the product label warns “Treatment 

inhibits germination; do not use on grain intended for seed or malting, or for use in 

human foods.” This indicates a potential for effects to non-target plants if they are 

exposed to propionic acid. Therefore, it can be assumed that if non-target plants are 

exposed, seed germination will be inhibited and plants may exhibit reproductive effects. 

Exposure Characteristics

Environmental Fate/Exposure:

Propionic acid's production and use as a grain preservative and as an additive in 

livestock drinking water, may result in its release to the environment through various 

waste streams. Propionic acid is formed from various enzymatic and fermentation 

processes and is produced during anaerobic carbohydrate fermentation in the stomachs of 

ruminants. It occurs in dairy products in small amounts and its esters are found in some 

essential oils.

TERRESTRIAL FATE: With an estimated Koc value of 36 derived from a log Kow 

of 0.33 propionic acid is expected to have very high mobility in soil, therefore, leaching 

into groundwater may occur. The pKa of propionic acid is 4.87, indicating that this 

compound will exist primarily in the anion form in the environment and anions generally 

do not adsorb more strongly to soils containing organic carbon and clay than their neutral 

counterparts.3Propionic acid in its anionic form would not volatilize from water or moist 

soil surfaces. The Henry’s Law Constant for Propionic acid is 4.45E-7 atm-cu m/mole. 

Propionic acid is expected to volatilize from dry soil surfaces based upon a vapor 

pressure of 3.53 mm Hg. Propionic acid is expected to be readily biodegradable under 

most environmental conditions based on the results of a sewage inoculum screening test 

that measured theoretical BODs ranging from 23-55%.4

AQUATIC FATE: The estimated Koc value of 36 suggests that propionic acid is not 

expected to adsorb to suspended solids and sediment. A pKa of 4.87 indicates propionic

acid will exist almost entirely in the anion form at pH values of 5 to 9 and therefore 

volatilization from water surfaces is not expected to be an important fate process.5

Leaching into groundwater may occur. Hydrolysis is not expected to be an important 

environmental fate process since this compound lacks functional groups that hydrolyze 

under environmental conditions. According to a classification scheme6, an estimated 

BCF of 3.2, from its log Kow and a regression-derived equation7, suggests the potential 

3 Doucette WJ; pp. 141-188 in Handbook of Property Estimation Methods for Chemicals. Boethling RS, 

Mackay D, eds. Boca Raton, FL: Lewis Publ (2000)

4 Heukelekian H, Rand MC; J Water Pollut Control Assoc 29: 1040-53 (1955)

5 Doucette WJ; pp. 141-188 in Handbook of Property Estimation Methods for Chemicals. Boethling RS, 

Mackay D, eds, Boca Raton, FL: Lewis Publ (2000)

6

Franke C et al; Chemosphere 29: 1501-14 (1994)

7 Meylan WM et al; Environ Toxicol Chem 18: 664-72 (1999)
7

for bioconcentration in aquatic organisms is low. Propionic acid is expected to be readily 

biodegradable in most environmental conditions based on the results of a sewage 

screening test that measured theoretical BODs of 23-55%.8

ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere9

, propionic acid, which has a estimated 

vapor pressure of 3.53 mm Hg at 25 deg C, is expected to exist solely as a vapor in the 

ambient atmosphere. Vapor-phase propionic acid is degraded in the atmosphere by 

reaction with photochemically-produced hydroxyl radicals; the half-life for this reaction 

in air is estimated to be 13 days, calculated from its rate constant of 1.22X10-12 cu 

cm/molecule-sec at 25 deg C.10 Propionic acid is not expected to directly photolyze due 

to the lack of absorbance in the environmental UV spectrum. Evaporation from dry

surfaces is expected, especially when present in high concentrations such as in spill 

situations.

Table 2 contains a summary of the physical-chemical properties of propionic acid.

Table 2. Chemical-Physical Properties

Property Value Reference

CAS 79-09-4 Hazardous Substance 

Data Base (HSDB)

Formula C3H6O2 HSDB

Molecular weight 74.08 HSDB

Dissociation constant; pKa 4.88 Serjeant EP, Dempsey B; 

Ionization Constants of 

Organic Acids in 

Aqueous Solution. 

IUPAC Chem Data Ser 

No. 23. NY, NY: 

Pergamon Press, Inc. 

1979

Koc 36 Swann RL et al; Res Rev 

85: 17-28. 1983.

Log Kow 0.33 Hansch C et al; 

Exploring QSAR. 

Hydrophobic, electronic, 

and Steric Constants. 

ACS Prof Ref Book. 

Heller SR, Consult. Ed., 

Wash., DC

Solubility (mg/L at 25°C) 1E+6 HSDB

Vapor pressure (mm Hg at 

25°C)

3.53 Lyman WJ; p. 31 in 

Environmental Exposure 

8 Heukelekian H, Rand MC; J Water Pollut Control Assoc 29: 1040-53 (1955)

9 Bidleman TF; Environ Sci Technol 22: 361-367 (1988)

10 Atkinson R; J Phys Chem Ref Data Monograph No. 1 (1989)
8

From Chemicals Vol I, 

Neely WB, Blau GE, 

eds, Boca Raton, FL: 

CRC Press. 1985

Henry’s law constant (atm-cu 

m/mole)

4.45E-7 HSDB

Characteristics of Ecosystems Potentially at Risk

For propionic acid and pesticides in general, the ecosystems at risk are those in close 

proximity to the use areas. These would include agricultural fields, surrounding 

terrestrial habitats, and water bodies directly adjacent to treated fields that may receive 

chemical residues via drift, volatilization, or runoff. Within water bodies, the water 

column, sediment, and pore water are all compartments of concern. In the case of 

propionic acid, which is applied during or after harvest, exposure to the environment 

decreases. The elements of the ecosystem that may be impacted include birds, 

amphibians, reptiles and small mammals that utilize the harvested field for all or part of 

their life-cycle. Non-target plants near the edge-of-field may be exposed by spray drift or 

over spray. 

The assessment endpoints are intended to reflect population sustainability and 

community structure within ecosystems and hence relate back to ecosystems at risk. If 

risks are expected for given species/taxa based on the screening-level assessment, then 

risks might be expected to translate to higher levels of biological organization.

Organisms of concern include birds, mammals, reptiles, fish, and terrestrial and 

aquatic invertebrates, plants, and amphibians. Based on the known effects to plants, as 

listed on the label, terrestrial plants may be the primary concern.

Assessment Endpoints

Assessment endpoints are defined as “explicit expressions of the actual environmental 

value that is to be protected.” Defining an assessment endpoint involves two steps: 1) 

identifying the valued attributes of the environment that are considered to be at risk; and 

2) operationally defining the assessment endpoint in terms of an ecological entity (i.e., a 

community of fish and aquatic invertebrates) and its attributes (i.e., survival and 

reproduction). Therefore, selection of the assessment endpoints is based on valued 

entities (i.e., ecological receptors), the ecosystems potentially at risk, the migration 

pathways of pesticides, and the routes by which ecological receptors are exposed to 

pesticide-related contamination. The selection of clearly defined assessment endpoints is 

important because they provide direction and boundaries in the risk assessment for 

addressing risk management issues of concern. Changes to assessment endpoints are 

typically estimated from the available toxicity studies, which are used as the measures of 
9

effects to characterize potential ecological risks associated with exposure to a pesticide, 

such as propionic acid.

To estimate exposure concentrations, the ecological risk assessment considers a 

single application at the maximum application rate to fields that have vulnerable soils. 

However, in this case, the pesticide is not applied to the field. The most sensitive 

toxicity endpoints are used from surrogate test species to estimate treatment-related direct 

effects on acute mortality and chronic reproductive, growth and survival assessment 

endpoints. Toxicity tests are intended to determine effects of pesticide exposure on birds, 

mammals, fish, terrestrial and aquatic invertebrates, and plants. These tests include shortterm acute, sub-acute, and reproduction studies and are typically arranged in a 

hierarchical or tiered system that progresses from basic laboratory tests to applied field 

studies. The toxicity studies are used to evaluate the potential of a pesticide to cause 

adverse effects, to determine whether further testing is required, and to determine the 

need for precautionary label statements to minimize the potential adverse effects to nontarget animals and plants. In past assessments of propionic acid, many of the effects 

testing requirements have been waived.

Conceptual Model

The conceptual model (see Figure TBD) depicts the potential pathways for ecological 

risk associated with propionic acid use. The conceptual model provides an overview of 

the expected exposure routes for organisms within the propionic acid action area. For 

terrestrial organisms, the major route of exposure considered is spray drift or overspray. 

Aquatic animal species are unlikely to be exposed to propionic acid due to label 

restrictions. For terrestrial and wetland plants, the major route is spray drift and 

overspray. 
10

Application of Propionic Acid During Baling Operations

Spray 

Drift

Overspray

Runoff/

Erosion

Stressor

Source: 

Transport 

Pathway

Source: 

Exposure 

Media

Exposure 

Point

Receptors

Direct 

Effects

Indirect 

Effects

Leaching

Terrestrial Food 

Residues 

(foliage, fruit, 

and insects

Upland Soil 

and foliage

Riparian/ 

Wetland

Foliage/ Soil

Surface 

Water and 

Sediment

Groundwater

Direct Contact & 

Ingestion

Direct 

Contact/ 

Root 

Uptake

Uptake/Ad

sorption

Gill Integument 

Uptake

Terrestrial 

Vertebrates 

and 

Invertebrates

Terrestrial 

Upland 

Plants

Riparian/ 

Wetland 

Plants

Aquatic 

Plants

Aquatic 

Vertebrates 

and 

Invertebrates

Terrestrial Animals:

•Lethality

•Reproductive/ 

developmental Effects

•Sublethal effects 

(corrosion and ocular 

damage)

Non-Target Plants:

•Plant Growth 

Abnormalities

•Lethality

•Developmental/ 

Reproductive Effects

Plant 

Population:

•Reduced 

Population 

Growth

Aquatic Animals and Plants: 

•Effects to survival, growth,

and reproduction

•Reductions in cell 

density/biomass in aquatic 

plants

Altered Terrestrial Community Assemblages: 

Reduced food supply and edge habitat availability

Altered Aquatic Community Assemblages:

•Effects to riparian habitat availability

•Effects to species abundance/diversity

•Changes in physical/chemical parameters

Figure 1. Conceptual Diagram of Ecological Exposure to Propionic Acid.

Risk Hypothesis

If propionic acid travels off field via spray drift, it is possible that non-target 

organisms may be affected, especially plants. Although no phytotoxicity tests have been 

submitted, the label warns that applying propionic acid to seed will inhibit germination. 

Therefore, it can be assumed that if non-target plants are exposed, seed germination will 

be inhibited and they may exhibit reproductive effects. In the absence of seedling 

emergence and vegetative vigor studies and information regarding the likelihood and 

quantity of spray drift, risk to non-target plants from propionic acid use will be assumed.

Propionic acid is classified as slightly toxic, to non-toxic on an acute basis. Most 

organisms will metabolize this basic carboxylic acid and therefore exposure by ingestion 

is not the route of concern. Contact exposure may result in adverse effects to both plants 

and animals. 

Based on a qualitative review of the available information and the associated 

assumptions outlined in the sections below, it is EFED’s preliminary conclusion 
11

that the current labeled uses for propionic acid will not pose a significant risk to 

non-target organisms other than terrestrial plants. 

Analysis Plan Options

Propionic acid is applied to crops post-harvest. There are no ground or aerial 

applications. Based on the propionic acid use profile and the assumptions listed below 

EFED continues to believe that exposure to non-target organisms will be extremely

limited. 

Assumptions:

- Numerous uses occur indoors. 

- When used outdoors, the product is applied simultaneously with baling 

activities. It is assumed that application during these activities will result in 

minimal spray drift off field because it is a contained operation. Small 

amounts of propionic acid may land in the field due to over spraying or windy

conditions. 

If these assumptions are confirmed, a quantitative assessment will not be conducted. If it 

is found that the listed assumptions are not accurate, a quantitative assessment may be 

required. 

Anticipated Data Needs

The Agency does not expect to require additional environmental fate studies but may

require ecological effects studies for plants, as listed in 40 CFR Part 158 prior to 

completing the Registration Review If a quantitative assessment is deemed necessary, 

seedling emergence and vegetative vigor data will be required to complete the 

assessment. The Agency will conduct a search of the open literature to ensure that all 

best available science is utilized. The Agency uses the ECOTOX database as its 

mechanism for searching the open literature for ecological effects information. 

ECOTOX integrates three previously independent databases - AQUIRE, PHYTOTOX, 

and TERRETOX - into a system which includes toxicity data derived predominately from 

the peer-reviewed literature, for aquatic life, terrestrial plants, and terrestrial wildlife, 

respectively.

Especially needed, in order to determine if a quantitative assessment is necessary, is 

information regarding the typical application process including methods, techniques and 

equipment. Several of the assumptions that preclude the necessity of a quantitative risk 

assessment are not included in the label but are based on assumed application practices. 

EFED is seeking answers to the following questions:
12

1. Is propionic acid sprayed over large areas before a crop is harvested (ie-corn)?

2. When propionic acid is applied during baling operations, does the method 

ensure that excess product (drips) is collected and not left on the field?

3. Do outdoor application equipment and techniques usually prevent spray drift?

The analysis plan will be revisited and may be revised 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.