Office of Water 

Office Science and 

Technology 

EPA 820-D-14-095 

May 2014

Draft Update of Human Health 

Ambient Water Quality Criteria: 

 

Chlorophenoxy Herbicide (2,4,5-TP)

93-72-1

 

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EPA 820-D-14-095

May 2014

 

Update of Human Health 

Ambient Water Quality Criteria: 

 

Chlorophenoxy Herbicide (2,4,5-TP)

93-72-1

Draft 

Office of Science and Technology 

Office of Water 

U.S. Environmental Protection Agency 

Washington, DC 20460

 
Chlorophenoxy Herbicide (2,4,5-TP) 93-72-1 

1 

Table of Contents 

Introduction: Plan and Scope of Update

Problem Formulation

Criteria Formulas- Analysis Plan

Exposure Factors

Body Weight

Drinking Water Intake

Fish Consumption Rate

Bioaccumulation Factor

Hazard Identification and Dose Response

Reference Dose

Relative Source Contribution

Criteria Derivation- Analysis

Criteria Characterization

Chemical Name / Synonyms

References

Introduction: Plan and Scope of Update 

Human health ambient water quality criteria (AWQC) are numeric values for pollutant 

concentrations in ambient waters that the U.S. Environmental Protection Agency (EPA) 

considers to be protective of human health. EPA periodically revises water quality criteria to 

ensure that they reflect the latest scientific knowledge. The current revisions of the criteria for 

chlorophenoxy herbicide (2,4,5-TP)

*

, contained in this document, incorporate updated 

information regarding reference dose, body weight, drinking water intake, fish consumption 

rate, and bioaccumulation. Updated reference dose information for chlorophenoxy herbicide 

(2,4,5-TP) is identified in EPA’s Office of Research and Development’s Integrated Risk 

Information System’s (IRIS) 1988 toxicology assessment (USEPA, 1988). Updated body weight 

and drinking water intake data are identified in EPA’s ‘Exposure Factors Handbook: 2011 

Edition’ (USEPA, 2011). The bioaccumulation factor data is updated using EPA’s Estimation 

Program Interface (EPI) Suite modeling program (USEPA, 2012a). The overall fish consumption 

rate and trophic level breakdowns are updated using EPA’s ‘Estimated Fish Consumption Rates 

for the U.S. Population and Selected Subpopulations (NHANES 2003-2010)’ (USEPA, 2014). 

Unless otherwise specified, all sources of information used in this update are from peer 

reviewed sources. 

Note that the term "water quality criteria" can carry one of two possible meanings, 

depending on the section of the Clean Water Act (CWA) associated with the particular criteria 

at issue. “Water quality criteria” may refer to national water quality criteria recommendations 

issued under CWA § 304. “Water quality criteria” may also refer to water quality criteria 

 

*

 This compound is not currently registered as a pesticide by EPA. 
Chlorophenoxy Herbicide (2,4,5-TP) 93-72-1 

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components of water quality standards adopted by states, territories, or authorized tribes 

under CWA § 303. 

National ambient water quality criteria recommendations for human health are issued 

by the EPA under CWA §304. They are based on the latest scientific information on the 

relationship between the effects of a constituent concentration and human health. Protective 

assumptions are made regarding the potential human exposure intakes. These criteria do not 

reflect consideration of non-human health endpoints or economic impacts. Nor do they reflect 

the technological feasibility of meeting the chemical concentrations in ambient water. National 

ambient water quality criteria recommendations for human health are not automatically 

incorporated into water quality standards adopted by states, territories, or authorized tribes. 

Rather, they provide scientific information to states, territories and authorized tribes to assist 

them in adopting ambient water quality criteria for human health in water quality standards 

that meet CWA requirements. National ambient water quality criteria recommendations for 

human health are not regulations themselves and they do not impose legally binding 

requirements on EPA, states, territories, authorized tribes, or the public. States, territories, and 

authorized tribes have the discretion to adopt, where appropriate, other scientifically 

defensible water quality criteria that differ from EPA’s national ambient recommended criteria 

for human health. 

Ambient water quality criteria components of water quality standards are generally 

adopted by the states, territories, and authorized tribes themselves, under §303(c)(2). (In 

certain circumstances EPA also may promulgate this type of criterion itself, pursuant to 

§303(c)(4)). State ambient water quality criteria for human health represent a quality of water 

that sufficiently protects human health to support a designated use of the state, territory, or 

authorized tribe. Such criteria may be expressed in terms of constituent concentrations, levels, 

or narrative statements. Once ambient water quality criteria for human health are adopted by a 

state, territory, or authorized tribe into their water quality standards, they provide a basis for 

controlling discharges or releases of pollutants, for developing permit limits, assessing waters, 

and developing total maximum daily loads (TMDLs) for waters that do not meet the water 

quality standard. Ambient water quality criteria for human health have a regulatory impact 

once they have been adopted into water quality standards by the state, territory, or authorized 

tribe under § 303(c)(2) (or alternatively issued by EPA pursuant to § 303(c)(4)). 

The water quality criteria at issue in this document are national ambient water quality 

criteria recommendations for human health issued under CWA § 304. Unless expressly 

indicated otherwise, all references to “criteria,” “water quality criteria,” “ambient water quality 

criteria (AWQC) recommendations,” or similar variants thereof, are references to national 

ambient water quality criteria recommendations for human health. 

Problem Formulation 

Problem formulation provides a strategic framework for water quality criteria 

development by focusing on the most relevant endpoints and increasing the transparency of 
Chlorophenoxy Herbicide (2,4,5-TP) 93-72-1 

3 

the effects assessment process. The structure of this criteria document is consistent with U.S. 

EPA’s ‘Framework for Human Health Risk Assessment to Inform Decision Making’ (USEPA, 

2012b). 

In the development of AWQC, EPA currently follows the deterministic assessment 

methodology outlined in EPA’s ‘Methodology for Deriving Ambient Water Quality Criteria for 

the Protection of Human Health (2000)’ (USEPA, 2000), hereafter known as the 2000 

Methodology. For pollutants that exhibit a threshold of exposure before deleterious effects 

occur, such as is the case for non-carcinogens, the 2000 Methodology applies a relative source 

contribution (RSC) to determine the amount of the reference dose (RfD) apportioned to fish 

consumption (freshwater and estuarine species) and drinking water intake. The RSC value is 

applied to chemicals with an RfD to ensure that exposure to these chemicals from drinking 

water and fish ingestion, when combined with all other sources, will not exceed the reference 

dose. Other exposures routes, including but not limited to, dermal exposure, inhalation 

exposure, marine fish and shellfish consumption (when not included in the fish consumption 

rate), and non-fish dietary exposures (fruits, vegetables, grains, meats or poultry) are 

accounted for in the percentage of the RfD that remains, after accounting for the RSC. 

Criteria Formulas- Analysis Plan 

The following formulas are used to develop the human health ambient water quality 

criteria. EPA develops criteria for ambient waters typically considering two routes of exposure. 

The first formula is for a criterion that assumes exposure through both the consumption of 

water and the consumption of aquatic organisms. The second formula is for a criterion that 

assumes exposure through the consumption of aquatic organisms, but not water. The use of 

one criterion over the other depends on the designated use of the water bodies in question (i.e. 

drinking water source and/or fishable waters). 

EPA recommends inclusion of the drinking water exposure pathway for ambient surface 

waters where drinking water is a designated use for the following reasons: (1) Drinking water is 

a designated use for surface waters under the CWA and, therefore, criteria are needed to 

assure that this designated use can be protected and maintained. (2) Although rare, there are 

some public water supplies that provide drinking water from surface water sources without 

treatment. (3) Even among the majority of water supplies that do treat surface waters, existing 

treatments may not necessarily be effective for reducing levels of particular contaminants. (4) 

In consideration of the Agency’s goals of pollution prevention, ambient waters should not be 

contaminated to a level where the burden of achieving health objectives is shifted away from 

those responsible for pollutant discharges and placed on downstream users to bear the costs of 

upgraded or supplemental water treatment (USEPA, 2000). 

EPA recommends the organism only criterion in those cases where the designated uses 

of a water body include only supporting fishable uses under Section 101(a) of the CWA and, 

thus, fish or shellfish for human consumption, but not as a drinking water supply source (e.g., 

non-potable estuarine waters) (USEPA, 2000).
Chlorophenoxy Herbicide (2,4,5-TP) 93-72-1 

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The formulas for deriving the criteria values are as follows (USEPA, 2000):

For consumption of water and organisms: 

AWQC (μg/L) = RfD (mg/kg·d) × RSC × BW (kg) × 1000 μg/mg† (Eq. 1) 

 DI (L/d) + ∑ (FCRi (kg d) AFi ( kg)) 4

i 2 

For consumption of organisms only: 

AWQC (μg/L) = RfD (mg/kg·d) × RSC × BW (kg) × 1000 (μg/mg)† (Eq. 2) 

 ∑ (FCRi (kg d) AFi ( kg)) 4

i 2 

Where: 

AWQC = ambient water quality criteria 

RfD = reference dose 

RSC = relative source contribution 

BW = body weight 

DI = drinking water intake 

∑

4

 i=2 summation of values for aquatic trophic levels (T ) where the letter “i” stands for the 

trophic levels to be considered, starting with TL 2 and proceeding to TL 4 

FCRi = fish consumption rate for aquatic trophic levels 2, 3, and 4 

BAFi = bioaccumulation factor for aquatic trophic levels 2, 3, and 4 

 The following sections identify each of the components of the formulas for the human 

health ambient water quality criteria and provide reference sources, previously used values 

when available, and the values to be used in the updated criteria. 

Exposure Factors: 

Body Weight 

 The updated recommended body weight (BW) is 80 kg which represents the mean 

weight for adults 21 years of age and older. This recommendation is found in EPA’s ‘Exposure 

Factors Handbook: 2011 Edition’ in Chapter 8. It was based on data derived from the National 

Health and Nutrition Examination Survey (NHANES) 1999−2006 (USEPA, 2011). This body 

weight replaces the recommended standard weight for adults of 70 kg that was described in 

the 2000 Methodology which was approximated from the mean body weight of adults from the 

National Health and Nutrition Examination Survey (NHANES) III database (1988-1994) and a 

1989 study by the National Cancer Institute (USEPA, 2000). 

 

† 1000 μg/mg is used to convert the units of mass into micrograms from milligrams. 
Chlorophenoxy Herbicide (2,4,5-TP) 93-72-1 

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Drinking Water Intake 

The updated drinking water intake (DI) is 3 L/day, rounded from 3.091 L/day for 

consumer-only estimates of direct and indirect water ingestion based on NHANES 2003-2006 

data for all sources of water at the 90th percentile for adults (≥21 years of age) (USEPA, 2011). 

Direct water is defined as water ingested directly as a beverage (from all sources); indirect 

water is defined as water added in the preparation of food or beverages, not including indirect 

consumption of bottled water. This recommended value is found in EPA’s ‘Exposure Factors 

Handbook: 2011 Edition’ in Table 3-36. It replaces the drinking water intake standard of 2 L/day 

described in the 2000 Methodology which represented the 86th percentile for adults 20 years 

and older in the US Department of Agriculture’s 1994-96 Continuing Survey of Food Intake by 

Individuals (CSFII) analysis or the 88th percentile of adults in the National Cancer Institute study 

of the 1977-78 Nationwide Food Consumption Survey (USEPA, 2000). 

Fish Consumption Rate 

The updated fish consumption rate (FCR) for the general adult population is 22 

grams/day (0.022 kg/day) (USEPA, 2014: see Table 9a). It represents the 90th percentile per 

capita consumption rate of freshwater and estuarine fish for the U.S. adult population 21 years 

of age and older based on the Centers for Disease Control and Prevention (CDC) National 

Health and Nutrition Examination Surveys (NHANES) conducted from 2003-2010. The previous 

criterion was developed without consideration of fish consumption (USEPA, 1976). 

As recommended in the 2000 Methodology, this update to the criteria distinguishes a 

trophic level (TL) breakdown of the fish consumption rate to provide a better representation of 

dietary exposure to fish at multiple trophic levels. An organism’s trophic position in the aquatic 

food web can have an important effect on the magnitude of bioaccumulation of certain 

chemicals. The trophic levels are numbered 2, 3, and 4 and account for different categories of 

fish and shellfish species based on their position in the aquatic food web. TL2 accounts for 

benthic filter feeders, TL3 accounts for forage fish, and TL4 accounts for predatory fish. 

In order to derive the trophic level breakdown of the 22 grams/day freshwater and 

estuarine FCR, the trophic level specific freshwater and estuarine FCR data sets for adults 21 

years of age and older were identified (USEPA, 2014: see Tables 16a, 17a, and 18a). In each 

trophic level specific data set, the ratio of that trophic level’s 90th percentile FCR compared to 

the summation of all three trophic level specific 90th percentile FCRs was applied to the 22 

grams/day FCR used in this update. The trophic level ratios were calculated as follows: TL ratio 

= 90th percentile FCR for the TL divided by the sum of the 90th percentile FCRs for all TLs. TL2 = 

7.6/21.3 = 0.3568 (35.68%), TL3 = 8.6/21.3 = 0.4038 (40.38%), and TL4 = 5.1/21.3 = 0.2394 

(23.94%). Applying these ratios to the updated FCR of 22 grams/day result in trophic level 

breakdowns of TL2 = 8 grams/day (0.008 kg/day); TL3 = 9 grams/day (0.009 kg/day); and TL4 = 5 

grams/day (0.005 kg/day). These resulting trophic level FCRs are well within the confidence 

intervals for each of the trophic level specific distributions’ 90th percentiles and add to the total 

of 22 grams/day (USEPA, 2014).
Chlorophenoxy Herbicide (2,4,5-TP) 93-72-1 

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Bioaccumulation Factor 

Several attributes of the bioaccumulation process are important to understand when 

deriving national BAFs for use in setting national 304(a) criteria. First, the term 

“bioaccumulation” refers to the uptake and retention of a chemical by an aquatic organism 

from all surrounding media (e.g., water, food, sediment). The term “bioconcentration” refers to 

the uptake and retention of a chemical by an aquatic organism from water only. For some 

chemicals (particularly those that are highly persistent and hydrophobic), the magnitude of 

bioaccumulation by aquatic organisms can be substantially greater than the magnitude of 

bioconcentration. Thus, an assessment of bioconcentration alone may underestimate the 

extent of accumulation in aquatic biota for these chemicals. Accordingly, EPA’s guidelines 

presented in the 2000 Methodology emphasize the measurement or estimation of chemical 

bioaccumulation by aquatic organisms (USEPA, 2000). 

The bioaccumulation factors (BAF) have been estimated using EPA’s Estimation Program 

Interface (EPI) Suite (USEPA, 2012a). The CF AFTM program within EPI Suite estimates fish 

bioaccumulation factors using octanol-water partition coefficients (KOW) and biotransformation 

data from a model designed by Arnot and Gobas (2003). The model includes mechanistic 

processes for bioaccumulation such as chemical uptake from the water at the gill surface and 

from the diet, chemical elimination at the gill surface, fecal egestion, growth dilution and 

metabolic biotransformation. Other processes included in the calculations are bioavailability in 

the water column (only the freely dissolved fraction can bioconcentrate) and absorption 

efficiencies at the gill and in the gastrointestinal tract. The model requires the octanol-water 

partition coefficient (KOW) of the chemical and the normalized whole-body metabolic 

biotransformation rate constant as input parameters to predict BAF values. Model predictions 

may be highly uncertain for chemicals that have estimated log KOW values > 9. The model is not 

recommended at this time for chemicals that appreciably ionize, for pigments and dyes, or for 

perfluorinated substances (USEPA, 2012a). 

For chlorophenoxy herbicide (2,4,5-TP), BAFs have been estimated using the EPI Suite 

model (USEPA, 2012a) as described above for trophic levels 2, 3, and 4. The estimated lower 

(TL2), mid (TL3), and upper (TL4) trophic level BAFs for chlorophenoxy herbicide (2,4,5-TP) (log 

KOW = 3.80) are 389.7 L/kg, 441.9 L/kg, and 662.9 L/kg wet-weight, respectively. The previous 

criterion for chlorophenoxy herbicide (2,4,5-TP) was derived prior to the current methodology 

and did not take bioaccumulation into consideration in its development (USEPA, 1976).

Hazard Identification and Dose Response: 

Reference Dose 

The reference dose (RfD) is an estimate (with uncertainty spanning approximately an 

order of magnitude) of a daily oral exposure for a chronic duration (up to a lifetime) to the 

human population (including sensitive subgroups) that is likely to be without an appreciable risk 

of deleterious effects during a lifetime. It can be derived from laboratory animal dosing studies 
Chlorophenoxy Herbicide (2,4,5-TP) 93-72-1 

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in which a no observed adverse effect level (NOAEL), lowest observed adverse effect level 

(LOAEL), or benchmark dose (with uncertainty factors generally applied to reflect limitations of 

the data used) can be obtained. The previously used RfD for chlorophenoxy herbicide (2,4,5-TP) 

was 2 × 10–3 mg/kg·day (Kraus, as cited by Mitchess, Hogson, and Gaetjens, 1946; USEPA, 

1976). The following information provides the basis for the updated RfD of 0.008 mg/kg·day 

(USEPA, 1988) for the updated AWQC. 

 The principle studies by Mullison (1966) and Gehring and Betso (1978) chosen to 

calculate the reference dose for chlorophenoxy herbicide (2,4,5-TP) showed histopathological 

changes in liver tissue as the critical effect above the NOAEL in dogs orally exposed to 

chlorophenoxy herbicide (2,4,5-TP). The study was chronic and had a NOAEL of 7.5 × 10-1

mg/kg·day. An uncertainty factor of 100× was applied to the NOAEL to account for interspecies 

extrapolation (10×) and intraspecies variation (10×) (USEPA, 1988).

Relative Source Contribution 

 The relative source contribution (RSC) component of the human health ambient water 

quality criteria (AWQC) calculation for threshold non-carcinogens and non-linear carcinogens 

allows a percentage of the reference dose’s exposure to be attributed to ambient water and 

freshwater and estuarine fish consumption (including estuarine species harvested in near 

coastal waters) when there are other potential exposure sources. The RSC describes the portion 

of the RfD available for AWQC-related sources (often a 20% default is utilized) (USEPA, 2000). 

The remainder of the RfD is allocated for other sources of the pollutant. The rationale for this 

approach is that for pollutants exhibiting threshold effects, the objective of the AWQC is to 

ensure that an individual’s total exposure from all sources does not exceed that threshold level. 

Exposures outside of the RSC include, but are not limited to, exposure to a particular pollutant 

from marine fish consumption (not included in the fish consumption rate), non-fish food 

consumption (fruits, vegetables, and grains), dermal exposure, and respiratory exposure. The 

percentage of exposure of the reference dose that these other exposures account for is equal 

to 100 percent minus the RSC. 

In the absence of scientific data, the application of the EPA’s default value of 20 percent 

RSC in calculating 304(a) criteria or establishing State or Tribal water quality standards under 

Section 303(c) will ensure that the designated use for a water body is protected. This 20 

percent default for RSC can only be replaced where sufficient data are available to develop a 

scientifically defensible alternative value. If appropriate, scientific data demonstrating that 

other sources and routes of exposure besides water and freshwater/estuarine fish are not 

anticipated for the pollutant in question, then the RSC may be raised to the appropriate level, 

based on the data (USEPA, 2000). 

 The AWQC for chlorophenoxy herbicide (2,4,5-TP) was/are calculated using a default 

RSC of 20 percent which complies with the 2000 Methodology (USEPA, 1976; USEPA, 2000). 
Chlorophenoxy Herbicide (2,4,5-TP) 93-72-1 

8 

Criteria Derivation- Analysis

Table 1 summarizes model inputs used to derive the 2014 updated human health 

ambient water quality criteria for chlorophenoxy herbicide (2,4,5-TP). Criteria calculations are 

presented below. These updated chlorophenoxy herbicide (2,4,5-TP) criteria recommendations 

are based on the 2000 Methodology and updated exposure assumptions as described above 

(Exposure Factors). 

Table 1. Summary of input parameters for 2014 human health ambient water quality criteria 

for chlorophenoxy herbicide (2,4,5-TP) 

Component Value Source Input Characterization

RfD 0.008 mg/kg·day USEPA, 

1988

uncertainty factor = 100 (10 for interspecies 

extrapolation; 10 for intraspecies variation)

RSC 0.20 USEPA, 

1976 default value

BW 80 kg USEPA, 

2011 mean weight for adults (≥21 years of age)

DI 3 L/day USEPA, 

2011 90th percentile for adults (≥21 years of age)

FCR

TL2 0.008 kg/day USEPA, 

2014

90th percentile consumption 

population (≥21 years of age)

rate for the U.S. adult TL3 0.009 kg/day

TL4 0.005 kg/day

TL2 389.7 L/kg EPI Suite KOW model estimated steady-state BAF 

BAF TL3 441.9 L/kg USEPA, 

2012a

values for non-ionic 

trophic levels of fish 

(10°C)

organic chemicals in 3 general 

in temperate environments 

TL4 662.9 L/kg

For consumption of water and organisms: 

AWQC (μg/L) = RfD (mg/kg·d) × RSC × BW (kg) × 1000 μg/mg 

 DI (L/d) + ∑ (FCRi (kg d) AFi ( kg)) 4

i 2 

 = 0.008 mg/kg·d × 0.20 × 80 kg × 1000 μg/mg 

 3 L/d + ((0.008 kg/d × 389.7 L/kg) + (0.009 kg/d × 441.9 L/kg) + (0.005 kg/d × 662.9 L/kg)) 

 = 9.546 μg/L (rounded to 10 μg/L because of significant figures) 

For consumption of organisms only: 

AWQC (μg/L) = RfD (mg/kg·d) × RSC × BW (kg) × 1000 (μg/mg) 

 ∑ (FCRi (kg d) AFi ( kg)) 4

i 2 

 = 0.008 mg/kg·d × 0.20 × 80 kg × 1000 μg/mg 

 (0.008 kg/d × 389.7 L/kg) + (0.009 kg/d × 441.9 L/kg) + (0.005 kg/d × 662.9 L/kg) 

 = 12.297 μg/L (rounded to 10 μg/L because of significant figures) 
Chlorophenoxy Herbicide (2,4,5-TP) 93-72-1 

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The updated human health ambient water quality criteria for chlorophenoxy herbicide 

(2,4,5-TP) are 10 μg/L (water and organism) and 10 μg/L (organism only) (Table 2). These 

updated criteria replace the previously published values (USEPA, 1976).

Table 2. Summary of EPA’s preciously recommended (1976) and updated (2014) human health 

ambient water quality criteria for chlorophenoxy herbicide (2,4,5-TP) 

1976 Human Health AWQC 2014 Human Health AWQC

Water and Organism 10 μg/L 10 μg/L

Organism Only --- 10 μg/L

These AWQC are meant to be protective of human health for the general adult 

population for a set percentage (RSC) of the total allowed daily oral exposure for a chronic 

duration (up to a lifetime) of chlorophenoxy herbicide (2,4,5-TP).

Criteria Characterization 

The updated 2014 human health AWQC for chlorophenoxy herbicide (2,4,5-TP) take into 

account current data on health effects and exposure input parameters, consistent with the 

2000 Methodology. The updated 2014 human health AWQC for chlorophenoxy herbicide (2,4,5-

TP) the same as EPA’s previously recommended 1976 criterion for water and organism 

exposures. The following paragraphs describe the individual influence of each of the revised 

model inputs and exposure assumptions on the overall change in value. 

Body Weight 

EPA’s updated AWQC assume a higher body weight compared to the previously 

recommended 1976 criterion, reflecting a recent rise in average adult body weight among the 

U.S. population. The updated body weight assumption of 80 kg based on recent survey data 

from the 1999−2006 NHANES data is 10 kg greater than the previous recommendation of 70 kg. 

Assuming all other input parameters remain constant, a higher average body weight in the 

AWQC calculations (Eq. 1 and 2 above) results in higher AWQC. That is, as body weight 

increases, the level of a contaminant in water at or below which negative health effects are not 

anticipated from a lifetime of exposure also increases. 

Drinking Water Intake 

The updated drinking water intake assumption is 3 L/day, which is higher than the 

previously recommended rate of 2 L/day. Assuming all other input parameters remain constant, 

a higher drinking water intake assumption in the AWQC calculations (Eq. 1 and 2 above) results 

in lower AWQC. That is, as drinking water intake increases, and thus overall exposure increases, 

the level of a contaminant in water at or below which negative health effects are not 

anticipated from a lifetime of exposure decreases. 
Chlorophenoxy Herbicide (2,4,5-TP) 93-72-1 

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Fish Consumption Rate 

The updated fish consumption rate is 22 g/day, divided into trophic level rates of 8 

g/day, 9 g/day, and 5 g/day for trophic levels 2, 3, and 4, respectively. The previous criterion did 

not consider exposure from fish consumption. Assuming all other input parameters remain 

constant, inclusion of a fish consumption rate in the AWQC calculations (Eq. 1 and 2 above) 

results in lower AWQC. That is, as fish consumption increases, and thus overall exposure 

increases, the level of a contaminant in water at or below which negative health effects are not 

anticipated from a lifetime of exposure decreases.

Bioaccumulation Factor 

The updated AWQC rely on EPI Suite model-estimated BAFs. The lower (TL2), mid (TL3), 

and upper (TL4) trophic level BAFs assumed in the updated criteria equations (Eq. 1 and 2 

above) are 389.7, 441.9, and 662.9 L/kg wet-weight, respectively. Assuming all other input 

parameters remain constant, the inclusion of BAFs along with FCRs when the previous criterion 

did not include them will result in lower AWQC. That is, as bioaccumulation or bioconcentration 

of a contaminant in fish and shellfish increases, and thus overall exposure increases, the level of 

a contaminant in water at or below which negative health effects are not anticipated from a 

lifetime of exposure decreases. 

Reference Dose 

The updated RfD of 0.008 mg/kg·day replaces the lower value of 2 × 10–3

 mg/kg·day. 

The change in the RfD was due to evaluation of more recent study data. Assuming all other 

input parameters remain constant, a higher RfD in the AWQC calculations (Eq. 1 and 2 above) 

results in higher AWQC. That is, as the RfD increases, the level of a contaminant in water at or 

below which negative health effects are not anticipated from a lifetime of exposure increases. 

Additional routes of exposure to a particular pollutant besides exposure from water 

intake and fish consumption are possible and may be considered when setting criteria for a 

state or tribe. Possible additional routes include, but are not limited to, dermal exposure, 

inhalation exposure, marine fish and shellfish consumption (when not included in the fish 

consumption rate), and non-fish dietary exposures (fruits, vegetables, grains, meats or poultry). 

If scientific evidence exists which indicate that one or more of these routes pose a significant 

risk of exposure, states and authorized tribes are encouraged to ensure that subpopulations are 

adequately protected. 

States, territories, and authorized tribes have the flexibility to develop criteria, on a sitespecific basis, that provide additional protection appropriate for highly exposed populations. 

EPA is aware that exposure patterns in general, and fish consumption in particular, vary 

substantially. EPA understands that highly exposed populations may be widely distributed 

geographically throughout a given state, territory, or authorized tribal area. EPA recommends 

that priority be given to identifying and adequately protecting the most highly exposed 
Chlorophenoxy Herbicide (2,4,5-TP) 93-72-1 

11

populations. Thus, if a state, territory, or authorized tribe determines that a highly exposed 

population is at greater risk and would not be adequately protected by criteria based on the 

general population, and by the national 304(a) criteria in particular, the state, territory, or 

authorized tribe may adopt more stringent criteria using alternative exposure assumptions 

(USEPA, 2000). Subpopulations that may be considered include, but are not limited to, 

recreational fishers, subsistence fishers, women of childbearing age, and children. When 

scientific data exist showing one of these subpopulations is at risk of greater exposure to the 

pollutant or are biologically more sensitive, then the relevant inputs should be considered in 

setting criteria. This could entail raising the fish consumption rate to a level more reflective of 

the subpopulation based on collected data or adjusting the body weight and drinking water 

intake. 

Chemical Name / Synonyms 

 Chlorophenoxy Herbicide (2,4,5-TP) (CAS Number 93-72-1) 

 2 (2,4,5-Trichlorophenoxy) Propionic Acid 

 Acide 2-(2,4,5-Trichloro-Phenoxy) Propionique 

 Acido 2-(2,4,5-Tricloro-Fenossi)-Propionico 

 Alpha-(2,4,5-Trichlorophenoxy)Propionic Acid 

 Propanoic Acid, 2-(2,4,5-Trichlorophenoxy)- 

 Propionic Acid, 2-(2,4,5-Trichlorophenoxy)- 

 Silvex 

 2,4,5-TP

 2-(2,4,5-Trichloor-Fenoxy)-Propionzuur 

 2,4,5-Trichlorophenoxy-Alpha-Propionic Acid 

 (+/-)-2-(2,4,5-Trichlorophenoxy)Propanoic Acid 

 2-(2,4,5-Trichlorophenoxy)Propionic Acid

 2,4,5-Trichlorophenoxypropionic Acid 

 Trichlorophenoxy Propionic Acid, 2 (2,4,5- 

 2-(2,4,5-Trichlor-Phenoxy)-Propionsaeure 

References 

Gehring, P.J. and J.E. Betso. 1978. Phenoxy acids: Effects and fate in mammals. In: Chlorinated 

Phenoxy Acids and Their Dioxins, Vol. 27, C. Ramel, Ed. Ecol. Bull., Stockholm. p. 122-

133. 

Kraus, as cited by Mitchess, J.W., R.E. Hogson, and C.R. Gaetjens, 1946. Tolerance of farm 

animals to feed containing 2,4-dichlorophenoxyacetic acid. Journal of Animal Science, 

5:226. 

Mullison, W.R. 1966. Some toxicological aspects of silvex. In: Proc. 19th Ann. Meet., Southern 

Weed Conference, Jacksonville, FL. p. 420-435. 
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