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Basic Information about the Integrated Risk Information System

Author Name, ProPublica

2014-03-25 16:24:34-04:00

EPA’s mission is to protect human health and the environment. EPA’s IRIS Program supports this mission by identifying and characterizing the health hazards of chemicals found in the environment. Each IRIS assessment can cover a chemical, a group of related chemicals, or a complex mixture. IRIS assessments are an important source of toxicity information used by EPA, state and local health agencies, other federal agencies, and international health organizations.

IRIS Toxicity Values

The IRIS Program is located within EPA’s Center for Public Health and Environmental Assessment (CPHEA) in the Office of Research and Development (ORD). The placement of the IRIS Program in ORD is intentional. It ensures that IRIS can develop impartial toxicity information independent of its use by EPA’s program and regional offices to set national standards and clean up hazardous sites.

IRIS assessments provide the following toxicity values for health effects resulting from chronic exposure to chemicals.

More information on deriving RfD and RfC values can be found in EPA’s 2002 A Review of the Reference Dose and Reference Concentration Processes.

Reference Concentration (RfC): An estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark concentration, with uncertainty factors generally applied to reflect limitations of the data used.

Reference Dose (RfD): An estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark dose, with uncertainty factors generally applied to reflect limitations of the data used. RfC An estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark concentration, with uncertainty factors generally applied to reflect limitations of the data used. Generally used in EPA's noncancer health assessments. [Durations include acute, short-term, subchronic, and chronic and are defined individually in this glossary]. RfC An estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark concentration, with uncertainty factors generally applied to reflect limitations of the data used. Generally used in EPA's noncancer health assessments. [Durations include acute, short-term, subchronic, and chronic and are defined individually in this glossary]. An estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark concentration, with uncertainty factors generally applied to reflect limitations of the data used. Generally used in EPA's noncancer health assessments. [Durations include acute, short-term, subchronic, and chronic and are defined individually in this glossary].

More information on deriving cancer risk estimates can be found in EPA’s 2005 Guidelines for Carcinogen Risk Assessment.

Cancer descriptors characterize the chemical as:

Carcinogenic to Humans

Likely to Be Carcinogenic to Humans

Suggestive Evidence of Carcinogenic Potential

Inadequate Information to Assess Carcinogenic Potential

Not Likely to Be Carcinogenic to Humans

Oral slope factor Oral slope factor An upper bound, approximating a 95% confidence limit, on the increased cancer risk from a lifetime oral exposure to an agent. This estimate, usually expressed in units of proportion (of a population) affected per mg/kg-day, is generally reserved for use in the low-dose region of the dose-response relationship, that is, for exposures corresponding to risks less than 1 in 100. (OSF) is an estimate of the increased cancer risk from oral exposure to a dose of 1 mg/kg-day for a lifetime. The OSF can be multiplied by an estimate of lifetime exposure (in mg/kg-day) to estimate the lifetime cancer risk.

Inhalation unit risk unit risk The upper-bound excess lifetime cancer risk estimated to result from continuous exposure to an agent at a concentration of 1 µg/L in water, or 1 µg/m³ in air. The interpretation of unit risk would be as follows: if unit risk = 2 × 10⁻⁶ per µg/L, 2 excess cancer cases (upper bound estimate) are expected to develop per 1,000,000 people if exposed daily for a lifetime to 1 µg of the chemical per liter of drinking water. (IUR) is an estimate of the increased cancer risk from inhalation exposure to a concentration of 1 µg/m3 for a lifetime. The IUR can be multiplied by an estimate of lifetime exposure (in µg/m3) to estimate the lifetime cancer risk.

Find other IRIS terminology in the IRIS Glossary.

What's the Role of IRIS Assessments in Risk Assessment?

Risk assessment is a four-step process described by the National Research Council (NRC) in 1983 as "the characterization of the potential adverse health effects of human exposures to environmental hazards." Characterizing risk involves integrating information on hazard, dose-response, and exposure.

Connection between IRIS, Risk Assessment, and Risk Management Click to enlarge: Connection Between IRIS and Risk Management

An IRIS assessment includes the first two steps of the risk assessment process:

Hazard Identification, which identifies credible health hazards associated with exposure to a chemical, and

Dose-Response Assessment, which characterizes the quantitative relationship between chemical exposure and each credible health hazard. These quantitative relationships are then used to derive toxicity values.

EPA’s program and regional offices identify human exposure pathways and estimate the amount of human exposure under different exposure scenarios (Exposure Assessment). Then they combine their exposure assessment with the hazard information and toxicity values from IRIS to characterize potential public health risks (Risk Characterization).
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[1] URL: https://www.epa.gov/iris/basic-information-about-integrated-risk-information-system#process
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