Update of Human Health

Ambient Water Quality Criteria:

Hexachlorocyclopentadiene

77-47-4 

Office of Water

Office of Science and

Technology

EPA 820-R-15-051 

June 2015
EPA 820-R-15-051 

June 2015

Update of Human Health

Ambient Water Quality Criteria:

Hexachlorocyclopentadiene

77-47-4 

Office of Science and Technology

Office of Water

U.S. Environmental Protection Agency

Washington, DC 20460
Hexachlorocyclopentadiene 77-47-4 

Table of Contents

1 Introduction: Background and Scope of Update..................................................................... 2

2 Problem Formulation............................................................................................................... 3

3 Criteria Formulas: Analysis Plan .............................................................................................. 4

4 Exposure Factors ..................................................................................................................... 5

4.1 Body Weight.................................................................................................................. 5

4.2 Drinking Water Intake................................................................................................... 6

4.3 Fish Consumption Rate ................................................................................................. 6

4.4 Bioaccumulation Factor................................................................................................ 7

4.4.1 Approach ......................................................................................................... 7

4.4.2 Chemical-specific BAFs.................................................................................... 9

5 Hazard Identification and Dose Response............................................................................. 10

5.1 Approach..................................................................................................................... 10

5.2 Chemical-specific Toxicity Value................................................................................. 11

5.2.1 Reference Dose.............................................................................................. 11

5.2.2 Cancer Slope Factor....................................................................................... 12

6 Relative Source Contribution................................................................................................. 12

6.1 Approach..................................................................................................................... 12

6.2 Chemical-specific RSC ................................................................................................. 13

7 Criteria Derivation: Analysis.................................................................................................. 15

7.1 AWQC for Noncarcinogenic Toxicological Effects ...................................................... 15

7.2 AWQC for Carcinogenic Toxicological Effects............................................................. 16

7.3 AWQC Summary ......................................................................................................... 16

8 Criteria Characterization........................................................................................................ 16

9 Chemical Name and Synonyms............................................................................................. 18

10 References............................................................................................................................. 19

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1 Introduction: Background and Scope of Update

EPA’s recommended ambient water quality criteria (AWQC) for human health are scientifically 

derived numeric values that EPA has determined will adequately protect human health from 

the adverse effects of pollutants in ambient water.

Section 304(a)(1) of the Clean Water Act (CWA) requires EPA to develop and publish, and from 

time to time revise, recommended criteria for the protection of water quality that accurately 

reflect the latest scientific knowledge. Water quality criteria developed under section 304(a) 

are based solely on data and scientific judgments on the relationship between pollutant 

concentrations and environmental and human health effects. Section 304(a) criteria do not 

reflect consideration of economic impacts or the technological feasibility of meeting pollutant 

concentrations in ambient water.

EPA’s recommended section 304(a) criteria provide technical information for states and 

authorized tribesa to consider and use in adopting water quality standards that ultimately 

provide the basis for assessing water body health and controlling discharges of pollutants into 

waters of the United States. Under the CWA and its implementing regulations, states and 

authorized tribes are required to adopt water quality criteria to protect the designated uses of 

waters (e.g., public water supply, aquatic life, recreational use, industrial use). EPA’s 

recommended water quality criteria do not substitute for the CWA or regulations, nor are they 

regulations themselves. Thus, EPA’s recommended criteria do not impose legally binding 

requirements. States and authorized tribes may adopt, where appropriate, other scientifically 

defensible water quality criteria that differ from these recommendations.

The water quality criteria that are the subject of this document are national AWQC

recommendations for human health issued under CWA section 304(a). Unless expressly 

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

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

recommendations for human health.

In this 2015 update, EPA has revised the human health criteria for hexachlorocyclopentadiene

to reflect the latest scientific information, including updated exposure factors (body weight 

[BW], drinking water intake [DI] rate, and fish consumption rate [FCR]), bioaccumulation factors 

(BAFs), and human health toxicity values (reference dose [RfD] multiplied by relative source 

contribution [RSC] or 10-6 divided by cancer slope factor [CSF]). The criteria continue to be 

based on EPA’s Methodology for Deriving Ambient Water Quality Criteria for the Protection of 

Human Health, which is referred to as the “2000 Methodology” in this document (USEPA 

2000a). EPA accepted written scientific views from the public on the draft updated human 

health criteria for this chemical (and 93 others) from May through August 2014.

a Throughout this document, the term states means the 50 states, the District of Columbia, the Commonwealth of 

Puerto Rico, the Virgin Islands, Guam, American Samoa, and the Commonwealth of the Northern Mariana Islands. 

The term authorized tribe or tribe means an Indian tribe authorized for treatment in a manner similar to a state 

under CWA section 518 for the purposes of section 303(c) water quality standards. 

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It is important for states and authorized tribes to consider any new or updated section 304(a) 

recommended criteria as part of their triennial review process to ensure that state or tribal 

water quality standards reflect current science and protect applicable designated uses. These 

final 2015 updated section 304(a) human health criteria recommendations supersede EPA’s 

previous recommendations.

2 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. The structure of this criteria document is intended to be consistent with general 

concepts of effects assessments as described in EPA’s Framework for Human Health Risk 

Assessment to Inform Decision Making (USEPA 2014a). 

In developing AWQC, EPA currently follows the assessment method outlined in its 2000 

Methodology (USEPA 2000a). The 2000 Methodology describes different approaches for 

addressing water and non-water exposure pathways to derive human health AWQC depending 

on the toxicological endpoint of concern, the toxicological effect (noncarcinogenic or 

carcinogenic), and whether toxicity is considered a linear or threshold effect. Water sources of 

exposure include both consuming drinking water and eating fish or shellfish from inland and 

nearshore waters that have been exposed to pollutants in the water body. For pollutants that 

exhibit a threshold of exposure before deleterious effects occur, as is the case for 

noncarcinogens and nonlinear carcinogens, EPA applies an RSC to account for other potential 

human exposures to the pollutant (USEPA 2000a). Other sources of exposure might include, but 

are not limited to, exposure to a particular pollutant from ocean fish or shellfish consumption 

(which is not included in the FCR), non-fish food consumption (e.g., consumption of fruits, 

vegetables, grains, meats, or poultry), dermal exposure, and inhalation exposure.

For substances for which the toxicity endpoint is carcinogenicity based on a linear low-dose 

extrapolation, only the exposures from drinking water and fish ingestion are reflected in human 

health AWQC; that is, non-water sources are not explicitly included and no RSC is applied 

(USEPA 2000a). In these situations, AWQC are derived with respect to the incremental lifetime 

cancer risk posed by the presence of a substance in water, rather than an individual’s total risk 

from all sources of exposure. The resulting criterion represents the water concentration that is 

expected to increase an individual’s lifetime risk of cancer from exposure to the particular 

pollutant by no more than one chance in one million for the general population. EPA calculates 

AWQC at a 10-6 (one in one million) cancer risk level for the general population (USEPA 2000a). 

The 2000 Methodology recommends that states set human health criteria cancer risk levels for 

the target general population at either 10-5 or 10-6 and also notes that states and authorized 

tribes can choose a more stringent risk level, such as 10-7. 

For substances that are carcinogenic, EPA takes an integrated approach and considers both

cancer and noncancer effects when deriving AWQC (USEPA 2000a; USEPA 2000b). Where 

sufficient data are available, EPA derives AWQC using both carcinogenic and noncarcinogenic 

toxicity endpoints and recommends the lower value for the AWQC. The AWQC might not utilize 

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Hexachlorocyclopentadiene 77-47-4 

the value obtained from the cancer analysis if it is less protective than that derived from the 

noncancer endpoint. 

3 Criteria Formulas: Analysis Plan

Human health AWQC for toxic pollutants are necessary to protect any designated uses related 

to ingestion of water and ingestion of aquatic organisms. These uses can include, but are not 

limited to, recreation in and on the water, consumption of fish or shellfish (including 

consumption associated with fishing or shellfish harvesting), and protection of drinking water 

supplies.

The derivation of human health AWQC requires information about both the toxicological 

endpoints of concern for water pollutants and the pathways of human exposure to those 

pollutants. EPA considers the following two primary pathways of human exposure to pollutants 

present in a particular water body when deriving human health 304(a) AWQC: (1) direct 

ingestion of drinking water obtained from the water body and (2) consumption of fish or 

shellfish obtained from the water body.

The equations for deriving human health AWQC for noncarcinogenic effects and carcinogenic 

effects are presented as Eqs. 1 and 2. EPA derives recommended human health AWQC based 

on the consumption of both water and aquatic organisms (Eq. 1) and based on the 

consumption of aquatic organisms alone (Eq. 2). The use of one criterion over the other 

depends on the designated use of a particular water body or water bodies (i.e., drinking water 

source and/or fishable waters). EPA recommends applying organism-only AWQC (Eq. 2) to a 

water body where the designated use includes supporting fishable uses under section 101(a) of 

the CWA but the water body is not a drinking water supply source (e.g., non-potable estuarine 

waters that support fish or shellfish for human consumption) (USEPA 2000a). 

EPA recommends including 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 ensure 

that this designated use can be protected and maintained; (2) although they are rare, some 

public water supplies provide drinking water from surface water sources without treatment; 

(3) even among the majority of water supplies that do treat surface waters, existing treatments 

might not be effective for reducing levels of particular contaminants; and (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 that must bear the costs of upgraded 

or supplemental water treatment (USEPA 2000a). 

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The equations for deriving the criteria values are as follows (USEPA 2000a): 

For consumption of water and organisms:

AWQC (μg/L) = toxicity value (mg/kg-d) × BW (kg) × 1,000 (μg/mg)b (Eq. 1)

 DI (L/d) + ∑ (FCRi (kg/d) × BAFi (L/kg)) 4

i=2

For consumption of organisms only:

AWQC (μg/L) = toxicity value (mg/kg-d) × BW (kg) × 1,000 (μg/mg)c (Eq. 2)

 ∑ (FCRi (kg/d) × BAFi (L/kg)) 4

i=2

Where:

AWQC = ambient water quality criteria

toxicity value = RfD x RSC (mg/kg-d) for noncarcinogenic effects

or

10-6/CSF (kg-d/mg) for carcinogenic effectsd

RSC = relative source contribution (applicable to only noncarcinogenic and nonlinear 

low-dose extrapolation for carcinogenic effects)

BW = body weight

DI = drinking water intake

∑ 4

i=2 = summation of values for aquatic trophic levels (TLs), where the letter i stands 

for the TLs to be considered, starting with TL2 and proceeding to TL4

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

BAFi = bioaccumulation factor for aquatic TLs 2, 3, and 4

EPA rounds AWQC to the number of significant figures in the least precise parameter as 

described in the 2000 Methodology (USEPA 2000a, section 2.7.3).

4 Exposure Factors

4.1 Body Weight

EPA updated the default BW assumption to 80.0 kg based on National Health and Nutrition 

Examination Survey (NHANES) data from 1999 to 2006 as reported in Table 8.1 of EPA’s 

Exposure Factors Handbook (USEPA 2011a). The updated BW represents the mean weight for 

adults ages 21 and older. EPA’s previously recommended BW assumption for adults was 70 kg, 

which was based on the mean BW of adults from the NHANES III database (1988–1994) and a 

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

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

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4.2 Drinking Water Intake

EPA updated the default DI to 2.4 L/d, rounded from 2.414 L/d, based on NHANES data from 

2003 to 2006 as reported in EPA’s Exposure Factors Handbook (USEPA 2011a, Table 3-23). This 

rate represents the per capita estimate of combined direct and indirect community watere

ingestion at the 90th percentile for adults ages 21 and older. EPA selected the per capita rate for 

the updated DI because it represents the average daily dose estimates; that is, it includes both 

people who drank water during the survey period and those who did not, which is appropriate 

for a national-scale assessment such as CWA section 304(a) national human health criteria 

development (USEPA 2011a, section 3.2.1).

EPA’s updated DI of 2.4 L/d is consistent with the 2000 Methodology. In that document, EPA 

recommended a default DI of 2 L/d, which represented the per capita community water 

ingestion rate at the 86th percentile for adults surveyed in the U.S. Department of Agriculture’s 

1994–1996 Continuing Survey of Food Intake by Individuals (CSFII) analysis (USEPA 2000a, 

section 4.3.2.1).

4.3 Fish Consumption Rate

The updated FCR for the general adult population is 22.0 g/d, or 0.0220 kg/d (USEPA 2014b, 

Table 9a). This FCR represents the 90th percentile per capita consumption rate of fish from 

inland and nearshore waters for U.S. adults ages 21 years and older based on NHANES data 

from 2003–2010. The 95 percent confidence interval (CI) of the 90th percentile per capita FCR is 

19.1 g/d and 25.4 g/d. This updated FCR replaces EPA’s previously recommended default FCR of 

17.5 g/d, which represented an estimate of the 90th percentile per capita consumption rate of 

fish from inland and nearshore waters for U.S. adults ages 21 years and older. That default FCR 

was based on USDA’s CSFII 1994–1996 data (USEPA 2002a). 

As recommended in the 2000 Methodology, EPA updated the AWQC to reflect trophic level- 

(TL-) specific FCRs to better represent human dietary consumption of fish. An organism’s 

trophic position in the aquatic food web can have an important effect on the magnitude of 

bioaccumulation of certain chemicals. The TL-specific FCRs are numbered 2, 3, and 4, and they 

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 (USEPA 2000a). 

EPA used the following TL-specific FCRs to derive the updated AWQC: TL2 = 7.6 g/d

(0.0076 kg/d) (95 percent CI [6.4, 9.1] g/d); TL3 = 8.6 g/d (0.0086 kg/d) (95 percent CI [7.2, 

10.2] g/d); and TL4 = 5.1 g/d (0.0051 kg/d) (95 percent CI [4.0, 6.4] g/d). Each TL-specific FCR 

represents the 90th percentile per capita consumption rate of fish and shellfish from inland and 

nearshore waters from that particular TL for U.S. adults ages 21 years and older (USEPA 2014b, 

e Community water includes direct and indirect use of tap water for household uses and excludes bottled water 

and other sources (USEPA 2011a, section 3.3.1.2). Direct ingestion is defined as direct consumption of water as a 

beverage, while indirect ingestion includes water added during food preparation (e.g., cooking, rehydration of 

beverages) but not water intrinsic to purchased foods (USEPA 2011a, section 3.1).

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Tables 16a, 17a, and 18a). The sum of these three TL-specific FCRs is 21.3 g/d, which is within 

the 95 percent CI of the overall FCR of 22.0 g/d. EPA recommends using the TL-specific FCRs

when deriving AWQC; however, the overall FCR rate (22.0 g/d) may be used if a simplified 

approach is preferred.

4.4 Bioaccumulation Factor

4.4.1 Approach

Several attributes of the bioaccumulation process are important to understand when deriving 

national BAFs for use in developing national recommended section 304(a) AWQC. First, the 

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

from all surrounding media, such as water, food, and 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 might underestimate the 

extent of accumulation in aquatic biota for those chemicals. Accordingly, the EPA guidelines 

presented in the 2000 Methodology emphasize using, when possible, measured or estimated 

BAFs, which account for chemical accumulation in aquatic organisms from all potential 

exposure routes (USEPA 2000a). 

EPA estimated BAFs for this updated AWQC using EPA’s 2000 Methodology (USEPA 2000a) and 

its Technical Support Document, Volume 2: Development of National Bioaccumulation Factors

(Technical Support Document, Volume 2) (USEPA 2003a). Specifically, these documents provide 

a framework for identifying alternative procedures to derive national TL-specific BAFs for a 

chemical based on the chemical’s properties (e.g., ionization and hydrophobicity), metabolism, 

and biomagnification potential (USEPA 2000a; USEPA 2003a). 

EPA’s approach for developing national BAFs represents the long-term average 

bioaccumulation potential of a pollutant in aquatic organisms that are commonly consumed by 

humans across the United States. National BAFs are not intended to reflect fluctuations in 

bioaccumulation over short periods (e.g., a few days) because human health AWQC are 

generally designed to protect humans from long-term (lifetime) exposures to waterborne 

chemicals (USEPA 2003a). 

EPA followed the approach described in Figure 3-1 of the Technical Support Document, Volume 

2 (USEPA 2003a). EPA used peer-reviewed, publicly available information to classify each 

chemical using this framework to derive the most appropriate BAFs according to EPA’s 2000 

Methodology (USEPA 2000a). The framework provides six alternatives, or procedures, resulting 

in up to four possible methods for each chemical, based on the chemical’s properties. These 

four methods follow:

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Hexachlorocyclopentadiene 77-47-4 

• BAF Method. This method uses measured BAFs derived from data obtained from field

studies. Field-measured BAFs were normalized by adjusting for the water-dissolved 

portions of the chemical and the lipid fraction of fish tissue for each species, as well as 

the fraction of the total concentration of chemical in water that is freely dissolved. EPA 

averaged multiple field BAFs using a geometric mean of the normalized BAFs by species 

and TL; then EPA further averaged the BAFs across species to compute TL baseline BAFs. 

The national-level BAF adjusts the TL baseline BAFs by national default values for lipid 

content, dissolved and particulate organic carbon content, and the n-octanol-water 

partition coefficient (Kow). EPA chose the recommended 50th percentile dissolved and 

particulate organic carbon content for the national-level default values, as described in 

section 6.3 of the Technical Support Document, Volume 2 (USEPA 2003a). 

• BSAF Method. This method uses biota-sediment accumulation factors (BSAFs) to 

estimate BAFs. EPA did not use measured BSAFs to calculate national BAFs because the 

two major compilations of these data—EPA’s Biota-Sediment Accumulation Factor Data 

Set, Version 1.0 (USEPA 2015a), and the U.S. Army Corps of Engineers’ BSAF database 

(USACE 2015)—have not been peer-reviewed.

• BCF Method. This method uses BAFs estimated from laboratory-measured

bioconcentration factors (BCFs) with or without adjustment by a food chain multiplier. 

Similar to field BAFs, laboratory-measured BCFs are normalized with the lipid fraction 

and the fraction of the total concentration of chemical in water that is freely dissolved, 

then multiplied by the food chain multiplier where applicable. Multiple values are 

averaged using a geometric mean across species and then across TL to compute 

baseline BAFs. The national-level BAF adjusts the TL baseline BAFs by national default

values for lipid content, dissolved and particulate organic carbon content, and the Kow. 

EPA chose the recommended 50th percentile dissolved and particulate organic carbon 

content for the national-level default values, as described in section 6.3 of the Technical 

Support Document, Volume 2 (USEPA 2003a). 

• Kow Method. This method predicts BAFs based on a chemical’s Kow, with or without 

adjustment using a food chain multiplier, as described in section 5.4 of the Technical 

Support Document, Volume 2 (USEPA 2003a). 

Following the decision framework presented in Figure 3-1 of the Technical Support Document, 

Volume 2 (USEPA 2003a), EPA selected one of the six procedures to develop a national-level 

BAF for this chemical. For a given procedure, EPA selected the method that provided BAF 

estimates for all three TLs (TL2–TL4) in the following priority:

1. BAF estimates using the BAF method (i.e., based on field-measured BAFs) if possible.

2. BAF estimates using the BCF method if (a) the BAF method did not produce estimates 

for all three TLs and (b) the BCF method produced national-level BAF estimates for all 

three TLs.

3. BAF estimates using the Kow method if (a) Procedure 1 or 3 was applicable (see Figure 

3-1 of the Technical Support Document, Volume 2 [USEPA 2003a]) and (b) the BAF and 

BCF methods did not produce BAF estimates for all three TLs.

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In cases where the procedure called for the BAF method but there were fewer than three TL

estimates and the Kow method did not apply (i.e., Procedures 2, 4, 5, and 6), EPA used the BAF 

method estimate for the reported TLs by averaging the estimates using a geometric mean when 

there were two BAFs and using the single estimate when only one was available. EPA did not 

mix values from the BAF and BCF methods. If the BAF method did not have sufficient reliable 

data for any TLs, EPA used the BCF method estimates in the same manner. If none of the four 

methods provided sufficient data, or if none were appropriate for the procedure, EPA used the 

BCF from the previously recommended 2002/2003 criteria (USEPA 2002b; USEPA 2003b). 

EPA primarily used field-measured BAFs and laboratory-measured BCFs available from peerreviewed, publicly available databases (Arnot and Gobas 2006; Environment Canada 2006) to 

develop national BAFs. If field-measured BAFs and laboratory-measured BCFs were not 

available from those sources, EPA selected Kow values from peer-reviewed sources (i.e., Agency 

for Toxic Substances and Disease Registry [ATSDR] preferentially, followed by U.S. Department 

of Health and Human Services’ Hazardous Substances Data Bank) for use in calculating national 

BAFs using the Kow method described in EPA’s Technical Support Document, Volume 2 (USEPA 

2003a). For those chemicals for which the Kow method was not applicable based on the

Technical Support Document, Volume 2 (USEPA 2003a), EPA performed open literature 

searches of peer-reviewed journal articles to find field-measured BAFs or laboratory-measured 

BCFs.

4.4.2 Chemical-specific BAFs

EPA selected national BAF values of 620 L/kg (TL2), 1,500 L/kg (TL3), and 1,300 L/kg (TL4) for 

hexachlorocyclopentadiene. EPA followed the framework for selection of methods for deriving 

national BAFs in Figure 3-1 of the Technical Support Document, Volume 2 (USEPA 2003a) to 

select a procedure for estimating national BAFs for hexachlorocyclopentadiene. Based on the 

characteristics of this chemical, EPA selected Procedure 1 for deriving a national BAF value. 

Hexachlorocyclopentadiene has the following characteristics:

• Nonionic organic chemical (USDHHS 2014)

• Moderate-high hydrophobicity (log Kow ≥ 4); log Kow = 4.52 (ATSDR 1999)

• Low/unknown metabolism

EPA was not able to locate peer-reviewed, field-measured BAFs, BSAFs, or lab-measured BCFs 

for TLs 2, 3, and 4. Therefore, EPA used the Kow method to derive the national BAF values for 

this chemical:

TL2 = 620 L/kg

TL3 = 1,500 L/kg

TL4 = 1,300 L/kg

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5 Hazard Identification and Dose Response

5.1 Approach

EPA considered all available toxicity values for both noncarcinogenic and carcinogenic 

toxicological effects to develop this updated AWQC for hexachlorocyclopentadiene. As 

described in the 2000 Methodology (USEPA 2000a), where data are available EPA derives 

AWQC for both noncarcinogenic and carcinogenic effects and recommends the more protective 

value for the AWQC. (See section 7, Criteria Derivation: Analysis.)

For noncarcinogenic toxicological effects, EPA uses a chronic-duration oral RfD to derive human 

health AWQC. An RfD is an estimate (with uncertainty spanning perhaps an order of magnitude) 

of a daily oral exposure of the human population to a substance that is likely to be without an 

appreciable risk of deleterious effects during a lifetime. An RfD is typically derived from a 

laboratory animal dosing study in which a no-observed-adverse-effect level (NOAEL), lowestobserved-adverse-effect level (LOAEL), or benchmark dose can be obtained. Uncertainty factors 

are applied to reflect the limitations of the data (USEPA 2000a).

For carcinogenic toxicological effects, EPA uses an oral CSF to derive human health AWQC. The 

oral CSF is an upper bound, approximating a 95 percent confidence limit, on the increased 

cancer risk from a lifetime oral exposure to a stressor.

For this update, EPA conducted a systematic search of eight peer-reviewed, publicly available 

sources to obtain the toxicity value (RfD or CSF) for use in developing AWQC. EPA’s primary 

source of toxicity values for developing human health AWQC is its Integrated Risk Information 

System (IRIS) program (USEPA 2015b). EPA also systematically searched for toxicological 

assessments from the following EPA program offices, other national and international 

programs, and state programs:

• EPA, Office of Pesticide Programs (USEPA 2015c)

• EPA, Office of Pollution Prevention and Toxics (USEPA 2015d)

• EPA, Office of Water (USEPA 2015e)

• EPA, Office of Solid Waste and Emergency Response (USEPA 2015f)

• U.S. Department of Health and Human Services, Agency for Toxic Substances and

Disease Registry (ATSDR 2015)

• Health Canada (HC 2015)

• California Environmental Protection Agency, Office of Environmental Health Hazard 

Assessment (CalEPA 2014a)

After identifying and documenting all available toxicity values, EPA followed a systematic 

process to select the toxicity values used to derive the AWQC for noncarcinogenic and 

carcinogenic effects. EPA selected IRIS toxicity values to derive the updated AWQC if any of the 

following conditions were met:

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1. EPA’s IRIS toxicological assessment was the only available source of a toxicity value.

2. EPA’s IRIS toxicological assessment was the most current source of a toxicity value.

3. EPA’s IRIS program was reassessing the chemical in question and had published the 

draft Toxicological Review for public review and comment, discussion at a public 

meeting, and subsequent expert peer review.

f

4. The toxicity value from a more current toxicological assessment from a source other 

than EPA IRIS was based on the same principal study and was numerically the same as 

an older EPA IRIS toxicity value.

5. A more current toxicological assessment from a source other than EPA IRIS was available, 

but it did not include the relevant toxicity value (chronic-duration oral RfD or CSF).

6. A more current toxicological assessment from a source other than EPA IRIS was 

available, but it did not introduce new science (e.g., the toxicity value was not based on 

a newer principal study) or use a more current modeling approach compared to an older 

EPA IRIS toxicological assessment.

EPA selected the toxicity value from a peer-reviewed, publicly available source other than EPA 

IRIS to derive the updated AWQC if any of the following conditions were met:

1. The chemical is currently used as a pesticide, and EPA Office of Pesticide Programs had a 

toxicity value that was used in pesticide registration decision-making.

2. A toxicological assessment from a source other than EPA IRIS was the only available 

source of a toxicity value.

3. A more current toxicological assessment from a source other than EPA IRIS introduced 

new science (e.g., the toxicity value was based on a newer principal study) or used a 

more current modeling approach compared to an older EPA IRIS toxicological 

assessment.

5.2 Chemical-specific Toxicity Value

5.2.1 Reference Dose

EPA selected an RfD of 6 × 10–3 mg/kg-d (0.006 mg/kg-d) for hexachlorocyclopentadiene based 

on a 2001 EPA IRIS assessment (USEPA 2001a). EPA’s IRIS program identified Abdo et al. (1984)

as the critical study and chronic irritation manifested by fore-stomach pathology as the critical 

effect in rats orally exposed to hexachlorocyclopentadiene. The subchronic study had a point of 

departure lower-bound confidence limit on the benchmark dose of 6 mg/kg-d. In deriving the 

RfD, EPA’s IRIS program applied a composite uncertainty factor of 1000 to account for 

interspecies extrapolation (10), intraspecies variation (10), subchronic-to-chronic study 

extrapolation (3), and database deficiency (3).

f Equivalent to Step 4 in the July 2013 EPA Process for Developing IRIS Health Assessments. Available online at 

http://www.epa.gov/iris/process.htm.

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EPA identified two other RfD sources through the systematic search described in section 5: a 

2014 California EPA assessment (CalEPA 2014b) and a 1999 ATSDR assessment (ATSDR 1999). 

Based on the selection process described in section 5, the 2001 IRIS RfD is preferred for use in 

AWQC development at this time. The CalEPA assessment is more current than the IRIS 

assessment and uses an updated benchmark modeling approach to derive a different point of 

departure (POD); however, several aspects of the CalEPA assessment use policies that differ 

from those currently applied by EPA Office of Water.g

5.2.2 Cancer Slope Factor

Under the 1986 EPA Guidelines for Carcinogen Risk Assessment (USEPA 1986), 

hexachlorocyclopentadiene is classified as Group E, “evidence of non-carcinogenicity to 

humans, via inhalation exposure” (USEPA 2001b). Under the 1996 EPA Proposed Guidelines for 

Carcinogen Risk Assessment (USEPA 1996), hexachlorocyclopentadiene is “not likely to be a 

human carcinogen by the inhalation route” (USEPA 2001b). Other carcinogenic pathways were 

not evaluated.

EPA identified no CSF sources through the systematic search described in section 5.

6 Relative Source Contribution

6.1 Approach

The RSC component of the AWQC calculation allows a percentage of the RfD’s exposure to be 

attributed to the consumption of ambient water and fish and shellfish from inland and 

nearshore waters when there are other potential exposure sources. The RSC describes the 

portion of the RfD available for AWQC-related sources (USEPA 2000a); the remainder of the RfD 

is allocated to 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 the RSC include, but are not limited to, exposure to a particular pollutant from ocean 

fish and shellfish consumption (which is not included in the FCR), non-fish food consumption 

(e.g., fruits, vegetables, grains, meats, poultry), dermal exposure, and respiratory exposure.

EPA derived an RSC for each chemical included in this 2015 update by using the Exposure 

Decision Tree approach described in the 2000 Methodology (USEPA 2000a). To use that

approach, EPA compiled information for each chemical on its uses, chemical and physical 

properties, occurrences in other potential sources (e.g., air, food), and releases to the 

environment, as well as regulatory restrictions on other sources that are specific to the 

chemical (e.g., air quality standards, food tolerance levels). The ATSDR “Toxicological Profiles”

g In particular, CalEPA considered oral, inhalation and dermal exposures from water as part of the quantitative 

evaluation for hexachlorocyclopentadiene whereas EPA Office of Water currently considers oral exposure only for 

hexachlorocyclopentadiene (and other volatile chemicals). CalEPA also used a normalized lifetime water intake to 

BW ratio as exposure variables (CalEPA 2014b) in place of a water intake and BW that represent adult-only 

exposures.

12

 
Hexachlorocyclopentadiene 77-47-4

(ATSDR 2015) were the primary sources for this information. EPA used the Hazardous 

Substance Data Bank (HSDB) (USDHHS 2015) from the National Library of Medicine’s Toxicology 

Data Network (TOXNET) as the primary source for chemicals without ATSDR Toxicological 

Profiles. Both sources are peer-reviewed compilations of chemical information.

EPA used additional references, including the following, to obtain specific types of information 

and to supplement the information from ATSDR and the HSDB:

• EPA’s Six-Year Reviews (drinking water data) (USEPA 2009a; USEPA 2009b).

• FDA Total Diet Study (USFDA 2015).

• FDA Everything Added to Food in the United States (USFDA 2013).

• EPA National Lake Fish Tissue Study (USEPA 2009c).

• EPA Toxic Release Inventory (USEPA 2015g).

• International Bottled Water Association Standards of Quality (IBWA 2012).

• NOAA Mussel Watch (NOAA 2014).

• Additional sources as needed.

To determine the RSC to be used in the AWQC calculation, EPA then used the information 

compiled for each chemical to address the questions posed in the Exposure Decision Tree. 

Some of the important items evaluated in the Exposure Decision Tree follow:

• The adequacy of the data available for each relevant exposure source and pathway.

• The availability of sufficient information to characterize the likelihood of exposure to 

relevant sources.

• Whether there are significant known or potential uses/sources other than the source of 

concern (i.e., ambient water and fish/seafood from those waters).

• Whether information on each source is available to make a characterization of 

exposure.

In cases where there is a lack of environmental or exposure data, or both, the Exposure 

Decision Tree approach results in a recommended RSC of 20 percent. This 20 percent value for 

the RSC may be replaced where sufficient data are available to develop a scientifically 

defensible alternative value. When appropriate, if scientific data demonstrating that sources 

and routes of exposure other than water and fish from inland and nearshore waters are not 

anticipated for the pollutant in question, the RSC may be raised to 80 percent based on the 

available data (USEPA 2000a).

6.2 Chemical-specific RSC

Hexachlorocyclopentadiene is primarily used to make a group of related pesticides, including 

endosulfan and pentac (ATSDR 1999). It is also used to make flame retardants, shock-proof 

plastics, esters, ketones, fluorocarbons, and dyes (ATSDR 1999). Hexachlorocyclopentadiene 

itself is not currently registered as a pesticide (USEPA 2015c). Ambient air is the primary source 

of hexachlorocyclopentadiene exposure (ATSDR 1999).

13
Hexachlorocyclopentadiene 77-47-4 

The vapor pressure of hexachlorocyclopentadiene (0.08 mm Hg at 25 °C) indicates that 

volatilization is an important fate process for this chemical (ATSDR 1999). However, due to its 

high reactivity, it is unlikely to remain in air or in other environmental media for extended 

periods, as it photolyzes rapidly (its half-life is approximately 10 minutes) (ATSDR 1999). 

Hexachlorocyclopentadiene is listed as a hazardous air pollutant (USEPA 2013). Recent data 

from EPA’s Toxic Release Inventory indicate that 411 pounds of hexachlorocyclopentadiene 

were released to the air in 2013 (USEPA 2015g). Thus, based on the chemical’s physical 

properties, air is a potentially significant source of exposure to it. 

Hexachlorocyclopentadiene is regulated under the Safe Drinking Water Act, and EPA’s drinking 

water standard (maximum contaminant level) is 50 μg/L (USEPA 2014c). It was a target analyte 

in EPA’s Six-Year Reviews and was detected in some groundwater and surface water samples 

(0.098 and 0.949 percent of samples with detections, respectively); with detection values of 

0.005–15 μg/L (median 0.275 μg/L) in groundwater and 0.001–10 μg/L (median 0.13 μg/L) for 

surface waters (USEPA 2009a; USEPA 2009b). Although unlikely, it is possible for 

hexachlorocyclopentadiene to form in chlorinated waters containing humic substances (ATSDR 

1999). There is a Standard of Quality for bottled water for hexachlorocyclopentadiene of 50 

μg/L (IBWA 2012). Therefore, based on the chemical’s presence in samples, ingestion of surface 

water and finished drinking water is a potentially significant source of exposure to it. 

The log Kow for hexachlorocyclopentadiene ranges from 4.0 to 5.04, with an average log Kow of 

4.52 (ATSDR 1999). The national-level BAF estimates for hexachlorocyclopentadiene range from 

620 L/kg (TL2) to 1,500 L/kg (TL4), which indicates that it has a moderate-to-high potential for 

bioaccumulation (USEPA 2011b). Information on hexachlorocyclopentadiene in ocean fish and 

shellfish was not found in ATSDR (1999). The chemical was not a target analyte in NOAA’s 

Mussel Watch Survey (NOAA 2014), and it was not a target analyte in EPA’s National Lake Fish 

Tissue Study (USEPA 2009c). Recent exposure information regarding concentrations of 

hexachlorocyclopentadiene in fish and shellfish is lacking. Thus, based on 

hexachlorocyclopentadiene’s potential for bioaccumulation, ingestion of fish and shellfish is a 

potentially significant source of exposure to this chemical. 

According to ATSDR (1999), it is unknown if hexachlorocyclopentadiene accumulates in plants, 

milk, or animals used for food. Therefore, the potential exposure from ingestion of food is 

unknown.

In summary, based on the physical properties and available exposure information for 

hexachlorocyclopentadiene, air, drinking water, and fish and shellfish are potentially significant 

sources of exposure. Following the Exposure Decision Tree in EPA’s 2000 Methodology (USEPA 

2000a), significant potential sources other than fish and shellfish from inland and nearshore 

waters and water ingestion exist (Box 8A in the Decision Tree); however, information is not 

available to quantitatively characterize exposure from those different sources (Box 8B in the 

Decision Tree). Therefore, EPA recommends an RSC of 20 percent (0.20) for 

hexachlorocyclopentadiene.

14
Hexachlorocyclopentadiene 77-47-4 

7 Criteria Derivation: Analysis

Table 1 summarizes the model inputs used to derive the 2015 updated human health AWQC 

that are protective of exposure to hexachlorocyclopentadiene from consuming drinking water 

and eating fish and shellfish (organisms) from inland and nearshore waters. The criteria 

calculations are presented below. These updated criteria recommendations are based on the 

2000 Methodology (USEPA 2000a) and the updated exposure assumptions described above. 

(See section 4, Exposure Factors; section 5, Hazard Identification and Dose Response; and 

section 6, Relative Source Contribution.)

Table 1. Summary of Input Parameters for 2015 Human Health AWQC for 

Hexachlorocyclopentadiene

Input Parameter Value

RfD 0.006 mg/kg-d

CSF No data

RSC 0.20

BW 80.0 kg

DI 2.4 L/d

FCR

TL2 0.0076 kg/d

TL3 0.0086 kg/d

TL4 0.0051 kg/d

BAF

TL2 620 L/kg

TL3 1,500 L/kg

TL4 1,300 L/kg

7.1 AWQC for Noncarcinogenic Toxicological Effects

For consumption of water and organisms:

AWQC (μg/L) = toxicity value (RfD [mg/kg-d] × RSC) × BW (kg) × 1,000 (μg/mg)

 DI (L/d) + ∑ (FCRi (kg/d) × BAFi (L/kg)) 4

i=2

 = 0.006 mg/kg-d × 0.20 × 80.0 kg × 1,000 μg/mg

 2.4 L/d + ((0.0076 kg/d × 620 L/kg) + (0.0086 kg/d × 1,500 L/kg) + (0.0051 kg/d × 1,300 L/kg))

 = 3.60 μg/L

 = 4 μg/L (rounded)

15
Hexachlorocyclopentadiene 77-47-4 

For consumption of organisms only:

AWQC (μg/L) = toxicity value (RfD [mg/kg-d] × RSC) × BW (kg) × 1,000 (μg/mg)

 ∑ (FCRi (kg/d) × BAFi (L/kg)) 4

i=2

 = 0.006 mg/kg-d × 0.20 × 80.0 kg × 1,000 μg/mg

 (0.0076 kg/d × 620 L/kg) + (0.0086 kg/d × 1,500 L/kg) + (0.0051 kg/d × 1,300 L/kg)

 = 3.96 μg/L

 = 4 μg/L (rounded)

7.2 AWQC for Carcinogenic Toxicological Effects

EPA identified no CSF sources through the systematic search described above. (See section 5, 

Hazard Identification and Dose Response.) Therefore, EPA was unable to derive AWQC for 

carcinogenic toxicological effects.

7.3 AWQC Summary

EPA derived the AWQC for hexachlorocyclopentadiene using a noncarcinogenic toxicity 

endpoint. The updated human health AWQC for hexachlorocyclopentadiene are 4 μg/L for 

consumption of water and organisms and 4 μg/L for consumption of organisms only (Table 2).

These updated criteria replace EPA’s previously published values (USEPA 2003b). 

Table 2. Summary of EPA’s Previously Recommended (2003) and Updated (2015) Human Health 

AWQC for Hexachlorocyclopentadiene

2003 Human Health AWQC 2015 Human Health AWQC

Water and Organism 40 μg/L 4 μg/L

Organism Only 1,100 μg/L 4 μg/L

These AWQC are intended to be protective of the general adult population from 

noncarcinogenic effects due to chronic (up to a lifetime) exposure to 

hexachlorocyclopentadiene from ingesting water and/or consuming fish and shellfish from 

inland and nearshore waters.

8 Criteria Characterization

The updated 2015 human health AWQC for hexachlorocyclopentadiene take into account 

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

Methodology (USEPA 2000a). The following paragraphs describe the individual influence of 

each of the revised inputs and exposure assumptions on the overall change in value.

16
Hexachlorocyclopentadiene 77-47-4

Body Weight

EPA’s updated AWQC assume a higher BW compared to the previously recommended 2002 

criteria, reflecting a recent rise in average adult BW among the U.S. population. The updated 

BW assumption of 80.0 kg, based on recent survey data from the 1999−2006 NHANES data, is 

10 kg greater than the previous assumption of 70 kg. Assuming all other input parameters 

remain constant, a higher average BW in the AWQC calculations (Eqs. 1 and 2 above) results in 

higher AWQC. That is, as BW 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 DI assumption is 2.4 L/d, which is higher than the previously recommended rate of 

2 L/d. Assuming all other input parameters remain constant, a higher DI assumption in the 

AWQC calculations (Eqs. 1 and 2 above) results in lower AWQC. That is, as DI 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.

Fish Consumption Rate

The updated FCR for fish and shellfish from inland and nearshore waters is 22.0 g/d; the 

TL-specific FCRs are 7.6 g/d, 8.6 g/d, and 5.1 g/d for TLs 2, 3, and 4, respectively. The previously 

recommended FCR was 17.5 g/d. Assuming all other input parameters remain constant, a 

higher FCR assumption in the AWQC calculations (Eqs. 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 national lower (TL2), mid (TL3), and upper (TL4) TL BAFs used in the updated AWQC (Eqs. 1 

and 2 above) are 620, 1,500, and 1,300 L/kg wet-weight, respectively. These BAFs were derived 

using EPA’s 2000 Methodology (USEPA 2000a) and its Technical Support Document, Volume 2

(USEPA 2003a). These national TL BAFs replace EPA’s previously recommended BCF of 

4.34 L/kg.

As an additional line of evidence, EPA used model-estimated BAFs from the Estimation Program 

Interface (EPI) Suite (USEPA 2012) to support field-measured or predicted BAFs developed using 

the four methods described above. The BCFBAF program within EPI Suite estimates fish BAFs by 

using 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 Kow of the chemical and the normalized whole-body metabolic 

17
Hexachlorocyclopentadiene 77-47-4

biotransformation rate constant as input parameters to predict BAF values. The EPI Suite model 

estimates are as follows:

TL2 = 7,310 L/kg

TL3 = 6,930 L/kg

TL4 = 6,502 L/kg

Assuming all other input parameters remain constant, higher BAFs or BCFs result in lower 

AWQC. That is, as bioaccumulation or bioconcentration of a contaminant in fish and shellfish 

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 national-level BAF rather than a BCF better represents the amount of a 

contaminant accumulating in an organism because it accounts not only for the organism’s 

exposure to the 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 TLs of fish and shellfish consumed, as opposed to 

representing all TLs of fish and shellfish consumed by a single value, allows for better exposure 

representation.

Reference Dose

EPA retained an RfD of 0.006 mg/kg-d for hexachlorocyclopentadiene based on a 2001 EPA IRIS 

assessment (USEPA 2001a; USEPA 2003b). EPA used this RfD to derive AWQC for 

noncarcinogenic effects. Assuming all other input parameters remain constant, no change in 

the values used for the RfD in the AWQC calculations (Eqs. 1 and 2) results in no change in 

AWQC.

Cancer Slope Factor

EPA did not select a CSF for hexachlorocyclopentadiene and therefore did not derive AWQC for 

carcinogenic effects. EPA did not derive AWQC for carcinogenic effects of 

hexachlorocyclopentadiene in its previous criteria update (USEPA 2003b).

Relative Source Contribution

An RSC of 20 percent is included in the AWQC calculation. This is the same RSC used in the 

previous AWQC (USEPA 2003b).

9 Chemical Name and Synonyms

• Hexachlorocyclopentadiene (CAS Number 77-47-4)

• C-56

• Graphlox

• HCCP

• HCCPD

18
Hexachlorocyclopentadiene 77-47-4

• Hex

• Hexachloro-1,3-cyclopentadiene

• Hexachloropentadiene

• PCL

• Perchlorocyclopentadiene

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