Definition Of Toxic Endpoint

Companies are required to run tests to assess how hazardous a compound (e.g., pesticides, manufacturing effluent) is before release into the environment. Regulatory agencies (e.g., the Environmental Protection Agency) require these tests, which function to keep these materials at environmental levels low enough to be considered safe for plants and animals. Many tests examine toxicity and include many different toxic endpoints.

A toxic endpoint is the result of a study conducted to determine how dangerous a substance is. The data collected from such studies are used to report the relative toxicity of the compound to various regulatory agencies and environmental compliance groups. Toxic endpoints can include mortality, behavior, reproductive status or physiological and biochemical changes.

Toxic endpoints are acute or chronic. Acute studies generally last no longer than a week and examine endpoints such as mortality and behavior. With acute studies, a common endpoint is an LD50, which is the dose of a compound required to kill half the organisms in the study. Chronic studies are longer in duration (more than a week) and include endpoints such as reproduction, long-term survival and growth. Chronic studies are valuable because they examine the effects of extremely low concentrations of compounds that may persist in the environment for long periods of time (e.g., DDT).

Scientists conduct in vitro studies in test vessels while in vivo studies are conducted within living organisms. Endpoints of in vitro studies include changes in reproductive status or hormone levels. The advantage of in vivo studies is that researchers can examine the effects of the compound on the entire organism. In vitro studies are advantageous and often considered more ethical, because they do not use living animals but only living cells in culture. In vivo endpoints may include enzyme production or gene expression.

Plants and animals are exposed to potential toxicants in a number of ways. Aquatic organisms are generally exposed through the water or sediment. The toxic endpoints for terrestrial animals may include data collected after exposure through the air, food or dermally.

Toxicity endpoints are used to establish toxicity thresholds, which are levels of a compound below which adverse effects are not seen.