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Air Risk Assessment

Risk is the "possibility of suffering harm or loss; danger." Scientists use the term risk when assessing potential human health threats from exposure to toxic chemicals in the environment.

The Air Toxics Program within IDEM’s Office of Air Quality works to understand and reduce potential health risks in areas from the cumulative effects of combined exposure to air toxics from regulated sources. Air risk assessments are special studies that the Air Toxics Program conducts in areas where air toxics may pose a public health and environmental threat. Air risk assessments enable IDEM and local communities to work together to identify what, if any emissions reductions may be needed for the protection of citizens.

How IDEM Selects Areas for Air Risk Assessments

Air risk staff in IDEM’s Air Toxics Program works in several ways to identify areas that are in need of an air risk assessment:

IDEM also may initiate special studies in response to concerns raised by other federal, state or local government agencies and/or citizen pollution complaints.

The Air Risk Assessment Puzzle

The primary pieces to the air risk assessment puzzle are the concentration of chemicals in the area of the study, toxicity of the chemical(s), and the public’s exposure to the chemical(s) of concern. Concentration is the amount of a chemical that is present in a sample of air, compared to the total amount of air in the sample. Today’s technology enables the measurement of extremely small concentrations. Toxicity refers to the degree to which a chemical is harmful to human health and chemical concentrations that increase cancer risks and cause other serious non-cancer health. IDEM calculates estimated cancer risks and non-cancer hazards using established dose-response [ZIP]. Exposure refers to the ways in which a person comes in contact with a chemical and the duration of that contact. As exposure, concentration or toxicity of a chemical increases, human health risks also increase.

Once IDEM identifies an area that may be in need of an air risk assessment, the Air Toxics Program generally follows a four step process to characterize risk:

  • Step 1) Hazard Identification, which involves reviewing key research to identify any potential health problems that a chemical can cause.
  • Step 2) Exposure Assessment, which involves determining the amount, duration and pattern of exposure to the chemical.
  • Step 3) Dose-Response Assessment, which involves estimating toxicity (how much of the chemical it would take to cause varying degrees of health effects that could lead to illnesses).
  • Step 4) Risk Characterization, which is the assessment of the risk for the chemical to cause cancer or other illnesses in the general population.

There are many variables that may affect estimations and their accuracy. Where there are two or more viable inputs, IDEM selects the input that is more protective of human health to prevent from underestimating risk.

Air risk assessments may lead to actions to reduce emissions in the area of the study, which may affect citizens and businesses. Examples include voluntary pollution prevention initiatives or the adoption of new rules.

IDEM has conducted several detailed studies to date, including the statewide ToxWatch Monitoring Data Study for 2006-2015 and local assessments including Indiana Lakeshore Air Toxics Screening, IPS School 21 Risk Characterization and Reduction Project, and Southwest Indianapolis Air Toxics Study.

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