Page 1 of 40

risk assessments and for the purposes of this problem formulation are considered equivalent as well and 

will be referred to collectively here as 2,4-DB unless otherwise noted. 

According to the Office of Pesticide Programs’ (OPP) Reregistration Eligibility Decision (RED) 

document completed in 2005 (USEPA 2005a), EPA has not made a common mechanism of toxicity 

finding for 2,4-DB and any other substances. However, 2,4-DB produces the transformation product 2,4-

D (PC Code 030001), which is a registered active ingredient. Risks posed to the environment from 2,4-D 

are addressed separately in the 2,4-D RED, and will be addressed as part of the currently ongoing 

Registration Review process for 2,4-D. The EFED problem formulation for 2,4-D was drafted in April 

2013 (D402410).

This problem formulation describes the methods planned to be used during the completion of drinking 

water and ecological risk assessments in support of registration review and provides an overview of the 

environmental fate, ecological effects, and potential risks associated with the use of 2,4-DB as well as 

uncertainties unique to risk assessment of 2,4-DB. This document also identifies additional studies that 

would be beneficial to the conduct of an ecological risk assessment. Major findings include:

• The fate database is incomplete based on the environmental fate data requirements outlined in the 

Code of Federal Regulations Title 40 Part 158 (40CFR158) Subpart N1

. Data are needed for 

aerobic soil metabolism (835.4100), aerobic and anaerobic aquatic metabolism (835.4300 & 

835.4400), bioconcentration in fish (850.1730), and environmental chemistry methods (with 

independent laboratory validations; 850.6100). 

• The ecological database is also incomplete based on the ecological effects data requirements 

outlined in the 40CFR158 Subpart G2

. The required studies are listed below. Use of either 2,4-

DB or 2,4-DB-DMAS is adequate to fulfill guideline requirements.

o Data are needed for acute studies on one estuarine/marine mollusk and one 

estuarine/marine shrimp (Guidelines 850.1025, 850.1035, 850.1045, 850.1055). 

o Saltwater invertebrate life cycle (Guideline 850.1350).

o Saltwater and freshwater fish early-life stage (Guideline 850.1400). EFED recommends 

testing on the rainbow trout (Oncorhynchus mykiss) for the freshwater species since this 

species resulted in the lowest 96-hour LC50 among tested species. If the test species for 

this data requirement is different from the species used for the freshwater and 

estuarine/marine fish acute toxicity tests, a 96–hour LC50 on that species must also be 

provided.

o Passerine acute toxicity study. (Guideline 850.2100).

o Avian reproduction study (Guideline 850.2300). An avian reproduction study is required 

for an upland and game bird species.

o Aquatic non-vascular plant (algal toxicity; Guideline 850.4500). Current guidelines 

require a minimum of three species; freshwater green algae, marine diatom, and 

freshwater diatom. The available study (MRID 41407803) only includes the green alga 

Raphidocelis subcapitata (formerly Pseudokirchneriella subcapitata).

o Cyanobacteria toxicity (Guideline 850.4550). Current Part 158 Guideline requirements 

include the cyanobacteria toxicity test in addition to the algal toxicity study previously 

cited.

 1 CFR. 2013. Title 40 (Protection of the Environment), Chapter 1 (Environmental Protection Agency), Subchapter E (Pesticide 

Programs), Part 158 (Data Requirements for Pesticides), Subpart N (Environmental Fate) http://www.ecfr.gov/cgi-bin/textidx?c=ecfr&SID=ff5c7fef3645e7cd5abceca0b597bccb&tpl=/ecfrbrowse/Title40/40cfr158_main_02.tpl

2 CFR. 2013. Title 40 (Protection of the Environment), Chapter 1 (Environmental Protection Agency), Subchapter E (Pesticide 

Programs), Part 158 (Data Requirements for Pesticides), Subpart G (Ecological Effects) http://www.ecfr.gov/cgi-bin/textidx?c=ecfr&SID=ff5c7fef3645e7cd5abceca0b597bccb&rgn=div6&view=text&node=40:25.0.1.1.9.7&idno=40
Page 2 of 40

o EFED has received the following studies and they are currently under review. Once the 

data evaluations are completed, a determination will be made whether they fulfill the 

associated data requirements.

 Acute toxicity with the Sheepshead Minnow (Guideline 850.1075)

 Seedling emergence, Tier II (Guideline 850.4225)

 Vegetative vigor, tier II (Guideline 850.4250)

1. Introduction

The herbicide 2,4-DB is a systemic pesticide and belongs to the chlorophenoxy class of herbicides. It is a 

synthetic plant auxin hormone and has a mode of action like indole acetic acid, a natural plant growth 

regulator that controls the rate of plant growth (USEPA 2013). The compound has been registered for use 

in controlling annual and perennial broadleaf weeds since 1958 (USEPA 2005a). Currently, there are 

seven active Section 3 registrations for 2,4-DB products and 13 active Section 3 registrations for 2,4-DBDMAS. 

EFED evaluated the most recent ecological risk assessments for 2,4-DB in association with any available 

updated toxicity, exposure, and usage information to determine if sufficient data are available and if 

further updates are needed to support Registration Review. Recent risk assessments include the 2004 

EFED risk assessment of 2,4-DB (USEPA 2004a; DP Barcode 291209) in support of the 2,4-DB RED 

(USEPA 2005a). No new uses have been assessed since that time. In addition, EFED considered the 

latest Agency science policies and risk assessment methodologies. 

2. Use Characterization

Based on information provided in the chemical profile created by the OPP Biologic and Economic 

Analysis Division (BEAD; USEPA 2013) for Registration Review, 2,4-DB is formulated as a liquid 

(emulsifiable, flowable or soluble concentrate) in multiple end-use products and can be applied as a 

ground broadcast application or a directed spray by ground or aerial application. The herbicide 2,4-DB is 

used on alfalfa, wheat, clover (pasture), peppermint, spearmint, peanuts, soybeans and birdsfoot trefoil, 

while 2,4-DB-DMAS is used on alfalfa, peanuts, and soybeans; 2,4-DB and 2,4-DB-DMAS have no nonagricultural use sites registered. The Screening Level Usage Analysis (SLUA; USEPA 2012b) conducted 

by BEAD estimates the following agricultural uses during 2003-2010: peanuts at 200,000 lbs acid 

equivalent (a.e.); alfalfa at 60,000 lbs a.e.; pasture at 40,000 lbs a.e.; soybeans at 20,000 lbs a.e.; and 

wheat at 20,000 lbs a.e. Use on peanuts has a percent crop treated range of 40-60%, while the range is 

<1-2.5% for all other crops listed. 

The chemical profile produced by BEAD, located in the docket, lists the use patterns associated with the 

active registrations of 2,4-DB. EFED will rely on the BEAD chemical profile when estimating 

environmental exposures that result from these registered uses. Additionally, in order to be protective, 

EFED will utilize the use information that results in maximum exposure estimates for a given use pattern

for the drinking water and ecological risk assessments. If the labels (and consequently the BEAD 

chemical profile) do not include information needed to estimate exposure, such as the maximum single 

application rate, the application interval, the annual maximum rate allowed (lbs a.i./year), and application 

method, EFED will make conservative assumptions.

One of the major degradates of 2,4-DB, 2,4-D, is a registered phenoxy herbicide and is also one 

of the most highly used herbicides in the US. Since 2,4-D is a major degradate of 2,4-DB, there 

is the potential for increased environmental loading of 2,4-D through the use of 2,4-DB. 

However, the relative amounts applied makes this unlikely. In all, 29 million pounds 2,4-D were 
Page 3 of 40

applied to agricultural crops in the United States annually between 2006 and 2010. An 

additional 5 million pounds were estimated average annual use on lawns, turf, nurseries, etc. in 

commercial settings. Homeowner and aquatic weed control uses have remained fairly constant 

with average annual uses of 9 to 9.5 million pounds per year (USEPA 2012a). In contrast, the 

use estimates for 2,4-DB combine for approximately 340,000 lbs between 2003-2010, less than 

1% of the total amount of 2,4-D applied annually. Because 2,4-D is a degradate of 2,4-DB and 

the amount of 2,4-DB used is less 1% of the total amount of 2,4-D, it is not likely that the use 

2,4-DB will significantly contribute to the overall environmental loading of 2,4-D.

3. Conclusions from Previous Risk Assessments

a. Ecological Risk Assessment 

The Agency issued a Reregistration Eligibility Decision (USEPA 2005a) for 2,4-DB that serves as a basis 

for this problem formulation. The RED concluded that 2,4-DB presents the greatest potential risks to: 1) 

terrestrial non-target plants through spray-drift and runoff into adjacent areas where these plants are 

present; 2) small and medium-sized mammals through direct application to treated fields; 3) small and 

medium-sized birds; and 4) Federally endangered or threatened species (hereafter referred to as “listed”)

freshwater fish through spray drift and runoff from use on alfalfa.

Because 2,4-DB-DMAS dissociates rapidly in water to form 2,4-DB, and ecotoxicity data were similar 

for 2,4-DB and 2,4-DB-DMAS, EFED bridged the ecotoxicity data studies for 2,4-DB-DMAS with 2,4-

DB. No ecotoxicity data were available to directly assess potential risks to aquatic vascular plants, or 

chronic toxicity to birds and estuarine/marine organisms for either 2,4-DB-DMAS or 2,4-DB. Risk 

quotients for terrestrial and aquatic organisms were calculated on an “acid equivalents (ae)” basis 

accounting for molecular weight differences between 2,4-DB and 2,4-DB-DMAS. EFED has considered 

available information on all formulations of 2,4-DB for toxicity, potential use areas, fate properties, and 

application methods in characterizing ecological risks related to labeled use.

Based on an acute contact honey bee study (Accession Number 00018842), previous risk assessments 

have concluded that the potential for 2,4-DB to have direct adverse effects on pollinators and other 

beneficial insects was low. Similarly, modeling results did not indicate potential concerns for freshwater 

invertebrates and freshwater fish. However, the acute risk Level of Concern (LOC) for listed fish was 

exceeded using the maximum application rate and minimum application interval. 

The major environmental fate and ecological risk conclusions identified in the RED are summarized in 

Table 1.

Table 1. Summary of Risk Concerns Identified for 2,4-DB in Previous Assessments

Birds Mammals Terr.

Plants

Terr.

Inverts Fish BCF Aquatic Inverts

Aquatic 

Plants

Groundwater 

Contamination Persistence Degradates of Concern

Yes a Yes Yes No Yesb No Noc Yes Yes Yes Yes a No reproduction data were available to allow for a chronic risk assessment b Acute risk LOC for listed fish was exceeded using the maximum application rate and minimum application interval c Acute and chronic data are currently not available for estuarine/marine invertebrates and fish

Yes = at least one LOC has been exceeded in previous assessments; “No“= LOCs have not been exceeded in previous assessments; NA = RQs 

have not been calculated previously.
Page 4 of 40

b. Drinking Water Exposure Assessments

A drinking water exposure assessment was conducted for 2,4-DB in 2004 (USEPA, 2004a) as part of the 

RED process. Exposure estimates of 2,4-DB from labeled uses at that time produced maximum 

exposures (for alfalfa in TX), on an acid-equivalents basis, of 318.7 μg ae/L (1-in-10-year peak), 72.4 μg 

ae/L (1-in-10-year annual mean), and 39.9 μg ae/L (30-year mean) for surface water and 0.51 μg ae/L for 

groundwater. At that time, estimated drinking water concentrations (EDWC) of 2,4-DB for drinking 

water from surface and groundwater for human health risk assessment were well below the level of 

concern [1 % of the acute population adjusted dose (aPAD), and < 2% of the chronic one (cPAD)] for the 

most highly exposed population subgroups for either acute or chronic exposures for the general U.S. 

population or any subgroups. Currently, the Health Effects Division (HED) does not anticipate updating 

the dietary exposure estimates from food, given that it is not likely to have a significant impact on 

aggregate risk (7/12/13 email from Wade Britton, HED, to Katherine St. Clair, PRD). Thus, an updated 

drinking water assessment will not be needed as part of the Registration Review process. Because EFED 

recently implemented revised percentage crop area (PCA) factors as well as introduced a PRZMGW model to determine EDWCs in groundwater, in the event that HED does need to update 

dietary exposure estimates from food, new EDWCs for surface and groundwater will be 

determined.

In 2005, a drinking water exposure assessment was conducted as part of the RED for the 2,4-DB 

degradate of concern, 2,4-D (USEPA 2005b), which is a registered active ingredient in the same family as 

2,4-DB. 

c. Clean Water Act Programs 

The herbicide 2,4-DB is not specifically identified as a cause of impairment for any water bodies listed as 

impaired under section 303(d) of the Clean Water Act. No Total Maximum Daily Load (TMDL) criteria 

have been developed for 2,4-DB. Aquatic benchmarks have been established for 2,4-DB; 2,4-DBDMAS; and the 2,4-DB degradate 2,4-D and are available at 

http://www.epa.gov/oppefed1/ecorisk_ders/aquatic_life_benchmark.htm. Any data submitted or 

otherwise located as part of the registration review process may be used to update aquatic life benchmarks 

if applicable. 

4. Environmental Fate and Transport

In aqueous environments, 2,4-DB-DMAS will rapidly dissociate to form 2,4-DB (acid form) and 

dimethyl ammonium (USEPA 2004a). Steady-state conductance was attained for 2,4-DB-DMAS in 

water in approximately 1.3 minutes (<80 seconds) at 85 μΩ. Therefore, studies conducted with the acid 

provide “surrogate data” for 2,4-DB-DMAS. 

Based on submitted data, 2,4-DB dissipates in the environment mainly through aqueous photolysis (halflife of 6-17 days), aerobic soil metabolism (half-life of 25 days) and leaching/runoff; plant uptake is also

expected to be a major factor in dissipation given that the pesticide works in the plants following uptake. 

The major degradates of 2,4-DB in aerobic soil are 2,4-dichlorophenoxyacetic acid (2,4-D acid; resulting 

from beta-oxidation) and 2,4-dichlorophenol (2,4-DCP); 2,4-DB does not photodegrade on soil and only 

metabolizes slowly in anaerobic soil. Thus, it may persist in subsurface soil, aquatic systems, and 

sediment, although uncertainties exist due to a lack of aquatic metabolism data. Although 2,4-DB-DMAS 

rapidly dissociates to 2,4-DB, the compound 2,4-DB is stable to hydrolysis. In the environment, because 

it is an ionizable compound (pKa of approximately 4.6, indicating that half of the 2,4-DB molecules will 
Page 5 of 40

be ionized at a pH of 4.6, with increasing percentage of the anionic form as pH increases), the fate of 2,4-

DB will be dependent on the pH of the soil or aquatic systems in which it is present. Adsorption (and 

mobility), solubility, and volatility may vary between soil and aquatic systems due to differences in pH 

and other soil properties that affect adsorption. At higher pH values, when the compound is present in 

greater proportions as an anion, the solubility of 2,4-DB will be greater. Also at higher pH values, the 

compound will be more hydrophilic and any potential hydrophobic adsorption to the soil will be lower. 

Because 2,4-DB will be present primarily as an anion in soil at environmental pH values, there is a 

potential for both surface runoff and leaching to groundwater, and therefore there is a potential 

groundwater concern for 2,4-DB. It is uncertain whether 2,4-DB will bioaccumulate in fish, although it is 

not expected due to its hydrophilicity at most environmental pH values. 

A selection of environmental fate and transport properties of 2,4-DB is summarized in Table 2.

Table 2. Chemical Properties and Environmental Fate Parameters of 2,4-DB (and 2,4-DB-DMAS

as noted, if available)

Parameter Value Description/Comments Source

Selected Physical/Chemical Parameters

Molecular mass (molecular 

formula)

249.1 g/mol for 2,4-DB 

acid (C10H10Cl2O3)

294.2 g/mol for 2,4-DBDMAS (C12H17Cl2NO3)

--

MRID 00153216

Vapor pressure (20°C) 7.1 x10-5 Torr

Not expected to 

volatilize from dry 

surfaces. Will vary with 

pH.

USEPA 2004a 

Aqueous solubility (25°C; pH 7) 46 mg/L Soluble, but level will 

vary with pH. MRID 00153216

Henry’s Law Constant (20°C; 

pH 7) 3.14 x 10-9 atm.m3

/mol

Not expected to 

volatilize from water or 

moist/wet soil surfaces.

Will vary with pH.

USEPA 2004a

Dissociation Constant pKa 

(25o

C)

4.56 (2,4-DB)

4.2-4.6 (2,4-DB-DMAS)

Compound is a weak 

acid and will exist 

mainly in the 

dissociated form at most 

environmental pH

values. As an ion, it will 

behave differently at 

various pH levels.

MRID 42741501;

45512401

Log octanol-to-water partition 

coefficient

(Log KOW)

3.91

--

MRID 00153216

Persistence

Hydrolysis half-life (22°C) Stable at pH 5, 7, 9 Does not hydrolyze. MRID 41101101
Page 6 of 40

Parameter Value Description/Comments Source

Aqueous photolysis half-life 

(25°C) pH 5: 6.3 days

pH 7: 17.2 days

pH 9: 6.9 days

May photolyze slowly 

in clear, shallow waters.

Adjusted for sunlight 

intensity at 40°N 

latitude.

MRIDs 41101102,

42067801 

Soil photolysis half-life (25°C)

Stable

-- MRIDs 41101103, 

41101104, 

42678401

Aerobic soil metabolism halflife (25°C) 24.5 days Slightly persistent* in a 

single aerobic soil.

MRID 41325501

Anaerobic soil metabolism halflife (25°C) 269.2 days Not a rapid degradation 

pathway (persistent*).

MRID 41325501

Anaerobic aquatic metabolism 

half-life (20-25°C) No data. -- --

Aerobic aquatic metabolism 

half-life (20-25°C) No data. -- --

Mobility

Freundlich soil-water partition 

coefficients (KF); organic 

carbon-normalized Freundlich 

coefficients (KFOC)

Adsorption

KF = 0.80 (sand), 0.46 

(silt loam), 1.5 (sandy 

loam), 3.3 (clay loam)

Desorption

KF = 1.0 (sand), 0.90 (silt 

loam), 2.1 (sandy loam), 

4.7 (clay loam)

Compound will exist

primarily in dissociated

form (as an anion) at 

most environmental 

pHs, and mobility may 

vary greatly with pH 

and other soil 

properties.

1/n range: 0.79-0.95

Koc values not reported, 

but are not meaningful 

due to the ionizable 

property of the 

pesticide.

MRIDs 41101105,

41617201

Field Dissipation

Terrestrial field dissipation halflife; leaching depth

GA: t1/2 = 3.5 days (max 

depth of leaching 0-6”)

IA: t1/2 = 2.0 days (max 

depth of leaching 6-12”; 

leached mainly to 0-6” 

depth)

NY: t1/2 = 6.7 days (max 

depth of leaching 0-6”)

GA: peanut cropped plot

IA: soybean cropped 

plot

NY: alfalfa cropped plot

MRIDs 44660502, 

44660503,44680701

Fish Bioconcentration
Page 7 of 40

Parameter Value Description/Comments Source

Fish bioconcentration factors 

(steady-state); depuration rate No data. -- --

*Goring et al. 1975 scale was used to describe persistence. Nonpersistent: t1⁄2 < 15 days; slightly 

persistent t1⁄2 15-45 days; moderately persistent t1⁄2 45-180 days; persistent t1⁄2 >180 days.

a. Transformation Products

The major organic degradates of 2,4-DB in submitted environmental fate studies were 2,4-D and 2,4-DCP 

in aerobic soil and field studies. Multiple minor degradates (not identified) were observed in the aqueous 

photolysis study. Table 3 summarizes the transformation products of 2,4-DB and their maximum 

amounts formed.

A recent problem formulation (DP barcode 402410; 4/12/2013) conducted for 2,4-D details the 

environmental fate properties of that compound. Similar to 2,4-DB, 2,4-D is primarily degraded through 

microbially-mediated metabolism and aqueous photolysis, although it also degrades in aerobic aquatic 

environments, forming 2,4-DCP and chlorohydroquinone (CHQ). Mobility data on the degradates of 2,4-

D were not available.

In all three terrestrial field dissipation studies, the degradates 2,4-D and 2,4-DCP were present at their 

maximum detected concentrations within a week of the final applications, and were not detected in 

surface soil by the end of the studies (approximately 1 year).
Page 8 of 40

Table 3. 2,4-DB (and 2,4-DB-DMAS) and Its Major Environmental Degradates 

Code Name/ 

Synonym Chemical Name Chemical Structure Study Type Ref.

(MRID)

Maximum 

%AR (day)A

Final %AR 

(study 

length)

PARENT

2,4-DB

4-(2,4-

dichlorophenoxy) 

butyric acid (IUPAC) 

or 4-(2,4-

dichlorophenoxy) 

butanoic acid (CAS)

2,4-DB-DMAS

Dimethylamine

4-(2'4-

dich1orophenoxy) 

butyrate

MAJOR TRANSFORMATION PRODUCTS
Page 9 of 40

Code Name/ 

Synonym Chemical Name Chemical Structure Study Type Ref.

(MRID)

Maximum 

%AR (day)A

Final %AR 

(study 

length)

2,4-D

2,4-

dichlorophenoxyacetic 

acid

835.2410 42678401 <1%

835.4100 41325501

835.4200 41325501

TFD (GA) 44660502 15% (3) n.d.

TFD (IA) 44660503 9.1% (1) n.d.

TFD (NY) 44680701 5% (7) n.d.

2,4-DCP 2,4-dichlorophenol 

TFD (GA) 44660502 10% (3) n.d. 

TFD (IA) 44660503 27.3% (7) n.d.

TFD (NY) 44680701 5% (3) n.d.

CO2 carbon dioxide 834.4100 41325501

n.d. means “not detected”.

Terrestrial field study percentages represent the ratio of degradate concentration to the maximum parent concentration, both in the top layer of soil. 
Page 10 of 40

5. Receptors

Table 4 and Table 5 provide a summary of the most sensitive acute and chronic toxicity values for 2,4-DB 

and 2,4-DB-MAS across aquatic and terrestrial taxonomic groups, respectively. Based on the available 

ecotoxicity information, freshwater aquatic and terrestrial plants appear to be the most sensitive taxa, 

which is expected for an herbicide. Among the other taxa, 2,4-DB is only slightly to moderately toxic to 

freshwater fish and aquatic invertebrates, slightly toxic to birds on an acute basis, and practically nontoxic 

via dietary exposure to birds, mammals, and terrestrial insects. 2,4-DB and 2,4-DB-DMAS have roughly 

equivalent acute toxicity to the waterflea (D. magna), likely owing to the rapid hydrolysis of the MAS. 

Since no data are available specific to aquatic-phase amphibians, freshwater fish are used as surrogate.

There are no data available examining the effect of either 2,4-DB or 2,4-DB-DMAS on estuarine/marine 

species. 

For terrestrial animals, 2,4-DB and 2,4-DB-DMAS are practically nontoxic to birds (birds also serve as 

surrogates for reptiles and terrestrial-phase amphibians) based on acute studies. There are no 2,4-DB 

chronic or reproductive studies available for birds. The registrant submitted a waiver request for an avian 

reproduction study. At the time of the RED, the Agency elected to hold the conduct of the avian 

reproduction study in reserve based on potential exposure through repeated dosing and potential 

persistence of the chemical in certain environments.

2,4-DB is slightly to moderately toxic to freshwater fish and aquatic invertebrates in acute studies. 

Chronic studies are not available to assess the chronic toxicity of 2,4-DB or 2,4-DB-DMAS in either fish 

or aquatic invertebrates. 

EFED has recently received two new terrestrial plant toxicity studies for 2,4-DB [seedling 

emergence/growth (MRID 481033-01) and vegetative vigor (MRID 481033-02)], as well as an 

estuarine/marine acute toxicity study with sheepshead minnows (MRID 479304-01). These studies are 

under review in EFED, and will be used to inform the risk assessment for 2,4-DB. 

a. Effects to Aquatic Organisms

Table 4. Summary of the Most Sensitive Endpoints from Aquatic Toxicity Studies for 2,4-DB and 

2,4-DBMAS (Test material is acid form unless otherwise noted.)

Taxonomic 

Group

Study 

Type Test Species

Toxicity 

Value

(all units in 

terms of 

acid 

equivalents)

Acute 

Toxicity 

Classification

Source

(MRID)

Freshwater fish1

Acute

Rainbow Trout

(Oncorhynchus 

mykiss)

LC50 = 2 

mg/L

Moderately 

toxic

03503

(Accession 

number)

Chronic (none) --

Freshwater 

invertebrates Acute Stonefly(Pteronarcys sp.)

EC50 = 15 

mg/L Slightly toxic 40094602
Page 11 of 40

Taxonomic 

Group

Study 

Type Test Species

Toxicity 

Value

(all units in 

terms of 

acid 

equivalents)

Acute 

Toxicity 

Classification

Source

(MRID)

Acute Waterflea (Daphnia 

magna)

EC50 = 25 

mg/L Slightly toxic 41407801

Acute* Waterflea (Daphnia 

magna)

EC50 = 20.3 

mg/L Slightly toxic 41642701

Chronic (none) --

Estuarine/marine 

fish

Acute (none)

Chronic (none)

Estuarine/marine 

shrimp Acute (none)

Estuarine/marine 

mollusk Acute (none)

Estuarine/marine 

invertebrate Chronic (none)

Aquatic plants 

and algae

Vascular (none)

Nonvascular

Green Algae 

(Pseudokirchneriella 

subcapitata formerly 

Selenastrum 

capricornutum)

LOAEC = 

1.1 mg/L 41407803

1 freshwater fish act as surrogates for aquatic phase amphibians

*Study conducted with 2,4-DB-DMAS
Page 12 of 40

b. Effects to Terrestrial Organisms

Table 5. Summary of the Most Sensitive Endpoints from Terrestrial Toxicity Studies for 2,4-DB and 

2,4-DB-DMAS. (Test material is acid form unless otherwise noted.)

Taxonomic 

Group Study Type Test Species

Toxicity Value

(all units in terms 

of measured acid 

equivalents)

Acute 

Toxicity 

Classification

Source

Birds1

Acute

Bobwhite quail

(Colinus 

virginianus)

LD50 = 1536 

mg/kg-bw Slightly toxic 41370102

Sub-acute 

dietary

Bobwhite quail LC50 >5,000 

mg/kg diet

Practically 

non-toxic

41370102, 

41370103

Bobwhite 

quail, Mallard 

Duck & Ringnecked 

Pheasant

LC50 >5,000 

mg/kg diet

Practically 

non-toxic 22923

Chronic (none) --

Mammals

Acute Oral

Laboratory rat

(Rattus 

norvegicus)

LD50 = 1470 

mg/kg-bw Slightly-toxic 41224401

Acute 

Inhalation

Laboratory rat

(Rattus 

norvegicus)

LD50 = >2.3 mg/L Toxicity 

Category IV 41774001

Chronic

Laboratory rat

(Rattus 

norvegicus)

NOAEL = 3 

mg/kg bw/day

LOAEL = 30 

mg/kg bw/day

Endpoint: 

decreased body 

weight gain and 

food consumption

-- 40257501

Insects Acute

Honey bee 

(Apis mellifera 

L.)

LD50 = 14.5 

μg/bee

Practically 

non-toxic 00018842

Terrestrial 

plants

*Seedling 

Emergence

Dicot – carrot

(Daucus 

carota)

NOAEC = 0.0028 

lbs/A

EC25 = 0.0032 

lb/A

Endpoint: shoot 

dry weight

-- 41605401
Page 13 of 40

*Seedling 

Emergence

Monocot –

Onion

(Allium cepa)

NOAEC = 

0.043lb/A

EC25 = 0.07 lbs/A

Endpoint: shoot 

dry weight

-- 41605401

1 Birds are surrogates for terrestrial-phase amphibians and reptiles.

*Study conducted with 2,4-DB-DMAS

c. Ecological Incidents

The ecological incident information system (EIIS) is an OPP database that houses ecological incidents that 

have been reported to the Agency. When available, EIIS includes date and location of an incident, type 

and magnitude of effects observed in various species, use(s) of pesticides known or suspected of 

contributing to the incident, and results of any chemical residue analysis or other analyses conducted 

during incident investigation. EIIS incidents are categorized according to the certainty that the incident 

resulted from pesticide exposure. The Avian Monitoring System (AIMS) is a database administered by the 

American Bird Conservancy that contains publicly available data on reported avian incidents involving 

pesticides. Many of the incidents listed in this database are also in the EIIS. 

There was a single incident reported in the EIIS database involving 2,4-DB. The incident was classified as 

highly probable to have been caused by 2,4-DB and involved a misuse of the application to soybean. The 

incident occurred in Iowa in 1991 and resulted in plant damage to honeysuckle and vegetable (species 

unknown; ID# 1000077-001). As of 15 July, 2013, AIMS identified no ecological incidents involving 2,4-

DB nor were there any incidents reported by the registrants. The lack of incident reports cannot be 

considered as evidence of lack of hazard. 

In comparison, there were several incident reports for 2,4-D. As of August 6, 2012, EIIS database returned 

more than 400 incidents between 1949 and the present. The majority of incidents were reported for 2,4-D 

acid and involved plants (although one involved the death of a single bird, and was classified as highly 

certain that 2,4-D caused the death). Many of the plant incidents appeared to result from over-application 

of 2,4-D products to lawns or application of 2,4-D products to types of grass that are sensitive to 2,4-D. 

Other plant incidents were the result of spray drift in agricultural settings. The larger number of reports 

compared to 2,4-DB is likely a reflection of the more extensive use of 2,4-D. For more details on the 2,4-

D incident reports, see the EFED Registration Review Problem Formulation for 2,4-D (D402410).

6. Exposure Pathways of Concern

The environmental fate properties and use patterns of 2,4-DB indicate that direct spray, spray drift, 

leaching through soil (to groundwater or in subsurface lateral flow), and runoff represent potential 

transport mechanisms of 2,4-DB to non-target aquatic and terrestrial organisms. Drinking water and 

inhalation exposure pathways were screened using the SIP (Screening Imbibition Program) and STIR 

(Screening Tool for Inhalation Risk) screening models. STIR indicated the inhalation pathway was of low 

concern (no LOC exceedances are expected) for birds and mammals. SIP indicated exposure through 

drinking water alone was of low concern for acute risk to birds and mammals. However, drinking water 

alone is a potential chronic concern for mammals. The data are insufficient to determine if exposure 

through drinking water is a potential chronic risk for birds, and therefore risk cannot be precluded. SIP 

and STIR are described in detail at http://www.epa.gov/oppefed1/models/terrestrial/index.htm.

Potential exposure through sediment was screened using EPI SuiteTM v4.11 

(http://www.epa.gov/opptintr/exposure/pubs/episuitedl.htm). Although there is a reasonable expectation of 

exposure in freshwater and marine water bodies as a result of spray drift and runoff and the half-life of 2,4-
Page 14 of 40

DB in aerobic soil metabolism studies >10 d (MRID 41325501), residues in sediment are expected to be 

negligible (i.e., <1% ). See Appendix B for EPI Suite model results. 

7. Analysis Plan

a. Stressors of Concern

i. Ecological Risk Assessment

The stressors of ecological concern for terrestrial organisms are 2,4-DB, 2,4-DB-DMAS, and the major 

degradates 2,4-D and 2,4-DCP, for terrestrial and aquatic species. Both 2,4-D and 2,4-DCP were 

identified in aerobic soil and field studies conducted with 2,4-DB. 2,4-DCP is also a major degradate in 

2,4-D anaerobic aquatic studies, and a product impurity of both 2,4-DB and 2,4-D. There are some 

toxicity data for 2,4-DCP available in the ECOTOX (http://cfpub.epa.gov/ecotox/), which suggest that it is 

more toxic than 2,4-D to selected aquatic organisms. EFED will use a total toxic residues approach for 

assessing 2,4-DB and the degradate 2,4-DCP unless sufficient data exist to determine EECs separately. 

The degradate 2,4-D will be assessed using submitted data for the pesticide, with the determination of 

separate EECs.

ii. Formulation Impurities

Another possible source of toxicity from the use of 2,4-DB products is the presence of impurities that may 

be present as a result of the manufacturing process. Dioxin/furan congeners and other possible 

organochlorine contaminants have been found in 2,4-DB products (Holt et. al., 2010). The term “dioxins” 

is used to represent polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans 

(PCDFs). There are 210 different congeners of dioxins (75 PCDDs and 135 PCDFs); however, only 17 

congeners are considered to be of toxicological concern (listed in Table 6). For these 17 congeners, 

evidence is sufficient to conclude that a common mechanism of action, involving binding of the chemicals 

to the aryl hydrocarbon receptor (AHR) as the initial step, underlies 2,3,7,8-TCDD-like toxicity elicited by 

these PCDDs, PCDFs, and Polychlorinated biphenyls (PCBs) (Van den Berg et al., 1998, 2006). It is 

worth noting here that not all of the 17 dioxins identified in Table 6 were found in the 2,4-DB 

formulations. 2,4-DB impurities are limited to a small subset of the toxic dioxin congeners listed below.

Table 6. Dioxin Congeners of Toxicological Concern and Toxicity Equivalency Factors for 

Mammals, Birds and Fish

Congener*

Toxicity Equivalency Factors from U.S. EPA 2008b

Mammal TEF Bird TEF Fish TEF

2378-TCDF 0.1 1 0.05

12378-PeCDF 0.03 0.1 0.05

23478-PeCDF 0.3 1 0.5

123478-HxCDF 0.1 0.1 0.1

123678-HxCDF 0.1 0.1 0.1

234678-HxCDF 0.1 0.1 0.1

123789-HxCDF 0.1 0.1 0.1

1234678-HpCDF 0.01 0.01 0.01

1234789-HpCDF 0.01 0.01 0.01

OCDF 0.0003 0.0001 <0.0001
Page 15 of 40

Congener*

Toxicity Equivalency Factors from U.S. EPA 2008b

Mammal TEF Bird TEF Fish TEF

2378-TCDD 1 1 1

12378-PeCDD 1 1 1

123478-HxCDD 0.1 0.05 0.5

123678-HxCDD 0.1 0.01 0.01

123789-HxCDD 0.1 0.1 0.01

1234678-HpCDD 0.01 <0.001 0.001

OCDD 0.0003 0.001 <0.001

*Abbreviations are as follows: TCDD = tetrachlorodibenzodioxin; PeCDD = pentachlorodibenzodioxin; HxCDD = hexachlorodibenzodioxin; 

HpCDD = Heptachlorodibenzodioxin; OCDD = Octachlorodibenzodioxin; TCDF = Tetrachlorodibenzofuran; PeCDF = Pentachlorodibenzofuran; 

HxCDF = Hexachlorodibenzofuran; HpCDF = Heptachlorodibenzofuran; OCDF = octachlorodibenzofuran

2,3,7,8-TCDD and other similar-acting PCDD, PCDF and PCB congeners have been shown to adversely 

affect reproduction, development, endocrine functions, wasting syndrome, immunotoxicity, and mortality 

in fish, birds, and mammals. The EPA (USEPA 2010) and the World Health Organization (Van Den Berg 

et. al. 1998, 2006) have established toxicity equivalency factors (TEFs) for dioxins as they relate to 

mammals, birds and fish (Table 6). In the TEF approach, the toxicities of individual congeners are 

normalized to 2,3,7,8-TCDD. For example, 2,3,7,8-TCDD has a TEF of 1 and 23478-PeCDF, which is 1/3 

as toxic to mammals, has a TEF of 0.3 (Table 6). For each PCDD and PCDF, the concentration (or mass) 

of the chemical is multiplied by its TEF. The sum of the products for each PCDD and PCDF represents the 

toxicity equivalent (TEQ) concentration relative to 2,3,7,8-TCDD (Equation 1; USEPA 2010).

Equation 1. 

For risk assessment, a TEQ approach may be used to evaluate the toxicity of the dioxin impurities found in 

the 2,4-DB formulations. Findings will be included in the overall risk conclusions.

ii. Drinking Water 

Currently, HED does not anticipate updating the dietary exposure estimates from food, given that it is not 

likely to have a significant impact on aggregate risk. Additionally, EFED believes recent changes in the 

drinking water exposure models will not impact the previously estimated EDWCs in a way that would

significantly impact the human dietary risk picture. Thus, an updated drinking water assessment will not 

likely be needed as part of the Registration Review process. 

b. Measures of Exposure 

EFED will use standard available models (identified in Table 7) to evaluate potential exposures to aquatic 

and terrestrial organisms as described at http://www.epa.gov/pesticides/science/models_db.htm. 

Aquatic exposure estimates will be based on estimated environmental concentrations (EECs) generated 

using the Pesticide Root Zone Model (PRZM 3.12.2 dated May 12, 2005) coupled with the Exposure 

Analysis Model System (EXAMS 2.98.04.06 dated April 25, 2005) to simulate a waterbody that is 

considered representative of vulnerable aquatic environments (e.g., ponds and streams in headwater 

watersheds). Terrestrial exposure will be estimated using a model (T-REX version 1.5) that assumes direct 

application to a variety of avian, mammalian and reptilian food items. Exposure to terrestrial plants will 

be estimated using a model (TerrPlant; version 1.2.2) that assumes 2,4-DB drifts or moves with runoff to 
Page 16 of 40

adjacent habitats. For more information on the various models that will be used in the risk assessment see 

the links as outlined in Table 7.

Two spray drift models, AgDISP and/or AgDRIFT, will be used to assess exposures of aquatic and 

terrestrial organisms to 2,4-DB deposited in terrestrial and aquatic habitats by spray drift. AgDRIFT 

(version 2.1.1; dated 03/07/2012) is the model most commonly used by EFED to simulate spray drift into 

terrestrial and aquatic environments. AgDISP (version 8.26; dated 03/07/2012) is used when a parameter 

needs to be modeled that is not available in AgDRIFT. Spray drift analysis will be an important part of the 

analysis in defining the potential area of effects for listed species.

Table 7. List of the various models and the related taxa for which the models will be used.

Environment Taxa of 

Concern Model(s) Link

Aquatic

Fish/ 

Invertebrates/

Plants

PRZM, EXAMS http://www.epa.gov/oppefed1/models/wate

r/

Terrestrial

Vertebrate 

T-REX (dietary item) http://www.epa.gov/oppefed1/models/terre

strial/trex/trex_v1_5_webversion.xlsm

AGDISP (Spray drift) http://www.continuum-dynamics.com/pragdisp.html

SIP (imbibition) http://www.epa.gov/oppefed1/models/t

errestrial/

STIR (Inhalation) http://www.epa.gov/oppefed1/models/t

errestrial/

Plant

TerrPlant (Run-off) http://www.epa.gov/oppefed1/models/terre

strial/index.htm#terrplant

AgDRIFT (Spray 

drift)

http://www.agdrift.com/AgDRIFt2/Downl

oadAgDrift2_0.htm

AGDISP (Spray drift) http://www.continuum-dynamics.com/pragdisp.html

Screening-level calculations using SIP have suggested that drinking water exposure alone may be 

significant for chronic risks in mammals. This exposure pathway may be further considered at the time of 

the risk assessment. The STIR model indicated that inhalation is not likely to be a significant pathway for 

exposure. (Appendix B). 

i. Available Monitoring Data

The Agency is aware of monitoring conducted by federal and state agencies and this information will be 

considered in the assessment to the extent that data on 2,4-DB or other residues of concern are available.
Page 17 of 40

c. Measures of Effect 

The most sensitive toxicity endpoints presented in Section 6 of this problem formulation will be used to 

calculate risk quotients for the respective taxa. Any additional information submitted by the registrant or 

found in the open literature prior to conduct of the risk assessment will also be considered. The open 

literature studies will be identified using EPA’s ECOTOXicology database (ECOTOX; 

http://cfpub.epa.gov/ecotox/), which employs a literature search engine for locating chemical toxicity data

for aquatic life, terrestrial plants, and wildlife. Data that meet the Agency’s standard for inclusion in risk 

assessments can also provide insight into the direct and indirect effects of pesticides on biotic 

communities. Such effects could include loss of species that are sensitive to the chemicals and from 

changes in structure and functional characteristics of the affected communities.

8. Endangered Species Assessments

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), the Agency will 

evaluate risks to listed species from registered uses of pesticides in Registration Review. The process for 

evaluating potential risks to listed species is further described at 

http://www.epa.gov/oppfead1/endanger/litstatus/riskasses.htm.

9. Endocrine Disruptor Screening Program

Under Federal Food Drug and Cosmetic Act (FFDCA) section 408(p), the Agency must screen all 

pesticide chemicals for potential endocrine disruptor activity. Between October 2009 and February 2010, 

EPA issued test orders/data call-ins for the first group of 67 chemicals, which comprises 58 pesticide 

active ingredients and 9 inert ingredients. The herbicide 2,4-DB is not among the group of 58 pesticide 

active ingredients on the initial list to be screened under the EDSP. For further information on the status of 

the EDSP, the policies and procedures, the list of 67 chemicals, future lists, the test guidelines and the Tier 

1 screening battery, please visit our website: http://www.epa.gov/endo/.

10. Preliminary Identification of Data Gaps 

a. Environmental Fate

Table 8 identifies environmental fate studies by MRID that offer data for each guideline requirement, as 

well as study classifications and whether or not further data are needed in order to support risk assessment.
Page 18 of 40

Table 8. Environmental Fate Data and Study Classifications for 2,4-DB.

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data 

needed to 

conduct risk 

assessment?

Justification and Assumptions 

EPA will Make in Absence of 

Data

835.2120 Hydrolysis 41101101 Acceptable No --

835.2240 Aqueous 

photolysis

41101102, 

42067801 Supplemental No --

835.2410 Soil photolysis 42678401 Supplemental No --

Photodegradation 

in Air 41479702 Supplemental No --

835.4100 Aerobic soil 

metabolism 41325501 Supplemental 

Yes. Data are 

needed for 

three 

additional 

soils.

The single available half-life is 

inadequate for risk assessment. 

In the absence of additional data, 

the value will be increased (3x)

for the purposes of modeling to 

account for uncertainty 

associated with using a single 

value.

835.4200 Anaerobic soil 

metabolism 41325501 Supplemental No --

835.4300 Aerobic aquatic 

metabolism No data. -- Yes

The assumption of compound 

stability will be made in the 

absence of acceptable data.

835.4400

Anaerobic 

aquatic 

metabolism

No data. -- Yes

The assumption of compound 

stability will be made in the 

absence of acceptable data.

835.1230

835.1240

Adsorption/ 

desorption and 

leaching

41101105 Acceptable No --

835.1410 Volatility –

laboratory No data. -- No

Not expected to be volatile 

under normal use conditions 

based on low vapor pressure and 

Henry’s Law Constant.

835.6100 Terrestrial field 

dissipation

44660502 Acceptable 

44660503 Acceptable No --

44680701 Acceptable

850.6100

Analytical 

method in soil 44660501 Acceptable No --

Analytical 

method in water No data. -- Yes

Environmental chemistry 

method (ECM) and independent 

laboratory validations (ILV) are 

required.

850.1730 Fish 

bioconcentration No data. -- Yes Based on a Kow = 3.91.
Page 19 of 40

Environmental chemistry methods (ECM) for 2,4-DB residues of concern in soil, water, and sediment as 

well as independent laboratory validation (ILV) of the methods are required to support monitoring for 2,4-

DB residues and to evaluate newly submitted environmental fate and ecological effects data. ILV methods 

submitted by the registrant are used to evaluate analyses described in submitted environmental fate and 

ecological effects studies. Submitted analytical methods are also used by various federal, state, tribal, and 

local agencies to detect and monitor residues that are or are suspected to be in environmental 

compartments from outdoor uses and accidental releases. Independent laboratory validations for submitted 

analytical methods are necessary to confirm that the methods are functional and to confirm the levels of 

detection and quantitation reported in registrant-prepared validations. Currently, ECMs have only been 

submitted for soil; ECMs and ILVs for water and sediment have not been submitted.

b. Effects

The database for the 2,4-DB is incomplete. There are a number of studies, including several 

estuarine/marine studies for fish and invertebrates, which are required for risk assessment. Studies may be 

performed with 2,4-DB salt or ester. The rationale for requiring chronic aquatic studies includes the 

following points:

• 2,4-DB is mobile and persistent under some conditions such that aquatic exposure is likely to 

occur

• The RED identified risk to non-target terrestrial plants through spray drift or runoff to areas 

adjacent to or near treated fields. Therefore, use sites in close proximity to marine/estuarine 

environments can expect to generate residues in sufficient quantity to result in risks of concern to 

marine/estuarine plants and animals.

In the absence of acceptable studies, EPA will make conservative assumptions to estimate an LC50/EC50 

using data such as QSAR3 estimates, open literature data, or data from other, similar chemicals (e.g., 2,4-

D). If no such data exist for a taxon, risk will be presumed. 

The following aquatic and terrestrial toxicity data are needed for the 2,4-DB ecological effects 

assessment:

• Data are needed for acute studies on one estuarine/marine mollusk and one estuarine/marine

shrimp (Guidelines 850.1025, 850.1035, 850.1045, 850.1055). The RED identified risk to nontarget terrestrial plants through spray drift or runoff to areas adjacent to or near treated fields. 

Therefore, use sites in close proximity to marine/estuarine environments can expect to generate 

residues in sufficient quantity to result in risks of concern to marine/estuarine plants and animals.

• Saltwater invertebrate life cycle (Guidelines 850.1300 and 850.1350). Tests on the freshwater and 

saltwater species are being recommended at this time. Although 2,4-DB is only slightly toxic to 

freshwater invertebrates, 2,4-D is moderately toxic to freshwater invertebrate species but very 

highly toxic to marine/estuarine species. Without an adequate acute study to determine the chronic 

toxicity to freshwater and estuarine/marine species to freshwater invertebrates, risk is presumed. 

In addition, chronic exposure can be expected through drift or runoff and persistence in soils.

• Saltwater and freshwater fish early-life stage (Guideline 850.1400). EFED recommends testing on 

the rainbow trout (Oncorhynchus mykiss) for the freshwater species since this species resulted in 

 3 QSAR Quantitative Structure-Activity Relationship a quantitative relationship between an endpoint (biological activity, e.g., toxicity) and one or 

more descriptors associated with the endpoint/activity. For more information on QSARs, see: 

http://www.epa.gov/oppfead1/international/naftatwg/guidance/qsar-guidance.pdf.
Page 20 of 40

the lowest 96-hour LC50 among tested species. If the test species for this data requirement is 

different from the species used for the freshwater fish acute toxicity test, a 96–hour LC50 on that 

species must also be provided. Testing is required at this time for the freshwater fish because the 

RED indicated potential risk and the absence of a chronic fish study to establish an RQ. Testing is 

also required on an estuarine/marine species at this time. One of the triggers for the 

estuarine/marine fish early-life stage test is an LC50 < 1mg/L in the saltwater fish acute toxicity. 

The acute LC50 in the freshwater rainbow trout for 2,4-DB is 2 mg/L (Accession No. 03503), 

which is greater than the trigger value stated. However, EFED has only recently received and is 

currently reviewing an acute study for an estuarine/marine species. Due to the relatively small 

difference between the trigger value of 1 mg/L and the LC50 for the trout of 2 mg/L, and the 

reasonable assumption of chronic exposure, the estuarine/marine early-life stage toxicity is 

currently being required. 

• Avian Acute Oral Toxicity Test (Passerine Species; Guideline 850.2100). Acute avian oral 

toxicity data are required for either one waterfowl or one upland game species and one passerine 

species under the 40 CFR Part 158 (2010) data requirements for conventional pesticides with 

outdoor uses. The lowest endpoint from submitted acute oral avian effects data shows an LD50 of 

1536 mg ae/kg-bw for the bobwhite quail (MRID 41370102). Given that passerine species have 

higher metabolic rates because of their smaller sizes than either waterfowl or upland game bird 

species and because they may utilize different metabolic pathways, they may be more or less 

sensitive to 2,4-DB. A passerine study protocol should be submitted for review by the Agency 

prior to initiation of the study. 

• Avian Reproduction (Guideline 850.2300). In the bobwhite quail, 2,4-DB is only slightly toxic 

after an acute exposure (MRID 41370102) and practically non-toxic in a subacute study (MRID 

41370102, 41370103). However, a guideline study compliant with the avian reproduction study 

for an upland and a game species is required. 2,4-DB may be persistent under certain conditions 

such that chronic terrestrial exposure is likely to occur. In the absence of an appropriate avian 

reproduction study, 962 mg ae/kg diet, taken from the 2,4-D reproduction study in bobwhite quail 

(MRID 45336401) may be used for risk assessment. 2,4-D appears to be more toxic to birds based 

on the results of the acute studies, i.e. 2,4-D LC50= 218 mg/kg bw compared to 2,4-DB which 

showed no effects at 1536 mg/kg bw. Therefore, the use of the value from the 2,4-D avian 

reproduction study is likely protective for 2,4-DB effects. Furthermore, subacute studies in both 

2,4-D and 2,4-DB resulted in no effects at the highest doses tested, indicating that dietary 

exposures are likely to result in significantly lower toxicity compared to acute oral studies. 

Therefore, the absence of this study is not likely to impact the overall risk.

• Aquatic non-vascular plant (algal toxicity; Guideline 850.4500). Current guidelines require a 

minimum of three species; freshwater green algae, marine diatom, and freshwater diatom. The 

available study (MRID 41407803) only includes the green alga Raphidocelis subcapitata 

(formerly Pseudokirchneriella subcapitata). This data gap is critical since plants are the most 

sensitive taxa and therefore are the main drivers in the risk assessment.

• Cyanobacteria toxicity (Guideline 850.4550). Current Part 158 Guideline requirements include 

the cyanobacteria toxicity test in addition to the algal toxicity study previously cited.

Table 9 and 10 identify ecological effects studies by MRID that provide data for each guideline 

requirement, as well as study classifications and whether or not further data are needed in order to support 

risk assessment. Additional rationale for the required studies is also presented.
Page 21 of 40

Table 9. Aquatic Ecological Effects Data and Study Classifications for 2,4-DB and 2,4-DB-DMAS.

OCSPP

Guideline

Data 

Requirement

Study 

Type

Submitted 

Studies 

(MRID)

Study 

Classification

Are data 

needed to 

conduct risk 

assessment

Justification and 

Assumptions EPA will 

Make in Absence of Data 

- Some Example texts 

are include

850.1010

Freshwater 

invertebrate

toxicity

Acute

40094602 Acceptable

No

--

41407801 Acceptable --

41642701

(2,4-DBDMAS)Acceptable --

850.1025

850.1035

850.1045

850.1055 

Saltwater 

invertebrate

toxicity

Acute Yes

A guideline study 

compliant to saltwater 

invertebrate acute toxicity 

is required. Data are 

required on one 

estuarine/marine mollusk

and one estuarine/marine 

shrimp.

850.1075 Freshwater 

fish Acute

00050682 Supplemental

No

--

40762601 Acceptable --

40762602 Acceptable --

41370104 

(2,4-DBDMAS)Acceptable --

40094602 Acceptable --

41407802 

(2,4-DBDMAS) Acceptable --

850.1075 Saltwater fish Acute 47930401 -- Under 

Review

Study is currently under 

review

850.1300

Freshwater 

invertebrates

life cycle

Chronic (None) (N/A) Yes

A study compliant with 

the freshwater invertebrate 

guideline is required

850.1350

Saltwater 

invertebrates 

life cycle 

Chronic (None) (N/A) Yes

A study compliant with 

the saltwater invertebrate 

life cycle guideline is 

required for the reasons 

listed above the current 

table. 
Page 22 of 40

850.1400

Freshwater 

fish

early-life stage

Chronic (None) (N/A) Yes

A study compliant with 

the freshwater fish early 

life-stage guideline is 

required. Previous risk 

assessments indicated 

risks above the LOC for 

listed species.

850.1400 Saltwater fish

early-life stage Chronic (None) (N/A) Yes Current study under review by EFED

850.1500 Fish life cycle Chronic (None) (N/A) No

This study is not currently 

required. There are 

currently no labels which 

allow for direct 

application of 2,4-DB to 

water bodies. 

Furthermore, the required 

early life-stage toxicity 

studies will likely account 

for toxicity to the sensitive 

life stages. 

850.1735

850.1740

10-day 

Sediment 

Toxicity Test

Subacute (None) NA No

There is a reasonable 

expectation of residue in 

freshwater and marine 

water bodies as a result of 

spray drift and runoff. In 

addition, the half-life of 

2,4-DB is aerobic soil 

metabolism studies >10 d

(MRID 41325501). 

Therefore, the sediment 

toxicity test is required.

850.4400

Aquatic plant 

Toxicity Test 

using Lemna 

minor.

-- 46395501 supplemental No

Lemmna gibba is the 

recommended test species. 

Although the current study 

is classified as 

supplemental. EFED has 

determined that the current 

study is sufficient for risk 

assessment and is not 

requiring an additional 

study with Lemna gibba 

(D290495).
Page 23 of 40

850.4500 Algal toxicity --

41407803 

(2,4-DBMAS) Supplemental Yes

A nonvascular plant 

guideline study compliant 

with the algal toxicity 

guideline is required. 

Current guidelines require 

a minimum of 3 species; 

freshwater green algae, 

marine diatom, freshwater 

diatom. The available 

study (MRID 41407803) 

only includes the green 

alga Pseudokirchneriella 

subcapitata (formerly 

Selenastrum 

capricornutum).

850.4550 Cyanobacteria none Yes

There are no studies 

available which satisfy 

this guideline requirement.

Table 10. Terrestrial Ecological Effects Data for 2,4-DB and 2,4-DB-DMAS.

OCSPP 

Guideline

Data 

Requirement

Study 

Type

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data 

needed for 

risk 

assessment

Current Additional 

Data Need

850.2100

Avian oral 

toxicity Acute

41370102 Acceptable No --

41767112

(2,4-DBDMAS)Supplemental --

Passerine Acute (None) (NA) Yes

Acute avian oral 

toxicity data are 

required for either one 

waterfowl or one 

upland game species 

and one passerine 

species under the 40 

CFR Part 158 (2010) 

data requirements for 

conventional 

pesticides with outdoor 

uses 

850.2200 Avian dietary 

toxicity

subacute 00036935 Supplemental No --

00092162 Supplemental --
Page 24 of 40

OCSPP 

Guideline

Data 

Requirement

Study 

Type

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data 

needed for 

risk 

assessment

Current Additional 

Data Need

41370103 

(2,4-DBDMAS)

Acceptable --

41767113

(2,4-DBDMAS)Supplemental --

41767114

(2,4-DBDMAS)Supplemental --

850.2300 Avian 

reproduction Chronic (None) (NA) Yes

A guideline study 

compliant with the avian 

reproduction test 

guideline is required. 

2,4-DB may be 

persistent under certain 

conditions such that 

chronic terrestrial 

exposure is likely to 

occur. 

NonguidelineAvian 

inhalation Acute (None) (NA) No

2,4-DB has a vapor point 

of 7.1 x10-5 Torr and is 

not expected to 

volatilize. EFED’s STIR

model further indicated 

that inhalation is not 

likely to be a significant

pathway for exposure. 

Therefore, this study is 

not required at this time.

850.3020

Honey bee 

acute contact 

toxicity

Acute 00018842 Acceptable No --
Page 25 of 40

OCSPP 

Guideline

Data 

Requirement

Study 

Type

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data 

needed for 

risk 

assessment

Current Additional 

Data Need

850.3030

Honey bee 

residue on 

foliage

-- (None) (NA) No

The LD50 for the honey 

bee acute contact study 

was 14.5 μg/bee, just 

slightly above the trigger 

for the honey bee residue 

on foliage study of 11 

μg/bee. However, 2,4-

DB has not been 

highlighted as a 

pervasive pesticide in 

bee colonies and oral 

exposure will be 

negligible based on the 

use pattern. Therefore, 

this study is not being 

required at this time.

850.3040

Field testing 

for 

pollinators

-- (None) (NA) No

See explanation for 

Honey bee residue on 

foliage.

NonGuidelineHoneybee 

Foraging -- 00071149 Supplemental --

NonGuidelineHoneybee 

development -- 00111490 Supplemental --

850.4225 Seedling 

Emergence -- 48103301 --

Under 

Review

Currently Under Review

850.4100

Seedling 

Emergence 

and Seedling 

Growth

--

41605401

(2,4-DBDMAS)Invalid DER not retrievable

850.4250

Vegetative 

vigor -- 48103302 --

Under 

Review Currently Under Review

850.4225

850.4250

Seedling 

Emergence 

and 

Vegetative 

Vigor --

43054001

(2,4-DBDMAS)Invalid

The study was 

determined to be invalid 

due to flaws in the study 

methodology (e.g., dry 

Petri dishes in the seed 

germination study and a 

lack of criterion for seed 

germination) along with 

other more minor 

deviations. 1

QSAR Quantitative Structure-Activity Relationship a quantitative relationship between an endpoint (biological activity, e.g., toxicity) and one or 

more descriptors associated with the endpoint/activity. For more information on QSARs, see: 

http://www.epa.gov/oppfead1/international/naftatwg/guidance/qsar-guidance.pdf. 
Page 26 of 40

11. References 

Food and Agriculture Organization of the United Nations. 2000. FAO PESTICIDE DISPOSAL SERIES 8. 

Assessing Soil Contamination: A Reference Manual. Appendix 2. Parameters of pesticides that 

influence processes in the soil. Editorial Group, FAO Information Division. Rome.

Goring, C.A.I., D.A. Laskowki, J.H. Hamaker, and R.W. Meikle. 1975. Principles of pesticide degradation 

in soil. Pages 135-172 in (R. Haque and V.H. Freed, eds.) Environmental dynamics of pesticides. 

Plenum Press, New York.

Holt. E., Weber, R., Stevenson, G., and Gaur, C. 2010. Polychlorinated Dibenzo-p-Dioxins and 

Dibenzofurans (PCDD/Fs) Impurities in Pesticides: A Neglected Source of Contemporary 

Relevance. Environ. Sci. Technol. 44: 5409-5415.

USEPA. 2002a. Guidance for Selecting Input Parameters in Modeling the Environmental Fate and 

Transport of Pesticides, Version II (February 28, 2002). Office of Pesticide Programs, 

Environmental Fate and Effects Division, U.S. Environmental Protection Agency. Arlington, VA.

U.S. EPA. 2002b. Pesticide Root Zone Model (PRZM) Field and Orchard Crop Scenarios: Standard 

Procedures for Conducting Quality Control and Quality Assurance. Office of Pesticide Programs, 

Environmental Fate and Effects Division, U.S. Environmental Protection Agency. Arlington, VA. 

USEPA. 2004a. Environmental Fate and Effects Division Revised Risk Assessment 2 for 4-(2,4-

dichlorophenoxy) Butyric Acid (2,4-DB) and Dimethylamine 4-(2,4-dichlorophenoxy) Butyrate 

(2,4-DB DMAS) Reregistration Eligibility Document. DP Barcode 291209. United States 

Environmental Protection Agency (USEPA). Environmental Fate and Effects Division. Office of 

Pesticide Programs. December 13, 2004.

USEPA. 2004b. Overview of the Ecological Risk Assessment Process in the Office of Pesticide Programs. 

United States Environmental Protection Agency (USEPA). Environmental Fate and Effects 

Division. Office of Pesticide Programs. Available at 

http://www.epa.gov/espp/consultation/ecorisk-overview.pdf.

USEPA. 2005a. Reregistration Eligibility Decision (RED) for 2,4-DB. United States Environmental 

Protection Agency (USEPA). Office of Chemical Safety and Pollution Prevention (OCSPP) 

formerly Prevention, Pesticides and Toxic Substances. EPA 738-R-05-001. January 2005. 

USEPA. 2005b. Reregistration Eligibility Decision for 2,4-D. Office of Prevention, Pesticides and Toxic 

Substances, (7508C) EPA 738-R-05-002 June 2005. 

USEPA. 2010. Recommended Toxicity Equivalence Factors (TEFs) for Human Health Risk Assessments 

of 2,3,7,8-Tetrachlorodibenzo-p-dioxin and Dioxin-Like Compounds. Risk Assessment Forum, 

Washington, DC. EPA/600/R-10/005.

USEPA. 2012a. Reregistration Review Problem Formulation for 2,4-D. United States Environmental 

Protection Agency (USEPA). Office of Chemical Safety and Pollution Prevention (OCSPP). 

D#402410. November 15, 2012.
Page 27 of 40

USEPA. 2012b. 2,4-DB (030801) Screening Level Usage Analysis (SLUA). United States Environmental 

Protection Agency (USEPA). Biological and Economic Analysis Division. Office of Pesticide 

Programs. August 3, 2012.

USEPA. 2013. BEAD Chemical Profile for Registration Review: 2,4-DB Case (includes 2,4-DB which is 

manufactured as an acid and the dimethylamine salt, 2,4-DB-DMAS( 030801, 030819). 

Memorandum From M. Kaul, S. Haddad, and D. Berwald to Jill Bloom. Biological and Economic 

Analysis Division to Pesticide Re-evaluation Division. February 19, 2013.

Van den Berg, et. al.,1998. Toxic Equivalency Factors (TEFs) for PCBs, PCDDs, PCDFs for Humans and 

Wildlife. Environ Health Perspect 106(12): 775-792.

Van den Berg, et. al., 2006. The 2005 World Health Organization reevaluation of human and mammalian 

toxic equivalency factors for dioxins and dioxin-like compounds. Toxicol Sci 93(2):223-41.
Page 28 of 40

Appendix A. Bibliography of Submitted Studies

Environmental Fate

161-1 Hydrolysis

41101101 2060107

2021630

Rustum, A. (1988) Hydrolysis of Carbon 14|-2,4-DB in Buffered 

Aqueous Solutions: Laboratory ID: HLA 6015-395. Unpublished 

study prepared by Hazleton Laboratories America, Inc. 77 p. 

41888001 2010427 Ruzo, L.; Ewing, A. (1989) Determination of the pKa Value for 2,4-

DB: Lab Project Number: 167-1: 167. Unpublished study prepared 

by Pharmacology and Toxicology Research Lab. 24 p. 

41890601 

or 

41888001

2010427 Ruzo, L.; Ewing, A. (1989) Determination of the pKa Value for 2,4-

DB (Environmental Fate Data): Lab Project Number: 167-1: 167. 

Unpublished study prepared by Pharmacology and Toxicology 

Research Lab. 24 p. 

45512401 

Ruzo, L.; Ewing, A. (2001) Determination of the (pKa) Value for 

2,4-DB: Lab Project Number: 167-1: 167W. Unpublished study 

prepared by Pharmacology and Toxicology Research Laboratory 

West, Inc. 24 p. 

161-2 Photodegradation-water

41101102 2021630 Rustum, A. (1988) Artificial Sunlight Photodegradation of ?carbon 14|-

,4 DB in a Buffered Aqueous Solution: Project ID: HLA 6015-396. 

Unpublished study prepared by Hazleton Laboratories America, Inc. 

146 p. 

42067801 Supplemen

t to MRID 

41101102

Obrist, J. (1989) Artificial Sunlight Photodegradation of (Carbon 14) 

2,4-DB in a Buffered Aqueous Solution: (Supplement to MRID 

41101102): Lab Project Number HLA 6015-396. Unpublished study 

prepared by Hazleton Labs America, Inc. 39 p. 

161-3 Photodegradation-soil
Page 29 of 40

41101103 2014639 Saxena, A. (1988) Artificial Sunlight Photodegradation of ?\carbon 14|-

2,4-DB on Soil: Project ID: HLA 6015-397. Unpublished study 

prepared by Hazleton Laboratories America, Inc. 90 p. 

41101104 2014639 Saxena, A. (1988) Artificial Sunlight Photodegradation of carbon 14|-

2,4-DB in Soil: HLA 6015-397. Unpublished study prepared by 

Hazleton Laboratories America, Inc. 39 p. 

42678401 2021630 Lawrence, B.; Mobley, S.; Kesterson, A. (1993) Soil Surface 

Photolysis of (carbon 14)2,4-DB in Artificial Sunlight: Lab Project 

Number: 729: 1499. Unpublished study prepared by PTRL East, Inc. 

69 p. 

162-1 Aerobic soil metabolism

38385 Open lit MacRae, I.C.; Alexander, M. (1965) Microbial degradation of selected 

herbicides in soil. Journal of Agricultural and Food Chemistry 13(1):72-

76. (Also in unpublished submission received Oct 2, 1967 under 8F0643; 

submitted by Stauffer Chemical Co., Richmond, Calif.; CDL:091118-S) 

41325501 2022165

2021630

Saxena, A. (1989) Aerobic and Aerobic/Anaerobic Soil Metabolism of 

Carbon - 14|-2,4- DB in a Sandy Loam Soil: Lab Project Number: 

HLS/6015/398. Unpublished study prepared by Hazleton Laboratories 

Americas, Inc. 108 p. 

162-2 Anaerobic soil metabolism

41325501 2022165

2021630

Saxena, A. (1989) Aerobic and Aerobic/Anaerobic Soil Metabolism of 

Carbon - 14|-2,4- DB in a Sandy Loam Soil: Lab Project Number: 

HLS/6015/398. Unpublished study prepared by Hazleton Laboratories 

Americas, Inc. 108 p. 

163-1 Leach/adsorp/desorption

143294 2014639 Hormby, T. (1978) Alanap Soil Persistence Study: PL No. 8PL-21-A. 

Unpublished study prepared by Biospherics Inc. 55 p. 

41101105 2058228

2058532 

2021630-

Rustum, A. (1987) The Adsorption and Desorption of ?carbon 14|-2, 4-

DB on Representative Agricultural Soils: Project ID: HLA 6015-394. 

Unpublished study prepared by Hazleton Laboratories America, Inc. 59 

p. 
Page 30 of 40

41617201 

or 

41101105

2058228 

2014639 

Rustrum, A. (1987) The Adsorption and Desorption of (Carbon 14)-2, 4-

DB on Representative Agricultural Skills: Desorption Coefficient Data: 

Lab Project Number: HLA 6015-394. Unpublished study prepared by 

Hazleton Laboratories America, Inc. 8 p. supplemental data

164-1 Terrestrial field dissipation

41325502 2021630- Norris, F. (1989) A Small Scale Field Soil Dissipation Study with 4-(2,4-

Dichlorophenoxy)Butyric Acid (2,4-DB) the Active Ingredient of Butyrac 

Brand Herbicide: Lab Project Number: 40643.4-1 Unpublished study 

prepared by Rhone-Poulenc Ag Co. in cooperation with A & L Eastern 

Agricultural Laboratories, Inc. and CYAL. 100 p. 

44660502 2021630- White, J.; Taulbee, L.; Horn, W. et al. (1998) Terrestrial Dissipation of 2,4 

Dichlorophenoxy Butyric Acid Applied to Peanuts: Lab Project Number: 

1007: 2010. Unpublished study prepared by PTRL East, Inc. and Hickey's 

Agri-Services Laboratory, Inc. 1007 p. 

44660503 2021630- White, J.; Taulbee, L.; Horn, W. et al. (1998) Terrestrial Dissipation of 2,4

Dichlorophenoxy Butyric Acid Applied to Soybeans: Lab Project 

Number: 1008: 2007:. Unpublished study prepared by PTRL East, Inc. 

and Easton Agri-Consulting, Inc. 526 p. 

44680701 2021630- White, J.; Horn, W.; Johnson, T. (1998) Terrestrial Dissipation of 2,4-

Dichloro-phenoxy Butyric Acid Applied to Alfalfa: Lab Project Number: 

1009: 2004. Unpublished study prepared by PTRL East, Inc., A.C.D.S. 

Research, Inc., and A & L Great Lakes Laboratories, Inc. 395 p.

165-4 Fish accumulation

2010407 2021630 - waiver request

Non Guideline or possibly Bridging Data

42741501 2021630- Andrews, K. (1993) Dissociation of 2,4-DB Dimethyl Amine Salt 

(DMAS) in Water: Lab Project Number: SC920205. Unpublished study 

prepared by Battelle Columbus Operations. 60 p.

43779601 2021630- Reynolds, J. (1995) Aerobic Aquatic Metabolism of (Carbon-14)-

Dimethylamine: Lab Project Number: XBL95031: RPT00231: 8437. 

Unpublished study prepared by XenoBiotic Labs, Inc. 118 p. PC Code 

030019

43908301 2021630- Reynolds, J. (1995) Anaerobic Aquatic Metabolism of (Carbon 14)-

Dimethylamine: Lab Report No. RPT00246; Study No. XBL95032. 

Unpublished study prepared by XenoBiotic Labs., Inc. 128 p. PC Code 
Page 31 of 40

030019

41479702 2021630- Shepler, K.; Chari, S.; Ruzo, L. (1990) Vapor Phase Photolysis of (Carbon 

14)4-(2,4-Dichlorophenoxy) Butyric Acid (2,4-DB Acid}: PTRl Report 

No.: 201W: 201W-1. Unpublished study prepared by Pharmacology & 

Toxicology Research Laboratories-West. 77 p. PC Code 030853
Page 32 of 40

Ecological Effects

2,4- DB PC Code 030801

71-1 Avian Single Dose Oral Toxicity

36395 2010395 Atkins, E.L.; Greywood, E.A.; Macdonald, R.L. (1975) Toxicity of 

Pesticides and Other Agricultural Chemicals to Honey Bees: Laboratory 

Studies. By University of California, Dept. of Entomology.: UC, 

Cooperative Extension. (Leaflet 2287; published study.) CALLED HILL 

et al.

92162 2010395 

2010399

Weatherholtz, W.M. (1969) Final Report: Acute Toxicity Study—Ducklings: Project No. 656-113. (Unpublished study received Dec 16, 1970 

under 1F1089; prepared by TRW, Inc., submitted by Rhodia, Inc., New 

Brunswick, N.J.; CDL:090849-E) 

41370102 2010401 Pederson, C. (1989) 2,4-DB Technical Acid: 21-Day Acute Oral LD50 

Study in Bobwhite Quail: Final Report: Lab Project ID: # 89 QD 132. 

Unpublished study prepared by Bio-Life Associates, Ltd. 33 p. 

41767112 2039718 Pedersen, C. (1991) Hinder: 21-Day Acute Oral LD50 Study in Bobwhite Quail: Lab Project Number: 109-003-03. Unpublished study 

prepared by Bio-Life Associates, Ltd. 32 p

71-2 Avian Subacute Dietary 

41767113 2039718 Pedersen, C. (1991) Hinder: 8-Day Acute Dietary LC50 Study in 

Bobwhite Quail: Lab Project Number: 109-001-01. Unpublished study 

prepared by Bio-Life Associates, Ltd. 27 p.

41767114 2039718 Pedersen, C. (1991) Hinder: 8-Day Acute Dietary LC50 Study in Mallard 

Ducklings: Lab Project Number: 109-002-02. Unpublished study prepared 

by Bio-Life Associates, ltd. 29 p. 

71-4 Avian Reproduction

46395401 2022164 Pigott, G. (2004) Request for a Waiver for a 2,4-DB Avian Reproduction 

Study. Project Number: DBTF/102604/1. Unpublished study prepared by 
Page 33 of 40

2,4-DB Task Force. 5 p.

72-1 Acute Toxicity to Freshwater Fish

50682 2010400 Bentley, R.E. (1974) Acute Toxicity of Three Anchem Compounds to 

Bluegill (Lepomis macrochirus) and Rainbow Trout (Salmo gairdneri). 

(Unpublished study received Sep 13, 1974 under 264-143; prepared by 

Bionomics EG&G, Inc., submitted by Union Carbide Agricultural 

Products Co., Inc., Ambler, Pa.; CDL: 131083-A)

40762601 2010398 McCann, J. (1976) Biological Report of Analysis of Amchem Technical 

2,4-DB: Rainbow Trout (Salmo gairdneri): Static Jar Test 928. 

Unpublished study prepared by Terrestrial and Aquatic Biology 

Laboratory. 2 p. 

40094602 2010396 Johnson, W.; Finley, M. (1980) Handbook of Acute Toxicity of 

Chemicals to Fish and Aquatic Invertebrates: Resource Publication 137. 

US Fish and Wildlife Service, Washington, D.C. 106.

40762602 2010397 McCann, J. (1976) Biological Report of Analysis of Amchem Technical 

2,4-DB: Bluegill (Lepomis macrochirus): Static Jar Test 938. Unpublished 

study prepared by Terrestrial and Aquatic Biology Laboratory. 1 p.

72-2 Acute Toxicity to Freshwater Invertebrates

MRID Citation Reference

41407801 2010404 McNamara, P. (1990) 2,4 DB-acid--Acute Toxicity to Daphnids (Daphnia 

magna) during a 48-hour Flow-through Acute Exposure: Final Report: 

Lab Report # 89-7-3031; Study # 10566.0289.6125.115. Unpublished 

study prepared by Springborn Laboratories, Inc., Environmental Sciences 

Div. 39 p. 

122-1 Seed Germination/Seedling Emergence and Vegetable Vigor

41605401 2101406 Hoberg, J. (1990) 2,4 DB Amine-Determination of Effects on Seedling 

Germination, Seed Emergence and Vegetative Vigor of Ten Plant Species: 

Lab Project Number: 10566-0289-6130-610: 90-4-3280. Unpublished 

study prepared by Springborn Laboratories, Inc. 150 p. 

123-1 Seed germination/seedling emergence and vegetative vigor
Page 34 of 40

43359001 Hoberg, J. (1994) 2,4-DB Amine--Determination of Effects on Seedling 

Germination, Shoot Emergence and Vegetative Vigor of Ten Plant 

Species: Supplement: Lab Project Number: 90-4-3280: 93-6-4820. 

Unpublished study prepared by Springborn Laboratories, Inc. 94 p. 

850.1075 Fish acute toxicity test, freshwater and marine

47930401 Warbritton, R. (2005) Butoxone 200: Flow-Through Acute Toxicity Test 

with the Sheepshead Minnow, Cyprinodon variegatus. Project Number: 

49718. Unpublished study prepared by ABC Laboratories, Inc. 46 p.

850.2300 Avian reproduction test

46395401 2022164 Pigott, G. (2004) Request for a Waiver for a 2,4-DB Avian 

Reproduction Study. Project Number: DBTF/102604/1. Unpublished 

study prepared by 2,4-DB Task Force. 5 p.

850.4000 Plants Aquatic Vascular

46395501 2022962

2022963

Mattock, S. 1999. 2,4-DB Sodium 400 g/L: Toxicity to Lemna minor. 

Unpublished study performed by Covance, North Yorkshire, England. 

Laboratory Project ID No. 78.516 1 -D2 145. Study submitted by 2,4-DB 

Task Force, Richard J. Otten, EPA Liason, Raleigh, North Carolina. Study 

initiated November 11, 1998 and completed

February 1999.

850.???? Plants Aquatic Growth and Reproduction 

41407803 2080565 Giddings, J.M. 1990. 2,4 DB Amine - Toxicity to the Freshwater Green 

Alga Selenastrum caricornutum. Report No. 90-1-3196. Conducted by 

Springborn Laboratories, Inc., Wareham, MA. Submitted by 2,4 DB Task 

Force, c/o Rhone-Poulenc Ag Company, Research Triangle Park, NC.
Page 35 of 40

PC Code 030819 2,4-DBMAS 

71-1 Avian Acute Toxicity

41407802 2010437 Sousa, J. (1990) 2,4 DB Amine--Acute Toxicity to Bluegill (Lepomis 

macrochirus) under Flow-through Conditions: Final Report: Lab Report # 

89-6-3059; Study # 10566.0289.6126.105. Unpublished study prepared by 

Springborn Laboratories Inc., Environmental Sciences Div. 38 p.

71-2 Avian Dietary Toxicity

108367 Fink, R. (1974) Final Report: Eight-day Dietary LC50--Bobwhite Quail: 

Butyrac 175|: Project No. 113-105. (Unpublished study received Apr 17, 

1974 under unknown admin. no.; prepared by Truslow Farms, Inc., 

submitted by Union Carbide Agricultural Products Co., Inc., Research 

Triangle Park, NC; CDL:131724-A) 

108368 Fink, R. (1974) Final Report: Eight-day Dietary LC50--Mallard Ducks: 

Butyrac 175|: Project No. 113-106. (Unpublished study received Mar 20, 

1974 under unknown admin. no.; prepared by Truslow Farms, Inc., 

submitted by Union Carbide Agricultural Products Co., Inc., Research 

Triangle Park, NC; CDL:131724-B) 

126694 Ross, D.; Burroughs, S.; Roberts, N. (1974) The Acute Toxicity (LC50) of 

Mecoprop Formulated to Japanese Quail: BTS63/74875. (Unpublished 

study received Apr 1, 1983 under 2217-EX-3; pre- pared by Huntingdon 

Research Centre, Eng., submitted by PBI- Gordon Corp., Kansas City, 

MO; CDL:071502-B) 

126695 Ross, D.; Burroughs, S.; Roberts, N. (1974) The Acute Toxicity (LD50) of 

Mecoprop Formulated to Mallard Duck: BTS64/74664. (Unpublished 

study received Apr 1, 1983 under 2217-EX-3; pre- pared by Huntingdon 

Research Centre, Eng., submitted by PBI- Gordon Corp., Kansas City, 

MO; CDL:071502-C) 

41370103 2010402 Pedersen, C. (1989) Butyrac 200: 8-Day Acute Dietary LC50 Study in 

Bobwhite Quail: Final Report: Lab Project ID: # 89 QC 130; HLA 6012-

273. Unpublished study prepared by Bio-Life Associates, Ltd. and 

Hazleton Laboratories, America, Inc. 71 p. 

72-1 Acute Toxicity to Freshwater Fish

92168 Syracuse University Research Corporation (1970) Report on the Acute 

Toxicity of Butoxone Amine, Butoxone Ester and Cantrol to the Fathead 

Minnow (Pimephales promelas Rafinesque) and the Rain- bow Trout 
Page 36 of 40

(?~Salmo guairdneri ~?sic|). (Unpublished study, including published 

data, received Dec 16, 1970 under 1F1089; submitted by Rhodia, Inc., 

New Brunswick, N.J.; CDL:090849-L) 

116347 Syracuse Univ. Research Corp. (1970) Report on the Acute Toxicity of 

Butoxone Amine, Butoxone Ester and Can-Trol to the Fathead Minnow 

(Pimephales promelas Rafinesque) and the Rainbow Trout (Salmo 

guairdneri). (Unpublished study received on unknown date under 1F1051; 

submitted by Rhodia, Inc., New Brunswick, NJ; CDL: 091885-I) 

41370104 2010403 Sousa, J. (1989) 2,4-DB Amine Acute Toxicity to Rainbow Trout 

(Oncorhynchus mykiss) under Flow-through Conditions: Final: SLS 

Report # 89-6-3003; Study 1056.0289.6126.108. Unpublished study 

prepared by Springborn Laboratories, Inc. Environmental Sciences Div. 

39 p. 

41407802 2010405 Sousa, J. (1990) 2,4 DB Amine--Acute Toxicity to Bluegill (Lepomis 

macrochirus) under Flow-through Conditions: Final Report: Lab Report # 

89-6-3059; Study # 10566.0289.6126.105. Unpublished study prepared by 

Springborn Laboratories Inc., Environmental Sciences Div. 38 p. 

41642701 2010432 

2010436

Putt, A. (1990) 2,4 DB Amine: Acute Toxicity to Daphnids (Daphnia 

magna) During a 48-hour Flow-through Exposure: Final Report. Lab 

Project Number: Report 90-8-3451; STUDY 10566.0289.6127.115. 

Unpublished study prepared by Springborn Labs, Inc. 63 p.

72-4 Fish Early Life Stage/Aquatic Invertebrate Life Cycle Study

54668 Davis, J.T.; Hardcastle, W.S. (1960) Biological assay of herbicides for fish 

toxicity. Weeds 7:397-404. (Also in unpublished submission received Aug 

26, 1977 under 4581-EX-30; submitted by Pennwalt Corp., Philadelphia, 

Pa.; CDL:231831-J)

122-2 Aquatic plant growth

41407803 Giddings, J. (1990) 2,4-DB Amine--Toxicity to the Freshwater Green Alga 

Selenastrum capricornutum: Final Report: Lab Report # 90-1- 3196; Study 

# 10566-0289-6129-430. Unpublished study prepared by Springborn 

Laboratories, Inc., Environmental Sciences Div. 29 p. 

123-1 Seed germination/seedling emergence and vegetative vigor

43054001 2010435 Hoberg, J. (1993) 2,4 DB Amine--Determination of Effects on Seed 

Germination and Seedling Emergence of Several Plant Species: 

Supplemental Report: Lab Project Number: 93/6/4820: 
Page 37 of 40

10566/0289/6130/610: 90/4/3280. Unpublished study prepared by 

Springborn Labs, Inc. 93 p. 

41605401 2010434

2010428

2010429

Hoberg, J. (1990) 2,4 DB Amine-Determination of Effects on Seedling 

Germination, Seed Emergence and Vegetative Vigor of Ten Plant Species: 

Lab Project Number: 10566-0289-6130-610: 90-4-3280. Unpublished 

study prepared by Springborn Laboratories, Inc. 150 p

850.1075 Fish acute toxicity test, freshwater and marine

47930401 Warbritton, R. (2005) Butoxone 200: Flow-Through Acute Toxicity Test 

with the Sheepshead Minnow, Cyprinodon varietgatus. Project Number: 

49718. Unpublished study prepared by ABC Laboratories, Inc. 46 p.

850.4225 Seedling emergence, Tier II

48103301 Aufderheide, J. (2005) Butoxone 200: Effects on the Seedling Emergence 

and Growth of Non-Target Terrestrial Plants (Tier II). Project Number: 

49715. Unpublished study prepared by ABC Laboratories, Inc. 82 p.

850.4250 Vegetative vigor, Tier II

48103302 Aufderheide, J. (2006) Butoxone 200: Effects on the Vegetative Vigor of 

Non-Target Terrestrial Plants (Tier II). Project Number: 49716. 

Unpublished study prepared by ABC Laboratories, Inc. 79 p.
Page 38 of 40

Appendix B. Ecological Model Results

A. SIP (version 1.0)

Table 1.Inputs

Parameter Value

Chemical name 2,4-DB

Solubility (in water at 25°C; mg/L) 46

Mammalian LD50 (mg/kg-bw) 1470

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian 

Mammalian NOAEL (mg/kg-bw) 3

Mammalian fest species laboratory rat

Body weight (g) of "other" mammalian 

i

Avian LD50 (mg/kg-bw) 1536

Avian test species northern bobwhite quail

Body weight (g) of "other" avian species

Mineau scaling factor 1.15

Mallard NOAEC (mg/kg-diet) 0

Bobwhite quail NOAEC (mg/kg-diet) 0

NOAEC (mg/kg-diet) for other bird species 0

Body weight (g) of other avian species

NOAEC (mg/kg-diet) for 2nd other bird

Bodyi weight (g) of 2nd other avian species

Table 2. Mammalian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 7.91 7.9120

Adjusted toxicity value (mg/kg-bw) 1130.6660 2.3075

Ratio of exposure to toxicity 0.0070 3.4288

Conclusion* Drinking water 

exposure alone is

NOT a potential 

concern for mammals

Exposure through

drinking water alone is

a potential concern for

mammals

Table 3. Avian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 37.2600 37.2600

Adjusted toxicity value (mg/kg-bw) 1106.5797 0.0000

Ratio of exposure to acute toxicity 0.0337 0.0000

Conclusion* Drinking water 

exposure alone is

NOT a potential 

concern for birds

Due to insufficient 

data, risk cannot be 

precluded
Page 39 of 40

STIR (version 1.0)
Page 40 of 40

EPI SuiteTM v4.11 Results

Level III Fugacity Model (Full-Output):

=======================================

 Chem Name : 2,4-Dichlorophenoxybutyric acid

 Molecular Wt: 249.1

 Henry's LC : 3.14e-009 atm-m3/mole (user-entered)

 Vapor Press : 7.1e-005 mm Hg (user-entered)

 Log Kow : 3.91 (user-entered)

 Soil Koc : 98.4 (KOCWIN MCI method)

 Mass Amount Half-Life Emissions

 (percent) (hr) (kg/hr)

 Air 0.0261 18 1000 

 Water 17.6 900 1000 

 Soil 82.3 1.8e+003 1000 

 Sediment 0.117 8.1e+003 0 

 Fugacity Reaction Advection Reaction Advection

 (atm) (kg/hr) (kg/hr) (percent) (percent)

 Air 1.18e-012 47 12.2 1.57 0.407 

 Water 5.18e-014 634 823 21.1 27.4 

 Soil 1.01e-012 1.48e+003 0 49.5 0 

 Sediment 5.12e-014 0.468 0.109 0.0156 0.00364 

 Persistence Time: 1.56e+003 hr

 Reaction Time: 2.16e+003 hr

 Advection Time: 5.61e+003 hr

 Percent Reacted: 72.2

 Percent Advected: 27.8

 Half-Lives (hr), (based upon Biowin (Ultimate) and Aopwin):

 Air: 18.02

 Water: 900

 Soil: 1800

 Sediment: 8100

 Biowin estimate: 2.542 (weeks-months)

 Advection Times (hr):

 Air: 100

 Water: 1000

 Sediment: 5e+004