FAQs about risk assessment

What are health benchmarks?

Health benchmarks are developed through scientific review of toxicity and exposure data. There are different benchmarks for ingestion and inhalation. The MPCA uses health benchmarks to assess the health risks from both short and long-term exposures to air pollutants. More information about health benchmarks is available on MPCA’s Air Toxics webpage.

How is non-cancer risk calculated?

The risk estimate for non-cancer is a number expressing a summed ratio between an air concentration and a level at which non-cancer health effects are unlikely. Air pollutants are compared to their respective health benchmarks individually, and then these ratios are summed. The resulting hazard index provides an assessment of the total potential risk, including cumulative effects, from all pollutants. The higher the number, the higher the risk.

What is a cancer risk?

The cancer risk estimates produced by MNrisks are different from non-cancer assessments because we assume that any exposure —no matter how small— to a carcinogen results in a health risk. The U.S. EPA sets a  general guideline for cancer risks based on a level that is not likely measureable in actual populations.

In Minnesota each year, there are roughly 26,000 new cancer cases. This means about one out of every two Minnesotans will be diagnosed with a potentially serious cancer during his or her lifetime. The cancer guideline for air pollutants is set to a value much lower than this: one additional case in a population of 100,000 people. This level is indistinguishable from the background risk. Cancer risks for a single pollutant represent a comparison of the pollutant’s concentration to a health benchmark set at a risk guideline of 1 in 100,000.

What are the limitations and uncertainties of MNrisks modeling?

The uncertainties in MNrisks come from two main sources:

  1. Emissions and source location data
  2. Air dispersion and health risk models

Use the following cautions when considering MNrisks results:

  • Estimates apply to areas, not specific locations
  • Estimates apply to populations, not to individuals
  • Estimates apply specifically to the year 2011 since emissions and weather data for that year were used
  • Estimates do not reflect exposures and risk from all compounds
  • Estimates do not reflect all pathways of exposure
  • Estimates do not include impacts from sources in neighboring states or countries
  • Estimates do not fully reflect variation in background pollutant concentrations
  • Estimates represent the potential risk to the most sensitive populations (e.g., children or those with pre-existing conditions)

Important uncertainties to note are:

  • Some air emissions estimates are known to be more accurate than others. There are no emissions inventory data for some pollutants, and The emission estimates for some sources, such as snowmobiles, are based on outdated emission factors and tend to overestimate emissions produced by newer equipment.
  • Health benchmarks are used to set health protective concentrations in air and food. They are not predictive of health effects.
  • Inhalation health risks assume people spend 24 hours of their day outdoors for their lifetime.
  • Air dispersion models calculate impacts over a limited area of 20-50 km (12-30 miles) from the source. There could be impacts beyond this distance.
  • Results may not accurately capture sources that have episodic emissions, such as prescribed burning or facilities with short-term deviations such as startups, shutdowns, or malfunctions.
  • Risk estimates require default assumptions when there is not specific data available. These default assumptions may not apply to all Minnesotans.

What’s the difference between a measurement and a modeled result?

There are two ways to find out what’s in the air: by measuring pollutant concentrations with monitors or by using a computer model to estimate concentrations. Measurements cannot be collected everywhere, so regulators use models to fill in the gaps. This is especially the case when we want to know what pollutant concentrations are likely to be in the future.

Where can I find information about measurements and monitoring results?

The MPCA’s Air Data webpage provides more information on air pollution monitoring and emissions data collected in Minnesota.

What is a receptor, and does it represent a person?

A receptor is a location where a computer model calculates a result. MNrisks results are commonly averaged across geographic areas and include multiple receptors, which are not meant to represent specific points, homes, or people.

What can I do if air pollutant concentrations are higher in my area?

There are three great ways to become more involved in reducing air pollution.

  • Become a public participant in MPCA work by commenting on the MPCA ambient air network plan, or attending a public meeting for an air permit in your area.
  • Reduce your emissions by driving less or using a more fuel-efficient vehicle, reducing emissions at home (e.g., by lowering the heat), and other low-impact behaviors.
  • Talk to others about reducing their impacts, or work with your employer or school to reduce impacts by doing things such as reducing vehicle idling during pick-up and drop-off.