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

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.  The 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).

Table 1.  Listing of the label uses, application rates, form and
equipment for propionic acid as an active ingredient.

  SEQ CHAPTER \h \r 1 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 areas-empty 

	.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 

//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. 

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 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 non-target 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.  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 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.  Propionic 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%. 

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.  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 scheme, an estimated BCF of 3.2, from its log Kow and a
regression-derived equation, suggests the potential 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%.

ATMOSPHERIC FATE: According to a model of gas/particle partitioning of
semi-volatile organic compounds in the atmosphere, 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.  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 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
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 short-term 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 non-target 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.  

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 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:

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

When propionic acid is applied during baling operations, does the method
ensure that excess product (drips) is collected and not left on the
field?  

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.

 USEPA 1991.  Reregistration Eligibility Document – Propionic Acid,
and Salts. Office of Pesticide Programs, Special Review and
Reregistration Division. September 1991.

 Acute Toxicity to Freshwater Fish. Animal Biol. Lab., EPA-TSD, Test No.
604, June 1973; Test No. 609, September 1973. 

 Doucette WJ; pp. 141-188 in Handbook of Property Estimation Methods for
Chemicals. Boethling RS, Mackay D, eds. Boca Raton, FL: Lewis Publ
(2000)

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

 Doucette WJ; pp. 141-188 in Handbook of Property Estimation Methods for
Chemicals. Boethling RS, Mackay D, eds, Boca Raton, FL: Lewis Publ
(2000)

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

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

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

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

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

 PAGE   

  PAGE  11 

