Teratogen

A substance that can cause malformation in the fetus following exposure of the mother. The malformation or abnormality may be biochemical or anatomic and be of genetic or environmental origin.

Tertiary Treatment

The advanced cleaning of wastewater that goes beyond secondary treatment. This process removes nutrients, such as phosphorus and nitrogen, and most biological oxygen demand and suspended solids.

Thermal Stratification

The layering of warmer waters over colder waters that can occur in lakes, usually in the summertime. This layering occurs because as surface waters are warmed they become less dense than the underlying colder waters. Differential rates of seasonal heating and cooling of shallow and deep waters result in the development of two horizontal layers of water having very different water temperatures. The depth where this abrupt temperature change occurs is known as the thermocline.

Total Maximum Daily Load (TMDL)

TMDLs are set by regulators to allocate the maximum amount of a pollutant that may be introduced into a water body and still assure attainment and maintenance of water quality standards.

Total phosphorus

The total concentration of phosphorus found in the water. Phosphorus is a nutrient and acts as a fertilizer, increasing the growth of plant life such as algae.

Toxaphene

One of the nine critical pollutants, toxaphene is an insecticide that was developed as a substitute for DDT. Its use is now restricted in the U.S. and Canada. Toxaphene has been detected in wildlife as far north as the Arctic.

Toxic Pollutant

A substance or combination of substances, including disease-causing agents, which may cause death, disease, behavioral abnormalities, cancer, genetic mutations, physiological malfunctions (including reproductive malfunctions), or physical deformation in organisms or their offspring. Also refers to those substances listed under Section 307(a) of the Clean Water Act. Also see "Toxic substance."

Toxic Release Inventory System (TRI)

The TRI system contains information regarding more than 650 toxic chemicals and compounds that are used, manufactured, treated, transported, or released into the environment, as required under Section 313 of the Emergency Planning and Community Right-to-Know Act. TRI contains release-transfer data by facility, year, chemical, and medium of release, as well as treatment and source reduction data.

Toxic substance

Any substance that can cause death, disease, behavioral abnormalities, cancer, genetic mutations, or physiological or reproductive malfunctions or physical deformities in any organism or its offspring, or a substance that can become poisonous after concentration in the food chain or in combination with other substances. Also see "Toxic pollutant."

Toxic Substances Management in the Great Lakes Basin Through the Permitting Process Agreement

A binational agreement entered into by the environmental administrators of the Great Lakes States in 1986 requiring that best available control technology be installed wherever possible on all new and existing sources of persistent air toxic pollutants which impact the Great Lakes. This agreement is pursuant to implementing the governors' Great Lakes Toxic Substances Control Agreement.

Toxicity

The inherent potential of a substance to cause adverse effects in a living organism. See acute toxicity and chronic toxicity.

Toxicity Test

A procedure that measures the degree of effect caused by a chemical or effluent, by exposing living test organisms to the substance. See also acute toxicity and chronic toxicity.

Toxicological profiles

Fact sheets prepared by the U.S. Agency for Toxic Substances and Disease Registry (ATSDR), "for hazardous substances which are most commonly found at facilities on the CERCLA National Priorities List and which pose the most significant potential threat to human health, as determined by ATSDR and the Environmental Protection Agency."

Trophic

Status characterization of the condition of a body of water as eutrophic, oligotrophic or mesotrophic. Indicators or certain characteristics of a lake are used to measure the productivity of a lake. Indicators can be chemical, physical or biological in nature. Having to do with various nutritional levels of the food chain.

Trophic guilds

Groups of organisms that are similar in their nutritional requirements and feeding habits, such as planktivores, piscivores, omnivores, etc.