Definitions

Section 302 Section 302.603  Definitions As used in this Subpart, the following terms have the meanings specified. "Bioconcentration" means an increase in the concentration of a chemical and its metabolites in an organism (or its specified tissues) relative to the concentration of the chemical in the ambient water acquired through contact with the water alone. "Carcinogen" means a chemical that causes an increased incidence of benign or malignant neoplasms, or a statistically significant decrease in the latency period between exposure and onset of neoplasms, in at least one mammalian species or man through epidemiological or clinical studies. "EC-50" means the concentration of a substance or effluent that causes a given effect to 50% of the exposed organisms in a given time period. "LC-50" means the concentration of a toxic substance or effluent that is lethal to 50% of the exposed organisms in a given time period. "LOAEL" or "Lowest Observable Adverse Effect Level" means the lowest tested concentration of a chemical or substance that produces a statistically significant increase in frequency or severity of non-overt adverse effects between the exposed population and its appropriate control. "MATC" or "Maximum Acceptable Toxicant Concentration" means the value obtained by calculating the geometric mean of the lower and upper chronic limits from a chronic test.  A lower chronic limit is the highest tested concentration that did not cause a specified adverse effect.  An upper chronic limit is the lowest tested concentration that did cause a specified adverse effect and above which all tested concentrations caused a specified adverse effect. "NOAEL" or "No Observable Adverse Effect Level" means the highest tested concentration of a chemical or substance which does not produce a statistically significant increase in frequency or severity of non-overt adverse effects between the exposed population and its appropriate control. "Resident or Indigenous Species" means species that currently live a substantial portion of their lifecycle or reproduce in a given body of water or that are native species whose historical range includes a given body of water.