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.

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. Related Program - Water Related CFRs and Rules, Federal and State Statutes

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 and levels in Lake Superior appear to be increasing in fish and sediments. Related Program - Binational Program

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 or Minnesota Statutes. Related Program - Clean Water Act, 40 CFRs

Toxic Substances
See Toxic Pollutants.

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