Toxicity Values


1. INTRODUCTION

The database of chemical-specific toxicity values contains the human health toxicological information needed to perform risk evaluations and assessments. This database contains toxicity information taken from the United States Environmental Protection Agency's (EPA) Integrated Risk Information System (IRIS), the Health Effects Assessment Summary Tables (HEAST), and other sources. In this database, all information is referenced. Additionally, the database contains supplemental information which clarifies some issues. If a user needs additional information about the application or contents of this database, please contact An RAIS Technical Assistant at fdolislager@utk.edu.

The toxicity database contains a variety of information that is used to either calculate risks or hazards (e.g., cancer slope factors and reference doses, respectively) or to derive dose estimates (e.g., volatilization factor). The database contains two levels of organization these are:

  • Nonradionuclides--defined in this database as chemicals that do not undergo nuclear decay and emit ionizing radiation. For example, the inorganic chemicals calcium, carbon, manganese, and iron are nonradionuclides. In addition, the organic compounds trichloroethene, carbon tetrachloride, etc. are also nonradionuclides. The nonradionuclide information provided in the database is discussed in Section 2.
  • Radionuclides--defined in this database as chemicals that do undergo nuclear decay and emit ionizing radiation. For example, the isotopes of uranium, uranium-235 (235U), uranium-236 (236U), and uranium-238 (238U) are radionuclides. Radionuclide information provided in the database is discussed in Section 3.

Within the nonradionuclide level of organization, chemicals are divided into two broad categories. These categories are:

  • Inorganic chemicals--defined as chemicals or compounds that do not contain a carbon skeleton. For example, manganese, mercury, and iron are inorganic chemicals.
  • Organic compounds--defined as chemicals or compounds that do contain a carbon skeleton. For example, trichloroethene, benzo(a)pyrene, and acetone are organic compounds.

It should be noted that the assignment of some chemicals and compounds to these categories is problematical because the chemical may form compounds that contain an organic carbon skeleton. For example, methyl mercury contains mercury which is defined as an inorganic chemical and a methyl group which contains a carbon skeleton. For chemicals and compounds such as these, the presence of the carbon skeleton takes precedence and the compound is categorized as a organic compound.

Although the database can be searched by levels of organization and categories, a more useful search in most applications will be by either chemical name or Chemical Abstracts Service and Registry (CAS) Number. When searching by chemical name, care must be taken because organic compounds, and some inorganic chemicals, are often called by more than one name. For example, 2-butanone is also called methyl ethyl ketone, methyl acetone, 2-oxybutane, or simply MEK, depending on the chemical application.

To assist the user of this database when determining the appropriate chemical name, a link to ChemFinder is provided. This service allows the user to determine synonyms for chemicals and compounds and learn about their chemical characteristics.

Because of the problem with synonyms, a more useful search may be performed using the Chemical Abstracts Service and Registry (CAS) number. This number is assigned by the Chemical Abstracts Service (CAS) which produces the world's largest and most comprehensive databases of chemical information. The CAS databases currently include nearly 14 million abstracts of chemistry-related and patent literature and more than 17 million substances. CAS is located in Columbus, Ohio and is a division of the American Chemical Society.

2. CHEMICAL INFORMATION

As noted earlier, for each chemical or compound a variety of information is provided. However, in some cases, information may be lacking for a chemical or compound. Reasons for this include that the information is not applicable to that chemical or compound or that the information is not available at this time. Toxicity information that is available in the database includes:

  • Chemical name--the common name of the chemical or compound. If the chemical or compound is on one of the lists provided for CERCLAs Contract Laboratory Program (CLP), that chemical or compound name is used. Synonyms are not included in the database.
  • CAS number--the Chemical Abstracts Service and Registry number discussed in the Introduction.
  • Reference Dose (RfD)--for those chemicals eliciting a toxic response, the oral chronic RfD, dermal chronic RfD, oral subchronic RfD, dermal subchronic RfD, inhalation chronic RfD, inhalation chronic RfD, and inhalation subchronic RfD are provided.
  • Cancer slope factor--for those chemicals which are carcinogens, the oral slope factor, inhalation slope factor, and dermal slope factor are provided.
  • EPA Classification--the cancer classification of the chemical or compound assigned by EPA.
  • Date withdrawn--the date which a toxicity value was withdrawn by EPA, if applicable. For withdrawn values, the most recent value prior to withdrawal is included in the database.

Other chemical-specific information that is available in the database includes:

  • Volatilization factor (VF)--an estimate of the rate at which a chemical is emitted from soil as a vapor.
  • Soil saturation concentration (Csat)--an estimate of the maximum concentration of a chemical that may exist in soil before free product is present.
  • Gastrointestinal absorption factor (GIAF)--an estimate of the rate at which a chemical or compound is absorbed from the gastrointestinal tract of a human.
  • Dermal absorption factor (ABS)--an estimate of the rate at which a chemical is partitioned between the skin and a solid medium such as soil.
  • Permeability constant (Kp)--an estimate of the rate at which a chemical is partitioned between the skin and water.
  • Beef transfer coefficient (Fb)--an estimate of the rate at which a chemical is transferred from soil or water through beef to humans as beef is consumed.
  • Fish bioaccumulation factor (BF)--an estimate of the rate at which a chemical is accumulated from water into the tissue of fish.
  • Milk transfer coefficient (Fm)--an estimate of the rate at which a chemical is transferred from soil or water through a cow to humans as milk is consumed.
  • Soil-to-Plant dry uptake factor (Bvdry)--an estimate of the rate at which a chemical in soil or water moves into plant tissues on a dried basis.
  • Soil-to-Plant wet uptake factor (Bvwet)--an estimate of the rate at which a chemical is soil or water moves into plant tissues on a wet basis.
  • Henry's Law Constant (H)--an estimate of the extent of chemical partitioning between air and water and equilibrium. A larger value indicates that the chemical is more likely to volatilize.
  • Molecular weight (MW)--the weight of the chemical.
  • Organic carbon partition coefficient (Koc)--an estimate of the extent of chemical partitioning between organic carbon and water at equilibrium. A larger value indicates that the chemical is more likely to remain bound to soil or sediment.
  • Octanol-water partition coefficient (Kow)--an estimate of the extent of chemical partitioning between water and octanol at equilibrium. A larger value indicates that the chemical is more likely to partition to octanol and, by analogy, more likely to be bioconcentrated in aquatic organisms.

This chemical-specific information is also available here.

2.1 RfDs, RfCs, Slope Factors, and Unit Risks

RfDs, RfCs, slope factors, and unit risks are values which are used to determine either the potential of a toxic effect (RfD and RfC) or the development of excess cancers (slope factors and unit risks) in a receptor. In the database, the following RfDs and slope factors are presented.

  • Oral chronic RfD--the RfD used with administered oral doses under chronic exposures (i.e., exposures lasting more than 7 years) to estimate the potential of a systemic toxic effect.
  • Oral subchronic RfD--the RfD used with administered oral doses under subchronic exposures (i.e., exposures lasting from 2 weeks to 7 years) to estimate the potential of a systemic toxic effect.
  • Inhalation chronic RfD--the RfD used with inhalation doses under chronic exposures to estimate the potential of a systemic toxic effect. The inhalation chronic RfD is derived from an inhalation chronic reference concentration (RfC).
  • Inhalation subchronic RfD--the RfD used with inhalation doses under subchronic exposures to estimate the potential of a systemic toxic effect. The inhalation subchronic RfD is derived from an inhalation subchronic RfC.
  • Dermal chronic RfD--the RfD used with absorbed doses under chronic exposures to estimate the potential of a systemic toxic effect. These are values are derived from the oral chronic RfD.
  • Dermal subchronic RfD--the RfD used with absorbed doses under subchronic exposures to estimate the potential of a systemic toxic effect. These values are derived from the oral subchronic RfD.
  • Oral slope factor--the slope factor used with administered doses to estimate the probability of increased cancer incidence over a lifetime (i.e., excess lifetime cancer risk [ELCR]).
  • Inhalation slope factor--the slope factor used with inhalation doses to estimate the ELCR. The inhalation slope factors in the database are derived from inhalation unit risk values.
  • Dermal slope factor--the slope factor used with absorbed doses to estimate ELCR. These values are derived from the oral slope factor.

In the database, the source of each toxicity value is identified. As noted earlier, the primary sources are EPA's IRIS and HEAST. However, for some chemicals, other sources were used.

2.2 EPA Cancer Classifications

In addition to simply reporting a slope factor for cancinogenesis, EPA also provides codes which indicate the weight-of-evidence available for the chemical. These codes are called EPA cancer classifications and are included in the database. They are defined as follows:

  • A--human carcinogen.
  • B--probable human carcinogen. There are two subclassification.
    • B1--agents for which there is limited human data from epidemiologic studies.
    • B2--agents for which there is sufficient evidence from animal studies and for which there is inadequate or no evidence from human epidemiologic studies.
  • C--possible human carcinogen.
  • D--not classifiable as to human carcinogenicity.
  • E--evidence of noncarcinogenicity for humans.

2.3 Derivation of Dermal Toxicity Values

The dermal chronic RfD, dermal subchronic RfD, and dermal slope factor are derived using the methods provided in the Risk Assessment Guidance for Superfund: Volume 1, Human Health Evaluation Manual, Part A (EPA/540/1-89/002). In addition to the uncertainties caused by route differences, further uncertainty is introduced by the fact that the oral dose-response relationaships are based on potential (i.e., administered) dose, whereas the dermal dose estimates are absorbed doses. Ideally, these differences in route and dose type should be resolved via pharmacokinetic modeling. Alternatively, if estimates of the gastrointestinal absorption fraction are available for the compound of interest in the appropriate vehicle, then the oral dose-response factor, unadjusted for absorption, can be converted to an absorbed dose basis as follows (see related discussion in Appendix A of RAGS, EPA) (Dermal Exposure Assessment: Principles and Applications, USEPA, Office of Research and Development, Washington, DC, EPA/600/8-91/011B, January, 1992):

Oral RfD × GI Absorption Factor = RfDabsorbed

Oral Slope Factor/GI Absorption Factor = Slope Factorabsorbed

All gastrointestinal absorption data used in the conversions were obtained from literature searches. However, for chemicals for which gastrointestinal absorption factors could not be found, default oral absorption efficiencies contained in EPA Region 4's Supplemental Guidance to RAGS: Region 4 Bulletins Human Health Risk Assessment, November 1995, were used. These default values are as follows :

  • 80% for volatile organic chemicals.
  • 50% for semi-volatile organic chemicals.
  • 20% for inorganic chemicals.

As with the toxicity values, references are provided for each of the gastrointestinal absorption factors used.

2.4 Derivation of Inhalation RfDs and Slope Factors from RfCs and Unit Risks

The inhalation chronic RfDs and inhalation subchronic RfDs in the database are derived from the inhalation chronic RfCs and inhalation subchronic RfCs. The RfDs are calculated as shown in the following equation (HEAST 1995):

[RfC (mg/m3) x 20 m3/day] / 70 kg = RfD (mg/kg*day)

Similarly, the inhalation slope factors in the database are derived from the inhalation unit risks. The inhalation slope factors are calculated as shown in the following equation taken from Supplemental Guidance to RAGS: Region 4 Bulletins Human Health Risk Assessment, November 1995:

Unit risk (ug/m3)-1 x 70 kg x (20 m3/day)-1 x 1000 ug/mg = SFI (mg/kg*day)-1

It should be noted that these conversions result in inhalation RfDs and slope factors that are specifically for an adult. If these derived inhalation RfDs and slope factors values are used for exposure by children, the uncertainty this introduces in the resulting hazard quotients and ELCRs should be discussed. It is permitted to change these equations by utilizing the body weight and inhalation rate of a child versus that of an adult to address this uncertainty; however, this change may be incorrect due to the methods used to derive the RfC or the unit risk. Therefore, changing these equations by utilizing the body weight and inhalation rate of a child versus that of an adult should be evaluated on a case-by-case basis by a risk assessment professional or a toxicologist prior to its implementation. Generally, individuals planning to use this technique to derive inhalation RfDs and slope factors should consider the discussion in Appendix A, Section II: Dose Conversions On HEAST (HEAST 1995).

2.5 Withdrawn Values

As noted earlier, some toxicity values contained in this database were previously listed in IRIS or HEAST but later removed or withdrawn. These values are included in the database in order to be consistent with EPA regional guidance (e.g., EPA Region 4's Supplemental Guidance to RAGS: Region 4 Bulletins Human Health Risk Assessment, November 1995, which states that it is appropriate to use these withdrawn toxicity values if no replacement value exists in approved sources). Each of the withdrawn values is referenced in the database along with date of withdrawal. (If the value was withdrawn before September 1993, a default date of 9/93 is listed.) Please note, if a chemical with a withdrawn toxicity value is determined to be a risk driver at a site (using a withdrawn toxicity value), the uncertainties in the withdrawn value should be discussed in the risk assessment, and the assessor should consult with their regulatory agencies.

2.6 Provisional Values

For most chemicals and compounds, when IRIS or HEAST does not provide either current or withdrawn toxicity values for a chemical, no toxicity value is provided in this database. In this case, the user should contact the Superfund Health Risk Technical Support Center at (513) 569-7300. However, in compiling this database, the Superfund Support Center was contacted, and a list of provisional values was obtained. The chemicals with provisional values are listed in the following table. Note, the provisional toxicity values contained in this list are in the database.

Provisional Toxicity Values

Ref. # Listed Below Chemical CAS Number Type of Value Toxicity Value Units
1 Chloromethane 74-87-3 Subchronic inhalation RfC 9.10E+00 mg/kg-day
2 Ethylbenzene 100-41-4 Subcronic oral RfD 9.70E-02 mg/kg-day
3 Hexachlorobutadiene 87-68-3 Subchronic oral RfD 6.67E-04 mg/kg-day
4 Naphthalene 91-20-3 Chronic oral RfD 3.57E-02 mg/kg-day
5 Tetrachloroethylene 127-18-4 Oral slope factor 5.20E-02 (mg/kg-day)-1
Inhalation slope factor 2.00E-03 (mg/kg-day)-1
6 1,1,1-Trichloroethane 71-55-6 Chronic inhalation RfC 1.00E+00 mg/kg-day
7 Trichloroethylene 79-01-6 Oral slope factor 1.10E-02 (mg/kg-day)-1
Inhalation slope factor 6.00E-03 (mg/kg-day)-1
8 Xylene, Mixture 1330-20-7 Subchronic oral RfD 3.57E-01 mg/kg-day
9 Xylene, p 106-42-3 Subchronic oral RfD 2.67E-01 mg/kg-day
10 Xylene, m 108-38-3 Subchronic oral RfD 6.67E-02 mg/kg-day

1) EPA. 1995. Risk Assessment Issue Paper for: Derivation of a Provisional Subchronic Inhalation RfC for Chloromethane (CASRN 74-87-3). Superfund Technical Support Center, National Center for Environmental Assessment, Cincinnati, OH.

2) EPA. 1995. Risk Assessment Issue Paper for: Derivation of a Provisional Subchronic Oral RfD for Ethylbenzene (CASRN 100-41-4). Superfund Technical Support Center, National Center for Environmental Assessment, Cincinnati, OH.

3) EPA. 1995. Risk Assessment Issue Paper for: Derivation of a Provisional Subchronic Oral RfD for Hexachlorobutadiene (CASRN 87-68-3). Superfund Technical Support Center, National Center for Environmental Assessment, Cincinnati, OH.

4) EPA. 1995. Risk Assessment Issue Paper for: Provisional Oral RfD for Naphthalene (CASRN 91-20-3). Superfund Technical Support Center, National Center for Environmental Assessment, Cincinnati, OH.

5) EPA. 1995. Risk Assessment Issue Paper for: Carcinogenicity Information for Tetrachloroethylene (perchloroethylene, PERC) (CASRN 127-18-4). Superfund Technical Support Center, National Center for Environmental Assessment, Cincinnati, OH.

6) EPA. 1995. Risk Assessment Issue Paper for: Derivation of An Inhalation Reference Concentration for 1,1,1-Trichloroethane (CASRN 71-55-6). Superfund Technical Support Center, National Center for Environmental Assessment, Cincinnati, OH.

7) EPA. 1995. Risk Assessment Issue Paper for: Carcinogenicity Information for Trichloroethylene (TCE) (CASRN 79-01-6). Superfund Technical Support Center, National Center for Environmental Assessment, Cincinnati, OH.

8) EPA. 1995. Risk Assessment Issue Paper for: Derivation of the Subchronic Oral Reference Dose for Mixed Xylenes (CASRN 1330-20-7). Superfund Technical Support Center, National Center for Environmental Assessment, Cincinnati, OH.

9) EPA. 1995. Risk Assessment Issue Paper for: Derivation of the Subchronic Oral Reference Dose for para-Xylenes (CASRN 106-42-3). Superfund Technical Support Center, National Center for Environmental Assessment, Cincinnati, OH.

10) EPA. 1995. Risk Assessment Issue Paper for: Derivation of the Subchronic Oral Reference Dose for meta-Xylene (CASRN 108-38-3). Superfund Technical Support Center, National Center for Environmental Assessment, Cincinnati, OH.

2.7 Polychlorinated Biphenyls

In September 1996, the EPA Office of Research and Development (ORD) issued new guidance on the use of slope factors for polychlorinated biphenyls (PCBs) entitled PCBs: Cancer Dose-Response Assessment and Application to Environmental Mixtures (EPA/600/P-96/001F).

The new ORD guidance contains new slope factors based on experimentation with commercial mixtures of PCBs that may be used for environmental mixtures. Although the guidance recognizes that the difference in the representation of various isomers containing different chlorine content and different chemical structures, also termed congeners, in the two types of mixtures can be great, and that environmental mixtures should not be assumed to have the same congener distribution as is present in the commercial mixtures, this guidance recommends that the new slope factors be used instead of the old slope factors. However, the ORD guidance also recommends that isomer and congener-specific analysis of PCBs be used if PCBs could pose a risk.

In their guidance, ORD provides both upper-bound slope factors and central estimate slope factors; however, because of human variability and uncertainty in the environmental mixture composition, the upper-bound slope factors which are listed in this database should be used in most cases to ensure risk estimates are conservative. The central estimate slope factors, which are also provided in the database, may be an appropriate when site characteristics are known in great enough detail.

The following is a suggested matrix for PCB toxicity values developed using information in the ORD document.

Scenario 1 (no knowledge of congeners)
Receptor: Adult (no child)

Media Pathway Slope Factor (mg/kg-d)-1
Soil/Sediment Ingestion 2.0
Dermal a 2.22
Inhalation 2.0
Groundwater Ingestion 0.4
Dermal a 0.444
Inhalation 2.0
Surface Water Ingestion 0.4
Dermal a 0.444
Inhalation 2.0
Fish Ingestion 2.0
Meat, Milk, or Crops Ingestion 2.0



Scenario 2 (no knowledge of congeners)
Receptor: Child

Media Pathway Slope Factor (mg/kg-d)-1
Soil/Sediment Ingestion 2.0
Dermal a 2.22
Inhalation 2.0
Groundwater Ingestion 2.0
Dermal a 2.22
Inhalation 2.0
Surface Water Ingestion 2.0
Dermal a 2.22
Inhalation 2.0
Fish Ingestion 2.0
Meat, Milk, or Crops Ingestion 2.0



Scenario 3 (knowledge of congeners with 4 chlorines in a media < 0.5% total)b
Receptor: Adult (no child)

Media Pathway Slope Factor (mg/kg-d)-1
Soil/Sediment Ingestion 0.07 & Dioxin Toxicity Equivalency
Dermal 0.07 & Dioxin Toxicity Equivalency
Inhalation 0.07 & Dioxin Toxicity Equivalency
Groundwater Ingestion 0.07 & Dioxin Toxicity Equivalency
Dermal 0.07 & Dioxin Toxicity Equivalency
Inhalation 0.07 & Dioxin Toxicity Equivalency
Surface Water Ingestion 0.07 & Dioxin Toxicity Equivalency
Dermal 0.07 & Dioxin Toxicity Equivalency
Inhalation 0.07 & Dioxin Toxicity Equivalency
Fish Ingestion 0.07 & Dioxin Toxicity Equivalency
Meat, Milk, or Crops Ingestion 0.07 & Dioxin Toxicity Equivalency



Scenario 4 (knowledge that congeners with 4 chlorines in each media < 0.5% total)b
Receptor: Child

same as Scenario 2

a Assumes that an absorption factor has been applied to reduce the external dose. If no absorption factor is applied, then the value of 0.4 (mg/kg-d)-1 should be used. It should be noted that this approach is inconsistent with other EPA approaches to dermal absorption of contaminants because the absorbed dose is normally used. However, for PCBs it is assumed that the administered dose is being used.

b Congeners or isomer analyses verified that congeners with more than four chlorines comprise less than 0.5 % of total PCBs in the medium. For Scenarios 3 and 4, where congener-specific knowledge is obtained, the total risk should be estimated by using both the PCB slope factor and the Dioxin Toxicity Equivalency Factors (see following table) for those PCBs that are diox in-like [Ahlborg, U. G., et al. (1994) Toxic equivalency factors for dioxin-like PCBs. Chemosphere, 28(6): 1049-1067.]. The Lowest Risk and Persistence category for PCBs has a pronounced dioxin-like toxicity mechanism in addition to the lower toxicity exerted through the typical PCB-like mechanism. The two different mechanisms of toxicity are only important for the Lowest Risk and Persistence category since the other PCB categories will predominantly exert their toxic effect through the typical PCB toxicity mechanism.

The following table contains the various dioxin-like toxicity equivalency factors for PCBs contained in Scenario 3 [Van den Berg et al. (2006)] which are the WHO 2005 values.

Dioxin Toxicity Equivalence Factors for Use with Polychlorinated Biphenyls


Type
Congener
TEF
IUPAC No. Structure
Non-ortho 77 3,3',4,4'-TetraCB 0.0001
81 3,4,4',5-TetraCB 0.0003
126 3,3',4,4',5-PeCB 0.1
169 3,3',4,4',5,5'-HxCB 0.03
Mono-ortho 105 2,3,3',4,4'-PeCB 0.00003
114 2,3,4,4',5-PeCB 0.00003
118 2,3',4,4',5-PeCB 0.00003
123 2',3,4,4',5-PeCB 0.00003
156 2,3,3',4,4',5-HxCB 0.00003
157 2,3,3',4,4',5'-HxCB 0.00003
167 2,3',4,4',5,5'-HxCB 0.00003
189 2,3,3',4,4',5,5'-HpCB 0.00003
Di-ortho* 170 2,2',3,3',4,4',5-HpCB 0.0001
180 2,2',3,4,4',5,5'-HpCB 0.00001

* Di-ortho values come from Ahlborg, U.G., et al. (1994) which are the WHO 1994 values from Toxic equivalency factors for dioxin-like PCBs : Report on WHO-ECEH and IPCS consultation, December 1993  Chemosphere, Volume 28, Issue 6, March 1994, Pages 1049-1067.

2.8 Carcinogenic Polycyclic Aromatic Hydrocarbons and Chlorinated Dioxins and Furans

2.8.1 Carcinogenic polycyclic aromatic hydrocarbons

In Provisional Guidance for Quantitative Risk Assessment of Polycyclic Aromatic Hydrocarbons (EPA/600/R-93/089, July 1993) and regional guidance, EPA recommends that a toxicity equivalency factor (TEF) be used to convert concentrations of carcinogenic polycyclic aromatic hydrocarbons (cPAHs) to an equivalent concentration of benzo(a)pyrene when assessing the risks posed by these substances. These TEFs are based on the potency of each compound relative to that of benzo(a)pyrene. For the toxicity value database, these TEFs have been applied to the toxicity values. Although this is not in complete agreement with the direction in the aforementioned documents, this approach was used so that toxicity values could be generated for each cPAH. Additionally, it should be noted that computationally it makes little difference whether the TEFs are applied to the concentrations of cPAHs found environmental samples or to the toxicity values as long as the TEFs are not applied to both. However, if the adjusted toxicity values are used, the user will need to sum the risks from all cPAHs as part of the risk assessment to derive a total risk from all cPAHs. A total risk from all cPAHs is what is derived when the TEFs are applied to the environmental concentrations of cPAHs and not to the toxicity values.

The following table presents the TEFs for cPAHs recommended in Provisional Guidance for Quantitative Risk Assessment of Polycyclic Aromatic Hydrocarbons and in regional guidance.

Toxicity Equivalency Factors for Carcinogenic Polycyclic Aromatic Hydrocarbons

Compound TEF
Benzo(a)pyrene 1.0
Benz(a)anthracene 0.1
Benzo(b)fluoranthene 0.1
Benzo(k)fluoranthene 0.01
Chrysene 0.001
Dibenz(a,h)anthracene 1.0
Indeno(1,2,3-c,d)pyrene 0.1

Provisional inhalation toxicity values for cPAHs

A provisional inhalation toxicity value for cPAHs has been developed by the National Center for Environmental Assessment, Cincinnati, Ohio. This inhalation toxicity value is based on a hamster inhalation study using benzo(a)pyrene. The inhalation slope factor is 3.1 (mg/kg-day)-1 and the inhalation unit risk is 0.88 (mg/m3)-1. Using this benzo(a)pyrene inhalation slope factor, the appropriate TEFs were used to derive the other cPAH inhalation slope factors contained in the toxicity value database.

2.8.2 Chlorinated dioxins and furans

Similar to the approach for cPAHs, EPA recommends using TEFs to adjust all chlorinated dioxin and furan concentrations into toxic equivalents of 2,3,7,8-tetrachlorodibenzodioxin (TCDD) prior to determining the risk posed by these substances. However, as with the cPAHs, the TEFs for dioxins and furans are used in this database to derive toxicity values for the various dioxins and furans. Please note, if the derived toxicity values for the chlorinated dioxins and furans presented in this database are used to assess risk, then it would not be appropriate to apply the TEFs to the environmental concentrations as well. Also, if the TEFs are applied to the environmental concentrations, then only the toxicity values for TCDD should be applied to the sum of the doses from all chlorinated dioxins and furans. Finally, if the derived toxicity values are used, it may be necessary to sum the risks from all chlorinated dioxins and furans to derive a total risk estimate for all chlorinated dioxins and furans. Van den Berg et al. (2006)

Toxicity Equivalency Factors for Chlorinated Dioxins

Compound TEF
2,3,7,8-TCDD 1.0
2,3,7,8-PeCDD 1.0
2,3,7,8-HxCDD 0.1
1,2,3,6,7,8-HxCDD 0.1
1,2,3,7,8,9-HxCDD 0.1
2,3,7,8-HpCDD 0.01
OCDD 0.0003
Other CDDs 0

Toxicity Equivalency Factors for Chlorinated Furans

Compound TEF
2,3,7,8-TCDF 0.1
1,2,3,7,8-PeCDF 0.03
2,3,4,7,8-PeCDF 0.3
2,3,7,8-HxCDF 0.1
1,2,3,6,7,8-HxCDF 0.1
1,2,3,7,8,9-HxCDF 0.1
2,3,4,6,7,8-HxCDF 0.1
2,3,7,8-HpCDF 0.01
1,2,3,4,7,8,9-HpCDF 0.01
OCDF 0.0003
Other CDFs 0

2.9 National Ambient Air Quality Standards

Another source of toxicity information that may be of some use is the National Ambient Air Quality Standards (NAAQS) developed under the Clean Air Act. Although these values are not toxicity values, they do set limits on the acceptable concentration of contaminants in air. The following table lists the NAAQS. These values are not contained in the toxicity value database because they represent different levels of review and methods of calculation and must be interpreted and used differently.

National Ambient Air Quality Standardsa
(as of December 2, 1991)

Pollutant Primary Standardsb Averaging Time Secondary Standardsb
Carbon Monoxide (CO) 9 ppm (10 mg/m3)
35 ppm (40 mg/m3)
8 hoursc
1 hourc
None
Lead (Pb)
(and Lead compounds)
1.5 g/m3 Quarterly Same as primary
Nitrogen dioxide (NO2)
(Nitrogen oxide)
(Nitric oxide)
0.053 ppm
(100 g/m3)
Annual Same as primary
Particulate Matter
(PM10)
50 g/m3
150 g/m3
Annuald
24 hourse
Same as primary
Ozone (O3) 0.12 ppm
(235 g/m3)
1 hourf Same as primary
Sulfur dioxide (SO2)
(Sulfur oxide)
0.03 ppm

(80 g/m3)

Annual __
0.14 ppm
(365 g/m3)
24 hoursc __
__ 3 hoursc 0.5 ppm
(1300 g/m3)

a Source: U.S. EPA 1991. Subchapter C-Air Programs. Part 50-National Primary and Secondary Ambient Air Quality Standards. Code of Federal Regulations 50: 693-697. Revised 7/1/91.

b Primary standards are designed to protect public health; Secondary standards are designed to protect public welfare.

c Not to be exceeded more than once per year.

d The standard is attained when the expected annual arithmetic mean concentration is less than or equal to 50 g/m3.

eThe standard is attained when the expected number of days per calendar year with a 24-hour average concentration above 150 g/m3 is less than 1.

f The standard is attained when the expected number of days per calendar year with maximum hourly average concentrations above 0.12 ppm is equal to or less than 1.

3. RADIONUCLIDE INFORMATION

Much of the chemical characteristics information contained in the database for radionuclides is similar to that for chemicals. Therefore, this discussion focuses on the sources and definitions of the radionuclide toxicity values.

In the radionuclide portion of the database, toxicity values for ingestion, inhalation, and external exposure are presented. In all cases, the only values presented are those for carcinogenesis (i.e., slope factors). If a RfD for a radionuclide is needed, the user should access the RfD for the inorganic chemical in the nonradionuclide portion of the database. For example, the radionuclide portion of the database contains ingestion, inhalation, and external exposure slope factors for each uranium isotope (e.g., 234U, 235U, 236U, 237U, 238U); however, the radionuclide portion of the database does not contain RfDs for these isotopes even though exposure to uranium may cause elicit a systemic toxic response. If the user requires an RfD for any of the uranium isotopes, the RfD for "Uranium (Soluble Salts)" should be used. This value is contained in the nonradionuclide portion of the database.

All slope factors contained in the radionuclide database were calculated by the EPA's Office of Radiation and Indoor Air (ORIA). These values were derived by ORIA using methods for estimating radiogenic cancer risks. A detailed discussion of ORIA's approach and assumptions for this methodology is presented in Estimating Radiogenic Cancer Risks (EPA/402/R-93/076).

For some radionuclides, two sets of slope factors are presented. For example, in the database there is a set of slope factors for 235U and a set of slope factors for 235U + D. In these cases, the set of slope factors for the radionuclide is used when estimating risk from exposure to pure radioisotope, and the set of slope factors for radionuclide + D is used when estimating risk from exposure to the radioisotope and its short-lived radioactive decay daughter products (i.e., those decay products with radioactive half-lives less than or equal to 6 months--see HEAST).

It should be noted that a slope factor for dermal contact is not included in the radionuclide portion of the database. These have not included because they are not available, and EPA has concluded that dermal uptake is generally not an important route of uptake for radionuclides (RAGS, 1989).

The only additional chemical-specific parameter contained in the radionuclide portion of the database that is not contained in the nonradionuclide portion of the database is radioactive half-life (TR). This value is provided to assist the risk assessor determine the importance of radioactive decay and daughter ingrowth in the risk evaluation.