Pollution - Environmental Science - page 164

In the United States, some substances do not require Food and Drug Administration (FDA) approval prior to
being released to the market, although many of these substances are then tracked and regulated through the
FDA, EPA, and other agencies. Many substances that are not regulated through laws are monitored by the EPA.
A key law that addresses the monitoring of toxic chemicals is the Toxic Substances Control Act (TSCA).
Workplace hazards and safety, including exposure to toxins, are monitored through the Occupational Safety
and Health Administration (OSHA).
Dose-Response
A dose-response relationship is used to represent the effect of a toxin on an organism or population. A dose is
the amount or concentration of a substance, while the response is an organism's reaction to a substance. Thus,
dose-response describes the effects of certain levels of a toxin, illustrating the tipping point at which a safe
level and exposure time becomes hazardous. In order to show this relationship, a dose-response curve can be
used, as illustrated in the following figures. The term LD 50 describes the lethal dose of a substance for 50 per-
cent of the test population. When 50 percent of the population is affected (but not killed) by a certain dose of a
substance, it is labeled ED 50 or effective dose-50 percent. The threshold dose is the amount of a substance
that has any effect on an organism or population.