Types of Guidance/Values
On this page:
Health Risk Values (for Air)
Health Risk Limits (for Groundwater)
Health-Based Values
Risk Assessment Advice
Health Risk Values (for Air)
A Health Risk Value (HRV) is the concentration of a chemical (or a defined mixture of chemicals) that is likely to pose little or no risk to human health. Most HRVs are expressed as concentrations of micrograms of chemical per cubic meter of air (µg/m3). HRVs are developed to protect human health for a specified length of exposure (e.g., one hour, 13 weeks, a lifetime). An HRV also may be expressed as micrograms of chemical per kilogram body weight per day of exposure (µg/kg-day). These values, called multi-media HRVs, are developed for chemicals emitted to ambient air where multi-media exposures are important to public health. These values are based on oral exposures.
Health Risk Values have been promulgated using the public process described in the Administrative Procedures Act (Minnesota Statutes Chapter 14). HRVs are used by agencies in evaluating health risks to humans from exposure to a chemical.
For additional information, see: Health Risk Values Rules and the Air Values Table.
Health Risk Limits (for Groundwater)
Under the Groundwater Protection Act of 1989, MDH protects public health by developing and establishing Health Risk Limits (HRLs) for contaminants in drinking water. An HRL is the concentration of a chemical (or a mixture of chemicals) in drinking water that is likely to pose little or no health risk to humans. HRLs are expressed as micrograms of chemical per liter of water (ug/L), which is the same as parts per billion (ppb).
Health Risk Limits have been promulgated using the public process described in the Administrative Procedures Act (Minnesota Statutes Chapter 14). HRLs are used by agencies in evaluating potential health risks to humans from exposures to a chemical.
- 2008 – present MDH-Derived HRLs:
In 2008 MDH revised the methods previously used for the 1993 and 1994 HRLs. The 2008 methods are an improvement over the earlier method because they are designed to take sensitive or highly exposed populations (e.g., infants and children) into account and are specific for different durations of exposure. HRLs promulgated after 2008 are intended to protect human health for a specified length of exposure (e.g., one day, one month, a lifetime). The 2008 to present HRL values based on these revised methods are shown as HRLyear (e.g., HRL08) in the Human Health-Based Water Guidance Table.
- 2008 US EPA MCL-Based HRLs:
The US Environmental Protection Agency (US EPA) has established standards for public drinking water systems. The US EPA values are called Maximum Contaminant Levels (MCLs). In 2007, before MDH had finished developing the new methods referred to above, the Minnesota Legislature required MDH to set its HRL value at the MCL if the MCL was lower than the HRL value in effect at the time. These MCL-based HRL values initially went into effect in July 2007 and were included in the 2008 promulgation process. These values will remain in effect until replaced through new rule making. MCL-based HRLs are shown as HRLMCL in the Human Health-Based Water Guidance Table.
- 1993/1994 MDH-Derived HRLs:
HRLs were first promulgated in 1993 and 1994 using earlier US EPA methods based on protecting human health following a lifetime exposure to a groundwater contaminant. The 1993 and 1994 HRL values are shown as HRL93or HRL94 in the Groundwater Values Table.
For additional information, see: HRL for Groundwater Rules.
Health-Based Values
A Health Based Value (HBV) is the concentration of a chemical (or a mixture of chemicals) that is likely to pose little or no risk to human health. MDH develops HBVs for water and for ambient air. An HBV for water is expressed as micrograms of a chemical per liter of water (µg/L) and is designated in the Human Health-based Water Guidance Table as HBVyear (e.g., HBV11). An ambient air HBV is expressed as micrograms per cubic meter of air (µg/m3). HBVs are developed to protect human health for a specified length of exposure (e.g., one hour, one day, one month, a lifetime). HBVs for water are calculated using the methodology set in the Health Risk Limits Rules. HBVs for air are calculated using the methodology set in the Health Risk Values Rules. HBVs meet the same data requirements as HRLs and HRVs.
MDH develops HBVs when Minnesota agencies need guidance for chemicals that do not have Health Risk Limits (HRLs) or Health Risk Values (HRVs). MDH may also calculate HBVs to update an existing value if there is significant new scientific information for the chemical and/or to apply new risk assessment methods. If there is reason to believe new toxicologically related information will be released in the near future, MDH will wait for those study or assessment results before developing an HBV.
HBVs have not been promulgated using the public process described by the Administrative Procedures Act (Minnesota Statutes Chapter 14). Instead, an HBV is technical guidance made available by MDH. These values may be used by the public, state and local risk managers, and other stakeholders to assist in evaluating potential health risks to humans from exposures to a chemical. In general, MDH anticipates that HBVs for water will become HRLs at the time that MDH next amends the Health Risk Limits for Groundwater rule.
For a complete list of MDH recommended values/guidance, see the Air Values Table and Human Health-Based Water Guidance Table.
For additional information see: Health-Based Guidance Development Process.
Risk Assessment Advice
Risk Assessment Advice (RAA) is technical guidance concerning exposures and risks to human health. MDH develops RAA for water and for air. RAA for water is designated in the Human Health-based Water Guidance Table as RAAyear (e.g., RAA11)Depending on the information available, RAA may be quantitative (e.g., a concentration of a chemical that is likely to pose little or no health risk to humans) or qualitative (e.g., a written description of how toxic a chemical is in comparison to a similar chemical). Generally, RAA contains greater uncertainty than HRLs, HRVs, and HBVs because the available information is more limited.
MDH develops RAA when Minnesota agencies need guidance for chemicals that do not have Health Risk Limits (HRLs) or Health Risk Values (HRVs). MDH may also calculate RAA to update an existing value if there is significant new scientific information the chemical and/or to apply new risk assessment methods. If there is reason to believe new toxicologically related information will be released in the near future, MDH will wait for those study or assessment results before developing a RAA.
RAA has not been promulgated using the public process described by the Administrative Procedures Act (Minnesota Statutes Chapter 14). Instead, RAA is technical guidance made available by MDH. These values may be used by the public, state and local risk managers, and other stakeholders to assist in evaluating potential health risks to humans from exposures to a chemical. RAA is not likely to change unless significant new data become available.
MDH also develops RAA on a case-by-case basis for specific conditions or specific sites. It is not appropriate to apply this site-specific RAA to other sites without consulting with MDH.
For a list of MDH recommended values/guidance, see the Air Values Table and Human Health-Based Water Guidance Table. Note: MDH does not post site-specific RAA in the air or groundwater values tables.
For additional information see: Health-Based Guidance Development Process.