Office of Water 

Office Science and 

Technology 

EPA 820-D-14-048 

May 2014 

Draft Update of Human Health
 

Ambient Water Quality Criteria:
 

 

Hexachlorobutadiene
 

87-68-3
 

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EPA 820-D-14-048 

May 2014 

Update of Human Health
 

Ambient Water Quality Criteria:
 

Hexachlorobutadiene
 

87-68-3
 

Draft 

Office of Science and Technology
 

Office of Water
 

U.S. Environmental Protection Agency
 

Washington, DC 20460
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Hexachlorobutadiene 87-68-3 

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: Cancer Slope Factor 

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 

hexachlorobutadiene, contained in this document, incorporate updated information regarding 

cancer risk, body weight, drinking water intake, fish consumption rate, and bioaccumulation. 

Updated cancer risk information for hexachlorobutadiene is identified in EPA’s Office of Water 

2003 toxicology assessment (USEPA, 2003). 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 

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 

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Hexachlorobutadiene 87-68-3 

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 

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 

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Hexachlorobutadiene 87-68-3 

Methodology. For the development of criteria for carcinogens that express a non-threshold, 

linear dose response, the 2000 Methodology takes into consideration exposure factors (body 

weight, drinking water intake, fish consumption, and bioaccumulation), the increased cancer 

risk due to exposure to the pollutant, and a 10-6 (or 1 in 1,000,000) risk level for the general 

population. The 10-6 risk level utilized in the derivation of the AWQC represents the water 

̽ΪΣ̽͋Σχι̯χΊΪΣ χ·̯χ ϮΪϢΜ͇ ̼͋ ͋ϳζ͋̽χ͇͋ χΪ ΊΣ̽ι̯͋ν͋ ̯Σ ΊΣ͇ΊϭΊ͇Ϣ̯Μ͛ν ΜΊ͕͋χΊ΢͋ cancer risk from 

exposure to the particular pollutant by no more than one chance in one million, regardless of 

the additional lifetime cancer risk due to exposure, if any, to that particular substance from 

other sources. States and authorized tribes may consider adjusting exposure assumptions and 

related model inputs according to guidance in the 2000 Methodology, to assure that 

subpopulations are adequately protected if data are available. 

Criteria Formulas- Analysis Plan

The following formulas are used to develop EPA’s CWA Section 304(a) human health 

ambient water quality criteria. EPA develops criteria for ambient waters typically considering 

two routes of exposure. The first formula can be used to derive a human health criterion that 

assumes exposure through both the consumption of water and the consumption of aquatic 

organisms. The second formula can be used to derive 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). 

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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) = [10-6* / CSF (kg·d/mg)] × BW (kg) × 1000 (μg/mg)† 

4 DI (L/d) + ∑ (F·Ί (Ιͽ/ ͇) ∓ !FΊ (ͫ Ιͽ)) Ί 2 

 

 

 

 

For consumption of organisms only: 

 

 

AWQC (μg/L) = [10-6* / CSF (kg·d/mg)] × BW (kg) × 1000 (μg/mg)† 

∑4 (F·Ί (Ιͽ/ ͇) ∓ !FΊ (ͫ Ιͽ)) Ί 2 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Where: 

AWQC = ambient water quality criteria (at the 10-6 risk level) 

CSF = cancer slope factor 

BW = body weight 

DI = drinking water intake 

∑ 4 νϢ΢΢̯χΊΪΣ Ϊ͕ ϭ̯ΜϢ͋ν ͕Ϊι ̯θϢ̯χΊ̽ χιΪζ·Ί̽ Μ͋ϭ͋Μν (Αͫ) Ϯ·͋ι͋ χ·͋ Μ͋χχ͋ι ͞Ί͟ νχ̯Σ͇ν ͕Ϊι χ·͋ i=2 

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 

 

 

 

* 10-6 or 1 in 1,000,000 risk level for the general population † 1000 μg/mg is used to convert the units of mass into micrograms from milligrams. 

Hexachlorobutadiene 87-68-3 

(Eq. 1) 

(Eq. 2) 

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). 

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Hexachlorobutadiene 87-68-3 

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. It replaces the 

FCR default of 17.5 grams/day, which represented an estimate of the 90th percentile per capita 

consumption rate of freshwater and estuarine fish for the U.S. adult population based on the 

U.S. Department of Agriculture’s (USDA’s) Continuing Survey of Food Intake by Individuals 

(CSFII) 1994-96 data (USEPA, 2002a). 

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 

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Hexachlorobutadiene 87-68-3 

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). 

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 ( AF) 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 hexachlorobutadiene, 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 hexachlorobutadiene (log KOW = 4.78) are 6,044 L/kg, 

8,953 L/kg, and 23,410 L/kg wet-weight, respectively. These estimated BAFs replace the 

bioconcentration factor (BCF) of 2.78 L/kg used in the 2002 criteria derivations, which was 

calculated from a mis-reported log octanol/water partition coefficient (log KOW) of 1.82 and 

represented all trophic levels (USEPA, 1980). The log KOW of 1.82 cited in the 1980 document is 

attributed to a manuscript by G. Dec et al. titled “Water Solubility and Octanol Water Partition 

Coefficients of Organics: Limitations of the Solubility-Partition Coefficient Correlation.” The 

published version of that paper, however, lists the octanol/water partition coefficient for 

hexachlorobutadiene as 6.09 with a resulting log KOW of 4.78, not 1.82 (Banerjee et al., 1980). 

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Hexachlorobutadiene 87-68-3 

Had the BCF been calculated using the 1980 methodology and the correct log KOW of 4.78, the 

resulting BCF would have been 911 L/kg, not 2.78 L/kg. 

Hazard Identification and Dose Response: Cancer Slope Factor 

Hexachlorobutadiene is characterized as a class C possible human carcinogen following 

the 1986 EPA Guidelines for Carcinogen Risk Assessment (USEPA, 1986; USEPA, 2003). 

The cancer slope factor (CSF) is an upper bound, approximating a 95% confidence limit, 

on the increased cancer risk from a lifetime oral exposure to an agent. The previously used CSF 

for hexachlorobutadiene was 7.8 × 10–2 per mg/kg·day (USEPA, 2003). In 2003, EPA’s Office of 

Water updated the toxicology assessment for hexachlorobutadiene. That assessment (USEPA, 

2003), which has been subject to extensive internal and external peer review, provides the 

basis for the updated CSF of 4×10–2 per mg/kg·day (0.04 per mg/kg·day) used to update the 

AWQC. 

The principle study by Kociba et al. (1977) chosen to calculate the cancer slope factor for 

hexachlorobutadiene was based on development renal tubular adenomas and 

adenocarcinomas in rats with oral exposure to hexachlorobutadiene (USEPA, 2003). 

Criteria Derivation- Analysis 

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

ambient water quality criteria for hexachlorobutadiene. Criteria calculations are presented 

below. These updated hexachlorobutadiene criteria recommendations are based on the 2000 

Methodology and updated exposure assumptions as described above (Exposure Factors). 

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Hexachlorobutadiene 87-68-3 

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

for hexachlorobutadiene 

Component Value Source Input Characterization 

CSF 0.04 per mg/kg·day USEPA, 

2003 

an upper bound, approximating a 95% confidence 

limit, on the increased cancer risk from a lifetime 

exposure to an agent by ingestion 

BW 80 kg USEPA, 

2011 ΢̯͋Σ Ϯ͋Ίͽ·χ ͕Ϊι ̯͇ϢΜχν (≥21 Θ̯͋ιν Ϊ͕ ̯ͽ͋) 

DI 3 L/day USEPA, 

2011 90th ζ͋ι̽͋ΣχΊΜ͋ ͕Ϊι ̯͇ϢΜχν (≥21 Θ̯͋ιν Ϊ͕ ̯ͽ͋) 

FCR 

TL2 0.008 kg/day USEPA, 

2014 

90th percentile consumption rate for the U.S. adult 

ζΪζϢΜ̯χΊΪΣ (≥21 Θ̯͋ιν Ϊ͕ ̯ͽ͋) TL3 0.009 kg/day 

TL4 0.005 kg/day 

BAF 

TL2 6,044 L/kg 

USEPA, 

2012a 

EPI Suite KOW model estimated steady-state BAF 

values for non-ionic organic chemicals in 3 general 

trophic levels of fish in temperate environments 

(10°C) 

TL3 8,953 L/kg 

TL4 23,410 L/kg 

For consumption of water and organisms: 

 

 

 

 

 

AWQC (μg/L) = [10-6 / CSF (kg·d/mg)] × BW (kg) × 1000 (μg/mg) 4 DI (L/d) + ∑ (F·Ί (Ιͽ ͇) ∓ !FΊ (ͫ/ Ιͽ)) Ί=2

= 10-6 / 0.04 kg·d/mg × 80 kg × 1000 μg/mg 

3 L/d + ((0.008 kg/d × 6,044 L/kg) + (0.009 kg/d × 8,953 L/kg) + (0.005 kg/d × 23,410 L/kg)) 

= 0.0080 μg/L (rounded to 0.008 μg/L because of significant figures, see 2000 Methodology) 

For consumption of organisms only: 

 

 

 

 

 

AWQC (μg/L) = [10-6 / CSF (kg·d/mg)] × BW (kg) × 1000 (μg/mg) 

∑4 (F·Ί (Ιͽ/ ͇) ∓ !FΊ (ͫ/ Ιͽ)) Ί=2

= 10-6 / 0.04 kg·d/mg × 80 kg × 1000 μg/mg 

(0.008 kg/d × 6,044 L/kg) + (0.009 kg/d × 8,953 L/kg) + (0.005 kg/d × 23,410 L/kg) 

= 0.0081 μg/L (rounded to 0.008 μg/L because of significant figures, see 2000 Methodology) 

The updated magnitude of the human health ambient water quality criteria for 

hexachlorobutadiene at the 10-6 risk level are 0.008 μg/L (water and organism) and 0.008 μg/L 

(organism only) (Table 2). These updated criteria replace the previously published values 

(USEPA, 2002b). 

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Hexachlorobutadiene 87-68-3 

Table 2. ΋Ϣ΢΢̯ιΘ Ϊ͕ E ́!͛ν ζι͋̽ΊΪϢνΜΘ ι͋̽Ϊ΢΢͋Σ͇͇͋ (2002) and updated (2014) human health 

ambient water quality criteria for hexachlorobutadiene 

2002 Human Health AWQC 2014 Human Health AWQC 

Water and Organism 0.44 μg/L 0.008 μg/L 

Organism Only 18 μg/L 0.008 μg/L 

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

population from an increased cancer risk due to exposure to hexachlorobutadiene at a 10-6 or 1 

in 1,000,000 risk level. The 10-6 risk level associated with the AWQC represents the 

̽ΪΣ̽͋Σχι̯χΊΪΣ χ·̯χ ϮΪϢΜ͇ ̼͋ ͋ϳζ͋̽χ͇͋ χΪ ΊΣ̽ι̯͋ν͋ ̯Σ ΊΣ͇ΊϭΊ͇Ϣ̯Μ͛ν ΜΊ͕͋χΊ΢͋ ̯̽Σ̽͋ι ιΊνΙ ͕ιΪ΢ 

exposure to the particular pollutant by no more than one chance in one million, regardless of 

the additional lifetime cancer risk due to exposure, if any, to that particular substance from 

other sources. 

Criteria Characterization 

The updated 2014 human health AWQC for hexachlorobutadiene take into account 

current data on health effects and exposure input parameters, consistent with the 2000 

Methodology. The updated 2014 human health AWQC for hexachlorobutadiene are 

approximately two to four orders of magnitude less than EPA’s previously recommended 2002

criteria; i.e. the water-and-organism criterion decreased from 0.44 to 0.008 μg/L and the 

organism-only criterion decreased from 18 to 0.008 μg/L (Table 2). 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 2002 criteria, 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. 

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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, which is higher than the 

previously recommended rate of 17.5 g/day. Assuming all other input parameters remain 

constant, a higher fish consumption rate assumption in the AWQC calculations (Eq. 1 and 2 

above) results in lower AWQC. That is, as fish consumption increase, 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 rather than the previously 

recommended and miscalculated BCF of 2.78 L/kg. The lower (TL2), mid (TL3), and upper (TL4) 

trophic level BAFs assumed in the updated criteria equations (Eq. 1 and 2 above) are 6,044, 

8,953, and 23,410 L/kg wet-weight, respectively. Assuming all other input parameters remain 

constant, the higher ratios of fish tissue concentrations to water concentrations of 

hexachlorobutadiene by aquatic organisms 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. The utilization of a bioaccumulation factor 

rather than a bioconcentration factor better represents the amount of a contaminant 

accumulating in an organism because it accounts not only for the organΊν΢͛ν ͋ϳζΪνϢι͋ χΪ χ·͋ 

pollutant in the water column, but also from the food chain and surrounding environment as 

well as biotransformation of the pollutant in the organism due to metabolic processes. The 

utilization of the three trophic levels of fish and shellfish consumed, as opposed to representing 

all trophic levels of fish and shellfish consumed by a single value, allows for better exposure 

representation, especially when pollutants bioaccumulate in significantly different amounts for 

organisms in different trophic levels at different positions in the food chain. 

Cancer Slope Factor 

The updated CSF of 4 × 10 –2 per mg/kg·day replaces the higher value of 7.8 × 10 –2 per 

mg/kg·day. The change in the CSF was due to a reassessment of the key study utilizing updated 

carcinogen risk assessment protocols, including an interspecies dose adjustment by a scaling 

factor of BW3/4 rather than BW2/3, utilization of data from both male and female rats, and use of 

a LED10 approach with linear extrapolation rather than a linearized multistage model as was 

seen in the previous assessment (USEPA, 2003). Assuming all other input parameters remain 

constant, a lower CSF in the AWQC calculations (Eq. 1 and 2 above) results in higher AWQC. 

That is, as the CSF decreases, the level of a contaminant in water at or below which the number 

of individuals at a specified risk level of developing cancer above the background rate 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 

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Hexachlorobutadiene 87-68-3 

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 

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 

 Hexachlorobutadiene (CAS Number 87-68-3) 

 1,3-Butadiene, Hexachloro­

 Dolen-Pur 

 GP-40-66:120 

 HCBD 

 Hexachlor-1,3-Butadien 

 1,1,2,3,4,4-Hexachloro-1,3-Butadiene 

 1,3- Hexachlorobutadiene 

 Perchlorobutadiene 

 RCRA Waste Number U128 

 UN 2279 

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Hexachlorobutadiene 87-68-3 

References 

Banerjee, S., S.H. Yalkoxsky and S.C. Valvani. 1980. Water solubility and octanol/water partition 

coefficients of organics. Limitations of the solubility-partition coefficient correlation. 

Environmental Science & Technology. 14(10): 1227-1229. 

Kociba, R.J., D.G. Keyes, G.C. Jersey, et al. 1977. Results of a 2-year chronic toxicity study with 

hexachlorobutadiene in rats. Am. Ind. Hyg. Assoc. J. 38:589-602. 

USEPA (U.S. Environmental Protection Agency). 1980. Ambient Water Quality Criteria for 

Hexachlorobutadiene. Office of Water. Washington, DC. EPA-440-5-80-053. 

http://water.epa.gov/scitech/swguidance/standards/upload/2001_10_12_criteria_ambi 

entwqc_hexachlorobutadiene80.pdf. 

USEPA (U.S. Environmental Protection Agency). 1986. Guidelines for Carcinogen Risk 

Assessment. Risk Assessment Forum. Washington, DC. EPA-630-R-00-004. 

http://www.epa.gov/raf/publications/pdfs/CA%20GUIDELINES_1986.PDF. 

USEPA (U.S. Environmental Protection Agency). 2000. Methodology for Deriving Ambient Water 

Quality Criteria for the Protection of Human Health. Office of Water. Washington, DC. 

EPA-822-B-00-004. 

http://water.epa.gov/scitech/swguidance/standards/upload/2005_05_06_criteria_hum 

anhealth_method_complete.pdf. 

USEPA (U.S. Environmental Protection Agency). 2002a. Estimated Per Capita Fish Consumption 

in the United States. Washington, DC. EPA-821-C-02-003. 

http://water.epa.gov/scitech/swguidance/standards/criteria/health/upload/consumpti 

on_report.pdf. 

USEPA (U.S. Environmental Protection Agency). 2002b. National Recommended Water Quality 

Criteria: 2002. Office of Water. Washington, DC. EPA-822-R-02-047. 

http://water.epa.gov/scitech/swguidance/standards/upload/2008_04_29_criteria_wqct 

able_nrwqc-2002.pdf. 

USEPA (U.S. Environmental Protection Agency). 2003. Health Effects Support Document for 

Hexachlorobutadiene. Office of Water. Washington, DC. EPA-822-R-03-002. 

http://water.epa.gov/action/advisories/drinking/upload/2004_01_16_reg_determine1_ 

support_cc1_hexachlorobutadiene_healtheffects.pdf. 

USEPA (U.S. Environmental Protection Agency). 2011. Exposure Factors Handbook: 2011 

Edition. Office of Research and Development. Washington, DC. EPA-600-R-09-052F. 

http://www.epa.gov/ncea/efh/pdfs/efh-complete.pdf. 

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Hexachlorobutadiene 87-68-3 

USEPA (U.S. Environmental Protection Agency). 2012a. Estimation Programs Interface SuiteTM 

for Microsoft® Windows, v 4.10. United States Environmental Protection Agency, 

Washington, DC, USA. http://www.epa.gov/oppt/exposure/pubs/episuite.htm. 

USEPA (U.S. Environmental Protection Agency). 2012b. Framework for Human Health Risk 

Assessment to Inform Decision Making. Office of the Science Advisor. Washington, DC. 

EPA-601-D-12-001. http://www.epa.gov/raf/files/framework-document-7-13-12.pdf. 

USEPA (U.S. Environmental Protection Agency). 2014. Estimated Fish Consumption Rates for 

the U.S. Population and Selected Subpopulations (NHANES 2003-2010). Office of Water. 

Washington, DC. EPA-820-R-14-002. 

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