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Some government agencies have developed standards and screening levels for toxic chemicals in the air based on health information about the chemicals. Some levels of concern are levels that state governments have designated as the maximum levels of toxics that are allowed to be in the air. These levels are called "standards" and are legally enforceable in states that have them.

Other levels of concern are developed by government agencies which survey scientific studies to figure out what levels of chemical exposure pose minimal risk to your health. The agencies consider these levels (called "screening levels" or "minimum risk levels") as something like a borderline between levels of chemical exposure that could do you harm and levels that probably won't do you any harm. They are not legally enforceable.

The levels of concern in our tool and the agencies that have developed them are listed below, with a brief description of the methods used in establishing the levels. Click on the agencies' web sites to go to the agencies' detailed and technical descriptions of these levels of concern. To compare your air data to these levels of concern, click on Create a report.

Note: All levels of concern in the tool were updated in May 2015: ATSDR Minimal Risk Levels, EPA Region 6 Screening Levels, Louisiana Ambient Air Quality Standards, North Carolina Ambient Air Standards, and Texas Effects Screening Levels -- any of these levels in the report are up-to-date as of May 2015.

ATSDR Minimal Risk Levels

Agency web site: http://www.atsdr.cdc.gov/mrls/index.asp

ATSDR Minimal Risk Levels are based on existing studies of chemical health effects. ATSDR stands for "American Toxic Substance and Disease Registry." Exposure at these levels is said to pose "minimal risks" of adverse health effects. The levels were derived from the experimentally-determined levels at which the chemicals caused adverse effects in study populations of people or animals, combined with uncertainty factors to account for the differences among human populations and between humans and animals. "Acute" exposure is defined as up to two weeks, "Intermediate" as between two weeks and one year, and "Chronic" as longer than a year. These levels reflect only non-cancer health effects. They are not legally enforceable.

EPA Region 6 Screening Levels

Agency web site: http://www.epa.gov/earth1r6/6pd/rcra_c/pd-n/screen.htm

EPA Region 6 Screening Levels are based on existing studies of chemical health effects. These levels are calculated for residential (as opposed to workplace) exposures. They reflect the risks of exposure to a certain level of the chemical. The levels listed as screening levels correspond to pre-determined levels of risk from exposure: either 1 in a million cancer risk or a "hazard quotient" of 1 for non-cancer effects, whichever corresponds to a lower concentration. These screening levels are not legally enforceable.

Louisiana Ambient Air Quality Standards

Agency web site: http://www.deq.louisiana.gov/portal/tabid/1674/Default.aspx

The Louisiana Ambient Air Quality Standards are legally enforceable standards in Louisiana, developed through Louisiana's regulatory process. If you live in Louisiana, you may want to look only at the legal limits which apply to you. They are found in Table 51.2 of Title 33, Part III. They are based on health effects information about the chemicals: the eight-hour standard modifies occupational exposure levels to be appropriate for residential exposures; the annual standard is based on EPA procedures for calculating cancer risks.

North Carolina Ambient Air Standards

Agency web site: http://www.ncair.org/rules/rules/D1104.pdf

The North Carolina Ambient Air Standards are legally enforceable in North Carolina, developed through North Carolina's regulatory process. If you live in North Carolina, you may want to look only at the legal limits which apply to you. They are based on health effects information about the chemicals.

Texas Effects Screening Levels

Agency web site: http://www.tceq.texas.gov/toxicology/esl

Texas Effects Screening Levels are based on existing studies of chemical health effects. Below these levels, no adverse health effects are thought likely to occur. They reflect the experimentally-determined levels at which the chemicals caused adverse effects in study populations of people or animals, combined with safety factors to account for the differences among human populations and between humans and animals. "Short-term" refers to an exposure duration of one hour. "Long-term" refers to a duration of one year. Texas Effects Screening Levels reflect both cancer and non-cancer effects. They are not legally enforceable.

Remember: Levels of Concern are only part of the story. There are limitations to what is known about the health effects of chemicals. There may be health impacts associated even with levels of chemicals below the levels of concern.