1 

Health Effects Information Used In Cancer and Noncancer Risk 

Characterization for the 2002 National-Scale Assessment 

Introduction 

Hazard identification and dose-response assessment information for the 2000 nationalscale assessment was obtained from various sources and prioritized according to (1) 

conceptual consistency with EPA risk assessment guidelines and (2) the level of review 

received. The prioritization process was aimed at incorporating into our assessment the 

best available science with respect to dose-response information. The following sources 

were used. 

US Environmental Protection Agency (EPA) 

EPA has developed dose-response assessments for chronic exposure to many of the 

pollutants in this study. These assessments typically specify a reference concentration, or 

RfC (to protect against effects other than cancer) and/or a unit risk estimate, or URE (to 

estimate the probability of contracting cancer). The RfC is an estimate, with uncertainty 

spanning perhaps an order of magnitude, of an inhalation exposure to the human 

population (including sensitive subgroups) that is likely to be without appreciable risks of 

deleterious effects during a lifetime. The URE is the upper-bound excess cancer risk 

estimated to result from a lifetime of continuous exposure to an agent at a concentration 

of 1 μg/m3

 in air. In assessing a substance’s carcinogenic potential, EPA evaluates 

various types of toxicological data and develops a weight-of-evidence (WOE) 

determination. Older WOE assessments use an alphanumeric categorization 

(recommended by EPA’s 1986 guidelines for carcinogen risk assessment); assessments 

developed since the 2005 revisions to the cancer guidelines (see: 

http://cfpub.epa.gov/ncea/raf/recordisplay.cfm?deid=116283) characterize the WOE with 

a paragraph of descriptive text. 

EPA disseminates dose-response assessment information in several forms, depending on 

the level of internal review. EPA publishes dose-response assessments that have 

achieved full intra-agency consensus on its Integrated Risk Information System (IRIS), 

which is regularly updated and available on-line at http://www.epa.gov/iris. All IRIS 

assessments since 1996 have also undergone external scientific peer review. 

Agency for Toxic Substances and Disease Registry (ATSDR) 

ATSDR, which is part of the US Department of Health and Human Services, develops 

and publishes Minimal Risk Levels (MRLs) for many toxic substances. The MRL is 

defined as 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. MRLs can be derived for acute, intermediate, and chronic duration exposures 

by the inhalation and oral routes. ATSDR describes MRLs as media-specific 
 

 2 

concentrations to be used by health assessors to select environmental contaminants for 

further evaluation. MRLs are presented with only 1 significant figure and are considered 

concentrations below which contaminants are unlikely to pose a health threat. 

Concentrations 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. 

Inhalation MRLs were used in the noncancer portion of this assessment when IRIS RfCs 

were not available because their concept, definition, and derivation are philosophically 

consistent (though not identical) with the basis for EPA’s RfCs. ATSDR MRLs are 

reviewed by an expert panel of external peers and also by an interagency workgroup that 

includes EPA. MRLs are published in pollutant-specific toxicological profile documents, 

and also in a table of “comparison values” that ATSDR regularly updates and distributes 

(available on-line at http://www.atsdr.cdc.gov/mrls.html ). 

 

California Office of Environmental Health Hazard Assessment (OEHHA) 

The California OEHHA has developed dose-response assessments for many substances, 

based both on carcinogenicity and health effects other than cancer. The process for 

developing these assessments is similar to that used by the EPA to develop IRIS values 

and incorporates significant external scientific peer review. The non-cancer information 

includes available inhalation health risk guidance values expressed as chronic inhalation 

reference exposure levels (RELs). OEHHA defines the REL as a concentration level at 

(or below) which no health effects are anticipated, a concept that is substantially similar 

to EPA’s non-cancer dose-response assessment perspective. This assessment uses 

chronic RELs in the same way as RfCs when no IRIS or ATSDR values exist. 

OEHHA’s quantitative dose-response information on carcinogenicity by inhalation 

exposure is expressed in terms of the URE, defined similarly to EPA’s URE. This 

assessment uses specific OEHHA UREs in the same way as EPA’s when no IRIS or 

values exist. OEHHA’s dose response information for carcinogens and noncarcinogens 

is available on-line at http://www.oehha.ca.gov/air/hot_spots/index.html. 

US EPA Health Effects Assessment Tables (HEAST) 

HEAST is a comprehensive listing consisting almost entirely of provisional UREs, RfCs, 

and other risk assessment information for chemicals of interest. Although the 

assessments summarized in HEAST have undergone review and have the concurrence of 

individual EPA program offices, and each is supported by an agency reference, they have 

not had enough review to be recognized as high-quality, EPA-wide consensus 

information. Because of these limitations, and the fact that HEAST has not been updated 

since 1997 and exists only in hard copy (PB97-921199), this assessment uses HEAST 

information only when no values from the other sources described above are available. 
 

 3 

Prioritization of Data Sources 

Some substances have been assessed for dose-response by more than one of the agencies 

used as sources for this analysis. Because different scientists developed these assessments 

at different times for purposes that were similar but not identical, it is inevitable that the 

results are not totally consistent. In some cases interagency differences were substantial, 

especially among assessments done many years apart. To resolve interagency 

discrepancies for this analysis, EPA applied a consistent priority scheme to the universe 

of dose-response information. 

Externally peer-reviewed assessments under development for the IRIS process were 

given first priority. These assessments reflect the most recent available toxicity 

information and data analysis, and were used in some cases to supersede existing values 

on IRIS. Where externally peer reviewed IRIS draft assessments were not available, the 

next preferred source was EPA’s IRIS database. For substances lacking IRIS 

assessments, ATSDR MRLs (available only for noncancer effects) received next 

preference, followed by OEHHA RELs and UREs. 

Adjustments to Dose-Response Information 

Following the prioritization of dose-response information, EPA made the following 

adjustments based on professional judgment: 

 Oral carcinogens lacking inhalation assessments. For 12 carcinogenic substances, 

(benzotrichloride, captan, DDE, dichlorvos, 3,3'-dimethoxybenzidine, 3,3'-

dimethylbenzidine, 1,4-dioxane, isophorone, pentachloronitrobenzene, propylene 

dichloride, quinoline, and trifluralin) that currently lack inhalation assessments 

from the sources described above, oral carcinogenic potency estimates were 

converted to inhalation UREs. The conversion from oral risk (per mg/kg/d oral 

intake) to inhalation risk (per μg/m3

 inhaled) was based on EPA’s standard 

assumptions of a 70-kg body mass and 20 m3

/d inhalation rate, as follows: 

Where: URE = Unit risk estimate for inhalation (risk per μg/m3

) 

CPS = Carcinogenic potency slope for ingestion (risk per mg oral 

intake per kg body mass per day) 

OAQPS understands that method used for the conversion of oral dose-response 

information to inhalation exposure is a problematic risk assessment practice. 

However, the alternative to this would have been to omit these substances from 

quantitative inhalation risk estimates altogether, thereby making a de facto

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 4 

assumption of zero carcinogenic potency. For the purposes of the national-scale 

assessment, OAQPS prefers to use the approach described above to screen these 

carcinogens for their potential contributions to risk. If a substance is determined 

to be a potentially important contributor to risk, it will be prioritized for further 

dose-response development through EPA’s IRIS process. 

 Hexavalent chromium compounds. The IRIS RfC for particulate hexavalent 

chromium was used in preference to the RfC for chromic acid mists and dissolved 

aerosols. 

 Formaldehyde. EPA no longer considers the formaldehyde URE reported in IRIS, 

which is based on a 1987 study, to represent the best available science in the peerreviewed literature. Since that time, significant new data and analyses have 

become available. Accordingly, risk estimates for formaldehyde are based on a 

dose-response value developed by the CIIT Centers for Health Research (formerly 

the Chemical Industry Institute of Toxicology) and published in 1999. This 

assessment incorporates mechanistic and dosimetric information on formaldehyde 

that had been accumulated over the past decade, and developed a URE using 

approaches that are consistent with EPA's guidelines for carcinogenic risk 

assessment. EPA had judged that this CIIT modeling effort currently represents 

the best application of available mechanistic and dosimetric science on the doseresponse for portal of entry cancers due to formaldehyde exposures. EPA is 

currently reviewing the CIIT analysis and other recent information, including 

recently published epidemiological studies, in our reassessment of our 

formaldehyde unit risk estimate (URE). 

 Glycol ethers. Most of the emission inventory information for the glycol ether 

category reports only the total mass for the entire group without distinguishing 

between individual glycol ether compounds. These individual compounds, 

however, vary substantially in toxicity. In order to avoid underestimating the 

health hazard associated with glycol ethers, EPA has protectively applied the RfC 

for ethylene glycol methyl ether (the most toxic for which an assessment exists) to 

the entire group. 

 Diesel emissions. The national-scale assessments do not include quantitative 

cancer risk estimates for diesel emissions because EPA has judged that 

toxicological data are not yet sufficient to develop a URE. However, diesel 

emissions have been assessed for effects other than cancer, using the 2003 IRIS 

RfC. 

 Nickel. The IRIS URE for nickel inhalation shown in Table 1 below was derived 

from evidence of the carcinogenic effects of insoluble nickel compounds in 

crystalline form. Soluble nickel species, and insoluble species in amorphous form, 

do not appear to produce genotoxic effects by the same toxic mode of action as 
 

 5 

insoluble crystalline nickel. Nickel speciation information for some of the largest 

nickel-emitting sources (including oil combustion, coal combustion, and others) 

suggests that at least 35% of total nickel emissions may be soluble compounds. 

The remaining insoluble nickel emissions are not well-characterized, however. 

Consistent with this limited information, this analysis has conservatively assumed 

that 65% of emitted nickel is insoluble, and that all insoluble nickel is crystalline. 

On this basis, the nickel URE (based on nickel subsulfide, and representative of 

pure insoluble crystalline nickel) was adjusted to reflect an assumption that 65% 

of the total mass of nickel may be carcinogenic. The ATSDR MRL in Table 2 

was not adjusted, however, because the noncancer effects of nickel are not thought 

to be limited to the crystalline, insoluble form. 

 2-Nitropropane. The assessment used a URE of 5.6 x 10-6 per ug/m3

 for 2-

nitropropane. This value was derived in 1999 by the Health Council of the 

Netherlands (available at: http://www.gr.nl/pdf.php?ID=423&p=1), based on 

induction of hepatocellular nodules in rats, and is consistent with weight-ofevidence determinations by the U.S. National Toxicology Program (“reasonably 

anticipated to be a human carcinogen”) and the IARC (“possibly carcinogenic to 

humans”).

 Polycyclic organic matter (POM). The assessment divided POM emissions into 

eight categories. The first two categories were assigned a URE equal to 5% of that 

for pure benzo[a]pyrene (the same assumption that the 1996 assessment used for 

all POM data). Categories 3-7 were composed of emissions that were reported as 

individual compounds. These compounds were placed in the category with an 

appropriate URE. Category 8, composed of unspeciated carcinogenic polynuclear 

aromatic hydrocarbons (a subset of POM called 7-PAH), was assigned a URE 

equal to 18% of that for pure benzo[a]pyrene. Details on the development of the 

5% and 18% URE estimates are available here: 

http://www.epa.gov/ttn/atw/sab/appendix-h.pdf. 

The process of URE estimation includes the following important sources of 

uncertainty: 

 Many of the substances in this assessment were classified as probable 

carcinogens, indicating that data were not sufficient to prove these substances 

definitely cause cancer in humans. It is possible that some of these substances 

are not human carcinogens at environmentally relevant doses, and that the true 

risk associated with them is zero. 

 All UREs used in this assessment were based on linear extrapolation from high 

to low doses. To the extent that true dose-response relationships for some 

substances are nonlinear, this assumption may result in significant over- or 

underestimates of risk. 
 

 6 

 UREs for most of these substances were developed from animal data using 

conservative methods to extrapolate between species. Actual human responses 

may differ from the predicted ones. 

 Most UREs used in this assessment (typically, those based on animal data) 

were based on the statistical upper confidence limit (UCL) of the fitted doseresponse curve. That means true risk would probably be less, but could be 

greater. A few (typically, those based on human data) were based on the 

statistical best fit (“maximum likelihood estimate,” or MLE). UREs based on 

the MLE are identified in a footnote to Table 1. This difference between UCLand MLE-based assessments results in some UREs that are somewhat less 

conservative than the rest. 

Table 1: Dose-Responses Values 

 

This table lists includes dose-response values and supporting information for both cancer 

and noncancer effects used in the 2002 national-scale assessment. The EPA weight-ofevidence (WOE) categories characterize the extent to which available data support the 

hypothesis that a pollutant causes cancer in humans. The EPA carcinogen categories are 

Group A—known, Group B1—probable, based on incomplete human data, Group B2—

probable, based on adequate animal data, Group C—possible, Group D—not classifiable, 

and Group E—evidence of non-carcinogenicity. The URE is the upper bound risk 

estimate of cancer risk from a lifetime exposure to a concentration of 1 microgram per 

cubic meter. The “RfC” column lists reference concentrations and similar values (i.e., 

RELs, MRLs) that were used in this assessment. The reference concentration (RfC) is an 

estimate, with uncertainty spanning perhaps an order of magnitude, of an inhalation 

exposure to the human population (including sensitive subgroups) that is likely to be 

without appreciable risks of deleterious effects during a lifetime. The “target system” 

columns show up to three organs or organ system adversely affected at the lowest dose in 

human or animal studies, but only the respiratory and neurological endpoints were 

assessed in the 2002 NATA because these two endpoints were identified as the noncancer 

drivers in previous NATA assessments. Other information on individual substances is 

shown in footnotes. 
 

Chemical Name CAS No. 

EPA 

WOE

URE 

(μg/m3

)-1

URE 

Source 

RfC1

(mg/m3) 

RfC 

 Source 

Target

System 114 

Target

System 2

Acetaldehyde 75070 B2 0.000002 IRIS 0.009 IRIS Respiratory Acetamide 60355 0.00002 CAL Acetonitrile 75058 D 0.06 IRIS Whole body Acrolein 107028 0.00002 IRIS Respiratory Acrylamide 79061 B2 0.0013 IRIS 0.0007 PCAL2 Neurological Acrylic acid 79107 0.001 IRIS Respiratory Acrylonitrile 107131 B1 0.000068 IRIS 0.002 IRIS Respiratory Allyl chloride 107051 C 0.000006 CAL 0.001 IRIS Neurological 4-Aminobiphenyl 92671 Aniline 62533 B2 0.0000016 CAL 0.001 IRIS Spleen o-Anisidine 90040 Antimony compounds 7440360 0.00023 IRIS Respiratory Arsenic compounds 7440382 A 0.0043 IRIS 0.00003 CAL Developmental Arsine 7784421 0.00005 IRIS Hematological Benzene 71432 A 0.0000078 IRIS 0.03 IRIS Immunological Benzidine 92875 A 0.10724 IRIS 0.01 PCAL2 Neurological Liver Benzotrichloride 98077 B2 0.0037 Conv. Oral5Benzyl chloride 100447 B2 0.000049 CAL Biphenyl 92524 D Beryllium compounds 7440417 B1 0.0024 IRIS 0.00002 IRIS Respiratory Bis(2-ethylhexyl) phthalate 117817 B2 0.0000024 CAL 0.01 PCAL2 Respiratory Liver Bis(chloromethyl) ether 542881 A 0.062 IRIS Bromoform 75252 B2 0.0000011 IRIS 1,3-Butadiene 106990 A 0.00003 IRIS 0.002 IRIS Reproductive Calcium cyanamide 156627 Cadmium compounds 7440439 B1 0.0018 IRIS 0.00002 CAL Kidney Captan 133062 B2 0.000001 Conv. Oral5Carbaryl 63252 Carbon disulfide 75150 0.7 IRIS Neurological Carbon tetrachloride 56235 B2 0.000015 IRIS 0.19 ATSDR Liver Carbonyl sulfide 463581 1 Includes EPA reference concentrations (RfCs) and similar values, i.e., California OEHHA reference exposure levels (RELs), and ATSDR mini

these chemicals are under review for the development of RfCs. A current status report for all EPA assessments is available at http://cfpub.epa.g

2 Proposed by California OEHHA; not yet adopted in final form. 3 RfC used for antimony compounds is derived from RfC for antimony trioxide. 4 Includes age-related adjustment factor (1.6 x) to account for early childhood exposures to a known mutagenic agent. See document at 

http://www.epa.gov/ttn/atw/childrens_supplement_final.pdf for further details. 5 Conversion of oral potency slope to inhalation unit risk estimate was based on the following assumptions: (1) whole-life, continuous exposure, 

meters of air per day, and (3) body mass of 70 kg. Further details are provided in the text above. 
 

Chemical Name CAS No. 

EPA 

WOE

URE 

(μg/m3

)-1

URE 

Source 

RfC1

(mg/m3) 

RfC 

 Source 

Target

System 114 

Target

System 2

Catechol 120809 Chlordane 57749 B2 0.0001 IRIS 0.0007 IRIS Liver Chlorine 7782505 0.0002 CAL Respiratory Chloroacetic acid 79118 2-Chloroacetophenone 532274 0.00003 IRIS Respiratory Chlorobenzene 108907 1 CAL Reproductive Kidney Chlorobenzilate 510156 B2 0.000078 HEAST Chloroform 67663 B2 0.098 ATSDR Liver Chloromethyl methyl ether 107302 A Chloroprene 126998 0.007 HEAST Respiratory Chromium VI compounds 18540299 A 0.012 IRIS 0.0001 IRIS Respiratory Cobalt compounds 7440484 0.0001 ATSDR Respiratory Coke Oven Emissions 8007452 A 0.00062 IRIS Cresols (mixed) 1319773 C 0.6 CAL Neurological Whole bod0-cresol6 95487 0.6 OAQPS Neurological m-cresol6 108394 0.6 OAQPS Neurological p-cresol6 106445 0.6 OAQPS Neurological Cumene 98828 D 0.4 IRIS Kidney Endocrine 2,4-d, salts and esters 94757 DDE 72559 B2 0.000097 Conv. Oral5 Diazomethane 334883 Dibenzofurans 132649 D Cyanide compounds 57125 D 0.0037 IRIS Neurological Thyroid 1,2-Dibromo-3-chloropropane 96128 B2 0.002 CAL 0.0002 IRIS Reproductive Dibutylphthalate 84742 D p-Dichlorobenzene 106467 C 0.000011 CAL 0.8 IRIS Liver 3,3'-Dichlorobenzidine 91941 B2 0.00034 CAL Dichloroethyl ether 111444 B2 0.00033 IRIS 1,3-Dichloropropene 542756 B2 0.000004 IRIS 0.02 IRIS Respiratory Dichlorvos 62737 B2 0.000083 Conv. Oral5 0.0005 IRIS Neurological Diesel emissions 0.005 IRIS Respiratory Diethanolamine 111422 0.003 CAL Respiratory N,N-Dimethyl aniline 121697 Diethyl sulfate 64675 3,3'-Dimethoxybenzidine 119904 B2 0.000004 Conv. Oral5p-Dimethylaminoazobenzene 60117 0.0013 CAL 3,3'-Dimethylbenzidine 119937 B2 0.0026 Conv. Oral56 The individual cresol and xylene isomers were modeled separately if their emissions were reported separately, and hazard quotients were gener

for their mixture. The final NATA results present their results combined under the HAP category of ‘cresol or xylene mixture’. 7 The RfC used is from the HAP, hydrogen cyanide. 
 

Chemical Name CAS No. 

EPA 

WOE

URE 

(μg/m3

)-1

URE 

Source 

RfC1

(mg/m3) 

RfC 

 Source 

Target

System 114 

Target

System 2

Dimethyl carbamoyl chloride 79447 Dimethylformamide 68122 0.03 IRIS Liver 1,1-Dimethylhydrazine 57147 Dimethyl phthalate 131113 D Dimethyl sulfate 77781 B2 4,6-Dinitro-o-cresol and salts 534521 2,4-Dinitrophenol 51285 2,4-Dinitrotoluene 121142 B2 0.000089 CAL 0.007 PCAL2 Liver Neurologic1,4-Dioxane 123911 B2 0.0000077 CAL 3 CAL Liver Hematolog1,2-Diphenylhydrazine 122667 B2 0.00022 IRIS Epichlorohydrin 106898 B2 0.0000012 IRIS 0.001 IRIS Respiratory 1,2-Epoxybutane 106887 0.02 IRIS Respiratory Ethyl acrylate 140885 B2 Ethylbenzene 100414 D 1 IRIS Developmental Ethyl carbamate 51796 0.000464 CAL Ethyl chloride 75003 10 IRIS Developmental Ethylene dibromide 106934 B2 0.0006 IRIS 0.009 IRIS Respiratory Ethylene dichloride 107062 B2 0.000026 IRIS 2.4 ATSDR Liver Ethylene glycol 107211 0.4 CAL Respiratory Ethylene imine 151564 Ethylene oxide 75218 B1 0.000088 CAL 0.03 CAL Neurological Ethylene thiourea 96457 B2 0.000013 CAL 0.003 PCAL2 Endocrine Ethylidene dichloride 75343 C 0.0000016 CAL 0.5 HEAST Kidney Formaldehyde 50000 B1 5.5e-9 OAQPS 0.0098 ATSDR Respiratory Heptachlor 76448 B2 0.0013 IRIS Glycol ether compounds 0.028 OAQPS Reproductive Hexachlorobenzene 118741 B2 0.00046 IRIS 0.003 PCAL2 Liver Hexachlorobutadiene 87683 C 0.000022 IRIS 0.09 PCAL2 Reproductive Hexachlorocyclopentadiene 77474 E 0.0002 IRIS Respiratory Hexachloroethane 67721 C 0.000004 IRIS 0.08 PCAL2 Kidney Liver Hexamethylene-1,6-diisocyanate 822060 0.00001 IRIS Respiratory n-Hexane 110543 0.7 IRIS Neurological Respiratory Hydrazine 302012 B2 0.0049 IRIS 0.0002 CAL Liver Thyroid Hydrochloric acid 7647010 0.02 IRIS Respiratory Hydrofluoric acid 7664393 0.014 CAL Skeletal Hydroquinone 123319 8 This RfC is for ethylene glycol methyl ether, the most toxic of this group for which an assessment exists. See note in text above for a more co
 

Chemical Name CAS No. 

EPA 

WOE

URE 

(μg/m3

)-1

URE 

Source 

RfC1

(mg/m3) 

RfC 

 Source 

Target

System 114 

Target

System 2

Isophorone 78591 C 2.7e-7 Conv. Oral5 2 CAL Liver DevelopmeLead compounds 7439921 B2 0.000159 OAQPS Neurological Lindane (all isomers) 0.00031 IRIS 0.0003 PCAL2 Kidney Liver Maleic anhydride 108316 0.0007 CAL Respiratory Manganese compounds 7439965 D 0.00005 IRIS Neurological Mercury compounds C 0.0003 IRIS Neurological Methanol 67561 4 CAL Developmental Methoxychlor 72435 D Methyl bromide 74839 D 0.005 IRIS Respiratory Methyl chloride 74873 D 0.09 IRIS Neurological Methyl isobutyl ketone 108101 3 IRIS Developmental Methyl iodide 74884 Methyl Hydrazine 60344 Methyl isocyanate 624839 0.001 CAL Respiratory Whole bodMethyl methacrylate 80626 E 0.7 IRIS Respiratory Methyl tert-butyl ether 1634044 2.6e-7 CAL 3 IRIS Liver Kidney 4,4'-Methylene bis(2-chloroaniline) 101144 B2 0.00043 CAL Methylene chloride 75092 B2 4.7e-7 IRIS 1 ATSDR Liver Methylene diphenyl diisocyanate 101688 D 0.0006 IRIS Respiratory 4,4'-Methylenedianiline 101779 0.00046 CAL 0.02 CAL Ocular Naphthalene 91203 C 0.000034 CAL 0.003 IRIS Respiratory Nickel compounds A 0.00031210 OAQPS 0.00009 D- ATSDR Respiratory ImmunologNitrobenzene 98953 C 0.00004 IRIS 0.009 IRIS Respiratory 4-Nitrobiphenyl 92933 4-Nitrophenol 100027 2-Nitropropane 79469 B2 0.0000056 OAQPS 0.02 IRIS Liver Nitrosodimethylamine 62759 B2 0.014 IRIS N-Nitrosomorpholine 59892 0.0019 CAL Parathion 56382 C PCB Group 1336363 B2 0.0001 IRIS Pentachloronitrobenzene 82688 C 0.000074 Conv. Oral5Pentachlorophenol 87865 B2 0.0000051 CAL 0.1 PCAL2 Liver Kidney Phenol 108952 D 0.2 CAL Liver p-Phenylenediamine 106503 Phosgene 75445 0.0003 IRIS Respiratory Phosphine 7803512 D 0.0003 IRIS Whole body Phosphorus 7723140 9 EPA has not developed an RfC for lead. The value shown is the quarterly National Ambient Air Quality Standard for lead, which EPA believe

effects. 

10 The URE used is derived by assuming 65% of the nickel subsulfide URE. See note in text above for a more complete explanation.
 

Chemical Name CAS No. 

EPA 

WOE

URE 

(μg/m3

)-1

URE 

Source 

RfC1

(mg/m3) 

RfC 

 Source 

Target

System 114 

Target

System 2

Phthalic anhydride 85449 0.02 CAL Respiratory Ocular Polycyclic organic matter11 group 1 12 0.0000884 OAQPS Polycyclic organic matter group 2 12 0.0000884,14 OAQPS Polycyclic organic matter group 3 12 0.164,14 OAQPS Polycyclic organic matter group 4 12 0.0164,14 OAQPS Polycyclic organic matter group 5 12 0.00164,14 OAQPS Polycyclic organic matter group 6 12 0.000164,14 OAQPS Polycyclic organic matter group 7 12 0.0000164,14 OAQPS Polycyclic organic matter group 8 12 0.000324,14 OAQPS 1,3-Propane sultone 1120714 0.00069 CAL beta-Propiolactone 57578 Priopionaldehyde 123386 0.008 IRIS Respiratory Propoxur 114261 Propylene dichloride 78875 B2 0.000019 Conv. Oral5 0.004 IRIS Respiratory Propylene oxide 75569 B2 0.0000037 IRIS 0.03 IRIS Respiratory 1,2-Propylenimine 75558 Quinoline 91225 B2 Quinone 106514 Selenium compounds 7782492 D 0.02 CAL Neurological Liver Styrene 100425 1 IRIS Neurological Styrene oxide 96093 0.006 PCAL2 Respiratory 1,1,2,2-Tetrachloroethane 79345 C 0.000058 IRIS Perchloroethylene 127184 B2C 0.0000059 CAL 0.27 ATSDR Neurological Titanium tetrachloride 7550450 0.0001 ATSDR Respiratory Toluene 108883 D 5.0 IRIS Respiratory Neurologic2,4-Toluene diamine 95807 B2 0.0011 CAL 2,4-Toluene diisocyanate 26471625 0.000011 CAL 0.00007 IRIS Respiratory o-Toluidine 95534 B2 0.000051 CAL Toxaphene 8001352 B2 0.00032 IRIS 1,2,4-Trichlorobenzene 120821 D 0.2 HEAST Liver 1,1,2-Trichloroethane 79005 C 0.000016 IRIS 0.4 PCAL2 Liver 1,1,1-Trichloroethane 71556 D 1 CAL Neurological Trichloroethylene 79016 B2C 0.000002 CAL 0.6 CAL Neurological Ocular 2,4,5-Trichlorophenol 95954 2,4,6-Trichlorophenol 88062 B2 0.0000031 IRIS Triethylamine 121448 0.007 IRIS Respiratory Trifluralin 1582098 C 0.0000022 Conv. Oral52,2,4-Trimethylpentane 540841 11 A full discussion of the risk assessment for polycyclic organic matter is available at: http://www.epa.gov/ttn/atw/sab/appendix-h.pdf. 12 EPA WOE varies among individual compounds. 
 

Chemical Name CAS No. 

EPA 

WOE

URE 

(μg/m3

)-1

URE 

Source 

RfC1

(mg/m3) 

RfC 

 Source 

Target

System 114 

Target

System 2

Vinyl acetate 108054 0.2 IRIS Respiratory Vinyl bromide 593602 B2 0.000032 HEAST 0.003 IRIS Liver Vinyl chloride 75014 A 0.0000088 IRIS13 0.1 IRIS Liver Vinylidene chloride 75354 C 0.2 IRIS Liver Xylenes (mixed) 1330207 0.1 IRIS Neurological o- Xylene6 95476 0.1 IRIS Neurological m-Xylene6 108383 0.1 IRIS Neurological P-Xylene6 106423 0.1 IRIS Neurological 13 URE based on whole life exposure was selected over a URE based on adult exposure only. 14 Multiple target organs listed if the concentration at the “critical effect” is the same at all targets.