UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON. D.C. 20460 

March 12, 2014 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

PC Codes: 019201, 019202 

MEMORANDUM DP Barcode: 414994 

SUBJECT: Registration Review; Preliminary Problem Formulation for Environmental Fate, 

Ecological Risk, Endangered Species, and Human Health Drinking Water 

Exposure Assessments for MCPB 

FROM: Hannah Yingling, Biologist-1JJ-~ (, '3~r~N Larry Liu, Environmental Scientist, Ph~~.,-...J?(/\-/ 

Environmental Risk Branch V 

Environmental Fate and Effects Division (7507P) • 

THROUGH: Mah Shamim, Branch Chief, Ph.D. A/l.dP...h !~ ..3/!2-/If 

Environmental Risk Branch V /1/frv~ Environmental Fate and Effects Division (7507P) 

TO: Khue Nguyen 

Neil Anderson 

RM 51 

Pesticide Re-Evaluation Division (7508P) 

Page 1 of46 
Page 2 of 46

1. Executive summary

The Environmental Fate and Effects Division (EFED), of OPP has completed the problem 

formulation for the ecological risk, environmental fate, endangered species, and drinking water 

assessments for the registration review of MCPB acid (PC code 019201) and associated sodium

salts (PC code 019202). The herbicide MCPB is currently manufactured as a sodium salt. 

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

environmental fate and ecological risk assessment and the drinking water assessment in support 

of registration review for MCPB acid. As such, it provides an overview of the environmental 

fate and ecological effects data available for MCPB as well as uncertainties unique to a risk 

assessment of MCPB. 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 40CFR158. The required studies are listed below. 

o Soil Photolysis (835.2410)

o Anaerobic Aquatic metabolism (835.4400)

o ILVs for the submitted Soil and Water ECMs (850.6100)

o Storage Stability (835.6100)

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

outlined in the 40CFR158. The required studies are listed below. 

o Freshwater invertebrate life cycle (850.1300)

o Estuarine/Marine invertebrate life cycle (850.1350)

o Estuarine/Marine fish ELS (850.1400)

o Adult and Larval acute oral honeybee study (OECD 213/237)

o Aquatic Plant Toxicity Test (850.4400)

o Algal Toxicity Study (850.4500)

o Avian Reproduction with Mallard (850.2300)

o Acute Avian Toxicity with Passerine species (850.2100)

• EFED has received the following studies which are currently under review. Once the 

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

associated data requirements. However, until these determinations have been made, these 

data are considered necessary for risk assessment.

o Terrestrial Field Dissipation (835.6100)

o ECMs for Soil and Water Analysis (850.6100)

o Acute toxicity with Sheepshead Minnow (850.1075)

o Freshwater fish ELS (850.1400)

2. Introduction

The herbicide MCPB is part of the phenoxy class of herbicides and acts as a systemic growth 

regulating hormone that disrupts hormone (auxin) balance and protein synthesis resulting in plant 
Page 3 of 46

growth abnormalities. The compound is registered for use on peas (field, canned, and dried) and 

mint. MCPB is applied once annually via aerial or ground spray. The purpose of this problem 

formulation is to broadly review the registered uses of MCPB and identify potentially complete 

environmental exposure pathways to be assessed during comprehensive ecological risk 

assessment. This document specifically addresses MCPB and its degradates MCPA, 4-(4-

hydroxy-o-tolyoxy) butyric acid, 2,4-dihydroxyphenyl formate, o-cresol, and 4-choloro-cresol.

EFED evaluated the most recent ecological risk assessments for MCPB in association with the 

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

available and if further data are needed to support registration review. Recent risk assessments

include a 2005 assessment in support of the reregistration eligibility decision (RED) for use on 

peas and a 2008 assessment for the use of MCPB on mint. In addition, EFED considered the 

latest Agency science policies and risk assessment methodologies. The structure of MCPB as 

well as the chemical names and other identifiers can be found in the chemical identity table.

3. Use Characterization

MCPB sodium salt is currently registered for use on field peas and mint. It is formulated as 

soluble concentrate, and applied as a postemergent herbicide to control or suppress Canada 

thistle bud formation. MCPB sodium salt is applied when the peas are tolerant to the herbicide, 

from shoot emergence until about three leaf nodes before flowering (typically 6 to 12 nodes). 

Canada thistle reduces pea yields through competition and presents problems during harvesting. 

The thistle plant material is difficult to remove from the harvested crop resulting in loss of crop 

quality and profit to the grower. Other target weeds include wild mustard, common 

lambsquarters, pigweed, cocklebur, smartweed, etc. There are two registered products: 

Thistrol® Herbicide (71368-5) and Sodium MCPB Solution (15440-38). The registrant is 

Nufarm, Inc. Both product labels list the active ingredient (23.5%) as sodium salt of 4-(2-

methyl-4-chlorophenoxy) butyric acid and 76.5% inert ingredients (not provided). Table 1

summarizes the application rates from the various product labels for all applications. 

Table 1. Use of MCPB and MCPB sodium salt.

Crop Products Single Appl. 

Rate (lb ae/A)

Max # 

Appl./Year

Minimum 

Appl. 

Interval 

(days)

Max 

Appl. 

Rate/Year 

(lb ae/A)

Appl. Methods

Peas and 

mint

Thistrol® 

Herbicide

Peas (0.5-1.5) 1 N/A 1.5 Spray/ground 

and aerial

Mint (0.25-

0.50) 2

6 months 

(spring and 

fall 

applications)

1.0 Spray/ground 

and aerial

Peas

Sodium 

MCPB 

Solution

Peas (0.5-1.5) 1 N/A 1.5 Spray/ground 

and aerial
Page 4 of 46

4. Conclusions from Previous Risk Assessments

a. Ecological Risk Assessment 

The most recent comprehensive assessment conducted for MCPB is the Environmental Fate and 

Ecological Risk Assessment for the Reregistration of MCPB and MCPB Sodium for use on peas, 

conducted in 2005 conducted in support of the RED. At the time of the RED, the Agency

concluded that MCPB estimated risks exceeded the level of concern (LOC) for the following: 1) 

chronic risk to mammals that consume grass, broadleaf plants, and small insects, 2) acute risk to 

small birds that consume short grasses, 3) non-target terrestrial plants, 4) federally endangered or 

threatened birds, mammals, aquatic and semi-aquatic plants.

The major ecological conclusions presented can be found in Table 2.

Table 2. Summary of Risk Concerns Identified for MCPB in Previous Assessments

Birds Mammals Terr.

Plants

Terr.

Inverts Fish BCF Aquatic Inverts

Aquatic 

Plants

Groundwater 

Contamination Persistence Degrades of Concern

Yes1 Yes2 Yes No No No No No Yes Yes Yes3

1

Acute risk to avian species. No chronic data was submitted 2

No acute risk; Chronic risk in all weight classes

3

Drinking water assessment completed in 2005 included MCPB and its degradates (MCPA, CHPA/CHPA hexose 

conjugate

One of the major degradates, MCPA, is a registered phenoxy herbicide. Refer to the 2014 

MCPA Problem Formulation for additional information on ecological risk conclusions.

b. Drinking Water Exposure Assessments

Two drinking water exposure assessments were previously conducted, one on pea and one on 

mint in 2005 and 2008, respectively. In the 2005 drinking water assessment from labeled uses 

on peas, the exposure estimates of MCPB residues produced maximum exposures, on an acidequivalents basis, of 54.7 μg ae/L (1-in-10-year peak to represent acute risk), 13.5 μg ae/L (1-in10-year annual mean to represent chronic risk), and 7.3 μg ae/L (30-year mean to represent 

cancer risk) for surface water and 2.1 μg ae/L for groundwater. 

In the 2008 drinking water assessment from labeled uses on mint, the estimates of MCPB 

residues produced maximum exposures, on an acid-equivalents basis, of 9.6 μg ae/L (1-in-10-

year peak to represent acute risk), 9.1 μg ae/L (1-in-10-year annual mean to represent chronic 

risk), and 7.8 μg ae/L (30-year mean to represent cancer risk) for surface water. Since the EECs 

calculated for the mint scenario are lower than the previous estimates in 2005, EFED concluded 

that, for the drinking water assessment purpose, the previous estimated drinking water 

concentrations for use on peas should be used as the representative drinking water concentrations 

for use on mint.
Page 5 of 46

At that time, estimated drinking water concentrations (EDWC) of MCPB for drinking water from 

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

[6 % of the acute population adjusted dose (aPAD), and < 22% 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. Therefore, the estimated levels in surface water and or 

ground water did not contribute to posing a dietary concern for MCPB

When EFED receives the anaerobic aquatic metabolism study as requested in this Problem 

Formulation, a Residue of Concern Knowledgebase Subcommittee (ROCKS) meeting and an 

updated drinking water assessment may be needed as part of the Registration Review process. 

EFED will include the recently revised percentage crop area (PCA) factors as well as the newlydeveloped PRZM-GW 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.

c. Clean Water Act Programs

The herbicide MCPB 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 MCPB. Aquatic benchmarks have not been 

established for MCPB 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. 

5. Environmental Fate and Transport

MCPB is an acidic compound (pKa value of 4.6). This acid strength is comparable to that for 

acetic acid (a component present at a concentration of 5% in vinegar). Because of its acidity, 

MCPB will exist predominately in the ionic (anionic) or salt form at typical environmental pHs. 

The calculated degree of ionization corresponding to MCPB’s acid strength is greater than 99% 

at pH 7, and ranges from approximately 70% to 99.99+% from pH 5 to 9, respectively. In all 

formulations registered for field application, MCPB is formulated as its sodium salt, which has a 

water solubility of approximately 200,000 mg/L. For quantification purpose, the application rate 

information is converted to acid equivalent (ae).

The relatively low vapor pressure (4.0 x10-7 torr) for MCPB and collateral evidence showing its 

absence in traps for volatile organic compounds in various laboratory studies indicate that it can 

be classified as between “non-volatile” and “intermediate to high volatility” under field 

conditions.

Two aerobic soil metabolism studies have been reviewed. In the first study (MRID 43247601), 

two by-products of MCPB, although minor (<10%) in concentration, are also of potential 

concern because of their structural similarity to parent MCPB. These are: (1) MCPA [(4-chloro-
Page 6 of 46

2-methylphenoxy)acetic acid], which is another registered herbicide of the phenoxy class, and 

(2) the closely related CHPA-hexose conjugate [(4-chloro-2-methylphenoxy)-2-βglucopyranoside acetic acid]. In the available aerobic soil metabolism study, these two 

compounds were each detected at average maxima of approximately 6-7% of applied 

radioactivity during the first 3 to 15 days of incubation, with both decreasing to less than 2% by 

the end of a 120-day study. The only major identified transformation product was carbon 

dioxide.

The biotransformation of [phenyl-U14C]-labeled 4-(4-chloro-2-methylphenoxy)butyric acid

(MCPB) under aerobic conditions was studied in three US soils from North Dakota (MRID 

47784801). MCPB dissipated with half-lives of 8.5 days in the sandy loam soil, 2.5 days in the 

silty clay loam soil and 4.3 days in the loam soil. Three transformation products were identified. 

MCPA (4-chloro-2-methylphenoxyacetic acid) was a major transformation product in all three

soils. HMCPA (4-chloro-2-hydroxymethylphenoxyacetic acid) and PCOC (4-chloro-2-

methylphenol) were minor products.

The MCPA metabolite, as previously documented in its USEPA Reregistration Eligibility 

Document (dated September 30, 2004) and evidenced in fate studies of MCPB, is similar to 

MCPB in many characteristics. Although information was lacking for the CHPA-hexose 

conjugate, it was assumed to share the same general chemical profile based on structural 

similarity. Because of their relatively minor presence and lack of persistence inclusion of these 

two metabolites had little influence on the overall risk assessment summarized in the RED. 

Nevertheless, both metabolites were included in combination with parent MCPB as total toxic 

residues (TTR) with a combined or overall half-life of 26 days and assumed toxicities and 

environmental fate properties equivalent to parent. For modeling purposes, in order to allow for 

natural variation in the microbiological activity of soils, the single soil half life value was 

multiplied by three to approximate an upper confidence bound for an average half-life from 

multiple soils. This yielded an aerobic soil metabolism half life of approximately 78 days. 

In the soil anaerobic metabolism study, MCPB had a half-life of approximately 11 days in the 

total water and soil system (MRID 43015501). Similarly, for modeling purposes, in order to 

allow for natural variation in microbiological activity of soils, EFED multiplied the single soil 

half life by three to approximate an upper confidence bound for an average half-life from 

multiple soils. This yielded an anaerobic soil metabolism half life of approximately 34 days. The 

major transformation product in the aerobic phase of this anaerobic soil metabolism study was 

MCPA [(4-chloro-2-methylphenoxy) acetic acid]. 

MCPB is essentially stable to hydrolysis (extrapolated half-life greater than 500 days based on a 

study lasting only 30 days. MRID 42574301), but photolyzes in water under optimal light 

exposure conditions with half-lives of approximately 2 to 3 days (MRID 425743052). When 

these photolysis half-lives are used in current EFED aquatic models, factors such as water clarity 

and depth increase the effective aquatic photolosys half life to approximately 124 times longer 

(250 to 400 days). Phototransformation products included 4 -(4-hydroxy-o-tolyloxy)butyric acid; 

2,4-dihyroxyphenyl formate; o-cresol; benzoic acid; and 2-hydroxyphenyl formate. Specific 

study information is not available concerning the fate of these products. These photolysis 

products are not being considered in the forthcoming the risk assessment in part because they 
Page 7 of 46

are not expected to be persistent in the aquatic environment based on chemical structure and 

because they are expected to occur at concentrations far below that of the parent compound.

Adsorption/desorption (batch equilibrium MRID 42693701) of MCPB in four soils and one 

sediment indicate that MCPB is classified as “highly mobile”. Mean adsorption coefficients 

(Kads) measured for each of the soils were 1.69, 0.26, 0.65, and 0.78 mL/g (median of 0.72, 

average of 0.85 mL/g); respective textures of these soils were sandy clay loam, sand, sandy 

loam, and clay loam. The sediment was a sandy loam (pH of 5.95 and 2.85% organic carbon) for 

which the mean Kads was 10.58 mL/g. Adsorption coefficients normalized for organic carbon 

(Koc) are 129.57, 47.91, 85.54, 31.27, and 371.17 mL/g organic carbon for the sandy clay loam, 

sand, sandy loam, and clay loam soils and sandy loam sediment, respectively (average Koc for 

the five values of 130 mL/g organic carbon, median of 86 mL/g organic carbon). The study was 

not consistent with guidelines because the soils used in the study were not the same as those used 

in the aerobic soil metabolism studies.

Based on its acid nature and consistent correlations among relatively high solubility, relatively 

low log octanol-water partitioning ratio (1.33 at pH 7), and relatively low sorption to soil, MCPB 

would be prone to leach to ground water and runoff to surface water. Judging from these factors 

and its lack of persistence in soil, bioconcentration of MCPB is not expected.

A study entitled, “Determination of the degradation of [14C]-MCPB in aerobic water/sediment 

systems” (MRID 46837205) was reviewed. This study is classified as supplemental. The 

material balance was highly variable during the study, ranging from 27.4-100.5% of the applied 

in the TNO system and from 55.7-101.1% in the Kromme Rijn system (reviewer-calculated 

values). Variability between replicate samples was high at some intervals. Also, the samples 

were analyzed for MCPB and its transformation product at only three intervals, which was 

insufficient to accurately define the rate and pattern of dissipation. 
Page 8 of 46

Table 3. Physical Chemical Properties and Environmental Fate Parameters of MCPB.

Parameter Value Description Source (MRID)

 Selected Physical/Chemical Parameters

Chemical Structure

MCPB

 Sodium MCPB

Test substance –

MCPB

Test substance –

sodium MCPB

2006 EFED Science 

Chapter

IUAPC Names

4-(4-Chloro-o-tolyloxy)butyric acid 

Sodium 4-(4-chloro-o-tolyloxy)butyric acid

Test substance –

MCPB

Test substance –

sodium MCPB

2006 EFED Science 

Chapter

CAS Names

4-(4-Chloro-2-methylphenoxy)butanoic 

acid 

Sodium 4-(4-chloro-2-

methylphenoxy)butyric acid

Test substance –

MCPB

Test substance –

sodium MCPB

2006 EFED Science 

Chapter

CAS No.

94-81-5

6062-26-6

Test substance –

MCPB

Test substance –

sodium MCPB

2006 EFED Science 

Chapter

Molecular Weight 

(molecular formula)

228.6 g/mol (C11H13ClO3)

250.7 g/mol (C11H12ClNaO3)

Test substance –

MCPB

Test substance –

sodium MCPB

2006 EFED Science 

Chapter

CH3

Cl

O

OH

O

O

H

H H

O –

O

Cl

Na +
Page 9 of 46

Parameter Value Description Source (MRID)

Smiles Code Cc1cc(Cl)ccc1OCCCC(=O)O 

C1C(Cl)=CC=C(OCCCC(=O)OH)C=1C(H

)(H)H 

Test substance –

MCPB

Test substance –

sodium MCPB

Online SMILES 

Translator and Structure 

File Generator at 

http://cactus.nci.nih.gov/s

ervices/translate/)

EPISUITE 4.0

Water Solubility (at 

20°C)

60.4 mg/L (purified technical substance in 

purified water)

29.9 mg/L at pH 4

3.83 mg/L at pH 7

> 250 g/L at pH 10

200,000 mg/L @ 25°C

Test substance –

MCPB

Test substance –

MCPB sodium salt

2006 EFED Science 

Chapter

2006 EFED Science 

Chapter

Vapor pressure 

(25°C)

4 x 10-7 mm Hg Test substance -

MCPB

2006 EFED Science 

Chapter

Dissociation 

constants (pKa ) in 

water 

4.6 at 20°C (in the natural environmental 

conditions, >50% is present as ionic form)

Test substance -

MCPB

2006 EFED Science 

Chapter

Henry’s Law 

Constant 

3.42 x 10-9 atm - m3/mol; estimated at 25°C Test substance -

MCPB

2006 EFED Science 

Chapter

Log octanol-water 

partition coefficient

(log KOW)

1.33 (at pH 7 and 20°C)

3.45 (at pH 4 and 20°C)

-0.21 (at pH 10 and 20°C) 

Test substance -

MCPB

2006 EFED Science 

Chapter

 Persistence

Hydrolysis half-life Stable Test substance -

MCPB 42574301

Aqueous photolysis 

half-life

2.6 days (pH 7)

Major degradates:

4-(4-hydroxy-o-tolyloxy)butyric acid, 2,4-

dihyroxyphenyl formate, o-cresol

Test substance -

MCPB

42574302

Soil photolysis halflife Unacceptable study Test substance -

MCPB 43829901
Page 10 of 46

Parameter Value Description Source (MRID)

Aerobic soil 

metabolism half-life 

(days)

Sandy loam – 27 days

Major degradates:

none

5.1 days in loam soil

3.6 days in silty clay loam soil

10.6 days in sandy loam soil

Major degradate:

MCPA

Test substance -

MCPB

43247601 

47784801

Anaerobic soil 

metabolism half-life 

7.8 days in soil

18.9 days in water

74.4 days in total system 

Major degradate in soil and water:

MCPA

Test substance -

MCPB

43015501

Aerobic aquatic 

metabolism half-life 

(total system)

TNO water-sediment system:

6.4 days in water

Insufficient data to estimate half-life in 

sediment

Kromme Rijn water-sediment system:

Insufficient data to estimate half-life in 

water

Insufficient data to estimate half-life in 

sediment

Major degradate in total system:

MCPA 

Test substance -

MCPB

46837205

 Mobility

Adsorption/desorptio

n (mL/g)

Adsorption

Freundlich adsorption Koc values:

Sandy loam 130

Sandy 48

Sandy loam 86

Clay loam 31

Clay loam 371

Test substance -

MCPB 

42693701

Leaching Column Study Test substance -

MCPB

43466401
Page 11 of 46

Parameter Value Description Source (MRID)

 Field Dissipation

Terrestrial field 

dissipation half-life

0-15 cm soil pH = 6.2

0-15 cm soil texture - sandy loam

Nonlinear MCPB half-life 6.8 days

Nonlinear degradate (MCPA) half-life 7.8 

days

Parent and degradate MCPA detected in 0-

15 cm only

(preliminary finding)

Test substance –

sodium MCPB

48242801 (in review)

a. Transformation Products

The major organic degradates of MCPB in submitted environmental fate studies were MCPA, 4-

(4-hydroxy-o-tolyloxy)butyric acid, 2,4-dihyroxyphenyl formate, and o-cresol and benzoic acid. 

MCPA was identified as the major degradate in all soil and aquatic metabolism studies whereas 

4-(4-hydroxy-o-tolyloxy)butyric acid, 2,4-dihyroxyphenyl formate, and o-cresol were identified 

as major degradates in the aqueous pH 7 photolysis study only. Table 4 summarizes the 

transformation products of MCPB and their maximum amounts formed.

In the terrestrial field dissipation study, the degradate, MCPA, was present at the maximum 

concentration of 0.1 ppm in the 0-15 cm soil zone within two weeks of the application (with a 

LOQ of 0.01 ppm), and was not detected in any other soil zones (i.e., 15-30 cm, 30-45 cm, and 

45-60 cm) from Day 0 to Days 282 (the end of the study).

A photodegradation pathway in water was proposed in the report (MRID 42574302). MCPB 

was dechlorinated and hydrolxylated, resulting in the formation of 4-(4-hydroxy-otolyloxy)butyric acid pretty rapidly (reached 27.5% of the applied at Days 7 in the pH 7 

solution). Thereafter, 4-(4-hydroxy-o-tolyloxy)butyric acid degrades to form 2,4-

dihydroxyphenol formate and o-cresol. 

A metabolism pathway was presented in an aerobic soil metabolism study (MRID 43247601). 

MCPB degrades to (4-chloro-2-methylphenoxy)acetic acid, which degrades to (4-chloro-2-

methylphenoxy-2-belta-glucopyranoside acetic acid and conjugates with hexose; there is 

significant production of CO2 and soil bound residues. Although the pathway was not proposed 

in the aerobic aquatic metabolism study (MRID 46837205), based on the study results, MCPB 

degrades to MCPA and is mineralized to bound residues and CO2.

Only one degradate (i.e., 4-chloro-o-cresol) has been identified as the major degradate in all 

MCPA fate studies. This degradate is also known as 4-chloro-2-methylphenol which was 

detected as a minor degradate (ranging from 0.8-3.9 % of the applied) in 3 aerobic metabolism 

soils conducted using MCPB, with study duration of 14-21 days (MRID 47787801).
Page 12 of 46

Table 3. Major Environmental Degradates in MCPB (Acid and Sodium Salt) Studies

Code Name/ 

Synonym Chemical Name Chemical Structure Study Type

Ref.

(MRID) Maximum %AR (day) Final %AR (study length

MCPA

4-chloro-o-tolyloxyacetic 

acid

835.2120 42574301 Not detected -

835.2240 42574302 Not detected -

835.2410 43829901 Unacceptable -

835.4100

43247601 Not major degradate -

47787801

28.2% (Days 11) in loam 

soil

29.0% (Days 9) in silty clay 

loam soil

35.1% (Days 18) in sandy 

loam soil

10.5% (21 

days)

21.9% (14 

days)

32.1% (21 

days)

835.4200 43015501 34.6% (Days 4)) in total 

system

34.6% (62 

days)

835.4300 46837205

15.5% (Days 7) in total 

system (TNO watersediment system)

14.6% (Days 7) in total 

system (Kromme Rijn watersediment system)

Not analyzed 

(98 days)

835.6100 48242801 Found in 0-15 cm only (0.1 

ppm) (Days 14)

Not detected 

(282 days)

4-(4-hydroxy-otolyloxy)butyric acid4-(4-hydroxy-otolyloxy)butyric acid 835.2240 42574302 27.5% (Days 7) 5.1% (30 days)

2,4-dihyroxyphenyl 

formate

2,4-dihyroxyphenyl 

formate

835.2240 42574302 35.3% (Days 14) 33.0% (30 

days)

CH3

Cl

O

OH

O
Page 13 of 46

Code Name/ 

Synonym Chemical Name Chemical Structure Study Type

Ref.

(MRID) Maximum %AR (day) Final %AR (study length

o-cresol 2-methylphenol 835.2240 42574302 47.3% (Days 30)

47.3% (30 

days)
14

6. Receptors

Table 5 and Table 6 provide a summary of the aquatic and terrestrial taxonomic groups, 

respectively, and the most sensitive surrogate species tested to characterize the potential acute and 

chronic ecological effects of MCPB. Available acute toxicity data indicate that MCPB is slightly 

to moderately toxic to freshwater fish and slightly toxic to freshwater invertebrates. There was no 

chronic data or estuarine/marine data submitted for fish or invertebrates. MCPB is classified as 

moderately toxic to birds on an acute oral basis and practically non-toxic on an acute dietary 

basis. The compound was classified as slightly toxic to practically non-toxic to small mammals 

on an acute oral basis, however, adverse effects were demonstrated in the mammalian subchronic 

and developmental toxicity studies. There is potential for MCPB exposure to non-target insects 

due to the foliar application. Available data from a honeybee acute toxicity study indicated that 

technical MCPB is practically non-toxic to the honeybee. Plant toxicity is expected due the 

herbicidal properties of MCPB.

EFED has recently received the following studies for MCPB. Upon review, the Agency will 

determine whether these submissions either satisfy the requirement and/or whether they can be 

used to inform the ecological risk assessment of MCPB. 

o Acute toxicity with Sheepshead Minnow (850.1075)

o Freshwater fish ELS (850.1400)

a. Effects to Aquatic Organisms

The following tables present measures of effect in terms acid equivalents. Conversion from 

active ingredient to acid equivalents was made in accordance with molecular weight difference. 

One gram-mole of MCPB acid has a mass of 228.67 grams and one gram-mole of MCPB sodium 

salt has a mass of 250.66 grams; therefore, one unit of the salt would be equivalent to 0.912 units 

of acid. Hence, the LC50 values from the toxicity tests with MCPB sodium were converted to acid 

equivalents by multiplying the values by 0.91.

Table 5. Summary of the Most Sensitive Endpoints from Aquatic Toxicity Studies for 

MCPB

Taxonomic 

Group

Study 

Type Surrogate Species

Toxicity 

Value

(all units in 

terms of 

measured 

acid 

equivalent)

Acute 

Toxicity 

Classification Source

Freshwater 

fish1

Acute

Rainbow Trout

(Oncorhynchus 

mykiss)

96-h LC50 = 

3.9 mg ae/L

Moderately 

toxic 42532608

Chronic2 -- -- -- --
15

Taxonomic 

Group

Study 

Type Surrogate Species

Toxicity 

Value

(all units in 

terms of 

measured 

acid 

equivalent)

Acute 

Toxicity 

Classification Source

Freshwater 

invertebrates

Acute Water Flea 

(Daphnia magna)

48-h EC50 = 

50.0 mg ae/L Slightly toxic 42532602

Chronic -- -- -- --

Estuarine/

marine fish

Acute2 -- -- -- --

Chronic -- -- -- --

Estuarine/

marine 

invertebrates

Acute2

Eastern Oyster

(Crassotrea 

virginica)

96-h EC50 = 

63 mg ae/L Slightly toxic 47613401

Chronic -- -- -- --

Aquatic plants 

and algae

Vascular Duckweed 

(Lemna gibba)

NOAEC = 

<0.01 mg 

ae/L*

EC50 = 

0.21 mg ae/L

-- 42532604

Nonvascular

Green Algae 

(Pseudokirchneriella 

subcapitata)

NOAEC = 

<0.31 me 

ae/L*

EC50 = 

0.38 mg ae/L

-- 42532605

1 Freshwater fish may be surrogates for aquatic-phase amphibians. 2

Studies have been submitted and are currently in review

*NOEC cannot be determined due to non-discreet toxicity value therefore definitive endangered species RQs cannot be calculated. 

EC05 was not available.

MCPA is not considered an appropriate substitute to fill MCPB data gaps for aquatic toxicity . 

Waiver requests submitted in 2007 requesting MCPA technical acid be used in place of MCPB 

for aquatic studies were denied on the basis of higher toxicity of MCPB to freshwater fish on an 

acute basis in comparison to MCPA (D340501). The acute oral toxicities for MCPB sodium and 

MCPA sodium conducted using the Rainbow trout are 3.9 mg ae/L (MRID 42532608) and >68 mg 

ae/L MRID (41800902) respectively. 

b. Effects to Terrestrial Organisms

The following tables present measure of effect both in terms of active ingredient and acid 

equivalents. Conversion from active ingredient to acid equivalents was made in accordance with 

molecular weight differences as described previously for the aquatic toxicity data. 
16

Table 6. Summary of the Most Sensitive Endpoints from Terrestrial Toxicity Studies for 

MCPB

Taxonomic 

Group

Study 

Type

Surrogate 

Species

Toxicity Value

(all units in terms 

of measured acid 

equivalent)

Acute 

Toxicity 

Classification

Source

Birds1

Acute

Bobwhite quail

(Colinus 

virginianus)

LD50 = 257 mg

ae/kg-bw Moderately 42560801

Sub-acute 

dietary

Bobwhite quail

(Colinus 

virginianus)

LC50 = >4,550

ppm ae

Practically 

non- toxic 42560802

Chronic -- -- -- --

Mammals

Acute Oral

Laboratory rat 

(Rattus 

norvegicus)

LD50 = 912

mg/kg-bw males

Practically 

non-toxic 116340

Acute 

Inhalation Laboratory rat LC50 = >1.14mg/L

Toxicity 

Category III 41630001

Chronic Rabbit

NOAEL = 5 

mg/kg/day

LOAEL = 20

mg/kg/day

Endpoint: 

Maternal toxicity; 

developmental 

effects

-- 40865401

Insects Acute 

contact

Honey bee 

(Apis mellifera 

L.)

LD50 = >25 μg/bee Practically 

non-toxic 42532607

Terrestrial 

plants

Seedling 

Emergence

Dicot –

cabbage

(Lactuca 

sativa)

EC05

2

= 0.01 lb 

ae/A

EC25 = 0.016 lb

ae/A

Endpoint: shoot 

length

-- 42560804

Monocot –

onion

(Avena sativa)

NOAEC = 0.01 lb

ae/A

EC25 = 0.02 lb

ae/A

Endpoint: shoot 

length

-- 42560804

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

2IC05 is used when NOAEC is unavailable

No chronic avian data on MCPB are available. A chronic avian reproduction study with the 

degradate MCPA was available for the Bobwhite quail and has been used to estimate the chronic 
17

avian risks of MCPB in previous assessments. For bird toxicity studies, MCPA is considered an 

appropriate surrogate because MCPB is expected to rapidly dissociate to MCPA in a bird’s gut 

due to the chemical properties of MCPB (DP340501). Furthermore, a comparison of the MCPB 

and MCPA avian acute toxicity studies with bobwhite quail indicates that the two compounds 

have an approximately equivalent acute toxic potential to birds. 

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. 

EIIS returned one terrestrial plant incident in Washington State attributed to MCPB use with a 

“possible” certainty classification. Incident I021457-021 occurred in July 2006 when a misuse of 

herbicides MCPA, Dicamba and carfentrazon were aerially applied to a crop of timothy hay and

drifted off-site and resulted in damage to trees. Several plants were damaged in the vicinity of the 

agricultural area as a result of drift. No other incidents were reported in EIIS, IDS or AIMS.

7. Exposure Pathways of Concern

The environmental fate properties and use patterns of MCPB indicate that runoff, leaching, and 

spray drift represent potential exposure pathways to aquatic organisms; ground deposition, 

runoff/leaching and spray drift resulting in residues on non-target plants represent potential 

exposure pathways to terrestrial organisms.

Avian and mammalian drinking water and inhalation exposure pathways were screened using the 

SIP (Screening Imbibition Program) and STIR (Screening Tool for Inhalation Risk) screening 

methods, respectively. SIP is used to provide an upper bound estimate of exposure of birds and 

mammals to pesticides through drinking water alone. It is used to determine whether or not 

drinking water exposure alone is a potential exposure pathway of concern; it does not aggregate 

drinking water exposure with other exposure routes. The results of SIP conclude that drinking 

water exposure alone is not a potential concern for mammals on an acute basis, but exposure 

through drinking water alone is a potential exposure pathway of concern for mammals on a 

chronic basis. For avian species, that the SIP results indicate exposure through drinking water 

alone is a potential pathway of concern on an acute basis but exposure through drinking water 

alone is not a potential pathway of concern on a chronic basis. STIR indicated that exposure via 
18

the inhalation pathway was not likely significant for mammals or avian species. SIP and STIR 

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

results of SIP and STIR are available in Appendix C and D.

8. Analysis Plan

a. Stressors of Concern

i. Ecological Risk Assessment

The stressors of ecological concern are MCPB, and degradates MCPA, 4-chloro-o-cresol, 4-(4-

hydroxy-o-tolyoxy) butyric acid, 2,4-dihydoxyphenyl formate, and o-cresol.. MCPA and 4-

chloro-o-cresol were both found in aerobic soil metabolism studies at 31% and 1-4% 

respectively. 4-chloro-o-cresol is considered a minor degradate with respect to MCPB and a 

major degradate for MCPA; however, it is included as a stressor of concern to MCPB because of 

its potential higher toxicity than MCPB, as indicated by toxicity estimations generated by QSAR.

4-(4-hydroxy-o-tolyoxy) butyric acid, 2,4-dihydoxyphenyl formate, and o-cresol are considered 

as part of the aquatic assessment because they were found as degradates in an aqueous photolysis 

study (835.2240, MRID 42574302).

MCPA (030501) is registered as an active ingredient and thus has a well established toxicity 

profile. However there is no toxicity data available in ECOTOX for the other degradates.

Therefore, quantitative structure activity relationships (QSARs) were used to estimate the acute 

toxicity of these degradates to aquatic organisms based on the USEPA ECOSAR program 

(version 1.0) with EPISUITE (version 4.0).ECOSAR is used to compare the toxicity of the parent 

chemical relative to the degradates and determine if the degradates have the potential to make a 

significant contribution to the overall risk to aquatic organisms and should therefore be included 

as a stressor of concern. All of the QSAR endpoints can be found in Appendix E. In comparing 

the known toxicity of MCPB to the calculated toxicity of MCPB, it was concluded that the 48-hr 

Daphnid predicted toxicities were most representative of the actual toxicity values with a known 

toxicity of 54.8 ppm (MRID 42532602) and a predicted toxicity of 59.2 ppm. Because the known 

and ECOSAR-predicted toxicities were one or more orders of magnitude different for other taxa 

evaluated (fish, algae), only the daphnia QSAR was used to evaluate the potential toxicity of the 

degradates. Table 7 shows the predicted toxicities for each of the degradates as generated by 

QSAR. QSAR estimates for aquatic species indicate a higher toxicity for o-cresol and 4-chlorocresol relative to that of MCPB.

Table 7. 48-hr LC50 values predicted for Daphnia using ECOSAR (ppm) 

MCPB MCPA

4-(4-hydroxyo-tolyloxy) 

butyric acid

2-4-

dihyroxyphenyl 

formate

o-cresol 4-chlorocresol

59.21 328.51 168.61 157.32 5.23 3.03

1

Endpoint based on Neutral Organics Acid QSAR

2

Endpoint based on Phenols, Poly QSAR 3

Endpoint based on Phenols QSAR
19

ii.Formulation Impurities

Various phenoxy herbicides are known to contain dioxin/furan impurities as a result of 

manufacturing processes (Holt, et. al. 2010). Data pertaining to dioxin/furan impurities in MCPB 

formulations (up to 17 known dioxin/furan congeners) will be considered in the upcoming 

environmental risk assessment. Previously submitted dioxin/furan data for MCPB were below 

levels of quantitation (LOQ) (MRIDs 45524105 and 47374801). However, the Agency is aware 

that lower limits of quantitation of dioxins/furans by one or more orders of magnitude are now 

achievable through technological advances in analytical chemistry. Therefore, the Agency 

requests any additional information on the presence of dioxins/furans impurities in MCPA 

formulated products that may be available based on currently achievable LOQs. Absent 

additional information, the Agency will use best available information (including appropriate 

assumptions related to reported LOQs) for determining the potential for exposures of concern at 

the time of risk assessment.

iii. Drinking Water 

When EFED receives an acceptable anaerobic aquatic metabolism study as requested in this PF, a 

ROCKS meeting and an updated drinking water assessment may be needed as part of the 

Registration Review process. EFED will include the recently revised percentage crop area (PCA) 

factors as well as the newly-developed PRZM-GW 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.

b. Measures of Exposure 

EFED will use standard available models to evaluate potential exposures to aquatic and terrestrial 

organisms as described at http://www.epa.gov/pesticide/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, 3005) 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 environmental (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 MCPB drifts or moves with runoff to adjacent habitats.

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

and terrestrial organisms to MCPB 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.
20

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

significant. This exposure pathway may be further considered at the time of the risk assessment 

(Appendix C and D). 

i. Available Monitoring Data

The Agency is aware of aquatic monitoring conducted by federal and state agencies and this 

information will be considered in the assessment to the extent that data on MCPB or other 

residues of concern are available. For example, according to the USGS database, MCPB was not 

detected in 3,232 surface water and ground water samples collected in the United States.

c. Measures of Effect 

Toxicity data presented in Section 3 of this problem formulation will be used to calculate risk 

quotients. 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 are 

identified using EPA’s ECOTOXicology database (ECOTOX) (USEPA, 2007c), which employs 

a literature search engine for locating chemical toxicity data for aquatic life, terrestrial plants, and 

wildlife. The evaluation of both sources of data can also provide insight into the direct and 

indirect effects of pesticides on biotic communities from loss of species that are sensitive to the 

chemicals and from changes in structure and functional characteristics of the affected 

communities.

9. Endangered Species Assessments

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

Agency will evaluate risks to federally listed threatened and/or endangered (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.

10. 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 issues test orders/data call-ins for the first group of 67 chemicals, which 

compromises 58 pesticide active ingredients and 9 inert ingredients. The herbicide MCPB 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, policies and procedures, the list of 67 

chemicals, future lists, the test guidelines and the Tier 1 screening batter, please visit our website 

http://www.epa.gov/endo/. 
21

11. 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 to support 

the risk assessment. 

• The soil photolysis study (MRID 43829901) was determined not scientifically valid and 

it does not provide useful information on the photodegradation of MCPB on sandy loam 

soil and is therefore classified as unacceptable. A new soil photolysis study (835.2410) is 

needed. 

• Since the registrant has not submitted any anaerobic aquatic metabolism study, as 

required for all pesticides with terrestrial use pattern, the registrant must submit an 

anaerobic aquatic metabolism study (835.4400).

• The registrant must submit ILVs (850.6100) for the ECMs (MRIDs 46837203 and 

47163505) that the registrant submitted.

• Storage stability information are needed to support the TFD study (MRID 48242801).

Table 8. Submitted Environmental Fate Data for MCPB

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 42574301 Acceptable No Not Applicable

835.2240 Aqueous 

photolysis 42574302 Acceptable No Not Applicable

835.2410 Soil photolysis 43829901 Unacceptable Yes Assuming stable

835.4100 Aerobic soil 

metabolism

43247601 Acceptable No Not Applicable 47784801 Supplemental

835.4200 Anaerobic soil 

metabolism 43015501 Acceptable No Not Applicable

835.4300 Aerobic aquatic 

metabolism 46837205 Supplemental No Not Applicable

835.4400

Anaerobic 

aquatic 

metabolism

No study 

submitted

--- Yes Assuming stable
22

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

835.1230

835.1240

Adsorption/ 

desorption 42693701 Acceptable No Not Applicable

Leaching 43466401 Supplemental No Not Applicable

835.1410 Volatilitylaboratory --- --- --- Not Applicable

835.8100 Volatility Field --- --- --- Not Applicable 

835.6100 Terrestrial field 

dissipation 48242801 In review No Not Applicable

850.6100

Analytical 

method in soil 

(ECM)

46837203 In review No Not Applicable

Analytical 

method in soil 

(ILV)

--- --- Yes ILV is needed to validate ECM

835.6200

Aquatic field 

dissipation --- --- --- Not Applicable

850.6100 Analytical 

method in water 

(ECM) 

47163505 In review --- Not Applicable

Analytical 

method in water 

(ILV) 

--- --- Yes ILV is needed to validate ECM

850.1730 Fish BCF --- ---- --- Not applicable due to low Log 

Kow

835.6100 Storage stability --- ---- Yes TFD study may be invalid

b. Effects

Table 9 and table 10 identify ecological effects studies by MRID that offer data for each 

guideline requirement, as well as study classifications and whether or not further data are needed 
23

in order to support risk assessment. Rationale for the additional data requested is presented below 

the tables.

Table 9. Aquatic Ecological Effects Data for MCPB

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

- Some Example texts are include

850.1010

Freshwater 

invertebrate 

acute toxicity

42532602 Acceptable No --

850.1025

850.1035

850.1045

850.1055

Saltwater 

invertebrate 

acute toxicity 

47613401 Acceptable No --

850.1075 Freshwater fish 

acute toxicity 

42532608 Acceptable

No -- 42532601 Acceptable

850.1075 Saltwater fish 

acute toxicity None NA Yes

Study is currently under review; data 

requirement still considered

outstanding.

850.1300

Freshwater 

invertebrate 

life cycle 

None NA Yes

A guideline study compliant to the 

saltwater invertebrate life cycle study 

is required.

850.1350

Saltwater 

invertebrates 

life cycle 

None NA Yes

A guideline study compliant to the

saltwater invertebrate life cycle study 

is required.

850.1400 Freshwater fish 

early-life stage None NA Yes

Study is currently under review; data 

requirement still considered 

outstanding.

850.1400 Saltwater fish 

early-life stage None NA Yes

A guideline study compliant to the 

saltwater fish early-life stage study is 

required.

850.1500 Fish life cycle None NA No

850.4400

Aquatic plant 

Toxicity Test 

using Lemna 

spp.

42532604 Acceptable Yes

NOAEC from listed studies cannot 

be determined due to treatmentrelated effects at all test 

concentrations. Therefore, definitive 

endangered species RQs, which are 

based on plant NOAECs, cannot be 

calculated. New studies are being 

requested for derivation of a 

definitive NOAEC endpoint.

850.4500 Algal toxicity

42532605

Acceptable Yes

NOAEC from listed studies cannot 

be determined due to treatmentrelated effects at all test concentions. 

Therefore definitive endangered 

species RQs, which are based on 

42532603
24

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

- Some Example texts are include

42532609 plant NOAECs, cannot be 

calculated. New studies are being 

requested for derivation of a 

definitive NOAEC endpoint.

42532606

Table10. Terrestrial Ecological Effects Data for MCPB

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies

(MRID)

Study 

Classifications

Are data 

needed for 

risk 

assessment?

Current Additional Data Need

850.2100 Avian oral 

toxicity

42560801 Acceptable Yes An acute oral toxicity test conducted 

using a passerine species is required.

In lieu of a passerine study conducted 

using MCPB, the Agency will accept 

acute passerine data on MCPA due to 

rapid bioatransofrmation of MCPB to 

MCPA expected in the avian gut and 

their similarity in avian oral toxicity to 

birds.

850.2200 Avian dietary 

toxicity 

42560802 Acceptable No --

42560803 Acceptable

850.2300 Avian 

reproduction

43505201 Acceptable Yes An avian reproduction toxicity 

performed using MCPA on the 

Bobwhite is available and considered 

an appropriate substitution for MCPB. 

There are currently no avian 

reproduction data available using 

MCPA or MCPB for the mallard and is 

thus considered a data gap.

In lieu of a mallard study conducted 

using MCPB, the Agency will accept 

mallard data on MCPA due to the rapid 

biotransformation of MCPB to MCPA

expected in the avian gut and their 

similarity in avian oral toxicity to 

birds..

MCPA

NonguidelineAvian 

inhalation

41630001 Acceptable No
25

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies

(MRID)

Study 

Classifications

Are data 

needed for 

risk 

assessment?

Current Additional Data Need

850.3020 Honey bee 

acute contact 

toxicity

42532607 Acceptable No --

OECD 

213/237

Acute Oral 

Adult and 

Larval 

Honeybee 

None NA Yes Studies are requested on basis of 

assessing risk to larval life stages of 

bees which are expected to be exposed 

via nectar and/or pollen through 

systemic transport of MCPB. 

850.3030 Honey bee 

residue on 

foliage

None NA No The LD50 for the honey bee acute 

contact study was >25 μg/L and 

considered practically non toxic the 

honey bee

850.3040 Field testing 

for pollinators

None NA No The LD50 for the honey bee acute 

contact study was >25 μg/L and 

considered practically non toxic the 

honey bee. At this time field testing 

for pollinators is not being requested.

850.4100 Seedling 

Emergence

and Seedling 

Growth

42560804 Acceptable No --

850.4150 Vegetative 

Vigor

42560804 Acceptable No --

42560804
26

12. References 

Jones, R.D. et al., 2000. Guidance for use of the Index Reservoir and Percent Crop Area Factor in 

Drinking Water Assessments (March 21, 2000). Office of Pesticide Programs, 

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

Arlington, VA.

USEPA. 1999. Guidance for Use of the Index Reservoir in Drinking Water Exposure 

Assessments. Arlington, VA.

USEPA. 2000. Drinking Water Screening Level Assessment. Part A: Applying a Percent Crop 

Area Adjustment to Tier II Surface Water Model Estimates for Pesticide Drinking Water 

Exposure Assessments. FQPA Science Policy Document .Public Comment Draft 

September 1, 2000. Federal Register: October 11, 2000 (volume 65, number 197). 

Electronic copy available at http://www.epa.gov/pesticides/trac/science/ .

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. 

U.S. EPA. 2003b. Use of Regional Percent Crop Area Factors in Refined Drinking Water 

Assessments. US EPA Office of Pesticide Programs (OPP), Environmental Fate and 

Effects Division (EFED), Water Quality Technical Team (WQTT). Arlington, VA

USEPA, 2003c. SCI-GROW 2.3: Windows Version of SCI-GROW. September 30, 2003. Office 

of Pesticide Programs, Environmental Fate and Effects Division, U.S. Environmental 

Protection Agency. Arlington, VA. 

USEPA. 2004. 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.

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.

45524105 Grienberger, G. (2000) Tetra--To Hepta-Chlorinated Dioxins and Furanes in Seven 
27

Batches of Technical 4-(4-Chloro-2-methylphenoxy)butanoic Acid (MCPB): Lab 

Project Number: NUFARM 1199 MCPB: 60288. Unpublished study prepared by 

Institut fur Industrie- und Umweltanalytik . 193 p. {OPPTS 830.1700} 

47374801 Grienberger, G. (2006) Tetra-To Hepta-Chlorinated Dioxins and Furans in Seven 

Batches of Technical 4-(4-Chloro-2-methylphenoxy) Butanoic Acid (MCPB). Project 

Number: 0306A, GLP/AM/001. Unpublished study prepared by UIS Umweltinstitut 

Synlab GmbH. 236 p.
28

Appendix A

OPPIN Bibliography for MCPB and its Salt

Environmental Fate

161-1 Hydrolysis

MRID Citation Reference

42574301 Das, Y. (1992) Hydrolysis of (carbon 14)MCPB in Aqueous Solutions 

Buffered at pH 5, 7 and 9: Lab Project Number: 92010: 92-06. 

Unpublished study prepared by Innovative Scientific Services, Inc. 77 p. 

161-2 Photodegradation-water

MRID Citation Reference

42574302 Das, Y. (1992) Photodegradation of (carbon 14)MCPB in Aqueous 

Solutions Buffered at pH 5, 7 and 9 under Artificial Sunlight: Lab Project 

Number: 92011: 92-07. Unpublished study prepared by Innovative 

Scientific Services, Inc. 174 p. 

161-3 Photodegradation-soil

MRID Citation Reference

43829901 Ferreira, E.; John, A.; Lowden, P.; et al. (1995) MCPB Soil Photolysis 

Study: Amended Report: Lab Project Number: P92/126 Unpublished 

study prepared by Rhone-Poulenc Agriculture Ltd. 75 p. (Amended 

version of 42519101). 
29

161-4 Photodegradation-air

MRID Citation Reference

46837204 Baxby, M. (2002) Validation of an Analytical Method for the 

Determination of 4-(4-Chloro-2-Methylphenoxy) Butyric Acid (MCPB) 

in Air: Final Report. Project Number: 02/0177. Unpublished study 

prepared by A H Marks & Co Ltd. 41 p.

162-1 Aerobic soil metabolism

MRID Citation Reference

47787801 J Oddy, A. and R. Brett. (2009). [14C]MCPB: Rate of degradation in 

three soils at 22°C. Unpublished study performed by Battelle UK Ltd., 

Ongar, Essex, UK; and sponsored and submitted by MCPB Task Force, 

Raleigh, North Carolina. Battelle UK Study No. and Battelle Report 

No.: FK/08/001. Study started November 11, 2008, and completed 

January 15, 2009 (p. 5). Final report issued June 11, 2009.

43247601 John, A.; Jones, M.; Lowden, P.; et al. (1994) MCPB: Aerobic Soil 

Metabolism: Lab Project Number: P/93/194. Unpublished study prepared 

by Rhone-Poulenc Agriculture Ltd. 108 p. 

162-2 Anaerobic soil metabolism

MRID Citation Reference

43015501 Goodyear, A. (1993) Carbon 14-MCPB: Anaerobic Soil Metabolism: 

Final Report: Lab Project Number: 68/131-1015: 68/131: 200352. 

Unpublished study prepared by Hazleton UK. 90 p. 

162-4 Aerobic aquatic metab.

MRID Citation Reference
30

46837205 van Dijk, N.; Pigott, G. (2003) Determination of the Degradation of 

[Carbon 14]-MCPB in Aerobic Water/Sediment Systems: Final Report. 

Project Number: 4985, 010/46139. Unpublished study prepared by TNO 

Voeding. 67 p.

163-1 Leach/adsorp/desorption

MRID Citation Reference

42693701 Robson, M. (1993) Determination of Adsorption/Desorption 

Characteristics of 4-(2-Methyl,4-Chlorophenoxy) Butyric Acid (MCPB) 

in Soil: Final Report: Lab Project Number: 68/127: 7414. Unpublished 

study prepared by Hazleton UK. 81 p. 

43466401 John, A.; Jones, M.; Lowden, P. (1994) MCPB: Fresh and Aged 

Leaching Study in Five Soils: Lab Project Number: P 92/333: 200724: 

RPAL P92/333. Unpublished study prepared by Rhone-Poulenc 

Agriculture Ltd. 142 p. 

164-1 Terrestrial field dissipation

MRID Citation Reference

48242801 Panara, J. (2010) Terrestrial Dissipation of MCPB Sodium Salt in 

Wisconsin: Final Report. Project Number: 09/00990. Unpublished study 

prepared by Eurofins / Grayson Research, Ltd. 541 p.

Analytical method

MRID Citation Reference

46837203 Mahmood, T. (2003) Validation of a Method for the Analysis of MCPB 

and MCPA in Soil: Final Report. Project Number: R/03/03. Unpublished 

study prepared by A H Marks & Co Ltd. 39 p.
31

47163505 Harper, H. (2005) MCPA, 2,4-D, Mecoprop, Dichlorprop, MCPB and 

2,4-DB: Validation of the Methodology for the Determination of Residue 

in Drinking and Surface Waters: Final Report. Project Number: 

TFT/005/052350. Unpublished study prepared by Huntingdon Research 

Center. 220 p.
32

Appendix B

OPPIN Bibliography for MCPB and its Salt

71-1 Avian Dietary Toxicity

MRID Citation Reference

116348

42560801

42532608

Weatherholtz, W. (1969) Dietary Administration--Pekin 

Ducklings: MCPB: Project No. 517-109. Final rept. (Unpublished 

study received on unknown date under 1F1051; prepared by 

TRW, Inc., sub- mitted by Rhodia, Inc., New Brunswick, NJ; 

CDL:091885-J) 

Pedersen, C.; Helsten, B. (1992) MCPB Sodium: 14-day Acute 

Oral LD50 Study in Bobwhite Quail: Lab Project Number: 108-

016-03. Unpublished study prepared by Bio-Life Associates, Ltd. 

59 p.

Bettencourt, M.J. 1992. MCPB Sodium - Acute toxicity to 

rainbow trout (Oncorhyn-chus mykiss) under flow-through 

conditions. Unpublished study performed by Springborn 

Laboratories, Inc., Wareham, MA and sponsored by RhanePoulenc Agrochemie, Research Triangle Park, NC. SLI Report 

Number 92-7-4228.

71-2 Avian Dietary Toxicity

MRID Citation Reference

116348

42560802

42560803

Weatherholtz, W. (1969) Dietary Administration--Pekin 

Ducklings: MCPB: Project No. 517-109. Final rept. (Unpublished 

study received on unknown date under 1F1051; prepared by 

TRW, Inc., sub- mitted by Rhodia, Inc., New Brunswick, NJ; 

CDL:091885-J

Pedersen, C.; Helsten, B. (1992) MCPB Sodium: 8-day Acute 

Dietary LC50 Study in Bobwhite Quail: Lab Project Number: 

108-014-01. Unpublished study prepared by Bio-Life Associates, 

Ltd. 103 p.

Pedersen, C.; Helsten, B. (1992) MCPB Sodium: 8-day Acute 

Dietary LC50 Study in Mallard Ducklings: Lab Project Number: 

108-015-02. Unpublished study prepared by Bio-Life Associates, 
33

Ltd. 103 p

72-1 Freshwater Fish Acute

MRID Citation Reference

84752 Bentley, R.E.; Macek, K.J. (1976) Some Effects of 

Exposure to Herbicides on Behavior, Survival and 

Selected Physiological Parameters of Carp (?~Cyprinus 

carpio~?): ?Submitter| T-2288. (Unpublished study 

received Oct 8, 1981 under 476-2107; prepared by EG & 

G, Bionomics, submitted by Stauffer Chemical Co., 

Rich42532608mond, Calif.; CDL:246020-S)

4253260

8 

Bettancourt, M. (1992) MCPB Sodium--Acute Toxicity 

to Rainbow Trout (Oncorrhynchus mykiss) under Flowthrough Conditions: Final Report: Lab Project Number: 

92-7-4338: 10566.0392.6227. 108. Unpublished study 

prepared by Springborn Labs, Inc. 64 p.

4253260

1

Bettencourt, M. (1992) MCPB Sodium--Acute Toxicity 

to Bluegill Sunfish (Lepomis macrochirus) under Flowthrough Conditions: Final Report: Lab Project Number: 

92-8-4363: 10566.0392.6226.105. Unpublished study 

prepared by Springborn Labs, Inc. 64 p.

850.1075 Fish acute toxicity test, freshwater and marine

MRID Citation Reference

47262101 Pigott, G. (2007) Rationale Document for Requesting a 

Waiver for Oyster Acute Toxicity Test (Shell Deposition) and 

Fish Acute Toxicity Test Freshwater and Marine: MCPB 

Technical Acid in Response to Generic and Product Specific 

Data Call-In Notice dated March 6, 2007. Unpublished study 

prepared by MCPB Task Force. 4 p.

72-2 Freshwater Invertebrate Acute

MRID Citation Reference

42532602 Christensen, K. (1992) MCPB Sodium: Determination of Effects 

on Seed Germination, Seedling Emergence and Vegetative 

Vigor of Ten Plant Species: Final Report: Lab Project Number: 
34

92-8-4377. Unpublished study prepared by Springborn Labs, 

Inc. 208 p.

850.1025 Oyster acute toxicity test (shell deposition)

MRID Citation Reference

47262101 Pigott, G. (2007) Rationale Document for Requesting a Waiver 

for Oyster Acute Toxicity Test (Shell Deposition) and Fish 

Acute Toxicity Test Freshwater and Marine: MCPB Technical 

Acid in Response to Generic and Product Specific Data Call-In 

Notice dated March 6, 2007. Unpublished study prepared by 

MCPB Task Force. 4 p.

47613401 Hicks, S. (2008) MCPB Na 400g/l: Effect on New Shell 

Growth of the Eastern Oyster (Crassostrea virginica). Project 

Number: 63950, 94/81/5, S756. Unpublished study prepared by 

ABC Laboratories, Inc. 58 p.

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

Study

MRID Citation Reference

84752 Bentley, R.E.; Macek, K.J. (1976) Some Effects of Exposure to 

Herbicides on Behavior, Survival and Selected Physiological 

Parameters of Carp (?~Cyprinus carpio~?): ?Submitter| T-2288. 

(Unpublished study received Oct 8, 1981 under 476-2107; 

prepared by EG & G, Bionomics, submitted by Stauffer 

Chemical Co., Rich- mond, Calif.; CDL:246020-S) 

850.1400 Fish early-life stage toxicity test

MRID Citation Reference

47261801 Pigott, G. (2007) Rationale Document for Requesting a 

Waiver for Fish Early-Life Stage Toxicity Test (Data 

Requirement 850.1400) for MCPB Technical Acid and MCPB 

Sodium Salt in Response to Generic and Product Specific Data 

Call-In Notice Dated March 6, 2007. Project Number: 

850/1400/WAIVER/MCPB. Unpublished study prepared by

A.H. Marks and Co, Ltd. 4 p.
35

122-1 Vegetative Vigor-tier I

MRID Citation Reference

42560804 Christensen, K. (1992) MCPB Sodium: Determination of Effects 

on Seed Germination, Seedling Emergence and Vegetative 

Vigor of Ten Plant Species: Final Report: Lab Project Number: 

92-8-4377. Unpublished study prepared by Springborn Labs, 

Inc. 208 p.

123-1a Seedling Emergence-Tier II

MRID Citation Reference

4256080

4

Christensen, K. (1992) MCPB Sodium: Determination of Effects 

on Seed Germination, Seedling Emergence and Vegetative 

Vigor of Ten Plant Species: Final Report: Lab Project Number: 

92-8-4377. Unpublished study prepared by Springborn Labs, 

Inc. 208 p.

123- 1b Vegetative Vigor-Tier II

MRID Citation Reference

42560804 Christensen, K. (1992) MCPB Sodium: Determination of Effects 

on Seed Germination, Seedling Emergence and Vegetative 

Vigor of Ten Plant Species: Final Report: Lab Project Number: 

92-8-4377. Unpublished study prepared by Springborn Labs, 

Inc. 208 p.

122-2 Aquatic Plant Algae-tier l

MRID Citation Reference

42532603 Hoberg, J. (1992) MCPB Sodium--Toxicity to the Freshwater 

Blue-green Alga, Anabaena flos-aquae: Final Report: Lab 

Project Number: 92-8-4381: 10566.0392.6230.420. Unpublished 

study prepared by Springborn Labs, Inc. 54 p.

42532604 Hoberg, J. (1992) MCPB Sodium--Toxicity to the Duckweed 

Lemna gibba: Final Report: Lab Project Number: 92-8-5368: 

10566. 0392.6229.410. Unpublished study prepared by 
36

Springborn Labs, Inc. 61 p.

42532605 Hoberg, J. (1992) MCPB Sodium--Toxicity to the Freshwater 

Green Alga, Selenastrum capricornutum: Final Report: Lab 

Project Number: 92-8-4361: 10566.0392.6232.430. Unpublished 

study prepared by Springborn Labs, Inc. 58 p.

42532606 Hoberg, J. (1992) MCPB Sodium--Toxicity to the Marine 

Diatom, Skeletonema costatum: Final Report: Lab Project 

Number: 92-8-4372: 10566.0392.6233.450. Unpublished study 

prepared by Springborn Labs, Inc. 59 p.

42532609 Hoberg, J. (1992) MCPB Sodium--Toxicity to the Freshwater 

Diatom, Navicula pelliculosa: Final Report: Lab Project 

Number: 92-10-4448: 10566.0392.6231 440. Unpublished study 

prepared by Springborn Labs, Inc. 60 p.

46743367 Albuquerque, R. (2003) MCPB 400 G/L Aqueous Formulation: 

Algal Growth Inhibition Assay (Selenastrum capricornutum). 

Project Number: AHM/147/023375. Unpublished study 

prepared by Huntingdon Life Sciences, Ltd. 41 p.

46743802 Albuquerque, R. (2003) MCPB 400 G/L Aqueous Formulation: 

Algal Growth Inhibition Assay (Navicula pelliculosa). Project 

Number: AHM/148/024534. Unpublished study prepared by 

Huntingdon Life Sciences, Ltd. 39 p.

46743803 Albuquerque, R. (2003) MCPB 400 G/L Aqueous Formulation: 

Higher Plant (Lemna) Growth Inhibition Test. Project Number: 

AHM/149/023838. Unpublished study prepared by Huntingdon 

Life Sciences, Ltd. 44 p.

47200201 Albuquerque, R. (2003) Supplemental Information to MRID 

46743801: MCPB 400 G/L Aqueous Formulation: Algal Growth 

Inhibition Assay (Selenastrum capricornutum). Project Number: 

AHM/147/023375, AHM/147. Unpublished study prepared by 

Huntingdon Life Sciences, Ltd. 33 p.

47200202 Albuquerque, R. (2003) Supplemental Information to MRID 

46743802: MCPB 400 G/L Aqueous Formulation: Algal Growth 

Inhibition Assay (Navicula pelliculosa). Project Number: 

AHM/148/024534, AHM/148. Unpublished study prepared by 

Huntingdon Life Sciences, Ltd. 78 p.

47200203 Albuquerque, R. (2003) Supplemental Information to MRID: 

46743803: MCPB 400G/L Aqueous Formulation: Higher Plant 

(Lemna) Growth Inhibition Test. Project Number: 

AHM/149/023828, AHM/149. Unpublished study prepared by 

Huntingdon Life Sciences, Ltd. 91 p.
37

123-2 Aquatic plant growth

MRID Citation Reference

46743801 Albuquerque, R. (2003) MCPB 400 G/L Aqueous Formulation: 

Algal Growth Inhibition Assay (Selenastrum capricornutum). 

Project Number: AHM/147/023375. Unpublished study 

prepared by Huntingdon Life Sciences, Ltd. 41 p.

46743802 Albuquerque, R. (2003) MCPB 400 G/L Aqueous Formulation: 

Algal Growth Inhibition Assay (Navicula pelliculosa). Project 

Number: AHM/148/024534. Unpublished study prepared by 

Huntingdon Life Sciences, Ltd. 39 p.

46743803 Albuquerque, R. (2003) MCPB 400 G/L Aqueous Formulation: 

Higher Plant (Lemna) Growth Inhibition Test. Project Number: 

AHM/149/023838. Unpublished study prepared by Huntingdon 

Life Sciences, Ltd. 44 p.

47200201 Albuquerque, R. (2003) Supplemental Information to MRID 

46743801: MCPB 400 G/L Aqueous Formulation: Algal Growth 

Inhibition Assay (Selenastrum capricornutum). Project Number: 

AHM/147/023375, AHM/147. Unpublished study prepared by 

Huntingdon Life Sciences, Ltd. 33 p.

47200202 Albuquerque, R. (2003) Supplemental Information to MRID 

46743802: MCPB 400 G/L Aqueous Formulation: Algal Growth 

Inhibition Assay (Navicula pelliculosa). Project Number: 

AHM/148/024534, AHM/148. Unpublished study prepared by 

Huntingdon Life Sciences, Ltd. 78 p.

47200203 Albuquerque, R. (2003) Supplemental Information to MRID: 

46743803: MCPB 400G/L Aqueous Formulation: Higher Plant 

(Lemna) Growth Inhibition Test. Project Number: 

AHM/149/023828, AHM/149. Unpublished study prepared by 

Huntingdon Life Sciences, Ltd. 91 p

850.5400 Algal toxicity, Tiers 1 and II

MRID Citation Reference

46743801 Albuquerque, R. (2003) MCPB 400 G/L Aqueous 

Formulation: Algal Growth Inhibition Assay (Selenastrum 

capricornutum). Project Number: AHM/147/023375. 

Unpublished study prepared by Huntingdon Life Sciences, 

Ltd. 41 p.
38

46743802 Albuquerque, R. (2003) MCPB 400 G/L Aqueous 

Formulation: Algal Growth Inhibition Assay (Navicula 

pelliculosa). Project Number: AHM/148/024534. Unpublished 

study prepared by Huntingdon Life Sciences, Ltd. 39 p.

47200201 Albuquerque, R. (2003) Supplemental Information to MRID 

46743801: MCPB 400 G/L Aqueous Formulation: Algal 

Growth Inhibition Assay (Selenastrum capricornutum). Project 

Number: AHM/147/023375, AHM/147. Unpublished study 

prepared by Huntingdon Life Sciences, Ltd. 33 p.

47200202 Albuquerque, R. (2003) Supplemental Information to MRID 

46743802: MCPB 400 G/L Aqueous Formulation: Algal 

Growth Inhibition Assay (Navicula pelliculosa). Project 

Number: AHM/148/024534, AHM/148. Unpublished study 

prepared by Huntingdon Life Sciences, Ltd. 78 

850.4400 Aquatic plant toxicity test using Lemna spp. Tiers I 

and II

MRID Citation Reference

46743803 Albuquerque, R. (2003) MCPB 400 G/L Aqueous 

Formulation: Higher Plant (Lemna) Growth Inhibition Test. 

Project Number: AHM/149/023838. Unpublished study 

prepared by Huntingdon Life Sciences, Ltd. 44 p.

47200203 Albuquerque, R. (2003) Supplemental Information to MRID: 

46743803: MCPB 400G/L Aqueous Formulation: Higher Plant 

(Lemna) Growth Inhibition Test. Project Number: 

AHM/149/023828, AHM/149. Unpublished study prepared by 

Huntingdon Life Sciences, Ltd. 91 p.

141- 1 Acute Honey Bee Contact

MRID Citation Reference

42532607 Maggi, V. (1992) Acute Contact Toxicity of MCPB Sodium 

Salt to Honey Bees (Apis melliflora L.): Lab Project Number: 

CAR 169-92. Unpublished study prepared by California 

Agricultural Research, Inc. 22 p.

Non-Guideline Study

MRID Citation Reference
39

21958

Mason, D.F.J. (19??) Summary of Toxicological Work. 

(Unpublished study received Apr 12, 1962 under unknown 

admin. no.; submitted by May Baker, Ltd., Montreal, Canada; 

CDL:102710-A) 

42669

Rhone-Poulenc Chemical Company (19??) Summary of 

Toxicological Work. (Unpublished study received Apr 12, 

1962 under unknown admin. no.; CDL:102686-A) 

42670

Rhone-Poulenc Chemical Company (1961) Biochemical Link 

between 4-Phenoxy butyric acids and Phenoxy acetic acid. 

(Unpublished study received Apr 12, 1962 under unknown 

admin. no.; CDL: 102686-B) 

53737

Thomson, W.T. (1967) Agricultural Chemicals--Book II: 

Herbicides. Rev. Davis, Calif.: Thomson Publications. (pp. 12-

14 only; also~In~unpublished submission received Aug 15, 

1977 under 38117-3; submitted by Akzo Zout Chemie 

Nederland, B.V., Amster- dam, Holland; CDL:231355-G) 

53754

Way, J.M. (1969) Toxicity and hazards to man, domestic 

animals, and wildlife from some commonly used auxin 

herbicides. Residue Reviews 26:37-62. (Also~In~unpublished 

submission received Aug 15, 1977 under 38117-2; submitted 

by Akzo Zout Chemie Neder- land, B.V., Amsterdam, 

Holland; CDL:231352-O) 

55823

Pimentel, D. (1971) Ecological Effects of Pesticides on Nontarget Species. By Cornell Univ., Dept. of Entomology and 

Limnology. Washington, D.C.: Executive Office of the 

President, Office of Science and Technology. (p. 113 only; 

available from: Super- intendent of Documents, U.S. 

Government Printing Office, Wash- ington, DC, 20402; stock 

no. 4106-0029, published study; CDL: 241577-U) 

73213

Guardigli, A.; Chow, W. (1970) Identification and 

Semiquantitative Determination of 4-(2-Methyl, 4-

chlorophenoxy) Butyric Acid (MCPB) and Its Metabolite 2-

Methyl, 4-Chlorophenoxy Acetic Acid (MCPA) by Thin Layer 

Chromatography. Method no. 106 dated Mar 3, 1970. 

(Unpublished study received on unknown date under 1F1051; 

submitted by Rhodia, Inc., New Brunswick, N.J.; CDL: 

098804-A)

158522 Rhodia Inc. (1969?) Summary of MCPB Toxicology. 

Unpublished study. 3 p. 
40

41578801

Tomerlin, J. (1990) Anticipated Residues and Dietary 

Exposure Anal- ysis for MCPB on Peas. Unpublished study 

prepared by Technical Assessment Systems, Inc. 11 p. 

47008601

Pigott, G. (2006) Phenoxy Herbicides: A Review of Studies 

with Aquatic Plants (MCPP-p and 2,4 DP-p). Unpublished 

study prepared by MCPP-P Task Force. 33 p.

47163505

Harper, H. (2005) MCPA, 2,4-D, Mecoprop, Dichlorprop, 

MCPB and 2,4-DB: Validation of the Methodology for the 

Determination of Residue in Drinking and Surface Waters: 

Final Report. Project Number: TFT/005/052350. Unpublished 

study prepared by Huntingdon Research Center. 220 p.

92087999

Rhone-Poulenc Ag Company (1990) Reregistration Phase 3 

Response: Methyl-4-chlorophenoxy)butyric acid. 

Correspondence and Supporting Material
41

Appendix C—SIP Results

Table 1. Inputs

Parameter Value

Chemical name MCPB

Solubility (in water at 25oC; mg/L) 100

Mammalian LD50 (mg/kg-bw) 912

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian species

Mammalian NOAEL (mg/kg-bw) 7.5

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian species

Avian LD50 (mg/kg-bw) 282

Avian test species northern bobwhite quail

Body weight (g) of "other" avian species

Mineau scaling factor 1.15

Mallard NOAEC (mg/kg-diet) 5000

Bobwhite quail NOAEC (mg/kg-diet) 5000

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

Body weight (g) of other avian species

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

Body weight (g) of 2nd other avian species

Table 2. Mammalian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 17.2000 17.2000

Adjusted toxicity value (mg/kg-bw) 701.4744 5.7687

Ratio of exposure to toxicity 0.0245 2.9816

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) 81.0000 81.0000

Adjusted toxicity value (mg/kg-bw) 203.1611 248.0628

Ratio of exposure to acute toxicity 0.3987 0.3265
42

Conclusion* Exposure through drinking 

water alone is a potential 

concern for birds

Drinking water exposure 

alone is NOT a potential 

concern for birds

*Conclusion is for drinking water exposure alone. This does not combine all routes of exposure. Therefore, 

when aggregated with other routes (i.e., diet, inhalation, dermal), pesticide exposure through drinking water 

may contribute to a total exposure that has potential for effects to non-target animals.
43

APPENDIX D—STIR Results

Input

Application and Chemical Information

Enter Chemical Name MCPB

Enter Chemical Use Peas

Is the Application a Spray? (enter y or n) y

If Spray What Type (enter ground or air) air

Enter Chemical Molecular Weight (g/mole) 228.6

Enter Chemical Vapor Pressure (mmHg) 4.00E-07

Enter Application Rate (lb a.i./acre) 1.6

Toxicity Properties

Bird

Enter Lowest Bird Oral LD50 (mg/kg bw) 282

Enter Mineau Scaling Factor 1.15

Enter Tested Bird Weight (kg) 0.178

Mammal

Enter Lowest Rat Oral LD50 (mg/kg bw) 912

Enter Lowest Rat Inhalation LC50 (mg/L) 1.14

Duration of Rat Inhalation Study (hrs) 4

Enter Rat Weight (kg) 0.35

Output

Results Avian (0.020 kg )

Maximum Vapor Concentration in Air at Saturation 

(mg/m3) 4.92E-03

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 6.19E-04

Adjusted Inhalation LD50 1.97E+00

Ratio of Vapor Dose to Adjusted Inhalation LD50 3.15E-04 Exposure not Likely Significant

Maximum Post-treatment Spray Inhalation Dose (mg/kg) 1.54E-01

Ratio of Droplet Inhalation Dose to Adjusted Inhalation 

LD50 7.82E-02 Exposure not Likely Significant

Results Mammalian (0.015 kg )

Maximum Vapor Concentration in Air at Saturation 

(mg/m3) 4.92E-03

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 7.78E-04

Adjusted Inhalation LD50 6.79E+01

Ratio of Vapor Dose to Adjusted Inhalation LD50 1.15E-05 Exposure not Likely Significant

Maximum Post-treatment Spray Inhalation Dose (mg/kg) 1.93E-01

Ratio of Droplet Inhalation Dose to Adjusted Inhalation 

LD50 2.85E-03 Exposure not Likely Significant
44

APPENDIX E—ECOSAR (v. 1.0) Results

96-hr Fish LC50

Chemical Neutral 

Organics Acid Phenols Phenols, Poly

Neutral 

Organic SAR

(Baseline 

Toxicity)

Aldehydes 

(Mono)

MCPB 84.011* - - - -

MCPB sodium 20772.877 - - - -

MCPA 539.179 - - - -

4-(4-hydroxy-o-tolyloxy) 

butyric acid 263.349 - - - -

2-4-dihyroxyphenyl formate - - 28.458 316.496 -

o-cresol - 14.568 - 74.103 -

4CC - 6.480 - 27.832 -

5-Chlorosalicylaldehyde - 7.782 - 99.893 4.338

4-Chloro-2-methylanisole 9.290 - - - -

14-d Fish LC50

Chemical Neutral 

Organics Acid Phenols Phenols, Poly

Neutral 

Organic SAR

(Baseline 

Toxicity)

Aldehydes 

(Mono)

MCPB 87.027* - - - -

MCPB sodium 20236.484 - - - -

MCPA 549.760 - - - -

4-(4-hydroxy-o-tolyloxy) 

butyric acid 269.982 - - - -

2-4-dihyroxyphenyl formate - - - - -

o-cresol - 74.684 - - -

4CC - 26.961 - - -

5-Chlorosalicylaldehyde - 32.939 - - -

4-Chloro-2-methylanisole 9.587 - - - -

48-hr Daphnid LC50 

Chemical

Neutral 

Organics 

Acid

Phenols Phenols, Poly

Neutral 

Organic SAR

(Baseline 

Toxicity)

Aldehydes 

(Mono)

MCPB 59.153* - - - -

MCPB sodium 8326.676 - - - -

MCPA 328.535 - - - -

4-(4-hydroxy-o-tolyloxy) 

butyric acid 168.576 - - - -

2-4-dihyroxyphenyl formate - - 157.345 171.713 -

o-cresol - 5.229 - 43.071 -

4CC - 2.974 - 17.488 -
45

5-Chlorosalicylaldehyde - 3.499 - 21.160 5.066

4-Chloro-2-methylanisole 6.317 - - - -

96-hr Green Algae EC50 

Chemical

Neutral 

Organics 

Acid

Phenols Phenols, Poly

Neutral 

Organic SAR

(Baseline 

Toxicity)

Aldehydes 

(Mono)

MCPB 53.913* - - - -

MCPB sodium 1450.214 - - - -

MCPA 195.339 - - - -

4-(4-hydroxy-o-tolyloxy) 

butyric acid 116.134 - - - -

2-4-dihyroxyphenyl formate - - 1.436 60.056 -

o-cresol - 23.911 - 19.033 -

4CC - 12.772 - 10.067 -

5-Chlorosalicylaldehyde - 15.108 - 11.918 9.720

4-Chloro-2-methylanisole 5.195 - - - -

96-hr Fish (SW) LC50 

Chemical Neutral 

Organics Acid Phenols Phenols, Poly

Neutral 

Organic SAR

(Baseline 

Toxicity)

Aldehydes 

(Mono)

MCPB 104.199* - - - -

MCPB sodium 34418.113 - - - -

MCPA 720.565* - - - -

4-(4-hydroxy-o-tolyloxy) 

butyric acid 343.026 - - - -

2-4-dihyroxyphenyl formate - - - - -

o-cresol - 10.326 - - -

4CC - 3.106 - - -

5-Chlorosalicylaldehyde - 3.852 - - -

4-Chloro-2-methylanisole 11.732 - - - -

96-hr Mysid Shrimp LC50 

Chemical Neutral 

Organics Acid Phenols Phenols, Poly

Neutral 

Organic SAR

(Baseline 

Toxicity)

Aldehydes 

(Mono)

MCPB 28.692* - - - -

MCPB sodium 1.08e+005* - - - -

MCPA 371.054 - - - -

4-(4-hydroxy-o-tolyloxy) 

butyric acid 142.435 - - - -

2-4-dihyroxyphenyl formate - - - - -

o-cresol - - - - -

4CC - - - - -
46

5-Chlorosalicylaldehyde - - - - -

4-Chloro-2-methylanisole 3.756 - - - -

14-d Earthworm LC50 

Chemical Neutral 

Organics Acid Phenols Phenols, Poly

Neutral 

Organic SAR

(Baseline 

Toxicity)

Aldehydes 

(Mono)

MCPB 2777.442* - - - -

MCPB sodium 756.321 - - - -

MCPA 3080.735 - - - -

4-(4-hydroxy-o-tolyloxy) 

butyric acid 2751.554 - - - -

2-4-dihyroxyphenyl formate - - - - -

o-cresol - 94.933 - - -

4CC - 68.229 - - -

5-Chlorosalicylaldehyde - 78.761 - - -

4-Chloro-2-methylanisole 201.268* - - - -