The PEC:PNEC (assessment factor) approach is a generic conservative approach assuming the presence of the most sensitive species. To derive a PNEC using the assessment factor approach, preferably, toxicity data on at least the three selected taxonomic or trophic levels (e.g., algae, crustaceans, and fish) are available. In principle, the PNEC is determined from the available toxicity data, by applying an assessment factor. The PNEC is calculated by dividing the lowest LC/EC50 or NOEC value by an appropriate assessment factor in accordance with the EU-TGD. The assessment factor is applied to extrapolate from laboratory single-species toxicity test data to multi-species ecosystem effects. The assessment factor addresses a number of uncertainties:
- Interspecies variation (biological variance);
- Short-term to long-term toxicity extrapolation;
- Laboratory data to field impact extrapolation.