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Air Emissions Risk Analysis (AERA) —
Chemical Information

Particular chemicals, or pollutants, are given special consideration in the AERA process. The Risk Assessment Screening Spreadsheet (RASS) and Q/CHI spreadsheet are updated with new pollutants as appropriate. Inhalation health benchmark changes are made and then posted on the Risk Assessment Screening (RASS) and Q/CHI Web page in the downloadable files.

MDH/MPCA AERA Hierarchy for Identifying Inhalation Health Benchmarks

Based on Minnesota Department of Health (MDH) guidance, the MPCA uses the following hierarchy to identify the inhalation health benchmarks for assessing screening level “risks” using the RASS. The hierarchy is followed to identify the inhalation health benchmarks available for each of the following four categories: acute, subchronic, chronic cancer, and chronic noncancer.

Minnesota Department of Health (MDH) Guidance

The Minnesota Department of Health (MDH) has posted information regarding exposures and health risks to chemicals in our environment on their Chemicals and Hazards Web page. The MDH is part of the AERA team and MPCA requests advice from them on specific chemical toxicity issues. MPCA requests submitted to MDH as well as MDH recommendations will be available on the MDH Rules/Guidance Web page.

Chemical Information Based on MDH Recommendations

  • Acrolein: In response to MPCA's request for guidance on assessing potential health impacts from short-term inhalation exposure to acrolein (a ubiquitous combustion byproduct) MDH developed an acute air health-based value (HBV). The acute HBV of 2 µg/m3 replaces the old Cal EPA value of 0.19 µg/m3.
  • 1,3-Butadiene: EPA recently updated the IRIS inhalation unit risk value for 1,3-Butadiene. In response to MPCA's request to review the updated literature on 1,3-Butadiene, MDH developed a chronic cancer HBV of 0.3 µg/m3. This value replaces the previous value of 0.04 µg/m3.
  • Dioxins/Furans: The MDH reviewed US EPA’s draft Dioxin Reassessment document in an effort to identify a consistent approach for agencies and programs to assess the carcinogenic health risks from exposure to dioxin-like compounds. In a memo to the MPCA dated March 2003, the MDH recommended a numerical cancer slope factor to evaluate incremental cancer risk from oral exposures. This memorandum can be found at the following link:
  • Ethanol Sector Specific Interim Exposure Values (ESSIEVs): In response to MPCA's request for inhalation health benchmarks for chemicals from ethanol facilities, MDH developed sector-specific acute and chronic benchmarks for thirteen chemicals. MDH's guidance on use of ESSIEVs can be found at the following link:
  • Formaldehyde: USEPA’s Office of Air Quality, Planning and Standards (OAQPS) is using a unit risk for formaldehyde that is 2000 times lower than the MDH and EPA formaldehyde value. The MPCA requested that MDH review the chronic Health Risk Value (HRV) for formaldehyde against EPA’s OAQPS’s value used for risk assessments of hazardous air pollutants.  MDH recommended that MPCA replace the old chronic HRV of 0.77 µg/m3 with a new value of 2.0 µg/m3 based on a MDH memorandum dated June 20, 2006.

  • Hexane:  MDH responded to MPCA’s request to comment on the subchronic HEAST value for n-hexane.  MDH recommended not using the subchronic value due to insufficient evidence being available to substantiate the value.  The subchronic HEAST value of 200 µg/m3 has been removed from the RASS. 

  • Nitrogen Oxides: MPCA requested guidance from MDH on using California EPA’s acute inhalation health benchmark to assess short-term exposures to hourly modeled Nitrogen Oxides concentrations in air. MDH’s response can be found below.
  • PAHs: MDH guidance on estimating health risks from carcinogenic polycyclic aromatic hydrocarbons (cPAHs) can be found at the following link:
  • Polycyclic Organic Matter: MPCA and MDH recently updated the cancer unit risk for Polycyclic Organic Matter (POM) in the RASS.  POM chemical constituents for which emissions have been characterized that have inhalation health benchmarks in the RASS can be speciated for chemical-specific risk computation. Cancer risks from the remaining POM emissions are estimated using 5% of the benzo(a)pyrene unit risk [0.05 x 0.0011 = 5.5E-05 (µg/m3) -1].  This new value replaces the CalEPA value of 1.1E-03, which was based on 100% of the surrogate benzo(a)pyrene. This update is based on guidance provided in EPA's "Air Toxics Risk Assessment Reference Library Volume 2 - Facility-Specific Assessment." Exit to Web

  • Tetrachloroethylene (Perchloroethylene):  MDH has provided guidance on the use of California EPA values for chronic cancer and noncancer exposure.  The RASS has been updated to reflect a cancer unit risk of 20 µg/m3 from a previous Cal EPA value of 1.7 µg/m3 and a chronic noncancer RfC of 100 µg/m3 from a previous Cal EPA value of 35 µg/m3.

  • Trichloroethylene (TCE):  MDH developed a chronic Health-Based Value of 3 µg/m3 for inhalation exposure to TCE.  MDH’s value replaces the CAL EPA value of 5 µg/m3.

Additional Chemical-specific Information

  • Mercury: Many of Minnesota’s surface waters are impaired by mercury from atmospheric origin. The MPCA’s goal is to minimize increases in mercury emissions associated with new facilities or expansions with the understanding that some releases are unavoidable. Risks from inhaling mercury emitted to the air from a facility are quantitatively evaluated in the AERA process. Risks from ingesting mercury-contaminated fish are not easily assessed because the magnitude of the risk depends on the presence and highly variable nature of the surrounding water bodies.

    Project proposers identified in MPCA’s guidelines for new and expanding sources of mercury should refer to MPCA’s guidelines on identifying mercury inputs and environmental releases. The types of facilities requested to follow these guidelines include: taconite production, secondary metal processors, fuel combustion in electricity generating stations and industrial boilers (except when burning only natural gas), sewage sludge incineration, municipal or other incineration. These facilities may also be asked to address the potential for adverse human health impacts through consumption of fish from fishable water bodies in the vicinity.
  • Total Petroleum Hydrocarbon Guidance: Total Petroleum Hydrocarbons are emitted in high quantities from some facilities. For this reason, health based Inhalation Health Benchmarks (IHB) for various Total Petroleum Hydrocarbon fractions were derived based on inhalation studies of petroleum mixtures from which aromatic hydrocarbons were removed. The results of the studies were reported in: Development of Fraction Specific Reference Doses and Reference Concentrations from Total Petroleum Hydrocarbons, Volume 4, Total Petroleum Hydrocarbon Working Group Series. The recommended values were reviewed by the MDH and one value was selected for use in air toxics reviews. The working group report can be viewed at:

Who to Contact

For additional information on chemical specific guidance, please contact: Environmental Analysis and Outcomes Division, Risk Evaluation/Air Modeling Unit

Last modified on November 02, 2012 12:09
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