PNEC (Predicted No Effect Concentration)

The predicted no-effect concentration (PNEC) is the concentration of a substance below which adverse effects on an ecosystem are not expected. It is derived by dividing the most sensitive available toxicity value by an assessment factor: an acute LC50 or EC50 divided by 1,000, or a chronic NOEC divided by 10 to 100 depending on how many species and trophic levels the dataset covers. The assessment factor covers the uncertainty in extrapolating from single-species lab tests to the field. PNEC is the effects half of the risk quotient (PEC/PNEC) under EU REACH; a higher-tier alternative uses a species sensitivity distribution.