Environmental Terms and Definitions

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.

National Institute for Occupational Safety and Health (NIOSH)
NIOSH, part of the Centers for Disease Control, conducts research on worker safety and health and recommends standards for worker protection to OSHA. For example, NIOSH recommends guidelines for workplace exposure to hazardous substances and has published criteria documents on many chemicals.

National Toxicology Program (NTP)
NTP, part of the U.S. Department of Health and Human Services (DHHS), coordinates the toxicology research being conducted within DHHS.

Detection limit
The smallest amount of substance that a laboratory test can reliably measure in a sample of air, water, soil or other medium.

HMTUSA
Hazardous Materials Transportation Uniform Safety Act (1999); amendments to HMTA including requirements for performance-oriented packaging.

Superfund (federal and state)
The federal and state programs to investigate and clean up inactive hazardous waste sites.

Agency for Toxic Substances and Disease Registry (ATSDR)
ATSDR is part of the U.S. Department of Health and Human Services. As mandated by the federal superfund law, the agency assesses health risks from hazardous waste sites on the National Priority List.

AHM
Acutely Hazardous Material

Material Safety Data Sheet (MSDS)
A compilation of information required under the OSHA Communication Standard on the identity of hazardous chemicals, health, and physical hazards, exposure limits, and precautions. Section 311 of SARA requires facilities to submit MSDSs under certain circumstances.

Exposure assessment
A process that estimates the amount of a chemical that enters or comes into contact with people or animals. An exposure assessment also describes how often and for how long an exposure occurred, and the nature and size of a population exposed to a chemical.