Office of Water Office Science and Technology EPA 820-D- 14 -0 48 May 2014



# Draft Update of Human Health Ambient Water Quality Criteria:

Hexachlorobutadiene
87

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# Update of Human Health Ambient Water Quality Criteria:

Hexachlorobutadiene
87

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Draft

Office of Science and Technology
Office of Water U.S. Environmental Protection Agency Washington, DC 20460Hexachlorobutadiene 87

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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

Bi oaccumulation 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)

consider s 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.

N ational 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

re lationship 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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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 healt h.

Amb ient 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 there of, are references to national ambient water quality criteria recommendations for human health.

P roblem Fo rmulation

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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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).

E PA 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).

3The 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 / ͇) ∓ !F Ί (ͫ Ιͽ)) Ί 2

For cons umption of organisms only:

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

4 ∑ (F· Ί (Ιͽ / ͇) ∓ !F Ί (ͫ 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

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

BAF i = 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

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(Eq. 1)

( E q. 2)

Th e foll o wing 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 replac es 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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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 90 th 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 86 th 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 88 th percentile of adults in the National Cancer Institute study of the 1977-78 Nationwide Food Consumption Survey (USEPA, 2000).

Fi sh 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 90 th 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 90 th percentile FCR compared to the summation of all three trophic level specific 90 th percentile FCRs was applied to the 22 grams/day FCR used in this update. The trophic level ratios were calculated as follows: TL ratio

= 90 th percentile FCR for the TL divided by the sum of the 90 th 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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gr ams/day (0.005 kg/day). These resulting trophic level FCRs are well within the confidence intervals for each of the trophic level specific distributions’ 90 th percentiles and add to the total of 22 grams/day (USEPA, 2014).

Bi oaccumulation 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 al l 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. Accordin gly, 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 (K OW ) 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 (K OW ) 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 K OW 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 K OW = 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 K OW ) of 1.82 and represented all trophic levels (USEPA, 1980). The log K OW 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-Partiti on Coefficient Correlation.” The published version of that paper, however, lists the octanol/water partition coefficient for hexachlorobutadiene as 6.09 with a resulting log K OW of 4.78, not 1.82 (Banerjee et al., 1980).

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Had the BCF been calculated using the 1980 methodology and the correct log K OW of 4.78, the resulting BCF would have been 911 L/kg, not 2.78 L/kg.

Hazard Identification and D ose Response: Cancer Slope Factor

Hexachlor obutadiene 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.

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

FCR TL2 0.008 kg/day USEPA,

2014 90 th 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 K OW 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 ͇) ∓ !F Ί (ͫ / 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) + (0.00 5 kg/d × 23,410 L/kg))

= 0. 0080 μg/L (rounded to 0.008 μg/L because of significant figures, see 2000 Methodology)

For cons umption of organisms only:

AWQC (μg/L) = [10 -6 / CSF (kg·d/mg)] × BW (kg) × 1000 (μg/mg) ∑ 4 (F· Ί (Ιͽ / ͇) ∓ !F Ί (ͫ / 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 upd ated magnitude of the human health ambient water quality criteria for

hexachloro b utadiene 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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Table 2. ΋Ϣ΢΢̯ιΘ Ϊ͕ E ́!͛ν ζι͋̽ΊΪϢνΜΘ ι͋̽Ϊ΢΢͋Σ͇͇͋ (2002 ) and updated ( 201 4) 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 0.00 8 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.

B ody 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.

D rinking 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 organ Ίν΢͛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 BW 3/4 rather than BW 2/3 , 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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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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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-6 30 -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

.

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