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Risk Analysis Glossary: J - L

Latency period
  1. period of time from exposure to an agent to the onset of a health effect.
LC50
  1. Lethal concentration fifty.
LD50
  1. Lethal dose fifty.
Leachate
  1. Liquid that has percolated through solid waste and has extracted dissolved or suspended materials from it.
Leaching
  1. The process by which nutrient chemicals or contaminants are dissolved and carried away by water, or are moved into a lower layer of soil.
Lethal concentration fifty (LC50)
  1. A calculated concentration [in air] which when administered by the respiratory route is expected to kill 50% of a population of experimental animals during an exposure of four hours. Ambient concentration is expressed in milligrams per liter.
  2. A calculated concentration in water which is expected to kill 50% of a population of aquatic organisms after a specified time of exposure. Concentration is usually expressed in milligrams per liter or ppm. [S. L. Brown]
Lethal dose fifty (LD50)
  1. A calculated dose of a chemical substance which is expected to kill 50% of a population of experimental animals exposed through a route other than respiration. Dose is expressed in milligrams per kilogram of body weight.
Leukemia
  1. A progressive, malignant disease of the blood-forming organs, characterized by distorted proliferation and development of leukocytes and their precursors in the blood and bone marrow.
Line source
  1. Consists of a number of point sources arranged in a straight line, usually across wind (see point source)
Logit model
  1. A dose-response model which, like the probit model, leads to an S-shaped dose-response curve, symmetrical about the 50% response point. The logit model leads to lower "very safe doses" than the probit model even when both models are equally descriptive of the data in the observable range.
Log-probit model
  1. A dose-response model which assumes that each animal has its own threshold dose, below which no response occurs and above which a tumor [or other effect] is produced by exposure to a chemical.