PNEC

Predicted No-Effect Concentration (PNEC) is a risk assessment metric used in ecotoxicology to estimate the highest concentration of a chemical in the environment that is expected to have no adverse effects on reference populations of aquatic or terrestrial organisms. The PNEC is intended to be protective, serving as a threshold below which adverse ecological effects are unlikely.

Derivation of a PNEC relies on toxicity data from laboratory studies. Data are typically drawn from chronic endpoints such as NOEC or EC10 across multiple species. The most sensitive species is identified, and an assessment factor is applied to account for uncertainties in extrapolating laboratory results to real-world exposures, including interspecies differences and data gaps. Alternatively, a species sensitivity distribution (SSD) approach can be used, where the PNEC corresponds to the fifth percentile of the fitted distribution (the HC5).

Applications of the PNEC include informing regulatory environmental risk assessments and setting water quality or soil concentration standards. In practice, regulatory agencies compare predicted environmental concentrations (PECs) with PNECs to assess risk, with a PEC/PNEC ratio above unity indicating potential concern.

Limitations of the PNEC concept include reliance on available data and the use of surrogate species, which may not capture all ecological sensitivities. PNECs do not directly address chemical mixtures, degradation products, long-term ecosystem dynamics, or site-specific conditions. They are typically used as part of a broader risk assessment framework and are complemented by other lines of evidence.

Note: PNEC most commonly refers to Predicted No-Effect Concentration in environmental science, though the acronym can have other meanings in different fields.