2

Acetic Acid and Sodium Diacetate – Table of Contents

I. Introduction ..........................................................................................................................3

A. General Background....................................................................................................4

II. Scientific Assessments.........................................................................................................4

A. Human Health Assessment..........................................................................................5

B. Environmental Assessment .........................................................................................5

C. Endangered Species Assessment.................................................................................7

D. Endocrine Disruptor Screening Program..................................................................7

III. Proposed Interim Registration Review Decision............................................................8

IV. Next Steps and Timeline ...................................................................................................8
3

I. Introduction

This document is the Environmental Protection Agency’s (EPA or the Agency) Proposed 

Interim Registration Review Decision for acetic acid and sodium diacetate and is being issued 

pursuant to 40 CFR sections 155.56 and 155.58. A registration review decision is the Agency’s 

determination whether a pesticide meets, or does not meet, the standard for registration in the 

Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). The Agency may issue, when it 

determines it to be appropriate, a proposed interim registration review decision before 

completing a registration review. Among other things, the proposed interim registration review 

decision may (1) require new risk mitigation measures; (2) impose interim risk mitigation 

measures; (3) identify data or information required to complete the review; and (4) include 

schedules for submitting the required data, conducting new risk assessments or revising 

preliminary assessments, and completing the registration review. For further information on 

acetic acid and sodium diacetate, additional documents can be found in EPA’s public docket 

(EPA-HQ-OPP-2008-0016) at www.regulations.gov.

FIFRA, as amended by the Food Quality Protection Act (FQPA) of 1996, mandated the 

continuous review of existing pesticides. All pesticides distributed or sold in the United States 

generally must be registered by the EPA based on scientific data showing that they will not cause 

unreasonable risks to human health or to the environment when used as directed on product 

labeling. The registration review program is intended to make sure that, as the ability to assess 

and reduce risk evolves and as policies and practices change, all registered pesticides continue to 

meet the statutory standard of no unreasonable adverse effects. Changes in science, public 

policy, and pesticide use practices will occur over time. Through the registration review 

program, the Agency periodically reevaluates pesticides to make sure that as these changes 

occur, products in the marketplace can continue to be used safely. Information on this program is 

provided as www.epa.gov/oppsrrd1/registration_review/.

In 2006, the Agency implemented the registration review program pursuant to FIFRA 

section 3(g) and will review each registered pesticide every 15 years to determine whether it 

continues to meet the FIFRA standard for registration.

Pursuant to 40 CFR Section 155.50, EPA formally initiated registration review for acetic 

acid and sodium diacetate (case 4001). Sodium diacetate is a salt of acetic acid. The following 

highlights significant events that have occurred during the registration review of acetic acid and 

sodium diacetate:

 March 26, 2008 - Publication of the Acetic Acid and Salts Summary Document for a 60-

day public comment period. The Summary Document included the preliminary work plan

(PWP) and was accompanied by the scoping document and problem formulation.

 August 21, 2008 - Final Work Plan (FWP) for acetic acid and sodium diacetate was 

signed -- no public comments were received during the 60-day comment period for the 

Acetic acid and Salts Summary Document. The FWP did not modify the Summary 

Document.
4

 January 2010 - Data Call-Ins (DCI) were issued for acetic acid (GDCI-044001-28802) 

and its salt, sodium diacetate (GDCI-044008-29025). For acetic acid, plant toxicity 

studies and an UV/absorption study were required. Only an UV/absorption study was 

required for sodium diacetate. The required studies were subsequently found not to be 

needed for the acetic acid and sodium diacetate risk assessments and can be waived. The 

preliminary human health and ecological risk assessments are now available in the docket 

for this registration review along with this Proposed Interim Registration Review 

Decision and a 60-day public comment period for the three documents has been initiated. 

Additional information about acetic acid and sodium diacetate, including this Proposed 

Interim Registration Review Decision and the following supporting documents can be found in 

EPA’s public docket, EPA-HQ-OPP-2008-0016, accessed at www.regulations.gov.

 Acetic acid: Science Review in Support of the Registration Review for Acetic Acid.

October 7, 2014.

 Sodium diacetate: Registration Review - Qualitative Ecological Risk Assessment 

and Effects Determination of Sodium Diacetate. April 25, 2012.

 Acetic Acid Registration Review Case No. 4001. Human Health Problem 

Formulation Document in Support of Registration Review. November 28, 2007.

A. General Background

The acetic acid and salts case is composed of two different active ingredients: acetic acid 

(PC Code: 044001) and its salt, sodium diacetate (PC Code: 044008). Acetic acid is registered 

for use as a preservative for post-harvest stored grains and hay intended for livestock feed. 

Additionally, it is also applied as a non-selective herbicide for control of broadleaf weeds and 

grasses. Vinegar is a solution of about 5% acetic acid in water. Both acetic acid and sodium 

diacetate are fungicides and bactericides registered to control molds and bacteria. They are 

applied to hay to prevent spoilage and to silage as an aid in fermentation. Non-pesticidal uses 

include use in food as a flavoring agent, or as a preservative. In water, sodium diacetate 

dissociates into an acetic acid and sodium acetate solution. There are residential uses for the 

herbicidal products containing acetic acid; there are no residential uses for sodium diacetate. A 

Reregistration Eligibility Decision (RED) was completed in September 1991 for sodium 

diacetate, since there were no registered uses of acetic acid at that time. Sodium diacetate was 

also the subject of a Tolerance Reassessment Eligibly Decision (TRED) in 2002, for the purpose 

of reassessing its exemption from the requirement of a tolerance. 

II. Scientific Assessments

A summary of the Agency’s ecological risk assessments, Science Review in Support of 

Registration Review for Acetic Acid (October 7, 2014) and Registration Review –Qualitative 

Ecological Risk Assessment and Effects Determination of Sodium Diacetate (April 25, 2012), is

presented below. The Agency determined that previous human health assessments for acetic 

acid and sodium diacetate were sufficient for registration review and no human health risks of 

concern were identified. Additional information about the human health risks is found in the 

Human Health Problem Formulation (November 28, 2007) in the Acetic Acid and Salts

Summary Document (March 2008). For the Summary Document and the actual ecological 
5

assessments, see the acetic acid and sodium diacetate public docket (EPA-HQ-OPP-2008-0016)

accessed at www.regulations.gov. 

A. Human Health Risk Assessment

No risks of concern were identified from previous reviews of acetic acid and sodium 

diacetate. There are no significant adverse effects to the general public or any population 

subgroup from consumption of residues of acetic acid or sodium diacetate resulting from 

pesticidal uses. 

Acetic acid is registered as a 6% active ingredient liquid formulation (approximately the 

same concentration of vinegar, which is 5% acetic acid in water) for consumer use as a home 

garden non-selective herbicide in non-food crop areas. No adverse effects are expected on 

humans from the use of these products according to label directions. There are no residential 

uses for sodium diacetate. 

A qualitative occupational exposure assessment for both acetic acide and sodium 

diacetate determined there are no risk concerns for handlers, including mixers, loaders, and 

applicators, or from post-application exposure. In addition, there are no adverse effects from 

aggregate exposure to sodium diacetate or acetic acid.

Food Tolerances

Acetic acid and sodium diacetate are exempt from the requirement of a tolerance when 

used post-harvest on grains and hays (40 CFR 180.1258(a) and 180.1058, respectively), and 

unintentional residues of acetic acid in non-target plants as a result of its herbicidal use are also 

exempt from the requirement of a tolerance (40 CFR 180.1258(b). Both acetic acid and sodium 

diacetate are affirmed as generally recognized as safe (GRAS) by the United States Food and 

Drug Administration (FDA) (21 CFR 184.1005 and 21 CFR 184.1754). There are no CODEX 

maximum residue limits established for acetic acid. There are no harmonization issues. No 

additional changes are necessary for the tolerances for acetic acid and sodium diacetate at this 

time.

B. Environmental Assessment

For sodium diacetate, the Agency concluded in the Registration Review – Qualitative 

Ecological Risk Assessment and Effects Determination of Sodium Diacetate (April 25, 2012) 

that, consistent with the conclusions of previous risk assessments, registered uses of sodium 

diacetate based on label directions should not result in unreasonable risks to non-target 

organisms, including a “no effect” characterization for federally-listed threatened or endangered 

species. The Agency reached this conclusion because of the low toxicity of sodium diacetate, 

and because the use of sodium diacetate to cure hay and silage should not result in a feasible 

route of exposure to non-target organisms.
6

For acetic acid, the Agency indicated in the initial problem formulation that the use of 

acetic acid to cure hay and silage, as with sodium diacetate, should not result in unreasonable 

risks to non-target organisms, including a “no-effect” characterization for federally listed 

threatened and endangered species. The Agency assessed the use of acetic acid as an herbicidal 

horticultural vinegar in the risk assessment, Acetic Acid: Science Review in Support of the 

Registration Review for Acetic Acid. (October 7, 2014). This assessment concluded that 

registered uses of acetic acid based on label directions should also not result in unreasonable 

risks to non-target organisms, including a “no effect” characterization for federally listed 

threatened or endangered species. 

Risk to Terrestrial Animals

Acetic acid was seen to be practically non-toxic to terrestrial mammals in acute studies, 

with no endpoint established at the highest dose tested. This is consistent with the FDA’s 

classification of acetic acid as a GRAS chemical. Because an endpoint could not be established 

at doses up to 11,700 mg/kg, the Agency concludes that acetic acid will not pose an acute risk to 

terrestrial mammals. The requirement for avian toxicity data for acetic acid had previously been 

waived. The Agency looked at the results of avian toxicity studies for comparable compounds 

such as peroxyacetic acid. The Agency’s Peroxy RED (EPA739 F 93 026, Dec. 1993) states that 

an avian acute dietary study on peroxy acetic acid showed that the compound was practically 

non-toxic (>2,000 mg/kg) on a dietary basis to bobwhite quail. For the current assessment, the 

toxicity data for acetic acid to mammals is used as a surrogate for birds, leading to a conclusion 

of no acute risk to birds. 

In addition to acetic acid being practically non-toxic in these toxicity tests, additional 

lines of evidence indicate that acetic acid should not pose acute or chronic risk to birds and 

mammals. First, acetic acid is a naturally occurring substance found in all plants, animals, and 

humans. In addition, exposure to acetic acid during or after application of acetic acid is unlikely 

because of immediate human activity (ground application), followed by degradation of acetic 

acid by aerobic processes thereafter with a half-life of about a day. Plants exposed to acetic acid 

quickly turn brown, thus reducing their food value, and the acrid smell/taste of acetic acid would 

act as a deterrent. 

An acute contact toxicity study on honey bees shows no toxicity from acetic acid 

exposure with an LD50 > 50 ug/bee, and suggests low risk to insects. In addition, an acute 

exposure of 26,225 mg ai of acetic acid per hive showed no mortality in honey bees nor the 

varroa mites inhabiting the hive. 

Risk to Terrestrial Plants

Acetic acid works as an herbicide by foliar contact which results in rapid desiccation of 

treated weeds. In order to be efficacious, the applied product must drench the target plant. Nontarget plants are not expected to be impacted because the use pattern includes only ground 

application using coarse spray nozzles that are calibrated to deposit large droplets directly on the 

target area. Hooded applicator equipment is used for localized spot treatment, minimizing any 

off-site drift.
7

Risk to Aquatic Animals and Plants

The Agency has assessed risk of exposure of acetic acid to aquatic organisms and has 

concluded that the potential for exposure and risk is very low. At current labeled uses, risks to 

aquatic organisms from these uses are expected to be minimal, since contamination of aquatic

environments from runoff will only result in short-term pH changes that will be counteracted by

the natural buffering capacity of the water and soil. This compound exhibits very low toxicity to 

fish, aquatic invertebrates, and aquatic plants. Risk quotients calculated at the highest 

application using a Tier 1 aquatic exposure model are below the Agency’s level of concern for 

risk to non-target aquatic organisms, as well as for aquatic endangered/threatened species.

C. Endangered Species Assessment

There is no reasonable expectation for registered uses of acetic acid and sodium diacetate 

to cause direct or indirect adverse effects to threatened and endangered species. No adverse 

modification of critical habitat is expected from the use of acetic acid and sodium diacetate. EPA 

has made a “no effect” determination under the Endangered Species Act (ESA) for all listed 

species as well as a “no habitat modification” determination for all designated critical habitats for 

the currently registered use of acetic acid and sodium diacetate. The Agency has therefore 

concluded that consultation with the Fish and Wildlife Service and the National Marine Fisheries 

Service under ESA section 7(a)(2) is not required. EPA anticipates conducting no further 

analysis of potential risks to endangered or threatened species, unless data or information are 

obtained during the Registration Review process that would indicate such an assessment would 

be needed to inform the Agency’s decision. 

D. Endocrine Disruptor Screening Program

EPA has developed the Endocrine Disruptor Screening Program to determine whether 

certain substances (including pesticide active and other ingredients) may have an effect in 

humans or wildlife similar to an effect produced by a “naturally occurring estrogen, or other such 

endocrine effects as the Administrator may designate.” Under FFDCA section 408(p), the 

Agency must screen all pesticide chemicals. Between October 2009 and November 2010, EPA 

issued test orders/data call-ins for the first group of 67 chemicals and published a second list of 

chemicals proposed for order issuance in the future. Acetic acid and sodium diacetate were not 

among the group of 58 pesticide active ingredients on the initial list nor is it proposed on the 

second list of chemicals to be screened under the EDSP. Accordingly, as part of registration 

review, EPA will issue future EDSP orders/data call-ins for registration review chemicals, 

including acetic acid and sodium diacetate. For further information on the status of the EDSP, 

the policies and procedures, the list of 67 chemicals, future chemical lists proposed for screening, 

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

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

In the interim, EPA is making no human health or environmental safety findings 

associated with the EDSP screening of acetic acid and sodium diacetate. Before completing this 

Registration Review, the Agency will make an EDSP FFDCA section 408(p) determination.
8

III. Proposed Interim Registration Review Decision

Per the acetic acid and salts Preliminary Work Plan (March 2008), EPA has completed 

ecological risk assessments as part of registration review. The Agency is issuing a Proposed 

Interim Registration Review Decision pursuant to 40 CFR Sections 155.56 and 155.58. The 

Agency determined that previous human health assessments for acetic acid and sodium diacetate 

were sufficient for registration review and no human health risks of concern were identified. The 

Agency completed a comprehensive ecological risk assessment for the nonselective herbicide 

use of acetic acid and a qualitative ecological risk assessment for sodium diacetate, including 

endangered species assessments. EPA has determined that use of acetic acid and sodium 

diacetate should not result in unreasonable risk to non-target organisms, including threatened and 

endangered species and their critical habitats, and concludes a "no effect" determination for the 

registered uses of acetic acid and sodium diacetate. No proposed mitigation measures are 

included in the proposed interim decision. The registration review timeline in the Acetic Acid 

and Salts Final Work Plan projected that the Agency would issue the preliminary risk 

assessments in the fall of 2011 and issue the proposed registration review decision in the spring 

of 2012. Since no risks of concern are indicated, the Agency has decided to issue for public 

comment this Proposed Interim Registration Review Decision concurrently with the preliminary 

risk assessments. The anticipated timeframes for the registration review of acetic acid and 

sodium diacetate were revised and the Agency now anticipates issuing an Interim Registration 

Review Decision in 2015.

In accordance with 40 CFR Sections 155.56 and 155.58, the Agency is issuing this 

Proposed Interim Registration Review Decision document. Except for the EDSP component of 

the acetic acid and sodium diacetate registration review case, the Agency has made the following

Proposed Interim Registration Review Decision: (1) no additional data are required at this time; 

and (2) no changes to the affected registrations or their labeling are needed at this time. EPA has 

not identified any risks of concern to human health. EPA has determined that use of acetic acid 

and sodium acetate should not result in any significant exposure or risk to non-target organisms.

As such, EPA concludes “no effect” for listed species and no adverse modification of designated 

critical habitat for all currently registered uses of acetic acid and sodium diacetate.

IV. Next Steps and Timeline

A Federal Register Notice will announce the availability of this Proposed Interim

Registration Review Decision for acetic acid and sodium diacetate and the preliminary risk 

assessments and allow a 60-day comment period. If there are no significant comments or 

additional information submitted to the docket during the comment period that leads the Agency 

to change its proposed decision, EPA may issue an Interim Registration Review Decision for 

acetic acid and sodium diacetate (case 4001). However, a final decision for acetic acid and 

sodium diacetate may be issued without having previously issued an Interim Registration Review 

Decision. A final decision on the acetic acid and sodium diacetate registration review case will 

occur after an FFDCA section 408(p) EDSP determination has been made.