A risk characterization consists of conducting a qualitative or quantitative assessment of the probability that a given chemical will produce an adverse effect at a given dose or exposure level. Conversely, an assessment could determine levels of exposure at which a chemical would not be expected to present a risk.
Companies and governments use the information learned from chemical testing and exposure assessments to make determinations about how to properly manage the risks posed by chemicals in their various uses.
Some examples include:
- Occupational Exposure Limits: Companies, independent professional associations and governments establish occupational exposure limits to assist in the management of chemical exposures in the workplace. (Chemical users are advised to consult the Safety Data Sheet for information specific to the chemicals in their workplaces.)
- The US Occupational Safety and Health Administration (OSHA) sets and enforces Permissible Exposure Limits (PEL). The MAK Commission sets occupational exposure limits in Germany, and other countries have similar occupational safety authorities who establish and enforce occupational exposure limits.
- The American Conference of Governmental Industrial Hygienists (ACGIH) sets Threshold Limit Values (TLV) which represent the concentration to which almost all workers can be exposed daily for a working lifetime without adverse effects.
- Dow sets Industrial Hygiene Guidelines (IHG) for the purpose of identifying suggested workplace exposure guidance.
- Acceptable Daily Intake: The Acceptable Daily Intake (ADI) is a numerical estimate of a daily oral exposure to the human population, including sensitive subpopulations such as children, that is not likely to cause harmful effects during a lifetime. ADIs are generally used for health effects that are thought to have a threshold or low dose limit for producing effects. (Also called reference dose, or RfD). An ADI is derived from a No Observed Adverse Effect Level (NOAEL) or the Lowest Observed Adverse Effect Level (LOAEL) by applying safety or uncertainty factors, and is usually expressed in milligrams per kilogram per day. ADIs are not normally used for chemicals if the endpoint of concern is the potential to cause cancer. Similar values are set and used by environment, health and safety authorities throughout the world.
- The US Environmental Protection Agency (EPA) calculates RfDs for chemical substances which form the basis for their regulatory limits, for example, for pesticide residues on food crops. These RfDs are also presented to state regulatory authorities for the purposes of establishing legal environmental exposure limits.
- The US Food and Drug Administration (FDA) uses ADIs to determine safe levels of chemical substances that may be directly or indirectly added to foods.
For substances thought to pose a risk of cancer, a different risk assessment procedure is frequently employed. Under some theories of cancer causation, substances thought to cause cancer are presumed to have no safe level of exposure. Some government agencies use mathematical computer models — linear non-threshold models — rather than NOAELs and safety factors to describe the dose-response relationship for animal carcinogens.
One example of a state government agency’s application of risk values for carcinogens is California’s Proposition 65, The Safe Drinking Water and Toxics Enforcement Act of 1986, which was enacted as a ballot initiative in November 1986. Proposition 65 was intended by its authors to inform California citizens about exposures to chemicals known to cause cancer, birth defects or other reproductive harm through risk assessment and product warnings. California’s Office of Environmental Health Hazard Assessment uses risk assessment methods to calculate lifetime No Significant Risk Levels (NSRL) for substances determined to be “known to the State of California to cause cancer.” Products that might expose a user to a level greater than this NSRL must be assessed for adequate warnings.