Page 3 of 36

handler and post-application assessment may be required under 2,4-D registration review if there 

are any significant changes to the current exposure assessment methodology, toxicological points 

of departure, or uncertainty factors.

In addition, quantitative residential post-application assessments have not been performed for 

exposures potentially resulting from pesticide drift or volatilization from neighboring 2,4-Dtreated agricultural fields; these assessments may be necessary under registration review. Any 

assessments would consider all 2,4-D forms.

In 2005 there were no aggregate (food, water, and residential exposure combined) risk estimates 

of concern for 2,4-D for adults or children. During registration review, updated aggregate 

assessments may be conducted as needed if, in the interim, there are any significant changes to 

the following: toxicological PODs, FQPA and other uncertainty factors, dietary exposure 

estimates, and the methods or data HED uses to calculate residential exposure estimates. Any 

significant changes to the estimated drinking water concentrations (EDWCs), which are under 

EFED purview, may also necessitate changes to the dietary assessment.

There are no outstanding worker exposure data requirements for 2,4-D. An updated 

occupational handler assessment and a dermal post-application assessment may be performed if 

warranted by significant changes to the current exposure assessment methodology, PODs, or 

uncertainty factors. A quantitative occupational post-application inhalation exposure assessment 

for 2,4-D, including assessment of field volatilization, may be necessary under registration 

review.

Polychlorinated dibenzo dioxins (PCDD) and polychlorinated dibenzo furans (PCDF) may be 

formed during the manufacture of 2,4-D and can remain in the 2,4-D technical products as 

impurities. According to 2,4-D registrants, since the 1990’s, the manufacturing processes for 

2,4-D and its chemical intermediate dichlorophenol (DCP), have been modified to reduce 

concentrations of PCDD and PCDF in the technical 2,4-D products. The 2005 RED concluded 

that, based on a worst-case scenario screen which included early 1990’s data on 2,4-D 

manufacturing impurities, both the cancer and non-cancer risks from dietary exposure to dioxins 

and furans as contaminants of 2,4-D acid were considered to be of no toxicological concern. 

HED will continue to monitor data on the impurities and reassess any potential risks as 

necessary.

Chemical Use Profile

2,4-Dichlorophenoxyacetic acid (2,4-D) is an alkylchlorophenoxy herbicide used to control a 

variety of broadleaf weeds. It is registered for use on many agricultural use sites including cereal 

grains, field, pop and sweet corn, sorghum, soybeans, sugarcane, rice, pome fruits, stone fruits, 

nut orchards, potatoes, hops, asparagus, strawberries, blueberries, grapes, cranberries, and citrus.

2,4-D is also registered for use on a variety of non-agricultural uses including residential turf, for 

industrial and commercial areas, on golf courses, non-cropland and for aquatic weed control. 

Permanent tolerances for 2,4-D are established under 40 CFR 180.142 for a wide variety of crops 

and livestock commodities. 
Page 4 of 36

There are eleven active ingredients (a.i.s) that are components of currently registered pesticide 

products. The list of active ingredients covered by the 2,4-D case (Case No. 0073) can be found 

in Appendix 1 and includes 2, 4-D acid, its sodium, choline, and amine salts, and its esters. It is 

to be noted that the choline salt was not in the reregistration case previously. The nomenclature 

and physiochemical properties of the 2,4-D a.i.s can be found in Appendix 2.

Hazard Identification/Toxicology

2, 4-D is a phenoxy herbicide and a plant growth regulator. Since toxicity following exposure of 

rats and dogs to the amine salts and esters of 2, 4-D was similar to that observed following 2, 4-

D acid exposure, the acid has been selected as being representative of all members of the 2,4-D 

reregistration case including 2, 4-D acid, the sodium, choline, and amine salts, and esters. 

In the acute lethality studies with 2, 4-D and its salts and esters, the clinical signs of toxicity 

consistently observed in rats following oral administration were ataxia, myotonia, and decreased 

limb tone. Following dermal administration, no dermal or systemic toxicity was observed in 

rabbits. Clinical signs of toxicity observed in rats during inhalation exposure were decreased 

activity and closed eyes. The acid and salt forms are severe eye irritants.

The subchronic database provides evidence that the kidney [increased kidney weight, 

histopathological lesions], thyroid [decreased thyroxine, increased thyroid weight, hypertrophy 

of follicular cells], liver [increased liver weight, increased ALT, and AST, histopathological 

lesions, including hypertrophy], adrenal [increased adrenal weight, histopathological lesions], 

eye [retinal degeneration, cataract formation], and ovaries/testes [atrophy] are target organs in 

the rat following exposure to 2,4-D via the oral route at dose levels above the threshold of 

saturation of renal clearance. No systemic toxicity was observed in rabbits following repeated 

exposure via the dermal route at dose levels up to the limit dose [1000 mg/kg/day]. In the dog, 

the kidney, thyroid, and testis are target organs [elevated blood urea nitrogen and creatinine, 

decreased glucose, decreased T4, increased kidney and thyroid weights, cellular alterations of the 

proximal tubule, decreased testes weight and hypospermatogenesis/juvenile testis] following 

exposure via the oral (diet and capsule) route at dose levels above the threshold of saturation of 

renal clearance. Effects in dogs were observed at lower dose levels than those observed in 

rodents, and this is attributed to the dog’s limited capacity to eliminate 2,4-D and other organic 

acids. Subchronic toxicity following exposure of rats and dogs to the amine salts and esters of 

2,4-D was similar to that observed following 2,4-D acid exposure. 

Chronic toxicity studies indicate that the kidney [increased kidney weight, proximal tubule 

degeneration], thyroid [increased thyroid weight, decreased T4, hyperplasia, hypertrophy], testes 

[decreased testes weight, atrophy], ovaries [decreased ovarian weight], and eyes [lens opacity, 

cataracts, retinal degeneration] are target organs in the rat following exposure to 2,4-D at dose 

levels at or above the threshold of saturation of renal clearance. In the dog, decreased brain 

weight [females], increased incidence of kidney lesions, and aspermatogenesis and testes 

degeneration were observed.

In general, 2,4-D undergoes limited metabolism in mammalian systems, although the metabolism 

that does occur primarily involves minor conjugation of the parent acid, which results in a more 
Page 5 of 36

water soluble compound that is then excreted in the urine. No detectable metabolites of 2, 4-D 

have been reported in the rat, i.e. only the parent acid was detected in rat urine. 2, 4-D 

conjugates have been found in the urine of dogs, humans, mice, and hamsters following oral 

exposure. In other metabolism studies, 2, 4-D was the predominant residue found in ruminant 

tissue, milk, poultry tissue, eggs, and fish.

2,4-D is classified as a Group D chemical [not classifiable as to human carcinogenicity]. Based 

on the overall pattern of responses observed in both in vitro and in vivo genotoxicity tests and a 

weight-of- evidence assessment, 2,4-D is not mutagenic, although some cytogenic effects were 

observed. 

In the previous human health risk assessment (T. Dole, D316597, 5/12/2005), the subchronic 

inhalation toxicity study was identified as a data requirement for 2,4-D. Additionally, there was 

evidence for neurotoxicity (clinical signs and neuropathology) in adult animals (rats and dogs) 

with 2,4-D acid as well as evidence of increased susceptibility (qualitative) in the prenatal 

developmental toxicity study in rabbits with the diethylamine salt of 2,4-D. To address the 

potential neurotoxicity concerns in the offspring, the Agency required a developmental 

neurotoxicity (DNT) study. Additionally, it was determined that a two-generation reproduction 

study using the post-1998 protocol (OCSPP 890.3800), designed to provide general information 

concerning the effects of a 2,4-D on the integrity and performance of the male and female 

reproductive system, was required. To account for the lack of these studies, the Agency retained 

a 10X FQPA safety factor in the 2005 human health risk assessment.

After the RED was completed, the Agency issued a Data Call-in Notice (DCI) for the subchronic 

inhalation, DNT, and the two-generation reproduction studies. In response to the latter two study 

requirements, the 2,4-D Task Force with approval from the Agency conducted an Extended One 

Generation Reproductive Toxicity (EOGRT) study (MRID 47972101; TXR Nos. 0055341 and 

0050697). This study included an evaluation of potential effects on parental male and female 

reproductive function, reproductive organ weight evaluations, and detailed histopathology of the 

reproductive organs. The study also evaluated potential effects in offspring on survival, growth, 

and the development of the immune, nervous, and reproductive systems. In addition, the study 

examined various endocrine-related parameters including estrous cycle evaluation (female adult 

rats and F1 offspring), qualitative ovarian follicle count (F1 females), evaluation of sperm 

parameters, anogenital distance, nipple retention, puberty onset (vaginal opening and balanopreputial separation), and thyroid effects (weight, hormone, and histopathological).

In the EOGRT, clear NOAELs and LOAELs were identified for systemic, thyroid, and 

reproductive effects in adult animals, as well as for growth and development of offspring, 

developmental neurotoxicity, and developmental immunotoxicity in the offspring. The EOGRT 

neither identified a more sensitive endpoint nor a lower Point of Departure (POD) than those 

used in the existing 2,4-D risk assessments. (See Appendix 3, Tables A3.1 and A3.2 for a 

summary of the most recent toxicological endpoints and PODs.)

In response to the subchronic inhalation study requirement, the 2,4-D Task Force conducted a 

28-day inhalation study (MRID 47398701; TXR No. 0054870). Following repeat dose nose-only 

inhalation exposure of rats to 2,4-D, the incidence and severity of the portal-of-entry effects 
Page 6 of 36

(squamous metaplasia and epithelial hyperplasia with increased mixed inflammatory cells within 

the larynx) were increased in a dose-related manner. Clinical signs associated with inhalation 

exposure at the high dose included excessive salivation, labored breathing, and 

chromodacryorrhea. A NOAEL for portal-of-entry effects was not determined. The LOAEL is 

0.05 mg/L, based on squamous metaplasia and epithelial hyperplasia with increased mixed 

inflammatory cells within the larynx.

The EOGRT study satisfies the DCI requirements for OCSPP 870.3800 (Reproduction and 

Fertility Effects), OCSPP 870.6300 (Developmental Neurotoxicity), and OCSPP 870.7800 

(Immunotoxicity) studies for 2,4-D. The 28-day subchronic inhalation toxicity study satisfies the 

DCI requirement for OCSPP 870.3465 (90-Day Inhalation) study for 2,4-D. (See Appendix 4 for 

a summary of the toxicology data requirements and Appendix 5 for study profiles.)

The National Resources Defense Council (NRDC) filed a petition on November 6, 2008 

requesting that EPA revoke all tolerances for 2,4-D. The petition raised a number of technical 

issues primarily pertaining toxicology, but also to exposure, epidemiology, and pet incidents. 

HED responded to issues specifically pertaining to the 2,4-D human health risk assessment (L. 

Taylor et al, 3/27/12, D392844). EPA concluded that the NRDC petition did not raise sufficient 

grounds for concern, and the petition was denied. [Federal Register/Vol. 77, No. 75; Wednesday, 

April 18, 2012/Rules and Regulations. EPA-HQ-OPP-2008-0877; FRL-9344-2 (23135-23158)]. 

The petition issues did not warrant any changes to the 2005 human health risk assessment.

In 2012, EPA re-examined the risks of 2,4-D in response to an application to amend a 2,4-D 

FIFRA registration. The re-examination took into account the newly submitted extended onegeneration reproduction study evaluating 2,4-D’s potential for causing endocrine, neurotoxic, or 

immunotoxic effects. As part of that assessment, EPA reevaluated the decision to retain the 

FQPA safety factor. Because the FQPA safety factor had previously been retained due to the 

absence of data on endocrine, neurotoxic, and reproductive effects and those data requirements 

had been met, EPA determined that the 10X FQPA safety factor should be reduced to 1X

(D398209).

Conclusion: The 2,4-D toxicity database is complete. All of the required toxicity data have been 

received and reviewed. Under registration review the toxicological endpoints and PODs for use 

in 2,4-D risk assessments will be reevaluated taking into account all studies, including those 

received since the 2005 RED (EOGRT and inhalation).

Dietary Exposure

Residue Chemistry

The magnitude of the residue database is complete. The nature of the residue is understood based 

on the available metabolism and residue studies; the residue of concern for tolerance regulation 

and risk assessment is 2,4-D per se (MARC 10/13/04, TXR. No. 0052264).

The 2005 2,4-D risk assessment requested field trial data on wheat hay and limited irrigated crop 

studies (strawberry and sugar beet). Those data requirements have since been waived (T. 
Page 7 of 36

Goodlow, D336596, 4/16/07 and D340921, 10/18/07). The 2007 waiver memos also 

recommended or reassessed several 2,4-D tolerances which are not currently reflected 40 CFR 

§180.142: In D340921 it was determined that a tolerance value of 50 ppm is appropriate for hay, 

and should be established for residues of 2,4-D in/on wheat hay, barley hay, millet hay and oat 

hay under 40 CFR §180.142(a). In D336596 it was recommended that a tolerance value of 0.1 

ppm be established under 40 CFR §180.142(a) for residues of 2,4-D in/on strawberries, grapes, 

Crop Groups 11 (pome fruit) and 12 (stone fruit), and on Crop Groups 1 and 2, root and tuber 

vegetables (excluding potatoes) and the leaves of root and tuber vegetables, respectively.

Dietary Assessment

Food Only

The 2005 acute dietary assessment (T. Jimerson, 4/18/05, D315512) was slightly refined with the

following assumptions: tolerance-level exposure values for most commodities, the highest field 

trial residue value for citrus commodities, and 100% crop treated (%CT). Half the average Limit 

of Detection (LOD) from Pesticide Data Program (PDP) monitoring data was used as the milk 

value as no milk samples contained detectable 2,4-D residues over several years of PDP 

sampling. The assessment was conducted using the Dietary Exposure Evaluation Model software 

with the Food Commodity Intake Database (DEEM-FCID , Version 1.33), which incorporates 

consumption data from USDA’s Continuing Surveys of Food Intakes by Individuals (CSFII), 

1994-1996 and 1998. The acute dietary (food only) risk estimates were below the Agency’s level 

of concern (100% of the aPAD) at the 95th exposure percentile for the general U.S. population and 

all population subgroups. The most highly exposed population subgroup was children 1-2 years 

old at 33% aPAD. 

The 2005 chronic dietary assessment was moderately refined, making use of the following: 

tolerance-level exposure values for most commodities; averages of field trial data and processing 

study factors for small grains, citrus, and sugarcane sugar and molasses; %CT information for all 

commodities. As in the case of the acute assessment, 1⁄2 of the average LOD from PDP 

monitoring data was used for milk. The chronic dietary (food only) risk estimates were below the 

Agency’s level of concern. Chronic dietary (food) risk estimates to children 1-2 years of age, the 

most highly exposed population subgroup, were 8.5% of the cPAD.

Water

In the 2005 RED, the Environmental Fate and Effects Division (EFED) derived Estimated 

Environmental Concentrations (EECs) in water through an evaluation of monitoring data and 

modeling. A number of different scenarios were assessed and EECs provided for each. 

Scenarios evaluated included the direct application of 2,4-D to water bodies for aquatic weed 

control, a rice use scenario, and terrestrial uses including food and nonfood uses. The EFED 

EECs for drinking water used in the 2005 human health risk assessment are listed below. As the 

direct aquatic uses and the terrestrial uses of 2,4-D are distinctly different, risk estimates 

associated with both of these major use patterns were assessed. The 2,4-D degradates detected in 

the various laboratory environmental fate studies were 1,2,4-benzenetriol, 2,4-dichlorophenol 

(2,4-DCP), 2,4-dichloroanisole (2,4-DCA), 4-chlorophenol, chlorohydroquinone (CHQ), volatile 
Page 8 of 36

organics, bound residues, and carbon dioxide. The OPP Metabolism Assessment Review 

Committee (MARC) determined that all residues other than 2,4-D are not of risk concern due to 

low occurrence under environmental conditions, comparatively low toxicity, or a combination 

thereof. The residue of concern in drinking water for human health assessment is 2,4-D (MARC 

memo, 10/13/04, TXR No. 0052264).

EECs selected for use in 2005 RED:

Acute EECs:

Surface Water (aquatic applications; Maximum Contaminant Level, Office of Water MCL) = 70 

ug/liter 

Surface water (worst case terrestrial use PRZM-EXAM; NC apple) = 118 ug/liter

Ground Water (the highest monitored value from the USGS NAWQA database) = 15 ug/liter

Chronic EECs:

Surface Water (maximum time weighted annual mean from the NAWQA database) = 1.5 ug/liter

Surface Water (dissipation modeling of aquatic application when 70 ppb occurs at time zero) = 

11 ug/liter

Surface Water (worst case terrestrial use PRZM-EXAMs; NC apple) = 23 ug/liter

Ground Water (the highest monitored value from the NAWQA database) = 15 ug/liter

Short- and Intermediate-Term EECs:

Surface Water (aquatic applications; Maximum Contaminant Level, MCL) = 70 ug/liter 

Surface Water (worst case terrestrial use PRZM-EXAMs, 1 in 10 year average; NC apple) = 64 

ug/liter 

Ground Water (the highest monitored value from the NAWQA database) = 15 ug/liter

Food plus Water

Previously, estimated drinking water concentrations were not directly incorporated into DEEM 

in the 2,4-D dietary assessment. At the time of the latest risk assessment, HED was calculating 

drinking water levels of comparison (DWLOCs) and comparing them to the estimated EECs 

(also called EDWCs, estimated drinking water concentrations) provided by EFED to determine 

whether or not the risk estimates were of concern. See the section of this document titled 

Aggregate Risk Assessment for a description of the DWLOC approach and aggregate dietary 

(food and water) risks estimated in the 2005 RED, which were not of concern for 2,4-D.

Conclusions: The 2,4-D residue chemistry database is complete No new data are needed to 

assess potential dietary exposure and risk for 2,4-D. During registration review, updated dietary 

food assessments may be conducted as needed to include any significant changes that might be 

made to toxicological PODs, FQPA and uncertainty factors, dietary exposure estimates, and 

EDWCs. If a revised drinking water assessment is warranted, EFED will conduct a drinking 

water assessment to support future human health dietary risk assessments of 2,4-D. The drinking 

water assessment will be performed based on EFED’s current guidance using appropriate surface 

and groundwater models. 
Page 9 of 36

Residential (Non-Occupational) Exposure

There are products containing 2,4-D registered for residential use or that may be applied by 

residential applicators or by commercial applicators to residential sites. The maximum 

application rate is 1.5 lb acid equivalent (ae) of 2,4-D/acre. 2,4-D is formulated with other 

herbicides such as MCPP-p and 2,4-DP. Products can be applied to ornamental turf, including 

golf courses, cemeteries, parks, sports fields, turfgrass, lawns and other grass areas. Residential 

handler exposure may occur. In addition, post-application exposure can result when people enter 

parks and athletic fields that have been treated with 2,4-D, or when golfers play golf on courses 

that have been treated. 2,4-D can also be used for aquatic weed control of surface weeds, which 

could potentially lead to recreational swimmer exposure.

The residential products are typically formulated as dry weed and feed products or as liquids in 

concentrates or ready-to-use sprays. Both spot and broadcast treatments are included on the 

labels. Exposures are expected to be short-term in duration for broadcast treatments because the 

label allows only two broadcast treatments per year. Exposures are also expected to be shortterm in duration for spot treatments because the labels recommend repeat applications for hard to 

kill weeds in two to three weeks. Liquid and granular formulations can be used to control 

aquatic weeds as well.

Residential Handler Exposure

A short-term residential handler exposure assessment for residential application of granules, 

spray, and ready-to-use products to lawns using handheld equipment was performed in the 2005 

RED using the maximum application rate; combined dermal and inhalation risks were not of 

concern (MOEs > LOC of 1000). Short-term residential handler MOEs range from 1,800 to 

29,000. Since the RED, the level of concern has been reduced to100 with the removal of the 10X 

safety factor.

The Health Effects Division’s 2012 Standard Operating Procedures for Residential Pesticide 

Exposure Assessment has updated exposure assessment methodology for residential exposure 

scenarios, including methodology for adult handler exposure assessment. A screening level 

residential handler assessment for 2,4-D, considering updated exposure methodology, indicates 

that handler risk estimates are not likely to be of concern. An updated residential handler 

assessment may be required under registration review if warranted by significant changes in 

exposure assessment methodology, toxicological points of departure or uncertainty factors. 

Residential Post-Application Exposure

Residential post-application exposure may occur after products containing 2,4-D have been 

applied to residential turf sites, including ornamental lawns and turf. Similar exposures may 

occur when people enter parks and athletic fields that have been treated with 2,4-D, or when 

golfers play golf on courses that have been treated. Chemical-specific turf transferable residue

(TTR) data are available for 2,4-D. Acute and short-term adult dermal exposure to treated turf 

(including golfers) and child dermal and incidental oral exposure to treated turf were assessed in 

the 2005 RED. Risks were not of concern for all routes of exposure (MOEs > LOC of 1000). 
Page 10 of 36

The acute child total MOE was 1,100; the short-term child total MOEs ranged from 1,200 to 

3,900. The adult dermal acute and short-term MOE was 1,000 for heavy yardwork activities on 

treated turf and 15,000 for golfing activities. A biomonitoring study was also used to calculate 

risk estimates for post-application exposure on turf in the 2005 RED. MOEs based on the 

biomonitoring data were not of concern and were greater than the modeled estimates from the 

RED.

2,4-D can be used for aquatic weed control of surface weeds and submersed weeds. According to 

the 2005 RED, many herbicide treatments are applied to aquatic areas where recreational 

swimming is not likely to occur; however, post-application scenarios for recreational swimmers 

(dermal and ingestion exposure for adults and children) were assessed in the RED. Because the 

2,4-D water concentrations can vary depending upon the application rate and site conditions, the 

maximum swimming water concentration (MSWC) was calculated. The MSWC is the water 

concentration at which the combined dermal and ingestion MOE met or exceeded the LOC of 

1000 (that is, the maximum water concentration where swimmer exposure did not pose a risk of 

concern). MSWCs were calculated for adults and children for acute and short-term durations for 

all 2,4-D forms. The maximum application rate for subsurface treatments is 4 ppm. Initial and 

average 2,4-D (acids and amines) and 2,4-D BEE (butoxyethyl ester) concentrations following 

application were determined in the 2005 RED. Although some concentrations exceeded

MSWCs for certain forms and under certain conditions, it was concluded that, overall, the 

concentrations were unlikely to be of concern. Current labels restrict swimming in treated water 

for at least 24 hours after application, as indicated in the RED. In addition, because the LOC is

now 100, MSWCs will increase. Thus, 2,4-D levels in water are expected to be lower than the 

MSWCs 24 hours after application, and would not be expected to be of concern for swimmer 

exposure.

Three turf transferable residue (TTR) studies specific for 2,4-D were submitted by the Broadleaf 

Turf Herbicide TTR Task Force and served as the data source for the RED assessment. A 

summary of the data used for exposure assessment can be found in the 2005 RED. These studies 

satisfy the turf transferable residue data requirement under 40 CFR Part 158.

The Health Effects Division’s 2012 Standard Operating Procedures for Residential Pesticide 

Exposure Assessment has updated exposure assessment methodology for residential exposure 

scenarios, including adult and children exposure to treated turf, and also for golfers on treated 

golf courses. Based on previous findings, the new SOPs, and the change in the FQPA safety 

factor, a screening level assessment would not likely indicate that these exposures result in risks 

of concern. An updated residential post-application assessment may be required under 

registration review if warranted by any significant changes in exposure assessment methodology, 

toxicological points of departure or uncertainty factors.

Pesticide drift is always a potential source of exposure for residents nearby to spraying 

operations. This is particularly the case with aerial application, but, to a lesser extent, could also 

be a potential source of exposure from the ground application methods employed for 2,4-D. The 

Agency has been working with the Spray Drift Task Force, EPA Regional Offices, and State 

Lead Agencies for pesticide regulation and other parties to develop the best spray drift 

management practices (see the Agency’s Spray Drift website for more information at 
Page 11 of 36

http://www.epa.gov/opp00001/factsheets/spraydrift.htm). The Agency has completed its 

evaluation of the new database submitted by the Spray Drift Task Force, a membership of U.S. 

pesticide registrants, and is developing a policy on how to appropriately apply the data and the 

AgDRIFT®computer model to its risk assessments for pesticides applied by air, orchard airblast,

and ground hydraulic methods. After the policy is in place, the Agency may impose further 

refinements in drift-management practices to reduce off-target drift with specific products with 

significant risks associated with drift.

A quantitative residential post-application dermal and inhalation exposure assessment has not 

been performed for pesticide drift from neighboring 2,4-D-treated agricultural fields; a drift 

assessment may be necessary during registration review. Risk estimates for post-application 

residential dermal exposure to treated turf may be considered protective of residential dermal 

exposure via drift from agricultural 2,4-D applications.

Volatilization of pesticides also may be a potential source of post-application inhalation exposure 

to individuals nearby pesticide applications. The Agency sought expert advice and input on 

issues related to volatilization of pesticides from its Federal Insecticide, Fungicide, and 

Rodenticide Act (FIFRA) Scientific Advisory Panel (SAP) in December 2009. The Agency 

received the SAP’s final report on March 2, 2010 

(http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html). A quantitative postapplication inhalation exposure assessment for field volatilization of 2,4-D has not been 

performed and may be necessary under registration review. A volatilization assessment would 

include all registered forms of 2,4-D.

Conclusions: The residential exposure database for 2,4-D is complete. Previous residential 

handler and related post-application exposure assessments (for the turf and aquatic uses) did not 

result in risk estimates of concern. The LOC (target MOE) was previously 1000 for residential 

assessments. The LOC for residential assessments has since been revised to 100 (a 10X FQPA 

factor has been removed). A screening level assessment indicates that residential handler and 

post-application exposures are not likely to be of concern when considering the updated 

exposure methodologies. An updated residential handler and post-application assessment may 

be required under 2,4-D registration review if there are any significant additional changes in 

exposure assessment methodology, toxicological points of departure, or uncertainty factors. 

In addition, a quantitative residential post-application exposure assessment has not been 

performed for exposures representing pesticide drift or volatilization from neighboring 2,4-Dtreated agricultural fields; these assessments may be necessary under registration review. 

Aggregate Risk Assessment

For aggregate risk assessment, risk estimates resulting from food, drinking water, and residential 

uses are combined. 

In the 2005 2,4-D RED drinking water levels of concern (DWLOCs) were calculated for 

comparison to the EECs. The respective DWLOCs and aggregate risk estimates were calculated 

for acute, short-term, and chronic (non-cancer) exposures.
Page 12 of 36

A DWLOC is the water concentration (ppb or ug/liter) that is associated with the drinking water 

exposure portion of the risk cup that remains after estimated dietary and residential exposures 

have been subtracted. This concentration value (DWLOC) represents the available or allowable 

exposure through drinking water. Estimated Drinking Water Concentrations (EDWCs) in 

drinking water that are less than the DWLOCs do not exceed HED’s level of concern. DWLOC 

values vary for population subgroups depending on dietary exposure through foods for each 

subgroup, assumptions made about the volume of drinking water consumed, and default body 

weights for each subgroup. 

Acute

The previous acute aggregate risk assessments addressed exposure to 2,4-D residues in food and 

water using the DWLOC approach. The acute DWLOCs were 432 ppb or greater with the most 

sensitive population being females 13-49 years old. The EECs of 118 ug/liter for surface water 

and 15 ug/liter for groundwater were substantially less than the DWLOCs which indicated that 

the acute aggregate risk estimates were not of concern.

Short-Term

Short-term aggregate risk assessments were conducted by calculating DWLOCs based upon 

short-term turf exposures, chronic food exposures and short-term endpoints. Short-term

exposures from swimming in treated water bodies were not included because these exposures 

represent high-end unlikely scenarios. The short-term DWLOCs were calculated only for females 

13-49 and children 1-6 because these population subgroups have the highest exposure and are 

protective of the other subgroups. The DWLOCS range from 24 to 54 ug/liter. These DWLOCs 

were all greater than the EECs, which range from 15 to 23 ug/liter, and indicated that short-term

aggregate risk estimates were not of concern.

Chronic 

Chronic DWLOCs were calculated based upon chronic dietary exposures. As there are no chronic 

residential exposures, residential exposures were not included in the chronic DWLOC 

calculations. The chronic DWLOCs were 47 ug/liter or greater with the most sensitive 

populations being infants and children. The EECs, which range from 1.5 to 23 ug/liter, were less 

than the DWLOCs. Chronic aggregate risk estimates were not of concern. It should be noted that 

the master label indicates that potable water consumption from a treated water body cannot begin 

until the 2,4-D concentration is 70 ug/liter or below, therefore an annual average exposure at the 

MCL of 70 ug/liter would not occur because dissipation would reduce the initial concentration of 

70 ug/liter to an annual average concentration of 11 ug/liter.

Conclusions: In 2005 there were no aggregate (food, water, and residential) risk estimates of 

concern for 2,4-D. During registration review, updated aggregate assessments may be conducted 

as needed to include any significant changes that might be made to toxicological PODs, FQPA 

and uncertainty factors, dietary exposure estimates, methods or data HED uses to calculate 
Page 13 of 36

residential exposure estimates, or EDWCs. Emerging policies related to pesticide drift and 

volatilization assessments may dictate further changes to the existing aggregate risk assessment. 

Cumulative Risk Assessment

The Food Quality Protection Act (FQPA) requires the Agency to consider the cumulative risks of

chemicals sharing a common mechanism of toxicity. 2,4-D is a member of the alkylphenoxy 

herbicide class of pesticides. This class also includes MCPA, 2,4-DB, and 2,4-DP. Although the 

various phenoxy herbicides have similar structural components, HED has no data indicating that 

they have a common mode of toxic action. Therefore, a cumulative risk assessment has not been 

performed for these compounds.

Occupational Exposure

Occupational Handler Exposure

The active ingredient 2,4-D, including its choline, sodium, and amine salts, and esters are

herbicides registered for preplant, preemergence, postemergence or preharvest use a variety of 

agricultural crops. Formulations include wettable powder, liquid, and granule formulations. 

Occupational handler exposure scenarios include mixing/loading all formulations; applying 

formulations by aerial, groundboom, airblast, or handheld equipment; mixing/loading/applying 

with handheld equipment; flagging; and applying product to submersed and floating aquatic 

weeds. Short- and intermediate-term occupational handler scenarios for all formulations, 

application rates and application methods have been previously assessed in the 2005 RED. 

Combined (dermal and inhalation) risk estimates (MOEs) ranged from >1 to >1000 for 

mixing/loading scenarios, from 78 to >1000 for applicators, from 500 to >1000 for 

mixer/loader/applicators, and 210 to >1000 for flaggers, depending on exposure scenario and 

level of PPE. The short-term and intermediate-term MOEs for all occupational handler scenarios 

except wettable powders exceeded the LOC of 100 with baseline or single-layer PPE and are not 

of concern. The MOEs for handling wettable powders were acceptable with engineering controls 

(i.e. water-soluble bags).

Recommended unit exposures for occupational handler assessments have generally been derived 

only from the Pesticide Handlers Exposure Database (PHED). However, recently both the 

Outdoor Residential Exposure Task Force (ORETF) and the Agricultural Handler Exposure Task 

Force (AHETF) have produced pesticide handler exposure monitoring data that the Agency is 

using in place of PHED (http://www.epa.gov/pesticides/science/handler-exposure-data.html). As 

more reliable data become available, the Agency will continue to replace existing data. 

Reviewers will incorporate new exposure monitoring data, as necessary, during registration 

review.

An updated occupational handler assessment may be required under registration review if 

warranted by any significant changes in exposure assessment methodology, toxicological points 

of departure, or uncertainty factors.

Occupational Post-application Exposure
Page 14 of 36

Occupational post-application dermal exposure is possible from post-emergent, broadcast foliar 

uses. Pre-emergent, ground directed uses would not result in significant occupational postapplication exposure. 

A short- and intermediate-term occupational post-application exposure assessment was 

completed in the 2005 RED; only uses resulting in significant foliar residue (not minimal 

exposure due to application timing or method) and post-application activities applicable based on 

application timing were assessed; uses likely to have limited exposure potential due to 

application timing or method were not assessed. Chemical-specific turf transferrable residue 

(TTR) data are available for 2,4-D and were used for the occupational post-application exposure 

assessment for turf uses. Chemical-specific dislodgeable foliar residue (DFR) data were not 

available for 2,4-D; default dislodgeable residue inputs were used for foliar post-application 

exposure scenarios. All assessed short- and intermediate-term post-application scenarios were 

not of concern (MOEs > LOC of 100). Post-application dermal short-term MOEs using 

maximum application rates ranged from 210 to 17,000; intermediate-term MOEs using average 

application rates ranged from 300 to 13,000.

Recommended transfer coefficients for occupational post-application assessments are derived 

from Agricultural Reentry Task Force (ARTF) exposure monitoring studies

(http://www.epa.gov/pesticides/science/post-app-exposure-data.html). These transfer 

coefficients have been updated in 2012 based on a reanalysis and submission of new monitoring 

data. Reviewers will incorporate new exposure monitoring data, as necessary, during 

registration review.

Volatilization of pesticides may be a potential source of post-application inhalation exposure to 

individuals nearby pesticide applications. A quantitative post-application inhalation exposure 

assessment for field volatilization of 2,4-D and its formulations has not been performed and may 

be necessary under registration review. The Agency sought expert advice and input on issues 

related to volatilization of pesticides from its Federal Insecticide, Fungicide, and Rodenticide Act 

(FIFRA) Scientific Advisory Panel (SAP) in December 2009. The Agency received the SAP’s 

final report on March 2, 2010 

(http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html). 

In accordance with the updated Part 158 data requirements (2007), one or more DFR studies are 

required when a pesticide has residential or occupational uses that could result in postapplication dermal exposure. As part of the recent revision to the Health Effects Division’s 2012 

Standard Operating Procedures for Residential Pesticide Exposure Assessment, HED analyzed a 

number of DFR studies and selected a new default value for the fraction of the application rate 

available to be dislodged after a foliar application (FAR). This default value is 25%. Of the 

analyzed DFR studies, the maximum FAR value seen was 89% or 3.6 times higher than the 

default residue transfer value. Therefore, a calculated MOE of approximately 4 times higher 

than the LOC, i.e. an MOE > 400 if the LOC = 100, using the default dislodged residue value 

would provide an adequate margin of safety for any potentially higher residues seen in a 

chemical-specific DFR study (Guidance for Requiring/Waiving Turf Transferrable Residue 

(TTR) and Dislodgeable Foliar Residue (DFR) Studies. 6/7/2012, Exposure Science Advisory 
Page 15 of 36

Council). Based on a screening level assessment, although some of the dermal post-application 

MOEs for 2,4-D were less than 4x the LOC (<400), there are no risks of concern; chemical 

specific DFR data are not being required at this time. Because of the conservative nature of the 

dermal endpoint and point of departure selected for 2,4-D, the MOEs calculated using default 

DFR data in the previous dermal assessments may be considered very conservative; there are no 

dermal risks of concern for 2,4-D when using the default DFR data.

An updated post-application occupational assessment may be required under registration review 

if warranted by any significant changes in exposure assessment methodology, toxicological 

endpoints or points of departure, or uncertainty factors.

Restricted Entry Interval (REI)

The WPS Restricted Entry Interval (REI) for 2,4-D is 12 hours for the ester and sodium salt 

forms and is 48 hours for the acid and amine salt forms.

All forms of 2,4-D are Acute Toxicity Category III or IV for acute dermal, inhalation and oral 

toxicity and primary skin irritation. The acid and amine salt forms of 2,4-D Toxicity Category I 

for primary eye irritation; therefore, based on the acute toxicity category the acid and amine salt 

forms of 2,4-D, a restricted entry interval (REI) of 48 hours is required under the Worker 

Protection Standard (WPS). The ester forms are toxicity Category III or IV for primary eye 

irritation; therefore a 12 hour REI is appropriate under WPS. For 2,4-D end use products where 

other active ingredients are included, the acute toxicity profile of the other ingredients should be 

checked to ensure the label lists the appropriate REI.

Conclusions: The occupational exposure database is complete for 2,4-D. There were no 

occupational handler or post-application exposure estimates of concern. A quantitative

occupational post-application inhalation exposure assessment for 2,4-D, including assessment of 

volatilization, may be necessary under registration review. An updated handler assessment and a 

dermal post-application assessment may also be necessary if warranted by any significant 

changes in exposure assessment methodology, toxicological points of departure, or uncertainty 

factors. 

Public Health and Pesticide Epidemiology Data

HED has evaluated the OPP Incident Data System (IDS) and the publications from the 

Agricultural Health Study (AHS). In general, there were few incidents reported for 2,4-D as a 

single chemical only, but there is a high absolute number of incidents reported involving 2,4-D 

with another active ingredient. Although vast majority of these incidents were of low severity, 

several high severity outcomes are reported in the IDS database. It is important to note that since 

most of these reported incidents involve more than one active ingredient (i.e. 2,4-D and another 

active ingredient), the incidents that were reported were not necessarily attributable to 2,4-D. 

Further, while incident information can be an important source of feedback to the Agency, 

reports of adverse health effects allegedly due to a specific pesticide exposure (i.e., an 

“incident”) are largely self-reported and therefore, generally speaking, neither exposure to a 

pesticide or reported symptom (or the connection between the two) is validated or otherwise 
Page 16 of 36

confirmed. Typically, causation cannot be determined based on incident data. Nevertheless, 

based on the absolute number of incidents and the few high severity outcomes that are reported, 

these incident data warrant further analysis in the preliminary risk assessment phase of 

Registration Review. Obtaining additional information on current usage data for 2,4-D would 

improve future assessments. Additionally, any follow-up studies from the AHS will be 

evaluated if available at the time of the risk assessment.

Tolerance Assessment and International Harmonization

Tolerances are established for residues of 2,4-D in a variety of food and feed, fish, and livestock 

commodities [40 CFR §180.142(a), (c) and (d)]. The residue of concern for tolerance 

enforcement and risk assessment (plants and livestock) is 2,4-D, both free and conjugated, 

determined as the acid. Adequate analytical methodology is available for data collection and 

2,4-D tolerance enforcement purposes. 

The U.S. tolerance definition is expressed as “2,4-D (2,4-dichlorophenoxyacetic acid), both free 

and conjugated, determined as the acid”. The definition for Canada is “(2,4-dichlorophenoxy) 

acetic acid” and for Codex is “2,4-D”. A summary of the U.S. tolerances, and Canadian and 

Codex MRLs is presented in Appendix 6. Canadian MRLs are harmonized with the US 

tolerance levels, with the exception of citrus. Several of the U.S. tolerances are harmonized with 

Codex MRLs, but there are many that are not harmonized. During registration review the 

Agency will further evaluate the tolerance levels to determine if they can be harmonized with 

Codex and/or Canada. 

Environmental Justice

Potential areas of environmental justice concerns, to the extent possible, were considered in the 

most recent human health risk assessment, in accordance with U.S. Executive Order 12898, 

"Federal Actions to Address Environmental Justice in Minority Populations and Low-Income 

Populations," http://www.epa.gov/fedreg/eo/eo12898.htm. The Office of Pesticide Programs 

(OPP) typically considers the highest potential exposures from the legal use of a pesticide when 

conducting human health risk assessments, including, but not limited to, people who obtain 

drinking water from sources near agricultural areas, the variability of diets within the U.S. 

(including different ages, regions, and ethnicities), and people who may be exposed when 

harvesting crops. Should these highest exposures indicate potential risks of concern, OPP further 

refines the risk assessments to ensure that the risk estimates are based on the best available 

information.

Human Studies

Past 2,4-D risk assessments rely in part on data from studies in which adult human subjects were 

intentionally exposed to a pesticide to determine their dermal and inhalation exposure. Many 

such studies, involving exposure to many different pesticides, comprise generic pesticide 

exposure databases such as the PHED, the Agricultural Reentry Task Force (ARTF) Database, 

and the Outdoor Residential Exposure Task Force (ORETF) Database. EPA has reviewed all the 

studies supporting these multi-pesticide generic exposure databases, and has found no clear and 
Page 17 of 36

convincing evidence that the conduct of any of them was either fundamentally unethical or 

significantly deficient relative to the ethical standards prevailing at the time the research was 

conducted. All applicable requirements of EPA’s Rule for the Protection of Human Subjects of 

Research (40 CFR Part 26) have been satisfied, and there is no regulatory barrier to continued 

reliance on these studies.

A human dermal absorption (in vivo) study (Maibach and Feldman, 1974) was considered for 

determining the dermal absorption factor in previous 2,4-D risk assessments. EPA has reviewed 

this study and determined that there was no clear evidence that the conduct was fundamentally 

unethical (J. Carley, 2006). 

Endocrine Disruption

EPA has received all required final study reports and data from the Tier 1 battery of tests for 

2,4-D. EPA waived the in vivo mammalian Tier 1 tests for 2,4-D due to the availability of a 

newly-submitted extended one generation reproduction study with 2,4-D. The submitted EDSP 

Tier 1 tests will be considered with regard to potential environmental effects and the need for 

Tier 2 in vivo studies for effects in wildlife. Although the submitted Tier 1 in vitro studies may 

inform EPA on mechanistic issues in mammalian systems (e.g., whether 2,4-D can bind to the 

estrogen or androgen receptor in mammals), the studies will not affect EPA’s conclusions on 

the quantitative endocrine risks posed by 2,4-D for humans given the availability of the 

extended one-generation reproduction study (an in vivo study in rats) that comprehensively 

examined the risks to human health from 2,4-D’s interaction with endocrine system endpoints. 

Data Requirements

None

References

S. Recore, 9/4/12, 2,4-D: Review of Human Incidents, D403874.

L. Taylor et al, 3/27/12, 2, 4-D: Revised Evaluation of Data Identified in NRDC Petition and 

Associated Documents, D392844.

A.LaMay et al., 2/22/12, Amended Petition for the Establishment of a New Formulation of 2,4-D 

Choline on Herbicide Tolerant Field Corn Containing the Aryloxyalkanoate Dioxygenase-1 

(ADD-1) Gene, D398209.

T. Goodlow, 10/18/07, 2,4-D: HED Response to Wheat Hay Waiver Request, D340921. 

T. Goodlow, 4/16/07, 2,4-D: HED Response to Irrigated Crop Waiver Request, D336596.

J. Carley, 7/27/06, Initial Ethics Review of Study of Percutaneous Penetration of Several 

Pesticides .
Page 18 of 36

USEPA, June 2005, Reregistration Eligibility Decision for 2,4-D.

T. Dole et al, 5/12/2005, 2,4-D. HED’s Revised Human Health Risk Assessment for the 

Reregistration Eligibility Decision (RED) Revised to Reflect Public Comments, D316597.

T. Jimerson, 4/18/05, 2,4-D. Revised Acute and Chronic Dietary Exposure Assessments 

Including Proposed New Uses Hops and Potatoes for the Reregistration Eligibility Decision, 

D315512.

T. Jimerson, 10/13/04, 2,4-D: Health Effects Division (HED) Metabolism Assessment Review 

Committee (MARC) Decision Document-Revised. DP Barcodes D309452 Chemical I.D. No. 

030001. Case No. 0073. Meeting date: 9/3/03. TXR No. 0052264

Maibach, HI; Feldman, RJ. (1974) Systemic absorption of pesticides through the skin of man. 

In: Occupational Exposure to Pesticides: Report to the Federal Working Group on Pest 

Management from the Task Group on Occupational Exposures to Pesticides. Appendix B. US 

Government Printing Office, 0-551-026, Washington, DC, pp120-127. MRID 46859102.
Page 19 of 36

Appendix 1

2,4-D ACTIVE INGREDIENTS IN CASE NO. 0073

Active ingredient name PC code

2,4-D acid 030001

2,4-D sodium salt 030004

2,4-D diethanolamine salt 030016 

2,4-D, dimethylamine salt 030019 

2,4-D, isopropylamine salt 030025

2,4-D, triisopropanolamine salt 030035

2,4-D, butoxyethyl ester or

2,4-D, butoxyethanol ester

030053

2,4-D, 2-ethylhexyl ester 030063

2,4-D, isooctyl (2-ethyl-4-methylpentyl) ester 030064

2,4-D, isooctyl (2-octyl) ester 030065*

2,4-D, isopropyl ester 030066 

2,4-D choline salt (choline) 051505

*No currently registered products
Page 20 of 36

Appendix 2

The chemical structure and physiochemical properties of 2,4-D acid is found in Table A2.1 and 

A2.2 below.

TABLE A2.1. Compound Nomenclature.

Compound

Common name 2,4-D

IUPAC name (2,4-dichlorophenoxy)acetic acid

CAS name 2,4-dichlorophenoxy acetic acid

CAS registry number 94-75-7

TABLE A2.2. Physicochemical Properties of Technical Grade 2,4-D.

Parameter Value Reference

Melting point/range 138-141 °C Revised Product Chemistry Chapter of the 

2,4-D RED (DP# 309451, 10/12/04, T. 

Jimerson)

pH 2.7 at 25 °C DP# 167302, 9/25/91, R. Perfetti

Density 1.416 at 25 °C (specific gravity) Revised Product Chemistry Chapter of the 

2,4-D RED (DP# 309451, 10/12/04, T. 

Jimerson)

Water solubility 569 mg/L (20 °C)

Solvent solubility g/100 g (25 °C)

acetone 85.0

benzene 1.07

diethyl ether 220

ethanol 130

isopropanol 31.6

toluene 0.067

xylene 0.58

Vapor pressure 1.4 x 10-7 mm Hg (25 °C)

Dissociation constant, pKa 3.0 at 25.2 °C DP#s 186542 & 190622, 6/1/93, W. Smith

Octanol/water partition coefficient, 

Log(KOW)

2.14 at pH 5; 0.177 at pH 7; 0.102 at pH 9

(0.001 M solution)

Revised Product Chemistry Chapter of the 

2,4-D RED (DP# 309451, 10/12/04, T. 

Jimerson)

UV/visible absorption spectrum Maxima at 208, 228.3 and 283.3 nm RD Memo DP# 245940, 6/9/98, S. Mathur

O

Cl Cl

OH

O
Page 21 of 36

Appendix 3 

Toxicological Doses and Endpoints for 2,4-D

Table A3.1. Summary of Current Toxicological Doses and Endpoints for 2,4-D for Use in Dietary and NonOccupational Human Health Risk Assessments

Exposure/ 

Scenario

Point of 

Departure

Uncertainty/FQPA 

Safety Factors

RfD, PAD, 

Level of 

Concern for 

Risk 

Assessment

Study and Toxicological Effects

Acute Dietary 

(General 

Population, 

including 

Infants and 

Children)

NOAEL= 

67 

mg/kg/day

UFA= 10x

UFH= 10x

FQPA SF= 1x

Acute RfD = 

0.67 

mg/kg/day

aPAD = 0.67 

mg/kg/day

Acute Neurotoxicity - Rat

LOAEL = 227 mg/kg/day, based on gait 

abnormalities

Acute Dietary

(Females 13-

49 years of 

age)

NOAEL = 

25 

mg/kg/day

UFA= 10x

UFH= 10x

FQPA SF= 1x

Acute RfD = 

0.25 

mg/kg/day

cPAD = 0.25 

mg/kg/day

Developmental Toxicity - Rat

LOAEL = 75 mg/kg/day, based on fetal 

skeletal abnormalities

Chronic 

Dietary (All 

Populations)

NOAEL= 5 

mg/kg/day

UFA= 10x

UFH= 10x

FQPA SF = 1x

Chronic RfD 

= 0.05 

mg/kg/day

cPAD = 0.05 

mg/kg/day

Combined Chronic 

Toxicity/Carcinogenicity- Rat 

LOAEL = 75 mg/kg/day, based on 

decreased body-weight gain (females) and 

food consumption (females), alterations in 

hematology [decreased RBC, HCT, and 

HGB (females), platelets (both sexes)] and 

clinical chemistry parameters [increased 

creatinine (both sexes), alanine and 

aspartate aminotransferases (males), 

alkaline phosphatase (both sexes), 

decreased T4 (both sexes), glucose 

(females), cholesterol (both sexes), and 

triglycerides (females)], increased thyroid 

weights (both sexes at study termination), 

and decreased testes and ovarian weights .

Incidental Oral 

Short-Term 

(1-30 days)

NOAEL= 

25 

mg/kg/day

UFA= 10x

UFH= 10x

FQPA SF= 1x

Residential 

LOC for 

MOE = 100

Developmental toxicity - Rat

LOAEL = 75 mg/kg/day based, on 

decreased maternal body weight gain

Incidental Oral 

IntermediateTerm (1-6 

months)

NOAEL= 

15 

mg/kg/day

UFA= 10x

UFH= 10x

FQPA SF= 1x

Residential 

LOC for 

MOE = 100

Subchronic Oral Toxicity - Rat

LOAEL = 100 mg/kg/day based on 

decreased body weight/body-weight gain, 

alterations in some hematology [decreased 

platelets (both sexes)] and clinical 

chemistry [decreased T3 (females) and T4 

(both sexes)] parameters, and cataract 

formation.
Page 22 of 36

Table A3.1. Summary of Current Toxicological Doses and Endpoints for 2,4-D for Use in Dietary and NonOccupational Human Health Risk Assessments

Exposure/ 

Scenario

Point of 

Departure

Uncertainty/FQPA 

Safety Factors

RfD, PAD, 

Level of 

Concern for 

Risk 

Assessment

Study and Toxicological Effects

Dermal ShortTerm (1-30 

days)

NOAEL= 

25 

mg/kg/day

UFA= 10x

UFH= 10x

FQPA SF= 1x

Residential 

LOC for 

MOE = 100

Rat developmental toxicity study

LOAEL = 75 mg/kg/day based, on 

decreased maternal body weight gain and 

the increased incidence of skeletal 

malformations and variations

Dermal 

IntermediateTerm (1-6 

months)

NOAEL= 

15 

mg/kg/day

UFA= 10x

UFH= 10x

FQPA SF= 1x

Residential 

LOC for 

MOE = 100

Subchronic oral toxicity study in rats

LOAEL = 100 mg/kg/day based on 

decreased body weight/body-weight gain, 

alterations in some hematology [decreased 

platelets (both sexes)] and clinical 

chemistry [decreased T3 (females) and T4 

(both sexes)] parameters, and cataract 

formation.

Dermal LongTerm (>6 

months)

NOAEL= 5 

mg/kg/day

UFA= 10x

UFH= 10x

FQPA SF = 1x

Residential 

LOC for 

MOE = 100

Rat chronic oral toxicity study in rats 

LOAEL = 75 mg/kg/day, based on 

decreased body-weight gain (females) and 

food consumption (females), alterations in 

hematology [decreased RBC, HCT, and 

HGB (females), platelets (both sexes)] and 

clinical chemistry parameters [increased 

creatinine (both sexes), alanine and 

aspartate aminotransferases (males), 

alkaline phosphatase (both sexes), 

decreased T4 (both sexes), glucose 

(females), cholesterol (both sexes), and 

triglycerides (females)], increased thyroid 

weights (both sexes at study termination), 

and decreased testes and ovarian weights .

Inhalation 

Short- Term 

(1-30 days)

NOAEL= 

25 

mg/kg/day

UFA= 10x

UFH= 10x

FQPA SF= 1x

Residential 

LOC for 

MOE = 100

Developmental toxicity - Rat

LOAEL = 75 mg/kg/day based, on 

decreased maternal body weight gain

Inhalation 

IntermediateTerm (1-6 

months)

NOAEL= 

15 

mg/kg/day

UFA= 10x

UFH= 10x

FQPA SF= 1x

Residential 

LOC for 

MOE = 100

Subchronic Oral toxicity - Rat

LOAEL = 100 mg/kg/day based on 

decreased body weight/body-weight gain, 

alterations in some hematology [decreased 

platelets (both sexes)] and clinical 

chemistry [decreased T3 (females) and T4 

(both sexes)] parameters, and cataract 

formation.
Page 23 of 36

Table A3.1. Summary of Current Toxicological Doses and Endpoints for 2,4-D for Use in Dietary and NonOccupational Human Health Risk Assessments

Exposure/ 

Scenario

Point of 

Departure

Uncertainty/FQPA 

Safety Factors

RfD, PAD, 

Level of 

Concern for 

Risk 

Assessment

Study and Toxicological Effects

Inhalation 

Long-Term 

(>6 months)

NOAEL= 5 

mg/kg/day

UFA= 10x

UFH= 10x

FQPA SF = 1x

Residential 

LOC for 

MOE = 100

Combined Chronic Toxicity/ 

Carcinogenicity - Rats 

LOAEL = 75 mg/kg/day, based on 

decreased body-weight gain (females) and 

food consumption (females), alterations in 

hematology [decreased RBC, HCT, and 

HGB (females), platelets (both sexes)] and 

clinical chemistry parameters [increased 

creatinine (both sexes), alanine and 

aspartate aminotransferases (males), 

alkaline phosphatase (both sexes), 

decreased T4 (both sexes), glucose 

(females), cholesterol (both sexes), and 

triglycerides (females)], increased thyroid 

weights (both sexes at study termination), 

and decreased testes and ovarian weights .

Cancer (oral, 

dermal, 

inhalation)

Classification: Group D - Not Classifiable as to Human Carcinogenicity. That is, the 

evidence is inadequate and cannot be interpreted as showing either the presence or 

absence of a carcinogenic effect. 

Point of Departure (POD) = A data point or an estimated point that is derived from observed dose-response data and 

used to mark the beginning of extrapolation to determine risk associated with lower environmentally relevant human 

exposures. NOAEL = no observed adverse effect level. LOAEL = lowest observed adverse effect level. UF = 

uncertainty factor. UFA = extrapolation from animal to human (interspecies). UFH = potential variation in 

sensitivity among members of the human population (intraspecies). FQPA SF = FQPA Safety Factor. PAD = 

population adjusted dose (a = acute, c = chronic). RfD = reference dose. MOE = margin of exposure. LOC = level 

of concern. N/A = not applicable.

Table A3.2. Summary of Toxicological Doses and Endpoints for 2,4-D for Use in Occupational Human 

Health Risk Assessments

Exposure/ 

Scenario

Point of 

Departure

Uncertainty 

Factors

Level of Concern 

for Risk 

Assessment

Study and Toxicological Effects

Dermal ShortTerm (1-30 

days)*

NOAEL= 

25 

mg/kg/day

UFA=10x

UFH=10x

Occupational 

LOC for MOE = 

100

Rat developmental toxicity study

LOAEL = 75 mg/kg/day based, on 

decreased maternal body weight gain and 

the increased incidence of skeletal 

malformations and variations
Page 24 of 36

Table A3.2. Summary of Toxicological Doses and Endpoints for 2,4-D for Use in Occupational Human 

Health Risk Assessments

Exposure/ 

Scenario

Point of 

Departure

Uncertainty 

Factors

Level of Concern 

for Risk 

Assessment

Study and Toxicological Effects

Dermal 

IntermediateTerm (1-6 

months)*

NOAEL= 

15 

mg/kg/day

UFA=10x

UFH=10x

Occupational 

LOC for MOE = 

100

Subchronic oral toxicity study in rats

LOAEL = 100 mg/kg/day based on 

decreased body weight/body-weight gain, 

alterations in some hematology [decreased 

platelets (both sexes)] and clinical 

chemistry [decreased T3 (females) and T4 

(both sexes)] parameters, and cataract 

formation.

Dermal LongTerm (>6 

months) *

NOAEL=5 

mg/kg/day

UFA=10x

UFH=10x

Occupational 

LOC for MOE = 

100

Rat chronic oral toxicity study in rats 

LOAEL = 75 mg/kg/day, based on 

decreased body-weight gain (females) and 

food consumption (females), alterations in 

hematology [decreased RBC, HCT, and 

HGB (females), platelets (both sexes)] and 

clinical chemistry parameters [increased 

creatinine (both sexes), alanine and 

aspartate aminotransferases (males), 

alkaline phosphatase (both sexes), 

decreased T4 (both sexes), glucose 

(females), cholesterol (both sexes), and 

triglycerides (females)], increased thyroid 

weights (both sexes at study termination), 

and decreased testes and ovarian weights .

Inhalation 

Short-Term (1-

30 days)*

NOAEL= 

25 

mg/kg/day

UFA=10x

UFH=10x

Occupational 

LOC for MOE = 

100

Rat developmental toxicity study

LOAEL = 75 mg/kg/day based, on 

decreased maternal body weight gain

Inhalation 

Intermediateterm (1-6 

months)*

NOAEL=15 

mg/kg/day

UFA=10x

UFH=10x

Occupational 

LOC for MOE = 

100

Subchronic oral toxicity study in rats

LOAEL = 100 mg/kg/day based on 

decreased body weight/body-weight gain, 

alterations in some hematology [decreased 

platelets (both sexes)] and clinical 

chemistry [decreased T3 (females) and T4 

(both sexes)] parameters, and cataract 

formation.
Page 25 of 36

Table A3.2. Summary of Toxicological Doses and Endpoints for 2,4-D for Use in Occupational Human 

Health Risk Assessments

Exposure/ 

Scenario

Point of 

Departure

Uncertainty 

Factors

Level of Concern 

for Risk 

Assessment

Study and Toxicological Effects

Inhalation 

Long-Term (>6 

months)*

NOAEL=5 

mg/kg/day

UFA=10x

UFH=10x

Occupational 

LOC for MOE = 

100

Rat chronic oral toxicity study in rats 

LOAEL = 75 mg/kg/day, based on 

decreased body-weight gain (females) and 

food consumption (females), alterations in 

hematology [decreased RBC, HCT, and 

HGB (females), platelets (both sexes)] and 

clinical chemistry parameters [increased 

creatinine (both sexes), alanine and 

aspartate aminotransferases (males), 

alkaline phosphatase (both sexes), 

decreased T4 (both sexes), glucose 

(females), cholesterol (both sexes), and 

triglycerides (females)], increased thyroid 

weights (both sexes at study termination), 

and decreased testes and ovarian weights .

Cancer (oral, 

dermal, 

inhalation)

Classification: Group D (not classifiable as to human carcinogenicity)

*The dermal absorption factor is 10 percent and the inhalation absorption factor is 100 percent. 

Point of Departure (POD) = A data point or an estimated point that is derived from observed dose-response data and 

used to mark the beginning of extrapolation to determine risk associated with lower environmentally relevant human 

exposures. NOAEL = no observed adverse effect level. LOAEL = lowest observed adverse effect level. UF = 

uncertainty factor. UFA = extrapolation from animal to human (interspecies). UFH = potential variation in 

sensitivity among members of the human population (intraspecies). MOE = margin of exposure. LOC = level of 

concern. N/A = not applicable.
Page 26 of 36

Appendix 4

Toxicology Data Requirements

The toxicology data requirements (40 CFR 158.340) for the food uses of 2,4-D are presented below. Use of the new 

guideline numbers does not imply that the new (1998) guideline protocols were used.

Study

Technical

Required Satisfied

870.1100 Acute Oral Toxicity.......................................................

870.1200 Acute Dermal Toxicity ..................................................

870.1300 Acute Inhalation Toxicity..............................................

870.2400 Primary Eye Irritation....................................................

870.2500 Primary Dermal Irritation ..............................................

870.2600 Dermal Sensitization......................................................

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

870.3100 Oral Subchronic (rodent)...............................................

870.3150 Oral Subchronic (nonrodent) .........................................

870.3200 21-Day Dermal ..............................................................

870.3250 90-Day Dermal ..............................................................

870.3465 90-Day Inhalation..........................................................

yes

yes

yes

no

yes

yes

yes

yes

-

yesA

870.3700a Developmental Toxicity (rodent)...................................

870.3700b Developmental Toxicity (nonrodent).............................

870.3800 Reproduction .................................................................

yes

yes

yes

yes

yes

yes

870.4100a Chronic Toxicity (rodent) ..............................................

870.4100b Chronic Toxicity (nonrodent)........................................

870.4200a Oncogenicity (rat)..........................................................

870.4200b Oncogenicity (mouse)....................................................

870.4300 Chronic/Oncogenicity....................................................

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

870.5100 Mutagenicity—Gene Mutation – bacterial ....................

870.5375 Mutagenicity—Structural Chromosomal Aberrations...

870.5550 Mutagenicity—Other Genotoxic Effects.......................

yes

yes

yes

yes

yes

yes

870.6100a Acute Delayed Neurotoxicity (hen)...............................

870.6100b 90-Day Neurotoxicity (hen)...........................................

870.6200a Acute Neurotoxicity Screening Battery (rat) .................

870.6200b 90-Day Neurotoxicity Screening Battery (rat)...............

870.6300 Develop. Neurotoxicity .................................................

no

no

yes

yes

yes

-

-

yes

yes

yes

870.7485 General Metabolism ......................................................

870.7600 Dermal Penetration ........................................................

870.7800 Immunotoxicity .............................................................

yes

no

yes

yes

yes

yes

Special Studies: Extended One-Generation Reproductive Toxicity 

(rat)

yes yes

A

28-day 
Page 27 of 36

Appendix 5 

Table A5.1. Acute Toxicity Data on 2,4-D.

Table A5.2. Subchronic, Chronic and Other Toxicity Profile – 2,4-D

Guideline 

No. 

Study Type MRID No. (year)/ 

Classification /Doses

Results

870.3100 90-Day oral 

toxicity (Fischer

344 rats)

MRID 41991501 (1991)

Acceptable/Guideline

0, 1, 15, 100, 300

mg/kg/day

NOAEL = 15 mg/kg/day

LOAEL = 100 mg/kg/day, based on decreases 

body weight/gain, alterations in hematology

and clinical chemistry parameters, and cataract

formation in females.

At HDT, effects listed above occurred more

frequently and/or to a greater extent, as well as 

histopathological lesions in eyes, liver, testes, 

adrenals, kidneys, thymus, bone marrow,

spleen, thyroids, lungs.

870.3150 Subchronic oral

(capsule) toxicity -

dogs

MRID 41737301 (1990)

Acceptable/Guideline

0, 0.3, 1.0, 3.0, and 10

mg/kg/day]

NOAEL = 1 mg/kg/day

LOAEL = 3 mg/kg/day, based on decreased 

body weight/body-weight gain and food

consumption (males), alterations in clinical

chemistry parameters [increased BUN (both

sexes), creatinine (males)], and decreased testis

weight in males. At the highest dose tested,

mortality (2 males, 1 female sacrificed

moribund), hematology alterations, and 

microscopic lesions of the kidneys and testes 

[hypospermatogenesis] were observed.

Guideline

No. Study Type MRID #(S) Results Toxicity Category

870.1100 Acute Oral 00101605 rat LD50 = 699 mg/kg III

870.1200 Acute Dermal 00101596 rabbits LD50 >2000 mg/kg III

870.1300 Acute Inhalation 00161660 rat LC50 >1.79 mg/L III

870.2400 Primary Eye Irritation 41125302 severe eye irritant I

870.2500 Primary Skin Irritation 42232701 non-irritating IV

870.2600 Dermal Sensitization 00161659 not a dermal sensitizer -
Page 28 of 36

Table A5.2. Subchronic, Chronic and Other Toxicity Profile – 2,4-D

Guideline 

No. 

Study Type MRID No. (year)/ 

Classification /Doses

Results

870.3150 Subchronic oral

(diet) toxicity (dog)

MRID 42780001 (1993)

Acceptable/Guideline

0, 0.5, 1.0, 3.75, and 7.5

mg/kg/day 

NOAEL = 1 mg/kg/day

LOAEL = 3.75 mg/kg/day, based on 

decreased body-weight gain (both sexes) and

food consumption (males), as well as

alterations in clinical chemistry parameters

[increased BUN, creatinine, and alanine 

aminotransferase] in both sexes, and decreased

testes weight and slightly higher incidence of

hypospermatogenesis/juvenile testis and

inactive/juvenile prostate were observed.

870.3200 21-Day dermal 

toxicity (rabbit)

MRID 41735301, 41735304 

(1990)

Acceptable/Guideline

0, 10, 100, 1000 mg/kg/day

NOAEL = 1000 mg/kg/day

LOAEL > 1000 mg/kg/day, no adverse 

effects observed at the limit dose

870.3465 90-Day inhalation 

toxicity (Sprague 

Dawley CD®)

6 hr/day, 5 

days/week for 28 

days

MRID 47398701 (2008)

Acceptable/Guideline

0, 0.05, 0.1, 0.3, 1.0 mg/L

Systemic NOAEL = 0.30 mg/L/day

Systemic LOAEL = 1.0 mg/L/day based on 

increased alkaline phosphatase and aspartate 

aminotransferase levels in females and 

decreased spleen weights in females. 

NOAEL (portal-of-entry effects) = not 

determined.

LOAEL (portal-of-entry effects) = 0.05 

mg/L/day, based on squamous metaplasia and 

epithelial hyperplasia with increased mixed 

inflammatory cells within the larynx; not totally 

resolved following a 4-week recovery period. 

870.3700a Developmental 

toxicity

Fischer 344 rats

(GD 6-15)

MRID 00130407, 00130408 

(1983)

Acceptable/Guideline

0, 8, 25, and 75 mg/kg/day

Maternal NOAEL = 25 mg/kg/day

Maternal LOAEL = 75 mg/kg/day, based on

decreased body weight gains. Survival was not 

affected by treatment.

Developmental NOAEL = 25 mg/kg/day

Developmental LOAEL = 75 mg/kg/day,

based on skeletal variations.

870.3700b Prenatal 

developmental in 

(New Zealand white 

rabbit)

GD 6-18

MRID 41747601 [1990]

Acceptable/Guideline

0, 10, 30, and 90 mg/kg/day

Maternal NOAEL = 30 mg/kg/day

Maternal LOAEL = 90 mg/kg/day, based on 

clinical signs [ataxia, decreased motor activity,

loss of righting reflex, cold extremities], 

abortion (2), decreased body-weight gains. 

Survival was not affected by treatment.

Developmental NOAEL = 30 mg/kg/day

Developmental LOAEL = 90 mg/kg/day, based

on abortions.
Page 29 of 36

Table A5.2. Subchronic, Chronic and Other Toxicity Profile – 2,4-D

Guideline 

No. 

Study Type MRID No. (year)/ 

Classification /Doses

Results

870.3800 Reproduction and 

fertility effects

(Fischer 344 rat)

MRID 00150557 and 

00163996 (19xx)

acceptable/guideline*

*new 870.3800 required 

(see MRID below)

Parental NOAEL = 5 mg/kg/day.

Parental LOAEL = 20 mg/kg/day based on 

decreased female body weight/body weight

gain (F1) and male renal tubule alteration

(F0 and F1). At HDT, excess toxicity and too 

few pups for second litter (dose group 

terminated).

Reproductive NOAEL = 20 mg/kg/day. 

Reproductive LOAEL = 80 mg/kg/day, based 

on increased gestation length.

Offspring NOAEL = 5 mg/kg/day

Offspring LOAEL = 20 mg/kg/day based on 

pup deaths.
Page 30 of 36

Table A5.2. Subchronic, Chronic and Other Toxicity Profile – 2,4-D

Guideline 

No. 

Study Type MRID No. (year)/ 

Classification /Doses

Results

870.3800 Reproduction and 

fertility effects

(Crl:CD(SD) rat)

Extended One 

Generation 

Reproductive 

Toxicity (EOGRT) 

study

47972101 (2010)

acceptable/non-guideline*

*satisfies the requirement 

for a reproduction and 

fertility effects study

Parental (male) systemic NOAEL = 300 ppm (16.6 

mg/kg/day).

Parental (male) systemic LOAEL = 800 ppm (45.3 

mg/kg/day), based on nephrotoxicity manifested as 

increased kidney weights, and degenerative lesions 

in the proximal convoluted tubules in the main study 

P1 rats.

Parental (female) systemic NOAEL = 600 ppm 

(40.2 mg/kg/day). No toxicologically relevant effects 

were identified in P1 females or in the GD 17 

satellite female groups at the highest dose tested.

Thyroid toxicity NOAEL = 800/600 ppm (45.3 

mg/kg/day in males and /40.2 mg/kg/day in females), 

the highest dose tested. The thyroid effects noted in 

the database were considered to be adaptive. 

Offspring (F1 adults) NOAEL = 300 ppm (20.9/ 

mg/kg bw/day in males and 23.3 mg/kg/day in 

females). 

Offspring (F1 adults) LOAEL = 800/600 ppm 

(55.6 mg/kg bw/day in males and 46.7 mg/kg/day in 

females), based on kidney toxicity manifested as 

increased kidney weights and increased incidence of 

degeneration of the proximal convoluted tubules. 

F1 offspring NOAEL = 300 ppm. The dose on a 

mg/kg/day basis for the PND 22 F1 offspring was 

not calculated.

F1 offspring (PND 22) LOAEL = 800/600 ppm, 

based on decreased body weight observed 

throughout lactation. 

DNT offspring NOAEL = 800 ppm/600 ppm (81.7 

mg/kg bw/day in males, 59.2 mg/kg bw/day in 

females), the highest dose tested [lack of evidence of 

DNT (FOB parameters, motor activity, and acoustic 

startle response)]. 

DIT offspring NOAEL = 800/600 ppm (71.8 mg/kg 

bw/day in males and 55.3 mg/kg bw/day in females), 

the highest dose tested [lack of evidence of DIT 

[SRBC antibody-forming cell assay (PND 66-70) 

and Natural Killer Cell assay (PND 87-93)]. 

Reproductive NOAEL = 800/600 ppm (45.3 mg/kg 

bw/day in males, 40.2 mg/kg bw/day in females), the 

highest dose tested [lack of effect on estrous 

cyclicity, (P1 females, satellite GD 17 dams, Set 3 

F1 offspring) or reproductive indices (mating, 

fertility, time to mating, gestation length, pre-and 

post-implantation loss, number of corpora lutea 

(satellite GD 17 dams), sperm parameters, ovarian 

follicle counts, and reproductive organ 

histopathology). 
Page 31 of 36

Table A5.2. Subchronic, Chronic and Other Toxicity Profile – 2,4-D

Guideline 

No. 

Study Type MRID No. (year)/ 

Classification /Doses

Results

870.4100a Chronic toxicity

(Fischer 344 rat)

MRID 43612001 (1995)

MRID 44284501 (19xx)

0, 5, 75, or 150 mg/kg/day

Acceptable/Guideline

NOAEL = 5 mg/kg/day. 

LOAEL = 75 mg/kg/day, based on decreased

body-weight gain (females) and food

consumption (females), alterations in

hematology [decreased RBC (females), HGB 

(females), platelets (both sexes)] and clinical

chemistry parameters [increased creatinine

(both sexes), alanine and aspartate

aminotransferase (males), alkaline

phosphatase (both sexes), decreased T4 (both 

sexes), glucose (females), cholesterol (both

sexes), and triglycerides (females)], increased

thyroid weights (both sexes at study

termination), decreased testes and ovarian 

weights, and microscopic lesions in the lungs

(females). At the high-dose level, there were

microscopic lesions in the eyes, liver, adipose

tissue, and lungs.

There was no treatment-related increase in

the incidence of any tumor.

870.4100b Chronic toxicity 

(Beagle dog)

MRID 43049001 (1993)

Acceptable/Guideline

0, 1, 5, or 7.5/10 

mg/kg/day

NOAEL = 1 mg/kg/day

LOAEL = 5 mg/kg/day, based on decreased

body-weight gain (both sexes) and food

consumption (females), as well as alterations

in clinical chemistry parameters [increased 

BUN, creatinine, and alanine

aminotransferase, decreased glucose] in both

sexes, decreased brain weight in females, and 

histopathological lesions in the liver and

kidneys. At the highest dose tested, 

aspermatogenesis and degeneration of the 

testes was observed in one male and decreased 

brain weight was observed in both sexes.

870.4200 Carcinogenicity

(Fischer 344 rat)

MRID 43612001 (1995)

MRID 44284501 (19xx)

0, 5, 75, or 150 mg/kg/day

Acceptable/Guideline

See under 870.4100a above

870.4300 Carcinogenicity

(B6C3F1 CRL BR 

mouse)

MRID 40061801 (1993)

Acceptable/Non-guideline

0, 1, 15, or 45 mg/kg/day

NOAEL = 1 mg/kg/day

LOAEL = 15 mg/kg/day, based on treatmentrelated increase in kidney weights in both

sexes and microscopic renal lesions in males.

There was no treatment-related increase in

the incidence of any tumor type.

Doses not adequate to assess carcinogenic 

potential.
Page 32 of 36

Table A5.2. Subchronic, Chronic and Other Toxicity Profile – 2,4-D

Guideline 

No. 

Study Type MRID No. (year)/ 

Classification /Doses

Results

870.4300 Carcinogenicity

(B6C3F1 CRL BR 

mouse)

MRID 43879801 (1995)

MRID 43597201(1995)

Acceptable/Guideline

0, 5, 62/150, or 120/300 

mg/kg/day (male/female)

NOAEL = 5 mg/kg/day

LOAEL =62/150 mg/kg/day, based on based

on an increased absolute and/or relative

kidney weights and an increased incidence

of renal microscopic lesions.

There was no treatment-related increase in

the incidence of any tumor type.

870.5100 Salmonella 

typhimurium

TA98, TA100, 

TA1535, Ta1537, 

Ta1538

MRID 41409801(1990)

Acceptable/guideline

100-1000 μg/plate w/ S9;

66.7-6670 μg/plate w/out

S9

No evidence of bacterial mutation w/ and

w/out S9

870.5395 in vivo mouse 

micronucleus assay

ICR mouse (bone 

marrow)

MRID 41409804,

41870101 (1990)

Acceptable/guideline

40-400 μg/kg

Negative.

870.5450 Unscheduled DNA

synthesis assay

MRID 41409807 (1990)

Acceptable/guideline

No evidence of induction of unscheduled

DNA synthesis

Literature 

studies 

cited by 

NRDC

Mutagenicity/

Genotoxicity

(in vivo and in vitro)

NA Office of Pesticide Programs, EPA, 

Reevaluation of the Genetic Toxicology 

Profile of 2,4-D. (December 12, 2011).

870.6200a Acute neurotoxicity 

screening battery

(Fischer 344 rat)

MRID 43115201 (1994)

Acceptable/guideline

0, 15, 75, or 250 

mg/kg/day 

Achieved: 0, 13, 67, or 

227 mg/kg/day

NOAEL = 67 mg/kg.

LOAEL = 227 mg/kg/day, based on an

increased incidence of incoordination and

slight gait abnormalities (described as

forepaw flexing or knuckling) and decreased

total motor activity.

870.6200b Subchronic 

neurotoxicity 

screening battery

(Fischer 344 rat)

MRID 43293901 (1994)

Acceptable/guideline

0, 5, 75, or 150 mg/kg/day 

Males 0, 4.6, 71.2, or 

141.1 mg/kg/day

Females 0, 4.6, 68, 138.9 

mg/kg/day

NOAEL = 71/68 mg/kg/day. 

LOAEL = 141/139 mg/kg/day, based on

increased relative forelimb grip strength and 

increased incidence of bilateral retinal 

degeneration.

870.6300 Developmental 

neurotoxicity

(Crl:CD(SD) rat)

MRID 47972101 (2010)

See under EOGRT

DNT offspring NOAEL = 800 ppm/600 ppm 

(81.7 mg/kg bw/day in males, 59.2 mg/kg 

bw/day in females), the highest dose tested 

[lack of evidence of DNT (FOB parameters, 

motor activity, and acoustic startle response)]. 

870.7485 Metabolism and 

pharmacokinetics

(Fischer 344 rat)

MRID 41737302 (19xx)
Page 33 of 36

Table A5.2. Subchronic, Chronic and Other Toxicity Profile – 2,4-D

Guideline 

No. 

Study Type MRID No. (year)/ 

Classification /Doses

Results

870.7600 Dermal penetration 

(human, male)

Feldman. R. J. and

Maibach, H. I. (1974).

Percutaneous Penetration

of Some Pesticides and 

Herbicides in Man. 

Toxicol. Appl. 

Pharmacol. 28: 126-132].

dermal application was 5.8% ± 2.4%

870.7800 Immunotoxicity

SRBC antibodyforming cell assay and 

Natural Killer Cell 

assay

(Crl:CD(SD) rat)

MRID 47972101 (2010)

See under EOGRT

DIT offspring NOAEL = 800/600 ppm (71.8 

mg/kg bw/day in males and 55.3 mg/kg bw/day 

in females), the highest dose tested [lack of 

evidence of DIT [SRBC antibody-forming cell 

assay (PND 66-70) and Natural Killer Cell 

assay (PND 87-93)]. 
Page 34 of 36

Appendix 6

International Residue Limits: 2,4- D (PC Code 030001; 6/14/12)

TABLE A6. Summary of US and International Tolerances and Maximum Residue Limits 

Residue Definition:

US Canada Mexico1 Codex2

40 CFR 180.142

Plant/Livestock: 2,4-D (2,4-dichlorophenoxyacetic 

acid), both free and conjugated, determined as the 

acid

(2,4-dichlorophenoxy) acetic acid 2,4-D

Commodity Tolerance (ppm) /Maximum Residue Limit (mg/kg)

US Canada Mexico1 Codex2

Almond hulls 0.1

Asparagus 5.0 5.0

Barley, bran 4.0

Barley, grain 2.0

Barley, straw 50

Berry, group 13 0.2 0.1 berries and other 

small fruits

Cattle, fat 0.3

Cattle, kidney 4.0 5 Edible offal 

(mammalian)

Cattle, meat 0.3 0.2 meat from 

mammals other than 

marine mammals)

Cattle, meat byproducts, except kidney 0.3 5 Edible offal 

(mammalian)

Corn, field, forage 6.0

Corn, field, grain 0.05 0.05 field corn 0.05 maize

Corn, field, stover 50 40 maize fodder (dry)

Corn, pop, grain 0.05

Corn, pop, stover 50

Corn, sweet, forage 6.0

Corn, sweet, kernel plus cob with husks 

removed

0.05 0.05 0.05 sweet corn (cornon-the-cob) (*)

Corn, sweet, stover 50

Cranberry 0.5 0.5 0.1 berries and other 

small fruits

Fish 0.1

Fruit, citrus, group 10 3.0 2.0 citrus fruits 1 citrus fruits Po

Fruit, pome, group 11 0.05 0.05 apples, asian pears, 

crabapples, loquats, mayhaws, 

pears, quinces

0.01 pome fruits (*)

Fruit, stone, group 12 0.05 0.05 apricots, nectarines, peaches, 

plumcots, plums, prune plums, 

sweet cherries, tart cherries

0.05 stone fruits (*)

Goat, fat 0.3

Goat, kidney 4.0 5 Edible offal 

(mammalian)

Goat, meat 0.3 0.2 meat from 

mammals other than 

marine mammals)

Goat, meat byproducts, except kidney 0.3 5 Edible offal 

(mammalian)
Page 35 of 36

TABLE A6. Summary of US and International Tolerances and Maximum Residue Limits 

Residue Definition:

US Canada Mexico1 Codex2

Grain, aspirated fractions 40

Grape 0.05 0.1 berries and other 

small fruits

Grass, forage 360

Grass, hay 300

Hop, dried cones 0.2

Horse, fat 0.3

Horse, kidney 4.0 5 Edible offal 

(mammalian)

Horse, meat 0.3 0.2 meat from 

mammals other than 

marine mammals)

Horse, meat byproducts, except kidney 0.3 5 Edible offal 

(mammalian)

Millet, forage 25

Millet, grain 2.0

Millet, straw 50

Milk 0.05 0.01 milks

Nut, tree, group 14 0.2 0.2 tree nuts

Oat, forage 25

Oat, grain 2.0

Oat, straw 50

Pistachio 0.05

Potato 0.4 0.2

Rice, grain 0.5 0.1 rice, husked

Rice, hulls 2.0

Rice, straw 10 10 rice straw and 

fodder, dry

Rye, bran 4.0

Rye, forage 25

Rye, grain 2.0 2 rye

Rye, straw 50

Sheep, fat 0.3

Sheep, kidney 4.0 5 Edible offal 

(mammalian)

Sheep, meat 0.3 0.2 meat from 

mammals other than 

marine mammals)

Sheep, meat byproducts, except kidney 0.3 5 Edible offal 

(mammalian)

Shellfish 1.0

Sorghum, grain, forage 0.2

Sorghum, grain, grain 0.2 0.01 (*)

Sorghum, grain, stover 0.2

Soybean, forage 0.02

Soybean, hay 2.0 0.01 soya bean fodder 

(*)

Soybean, seed 0.02 0.01 soya bean (dry) 

(*)

Strawberry 0.05 0.05

Sugarcane, cane 0.05 0.05 

Sugarcane, molasses 0.2

Teff, bran 4.0

Teff, forage 25.0

Teff, grain 2.0

Teff, straw 50.0
Page 36 of 36

TABLE A6. Summary of US and International Tolerances and Maximum Residue Limits 

Residue Definition:

US Canada Mexico1 Codex2

Vegetable, leaves of root and tuber, 

group 2

0.1

Vegetable, root and tuber, except potato, 

group 1

0.1

Wheat, bran 4.0

Wheat, forage 25

Wheat, grain 2.0 2

Wheat, straw 50 100 wheat straw and 

fodder, dry

(c) Tolerances with regional registrations. Tolerances with regional registration, as defined in §180.1(l), are established for 

residues of the herbicide, plant regulator, and fungicide 2,4-D, including its metabolites and degradates, in or on the commodities 

in the table below. Compliance with the tolerance levels is to be determined by measuring residues of 2,4-D (2,4-

dichlorophenoxyacetic acid), both free and conjugated, determined as the acid, in or on the follow commodities:

Rice, wild, grain 0.05

(d) Indirect or inadvertent residues. Tolerances are established for indirect or inadvertent residues of the herbicide, plant 

regulator, and fungicide 2,4-D, including its metabolites and degradates, in or on the commodities in the table below. Compliance 

with the tolerances levels is to be determined by measuring residues of 2,4-D (2,4-dichlorophenoxyacetic acid), both free and 

conjugated, determined as the acid, in or on the following commodities:

Animal feed, nongrass, group 18 0.2

Avocado 0.05

Cotton, undelinted seed 0.05

Dill, seed 0.05

Okra 0.05

Vegetable, brassica leafy, group 5 0.4

Vegetable, bulb, group 3 0.05

Vegetable, cucurbit, group 9 0.05

Vegetable, foliage of legume, group 7 0.2

Vegetable, fruiting, group 8 0.05

Vegetable, leafy, except brassica, group 

4

0.4

Vegetable, legume, group 6 0.05

MRLs with No US Equivalent

Eggs 0.01 (*)

Hay or fodder (dry) of grasses 400

Poultry meat 0.05 (*)

Poultry, edible offal of 0.05 (*)

Completed: M. Negussie; 06/21/2012

1 Mexico adopts US tolerances and/or Codex MRLs for its export purposes.

2 * = absent at the limit of quantitation; Po = postharvest treatment, such as treatment of stored grains. PoP = processed 

postharvest treated commodity, such as processing of treated stored wheat. (fat) = to be measured on the fat portion of the 

sample. MRLs indicated as proposed have not been finalized by the CCPR and the CAC.