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Toxicity Values - Information

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Measures of the level (i.e., concentration or dose) of a chemical stressor at which a specific level of toxicity is observed in a receptor (eg LC50).

Toxicity values are determined by the exposure - effect relationship generated in toxicity tests, and are generally expressed as the concentration(s) or dose(s) that evoke a specific effect (in the measurement end point) over a fixed exposure duration. An example of a concentration - response curve is given below.

Toxicity values are derived from toxicity tests which are usually conducted on one or more species. Toxicity data may be derived from single chemical exposures or by testing samples of material removed from the contaminated site. In ecotoxicological assessments, toxicity tests may measure lethal or sublethal end points, as long as the endpoint measured can be related to an ecologically relevant impact.

Examples of commonly reported toxicity values are:

  • LD or LC Lethal Dose or Lethal Concentration - the dose or concentration which produces a specified level of mortality in the test population within a specified time, eg LC50 is the median lethal concentration or the concentration of a substance at which 50% of the test population are killed. Typical levels are LC10, LC25, LC50, LC75, LC100.
  • ED or EC Effective Dose or Effective Concentration - the dose or concentration that produces a specified level of effect in the test population within a specifed time, eg EC50 is median effective concentration or the concentration of a substance at which 50% of the test population are affected. Typical levels are EC10, EC25, EC50, EC75, EC100.
  • NOEC No observable effect concentration
  • LOEC Lowest observable effect concentration

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