Draft Risk Assessment for Chrome Plating Source Categ ories

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## Draft Residual Risk Assessment for the Chromic Acid Anodizing, Decorative Chromium Electroplating, and Hard Chromium

Electroplating Source Categor ies

by EPA’s Office of Air Quality Planning and Standards

Office of Air and Radiation September 2010Draft Risk Assessment for Chrome Plating Source Categ ories

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### Table of Contents

1 Introduction

................................ ................................ ................................ .............................. 4 2 Methods

................................ ................................ ................................ ................................ .... 5 2.1 Emission s and source data

................................ ................................ .............................. 5 2.2 Dispersion modeling for inhalation exposure assessment

................................ ............ 5 2.3 Estimating human inhalation exposure

................................ ................................ .......... 8 2.4 Acute Risk Screening and Refined Assessments

................................ .......................... 8 2.5 Multipathway and environmental risk screening

................................ .......................... 9 2.6 Dose

- Response Assessment

................................ ................................ ........................... 9 2.6.1 Sources of chronic dose

- response information

................................ ..................... 9 2.7 Risk Characterization

................................ ................................ ................................ .... 11 2.7.1 General

................................ ................................ ................................ .................. 11 2.7.2 Mixtures

................................ ................................ ................................ ................. 13 2.7.3 Fac ility

- Wide Risk

................................ ................................ ................................ 14 3 Risk Results for the Chromium Anodizing, Decorative Chromium Electroplating, and Hard Chromium Electroplating Source Categories

................................ ................................ ..... 14 3.1 Source Category Descriptions and Results

................................ ................................ .. 14 3.2 Risk Characterization

................................ ................................ ................................ .... 24 4 General Discussion of Unc ertainties and How They Have Been Addressed

.................... 25 4.1 Exposure Modeling Uncertainties

................................ ................................ ................ 25 4.2 Uncertainties in the Dose

- Response Rel ationships

................................ ..................... 26 5 References

................................ ................................ ................................ .............................. 33

Index of Tables

Table 2.2

- 1 AERMOD version 09292 model options for R TR II modeling

.............................. 6 Table 2.6

- 1 Dose

- Response Values for Chronic Inhalation Exposures

................................ .... 11 Table 3.1

- 1 Summary of Emissions from th e Hard Chromium Electroplating Source Category

................................ ................................ ................................ ................................ ......................... 19 Table 3.1

- 2 Summary of Source Category Level Risks for Hard Chromium Electroplating

.. 20 Table 3.1

- 3 Summary of Emissions from the Decorative Chromium Electroplating Source Category

................................ ................................ ................................ ................................ ......... 21 Table 3.1

- 4 Summary of Source Category Level Risks for Decorative Chromium Electropl ating

................................ ................................ ................................ ................................ . 22 Table 3.1

- 5 Summary of Emissions from the Chromium Anodizing Source Category

.......... 22 Table 3.1

- 6 Summary of Source Categor y Level Risks for Chromium Anodizing

................. 22 Table 3.1

- 7 Chromium Electroplating and Anodizing Population Risk Inhalation Risk Assessment Results

................................ ................................ ................................ ........................ 22Draft Risk Assessment for Chrome Plating Source Categ ories

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Appendices

Appendix 1 Emissions Inventory Sup port Memorandum Appendix 2 Technical Support Document for HEM

- AERMOD Modeling Appendix 3 Meteorological Data for HEM

- AERMOD Modeling Appendix 4 Analysis of D ata on S hort

- T erm E mission R ates R elative to L ong

- T erm

E mission R ates Appendix 5 Detailed Risk Mode ling Results

Index of Acronyms

AERMOD American Meteorological Society/EPA Regulatory Model AEGL Acute exposure guideline l evel ASTDR US Agency for Toxic Substances and Disease Registry CalEPA California Environmental Agency ERPG Emergency Response Plan ning Guideline HAP Hazardous Air Pollutant HEM Human Exposure Model HI Hazard index HQ Hazard quotient IRIS Integrated Risk Information System MACT Maximum Achievable Control Technology MIR Maximum Individual Risk MOA Mode of a ction NAC National A dvisory Committee NATA National Air Toxics Assessment NEI National Emissions Inventory NPRM Notice of Proposed Rulemaking PB

- HAP Persistent and Bioaccumulative HAP POM Polycyclic organic m atter REL Reference exposure l evel RfC Reference c oncentration RfD Reference d ose RTR Risk and Technology TOSHI Target

- organ

- specific hazard index URE Unit risk e stimateDraft Risk Assessment for Chrome Plating Source Categ ories

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### 1 Introduction

Section 112 of the Clean Air Act (CAA) establishes a two

- stage regulatory process for addressing emissions of hazardous air pollut ants (HAPs) from stationary sources. In the first stage, section 112(d)(2) requires the Environmental Protection Agency (EPA, or the Agency) to develop tec hnology

- based standards for categories of industrial sources (e.g., petroleum refineries, pulp and p aper mills, etc.) [ 1 ]. EPA has largely completed the initial Maximum Achievable Control Technology ( MACT ) standards as required under this provision. Under section 112(d)(6), EPA must review each of these technology

- based standards at least every eight y ears and revise a standard, as necessary, ―taking into account developments in practices, processe s and control technologies.‖ In the second stage, EPA is required under section 112(f)(2) to assess the health and environmental risks that remain after impl ementation of the MACT standards . If additional risk reductions are necessary to protect public health with an ample margin of safety or to prevent an adverse environmental effect, EPA must develop standards to address these remaining risks. This second stage of the regulatory process is known as the residual risk stage. For each source category for which EPA issued MACT standards, the residual risk stage must be completed within eight years of promulgation of the initial technology

- based standard.

In D ecember of 2006 we consulted with a panel from the EPA's Science Advisory Board (SAB) on the ―Risk and Technology Review (RTR) Assessment Plan‖ and in June of 2007, we received a letter wit h the results of that consultation

. Subsequent to the consultation , in Ju ly of 2009 a meeting was held with an SAB panel for a formal peer review of the ― Risk and Technology Review (RTR) Risk Assessment Methodologies ‖ [ 2 ]

. We received the final SAB report on this review in May of 2010. Where appropriate, we have respon ded to the key messages from this review in developing our current risk assessment s and we will be continuing our efforts to improve our assessments by incorporating updates based on the SAB recommendations as they are developed and become available

.

Thi s document contains the methods and results of baseline risk assessment s (i.e., after the implementation of the respective MACT standard s ) performed for the chromium a nodizing, d ecorative c hromium e lectroplating, and h ard c hromium e lectroplating s ource c at egories

. The methods discussion includes descriptions of the methods used to develop refined estimates of chronic inhalation exposures and human health risks for cancer and non

- cancer endpoints, as well as descriptions of the methods used to screen chronic non

- inhalation health risks and adverse environmental effects. Since none of the screening assessments indicated any significant potential for chronic non

- inhalation health effects or environmental impacts

, including effects to threatened and endangered species , no further refinement of these

assess m ents w as performed. Because t here are no HAP with an acute dose

- response benchmark value, we did not perform a quantitative risk assessment for acute exposures to these pollutants

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### 2 Methods

2.1 Emissions and so urce data
The 200 5 National

- Scale Air Toxics Assessment (NATA) National Emissions Inventory (NEI) served as the starting point for this assessment. The 200 5 NEI purportedly contains information on actual emissions during the entire 200 5 base year. Using the process MACT code s 1 , we developed a subset of this inventory that contains emissions and facility data for the source categor ies addressed. Next, we performed an engineering review of the information using EPA engineers who were directly involved in t he development of the MACT standards for the source categor y , and/or who have extensive knowledge of the characteristics of th i s industr y . NEI data w ere updated with available industry supplied data. The goal of the engineering review was to identify li mitations and issues with the emissions data (particularly those that would greatly influence risk estimates) and to make changes to the data where possible to address these issues and decrease the uncertainties associated with the assessment.

A review o f the NEI data indicated that not all chromium electroplating facilities were included in the data set. To address this situation, an additional data set was developed based

on 1629 facilities with known addresses. Emissions for each type of plant were e stimated based on the model plants developed for the MACT standard s , with hard chromium model plants having the highest emissions, followed by decorative chromium electroplating, and then chromium anodizing.

Details on the development of the emissions and source data for th ese source categor ies are discussed in Section 3. The emissions data and modification s made to the NEI data are discussed in Appendix 1, entitled ― Emissions Inventory Support Memorand um

. ‖



### 2.2 Dispersion modeling for inhalation exposure as sessment Both long

- and short

- term inhalation exposure concentrations and associated health risk s from each facility in the source category of interest were estimated using the Human Exposure Model in combination with the American Meteorological Society/EP A Regulatory Model dispersion modeling system (HEM

- AERMOD). The approach used in applying this modeling system is outlined below, and further details are provided in Appendix 2 . HEM

- AERMOD performs three main operations: atmospheric dispersion modeling, estimation of individual human exposures and health risks, and estimation of population risks. This section focuses on the dispersion modeling component. The exposure and risk characterization components a re discussed in other subsections of S ection s 2 a nd 3

. The dispersion model in the HEM

- AERMOD system, AERMOD version 09292 , is a state

- of

the

- science Gaussian plume dispersion model that is preferred by EPA for modeling point,

1 The tagging of data with MACT codes allows EPA to determine reductions attributable to the MACT program. The N E I associates MACT codes corresponding to MACT source categories with stationary major and area source data. MACT codes may be assigned either at the process level or at the site level in the point source data ( e.g., the MACT code for municipal waste combustors (MWCs) is assigned at the site level whereas the MACT code for petroleum refinery catalytic cracking is assigned at the process level )

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area, and volume sources of continuous air emissions from facility applicatio ns [ 3 ]. Further details on AERMOD can be found in the AERMOD Users Guide [ 4 ]. The model is used to develop annual average ambient concentration s through the simulation of hour

- by

- hour dispersion from the emission sources into the surrounding atmosphere. Hourly emission rates used for this simulation are generated by evenly dividing the total annual emission rate from the inventory into the 8,760 hours of the year.

The first step in the application of the HEM

- AERMOD modeling system is to predict ambient concentrations at locations of interest. The AERMOD model options employed are summarized in Table 2.2

- 1 and are discussed further below.

Table 2.2

- 1 AERMOD version 09292 mo del options for RTR II modeling

Modeling Option Selected Parameter for chronic exposure
Type of calculations Hourly a mbient c oncentration
Source type Point, area represented as pseudo point source

Receptor orientation Polar (1 3 rings a nd 16 radials ) Discrete (census block centroids )

Terrain characterization Actual from USGS 1

- degree DEM data
Building downwash Not Included

Plume d eposition/ d epletion Not Included

Urban s ource o ption No
Meteorology 1 year representative NWS from nearest site (1 58 stations)

Meteorological data fo r HEM

- AERMOD is selected from a list of 158 National Weather Service (NWS) surface observation stations across the continental United States, Alaska, Hawaii, and Puerto Rico. In most cases

, the nearest station is selected as representative of the cond itio ns at the subject facility. Ideally, when considering off

- site meteorological data

, most site specific dispersion modeling efforts will employ up to five years of data to capture variability in weathe r patterns from year to year. However, because we had an insufficient number of appropriately formatted model input files derived from available meteorological data , we modeled only a single year, typically 1991 . While the selection of a single year may result in underprediction of long

- term ambient levels a t some locations, likewise it may result in overprediction at others. For each facility identified by its characteristic latitude and longitude coordinates, the closest meteorological station was used in the dispersion modeling. The average distance betw een a modeled facility and the applicable meteorological station was 40 miles (72 km). Appendix 3 (Meteorological Data Processing Using AERMET for HEM

- AERMOD) provides a complete listing of stations and assumptions along with further details used in proce ssing the data through AERMET. The sensitivity of model results to the selection of the nearest weather station and the use of one year of meteorological data is discussed in ― Risk and Technology Review (RTR) Risk Assessment Methodologies .‖Draft Risk Assessment for Chrome Plating Source Categ ories

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The HEM

- AERMO D model estimates ambient concentrations at the geographic centroids of census blocks (using the 2000 Census), and at other receptor locations that can be specified by the user. The model accounts for the effects of multiple facilities when estimating

con centration impacts at each block centroid. Typically, w e combined only the impacts of facilities within the same source category, and assessed chronic exposure and risk only for census bl ocks with at least one resident ( i.e., locations where people may re asonably be assumed to reside rather than receptor p oints a t the fenceline of a facility ) . Chronic ambient concentrations were calculated a s the annual average of all estimated short

- term ( one

- ho ur) concentrations at each block centroid . Possible future residential use of currently uninhab ited areas was not considered. Census blocks, the finest resolution available in the census data,

are typically comprised of approximately 40 people or about ten households.

In contrast to the development of ambient concentrations for evaluating long

- term exposures, which was performed only for occupied census blocks, worst

- case short

- term ( one

- hour) concentrations were estimated both at the census block centroids and at points nearer the facility that represent loca tions where people may be present for short periods, but generally no nearer than 100 meters from the center of the facility (note that for large facilities, this 100

- meter ring could still contain locations inside the facility property) . Since short

- term emission rates were needed to screen for the potential for hazard via acute exposures, and since the NEI contains only annual emission totals , we applied the general assumption to all source categories that the maximum one

- hour emission rate from any sour ce was ten times the average annual hourly emission rate for that source. Average hourly emissions rate is defined as the total emissions for a year divided by the total number of operating hours in the year. This choice of a factor of ten for screenin g was originally based on engineering judgment

. To develop a more robust peak

- to

- mean emissions factor, and in response to one of the key
messages from the SAB consultation on our RTR Assessment Plan, we recently performed an analysis using a short

- term e missions data set from a number of source s located in Texas (originally reported on by Allen et al

. 2004) [ 5 ]. In that report, t h e Texas Environmental Research Consortium Project compared hourly and annual emissions data for volatile organic compound s for a ll facilities in a heavily

- industrialized 4

- county area (Harris, Galveston, Chambers, and Brazoria Counties , TX) over an eleven

- month time period in 2001 . We obtained the dataset and performed our own analysis, focusing that analysis on sources whic h
repo rted emitting high quantities of HAP over short periods of time (see Appendix 4

,
― Analysis of data on short

- term emission rates relative to long

- term emission rates ‖ ) . Most peak emission events were less than twice the annual average, and the highest was a factor of 11 times the annual average

. The factor of ten is intended to cover both routinely

- variable emissions a s well as startup, shutdown, an d malfunction (SSM) emissions. While there are some documented emission excursions above this level, our ana lysis of the data from the Texas Environmental Research Consortium suggests that this factor should cover more than 99% of the short

- term peak gaseous or volatile HAP emissions from typical industrial

sources.

Census block elevations for HEM

- AERMOD mo deling were determined nationally from the US Geological Service 1

- degree digital elevation model (DEM) data files, which have a spatial resolution of about 90 meters. Polar grid elevations (used in estimating short

- and long

- term ambient concentrations) were evaluated at the highest elevation of any census blockDraft Risk Assessment for Chrome Plating Source Categ ories

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in that sector. If a sector does not contain any blocks, the model defaults to the elevation of the nearest block. If the elevation is not provided for the emission source, the model takes the

a verage elevation of all sectors of the nearest model ring.

In addition to u sing receptor elevation to determine plume height, AERMOD adjusts the plume’s flow if nearby elevated hills are expected to influence the wind patterns. For details on how hill h eights were estimated and used in the AERMOD modeling

, see Appendix 2

.


### 2.3 Estimating human inhalation exposure

For this assessment, we used the annual average ambient air concentration of each HAP at each census block centroid as a surrogate for the life time inhalation exposure concentration of all the people who reside in the census block. That is, this risk analysis did not consider either the short

- term or long

- term behavior (mobility) of the exposed populations and its potential influence on their ex posure.

We did not address short

- term human activity in th is assessment for two reasons. First, our experience with the 1996, 1999, 2002 and 2005 NATA assessments [ 6 ] (which modeled daily

a ctivity using EPA’s HAPEM model ) suggests that, given our curr ent understanding of microenvironment concentrations and daily activities, modeling short

- term activity would, on average, reduce risk estimates about 25% for particulate HAPs; it will also reduce risk estimates for gaseous HAPs, but typically by much less

. Second, basing exposure estimates on average ambient concentrations at census block centroids may underestimate or overestimate actual exposure concentrations at some residences. Further reducing exposure estimates for the most highly

- exposed residents by modeling their short

- term behavior could add a systematic low bias to these results.

We did not address long

- term migration in this assessment nor population growth or decrease over 70 years , instead basing the assessment on the assumption that each p erson’s predicted exposure is constant over the course of their lifetime which is assumed to be 70 years

. In assessing cancer risk, three metrics are generally estimated, the maximum individual risk (MIR) which is defined as the risk associated with a lif etime of exposure at the highest concentration, the population risk distribution, and the cancer incidence. This assumption of not considering short or long

- term population mobility does not bias the estimate of the theoretical MIR nor does it affect the estimate of cancer incidence since the total population number remains the same . It does, however, affect the shape of the distribution of individual risks across the affected population, shifting it toward higher estimated individual risks at the
upper e nd and reducing the number of people estimated to be at lower risks , thereby biasing the risk estimates high

.


### 2.4 Acute Risk Screening and Refined Assessments

In establishing a scientifically

- defensible approach for the assessment of potential health risks du e to acute exposures to HAP , we f ollow the same general approach that is used for developing chronic health risk assessments under the residual risk program. However, for these source categories, t here are no HAP with an acute dose

- response benchmark valu e

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Therefore

, we did not perform a quantitative risk assessment for acute exposures to these pollutants

.


### 2.5 Multipathway and environmental risk screening

The potential for significant human health risks due to exposures via routes other than inhalation (i.e ., multipathway exposures) w as screened by first determining whether any sources emitted any hazardous air pollutants known to be persistent and bioaccumulative in the environment (PB

- HAP). The PB

- HAP compounds or compound classes are identified for th e s creening from the EPA’s Air Toxics Risk Assessment Library [ 7 ]. Examples of PB

- HAP

are cadmium compounds, chlordane, chlorinated dibenzodioxins and furans, DDE, heptachlor, hexachlorobenzene, hexachlorocyclohexane, lead compounds, mercury compounds, metho xychlor, polychlorinated biphenyls, polycyclic organic matter, toxaphene, and trifluralin . PB

- HAP emissions were not identified from the chromium a nodizing, d ecorative c hromium e lectroplating, and h ard c hromium e lectroplating s ource c ategories

, indicating that exposures due to non

- inhalation routes of exposure were not significant. The lack of PB

- HAP emissions from th ese source categor ies indicates a very low potential for adverse environmental effects due to exposures resulting from atmospheric depositio n of PB

HAPs. Thus, even if sensitive species are present in the areas surrounding these facilities with no PB

- HAP emissions, it is still reasonable to assume that there are no adverse effects to populations in the areas surrounding these facilities.

Add itionally, we evaluated the potential for significant ecological exposures to non PB

- HAP from exceedances of chronic human health inhalation thresholds in the ambient air near these facilities. Human health dose

- response threshold values are generally der ived from studies conducted on laboratory animals (such as rodents) and developed with the inclusions of uncertainty factors that could be as high as 3000. As a result, these human threshold values are often significantly lower than the level expected to cause an advers e effect in an exposed rodent. It should be noted that there is a scarcity of data on the direct atmospheric impact of these HAPs on other receptors, such as plants, birds, and wildlife. Thus, if the maximum inhalation hazard in an ecosyst em is below the level of concern for humans, we have generally concluded that mammalian receptors should be at no risk of adverse effects due to inhalation exposures from non PB

- HAP, and have assur ance that other ecological receptors are also not at any si gnificant risk fr om direct atmospheric impact. In some isolated cases where we have data indicating potential adverse impacts on plants, birds, or other wildlife due to the direct atmospheric impacts of specific HAPs , we note that as an uncertainty and , w here possible, refine our analysis by comparing our modeled impacts to available threshold values from the scientific literature.



### 2.6 Dose

- Response Assessment

2.6.1 Sources of chronic dose

- response information

Dose

- response assessment information (carcinogenic an d non

- carcinogenic) for chronic exposure (either by inhalation or ingestion) for the HAPs reported in the emissions inventoryDraft Risk Assessment for Chrome Plating Source Categ ories

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is based on the EPA Office of Air Quality Planning and Standards’ existing recommendations for HAPs , also used for NATA 1999, 2002 , and 2005 [ 8 ]. This information has been obtained from various sources and prioritized according to (1) conceptual consistency with EPA risk assessment guidelines and (2) level of peer review received. The prioritization process was aimed at incorporati ng into our assessments the best available science with respect to dose

response information. The recommendations are based on the following sources, in order of priority:

1) US Environmental Protection Agency (EPA). EPA has developed dose

- response

assessm ents for chronic exposure for many of the pollutants in this study. These assessments typically provide a qualitative statement regarding the strength of scientific data and specify a reference concentration (RfC, for inhalation) or reference dose (RfD, f or ingestion) to protect against effects other than cancer and/or a unit risk estimate (URE, for inhalation) or slope factor (SF, for ingestion) to estimate the probability of developing

cancer. The RfC is defined as an ― estimate (with uncertainty spannin g perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. ‖ The URE is defined as ― the upper

- bound excess cancer risk estimated to result from continuous lifetime exposure to an agent at a concentration of 1 μg/m 3 in air. ‖ The SF is ―a n upper bound, approximating a 95% confidence limit, on the increased cancer risk from a lifetime exposure to an agent . This estimate, [is] usually expressed in units of proportion (of a population) affected per mg/kg

- day ...‖ EPA disseminates dose

response assessment information in several forms, based on the level of review. The Integrated Risk Information System (IRIS) [ 9 ] is an EPA database that contains scientific health assessment information, including dose

- response information. All IRIS assessments since 1996 have also undergone independent external peer review. The current IRIS process includes review by EPA scien tists, interagency reviewers from other federal agencies, and the public, and peer review by independent scientists external to EPA. EPA’s science policy approach , under the current carcinogen guidelines, is to use linear low

- dose extrapolation as a defau lt option for carcinogens for which the mode of action (MOA) has not been identified. We expect future EPA dose

- response assessments to identify nonlinear MOAs where appropriate, and we will use those analyses (once they are peer reviewed) in our risk ass essments. At this time, however, there are no available carcinogen dose

- response assessments for inhalation exposure that are based on a nonlinear MOA

.
2) US Agency for Toxic Substances and Disease Registry (ATSDR). ATSDR, which is part of the US Departme nt of Health and Human Services, develops and publishes Minimum Risk Levels (MRLs) [ 10 ] for inhalation and oral exposure to many toxic substances. As stated on the ATSDR web site: ― Following discussions with scientists within the Department of Health and H uman Services (HHS) and the EPA, ATSDR chose to adopt a practice similar to that of the EPA's Reference Dose (RfD) and Reference Concentration (RfC) for deriving substance specific health guidance levels for non neoplastic endpoints .‖ The MRL is defined a s ―an estimate of daily human exposure to a substance that is likely to be without an appreciable risk of adverse effects (other than cancer) over a specified duration of exposure.‖ ATSDR describes MRLs as substance

- specific estimates to beDraft Risk Assessment for Chrome Plating Source Categ ories

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used by health assessors to select environmental contaminants for further evaluation. Exposures above an MRL do not necessarily represent a threat, and MRLs are therefore not intended for use as predictors of adverse health effects or for setting cleanup levels.

3) Calif ornia Environmental Protection Agency (CalEPA). The CalEPA Office of Environmental Health Hazard Assessment has developed dose

- response assessments for many substances, based both on carcinogenicity and health effects other than cancer. The process for de veloping these assessments is similar to that used by EPA to develop IRIS values and incorporates significant external scientific peer review. As cited in the CalEPA Technical Support Document for developing their chronic assessments 2 : ―The guidelines for developing chronic inhalation exposure levels incorporate many recommendations of the U.S. EPA [ 11 ] and NAS [ 12 ] .‖ The non

- cancer information includes available inhalation health risk guidance values expressed as chronic inhalation reference exposure level s (RELs) [ 13 ]. CalEPA defines the REL as ―the concentration level at or below which no health effects are anticipated in the general human population.‖ CalEPA's quantitative dose

- response information on carcinogenicity by inhalation exposure is expressed in terms of the URE [ 14 ], defined similarly to EPA's URE.

The emissions inventor y for the source categor ies include emissions of three HAP with available quantitative inhalation dose

- response values. These HAP, their dose

- response values, and the sour c e of the value s are listed in Table 2 .6

- 1

.

Table 2.6

- 1 Dose

- Response Values for Chronic Inhalation Exposures

Pollutant CAS Number RfC

(mg/m

3 ) URE (1/μg/m

3 ) Source a Chromium III Compounds 16065831 Chrom ium VI Compounds 18540299 0.0001 0.012 IRIS

-- L Chromium Trioxide (VI), chromic acid mist 11115745 0.000008 IRIS

-- L

a The descriptors L (low), M (medium), and H (high) have been added for IRIS RfC values to indicate the overall level of confidence in the RfC value, as reported in the IRIS file.



### 2.7 Risk Characterization

2.7.1 General

The final product of the risk assessment is the risk characterization, in which the information from the previous steps is integrated and an overall conclusion about risk is synt hesized that is complete, informative, and useful for decision makers. In general, the nature of this risk characterization depends on the information available, the application of the risk information and the resources available. In all cases, major iss ues associated with determining the nature and extent of the risk are identified and discussed. Further, the EPA Administrator’s March 1995 Policy for Risk Characterization [ 15 ] specifies that a risk characterization ―be prepared

2 Air Toxics Hot Spots Program, Risk Assessment Guidelines, Part III

- Technical Support Document for the Determination of Non

- cancer Chronic Reference Exposure Levels. Air Toxicology and Epidemiology Section, Office of Environmental Health Hazard Assessment, California Environmental Protection Agency. February 2000 ( http://www.oehha.ca.gov/air/chronic_rels/pdf/relsP32k.pdf )Draft Risk Assessment for Chrome Plating Source Categ ories

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in a manner that is clear, transparent, reasonable, and consistent with other risk characterizations of similar scope prepared a cross programs in the Agency.‖ These principles of transparency and consistency have been reinforced by the Agency’s Risk Characterization Handbook [ 16 ], in 2002 by the Agency’s information quality guidelines [ 17 ] , and in the OMB/OSTP September 2007 Memo randum on Updated Principles for Risk Analysis 3 , and are incorporated in these assessments.

Estimates of health risk are presented in the context of uncerta inties and limitations in the data and methodology. Through our tiered

, iterative analytical approach , we have attempted to reduce both uncertainty and bias to the greatest degree possible in these assessments. In our assessments we provide summaries of risk metrics (including maximum individual cancer risks and non

- cancer hazards, as well as cancer incidence estimates) along with a discussion of the major uncertainties associated with their derivation to provide decision makers with the fullest picture of the assessment and its limitations.

For each carcinogenic HAP included in an assessment that has a potency estimate available, individual and population cancer risks are calculated by multiplying the corresponding lifetime average exposure estimate by the appropriate URE. This calculated cancer risk is defined as the upper

- bound probability of developing cancer over a 70

- y r period (i.e., the assumed human lifespan) at that exposure. Because UREs for most HAPs are upper

- bound estimates, actual risks at a given exposure level may be lower than predicted, and could be

zero.

For EPA’s list of carcinogenic HAPs that act by a mutagenic mode

- of

- action [ 18 ], we apply EPA’s Supplemental Guidance for Assessing Susceptibility from Early

- Life Exposure to Carcinoge ns [ 19 ]

. This guidance has the effect of adjusting the URE by factors of 10 (for children aged 0

- 1), 3 (for children aged 2

- 15), or 1.6 (for 70 years of exposure beginning at birth), as needed in risk assessments . In this case, this has the effect of incr easing the estimated life time risks for these pollutants by a factor of 1.6. In addition, although only a small fraction of the total POM emissions may be reported as individual compounds, EPA expresses carcinogenic potency for compounds in this group in terms of benzo[a]pyrene equivalence, based on evidence that carcinogenic POM have the same mutagenic mechanism of action as does benzo[a]pyrene. For this reason

, EPA implem entation policy [ 20 ] recommends applyi ng the Supplemental Guidance to all carcinoge nic PAHs for which risk estimates are based on relative potency. Accordingly, we apply the Supplemental Guidance to all unspeciated POM mixtures.

Increased cancer incidence for the entire receptor population within the area of analysis is estimated by mu ltiplying the estimated lifetime cancer risk for each census block by the number of people residing in that block, then summing the results for the entire modeled domain. This lifetime population incidence estimate is divided by 70 years to obtain an esti mate of the number of cancer cases per year.

3 Memorandum f

or t he Heads o f Executive Departments a nd Agencies

- Updated Pri nciples for Risk Analysis ( September 19, 2007 ), From Susan E. Dudley, Administrator, Office of Information and Regulatory Affairs, Office of Management and Budget; and Sharon L. Hays, Associate Director and Deputy Director for Science, Office of Science and Technology Policy ( http://www.whitehouse.gov/omb/memoranda/fy2007/m07

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In the case of benzene, the high end of the reported cancer URE range is used in our assessments to provide a conservative estimate of potential cancer risks. Use of the high end of the range provides risk est imates that are approximately 3.5 times higher than use of the equally

- plausible low end value. If the estimated benzene

– associated risks exceed 1 in a million, we evaluate the impact of using the low end of the URE range on our risk results.

Unlike lin ear dose

- response assessments for cancer, non

- cancer health hazards generally are not expressed as a probability of an adverse occurrence. Instead, ―risk‖ for non

- cancer effects is expressed by comparing an exposure to a reference level as a ratio. The ― hazard quotient‖ (HQ) is the estimated exposure divided by a reference level (e.g., the RfC). For a given HAP, exposures at or below the reference level (HQ<1) are not likely to cause adverse health effects. As exposures increase above the reference leve l (HQs increasingly greater than 1), the potential for adverse effects increases. For exposures predicted to be above the RfC, the risk characterization includes the degree of confidence ascribed to the RfC values for the compound(s) of concern (i.e., hig h, medium, or low confidence) and discusses the impact of this on possible health interpretations.

The risk characterization for chronic effects other than cancer is expressed in terms of the HQ for inhalation, calculated for each HAP at each census block centroid. As discussed above, RfCs incorporate generally conservative uncertainty factors in the face of uncertain extrapolations, such that an HQ greater than one does not necessarily suggest the onset of adverse effects. The HQ cannot be translated to a probability that adverse effects will occur, and is unlikely to be proportional to adverse health effect outcomes in a population

.

2.7.2 Mixtures

Since most or all receptors in these assessments receive exposures to multiple pollutants rather than a single pollutant, we estimated the aggregate health risks associated with all the exposures from a particular source category combined.

To combine risks across multiple carcinogens, our assessments use the mixtures guidelines’ [ 21

, 22 ] default assumption of additiv ity of effects, and combine risks by summing them using the independence formula in the mixtures guidelines.

In assessing non

- cancer hazard from chronic exposures, in cases where different pollutants cause adverse health effects via completely d ifferent m odes of action, it may be inappropriate to aggregate HQs. In consideration of these mode

- of

- action differences, the mixtures guidelines support aggregating effects of different substances in specific and limited ways. To conform to these guidelines, we a ggregated non

- cancer HQs of HAPs that act by similar toxic modes of action, or (where this information is absent) that affect the same target organ. This process creates, for each target organ, a target

- organ

- specific hazard index (TOSHI), defined as the sum of hazard quotients for individual HAPs that affect the same organ or organ system. A ll TOSHI calculations presented here were based exclusively on effectsDraft Risk Assessment for Chrome Plating Source Categ ories

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occurring at the ― critical dose‖ (i.e., the lowest dose that produces adverse health effects)

. Although HQs associated with some pollutants have been aggregated into more than one TOSHI, this is done only in cases where the critical dose affects more than one target organ

. Because impacts on organs or systems that occur above the critical dose hav e not been included in the TOSHI calculations, some TOSHIs may be underestimated. As with the HQ, the TOSHI should not be interpreted as a probability of adverse effects, or as strict delineation of ―safe‖ and ―unsafe‖ levels. Rather, the TOSHI is anothe r measure of the potential for adverse health outcomes associated with pollutant exposure, and needs to be interpreted carefully by health scientists and risk managers.

2.7.3 Facility

- Wide Risk s

To help place the source category risks in context, we examined ― facility

- wide‖ risks using the results of the 2005 NATA. For the facilities in the se source categor ies , we extracted (based on facility ID) t he NATA estimates of inhalation cancer and chronic non

- cancer risks associated with all HAP emissions sources at t he facilit ies , including emissions sources that are not part of th e source categor ies but that are located within a contiguous area and are under common control. We analyzed risks due to the inhalation of HAP for the populations residing within 5 0 kilomet ers of each facility. The results of this facility

- wide assessment are provided for the highest

- risk facility below in the Risk Results section of this document. The complete results of the facility

- wide assessment are provided in Appendix 5

.


### 3 Risk Results for the Chromium Anodizing, Decorative Chromium Electroplating, and Hard Chromium Electroplating Source Categories

3.1 Source Category Description s and Results

The h ard c hromium e lectroplating source category consists of facilities that plate base metals wit h a relatively thick layer of chromium using an electrolytic process. Hard chromium electroplating provides a finish that is resistant to wear, abrasion, heat, and corrosion. These facilities plate large cylinders and industrial rolls used in constructio n equipment and printing presses, hydraulic cylinders and rods, zinc die castings, plastic molds, engine components, and marine hardware.

The d ecorative c hromium e lectroplating source category consists of facilities that plate base materials such as brass , steel, aluminum, or plastic with layers of copper and nickel, followed by a relatively thin layer of chromium to provide a bright, tarnish

- and wear

- resistant surface. Decorative chromium electroplating is used for items such as automotive trim, metal f urniture, bicycles, hand tools, and plumbing fixtures.

The c hromium a nodizing source category consists of facilities that use chromic acid to form an oxide layer on aluminum to provide resistance to corrosion. The chromium anodizing process is used to coat aircraft parts (such as wings and landing gears) as well as architectural structures that are subject to high stress and corrosive conditions.Draft Risk Assessment for Chrome Plating Source Categ ories

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The HAP emission sources subject to the c hromium e lectroplating MACT standards are the tanks in which th e chromium deposition takes place. For hard chromium and decorative chromium electroplating facilities, the emission sources are electroplating tanks. For the

c hromium a nodizing source category, the emission sources are anodizing tanks.

The primary em ission controls used by the facilities in these source categories include packed bed scrubbers, mesh pad mist eliminators, composite mesh pad (CMP) systems, high efficiency particulate air (HEPA) filters, and wetting agent/fume suppressants (WAFS). Most d ecorative chromium electroplating plants comply with the MACT standards by using WAFS in the tank bath to control surface tension, which in turn reduces emissions. Some plants use a combination of WAFS and add

- on control to meet the MACT emission limits. If a facility controls emissions using an add

- on control device, the tank is generally equipped with a hood and duct work to exhaust emissions through the control device and out the stack. However, when WAFS are used as the only means of emission control , the tanks often are not equipped with exhaust hoods. In such cases, emissions from the tank are fugitive and are exhausted to the outside using wall

- mounted exhaust fans.

We estimate there are approximately 1,770 plants currently subject to the c hromiu m

e lectroplating MACT standards. Of these, we estimate there are 790 hard chromium electroplating plants, 740 decorative chromium electroplating plants, and 240 chromium anodizing plants. Some facilities perform more than one type of chromium electroplat ing or anodizing. For purposes of our estimates, we classified facilities as hard chromium, decorative chromium, or chromium anodizing based on the primary type of electroplating operation performed at the facility. Some chromium electroplating facilitie s electroplate items that are used internally in the manufacturing process at the same facility or within the same company. For example, some large printing facilities electroplate their printing rollers in house, and the chromium electroplating processes are located at the same site as the printing and publishing processes.

For the chromium electroplating source categories, we compiled a preliminary data set using data in the 2005 NEI. A review of the NEI resulted in the identification of data for 122 chromium electroplating facilities. These data were reviewed and the data for eight hard chromium and six decorative chromium electroplating plants were revised based on information in the facilities’ permits or permit applications. Additional data were available for 44 facilities through responses to a CAA section 114 information request that was sent to facilities for the Plating and Polishing Area Source rule. The data for these facilities were added to the NEI data set and, as with the original data , represent actual emission levels for these chromium electroplating facilities. Most of these facilities have low emissions, which are generally less than two pounds per year. These 166 facilities now included in the NEI comprise approximately nine perc ent of the estimated 1,770 facilities covered by the MACT standards and include 63 hard chromium electroplating, 96 decorative chromium electroplating, and seven chromium anodizing facilities. This data set of 166 facilities w as modeled to determine the m aximum individual cancer risk, the population cancer risk, the cancer incidence, and the maximum chronic non

- cancer risk for the three source categories based on actual emissions. The maximum individual cancer risk and the maximum chronic

non

- cancer risk estimated from this data set were also compared to the maximum individualDraft Risk Assessment for Chrome Plating Source Categ ories

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cancer risk and the maximum chronic non

- cancer risk estimated from MACT

- allowable emissions for the three source categories

. A description of the available data on actual emissions f

or chromium electroplating sources and a compar ison of those data to emissions that would be allowed under the MACT standards is given in a separate memorandum [ 23 ]

. To address the possibility that the 166 facilities might not be fully representative of th e source categories and their risks, we developed an additional data set. In the development of this data set we used ―model plants‖ developed for the original MACT standard s to represent the individual facilities. For hard and decorative chromium electr oplating

, we used three model plants (large, medium, and small) that represent average characteristics for each of these groups. For each of these plant sizes, there is an annual emissions rate (lbs/yr) that is derived from the design and operating parame ters and is specific to the size and type of model plant. For chromium anodizing we have two model plants (large and small). The model plants were based on data collected during development of the original MACT standards from 1988 to 1993 f or more than 1 00 facilities that responded to an information collection request for the chromium electroplating and anodizing industry. Data from site visits and other information also were used in developing the model plants. A complete description of the model plant s developed for the MACT standard is provided in the Background Information Document for the original MACT standard. [ 24 ]

The basis for this additional data set is 1,629 chromium electroplating facilities with known addresses. For about half of these fa cilities

, the type of electroplating performed is known but the size of the facility is not known. For the remaining facilities

, neither the type of chromium electroplating process or processes nor the facility size is known. For use in the risk analysis , the limited available data were used to divide these facilities into six groups. Facilities in three of the six groups were assigned to be hard chromium electroplating facilities. Those groups include: hard chromium facilities; facilities with combine d hard chromium operations and other electroplating or anodizing; and facilities with unknown processes. Together, these three groups yielded a total of 1,219 plants, all of which we modeled as hard chromium electroplating facilities. The 1,219 model pla nts included in this data set are substantially higher than the 790 hard chromium facilities that we estimate exist in the United States. However, because hard chromium facilities have the highest emissions among the three source categories, we made these selections as a conservative or health

protective assumption. The purpose of the residual risk standards under section 112(f) is to ensure protection of public health and the environment. Thus, we believe it is important to develop a conservative risk a nalysis and err on the side of potential overestimation of risk where we are missing data.

To represent the decorative chromium electroplating facilities, we combined two of the six groups of facilities

, decorative chromium facilities and facilities tha t perform both decorative chromium and chromium anodizing. This results in 3 37 decorative chromium facilities in this data set, which

, even when combined with the 96 decorative chromium electroplating facilities in the NEI data set, is less than the 740 f acilities that we believe exist in the industry. Because we modeled all of the unknown electroplating type facilities as the highest

- emitting hard chromium electroplating facilities, we consider this assessment to be conservative even though it appears to under

- represent decorative chromium facilities.Draft Risk Assessment for Chrome Plating Source Categ ories

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Similarly, the last of the six groups are all known chromium anodizing facilities. This group includes 73 facilities, and when combined with the seven chromium anodizing facilities in the NEI data set, sti ll represents only about a third of the 240 facilities chromium anodizing facilities. Again, we believe this is conservative because those facilities not modeled as chromium anodizing plants were modeled as the higher

- emitting hard chromium facilities in the analysis.

To perform the risk assessment, we needed to establish estimated emissions for each of the electroplating and anodizing types. To ensure that we did not underestimate cancer risk to the most exposed individual, we originally planned to use the large plant emission factors that we had developed for the original MACT standard s to represent all model plants for each type of chromium electroplating processing. In reviewing available emissions data, we found that while the large plant emission factors adequately represent the average chromium emissions from known large decorative chromium electroplating and large chromium anodizing facilities, they are not representative of the average chromium emissions from large hard chromium electroplating f acilities.

The emission factor for large hard chromium electroplating developed as part of the model plant analysis for the original MACT standard s was 35.3 pounds per year (lbs/yr). However, in comparing this emission factor to available emissions dat a for individual facilities

, we find that this emissions factor is unrealistically high and does not represent the average level of emissions for large facilities as we would expect to see under the current MACT standard s

. As explained more fully in "Mode l Plant Data Used to Estimate Risk from Chromium Electroplating Sources

, " [ 25 ] based on the large model plant design flow rate and operating hours, a large hard chromium model plant operating at the MACT emission limit of 0.015 milligrams per dry standard c ubic meter (mg/dscm) would emit a maximum of only 23.6 lbs/yr of chromium compounds. Moreover, the available data on actual emissions for hard chromium electroplating plants indicate there are only four plants with annual emissions greater than 10 lbs/yr. As a result, we determined that the large size model plant emissions factor, as defined for the original MACT standard, is not representative of existing large hard chromium electroplating facilities on a nationwide basis. However, the emission factor

a ssociated with a medium size hard chromium electroplating model plant (9.26 lbs/yr) falls between the 90th percentile (8.04 lbs/yr) and the 95th percentile (11.6 lbs/yr) of the available emissions data for hard chromium electroplating facilities. Because this emission factor is representative of the emissions from large facilities, the emissions factor of 9.26 lbs/yr was used to represent current large hard chromium electroplating facilities. Thus, for purposes of this residual risk review, we refer to 9. 26 lbs/yr as the emissions factor for a "large" hard chromium electroplating facility.

We believe the approach of using the ―large‖ facility emissions factor to represent all facility sizes is reasonable to ensure that we did not underestimate maximum i ndividual cancer risk. Although we believe that only a small percentage of the facilities are large, we recognize that we do not have emissions data for approximately 90% of the sources. Thus, by assuming all sources are large, we have ensured that we wi ll not underestimate the maximum individual risk.Draft Risk Assessment for Chrome Plating Source Categ ories

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For hard chromium electroplating, the model plant emission factors for small, medium, and large facilities range from 0.55 to 9.26 lbs/yr. While we expect only 10 percent of the facilities to be large based on the distribution of model plant sizes developed for the MACT standard, we used the emissions factor for a large facility (9.26 lbs/yr) for all of the 1,219 facilities that we considered as hard chromium electroplating facilities. Similarly, for d ecorative chromium electroplating, the emission factors for small, medium, and large facilities are 0.065, 0.27, and 2.65 lbs/yr, respectively, and the large facility emissions factor was used in the risk assessment for decorative chromium. For the decora tive chromium category, we estimate that only five percent of the facilities are large, based upon the distribution of decorative chromium plants nationwide when the original MACT standards

w ere developed. Finally, for chromium anodizing, the emission fac tor for small facilities is 0.036 lbs/yr and for large facilities is 0.44 lbs/yr. The large facility emissions factor (0.44 lbs/yr) was used in the conservative analysis for all of the anodizing facilities even though we estimate that only 25 percent are large.

Population risk indicators can be greatly overstated when highly conservative emission estimates are applied to every facility in the source category. Recognizing this fact, we performed a supplemental analysis to assess the sensitivity of our p opulation risk estimates. Thus, as described further below, the supplemental analysis was performed to understand the degree to which the risk might be overstated

. For the supplemental analysis, we assigned unique emission factors to each of the 6 groups of facilities in our 1,629 facility data set. These emission factors were developed to better estimate the average emissions for all of the sources within each group. The new emission factors are:

• 2.24 lbs/yr for known hard chromium electroplating fac ilities ;

• 0.225 lbs/yr for known decorative chromium electroplating facilities ;

• 0.137 lbs/yr for known chromium anodizing facilities ;

• 1.23 lbs/yr for facilities with combinations of hard chromium electroplating and either decorative electroplating or anodizing ;

• 0.181 lbs/yr for facilities with combinations of decorative electroplating and anodizing ; and

• 1.11 lbs/yr for facilities where the type of process (electroplating or anodizing) is unknown.

These weighted average emission factors account for the plant type (hard chromium electroplating, decorative chromium electroplating, or chromium anodizing) and the distribution of plant sizes (large, medium, or small). For example, the average emissions factor for hard chromium electroplating (2.24 lb s/yr) is the weighted average of the model plant emission factors for large plants (10 percent of plants at 9.26 lbs/yr per plant); medium plants (20 percent of plants at 4.63 lbs/yr per plant, and small plants (70 percent of plants at 0.55 lbs/yr per plan t). This distribution of plant sizes is based on actual data collected during development of the original MACT rule. We have no reason to believe the distribution of facility sizes has changed significantly since then.

The uncertainties associated wit h both the conservative analysis and the supplemental analysis include the estimated distribution of plant types and sizes as well as the facility emissionsDraft Risk Assessment for Chrome Plating Source Categ ories

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factors. Although the types of plants used in the both analyses are based on a variety of reliable sources, including ICR responses for the Plating and Polishing MACT standards

, trade association data, data from State agencies, and information from websites, we were unable to identify the plant type for nearly half of the data set. For those plants of unknown type, we used the highest emissions factor, which corresponds to a large hard chromium plant, in the conservative analysis. For the supplemental analysis, we developed an emissions factor using a weighted average across all plant types and sizes.

In all the data sets, chromium compounds account for all the HAP emissions from the chromium electroplating and chromium anodizing source categories. For the h ard c hromium

e lectroplating source category, in the NEI data set, chromium VI compounds accoun t for 98 percent of the emissions, with chromium III and chromium trioxide compounds comprising the remaining HAP. Here, we made the conservative assumption that 100 percent of the emissions are chromium VI compounds. For the d ecorative c hromium e lectrop lating source category, in the NEI data set, chromium VI compounds account for 94 percent of the emissions, with chromium III and chromium trioxide compounds comprising the remaining HAP. Again, we made the conservative assumption that 100 percent of the emissions are chromium VI compounds. For the c hromium a nodizing source category, in the NEI data set, chromium VI compounds account for 99 percent of the emissions with chromium III compounds comprising the remaining HAP. In this case, we also made the c onservative assumption that 100 percent of the emissions are chromium VI compounds.

Table s 3.1

- 1 through 3.1

- 6 summarize the estimated emissions and health risks for each source category for the conservative analysis

. Table 3.1

- 7 summarizes the populat ion risk estimates for the conservative and supplemental analyses.

Table 3.1

- 1 Summary of Emissions from the Hard Chromium Electroplating Source Category a

HAP NPRM

Emissions (tpy) Number of

Facilities in the dataset Prioriti zed Inhalation Dose

- Response Value Identified by OAQPS b
PB

HAP ? Unit Risk Estimate for Cancer? Reference

Concentration for Chronic Non

- cancer ? Health

Benchmark Values for Acute Non

cancer ? Chromium III Compounds 0.0008 48

Chromium VI Compounds 5. 7 1,2 8 2 Y

Chromium Trioxide (VI), chromic acid mist 0.0003 1 Y

a This summary combines emissions data based on site

- specific data and model plant data. b Specific dose

- response values for each chemical are identified on EPA’s Technology Transfe r Network website for air toxics
at http://www.epa.gov/ttn/atw/toxsource/summary.html and are available in Appendix 5 of the Development of Preliminary Risk Estimates for Source Categories Previously Subjected to Technology

- based Standards document.Draft Risk Assessment for Chrome Plating Source Categories

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Table 3.1

- 2 Summary of Source Category Level Risks for Hard Chromium Electroplating a Result HAP “Drivers” Facilities in Source Category Number of Facilities Estimated to be Subject to MACT in Source Category 79 0 n/a

Number of Facilities Identified Modeled in NPRM Risk Assessment 1,2 82 b n/a

Cancer Risks Maximum Individual Lifetime Cancer Risk (in 1 million) from any Facility in the Category 70 Chromium compo unds

Number of Facilities with Maximum Individual Lifetime Cancer Risk: Greater than or equal to 100 in 1 million 0 n/a Greater than or equal to 10 in 1 million 3 42 Chromium compounds Greater than or equal to 1 in 1 million 11 75 Chromium compounds

Chronic Non

- cancer Risks Maximum Respiratory Hazard Index 0.06 Chromium compounds Number of Facilities with Maximum Respiratory Hazard Index: Greater than 1 0 n/a Acute Non

- cancer Screening Results Maximum Acute Hazard Quotient c n/a Number of Faci lities With Potential for Acute Effects c n/a Population Exposure Number of People Living Within 50 Kilometers of Facilities Modeled 22 4 ,000,000 n/a
Number of People Exposed to Cancer Risk: Greater than or equal to 1 00 in 1 million 0 n/a

Greater tha n or equal to 10 in 1 million 7 1 ,000 Chromium compounds Greater than or equal to 1 in 1 million 14, 2 00,000 Chromium compounds
Number of People Exposed to Non

- cancer Respiratory Hazard Index: Greater than 1 0 n/a Estimated Cancer Incidence (excess ca ncer cases per year) 0.8 Chromium compounds
Contribution of HAP to Cancer Incidence Chromium compounds 100%

a This summary combines the results of the assessments based on site

- specific data and model plant data.
b For those facilities for which the s ource category is unknown, we assigned them to the hard chromium electroplating source category for the purposes of assessment because those sources have the highest estimated emissions. Consequently, we modeled more hard chromium electroplating sources t han the 790 we estimate are in the source category.

c Because there are no HAP with an acute dose

- response benchmark value, no acute hazard quotients were calculated.Draft Risk Assessment for Chrome Plating Source Categories

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Table 3.1

- 3 Summary of Emissions from the Decorative Ch romium Electroplating Source Category a

HAP NPRM

Emissions (tpy) Number of

Facilities in the data set Prioritized Inhalation Dose

- Response Value Identified by OAQPS b
PB

HAP ? Unit Risk Estimate for Cancer? Reference

Concentration for Chronic Non

- cancer ? Health

Benchmark Values for Acute Non

cancer ? Chromium III Compounds 0.002 3 8

Chromium VI Compounds 0.4 3 4 33 Y

Chromium Trioxide (VI), chromic acid mist 0.00002 1 Y

a This summary combines emissions data based on site

- specific data and m odel plant data. b Specific dose

- response values for each chemical are identified on EPA’s Technology Transfer Network website for air toxics
at http://www.epa.gov/ttn/atw/toxsource/summary. html and are available in Appendix 5 of the Development of Preliminary Risk Estimates for Source Categories Previously Subjected to Technology

- based Standards document.

Table 3.1

- 4 Summary of Source Category Level Risks fo r Decorative Chromium Electroplating a Result HAP “Drivers” Facilities in Source Category Number of Facilities Estimated to be Subject to MACT in Source Category 7 4 0 n/a

Number of Facilities Identified Modeled in NPRM Risk Assessment 4 33 b n/a

Cancer Ri sks Maximum Individual Lifetime Cancer Risk (in 1 million) from any Facility in the Category 70 Chromium compounds

Number of Facilities with Maximum Individual Lifetime Cancer Risk: Greater than or equal to 100 in 1 million 0 n/a Greater than or equ al to 10 in 1 million 5 8 Chromium compounds Greater than or equal to 1 in 1 million 301 Chromium compounds

Chronic Non

- cancer Risks Maximum Respiratory Hazard Index 0.06 Chromium compounds Number of Facilities with Maximum Respiratory Hazard Index: Greater than 1 0 n/a Acute Non

- cancer Screening Results Maximum Acute Hazard Quotient c n/a Number of Facilities With Potential for Acute Effects c n/a Population ExposureDraft Risk Assessment for Chrome Plating Source Categories

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Table 3.1

- 4 Summary of Source Category Level Risks fo r Decorative Chromium Electroplating a Result HAP “Drivers” Number of People Living Within 50 Kilometers of Facilities Modeled 1 66 ,000,000 n/a
Number of People Exposed to Cancer Risk: Greater than or equal to 100 in 1 million 0 n/a Greater than or equal to 10 in 1 million 4

, 0 00 Chromium compounds Greater than or equal to 1 in 1 million 3 9 0,000 Chromium compounds
Number of People Expos ed to Non

- cancer Respiratory Hazard Index: Greater than 1 0 n/a Estimated Cancer Incidence (excess cancer cases per year) 0. 0 8 Chromium compounds
Contribution of HAP to Cancer Incidence Chromium compounds 100%

a This summary combines the results o f the assessments based on site

- specific data and model plant data.
b For those facilities for which the source category is unknown, we assigned them to the hard chromium electroplating source category for the purposes of assessment because those sources h ave the highest estimated emissions. Consequently, we modeled fewer than the 7 4 0 sources estimated to be in the decorative chromium electroplating source category.

c Because there are no HAP with an acute dose

- response benchmark value, no acute hazard quo tients were calculated.

Table 3.1

- 5 Summary of Emissions from the Chromium Anodizing Source Category a

HAP NPRM

Emissions (tpy) Number of

Facilities in the data set Prioritized Inhalation Dose

- Response Value Identified by OAQPS b
PB

HAP ? Unit Risk Estimate for Cancer? Reference

Concentration for Chronic Non

- cancer ? Health

Benchmark Values for Acute Non

cancer ? Chromium III Compounds 0.0002 4

Chromium VI Compounds 0. 0 4 80 Y

a This summary combines emissions data based on site

- specific data and model plant data. b Specific dose

- response values for each chemical are identified on EPA’s Technology Transfer Network website for air toxics
at http:/ /www.epa.gov/ttn/atw/toxsource/summary.html and are available in Appendix 5 of the Development of Preliminary Risk Estimates for Source Categories Previously Subjected to Technology

- based Standards document.

Table 3.1

- 6 S ummary of Source Category Level Risks for Chromium Anodizing a

Result HAP “Drivers” Facilities in Source Category Number of Facilities Estimated to be Subject to MACT in Source Category 2 4 0 n/aDraft Risk Assessment for Chrome Plating Source Categories

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Table 3.1

- 6 S ummary of Source Category Level Risks for Chromium Anodizing a

Result HAP “Drivers” Number of Facilities Identified Modeled in NPRM Risk Assess ment 80 b n/a

Cancer Risks Maximum Individual Lifetime Cancer Risk (in 1 million) from any Facility in the Category 5 Chromium compounds

Number of Facilities with Maximum Individual Lifetime Cancer Risk: Greater than or equal to 100 in 1 million 0 n/a Greater than or equal to 10 in 1 million 0 Chromium compounds Greater than or equal to 1 in 1 million 2 8 Chromium compounds

Chronic Non

- cancer Risks Maximum Respiratory Hazard Index 0.0 04 Chromium compounds Number of Facilities with Maximum Respira tory Hazard Index: Greater than 1 0 n/a Acute Non

- cancer Screening Results Maximum Acute Hazard Quotient c n/a Number of Facilities With Potential for Acute Effects c n/a Population Exposure Number of People Living Within 50 Kilometers of Facilities Modeled 1 0 8 ,000,000 n/a
Number of People Exposed to Cancer Risk: Greater than or equal to 100 in 1 million 0 n/a Greater than or equal to 10 in 1 million 0 Chromium compounds Greater than or equal to 1 in 1 million 2

, 7 00 Chromium compounds

Number of People Exposed to Non

- cancer Respiratory Hazard Index: Greater than 1 0 n/a Estimated Cancer Incidence (excess cancer cases per year) 0.0 03 Chromium compounds
Contribution of HAP to Cancer Incidence Chromium compounds 100%

a This summary combin es the results of the assessments based on site

- specific data and model plant data.
b For those facilities for which the source category is unknown, we assigned them to the hard chromium electroplating source category for the purposes of assessment because those sources have the highest estimated emissions. Consequently, we modeled fewer than the 24 0 sources estimated to be in the chromium anodizing source category.

c Because there are no HAP with an acute dose

- response benchmark value, no acute hazard quo tients were calculated.Draft Risk Assessment for Chrome Plating Source Categories

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Table 3.1

- 7 Chromium Electroplating and Anodizing Population Risk Inhalation Risk Assessment Results

Source Category Number of

Facilities (NEI/Model Plant) Conservative Assessment

Population at R isk Conservative

Annual C anc er I ncidence (cases per year) Supplemental Assessment Population at R isk Supplemental

Annual C ancer I ncidence (cases per year) ≥ 1

- in

- 1 M illion ≥ 10

- in

- 1

M illion ≥ 1

- in

- 1 M illion ≥ 10

- in

- 1 M illion Hard Chromium Electroplating 63/1,219 14,200,000 71,000 0.8 360,000 5,100 0.1

Decorative Chromium Electroplating 96/337 390,000 4,000 0.08 30,000 1,300 0.01

Chromium Anodizing 7/73 2,700 0 0.003 540 0 0.001



### 3.2 Risk Characterization

The results of the risk assessment for the hard chromium electroplating source category indicate the maximum lifetime individual cancer risk could be as high as 70

- in

- 1 million based on actual emissions, and as high as 90

- in

- 1 million based on allowable emissions. This maximum individual cancer risk is based on the highest risk facility out of the 63 actual facilities and the 1,219 model plants. The highest risk facility is one for which we have design a nd operating data, and we believe it is both the largest and highest emitting hard chromium electroplating facility in the United States. Thus, we conclude that this level accurately reflects the maximum individual exposure. The maximum chronic non

- cance r TOSHI value could be as high as 0.06 based on the actual emissions level, and up to 0.09 based on allowables. This value is also based on known emission levels from the largest facility in the nation.

The total estimated national cancer incidence from hard chromium electroplating facilities based on actual emission s levels is 0.8 excess cancer cases per year, or approximately one case every year for the conservative assessment. We estimate that 14.2 million people have a cancer risk greater than 1

- in

- 1 million and 71,000 people have a cancer risk of at least 10

- in

- 1 million. For the supplemental analysis , we estimate 0.1 excess cancer cases per year, or one case every 10 years. Additionally, we estimate that 360,000 people have a cancer risk greater
t han 1

- in

- 1 million and 5,100 people have a cancer risk of at least 10

- in

- 1 million.

The results of the risk assessment for the d ecorative c hromium e lectroplating source category indicate the maximum lifetime individual cancer risk could be as high as 70

- i n

- 1 million, and the maximum chronic non

- cancer TOSHI value could be as high as 0.06, based on the actual emissions level. We do not believe these values would be any higher based on allowable emissions. The total estimated national cancer incidence ba sed on actual emissions levels is 0.08 excess cancer cases per year, or approximately one case every 10 years for the conservative a nalysis . We estimate that 390,000 people have a cancer risk greater than 1

- in

- 1 million and 4,000 people have a cancer risk of at least 10

- in

- 1 million. For the supplemental analysis, we estimate 0. 0 1 excess cancer cases per year, or one case every 1 0 0 years. Additionally, we estimate that 3 0 ,000 people have a cancer risk greater than 1

- in

- 1 million and 1,3 00 people have a c ancer risk of at least 10

- in

- 1 million.Draft Risk Assessment for Chrome Plating Source Categories

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The results of the risk assessment for the c hromium a nodizing source category indicate the maximum lifetime individual cancer risk could be as high as 5

- in

- 1 million

, and the maximum chronic non

- cancer TOSHI value c ould be up to 0.004, based on the actual emissions level. We do not believe these values would be any higher based on allowable emissions. The total estimated national cancer incidence based on actual emissions levels is 0.003 excess cancer
cases per year , or approximately one case every 30 0 years. We estimate that 2

, 7 00 people have a cancer risk greater than 1

- in

- 1 million and no people have a cancer risk of at least 10

- in

- 1 million.

T he maximum individual cancer risks from all HAP emissions at facili ties that perform hard chromium electroplating, decorative chromium electroplating, and chromium anodizing are estimated to be 90

- in

- 1 million, 90

- in

- 1 million, and 20

- in

- 1 million, respectively. For the facilities where these maximum risk values occur, t he estimated proportion of the cancer risk attributable to the hard chromium electroplating, decorative chromium electroplating, and chromium anodizing processes is less than 1 percent, 7 percent, and 75 percent, respectively. The facility

- wide maximum ch ronic non

- cancer TOSHI values for facilities that include h ard

c hromium e lectroplating, d ecorative c hromium e lectroplating, and c hromium a nodizing processes are estimated to be 2, 0.8, and 0.2, respectively. At the facilities where these maximum risk valu es occur, the estimated proportion of the non

- cancer risk attributable to the h ard c hromium e lectroplating, d ecorative c hromium e lectroplating, and c hromium a nodizing source category processes is less than 1 percent for each source category.

As discussed above, there are no HAP with an acute dose

- response benchmark value emitted from the sources in these source categories . Therefore, we did not perform a quantitative risk assessment for acute exposures to these pollutants. Also, n o PB

- HAP emissions were identified from the se s ource c ategories , indicating that exposures due to non

- inhalation routes of exposure a re not significant.



### 4 General Discussion of Uncertainties and How They Have Been Addressed

While some of the preceding section s discuss ed speci fi c uncertainties unique to the source categor ies , the following includes a general discussion of unce rtainties associated with RTR
assessments

.


### 4.1 Exposure Modeling Uncertainties

Emission i nventory uncertainties were previously dis cussed in section s 2.1 and 3 .1

. We have used model plant emissions for most of the sources in the categories because of the lack of site

- specific emissions data , and we have purposely biased the emission estimates high in all of the model plants (in the conservative analysis) in ord er to ensure that we do not underestimate potential cancer risks

. The chronic exposure modeling uncertainties are considered relatively small since we are using EPA’s refined local dispersion model with reasonably representative meteorology. It is possibl e that population exposure estimates areDraft Risk Assessment for Chrome Plating Source Categories

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also biased slightly higher by not accounting for short

- or long

- term population mobility, and by neglecting processes like deposition, plume depletion, and atmospheric degradation.



### 4.2 Uncertainties in the Dose

- Res ponse Relationships

In the sections that follow, separate discussions are provided on uncertainty associated with cancer potency factors and for non

- cancer reference values. Cancer potency values are derived for chronic (lifetime) exposures. Non

- cancer reference values are generally derived for chronic exposures (up to a lifetime), but may also be derived for acute ( <24 hours), short

term (>24 hours up to 30 days), and subchronic (>30 days up to 10% of lifetime) exposure durations, all of which are deri ved based on an assumption of continuous exposure throughout the duration specified. For the purposes of assessing all potential health risks associated with the emissions included in an assessment, we rely on both chronic (cancer and non

- cancer) and
acut e (non

- cancer) benchmarks, which are described in more detail below.

Although every effort is made to identify peer

- reviewed dose

- response values for all HAPs emitted by the sources included in an assessment, some HAP have no peer

- reviewed cancer potency values or reference values for chronic non

- cancer or acute effects (inhalation or ingestion). Since exposures to these pollutants cannot be included in a quantitative risk estimate, an understatement of risk for these pollutants at environmental exposure levels is possible. As discussed above, t here are no HAP s with an acute dose

- response benchmark value in these source categories. Therefore , no acute hazard quotients were calculated

. Additionally, chronic dose

- response values for certain compounds inc luded in an assessment may be under EPA IRIS review and revised assessments may determine that these pollutants are more or less potent than currently thought. We will re

- evaluate risks if, as a result of these reviews, a dose

- response metric changes enou gh to indicate that the risk assessment may significantly mischaracterize human health risk.

Cancer assessment

The discussion of dose

- response uncertainties in the estimation of cancer risk below focuses on the uncertainties associated with the specific approach currently used by the EPA to develop cancer potency factors. In general, these same uncertainties attend the development of cancer potency factors by CalEPA, the source of peer

- reviewed cancer potency factors used where EPA

- developed values are n ot yet available. To place this discussion in context, we provide a quote from the EPA’s Guidelines for Carcinogen Risk Assessment [ 26 ] (herein referred to as Cancer Guidelines ) . ―The primary goal of EPA actions is protection of human health; accordingly, as an Agency policy, risk assessment procedures, including default options that are used in the absence of scientific data to the contrary, should be health protective.‖ The approach adopted in this document is consistent with this approach as described in the Cancer Guidelines

. For cancer endpoints EPA usually derives an oral slope factor for ingestion and a unit risk value for inhalation exposures. These values allow estimation of a lifetime probability ofDraft Risk Assessment for Chrome Plating Source Categories

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developing cancer given long

- term exposures t o the pollutant. Depending on the pollutant being evaluated, EPA relies on both animal bioassay and epidemiological studies to characterize cancer risk. As a science policy approach, consistent with the Cancer Guidelines , EPA uses animal cancer bioassays as indicators of potential human health risk when other human cancer risk data are unavailable.

Extrapolation of study data to estimate potential risks to human populations is based upon EPA’s assessment of the scientific database for a pollutant usin g EPA’s guidance documents and other peer

- reviewed methodologies. The EPA Cancer Guidelines describes the Agency’s recommendations for methodologies for cancer risk assessment. EPA believes that cancer risk estimates developed following the procedures de scribed in the Cancer Guidelines and outlined below generally provide an upper bound estimate of risk. That is, EPA’s upper bound estimates represent a ―plausible upper limit to the true value of a quantity‖ (although this is usually not a true statistica l confidence limit). 4 In some circumstances, the true risk could be as low as zero; however, in other circumstances the risk could also be greater. 5 When developing an upper bound estimate of risk and to provide risk values that do not underestimate ri sk, EPA generally relies on conservative default approaches. 6 EPA also uses the upper bound (rather than lower bound or central) estimates in its assessments, although it is noted that this approach can have limitations for some uses (e.g. priority setti ng, expected benefits analysis).

Such health risk assessments have associated uncertainties, some which may be considered quantitatively, and others which generally are expressed qualitatively. Uncertainties may vary substantially among cancer risk asses sments associated with exposures to different pollutants, since the assessments employ different databases with different strengths and limitations and the procedures employed may differ in how well they represent actual biological processes for the assess ed substance. EPA’s Risk Characterization Handbook also recommends that risk characterizations present estimates demonstrating the impact on the assessment of alternative choices, data, models and assumptions [ 27 ] . Some of the major sources of uncertainty and variability in deriving cancer risk values are described more fully below.

(1) The qualitative similarities or differences between tumor responses observed in experimental animal bioassays and those which would occur in humans is a source of
uncert ainty in cancer risk assessment. In general, EPA does not assume that tumor sites

4 IRIS glossary (www.epa.gov/NCEA/iris/help_gloss.htm).
5 The exception to this is the URE for benzene, which is considered to cover a range of values, each end of which is considered to be equally plausible, and which is based on maximum likelihood estimates.
6 According to the NRC report Science and Judgment in Risk Assessment (NRC, 1994) ―[Default] options are generic approaches, based on general scientific knowledge and p olicy judgment, that are applied to various elements of the risk

- assessment process when the correct scientific model is unknown or uncertain.‖ The 1983 NRC report Risk Assessment in the Federal Government: Managing the Process defined default option as ― the option chosen on the basis of risk assessment policy that appears to be the best choice in the absence of data to the contrary‖ (NRC, 1983a, p. 63). Therefore, default options are not rules that bind the agency; rather, the agency may depart from them in evaluating the risks posed by a specific substance when it believes this to be appropriate. In keeping with EPA’s goal of protecting public health and the environment, default assumptions are used to ensure that risk to chemicals is not underestimated (although defaults are not intended to overtly overestimate risk). See EPA 2004 An Examination of EPA Risk Assessment Principles and Practices, EPA/100/B

- 04/001 available at: http://www.epa.gov/osa/pdfs/ratf

- final.pdf.Draft Risk Assessment for Chrome Plating Source Categories

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observed in an experimental animal bioassay are necessarily predictive of the sites at which tumors would occur in humans. 7 However, unless scientific support is available to show otherwise, EPA assumes that tumors in animals are relevant in humans, regardless of target organ concordance. For a specific pollutant, qualitative differences in species responses can lead to either under

- estimation or over

- estimation of human c ancer risks.

(2) Uncertainties regarding the most appropriate dose metric for an assessment can also lead to differences in risk predictions. For example, the measure of dose is commonly expressed in units of mg/kg/d ingested or the inhaled concentrati on of the pollutant. However, data may support development of a pharmacokinetic model for the absorption, distribution, metabolism and excretion of an agent, which may result in improved dose metrics (e.g., average blood concentration of the pollutant or the quantity of agent metabolized in the body). Quantitative uncertainties result when the appropriate choice of a dose metric is uncertain or when dose metric estimates are themselves uncertain (e.g., as can occur when alternative pharmacokinetic models are available for a compound). Uncertainty in dose estimates may lead to either over or underestimation of risk.

(3) For the quantitative extrapolation of cancer risk estimates from experimental animals to humans, EPA uses scaling methodologies (relating expected response to differences in physical size of the species), which introduce another source of uncertainty. These methodologies are based on both biological data on differences in rates of process according to species size and empirical comparisons of toxicity between experimental animals and humans. For a particular pollutant, the quantitative difference in cancer potency between experimental animals and humans may be either greater than or less than that estimated by baseline scientific scaling p redictions due to uncertainties associated with limitations in the test data and the correctness of scaled estimates.

(4) EPA cancer risk estimates, whether based on epidemiological or experimental animal data, are generally developed using a benchmark dose (BMD) analysis to estimate a dose at which there is a specified excess risk of cancer (a POD). Statistical uncertainty in developing a POD using a benchmark dose (BMD) approach is generally addressed though use of the 95% lower confidence limit on t he dose at which the specified excess risk occurs (the BMDL), decreasing the likelihood of understating risk. EPA has generally utilized the multistage model for estimation of the BMDL using cancer bioassay data (see further discussion below).

(5) Extrap olation from high to low doses is an important, and potentially large, source of uncertainty in cancer risk assessment. EPA uses different approaches to low dose risk assessment (i.e., developing estimates of risk for exposures to environmental doses of a n agent from observations in experimental or epidemiological studies at higher dose) depending on the available data and understanding of a pollutant’s mode of action (i.e., the manner in which a pollutant causes cancer). EPA’s Cancer Guidelines express a preference for the use of reliable, compound

- specific, biologically

- based risk models when feasible; however, such models are rarely available. The mode of action for a pollutant (i.e., the manner in which a

7 Per the EPA Cancer Guidelines: ―T he default option is that positive effects in animal cancer studies indicate that the agent under study can have carcinogenic potential in humans.‖ and ―Target organ concordance is not a prerequisite for evaluating the implications of animal study results for humans.‖Draft Risk Assessment for Chrome Plating Source Categories

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pollutant causes cancer) is a key consideratio n in determining how risks should be estimated for low

- dose exposure. A reference value is calculated when the available mode of action (MOA) data show the response to be nonlinear (e.g., as in a threshold response). A linear low

- dose (straight line from POD) approach is used when available mode of action data support a linear (e.g., nonthreshold response) or as the most common default approach when a compound’s mode of action is unknown. Linear extrapolation can be supported by both pollutant

- specific d ata and broader scientific considerations. For example, EPA’s Cancer Guidelines generally consider a linear dose

- response to be appropriate for pollutants that interact with DNA and induce mutations. Pollutants whose effects are additive to background bi ological processes in cancer development can also be predicted to have low

- dose linear responses, although the slope of this relationship may not be the same as the slope estimated by the straight line approach.

EPA most frequently utilizes a linear low

- dose extrapolation approach as a baseline science

policy choice (a ―default‖) when available data do not allow a compound

- specific determination. This approach is designed to not underestimate risk in the face of uncertainty and variability. EPA believe s that linear dose

- response models, when appropriately applied as part of EPA’s cancer risk assessment process, provide an upper bound estimate of risk and generally provide a health protective approach. Note that another source of uncertainty is the char acterization of low

- dose nonlinear, non

- threshold relationships. The National Academy of Sciences has encouraged the exploration of sigmoidal type functions (e.g., log

- probit models) in representing dose response relationships due to the variability in re sponse within human populations. A recent National Research Council (NRC) report [ 28 ] suggests that models based on distributions of individual thresholds are likely to lead to sigmoidal

- shaped dose

- response functions for a population. This report notes s ources of variability in the human population: ―One might expect these individual tolerances to vary extensively in humans depending on genetics, coincident exposures, nutritional status, and various other susceptibility factors...‖ Thus, if a distribut ion of thresholds approach is considered for a carcinogen risk assessment, application would depend on ability of modeling to reflect the degree of variability in response in human populations (as opposed to responses in bioassays with genetically more uni form rodents). Note also that low dose linearity in risk can arise for reasons separate from population variability: due to the nature of a mode of action and additivity of a chemical’s effect on top of background chemical exposures and biological
process es.

As noted above, EPA’s current approach to cancer risk assessment typically utilizes a straight line approach from the BMDL. This is equivalent to using an upper confidence limit on the slope of the straight line extrapolation. The impact of the choi ce of the BMDL on bottom line risk estimates can be quantified by comparing risk estimates using the BMDL value to central estimate BMD values, although these differences are generally not a large contributor to uncertainty in risk assessment (Subramaniam et

. al., 2006) [ 29 ] . It is important to note that earlier EPA assessments, including the majority of those for which risk values exist today, were generally developed using the multistage model to extrapolate down to environmental dose levels and did not i nvolve the use of a POD. Subramaniam et

. a l

. (2006) also provide comparisons indicating that slopes based on straight line extrapolation from a POD do notDraft Risk Assessment for Chrome Plating Source Categories

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COMMENT, DO NOT CITE O R QUOTE 30

show large differences from those based on the upper confidence limit of the multistage model.

(6) Cancer risk estimates do not generally make specific adjustments to reflect the variability in response within the human population

— resulting in another source of uncertainty in assessments. In the diverse human population, some individuals are likely t o be more sensitive to the action of a carcinogen than the typical individual, although compound

- specific data to evaluate this variability are generally not available. There may also be important life stage differences in the quantitative potency of carc inogens and, with the exception of the recommendations in EPA’s Supplemental Cancer Guidance for carcinogens with a mutagenic mode of action, risk assessments do not generally quantitatively address life stage differences. However, one approach used commo nly in EPA assessments that may help address variability in response is to extrapolate human response from results observed in the most sensitive species and sex tested, resulting typically in the highest URE which can be supported by reliable data, thus s upporting estimates that are designed not to underestimate risk in the face of uncertainty and variability.

Chronic non - cancer assessment

Chronic non

- cancer reference values represent chronic exposure levels that are intended to be health

- protective. Tha t is, EPA and other organizations which develop non

- cancer reference values (e.g., the Agency for Toxic Substances and Disease Registry

– ATSDR) utilize an approach that is intended not to underestimate risk in the face of uncertainty and variability. Whe n there are gaps in the available information, uncertainty factors (UFs) are applied to derive reference values that are intended to be protective against appreciable risk of deleterious effects

. Uncertainty factors are commonly default values 8 e.g., fact ors of 10 or 3, used in the absence of compound

- specific data; where data are available, uncertainty factors may also be developed using compound

- specific information. When data are limited, more assumptions are needed and more default factors are used. Thus there may be a greater tendency to overestimate risk

— in the sense that further study might support development of reference values that are higher (i.e., less potent) because fewer default assumptions are needed. However, for some pollutants it is po ssible that risks may be underestimated.

For non

- cancer endpoints related to chronic exposures, EPA derives a Reference Dose (RfD) for exposures via ingestion, and a Reference Concentration (RfC) for inhalation exposures.

8 According to the NRC report Science and Judgment in Risk Assessment (NRC, 1994) ―[Default] options are generic approaches, based on general scientific knowledge and policy judgment, that are applied to various elements of the risk

- assessmen t process when the correct scientific model is unknown or uncertain.‖ The 1983 NRC report Risk Assessment in the Federal Government: Managing the Process defined default option as ―the option chosen on the basis of risk assessment policy that appears to b e the best choice in the absence of data to the contrary‖ (NRC, 1983a, p. 63). Therefore, default options are not rules that bind the agency; rather, the agency may depart from them in evaluating the risks posed by a specific substance when it believes thi s to be appropriate. In keeping with EPA’s goal of protecting public health and the environment, default assumptions are used to ensure that risk to chemicals is not underestimated (although defaults are not intended to overtly overestimate risk). See EPA 2004 An examination of EPA Risk Assessment Principles and Practices, EPA/100/B

- 04/001 available at: http://www.epa.gov/osa/pdfs/ratf

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These values provide an estimate (with uncertainty spanning perhaps an order of magnitude) of daily oral exposure (RfD) or of a continuous inhalation exposure (RfC) to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious eff

ects during a lifetime. 9 To derive values that are intended to be ―without appreciable risk,‖ EPA’s methodology relies upon an uncertainty factor (UF) approach [ 30 ],[ 31 ] which includes consideration of both uncertainty and variability.

EPA begins by eval uating all of the available peer

- reviewed literature to determine non

cancer endpoints of concern, evaluating the quality, strengths and limitations of the available studies. EPA typically chooses the relevant endpoint that occurs at the lowest dose, ofte n using statistical modeling of the available data, and then determines the appropriate point of departure (POD) for derivation of the reference value. A POD is determined by (in order of preference): (1) a statistical estimation using the benchmark dose (BMD) approach; (2) use of the dose or concentration at which the toxic response was not significantly elevated (no observed adverse effect level

— NOAEL); or (3) use of the lowest observed adverse effect level (LOAEL).

A series of downward adjustments usi ng default UFs is then applied to the POD to estimate the reference value

, [ 32 ]. W hile collectively termed ―UFs‖, these factors account for a number of different quantitative considerations when utilizing observed animal (usually rodent) or human toxicity d ata in a risk assessment. The UFs are intended to account for: (1) variation in susceptibility among the members of the human population (i.e., inter

- individual variability); (2) uncertainty in extrapolating from experimental animal data to humans (i.e., interspecies differences); (3) uncertainty in extrapolating from data obtained in a study with less

- than

- lifetime exposure (i.e., extrapolating from subchronic to chronic exposure); (4) uncertainty in extrapolating from a LOAEL in the absence of a NOAEL; a nd (5) uncertainty when the database is incomplete or there are problems with applicability of available studies

. When scientifically sound, peer

- reviewed assessment

- specific data are not available, default adjustment values are selected for the individua l UFs. For each type of uncertainty (when relevant to the assessment) , EPA typically applies an UF value of 10 or 3 with the cumulative UF value leading to a downward adjustment of 10

- 3000 fold from the selected POD. An UF of 3 is used when the data do no t support the use of a 10

- fold factor. If an extrapolation step or adjustment is not relevant to an assessment (e.g., if applying human toxicity data and an interspecies extrapolation is not required) the associated UF is not used. The major adjustment s teps are described more fully below.

1) Heterogeneity among humans is a key source of variability as well as uncertainty. Uncertainty related to human variation is considered in extrapolating doses from a subset or smaller

- sized population, often of one sex or of a narrow range of life stages (typical of occupational epidemiologic studies), to a larger, more diverse population. In the absence of pollutant

- specific data on human variation, a 10

- fold UF is used to account for uncertainty associated with h uman variation. Human variation may be larger or smaller; however, data to examine the potential magnitude of human variability are often unavailable. In some situations, a smaller UF of 3 may be applied to reflect a known lack of significant variability among humans.

9 See IRIS glossaryDraft Risk Assessment for Chrome Plating Source Categories

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2) Extrapolation from results of studies in experimental animals to humans is a necessary step for the majority of chemical risk assessments . When interpreting animal data, the concentration at the POD (e.g. NOAEL, BMDL) in an animal mode l (e.g. rodents) is extrapolated to estimate the human response. While there is long

- standing scientific support for the use of animal studies as indicators of potential toxicity to humans , there are uncertainties in such extrapolations. In the absence o f data to the contrary, the typical approach is to use the most relevant endpoint from the most sensitive species and the most sensitive sex in assessing risks to the average human. Typically

, compound specific data to evaluate relative sensitivity in hum ans versus rodents are lacking, thus leading to uncertainty in this extrapolation. Size

- related differences (allometric relationships) indicate that typically humans are more sensitive than rodents when compared on a mg/kg/day basis. The default choice o f 10 for the interspecies UF is consistent with these differences. For a s pecific chemical, differences in species responses may be greater or less than this value

. Pharmacokinetic models are useful to examine species differences in pharmacokinetic
proce ssing and associated uncertainties; however, such dosimetric adjustments are not always possible. Information may not be available to quantitatively assess toxicokinetic or toxicodynamic differences between animals and humans, and in many cases a 10

- fold UF (with separate factors of 3 for toxicokinetic and toxicodynamic components) is used to account for expected species differences and associated uncertainty in extrapolating from laboratory animals to humans in the derivation of a reference value. If inf ormation on one or the other of these components is available and accounted for in the cross

- species extrapolation, a UF of 3 may be used for the remaining component.

3) In the case of reference values for chronic exposures where only data from shorter d urations are available (e.g., 90

- day subchronic studies in rodents) or when such data are judged more appropriate for development of an RfC, an additional UF of 3 or 10

- fold is typically applied unless the available scientific information supports use of a different value.

4) Toxicity data are typically limited as to the dose or exposure levels that have been tested in individual studies; in an animal study, for example, treatment groups may differ in exposure by up to an order of magnitude. The preferred approach to arrive at a POD is to use BMD analysis; however, this approach requires adequate quantitative results for a meaningful analysis, which is not always possible. Use of a NOAEL is the next preferred approach after BMD analysis in determining a P OD for deriving a health effect reference value. However, many studies lack a dose or exposure level at which an adverse effect is not observed (i.e., a NOAEL is not identified). When using data limited to a LOAEL, a UF of 10 or 3

- fold is often applied.

5) The database UF is intended to account for the potential for deriving an underprotective RfD/RfC due to a data gap preventing complete characterization of the chemical’s toxicity. In the absence of studies for a known or suspected endpoint of concern , a UF of 10 or 3

- fold is typically applied.Draft Risk Assessment for Chrome Plating Source Categories

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### 5 References

1

. US EPA, 2006. Emission Standards for Hazardous Air Pollutants

. http://www .epa.gov/ttn/atw/mactfnlalph.html

.
2

. US EPA, 2009. Risk and Technology Review (RTR) Risk Assessment Methodologies: For Review by the EPA’s Science Advisory Board with Case Studies

– MACT I Petroleum Refining Sources and Portland Cement Manufacturing

. EPA

- 452/R

- 09

- 006

. http://www.epa.gov/ttn/atw/rrisk/rtrpg.html.

3

. US EPA, 2005. Revision to the Guideline on Air Quality Models: Adoption of a Preferred General Purpose (Flat and Complex Terrain) Dispersion Model and Other Revisions; Final Rule. 40 CFR Part 51. http://www.epa.gov/EPA

- AIR/2005/November/Day

- 09/a21627.htm

4

. US EPA, 2004. Users’ guide for the AMS/EPA regulatory model

– AERMOD. EPA

- 454/B

03

- 001

. http://www.epa.gov/scram001/7thconf/aermod/aermodugb.pdf

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5

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. Vizuete, T

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, H

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. Kim, M

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, and M

. Symons , 2004. Variable industrial VOC e missions and their impact on ozone formation in the Houston Galveston Area. Final Report: Texas Environmental Research Consortium Project H

- 13. http://files.h arc.edu/Projects/AirQuality/Projects/H013.2003/H13FinalReport.pdf

6

. US EPA, 1996, 1999, 2002, 2005. National

- Scale Air Toxics Assessments (NATA), Technology Transfer Network Air Toxics web site: http://www.epa.gov/airtoxics/natamain/

.
7

. US EPA, 2004. A ir Toxics Risk Assessment Reference Library, Volume 1. EPA

- 453

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- 001A. http://www.epa.gov/ttn/fera/risk_atra_vol1.html.

8

. US EPA, 2005. Table 1. Prioritized Chronic Dose

- Response Values (2/28/05). Office of Air Quality Planning and Standards. http://www.epa.gov/ttn/atw/toxsource/table1.pdf

9

. US EPA, 2006. Integrated Risk Information System. http://www.epa.gov/iris/index.html

.
10

. US Agency for Toxic Substances and Disease Registry. 2006. Minimum Risk Levels (MRLs) for Hazardous Substances. http://www.atsdr.cdc.gov/mrls/index.html

.
11

. US EPA, 1994

. US Environmental Protect ion Agency. Methods for Derivation of Inhalation Reference Concentrations and Application of Inhalation Dosimetry. EPA/600/8

- 90/066F. Office of Research and Development. Washington, DC: U.S.EPA.

12

. NRC, 1994. National Research Council. Science and Judgmen t in Risk Assessment. Washington, DC: National Academy Press.

13

. CA Office of Environmental Health Hazard Assessment, 2005. Chronic Reference Exposure Levels Adopted by OEHHA as of December 2008. http://www.oehha.ca.gov/air/chronic_rels/AllChrels.html

.

14

. CA Office of Environmental Health Hazard Assessment, 2005. Technical Support DocumentDraft Risk Assessment for Chrome Plating Source Categories

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COMMENT, DO NOT CITE O R QUOTE 34

for Describing Available Cancer Potency Factors, May 2005

. http://www.oehha.ca.gov/air/hot_spots/may2005tsd.html

.
15

. US EPA, 1995. Guidance for Risk Characterization. Science Policy Council. http://www.epa.gov /OSA/spc/pdfs/rcguide.pdf

.
16

. US EPA, 2000. Risk Characterization Handbook. EPA 100

- B

- 00

- 002.

17

. US EPA, 2002. EPA’s Guidelines for Ensuring and Maximizing the Quality, Objectivity, Utility, and Integrity of Information Disseminated by the Environmental Protection Agency. EPA Office of Environmental Information. EPA/260R

- 02

- 008

. http://www.epa.gov/quality/informationguidelines/documents/EPA_InfoQua lityGuidelines.pdf

18

. US EPA, 2006. Performing risk assessments that include carcinogens described in the Supplemental Guidance as having a mutagenic mode of action. Science Policy Council Cancer Guidelines Implementation Workgroup Communication II: Mem o from W.H. Farland dated 14 June 2006. http://www.epa.gov/osa/spc/pdfs/CGIWGCommunication_II.pdf

19

. US EPA, 2005. Supplemental guidance for assessing early

- life exposure to carcin ogens. EPA/630/R

- 03003F. http://www.epa.gov/ttn/atw/childrens_supplement_final.pdf

.

20

. US EPA, 2005. Science Policy Council Cancer Guidelines Implementation Workgroup Communicati on I: Memo from W.H. Farland dated 4 October 2005 to Science Policy Council. http://www.epa.gov/osa/spc/pdfs/canguid1.pdf

21

. US EPA, 1986. Guidelines for the Health Risk Assessment of Che mical Mixtures. EPA

- 630

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- 002. http://www.epa.gov/NCEA/raf/pdfs/chem_mix/chemmix_1986.pdf

22

. US EPA, 2000. Supplementary Guidance for Conducting Health Risk Assessment of C hemical Mixtures. EPA

- 630/R

- 00

- 002. http://www.epa.gov/ncea/raf/pdfs/chem_mix/chem_mix_08_2001.pdf

.
23 RTI International, 2010. Memorandum from R. Marinshaw, RTI Internation al, to P. Mulrine, US EPA. Actual vs. Allowable Emissions for Chromium Electroplating Plants

- Emission Standards Technical Support and Post Promulgation Activities.

24 US EPA, 1993. Chromium Emissions from Chromium Electroplating and Chromic Acid Anodiz ing Operations

-- Background Information for Proposed Standards, Volume I. 453/R

93

- 030a. http://www.epa.gov/ttn/atw/chrome/chromepg.html#RULE

25 RTI International, 2010. Memorandum from R. Marinshaw, RTI International, to P. Mulrine, US EPA. Model Plant Data Used to Estimate Risk from Chromium Electroplating Sources

. 26

. US EPA, 2005. Guidelines for Carcinogen Risk Assessment (2005). U.S. Environmental Protection Agency, Washington, DC, EPA/630/P

- 03/001F, 2005. http://cfpub.epa.gov/ncea/raf/recordisplay.cfm?deid=116283

27

. US EPA, 2000

. Risk Characterization Handbook. EPA 100

- B

- 00

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