Navy Human Health Risk Assessment Web Site

Navy Risk Communication Web Site

Glossary

Select a letter from the list below to view other definitions.

A B C D E F G H I L M N O P R S T U V W

Threshold Values
Values (concentrations) above which some effect (or response) will be produced and below which it will not (EPA 1997).

Toxic Mechanism (or Mode) of Action
The mechanism by which chemicals produce their toxic effects (i.e., the mechanism by which a chemical alters normal cellular biochemistry and physiology). Mechanisms can include: interference with normal receptor-ligand interactions, interference with membrane functions, interference with cellular energy production, and binding to biomolecules (Amdur et al. 1991).

Toxicity Test
The means by which the toxicity of a chemical or other test material is determined. A toxicity test is used to measure the degree of response produced by exposure to a specific level of stimulus (such as concentration of chemical) compared with a unexposed control.

Treatment, Storage and Disposal Facilities (TSDFs)
Sites where a hazardous substance is treated, stored, or disposed. The EPA and states under RCRA regulate TSDFs.

Trophic Level
A functional classification of taxa within a community that is based on feeding relationships (e.g., plants make up the first trophic level, herbivores make up the second).

Type A Assessment
Standard procedures for simplified assessments requiring minimal field observations to determine damages, as specified in Section 301(c)(2)(A) of CERCLA.

Type B Assessment
Alternative methodology for conducting assessments in individual areas to determine the type and extent of short- and long-term injury and damage, as specified in Section 301(c)(2)(B) of CERCLA.

Last Modified: 02/27/2003

This website complies with the Electronic and Information Technology Accessibility Standards set forth in U.S. Section 508 of the 1998 Rehabilitation Act Amendments