Concentration of a potentially toxic substance at which undesirable (or adverse) functional changes, reversible or irreversible, occur in the cell or organ
International Union of Pure and Applied Chemistry IUPAC, Glossary for Chemists of Terms Used in Toxicology, Prepared for publication by J.H. Duffus, NC., USA 1993. http://www.inchem.org/documents/harmproj/harmproj/ harmproj1.pdf & http://old.iupac.org/reports/1993/6509duffus/c.htm l, (IUPAC/ Tox - Amer) {107}