Environmental Terms and Definitions

Latency period
The period of time between exposure to something that causes a disease and the onset of the health effect. Cancer caused by chemical exposure may have a latency period of 5 to 40 years.

World Health Organization (WHO)
WHO, an agency of the United Nations, carries out public and environmental health programs throughout the world.

Route of exposure
The way in which a person may contact a chemical substance. For example, drinking (ingestion) and bathing (skin contact) are two different routes of exposure to contaminants that may be found in water. See "Exposure".

Gradient
The change in a property over a certain distance. For example, lead can accumulate in surface soil near a road due to automobile exhaust. As you move away from the road, the amount of lead in the surface soil decreases. This change in the lead concentration with distance from the road is called a gradient.

Remediation
Correction or improvement of a problem, such as work that is done to clean up or stop the release of chemicals from a contaminated site. After investigation of a site, remedial work may include removing soil and/or drums, capping the site or collecting and treating the contaminated fluids.

HSWA
Hazardous and Solid Waste Amendments (1984); amendments to RCRA establishing a timetable for landfill bans and more stringent UST requirements.

Odor threshold
The lowest concentration of a chemical that can be smelled. Different chemicals have different odor thresholds. Also, some people can smell a chemical at lower concentrations than others can.

Solubility
The largest amount of a substance that can be dissolved in a given amount of a liquid, usually water. For a highly water-soluble compound, such as table salt, a lot can dissolve in water. Motor oil is only slightly soluble in water.

CERCLA
Comprehensive Environmental Response, Compensation and Liability Act. See "Superfund."

Interim Remedial Measure (IRM)
An action taken at a contaminated site to reduce the chances of human or environmental exposure to site contaminants. Interim remedial measures are planned and carried out before comprehensive remedial studies.