09/10/09 

 

1 of 24 

Schools Air Toxics Monitoring Activity (2009) 

Uses of Health Effects Information in Evaluating Sample Results ________________________________________________________________________ 

1. Introduction 

 EPA has developed an initiative to implement Administrator Jackson’s commitment to 

assess potentially elevated ambient (outdoor) concentrations of air toxics at some of our 

nation’s schools (generally described at www.epa.gov/schoolair). This monitoring activity is 

described in the project monitoring plan and quality assurance project plan (available on the 

schools web site: http://www.epa.gov/schoolair/techinfo.html). This monitoring is targeting 

key hazardous air pollutants (HAPs or air toxics) at each site (i.e., those identified by either 

the Risk-Screening Environmental Indicators (RSEI) Model or the National Air Toxics 

Assessments (NATA) national-scale assessment as the local risk drivers, or by information 

provided by EPA, Regions and States). Key pollutants differ among the monitored schools 

based on what this background information indicated regarding pollutant emissions, and 

potential air concentrations and risk in each area. The monitoring data and other information 

collected for each school during this initiative will allow us to assess levels of the key 

pollutantsa

 occurring at these sites including the potential for contributions from nearby 

sources. 

The ambient air monitoring data collected at each site (along with other site- or sourcespecific information as well as information on typical regional or national levels) will be used 

to facilitate decisions regarding priority for and type of any follow-up actions near each 

school. In considering the pollutants monitored at each site and potential follow-up actions, 

EPA recognizes that data from ongoing monitoring programs (e.g., monitoring at the 

National Air Toxics Trends Sites or NATTS) indicate that levels of some pollutants are 

commonly higher in urban areas than elsewhere. While in some locations these pollutants 

(e.g., benzene and acrolein) may be associated with specific industrial facilities, they are also 

associated with mobile source emissions and are commonly occurring at sites near urban 

areas or near large roadways and other transportation facilities 

(http://www.epa.gov/otaq/toxics.htm). Accordingly, EPA has taken several actions to reduce 

mobile source emissions nationally and maintains several ongoing programs aimed at 

achieving reductions in ambient air concentrations of these hazardous air pollutants from 

mobile sources (http://www.epa.gov/otaq/toxics.htm#epamsat). In addition to these national 

steps that are expected to reduce concentrations on a local basis as they are implemented, 

there are steps that individuals and communities can take to achieve additional reductions 

(http://www.epa.gov/otaq/consumer.htm). 

 

a

 At each site, monitoring has been targeted to get information on the key HAPs about which the background 

information indicated a potential for concern. In analyzing air samples for these key pollutants, samples are 

also being analyzed for some additional pollutants that are routinely included in the analytical methods for the 

key pollutants. While analysis of the dataset collected for each school will focus attention on the key HAPs, 

results for other HAPs monitored at the school will also be reviewed consistent with the approach described in 

this document. 
 09/10/09 

 

2 of 24 

EPA/OAQPS will evaluate the full dataset for the key pollutants at each school, in light of 

information particular to the school and its location, in order to identify the school’s priority 

for follow-up activities. That evaluation will include consideration of several analyses and 

factors. These will generally include the site-specific ambient air measurements along with 

other site and source-specific information, as well as, information on typical national and 

regional levels and long-term health risk-related exposure concentrations for monitored 

pollutants. Prior to the availability of a full dataset for each location, EPA will be making 

available on the public web site (www.epa.gov/schoolair) an interim presentation, including 

individual sample measurements for key pollutants. As part of this interim presentation, 

EPA also intends to provide, as described in section 3 below, conservatively developed 

health risk-related individual sample screening levels for all key pollutants. In instances 

where individual sample concentrations occur above these sample screening levels, the 

pollutant-specific health effects information will be evaluated along with information 

concerning the sample collection and potential sources of the monitored pollutant.b

 

Additionally, for some nationally key pollutants, such as those associated with mobile 

sources, EPA may provide information on nationally common concentrations for reference. 

This document, prepared for reference by the EPA schools air toxics team, describes the 

various uses of health effects information in evaluating sample results, using screening or 

comparison levels and in further investigation of results higher than such screening or 

comparison levels. 

2. Uses of Health Effects Information 

There are several uses of health effects information for the pollutants monitored in this 

project. As sample results are received from the analytical laboratoryc

, EPA will be 

reviewing the data to identify any situations where additional attention may be appropriate to 

confirm sample results and to assess the potential for immediate health concerns. To 

facilitate the identification of sample results to receive such additional attention, we have 

developed individual sample screening levels (described below in section 3).d Any sample 

results higher than these sample screening levels will be further considered in light of 

chemical-specific information on health effects (section 4), along with information 

concerning the sample collection and potential sources of the monitored pollutant. Lastly, 

the multi-faceted analysis of the full monitoring dataset at a site, which will not entail a 

detailed risk assessment, will include consideration of projected estimates for the long-term 

average concentration of the monitored air toxics in light of health-based comparison levels. 

Accordingly, long-term comparison levels have been developed for use in the full dataset 

analysis (described below in section 5). 

 

b

 While our main focus is on the key pollutants at each school (i.e., those pollutants for which background 

information indicated emissions and potential concentrations that supported the monitoring activity), we are 

screening sample results for other pollutants monitored using individual sample screening levels and approach 

described in sections 3 and 4 below. 

c

 A quality assurance and quality control program is a component of the monitoring program that is followed by 

the sample collection team and analytical laboratory in producing sample results. 

d

 At this step we are also reviewing national levels of some air toxics in recognition of their common occurrence 

at levels of risk-related interest nationally or in some regions. These typical ambient levels are not the focus of 

nor are they otherwise discussed in this document. 
 09/10/09 

 

3 of 24 

3. Development of Individual Sample Screening Levels 

This section describes the approach employed for developing screening-level values for use 

in reviewing individual sample measurements. Prior to developing or identifying these 

screening levels, priority was given to recognition of relevant and appropriate air standards or 

regulations, such as in the case of the recently updated National Ambient Air Quality 

Standards (NAAQS) for lead. For the remaining chemicals, health risk-related sample 

screening levels were calculated using EPA risk assessment guidance and precedents. The 

objective in developing individual sample screening levels for these air toxics is to identify 

air concentrations to which continuous exposures over a few days would be unlikely to be 

associated with appreciable risk of adverse health effects. These values are intended to help 

EPA to identify contaminants for which closer attention may be appropriate to confirm 

sample results and to assess the potential for any immediate health concerns. These sample 

screening values are considered reasonably conservative for the presumed exposure scenario 

at hand, such that individual results above these concentrations should not be presumed to be 

cause for alarm. These sample screening levels are not intended to define clean up or action 

levels. 

As the ambient air samples are collected over a 24-hour period, the exposure duration of 

interest in developing individual sample screening levels is on the order of a few days (shortterm). As described below, established reference concentrations, dose-response assessments 

or other similar benchmarks for a time period of this length are not available for all of the 

monitored pollutants. In identifying surrogate exposure levels for use in lieu of short-term 

values, we have chosen to consider longer-term (intermediate) screening levels for which the 

exposure duration extends from weeks to a year. These intermediate screening levels have 

been developed consistent with the use of such levels in the 2005-06 monitoring conducted in 

association with activities in response to hurricane Katrina in the Louisiana, Mississippi, and 

Alabama.e

In summary, the individual sample screening levels presented here represent short-term (or 

intermediate) duration inhalation exposure estimates that are unlikely to be associated with 

appreciable risk of adverse health effects for continuously exposed populations (including 

sensitive subgroups). These levels are not designed to predict the occurrence of effects, and 

individual sample measurements greater than the screening levels do not imply an immediate 

health threat. Rather, findings of individual sample measurements above these screening 

levels will receive additional attention to confirm sample results and to assess the potential 

for any immediate health concerns (as described in section 4 below). 

At each site, monitoring has been targeted to get information on a limited set of key 

hazardous air pollutants (HAPs or air toxics)f

. These pollutants are the primary focus of our 

 

e

 Intermediate duration values were selected in the Katrina recovery monitoring activity with the presumption 

that a one-year exposure duration would conservatively and reasonably account for the potential of burning 

and/or demolition activities to go on longer than the presumed initial 3-month estimate for such activities. 

f

 Section 112(b) of the Clean Air Act identifies 189 hazardous air pollutants, three of which have subsequently 

been removed from this list. These pollutants, commonly called “air toxics” are the focus of regulatory actions 

involving stationary sources described by CAA section 112 and are distinguished from the six pollutants for 
 09/10/09 

 

4 of 24 

monitoring activities at a site and a priority for us based on our emissions, modeling and 

other information. Accordingly, the sample screening levels for the full set of these key 

pollutants are presented in the first table at the end of this section (Table 1). In analyzing air 

samples for these key pollutants, we will also be analyzing samples for some other pollutants 

(both HAPs and others) that can be economically measured at the same time. Sample 

screening levels for these additional HAPs are presented in Appendix A. Similar information 

for pollutants that are not HAPs is described in Appendix B. 

Individual sample screening levels were set for the monitored HAPs, using the following 

prioritized approach.g

 

1. In considering a sample screening level for lead, preference was given to use of the 

National Ambient Air Quality Standards. A review of the NAAQS for lead was 

completed in October 2008. The revised primary standardh

 reflects the health effects 

evidence available in that review and provides increased protection for children and 

other at-risk populations against an array of adverse health effects, most notably 

including neurological effects in children, including neurocognitive and 

neurobehavioral effects (73 FR 66964). 

2. For pollutants for which ATSDR has developed acute Minimal Risk Levels (MRLs), 

the individual sample screening levels were set to these MRLs. ATSDR defines each 

MRL as “an estimate of the daily human exposure to a hazardous substance that is 

likely to be without appreciable risk of adverse noncancer health effects over a 

specified duration of exposure” (http://www.atsdr.cdc.gov/mrls/). Acute MRLs are 

considered appropriately protective comparison levels for screening of individual 

samples in this project because they were developed to be protective of short-term 

continuous exposures lasting up to 14 days (24 hours each day). 

3. In looking for surrogates for chemicals for which no ATSDR acute MRL or similar 

duration value was available, we looked to longer- vs shorter-term duration exposure 

levels in keeping with the description that the sample screening levels be reasonably 

conservative for the presumed exposure scenario and that the exposure duration of 

interest is on the order of a few days. i Thus, for the remaining pollutants for which 

ATSDR has not established acute MRLs and for which longer-term risk-related 

exposure concentrations were available, surrogates for short-term screening levels 

were developed from longer-term risk-related exposure concentrations. The approach 

for these surrogates focuses on what are termed “intermediate” duration exposures, 

which range up to one year duration. Thus, when used in lieu of short-term values 

 which criteria and national ambient air quality standards (NAAQS) are developed as described in section 108. 

One of the criteria pollutants, lead, is also represented, as lead compounds, on the HAP list. g

 Although this project targets HAPs, the analytical methods employed include several non-HAPs, such that 

data are being generated for those pollutants as well. Although the air toxics to which EPA assigns greatest 

concern nationally are the HAPs, a health risk-related screening was also applied to the individual sample 

results for the non-HAPs. The screening levels employed for this purpose are identified in Appendix A. 

h

 The NAAQS for lead is 0.15 μg/m3 in total suspended particles, applied as an average over a 3-month period. i

 Other short-term duration exposure levels presented in OAQPS Table 2 include the California Environmental 

Protection Agency’s acute reference exposure levels, the exposure durations for which are 24 hours for most 

pollutants and somewhat shorter than that for a few. 
 09/10/09 

 

5 of 24 

these values for most pollutants are considered to inherently have an extra level of 

conservatism than would short-term values had they been available. 

The approach for deriving intermediate screening levels described here is that which 

EPA relied upon in the Hurricane Katrina ambient air monitoring activity. 

Preliminary screening values were first identified separately for (a) effects for which 

reference concentrations have been developed (usually considered to have nonlinear 

or “threshold” exposure-response relationships) and, (b) if pertinent to the pollutant, 

linear cancer risk (built upon EPA’s default carcinogen assumption, which is accepted 

in lieu of a conclusion to the contrary, of some cancer risk associated with any level 

of exposure). The final intermediate screening level is the lower of the subsequent 

two values (described in sections (a) and (b) below). 

a. To develop a preliminary screening level for “threshold” effects for these 

pollutants, the ATSDR intermediate inhalation minimal risk level was used 

(MRLinter; see http://www.atsdr.cdc.gov/mrls.html). Values for the MRLinter

are developed to be protective of exposures ranging from two weeks to a year. 

When the MRLinter was not available for a compound, a value of ten times the 

chronic Reference Concentration (RfC) or other similar valuej

 was used 

instead as an estimate of the intermediate (subchronic) comparison value. 

Specifically, the preliminary screening level (SL) for a threshold chemical (in 

the absence of a MRLinter) is:

SLthreshold = (10)(RfC)

The application of a factor of 10k is commonly used by the Superfund 

program for making decisions regarding emergency removal actions using a 

time frame with an upper bound of approximately a year (USEPA, 1997) to 

account for the fact that chronic toxicity values (e.g., RfCs) are being applied 

to the less than chronic (sub-chronic) time periods of expected exposure. 

b. For linear carcinogenic compounds, the linear cancer risk-based screening 

levels were set at concentrations for which the upper-bound lifetime 

probability of developing cancer would be one hundred-in-a-million (1x10-4), 

if exposure occurred continuously at the concentration for one year.l The one-

 

j

 After EPA IRIS chronic RfCs (referred to as “chronic RfCs” in Tables 1-3 in this document), the next source 

consulted was ATSDR chronic MRLs, then California EPA chronic Reference Exposure Levels, and lastly 

HEAST chronic RfCs. This hierarchy for identification of chronic reference concentrations is consistent with 

that used in Table 1 of OAQPS toxicity values available on the EPA web site 

(http://www.epa.gov/ttn/atw/toxsource/summary.html). Information from that table was updated as needed. k

 In recognition of the uncertainty of this approach for developing an intermediate duration screening level from 

a value derived for chronic exposures, we have deviated from this in some instances. For example, where the 

chronic RfC was set with human data and with a cumulative uncertainty factor equal to or less than 10), the 

factor of 10 was not applied and the chronic RfC was used as is. This was the case for cobalt, beryllium and 

selenium.

l

 The cancer risk level used here (1x10-4) reflects the upper bound of the Agency’s traditional acceptable risk 

range (10-4 to 10-6), which plays a role in both the hazardous air pollutant and Superfund programs. For 

example, in the 1989 setting of the “benzene NESHAP”, which has a precedent-setting role in the HAP 

program, EPA stated that an additional cancer risk (associated with air toxics emitted from a stationary source) 
 09/10/09 

 

6 of 24 

year exposure duration is consistent with the time frame of the intermediate 

MRLs. Specifically, the preliminary linear cancer risk-based screening levels 

were calculated as: 

SLcancer = (1E-04/IUR)(70) 

where the IUR is the inhalation unit risk factor (or slope), expressed as 

(μg/m3

)

-1. The IURs used in this exercise are those in the EPA OAQPS 

Toxicity Table 1 (http://www.epa.gov/ttn/atw/toxsource/summary.html).m

 

Table 1. Individual Sample Screening Levels for Key (aka “driver”) HAP Analytes. 

Analyte Individual Sample 

Screening Level1

Value from which 

Screening Level 

Derived 

Metals2 ng/m3 

Arsenic (PM10 focus) 150 (I)3 chronic REL 

Chromium-hexavalent 580 (I) IUR 

Cobalt (PM10 focus) 100 (I) chronic MRL 

Lead4-TSP The lead NAAQS is a rolling 3-month average of 

150 (I) ng/m3 lead in TSP. 

Manganese (PM10 focus) 500 (I) chronic RfC 

Nickel (PM10 focus) 200 (I) inter. MRL 

VOCs/Carbonyls μg/m3 

Acetaldehyde 90 (I) chronic RfC 

Acrolein 7 acute MRL (0.003 ppm) 

Benzene 30 acute MRL (0.009 ppm) 

1,3-Butadiene 20 (I) chronic RfC 

4,4’-methylenedianiline 15 (I) IUR 

Naphthalene 30 (I) chronic RfC 

POM-PAHs5:

Benzo(a)pyrene

Benzo(a)anthracene 

Benzo(b)fluoranthene 

Benzo(k) fluoranthene 

Chrysene 

Dibenz(a,h)anthracene 

Indeno(1,2,3-cd)pyrene

ng/m3

6,400 (I)

64,000 (I)

64,000 (I)

64,000 (I)

640,000 (I)

5,800 (I)

64,000 (I)

IUR 

“ 

“ 

“ 

“ 

“ 

“ 

Diisocyanates μg/m3 

1,6-hexamethylene diisocyanate 0.2 (I) inter. MRL 

Methylenediphenyl diisocyanate 6 (I) chronic RfC 

2,4-toluene diisocyanate 0.7 (I) chronic RfC 

 of 100-in-a-million should ordinarily be the upper end of the range of acceptability, with risks increasing above 

this benchmark becoming presumptively less acceptable under the HAP program. Additionally, in the 

Superfund program, acceptable exposure levels for known or suspected linear carcinogens are generally those 

that, using information on the relationship between dose and response, represent an excess upper-bound lifetime 

individual cancer risk between 10−4

 and 10−6 [e.g., see 40 CFR 300.430(e)(2)(i)(A)(2)]. m Where the OAQPS table on web did not represent the most current information, the information was updated. 
 09/10/09 

 

7 of 24 

 Notes for Table 1

1 Values derived for this document, or for which units conversions were performed are assigned the same 

number of significant figures as those specified in the source value. 

2 Metal samples will be of 2 different types: PM10 and total suspended particles (TSP). With the exception of 

lead (for which the NAAQS was developed with explicit recognition of non-inhalation exposure pathways), metals 

screening levels are more suited for use with the concentration of metal in particles captured in a PM10 sample. 

3The superscript (I) indicates where an intermediate duration exposure screening levels has been assigned as a 

surrogate in lieu of a short-term screening level. 

4This value for lead is the level of the NAAQS, which is in terms of a 3-month average level of lead in TSP. 

5PAHs are components of the HAP polycyclic organic matter (POM). The PAH analytes listed here are those 

which EPA has identified as carcinogens, and for which inhalation unit risk estimates are available (from the 

OAQPS Toxicity Table, per section 3.3.b above)). In assessing carcinogenicity for chemicals concluded to be 

carcinogenic by a mutagenic mode of action and for which early lifestage dose-response information is not 

available, EPA recommends use of age-dependent adjustment factors (ADAFs) which effectively increase the 

potency when applied to the first 16 years of age (USEPA, 2005). Dibenz[a,h] anthracene (DBA) and 

benzo[a]pyrene (BaP), and the other PAHs for which IURs are indexed to that of BaP are considered by EPA to 

act by mutagenic modes of action (Farland, 2006). In considering potential use of ADAFs in the context of the 

individual sample screening levels, we recognize several considerations: (1) the objective for the sample 

screening levels is a short-term exposure estimate (on the order of weeks), (2) application of EPA’s traditional 

cancer risk assessment methods to such short periods is inherently uncertain, (3) the sample screening levels 

for these PAHs are actually surrogates for short-term levels and have been derived for a 1-year exposure, (4) 

the full data analysis for each school (see section 5) will consider potential risk of chronic exposure, and (5) if in 

the calculation of these levels, we had substituted a short-term exposure duration (e.g., 2 weeks), their values 

would be increased by a factor of 20, which is more than twice the value of the highest ADAF. Thus, rather than 

implement a cancer risk calculation specific to a 2-week duration exposure, which is not generally recommended 

by EPA guidance, we have retained the 1-year values and recognize that they are appropriately protective of 

shorter-term exposures with a potential for increased early-life susceptibility. 

4. Pollutant-specific Health Effects Information 

As mentioned in the previous sections, findings of sample measurements above the 

individual sample screening levels will be given closer attention to confirm sample results, to 

assess a potential for unusual circumstances at nearby sources, and to assess the potential for 

any immediate health concerns for the exposed population. Additionally, longer-term 

concentration estimates developed in the analysis of the full set of results for a school (see 

section 5 below) that are above long-term comparison levels (particularly in the case of 

noncancer-based comparison levels) will also be given close attention. In assessing the 

potential for any health concerns regarding the reported levels, we will be considering the 

health effects and toxicity information available for that pollutant and the details associated 

with the derivation of the particular screening or comparison level, as well as the likely 

exposure circumstances at the monitored location. The type of health effects and toxicity 

information to be considered for a particular pollutant would be expected to include the type 

of effects and exposure conditions (including duration, frequency and inhalation 

concentrations) with which they are associated, as well as the confidence level and type and 

magnitude of uncertainty associated with applicable reference or toxicity values. 

Sources of information on toxicity and health effects that may be consulted include, but are 

not necessarily limited to, materials developed by: 
 09/10/09 

 

8 of 24 

 ATSDR, including their Toxicological Profiles, ToxGuidesTM, Case Studies in 

Environmental Medicine, Medical Management Guidelines for Acute Chemical 

Exposures and Public Health Statements; 

 EPA, including the OAQPS Health Effects Notebook, the OAQPS Air Toxics Risk 

Assessment library and toxicity tables, the Integrated Risk Information System, and 

technical support documents for acute exposure guideline levels; and 

 American Industrial Hygiene Association, the American Conference of Governmental 

Industrial Hygienists, the National Institute of Occupational Safety and Health and the 

Occupational Safety and Health Administration. 

5. Development of Long-term Comparison Levels 

5.1 Background and Objectives for Use of Comparison Levels

The majority of schools being monitored in this initiative were selected based on modeling 

analyses that indicated the potential for annual average air concentrations of some HAPs (air 

toxics) to be of particular concern based on approaches that are commonly used in the air 

toxics program for considering potential for long-term risk. For example, these analyses 

suggested annual average concentrations of some air toxics to be greater than long-term riskbased concentrations associated with an additional cancer risk greater than 1-in-10,000 or a 

hazard index on the order of or above 10. These long-term risk-based concentrations 

presume continuous (all-day, all-year) exposure over a lifetime. To make projections of air 

concentrations, the modeling analyses combined estimates of air toxics emissions from 

industrial, motor vehicle and other sources, with past measurements of winds, and other 

meteorological factors that can influence air concentrations, from a weather station in the 

general area. In some cases, the weather station was very close (within a few miles) but in 

other cases, it was much further away (e.g., up to 60 miles), which may contribute to quite 

different conditions being modeled than actually exist at the school. The modeling analyses 

are intended to be used to prioritize locations for further investigation. 

The primary objective of this initiative is to investigate - through monitoring air 

concentrations of the key HAPs at each school over a 2-3 month period - whether the levels 

measured and associated longer-term concentration estimates are of a magnitude, in light of 

health risk-based criteria, for which follow-up activities may need to be considered. To 

evaluate the monitoring results consistent with this objective, we developed health risk-based 

air concentrations (the long-term comparison levels described below) for each monitored 

pollutant using established EPA methodology and practices for health risk assessmentn

 and, 

in the case of cancer risk, consistent with the implied level of risk considered in identifying 

schools for monitoring. Consistent with the long-term or chronic focus of the modeling 

analyses based on which these schools were selected for monitoring, we intend to analyze the 

complete dataset of measured concentrations using routine statistical tools to derive a 95 

percent confidence interval for the estimate of longer-term average concentration for each 

 

n

 While this EPA initiative will rely on EPA methodology, practices, assessments and risk policy 

considerations, we recognize that individual state methods, practices and policies may differ and subsequent 

analyses of the monitoring data by state agencies may draw additional or varying conclusions. 
 09/10/09 

 

9 of 24 

HAP monitored at a given school. This projected range (most particularly the upper end of 

the range) will be compared to the long-term comparison levels. The analysis of the air 

concentrations will also include a consideration of the potential for cumulative multiple 

pollutant impacts in drawing conclusions regarding air toxics at each location.o

 

In drawing conclusions regarding potential follow-up activities for a particular school 

location EPA will evaluate the air quality information provided by the full monitoring 

dataset, in light of various other types of information and considerations pertinent to the air 

quality at each location. For the purposes of providing context, some quite general examples 

of key considerations and potential resulting decisions are described in Table 4 below. 

In general, where the monitoring results indicate estimates of longer-term average 

concentrations that are above the comparison levels – i.e., above the cancer-based 

comparison levels or notably above the noncancer-based comparison levels - we will 

consider the need for follow-up actions such as: 

 Additional monitoring of air concentrations and/or meteorology in the area, 

 Evaluation of potentially contributing sources to help us confirm their emissions 

and identify what options (regulatory and otherwise) may be available to us to 

achieve emissions reductions, and 

 Evaluation of actions being taken or planned nationally, regionally or locally that 

may achieve emission and or exposure reductions. An example of this would be 

the type of ubiquitous emissions from mobile sources. 

Where the monitoring data analyses do not project longer-term average concentration 

estimates above the comparison levels, we will further analyze the dataset to describe what it 

indicates in light of other criteria and information commonly used in prioritizing state, local 

and national air toxics program activities. State, local and national programs often develop 

longer term monitoring data sets in order to better characterize pollutants near particular 

sources. The 2-3 month dataset developed under this initiative will be helpful to those 

programs in setting priorities for longer term monitoring projects. The intent of this analysis 

is to make this 2-3 month monitoring dataset as useful as possible to state, local and national 

air toxics program in their longer term efforts to improve air quality nationally. To that end, 

this analysis will: 

 Describe the air toxics measurements in terms of potential longer-term 

concentrations, and, as available, compare the measurements to monitoring data 

from national monitoring programs. 

 Describe the meteorological data by considering conditions on sampling days as 

compared to those over all the days within the 2-3 month monitoring period and 

what conditions might be expected over the longer-term, as indicated, for 

example by information from a nearby weather station. 

 

o

 As this analysis of a 2-3 month monitoring dataset is not intended to be a full risk assessment, consideration of 

potential multiple pollutant impacts may differ among sites. For example, in instances where no individual 

pollutant appears to be present above its comparison level, we will also check for the presence of multiple 

pollutants at levels just below their respective comparison levels (giving a higher priority to such instances). 
 09/10/09 

 

10 of 24 

 Describe available information regarding activities and emissions at the nearby 

source(s) of interest, such as that obtained from public databases such as TRI 

and/or consultation with the local air pollution authority. 

 

5.2 Long-term Comparison Levels

The risk or hazard levels considered in interpreting modeling analysis results with regard to 

identifying schools for monitoring under this initiative (e.g., 1-in-10,000 cancer risk and 

hazard index of 1) derive from aspects of the framework for regulatory decisions in the Clean 

Air Act (CAA) residual risk program for stationary sources of air toxics (USEPA, 1999; 70 

FR 19992).p

 While the CAA identifies different criteria for different types of air sources, 

with technological feasibility being the key criterion for decisions on controlling air toxics 

from mobile sources (e.g., cars and trucks), in the risk management framework for the 

residual risk program, regulatory actions may generally be considered when estimated 

ambient concentrations from the source emissions being assessed are equal to a continuous 

lifetime exposure concentration associated with an estimated increase in lifetime cancer risk 

greater than 100-in-a-million (or 1-in-10,000). The 100-in-a-million cancer risk level is the 

approximate upper end of the range that is commonly described in EPA risk-based decision 

making (see footnote l on page 5). The lower end of the range is 1-in-a-million. 

In our analysis of the air toxics measurements at each school, we recognize two areas of 

interest. First and most importantly, as described in section 5.1 above, we are interested in 

identifying circumstances for which follow-up activities need to be considered (i.e., air 

concentrations at or above levels considered in identifying schools for monitoring under this 

initiative, such as those for which long-term exposure is associated with 100-in-a million or 

greater cancer risk). In addressing this most important area of focus, we developed long-term 

health risk-related comparison levels based on cancer risk using the 100-in-a million level of 

additional risk (see below). This is consistent with criteria that were considered in 

identifying schools for this monitoring. Secondly, as we are interested in making these 

monitoring data as useful as possible to ongoing state, local and national air toxics programs 

in their air quality improvement activities, we also intend to describe findings in light of 

other criteria that may indicate the potential for longer-term air concentrations that while 

somewhat lower, may still be of a magnitude that would inform EPA, state and local 

decision-making on risk reduction actions for air toxics more broadly. In our analyses of the 

monitoring data, we intend to also provide information useful to this second area of interest, 

such as noting how longer-term concentration estimates relate to 10% or 1% of the cancerbased comparison level. 

With regard to effects other than cancer, EPA’s residual risk program for stationary sources 

of air toxics has not established a strict regulatory decision framework. Secondly, while EPA 

develops and uses estimates of cancer risk per concentration of lifetime continuous exposure 

to carcinogenic air toxics in assessing potential cancer risk (and in deriving cancer risk-based 

 

p

 Section 112 of the Clean Air Act describes a two-step approach for regulating categories of stationary sources 

of HAPs. In the first step, EPA set technology-based standards for all categories. In the second step, EPA is 

required to assess the residual risk remaining in areas near these sources and where necessary set additional 

source standards. This second step is referred to as the residual risk program. 
 09/10/09 

 

11 of 24 

concentrations), we use a different type of tool for analyses that consider the potential for risk 

of other (noncancer) health effects. This noncancer assessment tool is the reference 

concentration (RfC) or comparable value. The RfC is a continuous inhalation estimate for 

the human population, including sensitive subgroups, that is likely to be without appreciable 

risk of adverse noncancer effects over a lifetime. The RfC is more informative with regard to 

exposures that are below it than those above it. That is, an RfC is not a direct estimator of 

risk but rather a reference point to gauge the potential for effects. Lifetime or chronic 

exposures at or below the RfC are concluded to be without significant risk of adverse effects. 

Lifetime exposures above the RfC, however, do not necessarily indicate a risk of adverse 

health effect. But with such exposures increasingly above the RfC, there is an increasing 

potential for risk of effects. This potential varies depending on the pollutant and information 

specific to that pollutant. Accordingly, we commonly use the RfC as a benchmark in 

considering potential concern for air toxics exposures posing risk of noncancer effects, 

recognizing its more direct strength in interpretations regarding exposures at or below it. For 

example, noncancer impacts associated with projected long-termexposures equal to or below 

the RfC are currently being given little regulatory attention in the residual risk program. 

Situations where projected long-term exposures are above the RfC may be further considered 

for additional regulation in light of other information, such as information specific to the 

pollutant and uncertainties in the assessment. 

This difference in how we assess potential noncancer effects and cancer risk affects our 

consideration of the two areas of focus mentioned above. As we do not have an upper and 

lower end of an established reference risk range to draw on for noncancer effects 

concentrations, our analyses involving the noncancer comparison levels take this into account 

through recognizing that longer-term average concentration estimates that are appreciably 

above the noncancer comparison level (e.g., by a factor of 5-10 or more) may be more 

relevant to gauging significance for health concerns than estimates falling much closer to or 

below this comparison level. That is, for some pollutants, a situation where the noncancer 

comparison level is exceeded by a factor on the order of 10 or more may be more relevant to 

consider for the purposes of our primary objective for this study, than one where the 

noncancer comparison level is only just exceeded. Thus, in drawing conclusions about 

potential concerns associated with estimated longer-term average concentration estimates 

higher than the long-term comparison level, we intend to consider a variety of factors, 

including those specific to the site or sources involved which might influence exposures (e.g., 

pending source actions), as well as factors particular to the health effects information (e.g., 

see section 4) including: the endpoints on which the RfC is based and our confidence in the 

RfC, its underlying database and the principal study; whether or not the RfC represents 

current methods and current information for the chemical, and; the magnitude of quantitative 

uncertainty associated with the RfC.q

 As a result, concerns regarding potential health 

impacts associated with estimated longer-term average concentrations above the noncancerbased comparison level may vary in light of factors other than or in addition to the amount by 

which the level is exceeded. 

 

q

 For example, derivation of the RfCs for acrolein and benzene included division of the exposure concentrations 

associated with the critical effect by cumulative uncertainty factors of 1000 and 300, respectively. For these 

pollutants, levels at which health effects have been observed are more than 10-fold higher than the RfCs. 
 09/10/09 

 

12 of 24 

In summary, depending on the information available for each pollutant, two types of longterm comparison levels have been derived for comparison to the projected range of longerterm average ambient concentration of each key pollutant at each school (Table 2).r

 

 The cancer-based comparison level is the estimated continuous (24 hours a day, daily), 

lifetime exposure concentration associated with an estimated 100-in-a-million lifetime 

cancer risks. 

 The noncancer-based comparison level is the EPA Reference Concentration (RfC) or a 

comparable valuet, which is the estimated continuous (24 hours-per-day daily) 

exposure concentration considered likely to be without adverse effects over a lifetime.

In developing or identifying these comparison levels, we have given priority to use of 

relevant and appropriate air standards and EPA risk assessment guidance and precedents. 

These levels are based upon the most recent assessments of potential toxicity of the 

monitored toxic air pollutants by EPA, and, as needed, the U.S. Agency for Toxic Substances 

and Disease Registry, and the California EPA. These agencies recognize the need to account 

for potential differences in sensitivity or susceptibility of different groups (e.g., asthmatics) 

or lifestages/ages (e.g., young children or the elderly) to a particular pollutant’s effects so 

that the resulting comparison levels are relevant for these potentially sensitive groups as well 

as the broader population. Further, the comparison levels are based on exposure to the 

pollutants all day, every day over a lifetime.u

 

5.3 Interpretation of Monitoring Results in Light of Comparison Levels

The report for each school that describes the analysis of the full monitoring dataset collected 

at each school (the school-specific report), will include discussion of all of the information 

collected as part of this initiative, including the meteorological measurements, information 

regarding nearby sources as well as the chemical concentration measurements. As 

mentioned above, analysis of the chemical concentration measurements will include 

consideration of what the full monitoring dataset indicates with regard to potential longerterm levels of the monitored pollutant. In doing this we will calculate the mean 

concentration for each pollutant during the monitoring period along with the 95% confidence 

limits on the mean which we will then use as an estimate of longer-term concentration in 

 

r

 Comparison levels will be developed consistent with the method described here for use in considering results 

for other HAPs monitored at each school. 

s

 This is derived by dividing 10-4 by the inhalation unit risk (IUR) value for a pollutant. IURs were taken from 

OAQPS toxicity table 2 (http://www.epa.gov/ttn/atw/toxsource/summary.html). In the case of the chemicals 

listed here as PAHs, which EPA considers to be carcinogenic by a mutagenic mode of action, either by explicit 

finding or by indirect finding due to the recognition of BaP as an index for IUR derivation, an additional step is 

taken as recommended by EPA guidance. Derivation of the cancer-based comparison levels for these pollutants 

included division by a factor of approximately 1.6 reflecting the application of age-dependent adjustment 

factors which effectively increase the potency when applied to the first 16 years of age (USEPA, 2005). t

 Where EPA Reference Concentrations are unavailable, ATSDR chronic Minimal Risk Levels or California 

EPA chronic Reference Exposure levels are substituted in that order, consistent with the hierarchy implemented 

in the OAQPS toxicity table 2 (http://www.epa.gov/ttn/atw/toxsource/summary.html). The term “RfC” is used 

here to indicate any of these values (which are similarly derived and defined). 

u

 This exposure assumption is explicit in its impact on derivation of the cancer-based comparison levels, such 

that an alternate assumption such as exposure limited to only childhood years would have resulted in higher 

(less protective) comparison levels. 
 09/10/09 

 

13 of 24 

considering the implications of the dataset with regard to longer-term levels. The paragraphs 

below provide a general description of how we intend to consider these summary statistics 

that describe the measurements at a school in light of the comparison levels described in the 

sections above. 

Cancer-based Comparison Levels: Air toxics for which the upper 95% confidence limit on 

the mean concentration falls above the cancer-based comparison level will be fully discussed 

in the school-specific report and may be considered a high priority for potential follow-up 

activities in light of the full set of information available for that site. Air toxics for which the 

upper 95% confidence limit falls below 1% of the comparison level (i.e., those for which 

longer-term average concentration estimates are below the corresponding 1-in-1-million 

cancer risk based concentration) are generally considered a low priority for follow-up 

activity. Situations where the summary statistics for a pollutant are below the cancer-based 

comparison level but above 1% of that level will be fully discussed in the school-specific 

report. 

Noncancer-based Comparison Levels: Air toxics for which the upper 95% confidence limit 

on the mean concentration is near or below the noncancer-based comparison level (i.e., those 

for which longer-term average concentration estimates are below a long-term health-related 

reference concentration) are generally of low concern and will generally be considered a low 

priority for follow-up activity. Pollutants for which the 95% confidence limits extend 

appreciably above the noncancer-based comparison level will be fully discussed in the 

school-specific report and may be considered a priority for follow-up activity, if indicated in 

light of the full set of information available for the pollutantv

 and the site. Interpretation in 

the case of lead entails additional specific considerations related to the use of the national 

ambient air quality standard as the comparison level. 

Multi-pollutant Cumulative Risk: The school-specific report will also consider and discuss 

the potential for multiple monitored pollutants (e.g., in addition to the key pollutant(s)) to be 

present at levels that might contribute to a potential for cumulative risk, particularly in 

situations where multiple pollutants are present at longer-term levels just below their 

respective comparison levels. 

 

v

 Such information includes that described in section 4 above. 
 09/10/09 

 

14 of 24 

 Table 2. Long-term Comparison Levels for Key (aka “driver”) Pollutants. 

Analyte 

Cancer-based 

Comparison 

Level1

source 

Noncancerbased 

Comparison 

Level1

source 

2004-07 

NATTS2

Arithmetic Mean 

(Median) 

[Maximum]

Metals3 ng/m3 ng/m3 PM10 Metals ng/m3

Arsenic (PM10 focus) 23 IUR 15 REL 1.1 (0.69) [48] 

Chromium-hexavalent 8.3 IUR 100 RfC 0.05 (0.03) [3] 

Cobalt (PM10 focus) - 100 MRL 0.32 (0.17) [20] 

Lead4 -TSP - 1503 NAAQS 5.6 (3.5) [751] 

Manganese (PM10 focus) - 50 RfC 11 (4.8) [410] 

Nickel (PM10 focus) 4205 IUR 90 MRL 2.6 (1.8) [110] 

VOCs/Carbonyls μg/m3 μg/m3 μg/m3

Acetaldehyde 45 IUR 9 RfC 1.9 (1.4) [93] 

Acrolein6 0.026 RfC6 0.63 (0.44) [7.3] 

Benzene 13 IUR 30 RfC 1.1 (0.86)[10] 

1,3-Butadiene 3.3 IUR 2 RfC 0.15 (0.09) [16] 

4,4’-methylenedianiline 20 Cal-IUR 0.22 REL -- 

Naphthalene 3 Cal-IUR 2.9 RfC 

PAHs7: 

Benzo(a)pyrene

Benzo(a)anthracene 

Benzo(b)fluoranthene 

Benzo(k) fluoranthene 

Chrysene 

Dibenz(a,h)anthracene 

Indeno(1,2,3-cd)pyrene 

ng/m3

57 

570 

570 

570 

5,700 

52 

570 

 

IUR 

IUR 

IUR 

IUR 

IUR 

IUR 

IUR 

 

Diisocyanates μg/m3 μg/m3 -- 

1,6-hexamethylene diisocyanate 0.01 RfC -- 

Methylenediphenyl diisocyanate 0.6 RfC -- 

2,4-toluene diisocyanate 9.1 Cal-IUR 0.07 RfC -- 

Table Notes 

1Values derived for this document, or for which units conversions were performed are shown here with the same 

number of significant figures as those specified in the source value. 

2 NATTS concentrations, presented to provide a reference for ambient levels of these pollutants, have been 

rounded to 2 significant figures. 

3Metal samples will be of 2 different types: PM10 and total suspended particles (TSP). With the exception of 

lead (for which the NAAQS was developed with explicit recognition of non-inhalation exposure pathways), metals 

comparison levels may be more suited for use with the concentration of metal in particles captured in a PM10

sample. While a Pb-PM10 average above the Pb comparison level is a finding of similar (or greater) interest than 

that for Pb-TSP, long-term averages for other metals in TSP that fall above a comparison level primarily indicate 

the need to consider results for that metal in PM10 on a case-by-case basis. 

4The value here is the level of the NAAQS, which is in terms of a 3-month average level of lead in TSP. 

5 The value here is based on the IRIS IUR for nickel refinery dust. 

6 The comparison level shown for acrolein is the EPA RfC which is set below a level associated with health 

effects. The RfC is set as a factor of 1000 below an exposure concentration associated with sensitive nasal 

effects in laboratory animals. Since the EPA RfC was derived, the California EPA has derived a chronic REL 
 09/10/09 

 

15 of 24 

based on more recently available information on acrolein and its effects. The Cal-EPA REL, which is 0.35 ug/m3, 

is somewhat more than a factor of 100 below the level associated with effects in the more recently available 

study. 

7The PAHs listed here are those identified as carcinogens, and for which inhalation unit risk estimates are 

available (from OAQPS Toxicity Table per section 3.3.b above)). The cancer-based comparison levels for these 

pollutants reflect EPA recommended application of age-dependent adjustment factors to reflect a potential for 

increased susceptibility to these substances in the first 16 years of life. 

Table 4. General examples of key considerations and potential follow-up conclusions. 

 If a key source of air pollution near a particular school is known to have temporarily ceased its operations 

during a significant portion of the monitoring period (e.g., due to temporary closure, periodic shutdowns, 

reduced operational capacity, etc.), EPA may not be able to draw conclusions from the initial 60-90 day 

dataset regarding the potential for “usual” air toxics levels to pose a potential for chronic health impacts and 

may wish to consider additional monitoring if and when the key source or sources restart operations 

 If the windrose during the sampling days shows significantly less windflow in the source-to-school direction 

as compared to what is seen across the full monitoring period or what might be expected over the longer 

term, EPA may choose to continue monitoring even if measurements suggest impacts are low 

 Frequent rainfall throughout the monitoring period may cause EPA to decide to continue monitoring even if 

measurements suggest impacts are low 

 If the concentrations of the key pollutants are all low, but the monitoring captures significant concentrations 

of an unexpected pollutant, EPA may choose to continue monitoring for that pollutant 

 If the entire estimated long-term concentration range for each key pollutant falls below the respective longterm comparison levels and the wind measurements indicate inclusion of sampling dates with winds in the 

direction of primary sources and the source activity has been consistent with usual conditions, EPA may 

conclude that there is low potential for significant risk of chronic health impacts associated with air toxics at 

that school and recommend that we cease monitoring there. 

 For pollutants where the measured concentrations are of a magnitude that may indicate some potential for 

chronic health concerns but where the measurements correspond to typical historic levels nationwide (e.g., 

this may be the case for acrolein and perhaps some others), EPA will give particular consideration to the 

school-specific data in light of the data for situations nationally, any associated national activities that are 

underway and information about other activities to address the pollutant sources. Such information will 

inform conclusions regarding next steps at the school. Based on this consideration, EPA may, for example, 

focus follow-up activities on a range of areas potentially including making the public aware of the available 

information, working with state and local partners to consider steps that may be available to us to reduce the 

pollutants locally, and/or examining how national activities underway may reduce the pollutants in the future. 

 For pollutants where measured levels are indicative of some potential for chronic impacts (for continuous 

long-term exposure scenarios), but where requirements are in place to reduce key source emissions within 

next year or so (e.g., consent order), EPA may indicate that while this school’s air has levels that might be of 

potential concern over a long term, source requirements are expected to preclude the occurrence of these 

levels over the long-term, and may conclude to revisit monitoring on some altered longer-term schedule. 

 If the entire estimated long-term concentration range for any key pollutant falls above the long-term 

comparison levels (and concentrations are not typical nationally and we have no information indicating 

activities in place to reduce concentrations in future), EPA may conclude that the potential for chronic health 

impacts of concern associated with that pollutant at that school indicate a need to pursue (in concert with 

the State or local air agency) options for emission reductions of that pollutant at the key source(s), while 

also continuing monitoring to more accurately characterize long-term concentrations and track the progress 

of emission reduction efforts. 
 09/10/09 

 

16 of 24 

REFERENCES 

ATSDR. 2008. MRLs. http://www.atsdr.cdc.gov/mrls/ . December. 

Cal-EPA 2008. RELs. http://www.oehha.ca.gov/air/hot_spots/index.html . December 18. 

Farland. 2006. Implementation of the Cancer Guidelines and Accompanying Supplemental 

Guidance – Science Policy Council Cancer Guidelines Implementation Workgroup 

Communication II: Performing Risk Assessments that include Carcinogens Described in 

the Supplemental Guidance as having a Mutagenic Mode of Action. Memorandum to 

Science Policy Council and Science Policy Council Steering Committee. June 14, 2006. 

OAQPS. 2007. Toxicity Table. http://www.epa.gov/ttn/atw/toxsource/summary.html

U.S. EPA Region III. 1997. Hazard Evaluation Handbook. A Guide to Removal Actions. EPA 

903/B-97-006. 

USEPA 1999. Residual Risk Report to Congress. EPA-453/R-99-001. Office of Air Quality 

Planning and Standards, Research Triangle Park, NC. March. 

USEPA 2005. Supplemental Guidance for Assessing Susceptibility from Early-Life Exposure to 

Carcinogens. EPA/630/R-03/003F. Risk Assessment Forum, Washington DC. 

USEPA. 2009. Information Risk Integrated System. http://cfpub.epa.gov/ncea/iris/index.cfm . 

April. 
 09/10/09 

 

17 of 24 

APPENDIX A. Individual Sample Screening Levels for Additional (non-key) HAP 

Analytes. The methodology and important considerations for their interpretation aredescribed in 

section 3 above and the footnotes following the table. 

Additional HAP Analytes Individual Sample 

Screening Level1

Value from which 

Screening Level Derived

Metals2 ng/m3 

Antimony7 (PM10 focus) 2,000 (I) 3 chronic RfC 

Beryllium (PM10 focus) 20 (I) chronic RfC 

Cadmium (PM10 focus) 30 acute MRL 

Mercury (elemental)8 3,000 (I) chronic RfC 

Selenium (PM10 focus) 20,000 (I) chronic REL 

VOCs/Carbonyls μg/m3

Acetonitrile 600 (I) chronic RfC 

Acrylonitrile 200 acute MRL 

Benzyl chloride 140 (I) IUR 

Bromoform 6,400 (I) IUR 

Carbon disulfide 7000 (I) chronic RfC 

Carbon Tetrachloride 200 (I) inter. MRL 

Chlorobenzene 10,000 (I) chronic REL 

Chloroform 500 acute MRL 

Chloroprene 70(I) chronic RfC 

1,4-Dichlorobenzene 10000 acute MRL 

1,3-Dichloropropene 40 (I) inter. MRL 

Ethyl acrylate 7000 [9] [9] 

Ethyl benzene 40,000 acute MRL 

Chloroethane (ethyl chloride) 40,000 acute MRL 

Ethylene dibromide 12(I) IUR 

Ethylene dichloride 270 (I) IUR 

Ethylidene dichloride (1,1-dichloroethane 4400 (I) HEAST chronic RfC 

Formaldehyde 50 acute MRL 

Hexachlorobutadiene 320 (I) IUR 

Bromomethane (methyl bromide) 200 acute MRL 

Chloromethane (methyl chloride) 1000 acute MRL 

1,1,1-Trichloroethane (methyl chloroform) 10,000 acute MRL 

Methyl isobutyl ketone 30,000(I) chronic RfC 

Methyl methacrylate 7000 (I) chronic RfC 

Methyl tert-butyl ether 7,000 acute MRL 

Methylene Chloride 2000 acute MRL 

Propionaldehyde 80 (I) chronic RfC 

μg/m3

Propylene dichloride (1,2-dichloropropane) 200 acute MRL 

Styrene 9,000 acute MRL 

1,1,2,2-Tetrachloroethane 120 (I) IUR 
 09/10/09 

 

18 of 24 

Additional HAP Analytes Individual Sample 

Screening Level1

Value from which 

Screening Level Derived

Tetrachloroethene 1,400 acute MRL 

Toluene 4,000 acute MRL 

1,2,4-Trichlorobenzene 2,000 (I) chronic RfC 

1,1,2-Trichloroethane 440 (I) IUR 

Trichloroethylene 10,000 acute MRL 

Vinyl Chloride 1,000 acute. MRL 

Vinylidene chloride (1,1-dichloroethylene) 80 (I) inter. MRL 

Xylene 9,000 acute MRL

Notes for Appendix A

1 Values derived for this document, or for which units conversions were performed are assigned the same number of 

significant figures as those specified in the source value. 

2 Metal samples will be of 2 different types: PM10 and total suspended particles (TSP). With the exception of lead 

(for which the NAAQS was developed with explicit recognition of non-inhalation exposure pathways), metals 

screening levels may be more suited for use with the concentration of metal in particles captured in a PM10 sample. 

While a Pb-PM10 sample above the Pb screening level is a finding of similar (or greater) interest than that for Pb-TSP, 

results for other metals in TSP that fall above a screening level may primarily indicate the need to consider results for 

that metal in PM10 on a case-by-case basis. 

3The superscript (I) indicates where an intermediate duration exposure screening levels has been assigned as a 

surrogate in lieu of a short-term screening level. 

4This value for lead is the level of the NAAQS, which is in terms of a 3-month average level of lead in TSP. 

5As neither an ATSDR intermediate MRL or a chronic value from the OAQPS table is available for total nickel, the 

screening level provided here is that for nickel refinery dust. 

6PAHs are components of the HAP polycyclic organic matter (POM). The PAH analytes listed here are those which 

EPA has identified as carcinogens, and for which inhalation unit risk estimates are available (from the OAQPS 

Toxicity Table, per section 3.3.b above)). In assessing carcinogenicity for chemicals concluded to be carcinogenic by 

a mutagenic mode of action and for which early lifestage dose-response information is not available, EPA 

recommends use of age-dependent adjustment factors (ADAFs) which effectively increase the potency when applied 

to the first 16 years of age (USEPA, 2005). Dibenz[a,h] anthracene (DBA) and benzo[a]pyrene (BaP), and the other 

PAHs for which IURs are indexed to that of BaP are considered by EPA to act by mutagenic modes of action 

(Farland, 2006). In considering potential use of ADAFs in the context of the individual sample screening levels, we 

recognize several considerations: (1) the objective for the sample screening levels is a short-term exposure estimate 

(on the order of weeks), (2) application of EPA’s traditional cancer risk assessment methods to such short periods is 

inherently uncertain, (3) the sample screening levels for these PAHs are actually surrogates for short-term levels and 

have been derived for a 1-year exposure, (4) the full data analysis for each school (see section 5) will consider 

potential risk of chronic exposure, and (5) if in the calculation of these levels, we had substituted a short-term 

exposure duration (e.g., 2 weeks), their values would be increased by a factor of 20, which is more than twice the 

value of the highest ADAF. Thus, rather than implement a cancer risk calculation specific to a 2-week duration 

exposure, which is not generally recommended by EPA guidance, we have retained the 1-year values and recognize 

that they are appropriately protective of shorter-term exposures with a potential for increased early-life susceptibility. 

7As neither an ATSDR intermediate MRL nor a chronic assessment from the OAQPS toxicity table is available for 

total antimony, the screening level provided here, and limited to use in this project, is that for antimony trioxide. 

8As neither an ATSDR intermediate MRL nor a chronic assessment from the OAQPS toxicity table (per Section 3.3) 

is available for particulate mercury, the screening level provided here is that for elemental mercury, which is expected 

to be lower than that which would be pertinent to particulate mercury (if one existed). 

9For ethyl acrylate, ATSDR has not established any MRLs of any exposure duration and OAQPS has identified no 

chronic dose-response values (http://www.epa.gov/ttn/atw/toxsource/summary.html). The value provided as a 

surrogate sample screening level is the screening level for methyl methacrylate, which is of the same chemical class 
 09/10/09 

 

19 of 24 

and which is lower than that indicated by other available health effects information. In considering additional health 

effects information for this pollutant, emergency planning guideline levels (Acute Exposure Guideline Levels and 

Emergency Response Planning Guidelines), developed for various levels of severity and durations of exposure up to 

8 hours, and their basis were reviewed. Additionally, chronic exposure values developed by the Occupational Safety 

and Health Administration and the American Conference of Governmental Industrial Hygienists (ACGIH) were 

reviewed, while recognizing that these values were developed for use in workplace environments and are not 

intended for ambient, environmental exposures of the general population. For example, the ACGIH threshold limit 

values (TLVs), while developed for use in considering time-weighted average worker exposures over an 8-hour shift, 

are based on recognition of repeated workday exposures in the context of 40-hour work weeks throughout a worker’s 

career. The ACGIH TLV of 5 ppm (20 mg/m3) is based on minimizing irritant effects of chronic exposures to ethyl 

acrylate, including such effects to the respiratory tract, skin, eyes, and gastrointestinal tract (as documented in 

Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices, ACGIH). As 

might be expected given the long-term exposure aspect of its basis, the ACGIH TLV is the lowest among the values 

considered here. The surrogate screening level shown in the table above, however, is lower than the ACGIH TLV.
 09/10/09 

 

20 of 24 

Appendix B. Individual Sample Screening Levels for non-HAPs 

As mentioned in section 1 above, the ambient air monitoring methods being used in this project 

for HAPs of interest also produce measurements for several non-HAPs. Some of these 

chemicals are well studied and individual sample screening levels (as described in section 2 

above) have been developed for them.23 These are presented in Table B-1 below. 

Table B-1. Analytes that are not CAA Section 112 Hazardous Air Pollutants for which 

data support development of sample screening levels 

Additional (non-HAP) 

Analytes CAS # 

Individual 

Sample 

Screening Level 

(ug/m3)1

Value from which 

Screening Level 

Derived

2003-2007 

Monitoring Data in 

AQS, Maximum 

(median) 

(μg/m3)

 

Acetone 67-64-1 62,000 acute MRL 2600 (4 x 10-3) 

Cis-1,2-dichloroethylene 156-59-2 value for trans isomer 0.52 (ND) 

Trans-1,2-dichloroethylene 156-60-5 800 acute MRL 0.53 (ND) 

Methyl ethyl ketone 78-93-3 50,000 (I) chronic RfC 16 (7 x 10-4) 

Propylene 115-07-1 30,000 (I) chronic REL 3.2 (8 x 10-4) 

m-dichlorobenzene (1,3-DCB) 541-73-1 10,000** Val for para- isomer 

(Appendix B) 

6.6 x 10-1 (ND) 

For the remaining non-HAP analytes, the available chemical-specific information (including that 

recognized in section 3 above) and sample screening levels for structurally similar chemicals in 

Tables 1 or Appendix A (see Table B-2 below) will be considered in reviewing individual 

sample results. 

 

23 In the case of 1,3-dichlorobenzene, no chemical-specific information useful to assigning a screening level was 

identified. So the sample screening level for the para-isomer (1,4-DCB), presented in Appendix A above was 

assigned (see Table A-1). 
 09/10/09 

21 of 24 

Table B2. Pollutants for which data limit development of sample screening levels* (e.g., no EPA, ATSDR or Cal-EPA assessments). 

Additional (non-HAP) 

Analytes CAS # Available information regarding levels of interest (ug/m3)1 Structurally simi

chemicals 

Acetylene 74-86-2 Lowest concentration at which effects reported is 108 μg/m3. 

CNS depression is most sensitive effect reported – it was used as anesthetic in 1920s. Use stopped due to explosive characteristics. The NIOSH REL, as a ceiling, is 2500 ppm, 3 x 106 μg/m3 (based on concern regarding phosphine which 

occurs in industrial grade acetylene, 2500ppm). 

There are no straight-

Alkyne HAPs. The m

structurally similar alk

propyne (74-99-7), h

ACGIH TLV-TWA of 

ppm. 1000 ppm 

acetylene=1x106μg/

Bromochloromethane 74-97-5 Lowest exposures in animal studies has been 370 ppm in dog 

and rat (subchronic [6mo] exposure) – some increased liver weight in rat. The ACGIH TLV-TWA is 200 ppm (106 μg/m3). 

This was developed based on consideration of animal exposure data and concerns regarding CNS and liver effects. 

Bromodichloromethane 75-27-4 Lowest exposures indicative of effects in animal studies has 

been 10 ppm in mice (prechronic [3 week] exposure) – some kidney effects which were not seen in exposures at this concentration lasting 13 weeks. The next lower concentration studied (3 ppm or 2x104μg/m3) did not show effects in mice at 3 

weeks or at 13 weeks of exposure (NTP). 

Dibromochloromethane 124-48-1 No inhalation studies identified (HSDB). 

The sample screening 

for a structurally similar 

chloroform, is 0.1 pp

In 

μg/m3, 0.1 ppm 

500 

μg/m3

bromochloromethan

700 

μg/m3 

bromodichlorometha

900 

μg/m3

dibromochlorometha
 09/10/09 

22 of 24 

Additional (non-HAP) 

Analytes CAS # Available information regarding levels of interest (ug/m3)1 Structurally simi

chemicals 

Dichlorodifluoromethane (Freon 12) 75-71-8 

Lowest concentration at which effects reported is 800 ppm (4 x 106 μg/m3) in guinea pig (subchronic [90day continuous] 

exposure) – liver pathological changes not seen in dog, monkey, rat or rabbit exposures. The ACGIH TLV-TWA is 1000 ppm (5 x 106 μg/m3). Sweden has an occupational value 

of 500 ppm (2 x 106 μg/m3). 

Dichlorotetrafluoroethane (Freon 114) 

76-14-2 Lowest concentration at which effects reported is 25,000 ppm ( 

μg/m3) in dog (acute exposure) – cardiac arrhythymia. No 

significant clinical, hematologic, histopathologic changes in rats and rabbits reported from repeated (2 hr/day; 5 day/wk) chronic (8-9 mos) exposure to 10,000 ppm. The ACGIH TLV-TWA is 1000 ppm (7 x 106 μg/m3) 

Trichlorotrifluoroethane (Freon 113) 

76-13-1 Short term exposure to fluorocarbon 113 can occur by 

inhalation, ingestion, and skin absorption. Inhalation and ingestion of fluorocarbon 113 will result in drowsiness, narcosis, central nervous system depression and significant impairment of manual dexterity and vigilance. Irritation of the eyes, nose, throat, and skin can also occur. Breathing concentrations that are greater than 2000 ppm may cause irregular heartbeat or heart arrest. Concentrations that exceed 2000 ppm are considered as immediately dangerous to life and health (NIOSH). 1000 ppm (7.6 x 106 μg/m3). A similar 

purpose standard in Sweden and Germany is 500 ppm (4 x 106

μg/m3). 

Trichlorofluoromethane (Freon 11) 

75-69-4 The ACGIH ceiling and the OSHA PEL is 1000ppm (5.6 x 106

μg/m3) based on a subchronic animal test NOAEL. 

Among these four Freo

lowest health-relate

concentration identified 

106 μg/m3
 09/10/09 

23 of 24 

Additional (non-HAP) 

Analytes CAS # Available information regarding levels of interest (ug/m3)1 Structurally simi

chemicals 

Ethyl tert-butyl ether 637-92-3 The ACGIH TLV-TWA is 5 ppm (20,000 

μg/m3). 

Tert-amyl methyl ether 994-05-8 

The sample screening 

for a structurally similar 

MTBE, is 2 ppm. In 

μg

ppm is: 

8000 

μg/m3 ETBE or T

n-octane 111-65-9 The NIOSH REL is 75 ppm (350,000 

μg/m3), on the basis of 

weight given to neurotoxic effects associated with hexane exposures. The ACGIH TLV-TWA is 300 ppm (1,400,000 μg/m3), established on the basis of comparison of the acute 

response to other paraffinic hydrocarbons. 

The sample screening 

for a structurally similar 

hexane, is 2 ppm. In 

μ

2 ppm is: 

9000 

μg/m3 octan

1,2,4-trimethylbenzene 95-63-6 1,3,5-trimethylbenzene 108-67-8 

The ACGIH TLV-TWA is 25 ppm (100,000 

μg/m3) The 8 hr 

AEGL-1 is 45 ppm. 

The sample screening 

for a structurally similar 

xylene, is 2 ppm. In 

μg

ppm is: 

10,000 

μg/m3 1,2,4- or 

trimethylbenzene

AldehydesBenzaldehyde 100-52-7 The ACGIH WEEL TWA is 2 ppm . Butyr- and Isobutyraldehyde 

123-72-8 

78-84-2 

The ACGIH WEEL TWA is 25 ppm (74 mg/m3) 

Crotonaldehyde 123-73-9 The ACGIH TLV-TWA Ceiling is 0.3 ppm (0.86 mg/m3) to 

protect the skin. The NIOSH REL-TWA is 2 ppm (6000 

μg/m3). 

The ACGIH TLV-TWA is 2 ppm to protect against the respiratory irritancy effects. The AEGL-1 (8hr)=0.2 ppm. 

2,5-Dimethylbenzaldehyde 5779-94-2 

The sample screening 

for a structurally similar 

formaldehyde, is 0.04 

In 

μg/m3, 0.04 ppm 

200 

μg/m3 benzaldeh

2,5-dimethylbenzalde

hexaldehyde, 

isovaleraldehyde, or 
 09/10/09 

24 of 24 

Additional (non-HAP) 

Analytes CAS # Available information regarding levels of interest (ug/m3)1 Structurally simi

chemicals 

Hexaldehyde (hexanal) 66-25-1 Isovaleraldehyde (3-methylbutanal) 

590-86-3 

o-, m- and p-tolualdehyde 529-20-4, 

620-23-5, 

104-87-0 

Valeraldehyde (pentanal) 110-62-3 The ACGIH TLV-TWA is 50 ppm (176 mg/m3). The NIOSH 

REL is 50 ppm. 

tolualdehydes

100 

μg/m3 butyraldehy

valeraldehyde