4. Impact assessment

One of the aims of ecotoxicity testing is to identify the effect(s) of concern of a substance on the environmental compartment concerned, and to determine the concentration below which this substance should no longer have an undesirable effect on organisms in that compartment. This concentration, known as the Predicted No Effect Concentration (PNEC), is one of the main parameters used in risk assessment methods set up at European and international (OECD) level.

The PNEC is obtained by applying an assessment factor to the values derived from tests carried out on organisms in the compartment concerned (e.g. to the CE ₅₀ , CL ₅₀ or NOEC). The assessment factor accounts for the degree of uncertainty that results from extrapolating the results of tests carried...