Health Effects Information Used In Cancer and Noncancer Risk Characterization for the NATA 1996 National-Scale Assessment

Health Effects Information Used In Cancer and Noncancer Risk
Characterization for the NATA 1996 National-Scale Assessment

Sources of Information

Hazard identification and dose-response assessment information for the NATA national-scale
assessment was obtained from various sources. Information was assigned greater weight if (1) it
was conceptually consistency with the EPA risk assessment guidelines and (2) the level of review it
received was high. This process of prioritizing information was aimed at ensuring the assessment
was based on the best available science. The following sources were used.

US Environmental Protection Agency (EPA)

The EPA has developed dose-response assessments for chronic exposure to many of the pollutants
in this study. These assessments typically give a reference concentration (RfC) to protect against
effects other than cancer, and/or a unit risk estimate (URE) to estimate the probability of contracting
cancer as a result of exposure to a pollutant. The RfC is an estimate of a concentration in air to
which a human population might be exposed (including sensitive subgroups) that is likely to be
without appreciable risks of deleterious effects during a lifetime. The uncertainty in this
concentration spans perhaps an order of magnitude. The URE is an upper-bound estimate of the
excess cancer risk resulting from a lifetime of continuous exposure to an agent at a concentration of
1 |ig/m3 in air. In assessing a substance's carcinogenic potential, the EPA evaluates various types
of toxicological data and develops a weight-of-evidence (WOE) determination. Current WOE
assessments include a system of categorizing carcinogens (recommended by the EPA's 1986
guidelines for carcinogen risk assessment) and a paragraph of descriptive text (recommended by the
current draft revisions to the 1986 guidelines).

The EPA disseminates dose-response assessment information in several forms, depending on the
level of internal review. The 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)

The 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 following inhalation and ingestion. The
ATSDR describes MRLs as concentrations to be used by health assessors in selecting
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.

G-1

-------
Inhalation MRLs were used in the non-cancer portion of this assessment when IRIS RfCs were not
available because the concept, definition, and derivation of MRLs and RfCs are philosophically
consistent (though not identical). The ATSDR publishes MRLs as part of pollutant-specific
toxicological profile documents, and also in a table of "comparison values" that the ATSDR
regularly updates and distributes (available on-line at http://www.atsdr.cdc.gov/mrls.html).

California Environmental Protection Agency (CalEPA)

The CalEPA Air Resources Board 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 is based on
significant external scientific peer review. The non-cancer information includes available
inhalation health risk guidance values expressed as chronic inhalation reference exposure levels
(RELs). The CalEPA defines the REL as a concentration level at (or below) which no health effects
are anticipated, a concept that is substantially similar to the EPA's approach to non-cancer dose-
response assessment. This assessment uses chronic RELs in the same way as RfCs when no IRIS or
ATSDR values exist.

The CalEPA's quantitative dose-response information on carcinogenicity by inhalation exposure is
expressed in terms of the URE, defined similarly to the EPA's URE. This assessment uses specific
CalEPA UREs in the same way as EPA's when no IRIS URE values exist.

The CalEPA's dose response information for carcinogens and noncarcinogens is available on-line at
http://www.oehha.ca.gov/air/hot spots/index.html.

International Agency for Research on Cancer (IARC)

The IARC, a branch of the World Health Organization, coordinates and conducts research on the
causes of human cancer and develops scientific strategies for cancer control. The IARC sponsors
both epidemiological and laboratory research and disseminates scientific information through
meetings, publications, courses, and fellowships.

As part of its mission, the IARC assembles evidence that substances cause cancer in humans and
issues judgments on the strength of evidence. The IARC's "degrees of evidence" categories are
Group 1 (carcinogenic in humans), Group 2A (probably carcinogenic), Group 2B (possibly
carcinogenic), Group 3 (not classifiable), and Group 4 (probably not carcinogenic). The
categorization scheme may be applied to either single chemicals or mixtures. The IARC does not
develop quantitative dose-response indices such as UREs.

The IARC's WOEs for substances are included as supporting information for this assessment as a
backup to the EPA's WOE determinations, which do not cover all substances and in some cases
may be out-of-date. The list of IARC evaluations to date is available at
http://193.51.164.ll/monoeval/grlist.html.

G-2

-------
Prioritizing and Combining Information from Data Sources

Some substances have been subjected to dose-response assessments by several of the agencies used
as sources for this assessment. Because different scientists developed these assessments at different
times for purposes that were similar but not identical, the results are not totally consistent. In some
cases interagency differences are substantial, especially between assessments done many years
apart. To resolve these differences the EPA applied a consistent priority scheme to the available
dose-response information.

Externally peer-reviewed draft RfCs and UREs 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 replace existing values on IRIS. This was only done for
assessments that had already undergone peer review and subsequent revision to reflect peer
comments. This assessment specifically did not use draft assessments that have not yet undergone
such review because the EPA judged that the soundness of assessments should receive a higher
priority than the date on which they were performed. In other words, an older assessment that had
received strong scientific review was preferred to a more recent unreviewed assessment. This
decision is fully consistent with the restructuring of the IRIS review process in 1996 to require such
external peer review. The EPA believes that using unreviewed information in this study would
undermine the quality of this assessment as well as the IRIS review process.

Where externally peer reviewed IRIS draft assessments were not available, this study relied on
information currently in the EPA's IRIS database. For substances lacking IRIS assessments,
ATSDR MRLs (for noncancer effects) received next preference, followed by CalEPA RELs and
UREs.

For two carcinogenic substances (quinoline and 1,2-dichloropropane) that lack UREs for inhalation
exposures, oral carcinogenic potency estimates were converted to inhalation UREs. The oral
potency estimate for quinoline came from an older EPA assessment cited in the EPA's 1997 Health
Effects Assessment Summary Tables (HEAST). The conversion from oral risk (probability of
cancer per mg/kg/d oral intake) to inhalation risk (probability of cancer per ug/m3 inhaled) was
based on the EPA's standard assumptions of a 70-kg body mass and 20 m3/d inhalation rate, as
follows:

The EPA understands that 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 risk estimates altogether, thereby making a de facto assumption
of zero carcinogenic potency. The EPA regards this alternative as unacceptable for the purposes of
the national-scale assessment.

G-3

-------
Assumptions on Speciation and Other Adjustments to Dose-Response Information

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

based on professional judgment:

1. Chromium. For chromium compounds, the IRIS RfC for particulate hexavalent chromium was
used in preference to the RfC for chromic acid mists and dissolved aerosols. Both the RfC and
the URE for hexavalent chromium shown in Tables 1 and 2 below were then adjusted to reflect
an assumption that 34% of all atmospheric chromium is hexavalent. This represents the best
judgment of EPA staff based on limited data on species of chromium emitted from five
significant source categories. The total chromium mass in these emissions ranged from 0.4% to
70%) hexavalent. Because the high end of the range was associated exclusively with
electroplating sources the EPA chose 34%, the upper end of the range for utility boilers. It is
likely that most sources of chromium emissions in the US contain lesser amounts of hexavalent
chromium.

2. 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 mode of action as 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.

3. Polycvclic Organic Matter. The assessment considered poly cyclic organic matter (POM)
emissions reported in the 1996 NTI as "total POM." Total POM reported as a group were
assumed to have a carcinogenic potency equal to 5% of that for pure benzo[a]pyrene. Details of
the derivation of these relative potency estimates are presented in Appendix H of the 2001
Science Advisory Board draft of this study. The draft version of the assessment also included a
separate dose-response value for a subgroup of seven carcinogenic polynuclear aromatic
hydrocarbon (PAH) compounds within the POM category, because these compounds were
tracked as a group in the 1996 NTI and their emissions were more completely characterized than
those of the rest of the POM category. The "7-PAH" compounds as a group were assumed to
have a carcinogenic potency equal to 18% of that for pure benzo[a]pyrene. However, risks
associated with 7-PAH alone were found to be an order-of-magnitude lower than risks from
total POM, and 7-PAH was dropped from the final assessment.

G-4

-------
Table 1: Dose-Responses Values for Cancer.

This table lists quantitative cancer risk potency estimates (summarized as a Unit Risk Estimate or URE) used in the initial 1996 national-scale
assessment. The EPA and IARC weight-of-evidence (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 carcinogen; Group B1—probable carcinogen, based on
incomplete human data; Group B2—probable carcinogen, based on adequate animal data; Group C—possible carcinogen; Group D—not classifiable;
and Group E—evidence of non-carcinogenicity. The IARC categories are Group 1—carcinogenic in humans; Group 2A—probably carcinogenic;
Group 2B—possibly carcinogenic; Group 3—not classifiable; and Group 4—probably not carcinogenic. 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 source of the URE, date of the assessment, and a
description of confidence in the assessment are provided, along with information about the EPA's IRIS schedule. Internet links to the sources for
assessments are provided where possible. Other information such as conformance with the revised cancer guidelines, use of UCL rather than MLE,
existence of URE ranges, etc., is shown in footnotes.

Pulliiliinl

Weijihl of
l'.\ irience
I'.PA IARC

I nil Risk
I'M i in ;i le
(per uii/iir,i

Source

Diilc ill'
Assessment

Oulsiric

Peer
Re\ ic'\\ ?

( onfiricnee
in I Ri:1

I-'.PA IRIS
Reassessment
r.xpeeled

Ciliilion for Ciinvnl Assessment

Acetaldehyde

2.2E-06

IRIS2

1988

Low

2002

www.eoa.sov/iris/subst/0290.htm

Acrylonitrile

6.8E-05

IRIS2

1987

Medium

www.eoa.sov/iris/subst/0206.htm

Arsenic compounds

4.3E-03

IRIS3

1994

High

2002

www.eoa.sov/iris/subst/0278.htm

Benzene

7.8E-06

IRIS3'4'5

1998

Yes

High

www.eoa.sov/iris/subst/0276.htm

Beryllium compounds

2.4E-03

IRIS2'5

1998

Yes

Medium

www.eoa.sov/iris/subst/0012.htm

1,3-Butadiene

3.0E-05

EPA

NCEA2'5'6

2001

Yes

Medium

2001

US EPA, 2001. Health Risk Assessment of 1,3-
Butadiene. IRIS consensus review draft, January,
2001.

Cadmium compounds

1.8E-03

IRIS2

1986

Medium

2002

www.eoa. sov/iris/subst/0141 .htm

Carbon tetrachloride

1.5E-05

IRIS2

1986

Low

2002

www.eoa.sov/iris/subst/0020.htm

1 High - URE incorporates high-quality human data. Medium - URE considers human data of lower quality. Low - URE does not incorporate human data.

2 Upper confidence limit URE (assessments that did not specify method were assumed to use UCL).

3 Maximum likelihood URE.

4 Higher of two recommended UREs used.

5 Consistent with 1996 proposed cancer guidelines.

6 Peer-reviewed draft IRIS assessment, expected to be finalized shortly.

G-5

-------
Polllllillll

Weight of
l.\ irience
I'. PA IARC

I nil Risk
I'.sliniiilc
(per iin/ni'')

Source

Diilc of
Assessment

Outsirie

Peer
Re\ ic\\ ?

( onfirience
in I Rl.1

I-'.PA IRIS
Reassessment
r.xpcclcil

Ciliilion forCuiTcnl Assessment

Chloroform

B2

2B

2.3E-05

IRIS2

1987

No

Low

2002

www.eoa. sov/iris/subst/0025 .htm

Chromium compounds

A

1

1.2E-02

IRIS3'5'7

1998

Yes

High

	

www.era.sov/iris/subst/0144.htm

Coke Oven Emissions

A

_

6.2E-04

IRIS2

1989

No

High

	

www.era. sov/iris/subst/03 95 .htm

1,3 -Dichloropropene

B2

2B

4.0E-06

IRIS2'5

2000

Yes

Low

	

www.eoa.sov/iris/subst/0224.htm

Ethylene dibromide (1,2-
dibromoethane)

B2

2A

2.2E-04

IRIS2

1987

No

Low

2002

www.era. sov/iris/subst/0361 .htm

Ethylene dichloride (1,2-
dichloroethane)

B2

2B

2.6E-05

IRIS2

1986

No

Low

2002

www.era.sov/iris/subst/0149.htm

Ethylene oxide

B1

1

8.8E-05

CAL EPA

1999

Yes

Low

2002

www.oehha.ca.sov/odf/HSCA2.i3df. ds. 290

Formaldehyde

B1

2A

1.3E-05

IRIS2

1991

Yes

Medium

2002

www.era. sov/iris/subst/0419.htm

Hexachlorobenzene

B2

2B

4.6E-04

IRIS2

1989

No

Low

2002

www.eoa.sov/iris/subst/0374.htm

Hydrazine, hydrazine
sulfate

B2

2B

4.9E-03

IRIS2

1987

No

Low



www.era. sov/iris/subst/03 52.htm

Lead compounds

B2

2B

1.2E-05

CAL EPA

1999

Yes

Low

	

www.oehha.ca.sov/odf/HSCA2.odf. os. 331

Methylene chloride
(dichloromethane)

B2

2B

4.7E-07

IRIS2

1989

No

Low

2002

www.eoa.sov/iris/subst/0070.htm

Nickel compounds

A

2B

4.8E-04

IRIS2'7

1987

No

High

2002

www.eoa.sov/iris/subst/0272.htm

Polychlorinated biphenyls
(PCBs)

B2

2A

1.0E-04

IRIS2

1996

Yes

Low



www.eoa.sov/iris/subst/0294.htm

Polycyclic Organic Matter

8

8

5.5E-05

OAQPS9

2001

Yes

Low

	

Appendix H

Carcinogenic PAHs: 7-
PAH

B2

8

2.0E-04

OAQPS9

2001

Yes

Low

200310

Appendix H

7	Number shown is derived from indicated data source, but risk estimates also include subsequent speciation assumptions. Details are provided in text above.

8	WOE varies among individual compounds.

9	Development by OAQPS staff of UREs for total POM and 7-PAH is described in Appendix H. These composite UREs are based on CalEPA estimates for various polycyclic
organic compounds using a toxic equivalency approach in which the potency of individual compounds is estimated based on relative activity rather than individual assessments of
bioassay data.

10	Assessment will be limited to polynuclear aromatic hydrocarbons, an important subset of POM.

G-6

-------
Pollutant

Weight of
Evidence
EPA IARC

Unit Risk
Estimate
(per ujj/m3)

Source

Date of
Assessment

Outside

Peer
Review?

Confidence
in URE1

EPA IRIS
Reassessment
Expected

Citation for Current Assessment

Propylene dichloride (1,2-
dichloropropane)

B2

3

1.9E-05

HEAST
oral211

1991

No

Low



US EPA, 1997. Health Effects Assessment Summary
Tables, EPA-540-R-97-036, FY 1997 Update.

Quinoline

C



3.4E-03

HEAST
oral211

1985

No

Low

2001

US EPA, 1997. Health Effects Assessment Summary
Tables, EPA-540-R-97-036, FY 1997 Update.

1,1,2,2-Tetrachloroethane

C

3

5.8E-05

IRIS2

1986

No

Low

	

www.era. sov/iris/subst/0193 .htm

Tetrachloroethylene
(perchloroethylene)

B2-C

2A

5.6E-06

CAL EPA

1999

Yes

Low

2002

www.oehha.ca.sov/odf/HSCA2.i3df. t>s. 465

Trichloroethylene (TCE)

B2-C

2A

2.0E-06

CAL EPA

1999

Yes

Low

2002

www.oehha.ca.sov/odf/HSCA2.i3df. t>s. 507

Vinyl chloride

A

1

8.8E-06

IRIS2'512

2000

Yes

High

—

www.eoa.sov/iris/subst/1001 .htm

11	Conversion or oral potency slope to inhalation unit risk estimate was based on the following assumptions: (1) whole-life, continuous exposure, (2) inhalation rate of 20 cubic
meters of air per day, and (3) body mass of 70 kg. Details are provided in the text.

12	URE based on whole life exposure was selected over a URE based on adult exposure only.

G-7

-------
Table 2: Dose-Response Values for Effects Other Than Cancer.

This table lists reference concentrations (RfCs) and similar values (i.e., RELs, MRLs) that were used in the initial 1996 national-scale assessment.
The RfC is an estimate of a concentration in air that is likely to be without appreciable risks of deleterious effects during a lifetime (including in
sensitive subpopulations). Where the EPA RfCs were absent, similar values developed by other agencies were used. The UF and MF are the
uncertainty factor and modifying factor used in the development of the RfC. The source of the RfC, date of the assessment, and a description of
confidence in the assessment are provided, along with information about the EPA's IRIS schedule. Internet links to the sources for assessments are
provided where possible. The target organ for critical effects is the organ or organ system adversely affected at the lowest dose in human or animal
studies. The target organs for other effects are those organs or systems adversely affected at higher doses. Other information on individual
substances is shown in footnotes.

Pollutant

RfC13
(mg/m3)

Target Organ
for Chronic
Critical

Effect14

Severity18

of
Critical
Effect

Target
Organs for
Other
Chronic

Effects

Sou rcc

Date of
Assmnt.

Outside

Peer
Review?

Confidence
in RfC16

UF(MF)17

EPA IRIS
Reassmnt.
Expected

Citation for Current Assessment

Acetaldehyde

9.0E-03

Degeneration of
nasal epithelium
in rats

Severe

Growth
retardation in
rats

IRIS

1991

Medium

1000

2002

www. era. ao v/iris/subst/0290 .htm

Acrolein

2.0E-05

Degeneration of
nasal epithelium
in rats

Severe

Lung lesions
in rats

IRIS

1991

Medium

1000

2002

www.eDa.aov/iris/subst/0364.htm

Acrylonitrile

2.0E-03

Degeneration of
nasal epithelium
in rats

Severe

Central
nervous
system

depress-sion in
humans

IRIS

1991

Medium

100(10)

www. epa. ao v/iris/subst/0206 .htm

13 Includes EPA reference concentrations (RfCs) and similar values, i.e., Cal EPA reference exposure levels (RELs), and ATSDR minimum risk levels (MRLs).

14 The critical effect is the adverse effect upon which the RfC or similar value is based.

15 Severe - substantial AND irreversible. Medium - substantial OR irreversible. Mild - not substantial AND not irreversible.

16 For IRIS values, this column shows confidence statement from IRIS. For other sources: High - value incorporates high-quality human data. Medium - value considers human
data of lower quality. Low - value does not incorporate human data.

17 UF - uncertainty factor. MF ~ modifying factor. MFs are shown in parentheses. MF values of 1 are not shown.

G-8

-------
I'olllllillll

Rl( Li

(iiiii/mJ)

T.iriiel ()r»;in
Id i- Chronic
( rilic.il
r.iW4

Se\ cri(\

of
Crilicsil
WTccl

T;irjie(
Oriiiins I'or
Ollicr
( hroilic
I'llccls

Soiiito

Dale of
Assmnl.

Oulsiric

Peer
Rc\ ie\\ ?

( onfiricnce
in Rl(

I 1 (Ml V"

I-'. PA IRIS
Reiissninl.
r.xpeeled

Ciliilion lor Currenl Assessment

Arsenic compounds

3.0E-05

Fetal

malformation in
mice

Severe

Irritation of
mucous mem-
branes in
humans

CAL
EPA

2000

Yes

Medium

1000

2002

www.oehha.ca.aov/air/chronic rels/ndf/acrol-
cresol.pdf vs.. A-8

Benzene

8.0E-02

Depressed
lymphocyte
count in humans

Medium

Central
nervous
system
depression in
humans

EPA
NCEA6

2001

Yes

Medium

100

200118

US EPA, 2001. Toxicological review of benzene
(noncancer effects). Consensus review draft, July
2001.

Beryllium compounds

2.0E-05

Chronic
inflammatory
lung lesions in
humans

Severe

Proliferation
of

lymphocytes
in human lung

IRIS

1998

Yes

Medium

10



www. eua. ao v/iris/subst/0012 .htm

1,3-Butadiene

2.0E-03

Ovarian atrophy
in mice

Severe

Mutation of
germ cells
leading to fetal
death in mice

EPA
NCEA6

2001

Yes

Low

100(3)

2001

US EPA, 2001. Health Risk Assessment of
1,3-Butadiene. IRIS consensus review draft,
lanuary, 2001.

Cadmium compounds

2.0E-05

Kidney damage
(proteinurea) in
humans

Severe

Reduction in
respiratory
capacity in
humans

CAL
EPA

2000

Yes

High

30

2002

www.oehha.ca.aov/air/chronic rels/pdf/acrol-
cresol.pdf vs.. A-40.

Carbon tetrachloride

4.0E-02

Fatty infiltration
in liver of
guinea pigs

Medium

Central
nervous
system
depression in
humans

CAL
EPA

2000

Yes

Low

300

2002

www.oehha.ca.aov/air/chronic rels/ndf/acrol-
cresol.pdf vs. A-47.

Chloroform

9.8E-02

Enlarged liver in
humans

Medium

Enlarged
spleen in
humans

ATSDR

1997

Yes

High

100

2002

ATSDR, 1997. Toxicological profile for
chloroform. US Dept. of HHS.

Chromium compounds

1.0E-047

Lung injury in
rats

Medium

Immune
system effects
in rats

IRIS

1998

Yes

Low

90



www.eDa.aov/iris/subst/0144.htm

18 IRIS assessment to include noncancer effects only.

G-9

-------
Polliiliinl

Rl( Li

(iiiii/mJ)

Tiiriiel ()r»;in
for C hronic
Crilicsil

i.nw-i14

Sc\ cri(\

of
Crilicsil
11 f feel

Tsirjid
Oriiiins for
Oilier
Chronic
IHcels

Soiiito

Diilc of
Assinnl.

Oulsiric

Peer
Rc\ ic\\ ?

( onl'iricncc
in Rl(

I 1 (Ml V"

I'. PA IRIS
Rciissninl.

I.\|)CC(C(I

Cilsilion lorCiirrcnl AsscssmciK

1,3-Dichloropropene

2.0E-02

Degeneration of
nasal epithelium
in rats

Medium

Cell prolifera-
tion in mouse
bladder

IRIS

2000

Yes

High

www. eua. ao v/iris/subst/0224.htm

Ethylene dibromide (1,2-
dibromoethane)

8.0E-04

Reduced sperm
count in humans

Medium

Degeneration
of respiratory
epithelium in
mice and rats

CAL

EPA19

1997

Yes

Medium

100

2002

California EPA, 1997. Technical Support
Document for the Determination of
Noncancer Chronic Reference Exposure Levels.

Ethylene dichloride (1,2-
dichloroethane)

2.4E+00

Liver and
kidney lesions
in rats

Severe

Cardiac
lesions in
several animal
species

ATSDR

1999

Yes

Low

2002

ATSDR, 1999. Toxicological profile for 1,2-
dichloroethane (update). US Dept. of HHS.

Ethylene oxide

3.0E-02

Neurobehavioral
effects (CNS) in
mice

Severe

Effects on
blood in
humans and
mice

CAL
EPA

2000

Yes

Low

100

2002

www.oehha.ca.20v/air/chronic rels/pdf/Dichlbenz-
Hvdr.pdL pa. A-125.

Formaldehyde

9.8E-03

Abnormalities
in nasal mucosa
in humans

Mild

ATSDR

1997

Yes

High

2002

ATSDR, 1999. Toxicological profile for
formaldehyde. US Dept. of HHS.

Hexachlorobenzene

3.0E-03

Liver

(developmental)
effects in animal
studies

Severe

CAL

EPA19

1997

Yes

Low

100

2002

California EPA, 1997. Technical Support
Document for the Determination of
Noncancer Chronic Reference Exposure Levels.

Hydrazine, hydrazine
sulfate

2.0E-04

Abnormal
protein deposits
in hamster liver

Severe

Inflammation
of respiratory
tissues in rats

CAL
EPA

2000

Yes

Low

300

www.oehha.ca.20v/air/chronic rels/pdf/302012.pdf

Lead compounds20

1.5E-03

Neurobehavioral
effects (CNS) in
humans

Severe

Blood,

cardiovascular,
and kidney
effects in
humans

NAAQS

1978

Yes

High

40 CFR 50.12

19 Proposed by Cal EPA in 1997; not yet adopted in final form.

20 EPA has not developed an RfC for lead. The NSA uses the National Ambient Air Quality Standard for lead, which was developed using the EPA Integrated Exposure, Uptake,
Biokinetic Model, and did not use the UF/MF method. Because sensitive human subpopulations were modeled, the effective UF is 1.

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Manganese compounds

5.0E-05

Neurobehavioral
effects (CNS) in
humans

Medium

Cough,
bronchitis in
humans

IRIS

1993

Medium

1000

www.eDa.aov/iris/subst/0373.htm

Mercury compounds21

3.0E-04

Neurobehavioral
effects (CNS) in
humans

Medium

Altered kidney
function in
humans

IRIS

1990

Medium

200122

www.eDa.aov/iris/subst/0370.htm

Methylene chloride

1.0E+00

Pathological
changes in liver
cells in rats

Medium

Effects on
blood

chemistry in
humans

ATSDR

2000

Yes

Low

2002

ATSDR, 2000. Toxicological profile for
methylene chloride. US Dept. of HHS.

Nickel compounds

2.0E-04

Respiratory tract
inflammation in
rats

Mild

Immune
system effects
in humans

ATSDR

1997

Yes

Low

2002

ATSDR, 1997. Toxicological profile for nickel.
US Dept. of HHS.

Propylene dichloride
(1,2-dichloropropane)

4.0E-03

Increase in cell
growth of nasal
epithelium in rat

Mild

Anemia in
rabbits

IRIS

1991

Medium

300

www.eDa.aov/iris/subst/0601 .htm

T etrachloroethy lene
(perchloroethylene)

2.7E-01

Neurobehavioral
effects (CNS) in
humans

Medium

Liver and
kidney damage
in humans

ATSDR

1997

Yes

High

100

2002

ATSDR, 1997. Toxicological profile for
tetrachloroethylene. US Dept. of HHS.

Trichloroethylene (TCE)

6.0E-01

Central nervous
system
depression in
humans

Medium

Respiratory
irritation in
humans

CAL
EPA

2000

Yes

High

100

2002

www.oehha.ca. aov/air/chronic rels/Ddf/79016.Ddf

Vinyl chloride

1.0E-01

Cellular changes
and cysts in rat
liver

Severe

Testicular
damage in rats,
CNS

depression in
humans

IRIS

2000

Yes

Medium

www.eDa.aov/iris/subst/1001 .htm

21 Hazard calculations for mercury compounds were based on the RfC for elemental mercury.

22 This IRIS assessment includes methyl mercury only, and would not have impacted the NATA national-scale assessment.

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